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Statement of Problem: Fundamental crown preparation principles are taught and are highly regarded in dental education. Whether tooth preparations made by dental students match these principles is unclear., Purpose: The purpose of this retrospective study was to report the total occlusal convergence (TOC) and margin widths of crown preparations clinically prepared by New Zealand predoctoral dental students between 2013 and mid-2015., Material and Methods: A total of 371 stereolithography files of tooth preparations for metal ceramic crowns prepared by predoctoral dental students were extracted from the Technical Services Laboratory database at the University of Otago. The files were put through the preparation measuring software Preppr, with outputs being TOC angles in faciolingual and mesiodistal cross sections and margin widths in facial, lingual, distal, and mesial aspects. Means, standard deviations, 95% confidence intervals, and distributions using box and whisker graphs were calculated and presented., Results: The majority of TOC angles fell within an acceptable range of 10 to 20 degrees; however, the angles ranged from undercuts (<0 degrees) to >60 degrees. The majority of margin widths were between 0.5 and 1 mm, while the maximum was approximately 2 mm and the minimum was 0 mm., Conclusions: Predoctoral dental students in New Zealand are able to produce literature-recommended TOC angles and margin widths for metal ceramic crowns; however, further attention and training are needed for excessive tooth preparations, mainly in the form of large TOC angles., (Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Determining the retention and resistance of a tooth preparation for a complete crown has only existed in theory, and these theories have never been measured on tooth preparations performed in vivo., Purpose: The purpose of this study was to measure the theoretical retention and resistance of clinically produced complete crown preparations by using an objective measuring method., Material and Methods: Stone dies from 236 complete crown preparations were collected from dental laboratories. The dies were scanned and analyzed with the coordinate geometry method. Cross-sectional images were captured, and the surface area was measured with a cone frustum and right truncated pyramid formula. Two different theories of resistance form, the "on" or "off" theory (limiting taper) and the linear model (resistance length), were calculated for premolar and molar preparations., Results: The mean surface areas ranged from 33.97 mm(2) to 105.44 mm(2) for the cone frustum formula and 41.75 mm(2) to 117.50 mm(2) for the right truncated pyramid formula. The facial side of maxillary premolars exhibited the highest percentage of resistance form with the limiting taper, at 58%, and the mesial side of the mandibular molars exhibited the lowest percentage of resistance form, at 6%., Conclusions: The objective method used in this study provides a way for retention and resistance theories to be tested and for further clinical implications to be investigated., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Scientific data about the long-term survival of teeth treated with cast post and cores are scarce. Retrospective studies often use different target events for their analyses. A comparison is therefore complicated. For associated tooth-, jaw-, and patient-related factors little evidence exists as to their effect on survival., Purpose: The purpose of this study was to extend the knowledge on the survival of teeth treated with cast post and cores for observation periods of more than 10 years. A decrease or increase in survival times according to the presence or absence of associated parameters needs to be evaluated., Material and Methods: A retrospective evaluation was conducted of all cast post and cores inserted in 1 university clinic between January 1992 and June 2011. A Kaplan-Meier survival analysis was carried out by using extraction as the target event. The survival curves for different tooth types, the presence or absence of adjacent teeth, and the prosthetic restoration of the respective jaws were compared by using the log-rank test (α=.05). A Cox regression model was calculated for multivariate analyses., Results: A total of 717 cast post and cores for 343 patients were recorded. The mean survival time was 13.5 years. A statistically significant decrease in survival times was found for canines (11.9 years) and premolars (13.4 years) versus molars (14.1 years), no adjacent teeth (10.6 years) versus at least 1 adjacent tooth (13.8 years), and the restoration with removable dental prostheses (12.5 years) versus fixed dental prostheses and single crowns (13.9 years). The largest reduction in survival time was found for teeth being used as an abutment for a double crown-retained removable partial dental prosthesis (telescopic denture) (9.8 years). Tooth type and adjacent tooth status remained as significant variables within the multivariate Cox regression model., Conclusions: Cast post and cores have an acceptable long-term survival time. Because different factors may influence survival, considering these factors in treatment planning may increase the long-term success of these restorations., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: An implemented objective measuring system for measuring clinical tooth preparations does not exist., Purpose: The purpose of this study was to compare clinically achieved tooth preparations for ceramic crowns by general dentists with the recommended values in the literature with an objective measuring method., Material and Methods: Two hundred thirty-six stone dies prepared for anterior and posterior complete ceramic crown restorations (IPS e.max Press; Ivoclar Vivadent) were collected from dental laboratories. The dies were scanned and analyzed using the coordinate geometry method. Cross-sectioned images were captured, and the average total occlusal convergence angle, margin width, and abutment height for each preparation was measured and presented with associated 95% confidence intervals., Results: The average total occlusal convergence angles for each tooth type was above the recommended values reported in the literature. The average margin widths (0.40 to 0.83 mm) were below the minimum recommended values (1 to 1.5 mm). The tallest preparations were maxillary canines (5.25 mm), while the shortest preparations were mandibular molars (1.87 mm)., Conclusions: Complete crown preparations produced in general practice do not achieve the recommended values found in the literature. However, these recommended values are not based on clinical trials, and the effects of observed shortfalls on the clinical longevity of these restorations are not predictable., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: A valid system for assessing and classifying functional occlusion has not been established. The prevalence of anterior protected articulation is not known., Purpose: The purpose of this study was to quantify the prevalence of various functional occlusal contact patterns, including anterior protected articulation, among dental students., Material and Methods: Occlusal contacts were examined during lateral excursions from the maximal intercuspal position to the canine-to-canine position in 100 young adults. A combination of 3 common clinical methods was used: a visual examination, articulating paper, and feedback from the participants., Results: Data from 3 classification systems were analyzed: (1) Occlusal contacts on the working side only – canine protected articulation was present in 25% of laterotrusions; anterior protected articulation was present in 18.5% of laterotrusions. Group function was present in 56% of laterotrusions. Other schemes were present in 0.5% of laterotrusions. (2) Contacts on both the working and the nonworking side. (3) Contacts on the working and nonworking side during both right and left laterotrusion. Nonworking side contacts were present in 33% of the participants. Nonworking side interference was present in 1 participant., Conclusions: The prevalence of anterior protected articulation found in this study was high enough to allow anterior protected articulation to be considered one of the fundamental working side occlusal contact patterns. More studies will be necessary to confirm this finding., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Little peer-reviewed information is available regarding the accuracy and reproducibility of digitally fabricated casts compared to conventional nondigital methods., Purpose: 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., Material and Methods: 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)., Results: 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., Conclusions: 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., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Milling is a central and important aspect of computer-aided design and computer-aided manufacturing (CAD/CAM) technology. High milling accuracy reduces the time needed to adapt the workpiece and provides restorations with better longevity and esthetic appeal. The influence of different milling processes on the accuracy of milled restorations has not yet been reviewed., Purpose: The purpose of this study was to investigate the influence of different milling processes on the accuracy of ceramic restorations., Material and Methods: Four groups of partial crowns were milled (each n = 17): Three groups in a 4-axial milling unit: (1) 1-step mode and Step Bur 12S (12S), (2) 1-step mode and Step Bur 12 (1Step), (3) 2-step mode and Step Bur 12 (2Step), and (4) one group in a 5-axial milling unit (5axis). The milled occlusal and inner surfaces were scanned and superimposed over the digital data sets of calculated restorations with specialized difference analysis software. The trueness of each restoration and each group was measured. One-way ANOVA with a post hoc Tukey test was used to compare the data (α = .05)., Results: The highest trueness for the inner surface was achieved in group 5axis (trueness, 41 ± 15 μm, P<.05). The 4-axial milling unit exhibited trueness at settings ranging from 61 μm (2Step) to 96 μm (12S). For the occlusal surface, the highest trueness was achieved with group 5axis (trueness, 42 ± 10 μm). The 4-axial milling unit exhibited trueness at settings ranging from 55 μm (1Step) to 76 μm (12S)., Conclusions: Restorations milled with a 5-axial milling unit have a higher trueness than those milled with a 4-axial milling unit. A rotary cutting instrument with a smaller diameter results in a more accurate milling process. The 2-step mode is not significantly better than the 1-step mode., (Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Total occlusal convergence of crown preparation is an important didactic and clinical concept in dental education., Purpose: The purpose of this study was to compare the discrepancy between the total occlusal convergence of dental students' typodont crown preparations and the ideal range (4 to 10 degrees) in 3 different regions of the mouth and in 4 different planes of the teeth., Material and Methods: The dental students of the Class of 2012 at Harvard School of Dental Medicine were asked to prepare typodont teeth for crowns on 3 different teeth, the maxillary left central incisor (ceramic), mandibular left first molar (complete metal), and mandibular left first premolar (metal ceramic), during their third year preclinical summative examination and the Comprehensive Clinical Examination in their fourth year. Eighteen students prepared 3 teeth in their third and fourth years, whereas 19 students participated only in their fourth year, for a total of 55 sets of 3 teeth. By using custom fit die bases to reproduce the position, a novel procedure of measuring each tooth was accomplished in 4 different planes: the faciolingual, mesiodistal, mesiofacial-distolingual, and mesiolingual-distofacial. The total occlusal convergence of each image was measured with a computer screen protractor. The gingival 2 mm of the axial wall was used to determine the taper of each wall. Linear mixed model analysis was used to estimate and compare the total occlusal convergences of different teeth and planes (α=.05). Bonferroni corrections were used to adjust for post hoc multiple comparisons., Results: The mean total occlusal convergence varied by tooth and plane (2-way interaction; P<.001). For the first molar, dental students excessively tapered in all 4 planes; the model-predicted 99% CIs for the total occlusal convergence were as follows: faciolingual (12.7, 19.4), mesiodistal (14.0, 19.3), mesiofacial-distolingual (13,4, 19.4), and mesiolingual-distofacial (13.7, 19.1). For the central incisor, 99% CIs for the total occlusal convergence were (15.9, 24.4) for the faciolingual measurement, providing strong evidence of excessive tapering, and (4.1, 8.0) for the mesiodistal measurement, which was within the ideal total occlusal convergence range. The mesiofacial-distolingual and mesiolingual-distofacial planes in the central incisor and all 4 planes in the first premolar had mean total occlusal convergences that exceeded 10 degrees; however, excessive tapering could not be statistically established, because their CIs included values within the ideal range., Conclusions: The present study found significant evidence of excessive tapering in a study comparing the total occlusal convergence values of crown preparations with those of the ideal preparation for 3 different teeth in 4 different planes. The total occlusal convergence for the molar preparations had the highest mean values., (Copyright © 2014 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

Statement of Problem: Limited clinical data exist on the survival of teeth relative to their treatment history., Purpose: This study evaluated failure of teeth relative to their treatment history., Material and Methods: Longitudinal data were collected for 3071 teeth from 148 fully compliant patients from 1 private practice in Yamagata, Japan. Follow-up times ranged from 15 to 23 years, with a mean of 19.2 years (SD 2.4). In this study, every tooth and its restoration were evaluated by one of the authors at the time of each maintenance visit. Treatment history of the teeth was categorized at baseline as follows: (1) sound, unrestored tooth (SUT); (2) 1-surface restoration (RT1); (3) 2-surface restoration (RT2); (4) 3-surface restoration (RT3); (5) 4+-surface restoration (RT4); (6) complete crown (CCT); (7) abutment for fixed partial dental prosthesis (AFT); (8) abutment for removable partial dental prosthesis (APDT); and (9) root canal treatment (RCT). Three types of failure modes were evaluated in this study: (1) restorative failure (secondary caries and/or fracture), (2) extraction, and (3) any failure (restorative failure or extraction). Multivariate survival analysis was used to determine the impact of the treatment history on failure (alpha=.05)., Results: Teeth with multi-surface restorations experienced the highest incidence of any failure (P<.001). For secondary caries, similar risks were noted for the different treatment histories. For failures resulting in extraction, the only teeth with an increased risk were abutments for removable partial dental prostheses (relative risk=5.5) (P=.008)., Conclusions: The data demonstrated that restored teeth experienced a higher incidence of failure compared with unrestored teeth. Complete crowns and abutments for fixed partial dental prostheses had fewer restorative failures when compared with teeth with complex multisurface restorations. Removable partial denture abutments experienced the highest failure rate.

Statement of Problem: The biocompatibility of titanium has been well documented, but clinical outcomes of ceramic-veneered titanium restorations were not conclusive., Purpose: The study presents the results of a 5-year clinical study of individual crowns and fixed partial dentures (FPDs) veneered with a low-fusing ceramic of the Procera system., Material and Methods: All patients at one clinic who required crowns or FPDs during a 2-year period were invited to participate. A total of 260 patients received 333 ceramic-veneered Procera restorations (242 single crowns and 91 FPDs). Clinical registrations were performed annually, and the restorations were evaluated according to the California Dental Association rating system. At the 5-year follow-up, 198 (76%) patients were examined. Most of the loss of patients could be explained., Results: Practically all Procera restorations were judged as satisfactory both at baseline and follow-up examinations. One artificial crown and 1 FPD were remade because of extensive fractures of ceramic veneers. Two FPDs had fractures of a soldered joint, but only 1 FPD was replaced. Some minor complications occurred, such as small porcelain fractures that could be polished (6% of single crowns, 13% of FPDs) and or loosened restorations that were recemented. Other recorded complications were not related to the Procera system but to dental caries, loosened posts and cores, and root fractures., Conclusion: Clinical outcomes over a 5-year period for ceramic-veneered titanium restorations with the Procera system were favorable.

Statement of Problem: Despite careful procedures, master stone dies may be damaged during laboratory procedures. The dentist routinely adjusts castings because the marginal fit of casting is not as accurate as on the dies., Purpose: This study evaluated the technique of internal adjustment of castings with use of duplicated stone dies and a disclosing agent to improve marginal fit discrepancy., Material and Methods: Thirty-two nickel-chromium copings were fabricated and simulated standard clinical and laboratory procedures with 2 variables: tooth preparation convergence angles of 6 and 18 degrees, with or without internal relief. Master stone dies and their duplicates were selected for coping construction and internal adjustment, respectively. A specimen positioning device was coupled with a Toolmakers microscope to allow reproducibility of measurements. Each coping was evaluated at 8 locations of its marginal perimeter, before and after internal adjustment., Results: Marginal fit discrepancy of copings were significantly reduced with an internal adjustment technique (mean > 52%) for all experimental groups. Tooth preparations with greater convergence and internally relieved castings recorded a better marginal fit., Conclusion: The casting internal adjustment technique with use of duplicated stone dies and a disclosing agent substantially reduced marginal fit discrepancy.

Statement of Problem: Gap measurements along margins are frequently used to assess the quality of single crowns. However, the number of gap measurements required for clinically relevant results in laboratory studies is not known., Purpose: This study estimated the minimum number of gap measurements on margins of single crowns to produce relevant results for gap analysis., Methods and Material: Ten all-ceramic crowns were fabricated on a master steel die. Gaps along crown margins were investigated in a scanning electron microscope on the master steel die without cementation and on replica dies after conventional cementation. Measurements were made in 100 microm steps according to 3 gap definitions. The initial number of measurements per crown (n = 230) was reduced to smaller subsets using both systematic and random approaches to determine the impact on the quality of results., Results: On the data of gap definition 1, reduction from 230 to about 50 measurements caused less than +/-5 microm variability for arithmetic means. Analysis of standard errors showed slowly increasing values smaller than 3 microm, both indicating no relevant impact on the quality of results. Smaller data sizes yielded accelerated increase of standard errors and divergent variabilities of mean. The minimum of 50 measurements did not depend on gap definition or on cementation condition., Conclusion: Fifty measurements are required for clinically relevant information about gap size regardless of whether the measurement sites are selected in a systematic or random manner, which is far more than what current in vitro studies use.

Statement of Problem: An inordinate amount of time is often required to adjust the occlusion of a newly fabricated crown., Purpose: This study determined whether the procedure of "cast adjustment" significantly decreases the time necessary to clinically adjust the occlusion of a newly fabricated crown., Material and Methods: Thirty-eight crowns were fabricated by a commercial dental laboratory for patients of senior dental students at the University of the Pacific School of Dentistry. After master casts were returned from the laboratory and then mounted on semiadjustable articulators by the students, the cases were divided randomly into 2 groups: (1) the control group, for which no further work was performed before fabrication of the restoration; and (2) the experimental group, in which casts were occlusally adjusted by a certified laboratory technician until there was at least 1 cusp tip to flat surface centric contact on each posterior tooth in maximum intercuspation position. After the crowns were delivered, the students filled out a survey. One question on the survey asked the student for the time required to adjust the occlusion on the crown., Results: Of the 19 crowns in the control group, 6 crowns required more than 1 hour for occlusal adjustment. Of the 19 crowns in the experimental group, 1 crown required more than 1 hour for occlusal adjustment., Conclusion: Performing a "cast adjustment" before fabricating a single unit casting can significantly decrease the chance of a lengthy clinical occlusal adjustment.

Statement of Problem: Studies have suggested that coating a temporary restoration with varnish material could replace time-consuming polishing procedures needed for achieving an optimally smooth surface., Purpose: This study examined the surface roughness of acrylic resins after having been polished or coated with different varnish materials., Material and Methods: A total of 360 cylindrical specimens were fabricated from 9 brands of resin. One surface on each specimen was machined flat and subsequently either polished with rubber polishers or coated with 1 of 9 varnishes. Selected specimens were subjected to thermal cycling (5 degrees C to 55 degrees C, 2000 cycles). Surface quality was assessed by means of a profilometer and by SEM examination., Results: Polished specimens had average surface roughness values (Ra) of 0.8 microm; differences in roughness between materials were small, but statistically significant. Type of coating had a significant influence on surface quality. Depending on the combination of materials used, the coating produced both smoother and rougher surfaces than polishing (0.4 microm < Ra < 4.6 microm). Five coatings were deemed not to be clinically applicable because of poor wetting properties. Thermal cycling did not significantly influence surface quality, but caused minute cracks in the cyanoacrylate coating., Conclusion: In regard to surface quality and applicability, the use of varnishes on temporary restorations is not advisable.

Statement of Problem: Immediate loading of implants may be a predictable treatment alternative when cross-arch stabilization with a fixed provisional is observed., Purpose: This study investigated the effect of immediate masticatory loading on the stability of single-standing dental implants with 4 different surfaces., Material and Methods: A total of 40 solid screw implants (diameter 3.3 mm, length 8 mm) were placed in the mandibles of 4 beagle dogs. Test groups included 3 hydroxyapatite (HA) coatings of titanium plasma-sprayed (TPS) implants. Implants with TPS alone served as control. Gold crowns were inserted 2 days after implant placement and the dogs were immediately put on a hard food diet. Implants were followed for 6 months after loading. Clinical and radiographic assessments of implants were performed at time of crown insertion (baseline) and after 1, 3, and 6 months of loading. The Periotest instrument was used for mobility measurements and radiographs were obtained for evaluation of peri-implant radiolucency and measurement of crestal bone changes., Results: Of 40 implants, 39 displayed no discernible mobility, corresponding to successful clinical function. Peri-implant radiolucencies were absent for all but the 1 mobile implant. The reduction in crestal bone levels adjacent to the implants between baseline and 6 months was statistically significant (P <.0001). No statistically significant differences in crestal bone level changes over time were found between the various coatings demonstrating the absence of a treatment effect initiated by the surface coatings., Conclusion: In this study in beagle dogs, immediate masticatory loading of single-standing dental implants did not jeopardize tissue integration, provided the implants had excellent primary stability.

Statement of Problem: All-ceramic molar crowns can be fabricated with CAD-CAM or laboratory methods with different materials, and a polished or oven-glazed surface., Purpose: This in vitro study determined the fracture strength of various all-ceramic crowns, with and without prior cyclic loading., Material and Methods: Standardized molar crowns were fabricated with a CAD-CAM machine (Cerec 2), software with machinable ceramic materials (Vita Mark II and ProCAD), and also conventional heat-pressed IPS Empress crowns fabricated at 2 dental laboratories. Groups of 40 crowns of each material were manufactured with either a polished or an oven-glazed surface finish. Cyclic loading that simulated oral conditions were performed on half of each group. Afterward, all crowns were loaded until catastrophic failure.Results. Fracture loads of the polished ProCAD crowns without prior cyclic loading was 2120 +/- 231 N, significantly higher than that of the polished Vita Mark II crowns (1905 +/- 235 N), but was not significantly different from the strength of 2 laboratory-fabricated Empress crowns. Oven-glazing of ProCAD crowns improved the fracture strength significantly, up to 2254 +/- 186 N. Prior cyclic loading decreased the strength of all tested crowns significantly, but the reduction was less for the Cerec crowns than the Empress crowns., Conclusion: Cerec ProCAD crowns demonstrated significantly greater strength than the Vita Mark II crowns, better resistance to cyclic loading and lower failure probability than the laboratory-fabricated IPS Empress crowns. Prior cyclic loading significantly reduced the strength of all-ceramic crowns, but had less effect on Cerec crowns than on the IPS Empress crowns. Oven-glazing of ProCAD crowns resulted in significantly higher strength and higher resistance to cyclic loading than surface polishing.

Purpose: This study developed a new device for measuring the internal setting expansion of phosphate-bonded investment and assessed the effect that different pattern materials may have on the internal setting expansion., Material and Methods: The measuring device consisted of 2 horizontal plungers, a vertical needle, 2 digital dial gauges, and a protection tube with a disk. Outward displacement of the 2 horizontal plungers by investment setting expansion was transmitted to a digital dial gauge through the vertical needle. Upward displacement of a protection tube was measured by another digital dial gauge. Three pattern materials, including soft and hard inlay waxes and an autopolymerizing resin, were used. Data were analyzed with ANOVA and Scheffe's F test for all post hoc pairwise comparisons (95% confidence level)., Results: For all pattern materials, vertical setting expansion (range of means, 2.26% to 2.73%) was significantly higher than the horizontal setting expansion (range of means, 0.09% to 1.50%) (P <.05). In addition, for the hard inlay wax pattern, the horizontal setting expansion for the cervical aspect (means, 1.39%) was significantly higher than that of the occlusal aspect (means, 0.54%) (P <.05)., Conclusion: In this study, the new measuring device was a convenient and reliable method for quantitative assessment of internal setting expansion. Regardless of the type of pattern material, a phosphate-bonded investment caused nonuniform setting expansion, especially in a horizontal direction, which lead to the distortion of the pattern.

Statement of Problem: Anecdotal reports based on clinical observation have recently linked resin-modified glass ionomer luting agents with postcementation fracture of all-ceramic crowns., Purpose: This study evaluated the fracture incidence of In-Ceram and VitaDur Alpha porcelain jacket all-ceramic crowns cemented with 5 luting agents (Fuji I, Fuji Plus, Vitremer, Advance, and Panavia 21) during 2 months storage in 0.8% NaCl solution., Material and Methods: Fifty human maxillary premolar teeth were prepared for each ceramic system and divided into 5 subgroups of 10 teeth to be cemented with 5 luting cements. Specimens were observed for fracture lines and crack initiation at storage times up to 2 months. Incidence of fracture was analyzed with Fisher's Exact test. Specimens that did not fracture during storage were loaded in compression to failure. Failure loads were analyzed by analysis of variance and multiple pairwise comparisons., Results: Only all-ceramic crowns cemented with Advance cement fractured during the 2-month observation period, and porcelain jacket crowns were found to fracture earlier and more frequently than In-Ceram crowns. Cracks initiated at the crown margin, and multiple crack lines were found as the time of storage increased. In-Ceram crowns were significantly stronger (140 +/- 21.5 kg) than porcelain jacket crowns (98.6 +/- 17.8 kg) at P <.05. For In-Ceram crowns, cement type did not influence failure load while for porcelain jacket crowns, Fuji I (110.5 kg) was significantly higher than Vitremer (86.6 kg) at P <.05., Conclusions: For the cements studied, only crowns cemented with Advance cement demonstrated fracture during 2-month storage. Results for the true resin-modified glass ionomer cements do not support anecdotal reports of fracture of all-ceramic crowns cemented with these materials.

A survey of dental schools in the United States and Puerto Rico was conducted concerning ceramometal crown margin design. The crown margin designs taught most often were the flat shoulder, the 45-degree bevel shoulder, and the chamfer.