Evaluation of marginal and internal adaptation of veneers generated by the guided prosthetic tooth preparation system.

OBJECTIVE: This in vitro study aimed to assess and contrast the marginal and internal adaptation of all-ceramic prefabricated veneers manufactured via the FirstFit guided tooth preparation system against all-ceramic veneers produced using the chairside Computer-Aided Design/Computer Aided Manufacture (CAD/CAM) system following identical guided preparation protocols. MATERIALS AND METHODS: Two main groups were included, with 16 lithium disilicate veneers per group. Four typodonts were used for the test (FirstFit) and control CAD/CAM groups. Intraoral scans created master casts and preparation guides. Guides performed preparations on typodont teeth (two central incisors and two lateral incisors). Prepared teeth were scanned (CEREC Omnicam) to design and mill CAD/CAM veneers. Marginal gap thickness and cement space thickness were measured using light microscopy at four locations: marginal, cervical internal, middle internal, and incisal internal. RESULTS: No significant difference existed between groups for marginal adaptation (p = 0.058) or incisal internal adaptation (p = 0.076). The control group had significantly lower values for middle internal adaptation (p = 0.023) and cervical internal adaptation (p = 0.019). CONCLUSIONS: Guided preparation evaluation showed no significant differences in marginal or incisal internal adaptation. The CAD/CAM group had significantly lower middle and cervical internal adaptation values.

Effect of a modified laminate veneer preparation design on absolute margin discrepancy and marginal overhang.

STATEMENT OF PROBLEM: Veneer preparation designs impact veneer accuracy. However, whether a modified design could reduce absolute margin discrepancy and marginal overhangs is unclear. PURPOSE: The purpose of this in vitro study was to investigate whether a modified veneer preparation design enhances the absolute margin discrepancy and marginal overhang. MATERIAL AND METHODS: The absolute margin discrepancy and the marginal overhang of 3 different veneer preparation designs on a typodont tooth (n=20): feather edge, shoulder, and shoulder with wings were measured. The feather edge design was prepared first and subsequently modified to create the shoulder and shoulder with wings preparations. Ceramic veneers were fabricated using computer-aided design and computer-aided manufacture with each veneer assessed for fit before cementation. Ten specimens were cut vertically, and 10 were cut horizontally in each group. The absolute margin discrepancy and marginal overhangs were measured for each cross-section with scanning electron microscopy. Descriptive data analysis and hypothesis testing were conducted using the nonparametric Kruskal Wallis test (α=.05). RESULTS: On the vertical sections, the shoulder with wings preparation had the best absolute margin discrepancy and overhang. The design was also best for mesial overhang and mesial absolute margin discrepancy when measuring horizontally. CONCLUSIONS: The shoulder with wings preparation design produced the smallest cervical absolute margin discrepancy and overhang. This design also produced absolute margin discrepancy and overhangs comparable with those of the shoulder design in the proximal areas.

Automated scoring and augmented reality visualization software program for evaluating tooth preparations.

STATEMENT OF PROBLEM: Tooth preparation is an essential part of prosthetic dentistry; however, traditional evaluation methods involve subjective visual inspection that is prone to examiner variability. PURPOSE: The purpose of this study was to investigate a newly developed automated scoring and augmented reality (ASAR) visualization software program for evaluating tooth preparations. MATERIAL AND METHODS: A total of 122 tooth models (61 anterior and 61 posterior teeth) prepared by dental students were evaluated by using visual assessments that were conducted by students and an expert, and auto assessment that was performed with an ASAR software program by using a 3-dimensional (3D) point-cloud comparison method. The software program offered comprehensive functions, including generating detailed reports for individual test models, producing a simultaneous summary score report for all tested models, creating 3D color-coded deviation maps, and forming augmented reality quick-response (AR-QR) codes for online data storage with AR visualization. The reliability and efficiency of the evaluation methods were measured by comparing tooth preparation assessment scores and evaluation time. The data underwent statistical analysis using the Kruskal-Wallis test, followed by Mann-Whitney U tests for pairwise comparisons adjusted with the Benjamini-Hochberg method (α=.05). RESULTS: Significant differences were found across the evaluation methods and tooth types in terms of preparation scores and evaluation time (P<.001). A significant difference was observed between the auto- and student self-assessment methods (P<.001) in scoring both the anterior and posterior tooth preparations. However, no significant difference was found between the auto- and expert-assessment methods for the anterior (P=.085) or posterior (P=.14) tooth preparation scores. Notably, the auto-assessment method required significantly shorter time than the expert- and self-assessment methods (P<.001) for both tooth types. Additionally, significant differences in evaluation time between the anterior and posterior tooth were observed in both self- and expert-assessment methods (P<.001), whereas the evaluation times for both the tooth types with the auto-assessment method were statistically similar (P=.32). CONCLUSIONS: ASAR-based evaluation is comparable with expert-assessment while exhibiting significantly higher time efficiency. Moreover, AR-QR codes enhance learning and training experiences by facilitating online data storage and AR visualization.

Stress distribution on teeth restored with veneers using various incisal preparation designs: A 3D finite element analysis study.

STATEMENT OF PROBLEM: The type of veneer preparation is often chosen according to the patient's tooth structure and occlusion. Taking biomechanics into account in this decision-making process provides the clinician with more technical information on how to improve the clinical longevity of restorations. However, biomechanical analyses of veneer preparation designs are sparse. PURPOSE: The purpose of this 3-dimensional (3D) finite element analysis with microcomputed tomography (µCT) data obtained from realistic models was to assess the influence of different preparations for ceramic and composite resin veneers on restoration and resin layer stress distribution. MATERIAL AND METHODS: Four replicas of a central incisor were printed and prepared for laminate veneers with 4 different incisal edge designs: shoulder (SH), palatal chamfer (PC), palatal chamfer and oblique fracture involving the distal angle (OF-PC), and palatal chamfer involving horizontal incisal fracture (IF-PC). After fabrication and cementation of the veneers, the restored replicas were assessed with µCT, and 3D finite element models were built. A 100-N load was applied on the palatal surface at 60 and 125 degrees relative to the longitudinal axis. Maximum principal stress and stress distribution on the veneers, cement layer, and tooth structure were calculated and analyzed. RESULTS: The SH preparation exhibited better stress distribution than the PC preparation, and the cement layer and the veneer were subjected to lower stress. The IF-PC preparation had better stress distribution than the OF-PC. The shoulder and IF-PC showed higher stress on laminate veneers, but lower stress on the cement layer. Ceramic veneers exhibited lower stress than composite resin veneers. CONCLUSIONS: The different incisal preparations for laminate veneers influenced stress distribution on restorations and on the resin cement layer. The shoulder type preparation showed better stress distribution and the composite resin veneers showed unfavorable results compared with the ceramic veneers.

Impact of marginal defects on the accuracy of automated finish line detection in tooth preparation.

AIM: The present study aimed to evaluate the accuracy of automated detection of preparation finish lines in teeth with defective margins. MATERIALS AND METHODS: An extracted first molar was prepared for a full veneer crown, and marginal defects were created and scanned (discontinuity of finish line: 0.5, 1.0, and 1.5 mm; additional line angle: connected, partially connected, and disconnected). Six virtual defect models were entered into CAD software and the preparation finish line was designated by 20 clinicians (CAD-experienced group: n = 10; CAD-inexperienced group: n = 10) using the automated finish line detection method. The accuracy of automatic detection was evaluated by calculating the 3D deviation of the registered finish line. The Kruskal-Wallis and Mann-Whitney U tests were used for between-group comparisons (α = 0.05). RESULTS: The deviation values of the registered finish lines were significantly different according to conditions with different amounts of finish line discontinuity (P < 0.001). There was no statistical difference in the deviation of the registered finish line between models with additional line angles around the margin. Moreover, no statistical difference was found in the results between CAD-experienced and CAD-inexperienced operators. CONCLUSIONS: The accuracy of automated finish line detection for tooth preparation can differ when the finish line is discontinuous. The presence of an additional line angle around the preparation margin and prior experience in dental CAD software do not affect the accuracy of automated finish line detection.

Effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations.

AIM: The aim of the present study was to evaluate the effect of cement gap and drill offset on the marginal and internal fit discrepancies of crowns designed with different tooth preparations. MATERIALS AND METHODS: Five tooth preparations were constructed, and crowns with different cement gaps and drill offsets were obtained. Then, best-fit alignment was performed on the crowns with the corresponding tooth preparations, and the fit discrepancies were expressed by color-coded difference images and root mean square (RMS) values. The RMS values of each group were analyzed by the rank-based Scheirer-Ray-Hare test (α = 0.05). RESULTS: The color segments in the sharp line angles area of the Sharp line angles group changed significantly before and after the drill offset. The cement gap had a significant effect on the marginal, internal, or overall fit discrepancies of the five design groups (P < 0.001), while the drill offset had a significant effect on the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.001). Additionally, the interaction effect between cement gap and drill offset was significant for the marginal fit discrepancies of the Shoulder-lip group and the internal or overall fit discrepancies of the Sharp line angles group (P < 0.01). CONCLUSIONS: The cement gap and drill offset had a significant adverse effect on the marginal or internal fit discrepancies of the crowns designed with the shoulder-lip and sharp line angles designs. Tooth preparation designs with intense curvature changes such as shoulder-lip and sharp line angles should be avoided clinically.

A pilot study on the use of a novel digital real-time evaluation system in undergraduate preclinical training of tooth preparation in fixed prosthodontics.

INTRODUCTION: In the light of the digital teaching, it is necessary that the effectiveness of a new digital real-time evaluation system in the preclinical training of tooth preparation be evaluated. MATERIALS AND METHODS: Forty undergraduate dental students of the fourth year were randomly divided into the control group and the experimental group to complete the training task of tooth preparation for porcelain fused to metal (PFM) crown restoring the upper right central incisor. The control students received conventional training with instructor's guidance. The experimental students received training with the digital system without instructor's guidance. Every student exercised preparation in two resin incisors in 3 h training by respective training methods. A third incisor was prepared on a dental model in the simulated head phantom by each student as the test on the next day. All students' tooth preparations were scored by the same two experienced experts. The experimental students were asked to answer a questionnaire regarding their attitudes and opinions on the digital evaluation system in preclinical training. RESULTS: There was no significant difference between the scores of the experimental group and the control group (p > .05). The students of two groups obtained the similar scores in the test (p > .05). Most of the students were supportive of the application of digital training system in the preclinical tooth preparation training course. CONCLUSIONS: The digital real-time evaluation system could provide effective training effects for the dental undergraduate students in the preclinical training of tooth preparation in fixed prosthodontics.

[Prediction, analysis and application of learning curve of tooth preparation for all ceramic crowns of maxillary central incisors].

OBJECTIVE: To predict the learning curve of tooth preparation for all ceramic crowns of maxillary central incisors on phantom head simulators for graduate students participating in standardized dental resident training based on the modified Wright learning curve model, then to analyze and applicate the learning curve. METHODS: Twelve graduate students participating in standardized dental resident training were selected to prepare the resin maxillary central incisors on phantom head simulators for all ceramic crowns 4 times. The results of preparation were evaluated by 3 prosthetic experts with at least 10 years' experience focusing on the reduction, contour, taper, shoulder, finish line, margin placement, adjacent tooth injury, and preparation time for tooth preparation. The learning rate of tooth preparation was calculated by scores of tooth preparation of 4 times. The learning curve of tooth preparation was predicted based on the modified Wright learning curve model. According to the criteria of standardized training skill examinations for dental residents in Beijing, 80 was taken as the qualified standard score. The minimum training times for tooth preparation to satisfy the qualified standard score (80) was calculated, to analyze the characteristics of learning curve and evaluate the effectiveness of tooth preparation. RESULTS: The scores of 4 tooth preparation were 64.03±7.80, 71.40±6.13, 74.33±5.96, and 75.98±4.52, respectively. The learning rate was (106±4)%, which showed the learning curve an upward trend. There were no significant differences between the qualified standard score and the predicted scores of tooth preparation from the 5th preparation to the 13th preparation (P > 0.05). The predicted score of the 14th preparation was higher than the qualified standard score (P < 0.05). CONCLUSION: The trend of the learning curve of tooth preparation for all ceramic crowns of maxillary central incisors on phantom head simulators for graduate students participating in standardized dental resident training is upward, which predicts the minimum training times higher than the qualified standard score is 14 times.

Influence of the Operator`s Experience, Working Time, and Working Position on the Quality of the Margin Width: In Vitro Study.

Background and Objectives: Appropriate tooth preparation is mandatory to obtain a perfect marginal fit of fixed restorations. The heavy chamfer is the most commonly used finish line, especially for minimally invasive tooth preparation. The aim of the study was to compare the width of the finish line obtained during tooth preparation performed by experienced (university lecturers) and inexperienced persons (dental students) in different working times and positions. Materials and Methods: Forty left upper-second molars were prepared on the simulator by each participant, totalizing 160 prepared teeth. A new round-end tapered diamond was used to obtain the 0.5 mm width of the heavy chamfer. The prepared teeth were photographed using a Canon D5300 camera with a macro lens attached to a tripod. The measurements were made with the Image-Pro Insight software selecting the same eight reference points. From these points, perpendicular lines were drawn above the finish line to the axial walls and the distance between the chamfer's outer edge and the axial wall's inner edge was measured. GraphPad Instat and NCSS Dowson Edition software were used. The statistical significance was set at p < 0.05. The mean (M) and standard deviation (SD) were calculated. The used tests: one sample t-test, ANOVA test, and Tukey-Kramer Multiple Comparisons Test. Results: Statistically significant differences were obtained according to the experience of the participant, preparation time, patient's position, and the chamfer width on the prepared tooth different surfaces. Conclusions: Daytime or weeklong tiredness and patient position do not affect the width of the heavy chamfer prepared by experienced and inexperienced persons. The experience and the operator's working position influence the width of the prepared finish line.

Evaluation of the Quality of Undergraduate Full Veneer Crown Preparations at a UK Dental Teaching Hospital.

OBJECTIVES: To determine the quality of full veneer crown preparations produced by supervised undergraduate students at a UK dental teaching hospital. METHODS: One hundred and eighty-five scanned digital dies between October 2019 and March 2021 were obtained. Using cross-sections in four planes, the total angle of convergence, abutment height, margin design and margin depth were evaluated. Statistical comparisons were made by plane, location, material-type, tooth-type, and inter- and intra-arch positions. RESULTS: Across all preparations the mean total angle of convergence was 24.8° ± 11.7°. and mean abutment height was 3.6 mm ± 1.0 mm. Mandibular and molar teeth were significantly more tapered (P ⟨0.001) and exhibited significantly shorter abutment heights (P ⟨0.001). Chamfer margins were the most frequently observed and mean margin depths ranged from 0.49-1.06 mm. The compliance to recommended taught parameters were 28.1%, 42.7%, 34.1% and 6.5% for total angle of convergence, abutment height, margin design and margin depth, respectively. CONCLUSIONS: The findings from this study suggest that compliance to taught parameters is poor, especially for molar teeth, and demonstrates the use of digital software in guiding future research and teaching.

Marginal Integrity of CAD/CAM Ceramic Crowns Using Two Different Finish Line Designs.

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.

A Digital Chairside Technique for an Accurate Evaluation of the Taper of the Prepared Teeth for the Restoration of Crowns and Fixed Partial Dentures.

AIM: The aim of the article was to provide a digital chairside method for the objective evaluation of the taper of prepared abutment teeth retaining a fixed partial denture (FPD). BACKGROUND: According to research, the taper of the abutment teeth supporting an FPD has a direct effect on both retention and stress transmission to the abutment teeth. However, no approaches have been documented in the literature that objectively quantify the taper of the prepared teeth chairside, in a simple and cost-effective manner. TECHNIQUE: The proposed technique utilized an intraoral camera with an on-the-go (OTG) connection, and a silicone dental bite block. The images of the prepared teeth were captured using this camera from the facial aspect. An indigenous program was developed using the MATLAB (Matrix Laboratory 2013) software for the analysis of the images and the taper of each abutment tooth was calculated in degrees using the software. CONCLUSION: The novel, chairside, digital technique utilizes an intraoral camera and a computer-generated software package to quantify and evaluate the taper of abutment teeth efficiently. This, in turn, can help minimize the errors in the treatment of FPD and improve the retention of the prosthesis. CLINICAL SIGNIFICANCE: The current technique enables the clinician to avoid over-preparation of the abutment teeth by assessing its taper chairside. This digital technique can be a beneficial alternative to the existing procedures for an accurate assessment of taper, especially for the inexperienced operator. Hence, the quality of retention, and thereby the long-term success of the crowns and FPDs, can be enhanced. This article was presented as a postgraduate paper titled "Scan and Plan" on March 6, 2020, at 22nd IPS (Indian Prosthodontic Society) PG Convention, Kochi, India.

Effect of a Standardized Training with Digital Evaluation on the Improvement of Prosthodontic Faculty's Performance in Crown Preparation: A Pre-Post Design.

PURPOSE: Standardized crown preparation is an important competency for prosthodontic faculty especially when they take on the dual role of clinician and clinical teacher. Effects of faculty training for enhancing crown preparation competency are seldom reported. This study aimed to analyze the impact of a standardized training workshop with digital evaluation on the dental faculty's performance in crown preparation. MATERIALS AND METHODS: The digitally evaluated grades of anterior (the maxillary right central incisor) and posterior (the mandibular left first molar) tooth preparations made by 76 participants who accomplished all six training tasks were collected, including off-site and on-site exercises before the didactic lecture and live demonstration, three rounds of practices with digital feedback, and a final test. Grades of preparations performed in the on-site exercise were adopted as pre-training scores, and those in the final test as post-training scores. Total scores and marks deducted for the parameters including amount of reduction, margin line, and taper were compared among each training task. RESULTS: The post-training scores of both anterior and posterior tooth preparations increased significantly more than the pre-training scores. The average increased score proportion was 22.95% ± 4.17% for anterior tooth preparations, and 21.78% ± 3.68% for posterior tooth preparations. For anterior tooth preparations, total scores and the parameters except taper significantly improved in the first practice and maintained the same level for the next sessions. Total scores and all parameters for posterior tooth preparations exhibited continual improvement during the training process. CONCLUSION: Standardized training can further improve dental faculty's crown preparation performance in a moderate way. Individual design for crown preparation training can be considered based on different tooth positions. Providing such training will aid the calibration of clinical teaching behavior and the elevation of clinical operative standards for prosthodontic faculty.

The Accuracy of Dental Students and Dentists Assessing the Total Occlusal Convergence of Crown Preparations.

This study examined the ability of dental students and qualified dentists to visually assess the total occlusal convergence of clinical crowns. 10 working casts of maxillary molar crown preparations were installed in phantom heads in a clinical skills laboratory. 87 participants assessed the buccolingual and mesiodistal total occlusal convergence of the casts. 2nd-year students with no experience in fixed prosthodontics served as a control group with 3rd, 4th and 5th-year students and qualified dentists including specialists in restorative dentistry involved. Differences were calculated between the measured angles and the subject's estimate to assess accuracy. For 8 of the 20 surfaces measured there were significant differences. (p ⟨ 0.05). Differences were not standardized between the groups, with no clear patterns of difference in tooth type or aspect assessed. Differences were primarily between the control group and the more experienced groups. The remaining groups were of similar ability. A minority of participants in each group were highly divergent from their peers. This study found significant differences between participants with no experience of fixed prosthodontics and those with experience, however, the ability to assess total occlusal convergence does not appear to improve significantly with experience.

Finish-line designs for ceramic crowns: A systematic review and meta-analysis.

STATEMENT OF PROBLEM: Different finish-line designs have been advocated for tooth preparations of ceramic crowns. However, scientific evidence is lacking to help clinicians make a proper selection. PURPOSE: The purpose of this systematic review and meta-analysis was to evaluate the effects of finish-line designs on the marginal and internal adaptations of ceramic crowns. MATERIAL AND METHODS: This report follows the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. The literature search was conducted in MEDLINE via the PubMed, Embase, and Web of Science databases with no publication year or language limits. In vitro studies comparing the marginal and internal adaptations of ceramic crowns with rounded shoulder and chamfer finish lines were included in the meta-analysis. RESULTS: Sixteen studies were included in the qualitative synthesis and meta-analyses. Statistical analyses were conducted using the Review Manager Software. Meta-analyses were performed with random-effects models (α=.05). Ceramic crowns with rounded shoulders exhibited significantly better marginal adaptation than those with chamfers (P<.001; mean difference=-7.8; 95% confidence interval=-11.6 to -4.1). Moreover, ceramic crowns with chamfers exhibited significantly better internal adaptation than those with rounded shoulders (P=.020; mean difference=35.0; 95% confidence interval=6.5 to 63.5). CONCLUSIONS: The difference in marginal adaptation of ceramic crowns using 2 finish-line designs was small, and the clinical significance was low, whereas the results of internal adaptation favored the chamfer finish line.

The Use of 3D Printed Tooth Preparation to Assist in Teaching and Learning in Preclinical Fixed Prosthodontics Courses.

Tooth preparation for fixed dental prostheses is not an easy procedure to understand spatially, especially for first-year dental students. This technical report describes an innovative technique for assisting learning in preclinical fixed prosthodontics courses. Ideal full-contour tooth preparations are digitally scanned and 3D printed to the exact specifications of the ideal preparation. Students and faculty use these printed tooth preparations as teaching and learning tools to facilitate in 3D visualization for fixed prosthodontics courses.

Marginal Fit of Metal-Ceramic Copings: Effect of Luting Cements and Tooth Preparation Design.

PURPOSE: To evaluate the effect of the triad finish line design, axial wall convergence angle, and luting cement on the marginal fit of metal copings used in metal-ceramic crowns. MATERIALS AND METHODS: Schematic dies and their respective copings were cast in NiCr alloy. The dies exhibited the following finish line/convergence angle combinations: sloping shoulder/6°, sloping shoulder/20°, shoulder/6°, shoulder/20°. Marginal fit was evaluated under a stereomicroscope, before and after cementation. Copings were air-abraded with 50 µm Al2 O3 particles and cemented with Cimento de Zinco, RelyX U100, or Panavia F cements (n = 10/group). Data were square-root transformed and analyzed by 3-way factorial random effect model and Tukey's post hoc test (α = 0.05). RESULTS: Statistical analysis showed significance for the interactions finish line and convergence angle (p < 0.05), convergence angle and time (p < 0.001), and luting cement and time (p < 0.001). Sloping shoulder/20° provided the highest marginal discrepancy when compared to the other finish line/convergence angle combinations, which were statistically similar among each other. For both convergence angles and for all luting cements, the marginal discrepancy was significantly higher after cementation. Before and after cementation, 6° provided better marginal fit than 20°. After cementation, Panavia F provided higher marginal discrepancy than Cimento de Zinco. CONCLUSION: Lower convergence angle combined with shoulder and a low-consistency luting cement is preferable to cement metal copings.

Preparation Ferrule Design Effect on Endocrown Failure Resistance.

PURPOSE: To evaluate the effect of preparation ferrule inclusion with fracture resistance of mandibular molar endocrowns. MATERIALS AND METHODS: Recently extracted mandibular third molars were randomly divided into 3 groups (n = 12) with the coronal tooth structure removed perpendicular to the root long axis approximately 2 mm above the cemento-enamel junction with a slow-speed diamond saw. The pulp chamber was exposed using a diamond bur in a high-speed handpiece with pulpal remnants removed and canals instrumented using endodontic hand instruments. The chamber floor was restored using a resin core material with a two-step, self-etch adhesive and photopolymerized with a visible light-curing unit to create a 2 mm endocrown preparation pulp chamber extension. One and two millimeter ferrule height groups were prepared using a diamond bur in a high-speed handpiece following CAD/CAM guidelines. Completed preparation surface area was determined using a digital measuring microscope. Scanned preparations were restored with lithium disilicate restorations with a self-adhesive resin luting agent. All manufacturer recommendations were followed. Specimens were stored at 37°C/98% humidity and tested to failure after 24 hours at a 45° angle to the tooth long axis using a universal testing machine. Failure load was converted to MPa using the available bonding surface area with mean data analyzed using Kruskal-Wallis/Dunn (p = 0.05). RESULTS: Calculated failure stress found no difference in failure resistance among the three groups; however, failure load results identified that the endocrown preparations without ferrule had significantly lower fracture load resistance. Failure mode analysis identified that all preparations demonstrated a high number of catastrophic failures. CONCLUSIONS: Under the conditions of this study, ferrule-containing endocrown preparations demonstrated significantly greater failure loads than standard endocrown restorations; however, calculated failure stress based on available surface area for adhesive bonding found no difference between the groups. Lower instances of catastrophic failure were observed with the endocrown preparations containing 1 mm of preparation ferrule design; however, regardless of the presence of ferrule, this study found that all endocrown restorations suffered a high proportion of catastrophic failures but at loads greater than reported under normal masticatory function.

Adequately Prepared? A Study Using an Innovative Computer Application to Measure Clinical Crown Convergence Angles Achieved by Students at a UK Dental School.

This study examined the total occlusal convergence angles created for full coverage crown preparations by students at a UK dental school. Working casts of 82 clinical crown preparations were scanned using a 3D scanner. Stereolithographic files were uploaded to Preppr, a crown preparation analysis application. Mean bucco-lingual convergence angle were 19.6° (+/-11.7) and mesial-distally 17.8° (+/-11.1). Smallest bucco-lingual convergence angles were achieved for canine teeth with the largest on molar teeth. The smallest mesio-distal values were on canine teeth with the largest on molar teeth. Ideal total convergence angles (4-14°) were achieved in 23% of bucco-lingual preparations and 33% of mesio-distal preparation. Results for clinically acceptable angles (10-20°) were 30% and 40% respectively. There were no statistically significant differences between tooth types for mean bucco-lingual values. (p=0.623), mesio-distal mean values were statistically different by tooth type (p=0.003). Mean values for mandibular molars were significantly higher than for maxillary incisors (p=0.001) and mandibular molars had significantly higher values than maxillary canines (p=0.045). Results in this study were comparable to those of other students and qualified clinicians, with a minority of preparation achieving ideal values.

Interventions for replacing missing teeth: attachment systems for implant overdentures in edentulous jaws.

BACKGROUND: Implant overdentures are one of the most common treatment options used to rehabilitate edentulous patients. Attachment systems are used to anchor the overdentures to implants. The plethora of attachment systems available dictates a need for clinicians to understand their prosthodontic and patient-related outcomes. OBJECTIVES: To compare different attachment systems for maxillary and mandibular implant overdentures by assessing prosthodontic success, prosthodontic maintenance, patient preference, patient satisfaction/quality of life and costs. SEARCH METHODS: Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 24 January 2018); Cochrane Central Register of Controlled Trials (CENTRAL; 2017, Issue 12) in the Cochrane Library (searched 24 January 2018); MEDLINE Ovid (1946 to 24 January 2018); and Embase Ovid (1980 to 24 January 2018). The US National Institutes of Health Trials Registry (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials on 24 January 2018. No restrictions were placed on the language or date of publication when searching the electronic databases. SELECTION CRITERIA: All randomised controlled trials (RCTs), including cross-over trials on maxillary or mandibular implant overdentures with different attachment systems with at least 1 year follow-up. DATA COLLECTION AND ANALYSIS: Four review authors extracted data independently and assessed risk of bias for each included trial. Several corresponding authors were subsequently contacted to obtain missing information. Fixed-effect meta-analysis was used to combine the outcomes with risk ratios (RR) for dichotomous outcomes and mean differences (MD) for continuous outcomes, with 95% confidence intervals (95% CI). We used the GRADE approach to assess the quality of evidence and create 'Summary of findings' tables. MAIN RESULTS: We identified six RCTs with a total of 294 mandibular overdentures (including one cross-over trial). No trials on maxillary overdentures were eligible. Due to the poor reporting of the outcomes across the included trials, only limited analyses between mandibular overdenture attachment systems were possible.Comparing ball and bar attachments, upon pooling the data regarding short-term prosthodontic success, we identified substantial heterogeneity (I2 = 97%) with inconsistency in the direction of effect, which was unexplained by clinical or methodological differences between the studies, and accordingly we did not perform meta-analyses for this outcome. Short-term re-treatment (repair of attachment system) was higher with ball attachments (RR 3.11, 95% CI 1.68 to 5.75; 130 participants; 2 studies; very low-quality evidence), and there was no difference between both attachment systems in short-term re-treatment (replacement of attachment system) (RR 1.18, 95% CI 0.38 to 3.71; 130 participants; 2 studies; very low-quality evidence). It is uncertain whether there is a difference in short-term prosthodontic success when ball attachments are compared with bar attachments.Comparing ball and magnet attachments, there was no difference between them in medium-term prosthodontic success (RR 0.84, 95% CI 0.64 to 1.10; 69 participants; 1 study; very low-quality evidence), or in medium-term re-treatment (repair of attachment system) (RR 1.75, 95% CI 0.65 to 4.72; 69 participants; 1 study; very low-quality evidence). However, after 5 years, prosthodontic maintenance costs were higher when magnet attachments were used (MD -247.37 EUR, 95% CI -346.32 to -148.42; 69 participants; 1 study; very low-quality evidence). It is uncertain whether there is a difference in medium-term prosthodontic success when ball attachments are compared with magnet attachments.One trial provided data for ball versus telescopic attachments and reported no difference in prosthodontic maintenance between the two systems in short-term patrix replacement (RR 6.00, 95% CI 0.86 to 41.96; 22 participants; 1 study; very low-quality evidence), matrix activation (RR 11.00, 95% CI 0.68 to 177.72; 22 participants; 1 study; very low-quality evidence), matrix replacement (RR 1.75, 95% CI 0.71 to 4.31; 22 participants; 1 study; very low-quality evidence), or in relining of the implant overdenture (RR 2.33, 95% CI 0.81 to 6.76; 22 participants; 1 study; very low-quality evidence). It is uncertain whether there is a difference in short-term prosthodontic maintenance when ball attachments are compared with telescopic attachments.In the only cross-over trial included, patient preference between different attachment systems was assessed after only 3 months and not for the entire trial period of 10 years. AUTHORS' CONCLUSIONS: For mandibular overdentures, there is insufficient evidence to determine the relative effectiveness of different attachment systems on prosthodontic success, prosthodontic maintenance, patient satisfaction, patient preference or costs. In the short term, there is some evidence that is insufficient to show a difference and where there was no evidence was reported. It was not possible to determine any preferred attachment system for mandibular overdentures.For maxillary overdentures, there is no evidence (with no trials identified) to determine the relative effectiveness of different attachment systems on prosthodontic success, prosthodontic maintenance, patient satisfaction, patient preference or costs.Further RCTs on edentulous cohorts must pay attention to trial design specifically using the same number of implants of the same implant system, but with different attachment systems clearly identified in control and test groups. Trials should also determine the longevity of different attachment systems and patient preferences. Trials on the current array of computer-aided designed/computer-assisted manufactured (CAD/CAM) bar attachment systems are encouraged.