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Aims: To determine the effect of different points of force application on dimensional positions and the ratio of space closure of maxillary canine using sliding mechanics. Materials and Methods: The study included eight groups which were categorized according to the differences in the points from which the retraction force was applied. A 180 gm was applied by short elastic chain to retract the right maxillary canine on 0.0180.025'' rectangular stainless steel (SS) wire and along 13 mm available space. In both vertical and horizontal direction, photographs were taken by digital camera and the angle between canine extension bar and bite plane extension bar was measured by protractor to determine tipping and rotation whereas rate of space closure was measured by digital vernia. Results: The results showed that the maximum rate of space closure was achieved when elastic chain was attached between molar hook to canine hook and the minimum degree of tipping was achieved when elastic chain attached between premolar bracket to canine hook while minimum rotation occurred when the attachment was between premolar hook to canine hook. Conclusions: Changing the distance between the points of force application significantly affects the rate of space closure, tipping and rotation. The use of hook significantly increases the rate of space closure and decreases tipping and rotation.

The purpose of this study was to examine the effectiveness of conventional pre-clinical training in dentistry and to determine if evaluation of a dental procedure at the beginning of dental training can be a predictor for future performance. A group of second year dental students with no previous experience in operative dentistry were asked to prepare a conventional class I cavity on a lower first molar typodont. Their first preparation was carried out after an introductory lecture and a demonstration and their second at the end of conventional training. The prepared typodonts were coded and blindly scored for the traditional assessment criteria of outline form, retention form, smoothness, cavity depth and cavity margin angulation. Once the codes were broken, a paired t-test was used to compare the difference between the means of before and after scores (P

Background: To determine and compare the force-deflection values of different types of nickel-titanium (NiTi) wires during unloading phase at varying deflections, that is 1 mm, 1.5 mm, 2 mm, and 2.5 mm, with the use of self-ligating ceramic brackets using modified bending test on a typodont under controlled temperature conditions. Materials and Methods: In this in vitro study total of 45 wires of ovoid shape of three different NiTi wires – pseudoelastic NiTi (Group I), heat activated NiTi (Group II), and esthetic coated NiTi (Group III) for maxillary arch were tested after insertion in ceramic self-ligating brackets bonded to plastic teeth of phantom jaw . The maxillary left lateral incisor was removed to simulate a malpositioned tooth which acted as the load site, and load-deflection characteristics were measured during unloading using Instron, and data analyzed statically by two-way analysis of variance ,Tukey's post hoc test, intraclass correlation coefficient and Pearson correlation coefficient. A two-sided (α = 2) P < 0.05 was considered statistically significant. Results: When wires were compared at each deflection statistically significant difference was observed between the three groups of wires (Group I > Group II > Group III) at all the four levels of deflection except for Group II versus Group III at 1 mm, 1.5 mm, and 2 mm of deflection. Statistically significant difference was noted in mean load values for comparisons made at different deflections for each wire except for the comparison made at 1.5 versus 2 mm for Group II and Group III. Conclusion: Overall comparison showed esthetic coated Ni-Ti wires gave significantly lower mean load values, followed by heat activated and pseudoelastic NiTi wires. Thus, heat activated NiTi wires are best suited in patients with severe malpositions/periodontitis, while for esthetically conscious patients esthetic coated NiTi can be used.

Purpose: To evaluate the effect of different incisal preparations on the fracture resistance of mandibular anterior veneers with the use of two routinely indicated ceramics. Method: 35 typodont teeth were randomly allocated to 3 groups according to the design (Group I Leucite reinforced glass ceramic, Group II Lithium disilicate glass ceramic and Group III Control). Veneers were fabricated and cemented using Rely X cement, and were tested under oblique loading to evaluate their fracture resistance and pattern. ANOVA and Post hoc Tukeys test were used to evaluate fracture strength and and Chi square test to evaluate fracture patterns (p

Aim The aim of the present study is to compare the various elastomeric impression materials in terms of accuracy and dimensional stability, with respect to obtaining multiple casts from a single elastomeric impression at various times of pours. Materials and methods Three master dies were prepared for the impression making, two of these were made of brass containing a central hole with undercuts. The third die simulated a conventionally prepared typodont maxillary central incisor. Three elastomeric impression materials were chosen for the study. Each impression was poured at various time periods. Casts thus obtained were evaluated under a traveling microscope to evaluate various dimensional changes. Results Addition silicones provided dies which were shorter in height and bigger in diameter. Polyethers provided dies which were shorter in both height and diameter. Condensation silicones showed insignificant changes from the master die at the immediate pour but deteriorated rapidly after that in subsequent pours. Conclusion None of the impression material showed a consistent behavior up to the fourth pour. They occasionally showed deviation from the pattern, but all these values were statistically insignificant. Polyethers showed lesser ability than both the addition silicones as well as the condensation silicones to recover from induced deformation. Clinical significance Addition silicones as well as the condensation silicones have better ability to recover from induced deformation when compared to polyether. How to cite this article Kumar D, Madihalli AU, Reddy KRK, Rastogi N, Pradeep NT. Elastomeric Impression Materials: A Comparison of Accuracy of Multiple Pours. J Contemp Dent Pract 2011;12(4):272-278.

The primary purposes of this investigation were to evaluate sophomore dental student performance in the production of a chamfer finish line using two diamond bur types-a round-ended bur and a torpedo-shaped bur-and to gain student feedback about their preferences for bur type. Fifty students took part in the study, each of whom prepared the buccal surfaces of two mandibular molar typodont teeth, producing chamfer finish lines. Students prepared both teeth in the same laboratory session and were randomly assigned to two groups that were required to prepare the first of the two molars with a specific bur type. The prepared chamfer finish lines were scored and the data analyzed using the Wilcoxon signed-rank test. Student performance was significantly better when the round-ended bur was used (p=0.005). Student feedback was collected with a survey that consisted of four questions and the opportunity to provide write-in comments. In response to the question "Overall, was one bur type better?" 58 percent of the students preferred the round-ended bur for creating a chamfer finish line. The most frequent write-in comment, made by twelve of the fifty students, criticized the torpedo-shaped bur for creating finish lines that were too shallow or too long.

Purpose: The aim of this in vitro study was to compare the marginal adaptation of a pressed ceramic material, when used with and without a metal substructure, to a traditional feldspathic porcelain-fused-to-metal restoration with a porcelain butt margin. Materials and Methods: A maxillary central incisor typodont tooth was prepared with a 1.5 mm 360° shoulder with rounded internal line angle, and 30 polyether impressions were made. Dies were poured in type IV dental stone, and 30 restorations were fabricated: 10 metal ceramic restorations (MCR) with porcelain butt joints, 10 pressed to metal restorations (PTM), and 10 all-ceramic restorations (PCR). All restorations were evaluated on their respective dies at 45× magnification using an Olympus SZX-12, measurements of the marginal openings were made, and ANOVA and Scheffe post hoc tests were used to evaluate the data. Results: The mean marginal opening was 72.2 ± 5.9 μm for MCR, 49.0 ± 5.9 μm for PTM, and 55.8 ± 5.9 μm for PCR. The post hoc tests showed that there was a statistical difference between the marginal adaptation of the PTM and MCR groups (p < 0.05). There was no significant difference in marginal adaptation between the PTM and the PCR groups, or the PCR and the MCR groups. Conclusions: The PTM group demonstrated a smaller mean marginal opening than the MCR group. The mean marginal openings of all three groups were within a clinically acceptable range.

There is a varying degree of hand torque abilities using finger drivers among clinicians. Calibrating one's own abilities requires complicated instruments not readily available. This study evaluated a simple-to-use method that allows dental practitioners to have a quantifiable clinical assessment of relative torque ability using finger drivers to torque down dental implant components. A typodont that includes dental implants was mounted in a mannequin placed in a patient-reclined position. The subjects were asked to torque as tightly as they could a new healing abutment to an implant secured firmly in resin within the typodont. All participants wore moistened gloves when using a finger driver. The healing abutment was countertorqued using a certified precalibrated precision torque measurement device. The reading on the torque driver was recorded when the healing abutment disengaged. An average of torque values of dentists and dental students was calculated. Fifty subjects had an average maximum torque ability of 24 Ncm (male dentists: 28 Ncm; students: 22 Ncm; male students: 24 Ncm; female students: 19 Ncm). Maximum torque values for all participants ranged from 11 Ncm to 38 Ncm. There was no significant difference between groups. This study showed a varying degree of hand torquing abilities using a finger driver. Clinicians should regularly calibrate their ability to torque implant components to more predictably perform implant dentistry. Dental implant manufacturers should more precisely instruct clinicians as to maximum torque, as opposed to “finger tighten only.”

Statement of problem A common technique used for making crown impressions involves use of a vinyl polysiloxane impression material in combination with a dual-arch tray. A leading dental manufacturer has reformulated its vinyl polysiloxane (VPS) impression line, but the accuracy of the new material has not been verified. Purpose The purpose of this study was to assess the accuracy of reformulated VPS impression materials using the single-step dual-arch impression technique. Material and Methods Dual-arch impressions were made on a typodont containing a master stainless steel standard crown preparation die, from which gypsum working dies were formed, recovered, and measured. The impression materials evaluated were Imprint 3 Penta Putty with Quick Step Regular Body (IP-0); Imprint 3 Penta Quick Step Heavy Body with Quick Step Light Body (IP-1); Aquasil Ultra Rigid Fast Set with LV Fast Set (AQ-1); and Aquasil Ultra Heavy Fast Set with XLV Fast Set (AQ-2) (n=10). All impressions were disinfected with CaviCide spray for 10 minutes prior to pouring with type IV gypsum. Buccolingual (BL), mesiodistal (MD), and occlusogingival (OG) dimensions were measured and compared to the master die using an optical measuring microscope. Linear dimensional change was also assessed for IP-0 and AQ-1 at 1 and 24 hours based on ANSI/ADA Specification No. 19. Single-factor ANOVA with Dunnett's T3 multiple comparisons was used to compare BL, MD, and OG changes, with hypothesis testing at α=.05. A repeated-measures ANOVA was used to compare linear dimensional changes. Results There were statistical differences among the 4 impression systems for 3 of 4 dimensions of the master die. IP-0 working dies were significantly larger in MD and OG-L dimensions but significantly smaller in the BL dimension. IP-1 working dies were significantly smaller in the BL dimension compared to the master die. With the exception of IP-0, differences detected were small and clinically insignificant. No significant differences were observed for linear dimensional change. Conclusions The single-step dual-arch impression technique produced working dies that were smaller in 3 of the 4 dimensions measured and may require additional die relief to achieve appropriate fit of cast restorations. Overall accuracy was acceptable for all impression groups with the exception of IP-0. (J Prosthet Dent 2009;101:332–341)

SUMMARY The objective of this investigation was to assess and compare the in vitro tribological behaviour of four commercially available self-ligating bracket systems. The frictional characteristics of the Damon3 ™ , Speed ™ , In-Ovation R ™ , and Time2 ™ bracket systems were studied using a jig that mimics the three-dimensional movements that occur during sliding mechanics. Each bracket system was tested on the following stainless steel archwires: 0.016 × 0.022, 0.019 × 0.025, 0.020 round , and 0.021 × 0.021 inch Speed ™ D-wire. An Instron testing machine with a 50 N load cell was used to measure the frictional resistance for each bracket/tooth assembly. The crosshead speed was set at a constant rate of 1 mm/minute, and each typodont tooth was moved along a fi xed wire segment for a distance of 8 mm. Descriptive statistical analysis for each bracket/archwire combination with regard to frictional resistance was performed with a two-way, balanced analysis of variance for bracket type and wire size. The Damon3 ™ bracket consistently demonstrated the lowest frictional resistance to sliding, while the Speed ™ bracket produced signifi cantly ( P < 0.001) more frictional resistance than the other brackets tested for any given archwire. The self-ligation design (passive versus active) appears to be the primary variable responsible for the frictional resistance generated by self-ligating brackets during translation. Passively ligated brackets produce less frictional resistance; however, this decreased friction may result in decreased control compared with actively ligated systems.

The aim of this in-vitro study was to analyze the forces and moments acting in the first molar region induced by the Keles Slider appliance for maxillary molar distalization, thereby investigating this appliance's suitability for translatory distalization of the upper molars. Over a working section of 3 mm with reactivation of the loaded spring systems, we analyzed the force systems of three laboratory-fabricated appliances of identical design using 3D measuring equipment. The force systems registered in-vitro exhibited complex biomechanics. Regular reactivation of the loaded coils resulted in consistent distalizing forces and uprighting moments, in forces and moments toward buccal and weak extrusive forces, and increasing mesial-inward rotating moments. The Keles Slider nearly achieves translatory molar distalization on a typodont in the sagittal plane. As a result, no uprighting activation is necessary for treatment. Because force application occurs palatally from the molars' center of resistance, there is a mesial-inward rotating moment that increases as distalization progresses, and this may lead to unwanted friction during clinical application. This is why regular reactivation of the coil spring systems, as well as subsequent measures for molar derotation, are indispensable. In the vertical plane, the molars are exposed to weak extrusive forces combined with moderate buccal rotating moments. These effects confirm that this appliance is indicated in patients with deep overbite.

SUMMARY The aims of this study were to design a twin-slot bracket featuring two horizontal slots and to examine its effi ciency in tooth displacement. Based on the structure of a traditional edgewise bracket, an additional slot was added to a twin-slot bracket and the prototype products were fabricated for the typodont experiments. The orthodontic correction of malpositioned canines was conducted on a typodont to examine the effi ciency of the twin-slot bracket in tooth displacement compared with a single-slot edgewise bracket. Three modalities of tooth movement requiring a heavy force moment, namely, axial rotation, mesiodistal tipping, and bodily translation, were conducted. The canine positions before and after simulation were measured and the changes identifi ed. Statistical analysis was undertaken using a t -test to determine the signifi cance of the differences in canine repositioning between the two bracket types. The results showed that in the twin-slot bracket group, the treatment changes in the canine position by derotation and uprighting were 40 ± 3 and 25 ± 2 degrees, respectively, compared with 20 ± 5 and 10 ± 2 degrees in the edgewise group ( P < 0.01). When retracted into an extraction space with an initial 10 degrees of mesial tip, the mesiodistal angulation of the canines in the twin-slot bracket group remained unchanged while in the edgewise group the canines became distally tipped by 5 ± 2 degrees ( P < 0.01). The twin-slot bracket signifi cantly increased the bracket width without reducing the interbracket span and therefore can generate increased force moments within the bracket, leading to an improved manipulation in tooth repositioning.

Objectives: To test the hypothesis that there is no difference between the actual mesiodistal root angulation and the mesiodistal root angulation as measured on the panoramic radiograph. Materials and Methods: A typodont dentition was set up into a Class I occlusion. Wire struts were placed on the buccal surface of each tooth to represent their long axes. The dentition was fixed into a natural skull for imaging. The radiographic and true mesiodistal angulation of each tooth to a horizontal reference plane (the arch wire) was measured using a coordinate measuring machine (CMM). The mesiodistal root positions were then altered to a more mesial and then more distal position and the measurements were repeated. Results: Only 26.7% of the radiographic root angulations were within the clinically acceptable angular variation range of ±2.5°. The greatest variation in the upper arch occurred in the canine-premolar area where the roots were projected as being more divergent. The greatest variation in the lower arch occurred in the lateral incisor-canine region where these roots were projected as being more convergent. The extent of radiographic distortion is statistically greater in the lower arch than in the upper arch in the ideal (P ≤ .05) and distal (P ≤ .01) root positions. Conclusions: The hypothesis is rejected. There is a clinically significant variation between the radiographic and the true root angulations recorded. Caution is advised when interpreting mesiodistal root angulation using this radiograph.

This was to determine the shear bond strength of composite resin bonded to preformed metal crowns with a new adhesive. Buccal surfaces of the crowns were roughened by two different methods to increase retention. Typodont mandibular second primary molars (38) were divided into two groups (19 per group). Preformed metal crowns were cemented to the teeth with glass-ionomer cement. To enhance retention, buccal surfaces of the crowns in group I were roughened with cross-cut carbide burs (SS White #56); crowns in group II were sandblasted (aluminium oxide, 50 µm). Scotchbond Universal Adhesive (3 M-ESPE) was used to bond composite resin to the crowns. A universal testing machine tested the maximum shearing force withstood by the veneered composite surfaces. Sandblasted crowns demonstrated significantly higher resistance (p = 0.001) to shearing force (324.4 N) than did the crowns that were roughened with a bur (234.2 N). Chairside veneering of composite resin to pretreated crowns could be a feasible, aesthetically pleasing, and an economical option in paediatric dentistry.

Background: Different CAD/CAM machinesâ generation may impact the restoration overall quality. The present study evaluated the marginal fit of CAD/CAM restorations manufactured with different generations of CEREC milling unit systems. Material and Methods: Sixteen typodont teeth were divided into two groups (n=8) according to the machineâ s generation assigned. These are control group (G1): Cerec AC with Bluecam/Cerec 3 milling unit and (G2): Cerec AC with Bluecam/MC XL Premium Package milling unit. Scanning of the preparation were performed and crowns were milled using the Vita Mark II blocks. Blocks were cemented using epoxy glue on the pulpal floor only and finger pressure applied for 1 min. Upon completion of the cementation step, misfits between the restoration and abutment were measured by microphotography and the silicone replica technique using light body silicon material on Mesial (M) and Distal (D) surfaces. Results: Mean and SDs of marginal gaps in micrometers were: G1/M: 94.90 (±38.52), G1/D: 88.53 (±44.87), G2/M: 85.65 (±29.89), G2/D: 95.28 (±28.13). Two-way ANOVA indicated no significant differences among different groups (P>0.05); surface area (P>0.05) and the interaction (P>0.05). Overall, G2 had greater margin gaps than G1, however, without statistical difference (P>0.05). Conclusions: Difference in milling unit generation did not significantly affect the marginal fit. Marginal gap means were in the range of the clinical acceptance levels for both generations of Cerec milling units, regardless the teeth site area.

Objective: To determine if there is any significant difference in excess adhesive flash (EAF) with the use of APC PLUS adhesive coated appliance system and Transbond XT and if other variables such as side of the mouth, time taken to bond the brackets, the age of the orthodontic specialist, or the years of clinical experience affected the amount of EAF. Materials and Methods: Twenty orthodontic specialists bonded 20 preadjusted straight wire brackets (Victory, 3M Unitek) on a typodont with a Class I crowded malocclusion in a split-mouth design, with one-half of the brackets bonded with APC PLUS adhesive system and the other half with Transbond XT. The teeth were sputter coated with gold and an image was taken at 32× magnification in a scanning electron microscope (Philips XL30). The resultant tagged image file (TIF) was opened in AnalySIS Pro 3.1 (Soft Imaging System, Munich, Germany) and the area of EAF was measured. Results: t-Tests demonstrated that: (1) there was no statistically significant difference in EAF between two adhesives when bonding in different quadrants of dentition; and (2) there was no statistically significant difference in EAF between two adhesives overall. Analysis of variance models demonstrated there were no statistically significant differences found regarding the age of the orthodontic specialists, years of clinical experience, and time in performing the bonding. Conclusions: The addition of a coloring agent to assist in the visualization of the excess adhesive does not reduce the amount of excessive adhesive around orthodontic brackets.

Objectives: To determine the amount of variation in overjet and overbite that may result from changes in upper and lower incisor angulations following upper first premolar extraction treatment in Class II malocclusions. Materials and Methods: Typodonts were set up to simulate a skeletal Class II occlusion treated with upper first premolar extractions. The upper incisor angulation was altered through a range from 100° to 120° to the palatal plane by 2° increments. The overjet and overbite were measured with every 2° of upper incisor angulation change. A regression analysis was performed on the experimental data, and the regression coefficients, slope, and intercept were estimated. Results: Excessive proclination of the lower incisors will result in an abnormal overjet and overbite relationship for any magnitude of upper incisor angulation. A normal lower incisor angulation facilitates the attainment of an optimal occlusion. Excessive palatal root torque of the upper incisors will result in an increase in overjet and a consequent decrease in overbite. If the upper incisors are excessively retroclined, an edge-to-edge incisor relationship will result. Conclusion: Class II camouflage treatment with upper first premolar extractions requires correctly angulated incisors to achieve optimal buccal segment interdigitation and incisor relationship. Labial root torque and interproximal reduction of the lower anterior teeth should be considered when the lower incisors are excessively proclined.

Tracking student performance in preclinical and clinical courses can be helpful in developing and refining a curriculum. Our objective was to correlate student performance on three fixed prosthodontic examinations taken by eighty junior dental students. Examinations included a knowledge-based objective structured clinical examination (OSCE), a manual skills exercise completed on a typodont (Typodont), and a competency casting exam (Casting CE) on a patient. Multiple regression analysis indicated that the OSCE and Typodont exam scores, as independent variables, were not statistically significant predictors (P=0.07; P=0.87, respectively) of Casting CE exam performance, which was the dependent variable. Correlations were weak for the OSCE (r=0.21) and nearly nonexistent for the Typodont exam(r=0.03) when compared to the Casting CE. Our results indicate a weak correlation between an OSCE-based knowledge exam measuring students' knowledge of critical errors in preparations and castings and a competency exam involving the preparation of a full veneer crown. Results also indicate virtually no correlation between a typodont preparation examination designed to provide a measure of students' clinical skill and a clinical competency exam involving the preparation of a full crown.

Objectives To examine the marginal fit of resin composite crowns manufactured with the CEREC 3 system employing three different margin designs; bevel, chamfer and shoulder, by means of a replica technique and a luting agent. Methods Three master casts were fabricated from an impression of a typodont molar tooth and a full-coverage crown prepared with a marginal finish of a bevel, a chamfer and a shoulder. Each cast was replicated 10 times ( n = 10). Scanning of the replicas and crown designing was performed using the CEREC Scan™ system. The crowns were milled from Paradigm MZ100™ composite resin blocks. The marginal fit of the crowns was evaluated with a replica technique (Aquasil™ LV, Dentsply), and with a resin composite cement (RelyX™ Unicem, Aplicap™) and measured with a travelling microscope. Statistical analysis was performed using two-way ANOVA. Results For the replica technique the average marginal gaps recorded were: Bevel Group 105 ± 34 μm, Chamfer Group 94 ± 27 μm and Shoulder Group 91 ± 22 μm. For the resin composite cement the average marginal gaps were: Bevel Group 102 ± 28 μm, Chamfer Group 91 ± 11 μm and Shoulder Group 77 ± 8 μm. Two-way ANOVA analysis showed that there was no statistically significant difference between the three groups of finishing lines regardless of the cementation technique used. Conclusions The marginal gap of resin composite crowns manufactured with the CEREC 3 system is within the range of clinical acceptance, regardless of the finishing line prepared or the cementation technique used.

The objective of this study was to evaluate the marginal and internal fit of zirconia copings obtained with different digital scanning methods. A human mandibular first molar was set in a typodont with its adjacent and antagonist teeth and prepared for an all-ceramic crown. Digital impressions were made using an intraoral scanner (3Shape). Polyvinyl siloxane impressions and Type IV gypsum models were also obtained and scanned with a benchtop laboratory scanner (3Shape D700). Ten zirconia copings were fabricated for each group using CAD-CAM technology. The marginal and internal fit of the zirconia copings was assessed by the silicone replica technique. Four sections of each replica were obtained, and each section was evaluated at four points: marginal gap (MG), axial wall (AW), axio-occlusal edge (AO) and centro-occlusal wall (CO), using an image analyzing software. The data were submitted to one-way ANOVA and Tukey’s test (α = 0.05). They showed statistically significant differences for MG, AO and CO. Regarding MG, intraoral scanning showed lower gap values, whereas gypsum model scanning showed higher gap values. Regarding AO and CO, intraoral digital scanning showed lower gap values. Polyvinyl siloxane impression scanning and gypsum model scanning showed higher gap values and were statistically similar. It can be concluded that intraoral digital scanning provided a lower mean gap value, in comparison with conventional impressions and gypsum casts scanned with a standard benchtop laboratory scanner.

The aim of this pilot study was to evaluate the feasibility of a new tooth preparation assessment software, Preppr, as an educational tool for dental students in achieving optimal parameters for a crown preparation. In February 2015, 30 dental students in their fourth year in a five-year undergraduate dental curriculum in New Zealand were randomly selected from a pool of volunteers (N=40) out of the total class of 85. The participants were placed into one of three groups of ten students each: Group A, the control group, received only written and pictorial instructions; Group B received tutor evaluation and feedback; and Group C performed self-directed learning with the aid of Preppr. Each student was asked to prepare an all-ceramic crown on the lower first molar typodont within three hours and to repeat the exercise three times over the next four weeks. The exercise stipulated a 1 mm finish line dimension and total convergence angles (TOC) between 10 and 20 degrees. Fulfillment of these parameters was taken as an acceptable preparation. The results showed that Group C had the highest percentage of students who achieved minimum finish line dimensions and acceptable TOC angles. Those students also achieved the stipulated requirements earlier than the other groups. This study’s findings provide promising data on the feasibility of using Preppr as a self-directed educational tool for students training to prepare dental crowns.

© 2015 Editorial Council for the Journal of Prosthetic Dentistry. Statement of problem Controlling tooth reduction for porcelain laminate veneers (PLVs) in fractions of millimeters is challenging. Purpose The purpose of this study was to assess an automated robotic tooth preparation system for PLVs for accuracy and precision compared with conventional freehand tooth preparation. Material and methods Twenty maxillary central incisor tooth models were divided into 2 groups. Ten were assigned to a veneer preparation with a robotic arm according to preoperative preparation design-specific guidelines (experimental group). Ten were assigned to conventional tooth preparation by a clinician (control group). Initially, all tooth models were scanned with a 3- dimensional (3D) laser scanner, and a tooth preparation for PLVs was designed on a 3D image. Each tooth model was attached to a typodont. For the experimental group, an electric high-speed handpiece with a 0.9-mm-diameter round diamond rotary cutting instrument was mounted on the robotic arm. The teeth were prepared automatically according to the designed image. For the control group, several diamond rotary cutting instruments were used to prepare the tooth models according to preoperative preparation design guidelines. All prepared tooth models were scanned. The preoperative preparation design image and scanned postoperative preparation images were superimposed. The dimensional difference between those 2 images was measured on the facial aspect, finish line, and incisal edge. Differences between the experimental and the control groups from the 3D design image were computed. Accuracy and precision were compared for all sites and separately for each tooth surface (facial, finish line, incisal). Statistical analyses were conducted with a permutation test for accuracy and with a modified robust Brown-Forsythe Levene-type test for precision (α=.05). Results For accuracy for all sites, the mean absolute deviation was 0.112 mm in the control group and 0.133 mm in the experimental group. No significant difference was found between the 2 (P=.15). For precision of all sites, the standard deviation was 0.141 mm in the control group and 0.185 mm in the experimental group. The standard deviation in the control group was significantly lower (P=.030). In terms of accuracy for the finish line, the control group was significantly less accurate (P=.038). For precision, the standard deviation in the control group was significantly higher at the finish line (P=.034). Conclusions For the data from all sites, the experimental procedure was able to prepare the tooth model as accurately as the control, and the control procedure was able to prepare the tooth model with better precision. The experimental group showed better accuracy and precision at the finish line.

To compare the accuracy and reproducibility of measurements of on-screen three-dimensional (3D) digital surface models captured by a 3Shape R700™ laser-scanner, with measurements made using a digital caliper on acrylic, plaster models or model replicas.Four sets of typodont models were used. Acrylic models, alginate impressions, plaster models and physical replicas were measured. The 3Shape R700™ laser-scanning device with 3Shape™ software was used for scans and measurements. Linear measurements were recorded for selected landmarks, on each of the physical models and on the 3D digital surface models on ten separate occasions by a single examiner.Comparing measurements taken on the physical models the mean difference of the measurements was 0.32 mm (SD 0.15 mm). For the different methods (physical versus digital) the mean difference was 0.112 mm (SD 0.15 mm). None of the values showed a statistically significant difference (p 0.05) on the Objet Eden 250™ 3D prints, alginate impressions, plaster and acrylic models.The comparison of measurements on the physical models showed no significant difference. The 3Shape R700™ is a reliable device for capturing surface details of models in a digital format. When comparing measurements taken manually and digitally there was no statistically significant difference. The Objet Eden 250™ 3D prints proved to be as accurate as the original acrylic, plaster, or alginate impressions as was shown by the accuracy of the measurements taken. This confirms that using virtual study models can be a reliable method, replacing traditional plaster models.

Purpose: The purpose of this study was to determine if differences existed in range of wrist movements and scaling time efficiency of dental hygienists using a rotating ultrasonic insert when compared with a standard universal insert. Methods: A convenience sample of 32 consenting experienced dental hygienists who met inclusion criteria was invited to participate. Using a cross-over research design, the 32 participants were randomly assigned to one of the two subgroups. Subgroup A (n = 16) used the rotating universal ultrasonic insert on a typodont, rested for 15 min and the standard universal insert on a different typodont. Subgroup B (n = 16) used the standard universal ultrasonic insert on a typodont, rested for 15 min and the rotating universal ultrasonic insert on a different typodont. Each participant used the rotating and standard universal ultrasonic scaling inserts to remove 2 cm3 artificial calculus from two different typodonts for up to 15 min per insert. Scaling time efficiency was determined using a Modified Volpe–Manhold Calculus Index, measuring the amount of artificial calculus remaining after ultrasonic scaling. While scaling, each participant wore the WristSensorTM goniometry gloves, which determined changes in wrist movements (flexion and extension and ulnar and radial deviations), measured as a deviation from the neutral position. Results: A paired t-test (P = 0.05) using 30 subjects with useable data, revealed no statistically significant differences between the two different inserts in terms of wrist movements and scaling time efficiency. A multivariate analysis of variance revealed no statistically significant differences in the percentage of time dental hygienists were in high, medium or low-risk posture categories while using the rotating ultrasonic insert compared with the standard universal insert. Based on the results of this laboratory study, dental hygienists using a rotating ultrasonic insert appear to experience no ergonomic advantage in terms of wrist postures or timesavings over a standard insert.

Convergence angles for complete crown preparations have been recommended at 4-12 degrees . However, practitioners have difficulty meeting these recommendations. This study measured and compared the convergence angles of tooth preparations for complete crowns prepared at three Colleges of Dentistry: the University of Tanta, Egypt, King Abdulaziz University, Saudi Arabia, and The Ohio State University, Columbus, Ohio.The convergence angles of 499 tooth preparations for complete crowns were evaluated. These comprised of a random sample of 262 teeth prepared by third-year dental students at the University of Tanta on extracted molars under normal preclinical conditions, 37 preparations on molar teeth on typodonts done by first-year dental students. The Ohio State University and 200 molar typodont complete crown preparations done by fourth-year dental students at King Abdulaziz University, Saudi Arabia. The bucco-lingual and mesio-distal convergence angles of each preparation were measured with a goniometer microscope. Mean convergence angles were calculated, and differences between groups were tested for statistical significance with analysis of variance (ANOVA) at 5% level of confidence.Convergence angle measurements were significantly different between the groups and the dimensions (P0.001). The greatest convergence value (19.8+/-10.0) was for bucco-lingual measurements prepared by Egyptian dental students. The smallest convergence value (14.1+/-3.8) was for mesio-distal measurements prepared by Saudi dental students.This study emphasized the difference between what is taught at dental schools (what is theoretically possible) and the school results of actual practice. There was a considerable disparity between the convergent angles recorded in this study and the ideal configurations recommended in fixed prosthodontic textbooks and the dental literature.

The purpose of this study was to explore how wearing, or not wearing, protective gloves affects the efficiency of orthodontists in performing certain orthodontic procedures. Thirty-six volunteers were randomly selected from members of the Taiwan Association of Orthodontists. A visual analogue scale (VAS) was used to determine the degree of convenience subjects felt in performing 11 specified orthodontic procedures, with and without gloves. In addition, the time required to bend round and rectangular archwires and to tie and untie ligature wires was recorded. The results showed that for 10 of the 11 orthodontic tasks there was perceived to be no difference when wearing, or not wearing, gloves. Only when bending a round archwire was there perceived to be a difference. When the four orthodontic procedures were undertaken on a typodont and timed, no significant difference was found between the use of gloves/no gloves.

Contemporary dental simulation systems were developed to improve dental students' transition from the preclinical laboratory to the clinic. The purpose of this study was to compare the efficacy of a virtual reality computer-assisted simulation system (VR) with a contemporary non-computer-assisted simulation system (CS). The objectives were to determine whether there were differences between the two systems in the quality of dental students' preparations and the amount of faculty instruction time. Students who completed their first year of dental school and had no previous experience preparing teeth were group matched according to their performance in the first-year Dental Anatomy laboratory course and assigned to VR (n=15) or CS (n=13). In the summer, they spent two weeks (approximately 3 hrs/day) executing amalgam and crown preparations on typodont teeth. Short presentations describing the preparations were given to both groups; however, preparation criteria were available on the computer for the VR group, while the CS group received handouts. Both groups could request feedback from faculty, although VR also obtained input from the computer. A log was kept of all student-faculty (S-F) interactions. Analysis of the data indicated significant differences between groups for the following variables: mean number of S-F interactions was sixteen for the VR group versus forty-two for the CS group; and mean time of S-F interactions was 1.9+/-2 minutes versus 4.0+/-3 minutes (p

Statement of problem Dual-arch trays are often used to generate impressions of prepared teeth and of the opposing arch simultaneously. There is concern that accuracy of the casts generated with this technique can be affected by the type of tray, viscosity of the impression material, and sequence of pouring the cast. Purpose This study compared the accuracy of working dies made from impressions with metal and plastic dual-arch trays, for 2 different viscosities of impression tray material and by altering which side of the impression was poured first. Material and methods Impressions were made of a typodont mandibular arch containing a circular stainless steel crown preparation (standard). There were 3 variables: type of dual-arch tray, impression material viscosity, and order of pour of the impressioned arches. A balanced design with independent samples was used (n=10). Two types of dual-arch trays, plastic (Triple Tray) and metal (COE Impression Tray), and 2 viscosities of addition silicone for the tray were used (Aquasil Rigid and Aquasil Monophase). Type IV gypsum (Fuji-Rock) with a ratio of 20 mL of distilled water to 100 g of powder was hand-mixed for 10 seconds then mixed under vacuum for 40 seconds and poured into the trays while being vibrated. One side of the dual-arch impression was poured with 35 g of stone and allowed to set for 1 hour before the other side was poured with 35 g of stone. The order of pour was randomized, and all casts were allowed to set for 24 hours at room temperature before removal. The dies were measured in 3 dimensions (buccolingual, mesiodistal, and occlusogingival) with a measuring microscope. The gypsum working dies were placed into a custom jig fabricated to permit measurement at a fixed, reproducible position under the microscope. Each dimension of the working dies was measured 3 times, and the mean was used for the sample value. The same 3 aspects of the stainless steel standard were measured multiple times, before and then at the conclusion of measuring all working dies, to arrive at the 3 standard values to which all working die means were compared. The means for the standard used in the statistical analysis were those taken at the conclusion of the study. The intraexaminer variation for measuring the standard was 0.001 mm. A 3-factor analysis of variance was used for the statistical analysis with hypothesis testing at α=.05. Results Statistically significant differences were found with viscosity selection for the buccolingual and occlusogingival dimensions of the working die. The rigid material produced working dies slightly taller (1 μm) than the standard, and those from the monophase material were 4 μm shorter. Regarding tray selection, metal trays were slightly more accurate in the mesiodistal dimension, and when monophase was used in a plastic tray, gypsum dies were nearly 30 μm smaller in the mesiodistal dimension ( P Conclusion Within the limitations of this study, the monophase material, when compared with the rigid impression material, was most accurate for the occlusogingival and mesiodistal dimensions, although not as accurate in the buccolingual. This buccolingual difference (0.002 mm-0.006 mm) would be clinically inconsequential with the application of die spacer. The rigid impression material was also unaffected by tray selection for the mesiodistal, whereas monophase was affected. When a monophase impression material was used, plastic dual-arch trays yielded gypsum dies which were significantly smaller (0.029 mm) than the ones generated from the metal trays (0.006 mm). Thus rigid impression materials can be recommended for use in dual-arch trays; however, the magnitude of the differences would generally not be clinically significant because they could be compensated for with several coats of die spacer.

Objectives: To determine the plaque-removing ability of a Sonicare Plus® electric toothbrush in an in vitro model. Material and Methods: Multispecies oral biofilms derived from human saliva were grown on hydroxyapatite discs in a constant-depth film fermenter. The biofilms were placed in a typodont model so that they mimicked the interproximal plaque between teeth 46 and 47 and were then treated with an electric toothbrush, both activated and inactivated. The distance from the bristle tips to the edge of the disc was 2.65 mm. Brushing action was controlled by a specially constructed brushing machine. After brushing, the number of viable bacteria removed from, and remaining in, the biofilms were determined. Results: In all, 73.70% of viable bacteria in the biofilms were dislodged from the discs using the activated toothbrush. An inactivated toothbrush removed only 3.66%. Scanning electron microscopy and confocal microscopy revealed differences between untreated and treated biofilms. Conclusion: The fluid shear forces generated by the electric toothbrush penetrated at least 2.65 mm beyond the reach of the bristles and these forces contributed to the toothbrush's plaque-removal ability (p

The accuracy of an implant fixture-level impression is affected by the type of impression tray used.The purpose of this in vitro study was to investigate the accuracy of open tray implant impressions comparing polycarbonate stock impression trays and rigid custom-made impression trays to make implant fixture-level impressions.Gold cylinder pairs, splinted by gold bars (reference frameworks) were constructed on an aluminum typodont. Polyether impressions were made of 2 pairs of Brånemark 3.75-mm diameter fixtures mounted in an aluminium typodont, with 3 stock impression trays, 3 close-fit custom trays, and 3 spaced custom impression trays, by use of an open tray technique. The casts produced were assessed for accuracy by attaching the reference frameworks with alternate single screws and measuring the vertical fit discrepancy of these reference frameworks to the analogs within the working cast using a traveling microscope. Comparison of gap dimensions by tray type was performed with a nonparametric Kruskal-Wallis analysis of variance (ANOVA) followed by pair-wise Mann-Whitney U tests. To adjust for multiple comparisons in the post-ANOVA contrasts (P.02). Comparison of gap dimensions between anterior and posterior regions were performed with Mann-Whitney U tests (P.05).The results showed that the mean fit accuracy, as measured by vertical fit discrepancy, of casts from the stock trays (23 +/- 20 microm) were statistically significantly less (P.001) than the spaced custom trays (12 +/- 10 microm) or close fit custom trays (11 +/- 10 microm). The difference in median gap size for analogs with a 20-mm separation was 10 microm.Within the limits of this in vitro study, rigid custom trays produced significantly more accurate impressions than the polycarbonate stock trays. The stock trays used in this study could not produce accurate impressions consistently. For analogs with a 20-mm separation, there was a difference in medians of 10 microm in accuracy between the stock and custom trays.

Introduction: For a successful fixed partial prosthodontics, obtaining an accurate impression for making an accurate cast is of prime importance. Aim: The study emphasizes on using modified impression techniques for fixed prosthodontics without using retraction cord. Various mechanical and chemical methods have been used for achieving gingival retraction. Most of them are expensive, time consuming and uncomfortable for the patient. Cordless impression procedures using conventional impression materials are alternative to these methods. Methodology: In the present study, two cordless fixed prosthodontic impression procedures, matrix impression system and prefabricated crown shell technique; have been described and compared in terms of dimensional accuracy.An articulated acrylic resin typodont prepared with reference points was used as a master model. Addition silicon impression materials in various consistencies were used for making impressions. The coordinate measurement machine (Llyod,Germany) was used for three dimensional measurement of master model and stone casts with an accuracy of 0.0001mm. Observations: When comparing the accuracy of casts as per statistical analysis Group B (prefabricated crown shell technique) casts were less accurate in relation to inter abutment distance whereas all other distances produced statistically insignificant mean deviation from the master model. Conclusion: It can be concluded that prefabricated crown shell technique is not recommended for a long span bridge framework but is well indicated while making cordless impressions for fabrication of single crown.

This study examines accuracy of dental impressions and following plaster models taken during treatment with fixed appliances. A maxillary typodont was provided with brackets. Three examiners took impressions three times each of the variants: brackets only, archwire fixed by alastics, ligatures or Kobayashi-hooks, and brackets and archwire covered completely or just on the gingival side by protection or impression wax. Casts were scanned using Activity102®. Virtual models were compared to the scan of the typodont using Comparison®. Differences were measured and descriptively analyzed. Estimated means with 95 % confidence intervals were computed. Significance was assessed using linear mixed models. While pyramidal reference blocks had a mean difference of 0.019 mm (95 % CI = 0.017–0.021 mm) to the master model, teeth without attachments showed 0.097 mm (95 % CI = 0.082–0.111 mm), and teeth with brackets 0.169 mm (95 % CI = 0.156–0.182 mm) (p

Objective: This study aimed to compare the accuracy of digital impressions obtained from various digital impression systems. Material and methods: A typodont was prepared for a three-unit bridge, and an epoxy resin model of this preparation was designed as a reference model. A lab scanner was then used to record a digital copy of the reference model. The different systems (3M Lava C.O.S., 3Shape D900, Cadent iTero, CEREC Bluecam, and E4D Dentist) were used to scan the epoxy resin reference model and create five digital impressions each (n=5). Using computer software, the differences in spatial measurements between the digital reference model and digital impressions and were calculated. The accuracy was evaluated based on the mean difference and standard deviation in micrometers (μm) for each system?s set of five digital impressions. Results: The measurements for mean difference (standard deviation) were as follows: CadentiTero-23 (3) μm, 3M Lava C.O.S. - 36 (19) μm, 3Shape D900- 44 (18) μm, CEREC Bluecam - 68 (12) μm, E4D Dentist - 84 (4) μm. The One Way ANOVA test was significant (p ≤ 0.001).Multiple comparison post-hoc tests showed that the E4D Dentist system was significantly different from the Cadent iTero, 3M Lava C.O.S., and 3ShapeD900systems. Also, CEREC Bluecam exhibited significant differences from Cadent iTeroand3M Lava C.O.S. At the same time, there were no significant differences between Cadent iTero, 3M Lava C.O.S., and 3ShapeD900. Conclusion: Within the limitations of this study, the following conclusions were drawn: 1) There were statistically significant differences between the accuracyof the digital impression systems. More specifically, this difference was most notable when comparing the systems that achieved lower accuracy measurements versus those that demonstrated accuracy on the high end. 2) Digital impressions from the Cadent iTero system were the most accurate. Clinical significance of the study: The results of this study could affect the decision of the clinician on selecting an appropriate Computer-Aided Design/Computer-Aided Manufacturing (CAD/CAM) scanner for digital impressions. Furthermore, the results carry implications of whether digital impressions are accurate enough to be used as an alternative to conventional impression techniques.

PURPOSE The aim of this study was to evaluate a novel technique of tooth preparation in fixed prosthodontics suitable for dental students and neophyte dentists. MATERIALS AND METHODS Twenty-four dental students of the sixth-year class were recruited to verify the predicibility of this technique. Each student prepared two mandibular second premolars on a typodont for a dental crown with a 90° shoulder finishing line. One tooth was prepared using standard procedures taught in the prosthodontic dental course; the other tooth was prepared with the new technique. Three Professors of Prosthodontics of the same University evaluated the result on the basis of 10 criteria. RESULTS A statistically significant difference between the two techniques was found in 8 out of 10 criteria. The new technique showed higher values (p

Because of an imagining principle called active triangulation in the Cerec system, a shadow is cast distal to the illuminated objects. This distal shadow may be enlarged when the occlusal-cervical height of the prepared tooth is increased. Depth data of the shadow are unreliable, so the internal fit of Cerec crowns has been questioned.This study evaluated the influence of different convergence angles and tooth preparation heights on the internal adaptation of Cerec crowns.Tooth preparations were made on typodont teeth with different combinations of convergence angles and occlusal-cervical heights: Group I = 20 degrees angle, 6 mm height; Group II = 20 degrees angle, 4 mm height; Group III = 12 degrees angle, 6 mm height; and Group IV = 12 degrees angle, 4 mm height. Ten Cerec crowns were fabricated for each type of tooth preparation. Measurements of the internal fit were performed with the cement space replica technique and an image analysis system. Three-way analysis of variance was used to analyze the differences in cement space with different tooth preparations and the number of times that milling tools were used to prepare the Cerec crowns (P.05). Multiple comparisons were made to evaluate differences between groups (P.0083).Cerec crowns with a 12 degrees convergence angle demonstrated the best internal fit (cement space in Groups III and IV = 121 +/- 41 microm and 115 +/- 42 microm, respectively). The difference between the 2 convergence types was within the range of the scanning error (25 microm) produced by the Cerec camera. The number of times that milling tools were used had no significant effect on internal fit (P=.78). Tooth preparation height equal to or shorter than 6 mm occlusal-cervically with both 12 degrees and 20 degrees convergence angles also had no significant effect on internal fit (P.0083). Cement space at distal walls (185 +/- 28 microm) was the thickest among all axial walls (P=.0001) and was twice as thick as that at the facial (90 +/- 14 microm) and palatal walls (92 +/- 15 microm).Within the limitations of this study, there was little difference in the internal fit of Cerec crowns prepared with convergence angles of 12 degrees and 20 degrees. Distal shadows influenced the thickness of the cement spaces, particularly at the distal walls. However, tooth preparations with an occlusal-cervical height not greater than 6 mm did not exaggerate the effect of the distal shadows.

The flow field and local hydrodynamics of high-velocity water microdrops impacting the interproximal (IP) space of typodont teeth were studied experimentally and computationally. Fourteen-day old Streptococcus mutans biofilms in the IP space were treated by a prototype AirFloss delivering 115 µL of water at a maximum exit-velocity of 60 ms(-1) in a 33-ms burst. Using high-speed imaging, footage was generated showing the details of the burst, and demonstrating the removal mechanism of the biofilms. Footage was also generated to characterize the viscoelastic behavior of the biofilms when impacted by an air-only burst, which was compared to the water burst. Image analysis demonstrated the importance of fluid forces on the removal pattern of interdental biofilms. X-ray micro-Computed Tomography (µ-CT) was used to obtain 3D images of the typodont and the IP spaces. Computational Fluid Dynamics (CFD) simulations were performed to study the effect of changing the nozzle position and design on the hydrodynamics within the IP space. Results confirmed our previous data regarding the wall shear stress generated by high-velocity water drops which dictated the efficacy of biofilm detachment. Finally, we showed how CFD models could be used to optimize water drop or burst design towards a more effective biofilm removal performance.

Background This study examined the effect of operator experience, dominance, tooth position and access, on frequency and extent of iatrogenic damage to approximal tooth surfaces during conventional Class II cavity preparations. The effectiveness of protective devices in minimizing damage was also explored. Methods 10 students and 10 experienced dentists each prepared 24 Class II cavity preparations in typodont teeth without protection; 10 utilizing stainless steel matrix bands and 10 utilizing protective wedges. The frequency and extent of damage were analysed with respect to the above variables. Subsequently, 20 natural and 20 typodont teeth were utilized to establish the relationship in depth of damage caused by a high-speed diamond bur on typodont versus natural teeth. Results Dentists caused iatrogenic damage on 74% of approximal surfaces without protection, which fell to 50% and 46% respectively when matrix bands and wedges were used as guards. The corresponding rates of damage for students were 94%, 80% and 44%. There was no difference in depth of damage caused on the two types of teeth when bur was in contact with teeth for a very short time. Conclusions Greater operator experience and the use of guards reduces iatrogenic damage to proximal surfaces during preparation with high-speed rotary instruments.

Statement of problem Conventional impression materials and techniques have been used successfully to fabricate fixed restorations. Recently, digital pathways have been developed, but insufficient data are available regarding their marginal accuracy. Purpose The purpose of this in vitro study was to compare the marginal gap discrepancy of lithium disilicate single crowns fabricated with computer-aided design and computer-aided manufacturing (CAD/CAM) technology by using both conventional and 2 digital impression techniques. Material and methods One typodont maxillary right central incisor was prepared for a ceramic crown. Ten impressions were made by using each method: conventional with polyvinyl siloxane impression material, Lava COS (3M ESPE), and iTero (Cadent) intraoral scanning devices. Lithium disilicate (e.max CAD) crowns were fabricated with CAD/CAM technology, and the marginal gap was measured for each specimen at 4 points under magnification with a stereomicroscope. The mean measurement for each location and overall mean gap size by group were calculated. Statistically significant differences among the impression techniques were tested with F and t tests (α=.05). Results The average (±SD) gap for the conventional impression group was 112.3 (±35.3) μm. The digital impression groups had similar average gap sizes; the Lava group was 89.8 (±25.4) μm, and the iTero group was 89.6 (±30.1) μm. No statistically significant difference was found in the effects among impression techniques ( P =.185) Conclusions Within the limitations of this study, digital and conventional impressions were found to produce crowns with similar marginal accuracy.

Statement of problem The sagittal and coronal orientation of the maxillary occlusal plane plays an important role in the esthetic and functional outcome of dental prostheses. The accuracy of contemporary facebow transfer systems in transferring this orientation to semiadjustable articulators has not been quantified. Purpose The purpose of this in vitro investigation was to analyze the sagittal and coronal orientation of the occlusal plane with 5 different facebow transfer systems. Material and methods A phantom head containing a maxillary typodont (control) was oriented so that the Frankfort horizontal plane was horizontal. The angle between the occlusal plane of the maxillary arch of the phantom head and the Frankfort horizontal plane was measured along the sagittal and coronal planes with a digital protractor. Fifteen facebow records using each of 5 facebow transfer systems (test groups) were made on the phantom head containing the maxillary typodont. Diagnostic casts of the maxillary typodont were mounted on semi-adjustable arcon articulators from the facebow records. The same angles measured on the control were measured on the test groups. These angles were compared with the same angle measured on the maxillary arch of the phantom head (control). All measurements were made by 2 operators. Results Significant differences in the sagittal and coronal orientation of the occlusal plane were noted. Compared with the control, the Denar system had the least significant difference in the coronal orientation of the occlusal plane, while the Pana-Mount system had the least significant difference in the sagittal orientation of the occlusal plane. An intergroup comparison of the test groups showed significant differences among the groups. The Kois system showed the greatest difference in the coronal plane orientation, while the Denar system showed the greatest difference in the sagittal plane orientation. Conclusions None of the tested facebow systems exactly replicated the sagittal and coronal orientation of the maxillary occlusal plane. Significant differences in the sagittal and coronal orientation of the occlusal plane were observed between the test groups and the control. Intergroup comparisons revealed significant differences in the sagittal and coronal orientation of the occlusal plane.

Studies have reported a high frequency of iatrogenic damage since it was first noted in association with Class II cavity preparations in the 1970’s. The utilisation of protective devices such as stainless steel matrix bands was recommended by multiple studies, but rarely exercised by dental practitioners. A consequence is unnecessary placement of restorations in a previously healthy tooth, due to caries development in the defect or inappropriate diagnosis of the radiolucency on dental radiographs. The research for this thesis was divided into two phases. The first phase extended knowledge gained from previous studies on the frequency and extent of iatrogenic damage to the contemporary situation. This phase commenced with an in vitro study that assessed the extent of the clinical problem, the outcome of which confirmed the need to manage it. The relevance of utilisation of plastic typodont teeth for investigating iatrogenic damage was examined. The second phase was dedicated to the development of a model for management of iatrogenic damage. Further in vitro studies were conducted to establish the effectiveness and feasibility of the proposed management model. The proposed model for the management of iatrogenic damage included: i) prevention of occurrence and minimisation of iatrogenic damage by utilisation of protective devices; ii) the effectiveness of clinical techniques for detection of residual damage occurring in spite of the use of protective devices; and iii) possible methods for mitigation of the consequences of residual damage through the application of a protective coating. The first in vitro study investigated the impact of various variables on frequency and extent of iatrogenic damage to approximal tooth surfaces during Class II cavity preparations, and the effectiveness of protective devices in minimising damage. A total of 10 experienced dentists and 10 senior students each prepared 24 Class II cavity preparations in typodont teeth without protection, 10 utilising protective stainless steel bands and 10 utilising novel protective wedges. The clinical relevance of the results was tested in a separate investigation that established a relationship in the depth of damage caused by a high-speed diamond bur on typodont versus natural teeth. The frequency of iatrogenic damage inflicted without the use of protective devices was in agreement with the results of previous studies, and the use of protection statistically significantly reduced the occurrence and depth of damage. The most effective method of reducing iatrogenic damage is prevention. However, before a recommendation for the use of matrix bands and wedges could be made, it was necessary to investigate potential risks or undesirable effects associated with the use of protective devices. The literature review found no information on this topic. Therefore, a study was conducted to test the hypothesis that protective devices impair direct vision of the cavity, resulting in greater destruction through wider and deeper cavity preparations. Further, the preparation time for operators utilising protective devices was examined to assess for a reduction in operator efficiency. 120 Class II cavity preparations on first molars prepared by students and experienced dentists with and without protective devices were examined. There was no significant difference in cavity preparation width or depth for the variable of operator experience, and likewise for the use of stainless steel bands or wedges. Furthermore, there was no increase in cavity preparation time when protective devices were used. The third study investigated operators’ ability to detect iatrogenic damage caused to adjacent teeth during routine Class II cavity preparations, as well as the possibility of protecting damaged surfaces by coating with a low-viscosity nano-filled adhesive resin. Some 17 second year dental students and 10 experienced dentists examined 5 sets of typodont teeth in phantom heads for iatrogenic damage. Further, 10 natural teeth with varying types of iatrogenic damage were coated with adhesive resin and the defects imaged using SEM. Both experienced dentists and students were able to detect the presence of iatrogenic damage in approximately 80% of cases. However, experienced dentists were significantly better than students in classifying the type of damage. The low-viscosity dental adhesive resin uniformly coated shallow to moderate defects. A number of recommendations can be made on the basis of these investigations. Firstly, the potential benefits of the use of protective devices in prevention of iatrogenic damage during Class II cavity preparations outweigh the commonly perceived disadvantages to operators and patients, none of which are shown to be valid in this study. Consequently, this study supports the general clinical use of protective devices, particularly in teaching clinics. Secondly, the results stress the need to raise awareness of the potential for iatrogenic damage and to remind clinicians of its consequences. Thirdly, due to the high detectability of iatrogenic damage, it is recommended that practitioners proactively mitigate the risks associated with untreated iatrogenically damaged teeth by examination of potentially damaged surfaces. Coating of fresh iatrogenic defects with an adhesive resin may be a viable clinical option.

Objective: To evaluate the effects of tooth displacement and vibration on frictional force and stick-slip phenomenon (SSP) when conventional brackets were used with a levelling/alignment wire. Materials and Methods: The samples consisted of six groups ( n = 10 per group) with combinations of tooth displacement (2mm lingual displacement [LD], 2mm gingival displacement [GD], and no displacement [control]) and vibration conditions (absence and presence at 30 Hz and 0.25 N). A stereolithographically made typodont system was used with conventional brackets and elastomeric ligatures. After application of artificial saliva, static/kinetic frictional forces (SFF/KFF) and frequency/amplitude of SSP were measured while drawing a 0.018-inch copper nickel-titanium (Cu-NiTi) archwire at a speed of 0.5mm/min for 5 minutes at 36.5 degree celsius. Two-way analysis of variance and independent t -test were performed. Results: Tooth displacement increased SFF and KFF (control [LD, GD], P < 0.01). Vibration reduced SFF, KFF, and SSP amplitude in the control group ( P < 0.05, P < 0.05, and P < 0.001, respectively), but not in the LD and GD groups. SSP frequency was increased by vibration in the control, LD, and GD groups (all P < 0.001), and it was lower in the LD and GD groups than in the control group ( P < 0.01). Conclusions: When conventional brackets and a 0.018-inch Cu-NiTi archwire were used in the tooth displacement conditions (LD and GD), vibration did not significantly reduce SFF, KFF, or SSP amplitude.

Ideal interproximal contacts between adjacent natural teeth or dental restorations are a critical factor for the health of the dental-alveolar complex. Interproximal contact tightness is a physiological entity affected by many patient-related and restorative parameters. This variation poses a challenge in defining the "clinically acceptable" contact area tightness (CAT) and therefore how students and clinicians should be trained to evaluate this parameter. The most widely used method to evaluate interproximal contacts is to pass dental floss between contact areas. Candidates for licensure exams are instructed to check contact areas with dental floss and are advised that this will be one of the crucial parameters to be evaluated in the overall restoration quality. The purpose of this study was to evaluate a standardized interproximal contact with six brands of dental floss. Thirty faculty members and thirty dental students at one U.S. dental school evaluated the tightness of a single interproximal contact on a typodont. The results showed that no difference was found between CAT evaluations by faculty and students, whereas significant differences were found between different floss brands. In light of the results, it is suggested that licensure boards should standardize the recommendation for which floss brand should be used in order to avoid inconsistencies in students' preparation.

Little peer-reviewed information is available regarding the accuracy and reproducibility of digitally fabricated casts compared to conventional nondigital methods.The purpose of this in vitro study was to compare the accuracy and reproducibility of a digital impression and cast fabrication with a conventional impression and cast fabrication.Conventional impressions were made via a 1-step single viscosity technique with vinyl siloxanether material of a typodont master model, and conventional casts were cast from dental stone. Digital impressions were obtained with a digital scanner, and digital stereolithographic models were printed. The typodont and fabricated casts were digitized with a structured light scanner and saved in surface tessellation language (STL) format. All STL records were superimposed via a best-fit method. The digital impression and cast fabrication method was compared with the conventional impression and cast fabrication method for discrepancy, accuracy, and reproducibility. The Levene test was used to determine equality of variances, and a 1-way ANOVA was conducted to assess the overall statistical significance of differences among the groups (n=5, α=.05).No significant statistical difference was found between the digital cast and conventional casts in the internal area or finish line area (P.05). In addition, there was no statistically significant difference between these 2 techniques for a fixed dental prosthesis or single crown (P.05). However, statistically significant differences were observed for overall areas of the casts in terms of accuracy (P.01) and reproducibility (P.001). Digital impression and cast fabrication were less accurate and reproducible than conventional impression and cast fabrication methods.No statistically significant difference was found between the digital cast and conventional cast groups in the internal and finish line areas. However, in terms of the reproducibility and accuracy of the entire cast area, the conventional cast was significantly better than the digital cast.

Objectives: To implement and evaluate the accuracy of a prototype dynamic computer-assisted surgery (CAS) system for implant osteotomy preparation and compare its accuracy vs. three commercial static CAS systems and the use of an acrylic stent. Material and methods: Eight osteotomies were prepared in radiopaque partially edentulous mandible and maxilla typodonts. After cone-beam CT acquisition, DICOM files were imported into a prototype dynamic, and three static CAS systems (NobelClinician, Simplant, and CoDiagnostiX). Implant placements were planned to replicate the existing osteotomies and respective guides were requisitioned, along with one laboratory-made acrylic guide. The eight osteotomies per jaw were transferred to one typodont pair mounted in a manikin in a clinical setting and the process was repeated for four additional pairs. The 80 (two jaws 9 eight holes 9 five pairs) osteotomies were filled with radiopaque cement in-between the testing series. Three clinicians experienced with the use of the static CAS softwares used in this study prepared each 400 (80 holes 9 five modalities) osteotomies. One clinician repeated the experiment twice, resulting in a total of 2000 (five clinicians 9 400) osteotomies. The lateral, vertical, total, and angular deviations of the actual vs. the original osteotomies in the master typodonts were measured using stereo optical tracking cameras. Linear regression statistics using generalized estimating equations were used for comparisons between the five modalities and omnibus chi-square tests applied to assess statistical significance of differences. Results: The prototype dynamic CAS system was as accurate as other implant surgery planning and transfer modalities. The dynamic and static CAS systems provide superior accuracy vs. a laboratorymade acrylic guide, except vertically. Both dynamic and static CAS systems show on average < 2m m and 5 degrees error. Large deviations between planned and actual osteotomies were occasionally observed, which needs to be considered in clinical practice. Conclusions: The prototype dynamic CAS system was comparably accurate to static CAS systems.

In an experimental typodont study simulating the third stage of Tip-Edge treatment, the effect of five torquing auxiliaries on upper four incisors was assessed using the method of laser reflection. The auxiliaries analysed were: (1) Two-Spurs 0.016", (2) Four-Spurs 0.016", (3) Reciprocal Lateral Torque 0.016", (4) Torque Bar 0.022x0.018", 20 degrees, and (5) Torque Bar 0.022x0.018, 30 degrees. When comparing the wires, the efficiency (amount and speed of root tipping) varied considerably: (1) The Two-Spurs wire was the most efficient auxiliary of the five tested and showed good torque effect on the central incisors. (2) The Four-Spurs wire acting on all four incisors was less efficient than the Two-Spurs wire. (3) The Reciprocal Lateral Torque wire exhibited good palatal root torque on the central incisors and labial root torque on the lateral incisors. (4) The Torque Bars (20 degrees and 30 degrees ) were the least efficient wires of the auxiliaries tested and showed only small torque effects on the central and lateral incisor teeth. In clinical work using the Tip-Edge technique, the Two-Spurs torquing auxiliary should be the wire of choice for an efficient palatal root torque of the upper central incisors.

This is a single-blind controlled study investigating the advantages of extended-setting time dental amalgam compared to a standard amalgam in the training of undergraduate dental students. 50 dental students were randomly assigned 1 of the 2 alloys for each restoration placed in the study. Each student placed class I and class II restorations in extracted human teeth mounted in typodont arches. 449 completed restorations were available for assessment, 228 restorations in the experimental group and 221 restorations in the control group. The test restorations were overall marginally inferior to those of the control group. There appears to be no advantage in using extended-setting time dental amalgam in undergraduate training.

Volume of tooth structure replaced by an existing restoration, as assessed by visual and radiographic examination, is one diagnostic measure used by dental practitioners and dental insurance agencies to determine the relative need to restore a tooth with a full-coverage cast restoration. However, use of these methods has not been validated.This study compared the volume of a range of dental amalgam restorations placed in typodont teeth, as estimated by dentists, dental students and laypersons, with the actual volume of each restoration.Sixty subjects (20 dental school faculty, 20 dental students, and 20 clerical staff [laypersons]) participated. After reviewing photographic images of typodont teeth with mesial-occlusal-distal dental amalgam restorations, subjects estimated the volume of each restoration using various restorations on different teeth as a percentage of its tooth's coronal volume. The actual volume of each dental amalgam restoration and that of the coronal portion of the prepared teeth was calculated with a volumetric displacement technique. The single sample 2-sided t test with a.05 level of significance was used to evaluate the null hypothesis (H0 ): The survey participant's estimates of each restoration's percentage volume are the same as the measured volume values versus the alternative hypothesis (H1 ): estimates differed from the measured volume values. One-way analysis of variance was used to determine the significance of any difference between the estimates of the 3 survey test groups.Average volumes reported by all 3 groups were significantly different than the measured volume values (P.05). Experience and dental training did not significantly affect a participant's ability to evaluate restoration volumes with greater accuracy. Results reported by dentists, dental students, and laypersons were not significantly different (P.05).The volume of a restoration is inaccurately assessed by visual and radiographic examination.

This ex vivo study was designed to investigate Andrews' hypothesis that there is a space implication when incisors are torqued correctly. A working model was constructed to allow acrylic typodont incisors of varying known values of inclination to be substituted into the model. The arch lengths of the various 'set-ups' were measured using a reflex microscope linked to a PC. In order to quantify the space requirement of clinical relevance for adequate incisor torque, the method was repeated by substituting replicas of patients' 'natural' incisors. For both acrylic and natural incisors it was found that, as the inclination of the teeth increased, there was an increase in all arch lengths, this being greater for the natural incisors. This larger increase for the natural incisors was related not only to their increased size, but was also dependent on the morphology of the incisor. Those incisors which were parallel-sided showed the greatest increase in arch length, whereas the incisors that were relatively triangular in shape showed the smallest increase. When the inclination of an 'average' set of 21/12 is increased by 5 degrees, an increase in the arch length of approximately 1 mm may be expected.

The influence of the impact of a high-velocity water microdrop on the detachment of Streptococcus mutans UA159 biofilms from the interproximal (IP) space of teeth in a training typodont was studied experimentally and computationally. Twelve-day-old S. mutans biofilms in the IP space were exposed to a prototype AirFloss delivering 115 µL water at a maximum exit velocity of 60 m/sec in a 30-msec burst. Using confocal microscopy and image analysis, we obtained quantitative measurements of the percentage removal of biofilms from different locations in the IP space. The 3D geometry of the typodont and the IP spaces was obtained by micro-computed tomography ( µ-CT) imaging. We performed computational fluid dynamics (CFD) simulations to calculate the wall shear stress ( τw) distribution caused by the drops on the tooth surface. A qualitative agreement and a quantitative relationship between experiments and simulations were achieved. The wall shear stress ( τw) generated by the prototype AirFloss and its spatial distribution on the teeth surface played a key role in dictating the efficacy of biofilm removal in the IP space.

This research seeks ways to distinguish beginners from competent students based on the manner in which they perform. Five "beginner" students who had passed preclinical operative dentistry technique and six "competent" students one month prior to graduation were videotaped performing an occlusal amalgam preparation on #19 on a typodont. The tapes were scored for time in cutting the preparation and observing it and for "unproductive work" (nonfluencies). The number of changes from one operation to another and the use of instruments as aids in measurement were also recorded. Three processes were identified in every student9s performance: rough outline form, making walls parallel and cavosurfaces level, and refinement. All preparations were scored as being clinically acceptable and indistinguishable in quality between the two groups. Beginning students required over twice as long to complete the preparation and changed operations more than twice as often as their competent classmates. Most of these differences between groups occurred in the third, refinement, process. Compared to beginners, competent students showed more evidence of using powerful, internalized schema to guide their performance, were smoother, and seemed less rule-driven.