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Objective: The purpose of this study was to determine the ability of a methacrylate resin dentin bonding agent to adhere to the dentin surfaces of prepared and conditioned root canals with either 32% phosphoric acid (PA) or 17% ethylenediaminetetraacetic acid (EDTA)., Methods: Prior to the application of the methacrylate resin, the root canals of 54 intact, caries-free, single- rooted, de-crowned, extracted human maxillary incisor and canine teeth were endodontically prepared and conditioned with either 32% PA or 17% EDTA or with distilled water as the unconditioned control. The resin-treated roots were cross-sectioned at three levels and scanning electron microscope (SEM) imaged for circumferential views of the root canals at 60-90× magnification and site-specific views at 250× magnification, and then randomly coded for independent and blind evaluation by four calibrated examiners. The circumferential surface of the root canals that showed no resin adhesion were digitally measured and subtracted from the digitally measured total root canal circumference, and resin adhesion was expressed as a percentage of the circumference., Results: The mean percentages of resin adhesion were 97% for the PA group, 94% for the EDTA group, and 76% for the control group. There were statistically significant differences among the PA, EDTA, and control groups., Conclusion: Root canals conditioned with 32% PA or 17% EDTA had more resin adhesion than unconditioned root canals. Root canals conditioned with 32% PA had more resin adhesion than those conditioned with 17% EDTA., Competing Interests: Conflict of Interest: No conflict of interest was declared by the authors., (Copyright: © 2020 European Endodontic Journal.)

Purpose: This study measured the bond strength of the self-adhesive resin cements and a bonded resin cement for crowns bonded to extracted teeth with preparations having a total taper greater than 30 degrees. A crown pull-off test was used with direction of pull along the path of insertion. The CAD/CAM system Cerec was used to create crowns with the pull-off loop as an integral part of the crown structure., Materials and Methods: One hundred extracted human molars were prepared for all-ceramic crowns with a 1.5-mm shoulder, greater than 30-degree axial wall convergence, a flat occlusal surface and 3 to 5 mm occlusal/ gingival height. All-ceramic crowns were cemented with five different self-adhesive cements (Rely X Unicem, Maxcem Elite, BisCem, SmartCem 2, and G-Cem) and one bonded resin cement (Multilink). Forfour cements (excluding GCem and Multilink) there were 2 groups, one with HF etching and one without ceramic surface treatment. The crowns were then subject to tensile stress until either the crown fractured or the crown was lifted off from the tooth., Results: For several cements, the bond strength exceeded the tensile strength of the all-ceramic crown; thus, the crown fractured, leaving the cemented part of the crown on the tooth. The effect of ceramic surface etching was not statistically significant at p = 0.05; however, for each cement, the treated crowns showed a lower coefficient of variance (COV). For this study, the COV ranged from 24.9 % to 97.9 %. Loads ranged from 41.3 to 190.3 N., Conclusion: Some of the new self-etching resin cements can create bonds to non-retentive crown preparations that are stronger than the strength of a ceramic crown; however, these high bond strengths may not be able to be achieved consistently.

Three-point bending technology has been widely used in the measurement of bone strength. Quantitative trait loci (QTLs) for bone strength have been identified using mouse femurs. In this study, we investigate the use of mouse tibiae in identification of QTLs that regulate bone strength. Mouse tibiae were from a F(2) population derived from C57BL/6J (B6) and C3H/HeJ (C3H). Three-point bending was measured using ISO 4049, with the support width adjustable to accommodate specimen sizes outside the scope of ISO 4049. The strain rate is selectable from 0.05 to 500 mm per min. All stress strain diagrams are recorded and retrieved in digital electronic form. Genome scan was performed in The Jackson Laboratory (TJL). QTL mapping was conducted using Map Manager QTX software. Data show that (i) both elastic modulus (stiffness) and maximum loading (strength) value appear as normal distributions, suggesting that multiple genetic factors control the bone strength; (ii) 11 QTLs, accounting for 90% of variation for strength, have been detected. More than half QTLs of three-point bending are located on the same locations of bone density earlier identified from mouse femurs; (iii) a major QTL of femoral and vertebral bone mineral density (BMD) was not detected for bone strength of tibiae; (iv) the QTL on chromosome 4 has extremely high LOD score of 31.8 and represents 60% of the variation of bone strength; and (v) four QTLs of stiffness (chromosomes 2, 11, 15 and 19) have been identified.

Objective: The aim of the study was to determine the Weibull distribution parameters S(0) and m of the tensile bond strength of a composite resin sandwiched between a noble metal alloy and a feldspathic porcelain using the Rocatec system., Methods: Specimens were prepared either as Au-Pt-Pd alloy cylinders alone or as alloy cylinders and a feldspathic porcelain. Surface treatments included 110 microm Al(2)O(3) sandblasting (Rocatec Pre), tribochemical silica coating (Rocatec Plus) and silane application (ESPE-Sil) prior to composite bonding. The tensile bond strengths of ceramic-resin-ceramic and metal-resin-metal specimens were determined before and after thermocycling at 5-60 degrees C for 1000 cycles. Statistical analyses were conducted using two parameter Weibull distributions determined by the characteristic strength (S(0)) at the 63% probability of failure, the Weibull modulus (m) and the 95% confidence intervals., Results: With respect to the control group (no Rocatec) (7.5MPa), the Rocatec system significantly augmented the characteristic tensile bond strength S(0) of metal (17-18MPa) and porcelain (20-28MPa) groups. Thermocycling had no effect on the tensile bond strength of the metal samples and increased (not significant) the bond of the porcelain group. The Weibull modulus m for all groups ranged from 2.8 to 3.7., Significance: This study confirmed the efficacy of the Rocatec system for bonding composite resin to metal or ceramic substrates. However, the variability of the strength of the bond is shown in the low Weibull modulus values obtained. This reflect the difficulties in controlling flaw formation and warrants research for future improvement.

This study reports the tensile bond strength of orthodontic eyelets (RMO, Inc, Denver, Colo) bonded to human extracted teeth with a resin-modified glass ionomer cement (RMGIC) (Fuji Ortho LC, GC America, Alsip, Ill) and various acid etchants (Etch-37 and All-Etch, Bisco, Schaumburg, Ill; Ultra Etch, 3M Unitek, St Paul, Minn) for enamel preparation before bonding. The enamel etch conditions were as follows: 37% phosphoric acid with silica; 37% phosphoric acid, silica-free; 10% phosphoric acid, silica-free; 10% polyacrylic acid; and unetched enamel. Bond strength was measured by pulling in tension on the eyelet with a 0.018-in steel wire perpendicular to the enamel surface with a testing machine (Instron model 1125, Canton, Mass) at a speed of 2 mm/min. A light-cured resin cement (Transbond XT, 3M Unitek, Monrovia, Calif) applied to enamel etched with 37% phosphoric acid containing silica served as a control. Each group included 30 specimens. The Weibull distribution (m) was used for statistical analysis with a 90% CI. The different etchants used with RMGIC did not affect tensile bond strength. The resin cement group had the highest tensile strength. Significantly lower bond strengths were observed when glass ionomer cement was used to bond orthodontic attachments to nonetched teeth. However, unlike resin cement, RMGIC can bond effectively to etched teeth in a moist environment without an additional bonding agent.

Purpose: To determine Kaplan-Meier survival estimates and Weibull lifetime predictions for four all-ceramic crown systems from long-term data (> 5 yrs)., Materials and Methods: Single unit crowns of Cerestore (n = 30), Dicor (n = 30), Hi-Ceram (n = 22) and In-Ceram (n = 68) were placed in 95 patients treated in a university clinic. They were cemented using glass-ionomer (GI) for Cerestore, zinc phosphate (ZP) for Dicor, and 75% ZP (n = 51), 20% GI (n = 13) and 5% resin-based cement (n = 4) for In-Ceram crowns. The follow-up times were 8 yrs for Cerestore, 7 yrs for Dicor, 6 yrs for Hi-Ceram and 5 yrs for In-Ceram. The statistical analyses were based on censored data sets. A progressively censored Weibull distribution allowing for lifetime predictions beyond the actual observation time was used as well as the Kaplan-Meier Survival Product Limit Estimate (PLE), which provides survival estimates up to the maximum time of follow-up., Results: Cerestore, Dicor and Hi-Ceram demonstrated molar fractures in the first 2 yrs, whereas for In-Ceram these occurred during the third and fourth year of the study. The Kaplan-Meier Survival PLE was 69% for Cerestore at 8 yrs, 86% for Dicor at 7 yrs, 81% for Hi-Ceram at 6 yrs, 92% for In-Ceram at 5 yrs. The predicted Weibull characteristic time T0 (time at which 63% of the restorations would have failed) was 23 yrs for Cerestore, 34 yrs for Dicor, 31 yrs for Hi-Ceram, and 16 yrs for In-Ceram. However, when using data sets arbitrarily limited to the three first years of follow-up, T0 decreased significantly for Cerestore, Dicor and Hi-Ceram due to the number of early fractures. Such Weibull lifetime data illustrate the risk of predicting long-term (> 5 yrs) survival using short-term (< or = 3 yrs) data on ceramic restorations, which exhibit fracturing in the initial years.

The removal of posts from endodontically treated teeth can be a major obstacle in the retreatment of teeth that have recurrent pathology, often leading to extraction of a tooth that could have been saved with endodontic retreatment. The use of a fiber post offers the advantages of a suitable elastic modulus and good bonding between post and cement, but also the advantage of easy removal, if so indicated by clinical findings. A special removal kit for fiber posts has been developed, and its use is illustrated, and described. The removal procedure can be completed in a very short time, usually less than 5 min. The tooth can then be restored with the same type and size of fiber post as was in the tooth prior to removal. Removal kits are found to be for single use only.

The tests commonly used for the evaluation of orthodontic adhesives measure tensile and shear bond strength. The two methods were compared with finite element analysis using a three-dimensional model and the effect of misalignment of the tensile and shear forces was calculated. Applying a shear load produces significant compressive and tensile stresses in the adhesive layer. Under ideal conditions of shear loading, the induced tensile stress is over 5 times the induced shear stress. The model shows that a tensile load induces predominantly tensile stresses in the adhesive layer. The calculations indicate that the tensile test method is a robust testing method with low sensitivity to misalignment of the applied load.

In this in vitro study, tensile strength tests were conducted with a visible light-cured glass ionomer cement (Fuji Ortho LC, GC America Inc.) bonded to extracted teeth under six different enamel surface conditions: (1) dry nonetched, (2) moist etched, (3) moist nonetched, (4) moist nonetched rebonded, (5) moistened with saliva substitute, and (6) moistened with human saliva. Two resin adhesives (Rely-A-Bond and Phase II, Reliance Orthodontic Products) were applied to dry and etched enamel and served as control agents. The glass ionomer cement approached the strength observed for resin adhesives and required the presence of moisture on the enamel surface for optimal performance.

This in vitro study measured the fracture resistance of intact extracted molars and three types of all-ceramic crowns; feldspathic porcelain, glass-ceramic, and glass-infiltrated alumina. All crowns were of a simplified three-cusp occlusal configuration, and were placed on prepared, extracted third molars. The ceramic crowns were bonded to dentin with a resin composite cement, except for 10 of the feldspathic crowns, which were luted with zinc phosphate cement. The fracture resistances was measured using a spherical steel indenter that contacted the occlusal surface at three points. A total of 40 ceramic crowns and 50 extracted maxillary third molars were tested. The Weibull distribution was used for data analysis. Intact extracted teeth were significantly stronger than all-ceramic crowns. Of the ceramic restorations, the glass-infiltrated alumina crowns exhibited the highest fracture resistance.

This in vitro study compared the tensile bond strength of gold and porcelain inlays to extracted molars in standardized cavities. Three cements were used: zinc phosphate, glass-ionomer, and a resin composite cement. The gold inlays were cemented using zinc phosphate or glass-ionomer cement, and the porcelain inlays were luted using resin composite or glass-ionomer cement. Surface treatments included, for gold inlays, either no treatment (zinc phosphate cement) or airborne particle abraded and tinplated (glass-ionomer cement); and for porcelain inlays, either no treatment (glass-ionomer cement) or etched and silane-treated (resin composite cement). Statistical analysis was performed using the Weibull distribution. Results showed no significant differences between gold inlays cemented using zinc phosphate or glass-ionomer cements and porcelain inlays luted using glass-ionomer cements. The bonded porcelain inlays (resin composite cement) showed tensile bond strengths two to three times higher than those obtained for cemented gold inlays.

A mechanical model (link quadrilateral bell crank) is used to demonstrate the equilibrium of normal force vectors transmitted to the masticatory system and maxillary occlusal biteplane splints with different designs. Occlusal contacts were imposed on the proposed models under the action of a masticatory force vector with an arbitrary value of 40 kgf. The consequence of this force action created different responses within the joint and at the level of the dentition. When compared to the intercuspal position in centric occlusion, intra-oral appliances with either smooth contacting surfaces or indentations, both with increased vertical dimension, forced the mandible to assume an anterior position with a concurrent increase of joint forces. The bite-splint that produced the least amount of joint force was the stabilization type with minimal increase of vertical dimension.

Objectives: The aim of this study was to determine the fracture resistance of a machinable glass-ceramic plate cemented to a resin composite block as a function of the cement film thickness for two types of cement., Methods: Ceramic plates were cemented to resin composite blocks using either zinc phosphate cement or a resin composite cement. For the zinc phosphate cement, the film thickness was 33 +/- 8 microns or 128 +/- 8 microns; for the resin composite cement, the thickness ranged from 26 +/- 11 microns to 297 +/- 48 microns. The elastic modulus was determined for each of the cements. Fracture loads were obtained by using a spherical steel indenter in the center of the glass-ceramic plate. The Weibull distribution was used for the statistical analysis., Results: For glass-ceramic plates cemented with zinc phosphate cement, the fracture resistance was independent of the film thickness. When the resin composite cement was used, a gradual decrease of the fracture strength was observed that became statistically significant at a cement thickness of 300 microns or more. The characteristic fracture strength of glass-ceramic plates cemented with the resin composite cement was about 75% higher than when using the zinc phosphate cement. This difference is attributed to the bonding of the resin cement to the ceramic plate and the supporting structure., Significance: The findings of this study suggest that the resistance to fracture due to indentation of the glass-ceramic may not be affected by the cement film thickness as much as previously thought.

Objectives: The aim of this study was to evaluate the effect of three different chemical surface modifications on the bond strength of light-activated denture repair resin (Triad, Dentsply International) to a heat-cured resin (Lucitone, Dentsply International)., Methods: Transverse flexure test specimens were made, with surface treatment of 1) Triad bonding agent, 2) unreacted Lucitone monomer, and 3) a 1:1 mixture of methylene chloride and monomer, using two different application times (2 and 4 min). For all except one group, 18 specimens were made. The controls were solid single composition bars, 18 for each material. The elastic modulus in transverse flexure was measured for each material. The statistical analysis employed the Weibull distribution. Fracture strength values were obtained in a three-point flexure test., Results: It was noted that many fractures occurred away from the interface and the center member of the test fixture. For those fractures, the observed fracture strength is a censored value of the fracture strength. Algorithms for the statistical treatment of censored data were used to get the maximum likelihood estimates of the fracture strength. A mechanical model showed that under three-point bending of a beam of two joined materials, fractures will occur in the part with the higher elastic modulus. This finding is indeed observed in the data. The 4 min monomer treatment showed the highest estimate of the bond strength (187.8 MPa)., Significance: Censored data can be used to obtain fracture strength estimates, and the censoring indicates that the bond strength may exceed the strength of the bulk material.

This in vitro study evaluated the fracture resistance of all-ceramic crowns as a function of the elastic modulus of the supporting die. All-ceramic crowns were made for dies with three different elastic moduli and two different crown lengths. The occlusal surface was loaded in compression with a 12.7-mm steel ball. The fracture load increased markedly with the increase in elastic modulus. The largest increase was seen when only the occlusal surface of the crown was covered. The characteristic fracture load of the complete-crown restorations was more than double that of the occlusal-cover restorations in the dies with the lowest modulus of elasticity, while for the dies with the highest modulus of elasticity the difference in the characteristic fracture load for the two configurations was not significant.

Purpose: Six impression techniques were evaluated using tapered and square impression copings., Materials and Methods: The absolute distortion was measured using a cast metal impression tray with fiduciary reference points external to the impression material. Measurements of the x, y, z coordinates on the master cast and the impressions were directly made with a travelling digitizing microscope. The difference between the coordinates of each of six sites in the impression and the corresponding reference site were compared., Results: There was no significant difference between the techniques for the square copings but that there was a significant loss of accuracy in the z-axis with the tapered copings., Conclusions: No significant differences were noted.

Despite relevant command of muscles in the chewing apparatus, occlusion of the upper/lower jaws is constrained by joints and opposing teeth. To describe this system performance, the link quadrilateral bell-crank comprised a suitable model to render vectorial analysis of forces transmitted to the masticatory system during mandibular elevation. Occlusal contacts were created in the above proposed model. No different mechanical responses in the system were found between maximum intercuspation contacts in centric occlusion as compared to long-centric reconstruction. There was a tendency for force decrease in joints and equal force distribution on dentition. Prematurities in centric relation, at least extent, and protrusive interferences produced concentration of forces at dentition and decrease of forces in the joint, while protrusive guidance tended to increase force in the joint.

This in vitro study measured the changes in the fracture resistance of posterior crowns as a function of crown length. The crowns, 10 for each group, were made of a feldspathic porcelain (Ceramco), a glass-ceramic material (Dicor), and an alumina-reinforced glass (In-Ceram). Three different crown lengths were tested on acrylic resin dies. The restorations were fractured in a testing machine using a steel ball, 12.7 mm in diameter, that contacted the occlusal surface at three distinct points. Statistical analysis was performed using the Weibull distribution. The fracture resistance increased significantly with increasing crown length for all crown materials.

Protrusive functional relationships between the upper and lower jaws are constrained by the structures of the temporomandibular joints (TMJs) and the opposing contacting surfaces of the anterior teeth. To check these biomechanical relationships, the link quadrilateral bell crank model was assumed in order to compute the instantaneous equilibrium of forces using vectorial analysis. Four anterior teeth configurations were analyzed to study the distribution of force components. The first represented normal bite (used as control), the second represented long anterior overjet, the third represented deep anterior overbite, and the fourth one represented freedom in centric. When three different interincisal contact positions were assumed, functional compromises concerning load/reaction between the TMJ and anterior dentition were found. In centric occlusion there was a tendency toward less loading in the joints and increased loading on the dentition. In intermediate positions and close to the edge-to-edge position, the mechanical tendencies were toward increased loading in the joints and decreased loading on the dentition.

Comments from the three previous speakers ranged from moderate satisfaction to strong dissatisfaction with the regulatory process. Three different types of research are identified that seem to predict the ease of compliance with the 510(k) process. No one expressed satisfaction with the PMA application. It seems that current evaluation procedures inhibit the developing and marketing of new devices, but foster only enhancements to existing devices. The development of new evaluation methods is advocated to provide fast, inexpensive, but rigorous assessment of the clinical safety and treatment value of new devices.

Strain gauges were used to determine the setting expansion of phosphate-bonded casting investments. The gauges were placed at the approximate site of the wax pattern. The isotropy of the expansion was evaluated with multidirectional strain gauges that measured the difference in expansion in two orthogonal directions. A large difference was found between the setting expansion measured externally (1% to 1.5%) and the method described here (0.01%). For casting rings lined with a nonasbestos layer, no statistically significant differences were found in the setting expansion parallel to the long axis of the ring and the expansion in the direction perpendicular to the long axis.

On August 13-18, 1989, a dental conference, entitled "Dental Biomaterials: Assessment of Performance Based on Engineering and Statistical Methods", was held in Santa Barbara, California. This conference was sponsored by the Engineering Foundation with co-sponsorship by the United States Army Institute of Dental Research, the United States Naval Dental Research Institute, Block Drug Co., Dentsply International, and the National Institute of Standards and Technology. The objective of this conference was to explore engineering and statistical methods for assessing the resistance of dental biomaterials to structural degradation and failure and for predicting the relative reliability of dental restorations and prostheses under clinical conditions. The conference was designed to evaluate the merits of established and new technology relative to the performance of dental materials. Analytical and experimental methods included fracture mechanics, conventional mechanical tests, adhesion tests, fractographic analysis, finite element analysis, statistical analysis, tribology, image analysis, x-ray diffraction, and scanning tunneling microscopy. The central theme was the development of a systematic approach to predict material performance under clinical conditions based on stress analysis, correlation of clinical data with in vitro data, and fracture surface characterization based on qualitative and quantitative methods. Supported in part by NIDR Grant No. DE06672.

A study was undertaken to investigate the feasibility of using strain gauges to evaluate the internal setting expansion of dental casting investments. A strain gauge was invested in the center of a casting ring to determine the linear setting expansion at the site of the wax pattern. The findings suggest that strain gauges can be used to measure setting expansion internally more accurately than volumetric or external surface measurement techniques. It was also found that winged strain gauges were more stable in the investment than wingless strain gauges.

An optical test was developed for amalgam alloys by condensing amalgams against stain-less steel blocks with regularly spaced grooves forming diffraction gratings. The quality of the diffraction pattern obtained with a He-Na laser from these amalgams is a measure of the adaptation to the grooves.