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The output torque delivered by a dental implant toggle-style torque wrench is known to be affected by activation rate. The International Organization for Standardization (ISO) established the ISO 6789-1 standard to provide guidance on activation rates relative to desired output torque in the Nm torque range. Whether the ISO 6789-1 standard applies at the relatively lower dental torque ranges is not known, and little information is available on the activation rates that clinicians use and how this may affect output torque.The purpose of this in vitro study was to determine how output torque values vary with the activation rates used by clinicians at dental implant-relevant target torque values.To determine clinically relevant activation rates, a new adjustable dental implant toggle-style torque wrench was activated from 0 to 25 Ncm target torque by 5 prosthodontists by using a custom mandibular and maxillary typodont model containing implants and abutments with screws. This provided a baseline of activation rates (mm/sec). Data were transferred to a computerized numerical control model incorporating a variable speed linear motor, which was used to drive a dental implant toggle-style torque wrench attached to an electronic torque measuring device. Constant speed and a regulated dual-speed-assigned 80/20 rate group, where 80% of target torque value was delivered first, then a pause, and the final 20% at different speeds as suggested by the ISO 6789-1 standard, were evaluated. Fast, medium, and slow rates were categorized and applied with target torque values of 10, 25, and 35 Ncm, respectively, for n=12 activations. The output torque values were recorded for both constant and 80/20 groups and compared with the desired target torque values. Data were statistically analyzed with 1-way ANOVA and the Scheffé post hoc paired t test (α=.05).The clinicians' activation rates from 0 to 25 Ncm on the typodont model converted into linear speeds resulted in fast =24.19 mm/sec, medium =14.5 mm/sec, and slow =7.25 mm/sec. When actioned at a constant rate, the mean output torque values were generally in the order of slowmediumfast in activation rates. Generally, precision output torque decreased as target torque increased, especially when slow and medium rates, either constant or regulated 80/20 were used. All mean output torque for slow, medium, and their 80/20 variants were greater than target torque. Fast and 80/20 fast produced the lowest mean output torque values for all torque settings, and at the 35 Ncm setting, the dental implant toggle-style torque wrench output torque mean values were lower than target torque. Statistically significant differences (P.05) were found among groups, most notably in the 80/20 dual-speed groups, especially in comparisons with the 80/20 fast rate group. When the target torque value was 10 Ncm with the 80/20 fast rate, the output torque value deviated from the maximum ISO limit by more than 6%.The rate of actioning a dental implant toggle-style torque wrench influenced the delivered torque value, with fast rate actioning producing lower and less precise output torque values.

Statement of problem Cement at the restorative margin after implementation of the manufacturer’s recommended procedure for cement cleanup has not been extensively evaluated. Purpose The purpose of this in vitro study was to use microcomputed tomography (μCT) to evaluate the number, volume, and width of voids left at the margin when dental cement is cleaned during the cementation process as per 2 manufacturer-prescribed methods for cement cleanup by evaluating a self-adhesive resin cement and a resin-modified glass ionomer cement. Material and methods Twenty molar Ivorine Typodont prepared teeth were scanned, and lithium disilicate crowns were milled and cemented to the prepared teeth as per the manufacturer-recommended cementation process. Two methods of cement cleanup were performed: the excess cement was tack-polymerized with a polymerization light, or a delay of 3 minutes was used for the excess cement to reach partial polymerization, and the excess cement was removed with a sharp sickle scaler. These 2 methods of cement cleanup were performed with 2 cements: a resin-modified glass ionomer cement and a self-adhesive resin. Each specimen was then scanned with a μCT machine. The buccal margin of each specimen, from mesiobuccal line angle to distobuccal line angle, was examined, and the number, volume, and width of any voids remaining at the margin open to the environment were measured. For statistical analysis, the specimens were first grouped by method of cement cleanup and then grouped by cement type. The Wilcoxon ranked sum test was implemented because of the lack of a normal distribution and the heterogeneity of the data (α=.05). Results No statistically significant difference was found in the median number of voids, median volume of voids, or median width per void between the 2 cleanup methods, irrespective of cement type (P>.05). Significant differences were found in the median number of voids, median volume of voids, and median width per void when comparing cement types, irrespective of cement cleanup methods (P Conclusions The choice of cement may be more important than the method of cement cleanup when considering voids left at the margin. Microcomputed tomography is an excellent nondestructive tool for volumetric measurements of voids at the margin.

The lack of passive fit in implant-supported restorations can lead to mechanical and biological complications and compromise the longevity of the prosthesis. The manufacturing technique and evaluation site are factors that may affect the passive fit of multiunit screw-retained implant frameworks. However, scientific information regarding this issue is lacking.The purpose of this in vitro study was to investigate the effect of manufacturing technique and evaluation site on the passive fit of multiunit screw-retained implant frameworks.Two multiunit implant analogs were placed into the right second premolar and second molar sites of a mandibular typodont model. A total of 50 3-unit Co-Cr frameworks were fabricated with 3 indirect (conventional technique, polymethyl methacrylate milling, stereolithography) and 2 direct techniques (selective laser melting and soft alloy milling). The patterns obtained by indirect techniques were subsequently cast. The Sheffield test was used for the assessment. Digital images of the sites were obtained by using a stereomicroscope at ×40 magnification, and the measurement points (n=10 for each site) were examined to record the vertical marginal discrepancy values (μm) with the aid of a measuring software program. The collected data were subjected to the 2-way ANOVA and Tukey honestly significant difference test (α=.05).The influence of the manufacturing technique (variable 1) on the vertical marginal discrepancy values was statistically significant (P.001). However, the evaluation site (variable 2) (P=.097) and the interaction of the variables (P=.960) were not statistically significant. The lowest misfit values were observed for selective laser melting (74.2 ±20.5 μm) followed by stereolithography (92.8 ±23.9 μm), soft alloy milling (108.4 ±12.0 μm), polymethyl methacrylate milling (116.7 ±17.0 μm), and conventional technique (137.5 ±18.9 μm). The vertical marginal discrepancy values of the selective laser melting group were significantly lower than those of all other groups (P.05).The manufacturing technique significantly affected the passive fit. selective laser melting-fabricated frameworks demonstrated superior fitting accuracy. Among the indirect techniques, stereolithography-fabricated frameworks revealed the lowest misfit values. The vertical marginal discrepancy values of all manufacturing groups were within the range of clinical acceptability (150 μm).

Statement of problem Studies evaluating the accuracy of edentulous arch impressions encompassing conventional and digital methods are lacking. Purpose The purpose of this in vitro study was to evaluate 8 impression-making methods for edentulous arches and to determine the effects of using a 3-dimensionally printed polyetheretherketone (PEEK) scanning aid on the accuracy of intraoral scanners. Material and methods Three sets of edentulous arch typodonts were scanned with an industrial scanner as a reference. Subsequently, a scanning aid for the edentulous arch was individually designed on each reference scan dataset by using a 3-dimensional modeling software program and fabricated in PEEK with a 3-dimensional printer. Each typodont was scanned with 2 intraoral scanners 12 times, with and without the assistance of a scanning aid for the edentulous arch. Impressions were made with 4 different conventional impression materials (irreversible hydrocolloid, polysulfide, polyether, and polyvinyl siloxane)—12 times for each typodont—the casts were poured and digitized with a tabletop scanner. Each scan data set was superimposed over the corresponding scan data set, and the original and absolute distance values from the paired surface points were obtained to measure the trueness and precision. These were expressed by using the mean, median, root mean square, and (90 percentile-10 percentile)/2 of the absolute distance value (NMT) concepts, based on the raw data extraction protocol. A repeated-measures ANOVA followed by a post hoc Bonferroni test was conducted (α=.05). Results The impression-making methods did not show statistically significant differences (P>.05) for either trueness or precision, particularly when the median values of the original and absolute distance values from the paired surface points were chosen as the standard values. One of the intraoral scanners used exhibited significantly superior outcomes to conventional impression materials when scanned with the scanning aid for the edentulous arch for both trueness and precision when the mean, root mean square, and NMT concepts were applied (P Conclusions Intraoral scanners demonstrated accuracy comparable with that of conventional impression materials for making edentulous arch impressions, regardless of the concepts used to express the trueness and precision. The PEEK-based scanning aid for the edentulous arch did not improve the accuracy of the intraoral scanners; however, its application resulted in higher accuracy compared with that of conventional impression materials.

Periodontal disease is one the most common disease pathologies in small animal medicine, yet new graduates report they feel unprepared to perform dentistry in general practice. Novel methodologies to close the knowledge gap in veterinary dentistry need to be identified. Typodonts (dental models) are commonly used in human dental schools to teach basic principles prior to practice on clinical patients and have been shown to be an effective teaching tool. The study aimed to determine if independent study and self-guided practice on a veterinary typodont prior to a structured, in-person cadaver laboratory with feedback increases students’ perceived dentistry clinical skills in performing periodontal techniques. We calculated the knowledge gap before and after the cadaver laboratory by comparing the students’ perceived and desired skill levels in performing periodontal charting, ultrasonic cleaning, hand scaling, and root planing. Ninety-six percent of students reported that practice with the dental typodont prior to the cadaver laboratory increased their comfort level in performing periodontal skills. However, practice did not result in a significant decrease in knowledge gap compared with participation in the cadaver laboratory alone. Although students perceived a benefit to practicing with the typodont, self-guided practice was not effective in decreasing the knowledge gap, most likely due to a lack of structured feedback with typodont use. Further investigation into the use of typodonts with direct feedback prior to structured laboratory or, alternatively, as an additional practice tool following a structured laboratory would further define if there is a benefit to typodont practice in veterinary dentistry.

The absolute marginal fit of CAD-CAM presintered fixed partial dentures has been poorly documented.The purpose of this in vitro study was to evaluate the marginal fit of presintered cobalt-chromium (Co-Cr) and zirconia 3-unit fixed partial dentures by using X-ray microcomputed tomography (μCT).A metal model was prepared from a typodont to receive fixed partial dentures (N=12). The maxillary first premolar and first molar were prepared with a circumferential 1.2-mm chamfer and 2-mm occlusal reduction. The dies were scanned and assigned to 1 of 2 groups to receive the prostheses made of presintered Co-Cr or presintered zirconia (n=6). Each framework was seated on its model without load application. The abutments were scanned by using μCT. A circle with 10 diameters, with a step of 18 degrees, was projected at the center of the obtained image. Absolute marginal discrepancy and marginal gap mean values were measured, and overextended and underextended margins determined. The data were analyzed by using the Levene t test and ANOVA (α=.05).No statistically significant difference was found in the marginal fit between the materials tested (P=.939). The mean values were 66 ±14 μm for Co-Cr and 61 ±12 μm for zirconia. The absolute marginal discrepancy mean value for the premolar was 69 ±12 μm and 41 ±9 μm for the molar (P.001). Overextension was predominant for both materials tested, with a higher percentage reported for the zirconia group.Presintered alloys presented clinically acceptable adaptation with a predominance of marginal overextensions.

PURPOSE To compare the accuracy of printed to digital casts produced from various intraoral and extraoral scanners with different scanning technologies. MATERIALS AND METHODS A conventional stone cast was fabricated from the reference typodont cast and scanned with two intraoral scanners (TRIOS 3 version 1.4.7.5, and Dental Wings version 2.1.0.421), and two extraoral scanners (S600 Arti, Zirkonzahn, and Ceramill map 600, Amann Girrbach GmbH). All digital scans were saved in the form of STL files and measurements were calculated using Geomagic analysis software. Two types of measurements were assessed on the casts: tooth- and arch-level measurements. Absolute errors were calculated by subtracting the measurements on 3D-printed, digital, and conventional stone casts from the measurements on the reference typodont cast. One-way ANOVA was used for comparing different measurement errors between groups. Linear regression was performed to determine the association between different explanatory variables, and the average measurement errors (dependent variable) adjusted to reference cast measurements. Regression coefficients (B) and 95% confidence intervals (CI) were calculated. RESULTS For both 3D printed, and digital casts, Dental Wings showed significantly greater error compared to other scanners and to the conventional stone cast at all measurements except AL (in the 3D printed modality only), while conventional casts showed the lowest error. Error was significantly higher in intraoral than extraoral scanners (B = 0.009, 95% CI = 0.005, 0.02), and in arch level measurements than tooth level measurements (B = 0.03, 95% CI = 0.01, 0.04), and significantly lower in 3D printed than digital casts (B = -0.04, 95% CI = -0.05, -0.04). There were no statistically significant differences between measurement errors of both arches (maxillary and mandibular arches). CONCLUSIONS Extraoral scanners showed higher accuracy than intraoral scanners, and 3D-printed casts showed higher accuracy than their digital counterparts. Dental Wings scanner had the greatest measurement error. This article is protected by copyright. All rights reserved.

Purpose To compare the accuracy of three commercially available intraoral scanners when imaging various dental material substrates. Materials and methods A maxillary dentate typodont model with 11 different dental material substrates was prepared and scanned using three intraoral scanners (TRIOS 3, 3Shape; CS 3600, Carestream; and Emerald S, Planmeca). The model was further scanned with a laboratory scanner (7series, Dental Wings) for reference. Files were exported in standard tessellation language format and inserted into a metrology 3D mesh software (CloudCompare). Results In terms of influence of different substrates on IOS trueness, a significant effect on the performance of TRIOS 3 and Emerald S was revealed. Concerning the accuracy of different intraoral scanners when scanning more translucent and reflective materials, pairwise comparisons revealed significant differences among scanners. In terms of complete-arch trueness and precision, pairwise comparisons revealed that TRIOS 3 had significantly higher trueness and precision compared to CS3600 and Emerald S. The complete-arch trueness and precision of CS3600 and Emerald S did not differ significantly. Conclusions Dental material substrates influenced the accuracy of all three tested scanners. The full metal crown exhibited significantly lower trueness compared to other substrates across all three scanners. For the high-translucency substrate group, TRIOS 3 exhibited significantly higher trueness compared to CS 3600. Polished and unpolished class II amalgam restorations of similar dimensions did not exhibit significant differences in trueness regardless of intraoral scanner. In terms of complete-arch accuracy, TRIOS 3 had significantly higher trueness and precision compared to CS 3600 and Emerald S. All three scanners exhibited complete-arch average accuracy below 100 μm.

Statement of problem Although studies have reported on selective laser melting (SLM)-fabricated removable partial dentures (RPDs), research addressing the trueness of SLM-fabricated RPD metal frameworks is sparse. Purpose The purpose of this in vitro study was to evaluate the trueness of powdered cobalt-chromium (Co-Cr) or titanium-6 aluminum-4 vanadium (Ti-6Al-4V) alloy frameworks for RPDs fabricated by SLM. Material and methods A digital scan of a Kennedy class II mandible typodont was obtained to design an RPD framework by using a computer-aided design (CAD) software program (denoted as CRF). Two experimental groups of frameworks were fabricated from the CRF by using SLM in alloys of Co-Cr (SLM-Co-Cr, n=6) and in Ti-6Al-4V (SLM-Ti-6Al-4V, n=6) while a control group was fabricated by using traditional lost-wax casting following stereolithography (CA-Co-Cr, n=6). In total, 18 RPD frameworks were digitally scanned (denoted as CRF), with each scan then superimposed on the CRF and evaluated for discrepancies by using a 3D analysis software program. A nonparametric Kruskal-Wallis test was performed to determine differences in trueness among groups (α=.05). Results The CA-Co-Cr group showed the highest discrepancy between CEF and CRF. Statistically significant differences were found between the CA-Co-Cr and SLM-fabricated groups (P=.03 for Co-Cr, and P=.016 for Ti-6Al-4V). However, no significant difference was found between the SLM-Co-Cr and SLM-Ti-6Al-4V groups (P=.787). Conclusions SLM-fabricated RPD frameworks exhibited higher trueness than CA-Co-Cr fabricated ones, indicating the potential of selective laser melting to produce the geometric shapes required for accurate dental restorations.

Background/purpose Advancements in digital dentistry and the development of intraoral scanners (IOS) have provided clinicians with an accurate and efficient alternative to analog impressions. The aim of this study was to assess the accuracy of the marginal and internal fit of 5-unit monolithic zirconia fixed dental prostheses (FDPs) fabricated with CAD/CAM technology using direct and indirect digitalization methods. Material and methods Three teeth in a maxillary typodont model were prepared to receive a 5-unit zirconia FDP. Six different groups were created according to the type of scanner (intraoral and extraoral) and the type of workflow. For direct workflow, the typodont was scanned with two different IOS (3Shape Trios 3 [3S-IOS] and Cerec Omnicam [C-IOS]). For indirect workflow, after conventional impressions were obtained, the impressions (IMP) were scanned with two different laboratory scanners (3S-IMP and C-IMP). After the impressions were poured, the stone (STN) casts were scanned with the same laboratory scanners (3S-STN and C-STN). Sixty 5-unit monolithic zirconia FDPs (10 in each group) were designed and milled. The marginal and internal fit was assessed. Results The mean marginal gap values were 78.2±9 μm in the IOS group, 82.6± 9 μm in the IMP group, and 82.6±9 μm in the STN group, indicating no statistically significant differences among groups (p > 0.05). The mean axial gap values were 77.7 ± 10 μm in IOS group, 83.61 ± 15 μm in the IMP group, and 84.5±9 μm in the STN group, indicating no statistically significant differences among groups (p > 0.05). Conclusion The marginal and internal fit of 5-unit monolithic zirconia FDPs fabricated with direct and indirect digital scans were similar. The smallest gap values were observed at the marginal region while the greatest gap values were detected at the occlusal region.

Whether cone beam computed tomography (CBCT) scans can be used for the fabrication of computer-aided design and computer-aided manufacturing (CAD–CAM) fixed dental prostheses (FDPs) is not known. The purpose of the present study was to compare the marginal fit of 3-unit zirconia FDPs fabricated by using CBCT or 3-dimensional (3D) laboratory scanning. Extracted second premolar and molar teeth in a maxillary typodont model were prepared. The first molar was removed and the typodont model was scanned with a laboratory or a CBCT scanner to generate two virtual 3D cast groups (3DL and CBCT). Forty four 3-unit zirconia FDPs were designed on virtual casts and milled. The vertical marginal discrepancy (VMD) was measured by ×100-magnification microscopy at seven locations on each abutment. A total of 616 measurements were made at 14 fixed locations in two groups of 22 specimens. The VMD data for 3DL and CBCT groups were statistically analyzed using the Mann–Whitney U test (α = 0.05). The mean VMDs on premolar ranged between 44 and 55 µm (median: 43–55 µm) in 3DL, and 74 and 100 µm (median: 72–93 µm) in CBCT; and on the molar, between 47 and 114 µm (median: 46–114 µm) in 3DL, and 91 and 162 µm (median: 93–156 µm) in CBCT. There was a significant difference between the gaps in 3DL and CBCT groups (p

Purpose: To evaluate the marginal and internal fit of endocrowns with different computer-aided design/computer-aided manufacturing (CAD-CAM) materials by measuring them with a stereomicroscope (μm). Materials and Methods: A mandibular first molar typodont tooth was prepared to receive an endocrown. The preparation was scanned using an extra-oral scanner. Endocrowns (n = 20) were fabricated using lithium disilicate (IPS e. max CAD LT block; CEREC Ivoclar Vivadent, Liechtenstein) and polyetheretherketone (PEEK) (breCAM. BioHPP®; Bredent, UK) using CAD-CAM technique. Marginal gap was evaluated using a stereomicroscope at the midpoint of all four surfaces (mid buccal, mid lingual, mid mesial, mid distal). This was followed by sectioning of the endocrowns in a sagittal plane along with the prepared tooth to evaluate the internal fit at four different points (A, B, C, D) using a stereomicroscope. Statistical analysis was performed using one-way analysis of variance test. Results: Mean values of marginal gap of lithium disilicate and PEEK endocrowns are 56.6 ± 6.1 μm and 81.3 ± 10.1 μm, respectively. Mean value internal gaps of lithium disilicate and PEEK endocrowns are 158.2 ± 11.1 μm and 199.1 ± 13 μm, respectively. Results in the present study have shown that the marginal and internal fits of lithium disilicate endocrowns are superior to that of PEEK endocrowns. Conclusions: Based on the outcomes of this in vitro study, the marginal and internal fit of lithium disilicate endocrowns is better than PEEK endocrowns. The marginal gap clinically acceptable is

Statement of the problem: Digital scanning has been widely used nowadays, however its accuracy in relation to the bridge span length needs further investigations. Objective: The aim of this study was to determine the effect of span length on the trueness of an intra-oral scanner. Materials and methods: On a typodont (Nissin Dental Model, Japan) preparations for two bridge span lengths were made. One resembling missing upper second premolar representing short straight span length (SS) while the second resembling missing upper first and second premolars representing long curved span (LS). Then typodont was scanned by a laboratory scanner (InEos X5 scanner) (Sirona Dental System, Bensheim, Germany) to act as a reference model scan to compare measurements for trueness. Then for each group five scans were taken for the typodont by Medit intraoral scanner (iScan version 1.2.0.1; Medit, Seoul, Korea) to be compared with the reference scan. Then data set from the scans were transferred to STL format and then exported to exocad (exocad version 2.3 Matera exocad GmbH,Darmstadt, Germany) software to get the measurements to determine the trueness. Results: Results of this study showed that in the comparison between short and long span bridges, the long span bridge scans showed statistically significant higher root mean square (RMS) mean value (0.23±0.10 mm), lower trueness than short span bridge scans (0.06±0.04 mm). Conclusions: Long span fixed bridge had an adverse effect on the scanning accuracy. Trueness of intraoral scanner may be affected by the complexity and length of the scanning area.

Background/purpose The orthodontic aligner becomes popular worldwide in orthodontic therapy as an esthetic alternative to fixed labial braces. This study evaluated orthodontic tooth movement behavior using different aligner materials and attachment shapes for the movement of a single tooth. Materials and methods First bicuspid extracted resin typodont models were printed with a 3D printer. Three type of attachments, an ellipsoid shape (thick and thin) and a bar, were designed to fit the canine crown surface. Three types of aligner materials, Polyethylene Terephthalate enhanced with glycol (BIOSTAR) Polyethylene Terephthalate (BenQ), and Thermoplastic polyurethanes (TPU) were used to fabricate different aligners. The typodonts with aligners were sunk in a water bath to simulate canine distal movement in vivo. The canine crown, root movement, and long axis angle changes in each step were calculated and recorded. The data were analysed using a oneway ANOVA statistical method. Results Comparing the three aligners, the changes the long axis of the canine showed that the BENQ group had a smaller change in the long axis angle. The BENQ group canine involved bodily movement, but the canine movement of the BIOSTAR and TPU group involved tipping. Comparing the three attachments, the bar type attachment had more canine crown tipping in the BIOSTAR and TPU groups. The thick and thin ellipsoid-shaped attachments showed no statistical differences in tooth movement. Conclusion Attachment shape or size had little influence on the bodily movement of the tooth. A high modulus material may thus be suitable for clinical applications.

Background/purpose: With the rise of digitalization in dentistry, intraoral scanners and digital impressions have recently been adopted by many clinicians. The aim of this study was to investigate surface topography of prepared teeth and the accuracy of digital impressions. Materials and methods: Twenty mandibular typodonts, containing left first premolar and left first molar abutment teeth manufactured by using CAD/CAM, were used in this study. An intraoral scanner was used to scan each typodont, and each STL file generated was exported in high resolution (Group H), moderate resolution (Group M), and low resolution (Group L). All 60 files were inspected in a 3-D mesh processing software. For each file, the number of triangulation points in the meshwork were obtained for both abutment teeth. Results: The measurements obtained from the 3-D mesh processing software revealed that the mean number of triangulation points on the 3-D surface of the abutment teeth (20 premolars + 20 M) were 790,625 ± 98,890 dots in Group H, 592,283 ± 74,881 dots in Group M, and 198,067 ± 19,328 dots in Group L. Significant differences were found between Group H and M (p

Statement of the problem: Extraoral scanners have been used widely nowadays however there are certain conditions that could affect their accuracy which will subsequently affect the success of the final restoration. Objective: The aim of this study was to determine the accuracy of extraoral scanner in relation to two span lengths. Materials and methods: A typodont (Nissin Dental, Kyoto Japan) was used and two bridges with different span lengths were prepared, the first one with missing upper left second premolar (short straight span (GS)) and the other with missing upper left first and second premolars (long curved span (GL)). Indentations were made on each abutment to be taken as a reference for measurements. For both groups reference scan was taken by inEos X5 extra-oral scanner. Then five physical impression was taken for each group using vinylpolysiloxane impression material (Honigum, Germany) and then poured into type IV dental stone. Casts of each group were scanned using DOF extraoral scanner (DOF Company, Korea). Measurements were made from the indentations on the reference scan and the sample scans, compared with each-other and root mean square value (RMS) was obtained to evaluate the trueness. Results: Comparison between short and long span bridges revealed that there was no statistically significant difference between trueness values of short and long span bridges. Where RMS mean for the short span was 0.0727 mm and that for the long span was 0.1069 mm. Conclusions: Different span lengths do not seem to affect the trueness of the extra-oral scanner tested.

Using software for assessment of restorative work on typodonts in the simulation laboratory may enhance the objective evaluation of student work. The study aimed to evaluate the inter-rater and intra-rater reliability using 3-D scans from the Planmeca Emerald™ intra-oral scanner with Romexis Compare® software for assessing preparations for preformed metal crowns (PMCs). Three operators independently recorded 3-D scans and digitally measured the features of 30 PMC preparations on typodont primary teeth (# 75). Using Romexis Compare® software, preparations were measured from mesial, distal and occlusal aspects. Measurements were repeated after 2 weeks. The intraclass correlation coefficient (ICC) was used to measure the reliability of measurements between operators and within the one operator. For measuring the extent of tooth reduction, there was excellent intra-rater reliability for each operator (ICC 0.96–0.99). The highest inter-rater reliability was for measurements of the occlusal surface (0.946 and 0.956), followed by the mesial surface (0.852 and 0.862) and then the distal surface (0.746 and 0.724). This method was useful and reliable for measuring features of PMC preparation, but with some limitations. Improving the software to provide specific assistance tools would empower greater uptake of this method as an adjunct to traditional visual grading tool in paediatric dentistry preclinical teaching.

Summary Background Orthodontic patients wearing fixed appliances are susceptible to traumatic dental injuries during contact-sport. This laboratory study investigated the protective qualities of orthodontic mouthguards using impact-testing to a typodont fitted with a fixed appliance through peak load transfer and retention of the mouthguard. Methods Seven orthodontic mouthguards [three custom-made (Medium-CM, Heavy-CM, Heavy-pro-CM); three commercially-available mouth-formed (Shock-Doctor® Ultra Braces, Opro® Ortho-Gold Braces, Opro® Ortho-Bronze Braces) and a Shock-Doctor® Instant-Fit] were fitted to a maxillary arch typodont bonded with a fixed appliance and impact-tested using 0.5 or 1 Joule (J) energy via hockey-ball, cricket-ball or steel-ball projectile. A load-cell recorded peak load transfer through mouthguard to typodont with retention scored in a binary manner dependent upon any displacement following impact. Differences across mouthguards were calculated with ANOVA or Kruskal–Wallis test for normal and non-normal data, respectively. Post hoc comparisons across mouthguards were conducted via Dunnett's test with Sidak correction. Results Only the three custom-made and Opro® Ortho-Gold Braces were not displaced by impact-testing. For these, Opro® Ortho-Gold Braces transferred the smallest load for 3/6 impact-tests, followed by Medium-CM. Heavy-pro-CM performed poorly, ranking penultimate or worst for all impact-tests. Significant differences were found between mouthguards for cricket-ball and steel-ball set-ups. The Opro® Ortho-Gold Braces performed better than the Heavy and Heavy-pro-CM for 0.5 J cricket-ball impact-test (P < 0.05), whilst Medium-CM performed better than Heavy-pro-CM. For 1 J cricket-ball, there were significant differences between Medium-CM and Heavy-pro-CM (P < 0.05). For 0.5 J steel-ball, the Medium-CM performed significantly better than both Heavy-pro-CM and Opro® Ortho-Gold Braces (P < 0.05), whilst Heavy-CM performed better than the Heavy-pro-CM (P < 0.05). For the 1 J steel-ball, Medium and Heavy-CM performed better than Opro® Ortho-Gold Braces (P < 0.05). Conclusions Opro® Ortho-Gold and Medium-CM mouthguards offer the best protection for low-impact sports, whilst Medium or Heavy-CM mouthguards are recommended for high-impact sport.

Purpose To evaluate the marginal and internal adaptation of all-ceramic crowns and inlays fabricated by different scanners of the same CAD/CAM system. Materials and methods All-ceramic crown preparations were performed on typodont maxillary first premolars, and mandibular first molars were prepared for ceramic Class II mesio-occlusal inlays. Two intraoral scanners (CEREC Bluecam and Omnicam, Dentsply Sirona) and one model scanner (CEREC inEos X5, Dentsply Sirona) were used to scan the preparations. All restorations were fabricated by milling single-feldspathic ceramic blocks (CEREC Blocks). The marginal and internal discrepancies of restorations were evaluated via micro-CT analyses. Results For linear crown measurements, the marginal gaps were 63.75 μm, 88.24 μm, and 90.89 μm for Bluecam, Omnicam, and inEos X5, respectively. For crowns at central groove areas, the maximum values for Bluecam, Omnicam, and inEos X5 were found to be 144.78 μm, 165.19 μm, and 129.49 μm, respectively. For inlays, the highest range at the midpoint of the axiopulpal line angle for Bluecam, Omnicam, and inEos X5 were determined as 138.57 μm, 184.33 μm, and 179.71 μm, respectively. In volumetric measurements, inEos X5 showed lower gap for both crowns (11.47 mm3) and inlays (5.65 mm3) compared to both intraoral scanners. These results are within a clinically acceptable range. Conclusion When all-ceramic crowns were evaluated, there were generally no significant differences found between scanners for the regional linear measurements, but more gaps occurred in restorations obtained with intraoral scanners for volumetric measurements. On the other hand, when the inlay restorations were evaluated, significant differences were found between groups except for the midpoint of the axio-pulpal line angle and the midpoint of the mesio-gingival margin. However, marginal and internal gaps of both crowns and inlays presented mean values less than 150 μm in many surfaces, which could be considered clinically acceptable.

Purpose To evaluate the effect of three two-retainer designs of a resin-bonded fixed dental prosthesis (RBFDP) on fracture resistance. Materials and methods A total of 21 three-unit, all-ceramic RBFPDs were fabricated to replace a missing maxillary lateral incisor. The prostheses were divided into three groups of 7 each: Group L (labial RBFPD); Group ML (modified labial RBFPD, fabricated the same as in Group L with additional preparation that included a shallow proximal groove at the pontic side); and Group P, an all-ceramic palatal RBFPD that acted as control. Preparations were done on the maxillary left central incisor and canine of a typodont model, and 21 epoxy resin models were duplicated for the three groups. The RBFPDs were designed using CAD software and constructed using the heat-pressed technique, after which the prostheses were bonded to their corresponding epoxy resin model according to the manufacturer's instructions. A fracture resistance test was performed on all specimens following aging. Data were analyzed using one-way ANOVA. Results The highest fracture load values were recorded in Group P (547.5 N), followed by Group ML (462.6 N) and then Group L (418.3 N). The difference among the three designs was not statistically significant (F = 2.5, P = 0.1). Conclusion Both labial and modified labial RBFDPs could be a viable alternative treatment option for replacement of missing maxillary lateral incisors.

AIM The World Health Organization (WHO) periodontal probe is recommended for epidemiologic surveys and periodontal screening, but its ability to identify subgingival dental calculus (DC) relative to a #11/12 explorer is not known. This study compared in vitro the ability of the WHO probe and a #11/12 explorer to detect subgingival DC. MATERIALS AND METHODS Three typodont models with randomly distributed artificial DC on mandibular molar and premolar root surfaces were assessed with a WHO periodontal probe and a #11/12 explorer by two periodontists. The diagnostic performance of the two instruments for subgingival DC detection was compared using 2 × 2 contingency table analysis. RESULTS A #11/12 explorer provided better reproducibility, a higher level of sensitivity, higher positive predictive values, higher negative predictive values, and greater overall accuracy (diagnostic effectiveness) (76.9% vs. 68.5% for the first periodontist; 87.0% vs. 75.0% for the second periodontist) for detection of subgingival DC than the WHO probe. CONCLUSION The in vitro diagnostic performance of a #11/12 explorer was superior to the WHO periodontal probe for identification of subgingival DC. CLINICAL SIGNIFICANCE A #11/12 explorer, rather than the WHO probe, is recommended for identification of subgingival DC.

Information on the morphological accuracy of crowns produced by different technologies is limited.The purpose of this in vitro study was to compare the morphology and contacts of crowns fabricated with intraoral systems, extraoral systems, and conventional method.A typodont mandibular first molar (Nissin Dental Product) received a complete ceramic crown preparation and a reference crown. Microcomputed tomography (μCT) was used to obtain the virtual data (REF) of the reference crown. Three groups of replicated crowns were made: intraoral scanning system (TRIOS), extraoral scanning system (D700), and the conventional method (CONV) (n=8). The groups TRIOS and D700 were designed by the correlation method. All crowns were scanned with μCT to obtain 3D data. The data were superimposed on each other or the REF in an inspection software to evaluate precision and trueness. The contact penetration area of the occlusal surfaces of the crowns was calculated. An independent sample t test and 1-way ANOVA with the post hoc least significant difference (LSD) test were used to compare the data (α=.05).The crowns fabricated with the extraoral scanners showed significantly lower root mean square (RMS) values for trueness (F=1456.90, df=2, P.001) and precision (F=188.88, df=2, P.001) than the others. The penetration contact area ratio and the differences in the CONV group were both significantly higher than those of the other groups.The average discrepancies of the crown morphology fabricated from the extraoral scanning were significantly lower than those from others. The conventional method restored the occlusal contact with significantly less accuracy than the other groups.

The stereolithography technique has been a promising method of fabricating fracture-resistant ceramic restorations efficiently. However, studies on the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the technique are lacking.The purpose of this in vitro study was to evaluate the dimensional accuracy and clinical adaptation of ceramic crowns fabricated with the stereolithography technique.A typodont maxillary right first molar abutment tooth was scanned by using an extraoral scanner, and a crown was designed by using 3Shape Dental System CAD software. Ten ceramic crowns were fabricated with 2 different stereolithography systems, CeraFab7500 (CF) alumina and CSL150 (CL) zirconia, and a conventional computer-aided design and computer-aided manufacturing system, X-MILL500 (XM) zirconia. The crowns were scanned, and the digital casts were exported. Dimensional accuracy was measured by superimposing the digital casts with the reference model by using Geomagic Qualify software. The silicone replica method was applied to measure clinical adaptation. Results were statistically analyzed by using a 1-way analysis of variance (α=.05).CeraFab7500 reported better dimensional accuracy (41 ±11 μm) than CSL150 (65 ±6 μm) or X-MILL500 (72 ±13 μm) (P.001). No significant difference was found between the CSL150 and X-MILL500 groups (P.05). X-MILL500 reported significantly better adaptation in the marginal, corner, and occlusal areas but inferior adaptation in the axial area compared with CeraFab7500 and CSL150 (P.05). Significant differences were only apparent in the axial and occlusal areas between CeraFab7500 and CSL150 (P.05). No significant difference was found in the marginal or corner area between CeraFab7500 and CSL150 (P.05).Both CeraFab7500 and CSL150 can fabricate ceramic crowns with high dimensional accuracy and marginal adaptation within clinically acceptable limits. The results indicate that the fabrication of ceramic crowns by using the stereolithography technique seems to be promising.

Purpose/objectives Dental students experience difficulties during the transition from preclinical to clinical curriculum. In order to help the students to adapt to the clinical education program, a simulated practice using patient-based customized models was introduced in this study to prepare for their first clinical practice. Methods This study included 45 Third year predoctoral students (D3 students) who were about to perform the preparation of a single crown abutment on their first patient. After practicing abutment preparation using simulated models and providing the actual treatment to their own patient, the students were surveyed to investigate their perceptions on the simulated practice using the 3D-printed customized typodont model. The statistical analysis of the quantitative data and the thematic analysis of the qualitative data were conducted. Results Regarding this simulation, more than 80% of the students gave positive feedback on their practice of (a) operative positions and postures, (b) finger rest, (c) occlusal reduction, (d) axial reduction, and (e) proximal reduction. Student responses on the open-ended questions about how they perceived the usefulness of this simulation were categorized as 'First clinical case', 'Patient-based model', and 'Realistic simulation environment'. In addition, a number of improvements of the simulation was also suggested by the students including the typodont and the manikin. Conclusions This study gives insights into the significance of simulated practice using patient-based customized typodonts as a transitional education tool and its direction of development in the field of restorative treatments accompanied by irreversible tooth preparations.

Introduction This study evaluated the success rate of and tooth substance removal required for computer-guided preparation of endodontic access cavities. Methods Thirty acrylic typodont teeth with root canals (10 each of tooth numbers 11, 14, and 17) were randomly allocated to a study or control group (15 teeth per group). In the study group, teeth were fixed in acrylic resin and subsequently digitized using a laboratory scanner. A cone-beam computed tomographic scan was then taken. Access cavity preparations were planned virtually, and a template was 3-dimensionally printed. In the control group, access cavities were prepared using the conventional access technique. Tooth substance removal was assessed by weighing teeth before and after preparation. Volume loss was analyzed statistically by use of the Wilcoxon-Mann-Whitney test at a significance level of P Results Using guided endodontics, 93.3% of root canals were located successfully compared with 100% of root canals using the conventional technique. In the control group, the mean tooth substance removal was 16.1 ± 3.7 mm³ for incisors, 44.2 ± 8.9 mm³ for premolars, and 99.3 ± 3.1 mm³ for molars. In the study group, significantly less tooth substance was removed; substance loss was 10.3 ± 1.1 mm³ for incisors, 29.3 ± 4.2 mm³ for premolars, and 51.8 ± 5.3 mm³ for molars. Conclusions The use of guided endodontics in normally calcified teeth enables the preservation of a significant amount of tooth substance. However, this advantage must be carefully balanced against a greater radiation burden and risk of perforation, higher costs, and more difficult debridement and visualization of the pulp chamber and root canals.

Background In restorative dentistry, the use of high-speed air turbine, which generates aerosols, can be associated with the transmission of airborne diseases. New laser technologies could be useful in reducing the amount of aerosols, but there is a lack of scientific research on this topic. Material and methods This is a descriptive study to analyze the amount of aerosols produced after class I cavity preparation using high-speed air turbine (group 1) and Er,Cr:YSGG laser with two different parameters (groups 2 and 3). Fluorescein dye was incorporated into the coolant reservoir in order to visualize the production of aerosols during each procedure. Tooth preparation was performed in a typodont with human lower molar tooth under rubber dam isolation. The procedure was carried out in a transparent plastic box to avoid aerosols dispersion. Sixteen grade I cellulose filter discs were distributed along the surfaces of the box. The area contaminated with aerosols in the filters was measured using ultraviolet illumination. Results In group 1, the contaminated surface area covered with fluorescein dye reached 77.3% (1349 cm2) of the total; in group 2 (laser with 80% water) we observed 7.3% (128 cm2) and in group 3 (laser with 40% water) it was 3.8% (68 cm2). The reduction in water parameter from 80% to 40% coincided with 48% reduction of the contaminated area on the filter discs. Focusing on the surfaces of the box, we noted that the mean contamination on the left side was more than on the right side in all three experimental groups. In group 1 using air turbine, we measured a mean of 102.6[±7.5 SD]cm2 on the left side, compared to 70.6[±32.3 SD]cm2 on the right side. In laser groups 2 and 3, a mean of 12.8[±14.9 SD]cm2 and 6.8 [±5.7SD]cm2, respectively, was described on the left surface versus 0 cm2 of surface contamination on the right surface. Conclusions The contaminated area during the procedure of class I cavity preparation, is reduced by 70% using Er,Cr:YSGG laser compared to high-speed turbine. A slightly higher contamination was observed between laser groups with 80% versus 40% water. The use of Er,Cr:YSGG laser in restorative dentistry can be a valid treatment alternative to reduce aerosols production compared to conventional high-speed rotary instruments. Key words:Er,Cr:YSGG laser, Aerosols, SARS-CoV-2, Rotary instruments, conservative dentistry.

Objective: Research on evaluation of crowns made by the latest contemporary dental computer-aided design/computer-aided manufacturing (CAD/CAM) systems for their marginal adaptation is scarce. The purpose of this in vitro study was to evaluate the marginal integrity of crowns fabricated by the latest Chairside Economical Restorations of Esthetic Ceramic (CEREC) system using 2 different finish line preparation designs: chamfer and shoulder. Materials and Methods: Typodont teeth were divided equally into 2 groups, A and B. The teeth were prepared for full coverage crowns with a shoulder (group A) and chamfer (group B) finish line design. An experienced prosthodontist prepared all crown preparations. Evaluation of 6 sites per sample was completed by 2 calibrated, experienced prosthodontists using the modified US Public Health Services (USPHS) criteria. The descriptive statistics and Z-test were used to evaluate the results. Results: A total of 180 teeth were included in the study (90 teeth in each group). Only 2 crowns in group A and 1 crown in group B were clinically unacceptable. There was no statistical significance (p = 0.282) between the 2 groups regarding finish line design. Conclusions: The CEREC system provides clinically acceptable crowns and can safely be utilized in dental treatment. Therefore, CAD/CAM restorations could be considered as a safe treatment modality by dental professionals.

Background Toothbrushes require flexibility to access all dental surfaces and remove plaque effectively, but they should also aim to prevent or limit overbrushing and consequent damage to teeth and gums. In two studies, the physical properties and cleaning performance of specialist test toothbrushes with flexible necks were compared to a reference rigid-necked toothbrush. Methods In Study 1, a universal testing machine (Instron E 10,000) with a specially designed setup was used to test the deflection behaviour of toothbrush head and neck. Untufted toothbrushes were fixed in a custom holder and force was applied to the head while the deflection was measured. In Study 2, one control and five test toothbrushes were assessed using a robot system to simulate the cleaning of artificial plaque from defined surfaces of artificial replicated human teeth in a model oral cavity (typodonts). Results Study 1 showed that the flexible-neck toothbrush deflected 2 to 2.5 times more than the rigid-neck reference toothbrush when same force was applied to the toothbrush head. Study 2 revealed that all five test toothbrushes showed statistically superior simulated plaque removal to the reference toothbrush. This superiority was observed for all test toothbrushes employing horizontal and rotating brushing action (all p = 0.001) but only three of the five toothbrushes when vertical brushing was employed (all p = 0.001). Cleaning efficacy of the test toothbrushes was demonstrated both interdentally and at the gumline locations. The Complete Protection toothbrush showed the most effective cleaning performance followed by the Repair and Protect and Rapid Relief toothbrushes. Conclusion The addition of a flexible-neck component to the toothbrush designs helped to reduce stiffness and may allow more effective cleaning compared to rigid designs with controlled force distribution on the teeth and gums. This may help to provide plaque control at all potential risk areas in an in vitro robot model and could support good oral hygiene in-use.

Statement of problem Whether the precision of fit of computer-aided design and computer-aided manufacturing (CAD-CAM) complete crowns is affected by the finish line configuration is unclear. Purpose The purpose of this in vitro study was to evaluate the marginal and internal fit of CAD-CAM ceramic crowns made from lithium disilicate based on 3 different finish lines (rounded shoulder, chamfer, feather-edge). Materials and methods Thirty anterior lithium disilicate complete crowns (n=10 per finish line group) were fabricated by following a completely digital workflow based on digital scans made with the TRIOS scanner. The crowns were adhesively cemented on duplicate dies of the respective prepared Typodont teeth, and the marginal gap, absolute marginal discrepancy, and internal gap were evaluated by using microcomputed tomography (μCT). A total of 66 values were obtained for each specimen from sagittal and transaxial sections, and a rendering software program was used to calculate the volume of the cement gap for each specimen by means of 3D region growing. Two-way ANOVA, Tukey post hoc tests with Bonferroni correction, and the Kruskal-Wallis test were used to compare the values between the experimental groups (α=.05). Results Marginal gap and absolute marginal discrepancy values were statistically significantly different between groups. In ascending order, marginal gap values were 23 ±14 μm for rounded shoulder, 54 ±28 μm for chamfer, and 96 ±36 μm for feather-edge finish lines. Absolute marginal discrepancy values were 96 ±34 μm for rounded shoulder, 124 ±37 μm for chamfer, and 157 ±34 μm for feather-edge finish lines. Internal gap values were 111 ±14 μm for feather-edge, 136 ±22 μm for chamfer, and 168 ±25 μm for rounded shoulder finish lines. The differences in cement volume between groups were not statistically significant (P=.200). Conclusions All 3 finish lines produced marginal gaps within the range of clinically accep table values. Lithium disilicate CAD crowns with a rounded shoulder finish line had the best marginal fit but the poorest internal fit, and lithium disilicate CAD crowns with a feather-edge finish line had the best internal fit but the poorest marginal fit.

There has been an increase in utilizing 3D printers in dental restorations. The purpose of the study is to compare mechanical properties of 3D-printed prostheses to those of self-cured and/or computer-aided design-computer-aided manufacturing (CAD-CAM) restorations. A metal master typodont was prepared for the mandibular left sextant with implant analogs embedded at the first premolar and first molar positions with a missing second premolar. Three-unit provisional fixed dental prosthesis (FDP) was designed utilizing the 3Shape tooth library and forty-five uniform specimens were fabricated with different materials: self-cured poly(methyl methacrylate) (PMMA) (N = 15), milled PMMA CAD-CAM blocks (N = 15) and 3D-printed resin (N = 15). All specimens were tested using an Instron machine at a crosshead speed of 0.5 mm/min by an axial load on the occlusal surface of the second premolar pontic site. Statistical analysis was completed with Shapiro-Wilk, ANOVA and Tukey post-hoc tests. Mean fracture force was 300.61 N, 294.64 N and 408.49 N for self-cured PMMA, milled PMMA and 3D-printed resin, respectively. Mean force at FDP fracture of 3D-printed resin was significantly greater than the mean fracture force of either self-cured (p = 0.016, 95% CI [17.86, 197.91]) or milled (p = 0.010, 95% CI [23.83, 203.88]) PMMA.

Statement of problem Digital scans should be able to accurately reproduce the different complex geometries of the patient's mouth. Mesh quality of the digitized mouth is an important factor that influences the capabilities of the geometry reproduction of an intraoral scanner (IOS). However, the mesh quality capabilities of IOSs and the relationship with different ambient light scanning conditions are unclear. Purpose The purpose of this in vitro study was to measure the impact of various light conditions on the mesh quality of different IOSs. Material and methods Three IOSs were evaluated—iTero Element, CEREC Omnicam, and TRIOS 3—with 4 lighting conditions—chair light, 10 000 lux; room light, 1003 lux; natural light, 500 lux; and no light, 0 lux. Ten digital scans per group were made of a mandibular typodont. The mesh quality of digital scans was analyzed by using the iso2mesh MATLAB package. Two-way ANOVA and Kruskal-Wallis 1-way ANOVA statistical tests were used to analyze the data (a=.05). Results Significant differences in mesh quality values were found among the different IOSs under the same lighting conditions and among the different lighting conditions using the same IOS. TRIOS 3 showed the highest consistency and mesh quality mean values across all scanning lighting conditions tested. CEREC Omnicam had the lowest mean mesh quality values across all scanning lighting conditions. iTero Element displayed some consistency in the mesh quality values depending on the scanning lighting conditions: chair light and room light conditions presented good consistency in mesh quality, indicating better mesh quality, and natural light and no light conditions displayed differing consistency in mesh quality values. Nevertheless, no light condition led to the minimal mean mesh quality across all IOS groups. Conclusions Differences in the mesh quality between different IOSs should be expected. The photographic scanning techniques evaluated presented higher mesh quality mean values than the video-based scanning technology tested. Moreover, changes in lighting condition significantly affect mesh quality. TRIOS 3 showed the highest consistency in terms of the mean mesh quality, indicating better photographic system in comparison with iTero Element.

The aim of this study was to compare the fit of feldspathic ceramic crowns fabricated via 3 different extraoral digitizing methods. Twelve maxillary first premolars were prepared and 36 single crowns were fabricated via 3 extraoral digitizing methods using a laboratory scanner (n = 12): (1) scanning the typodont (ST [control] group); (2) scanning the impression (SI group); (3) scanning the stone cast (SC group). Micro-computed tomography was used to calculate two-dimensional marginal-internal gap and the three-dimensional volumetric gap between the crowns and their corresponding dies. The measured gaps were divided into 6 location categories as follows: marginal gap (MG), finish line gap (FLG), axial wall gap (AWG), cuspal gap (CG), proximal transition gap (PTG), and central fossa gap (CFG). The correlation between each of the 3 extraoral digitizing methods and the adaptation status of the crown margins were also evaluated. The Wilcoxon signed-rank test, Spearman's rank test, and Chi-square test were used for data analysis (α = 0.05). The marginal gaps in the ST, SI, and SC groups differed significantly (24, 198 and 117.6 µm, respectively) (p 0.05). Significant differences were found between the groups with regard to internal gap measurements, with SI representing higher gap measurements at FLG, PTG and CFG locations (p 0.05). 3D volumetric gap measurements did not differ significantly (p 0.05). Under-extended margins observed in the SI and SC groups were correlated with the digitizing method (Cramer's V-square: 0.14). When performing extraoral digitalization, clinicians should choose to scan the stone cast as scanning the stone cast resulted in better internal and marginal fit compared to scanning the impression.

Introduction No commercially available solution to improve the teaching of a crown preparation directly on typodont teeth exists at the moment. To fill this gap and support the supervisors of dental courses, a printable and inexpensive tooth was created for structured self-assessment. The aim of this study was to test this printable tooth under realistic pre-clinical situations. Materials and methods A two-coloured, double-layer practice tooth was developed. This tooth was consisting of a layer for a correct preparation and the crown. All printed teeth were produced with a stereolithographic printer. 35 voluntary second-year dental students in the second pre-clinical course in prosthodontics were randomly divided into two groups. All students had experience with typodont teeth and models. The first group was trained on four standard model teeth. The second group used model teeth for the first and fourth attempt and printed teeth for second and third attempt. The preparations of the students were scanned by an in-lab scanner and the surface deviations in contrast to a perfect preparation were measured. The differences between the first and fourth attempt were calculated. Benefits of the printed tooth were also evaluated by a questionnaire using German school grades completed by the students (1 = Excellent, 2 = Good, 3 = Satisfactory, 4 = Adequate, 5 = Poor, 6 = Unsatisfactory). Results The workflow was feasible and cost-effective regarding the production of the printed teeth. The overall rating of the printed tooth in the questionnaire was good (O 2.1 ± 0.22). Students reported different advantages of this method in the free text. The comparison of the preparation between the first and fourth attempt showed that there was a significant better preparation with the printed teeth. The complete preparation had median values of 0.05 mm (Group1: standard model tooth) and -0.03 mm (Group2: printed tooth) (P = .005). Divided into single surfaces, the vestibular and occlusal regions were significantly better. The vestibular surface was 0.11 mm (Group1) and -0.04 mm (Group2) (P = .018). The occlusal surface was 0.13 mm (Group1) and -0.05 mm (Group2) (P = .009). Conclusions The aim of this study was fulfilled. The printed tooth was tested successfully in a pre-clinical course. The feasibility of this teaching concept was confirmed by the questionnaire and the analysis of the preparation form. A significant difference to a standard model tooth was measurable. The students had the possibility to learn a correct crown preparation on a standardised two-layered tooth with included preparation. This printed tooth enabled the students to control the crown preparation directly on their own.

Statement of problem Digital scans have increasingly become an alternative to conventional impressions. Although previous studies have analyzed the accuracy of the available intraoral scanners (IOSs), the effect of the light scanning conditions on the accuracy of those IOS systems remains unclear. Purpose The purpose of this in vitro study was to measure the impact of lighting conditions on the accuracy (trueness and precision) of different IOSs. Material and methods A typodont was digitized by using an extraoral scanner (L2i; Imetric) to obtain a reference standard tessellation language (STL) file. Three IOSs were evaluated—iTero Element, CEREC Omnicam, and TRIOS 3—with 4 lighting conditions—chair light 10 000 lux, room light 1003 lux, natural light 500 lux, and no light 0 lux. Ten digital scans per group were recorded. The STL file was used as a reference to measure the discrepancy between the digitized typodont and digital scans by using the MeshLab software program. The Kruskal-Wallis, 1-way ANOVA, and pairwise comparison were used to analyze the data. Results Significant differences for trueness and precision mean values were observed across different IOSs tested with the same lighting conditions and across different lighting conditions for a given IOS. In all groups, precision mean values were higher than their trueness values, indicating low relative precision. Conclusions Ambient lighting conditions influenced the accuracy (trueness and precision) of the IOSs tested. The recommended lighting conditions depend on the IOS selected. For iTero Element, chair and room light conditions resulted in better accuracy mean values. For CEREC Omnicam, zero light resulted in better accuracy, and for TRIOS 3, room light resulted in better accuracy.