Taper of Full-Veneer Crown Preparations by Dental Students at the University of the West Indies

Effect of Indirect Visual Course on Full Crown Preparation Skills in Preclinical Dental Students

OBJECTIVES

Indirect vision is a crucial skill for dentists and should be developed during undergraduate training. This study aimed to evaluate the impact of an indirect visual course on students' competence in abutment tooth preparation and compare their self-assessments with instructor assessments.

METHODS

Thirty-seven third-year dental students participated in an indirect vision preclinical training course, which involved drawing shapes in a reflection box. Before and after the course, students performed 296 full crown preparations on canine teeth over four practical sessions. Students self-assessed their performance using a 5-item scoring rubric, and their scores were compared with the instructor's technical assessments. Data were analyzed using one-way ANOVA, post hoc tests, paired samples t-tests, and Spearman's rho (∝ = 0.05).

RESULTS

Both self-assessment and technical assessment scores improved significantly after the indirect visual course (p < 0.001). The correlation between self-assessments and instructor assessments was moderate both before (Spearman's rho 0.48) and after the course (Spearman's rho 0.42) (p < 0.001). Repetitive practical sessions did not further improve the scores (p > 0.05). However, the average time for crown preparation decreased significantly, from 46 to 38 min, showing an 18% improvement (p < 0.001).

CONCLUSION

The indirect visual course significantly enhanced students' crown preparation skills and reduced preparation time. The course also improved the overall agreement between students' self-assessments and instructor assessments, indicating a better understanding of their performance.

Influence of Glass Ionomer-based Luting Cements on the Clinical Success of Zirconia Crowns: Randomized Clinical Trial

OBJECTIVE

This study evaluated the influence of two types of glass ionomer-based luting agent on the clinical performance of metal-free zirconia crowns.

METHODS AND MATERIALS

Thirty participants received two full crown restorations in either anterior or posterior teeth, in a split-mouth design. After tooth preparation, impressions with addition-cured silicone were made and casts were obtained. The casts were scanned and 3Y-TZP zirconia copings (Ceramill ZI - Amann Girrbach) were milled using a CAD/CAM system. Glass ceramic (IPS E.max Ceram, Ivoclar Vivadent) was used to create the crown shape. For each participant, one crown was cemented using a conventional glass ionomer (GIC - Meron, Voco), while the other received a resin-modified glass ionomer cement (RMGIC - Meron Plus QM, Voco). The restorations were evaluated by two calibrated examiners after seven days, one year, and two years. The parameters at each evaluated time were analyzed by the Fisher exact test (α=0.05).

RESULTS

At two years postoperatively, 24 participants attended the recall, and 46 (76.67%) restorations were evaluated. No fractures or secondary caries were diagnosed. Minimal marginal staining was verified in both cements. During the follow-up period, only two anterior crowns cemented with conventional glass ionomer showed loss of retention. No loss of retention was detected in posterior crowns.

CONCLUSION

After two years of intraoral service, the crowns cemented with either conventional glass ionomer cement or resin-modified glass ionomer presented acceptable and similar clinical performance for all parameters analyzed in both anterior and posterior teeth.

Laboratory Technician Assessment of the Quality of Single-Unit Crown Preparations and Impressions as Predictors of the Clinical Acceptability of Crowns as Determined by the Treating Dentist: Findings from the National Dental Practice-Based Research Network

PURPOSE

In-laboratory assessment by laboratory technicians may offer insight to increase clinical success of dental crowns, and research in this area is lacking.

MATERIALS AND METHODS

Dentists in the National Dental Practice-Based Research Network enrolled patients in a study about single-unit crowns; laboratory technicians evaluated the quality of tooth preparations and impressions. The primary outcome for each crown was clinical acceptability (CAC), as judged by the treating dentist. A secondary outcome was "Goodness of Fit (GOF)," a composite score of several aspects of clinical fit, also judged by the study dentist. A mixed-effects logistic regression was used to analyze associations between laboratory technician ratings and the CAC and GOF.

RESULTS

Dentists (n = 205) evaluated 3731 crowns. Technicians ranked the marginal detail of impressions as good or excellent in 92% of cases; other aspects of the impression were ranked good or excellent 88% of the time. Regarding tooth preparation, about 90% of preparations were considered adequate (neither excessive nor inadequate reduction). Factors associated with higher CAC were more preparation taper, and use of optical imaging. Factors associated with better GOF were higher impression quality, greater occlusal reduction, more preparation taper, and optical imaging.

CONCLUSIONS

Overall quality of preparations and impressions was very high, as evaluated by laboratory technicians. Several clinical parameters were associated with higher CAC and GOF. Clinicians who struggle with crown remakes might consider less conservative tooth preparation, as well as using digital impression technology.

Crown Taper Angles Achieved by Dental Students: A Systematic Review

The aim of this systematic review was to examine the literature on clinical taper angles achieved by dental students during crown preparation to determine the theoretical and clinically acceptable values identified in research studies. Medline, Embase, Web of Knowledge, the Cochrane Library, the British Dental Journal, and the Journal of the American Dental Association were searched to identify relevant studies. Studies were included if they were in vivo research on full crown preparations by dental students and published in English. Data extracted were country, year of publication, model selection and measurement methods, tests for reproducibility, tooth type, number of teeth assessed, and tapers achieved. The search resulted in 12 included articles from 11 countries published between 1978 and 2014 featuring a total of 2,306 preparations. In those studies, students failed to achieve ideal convergence angles (between 4° and 14°) but produced clinically acceptable results (between 10° and 20°). These findings should be taken into account when assessing dental students during their training programs.

All-ceramic crown preparations: An alternative technique

BACKGROUND

The aim of this study was to compare the crown preparation dimensions produced from two different techniques of preparation for posterior all-ceramic crowns.

METHODS

Twenty-four fourth year dental students undertook a course of advanced simulation training involving education in an alternative technique of preparation for a 36 all-ceramic crown. Crown preparations performed using the traditional technique were compared with an alternative technique for total occlusal convergence (TOC) and reduction difference (RD) using digital scanning and comparative software.

RESULTS

Groups that spent the most time performing the alternative technique produced crown preparations with significantly lower buccolingual (BL) TOC. The training resulted in crown preparations that were closer to ideal TOC and RD measurements.

CONCLUSIONS

The alternative technique of crown preparation for a posterior all-ceramic crown showed initial promise in creating a less buccolingually tapered and more ideally occlusally reduced crown preparation.

Impact of a Core Ferrule Design on Fracture Resistance of Teeth Restored with Cast Post and Core

Objectives. To investigate the influence of a contra bevel on the fracture resistance of teeth restored with cast post and core. Materials and Methods. Sixty plastic analogues of an upper incisor were endodontically treated and prepared with 6° internal taper and 2 mm of ferrule in order to receive a cast post and core. The prepared samples were divided into two groups (n = 30); the first group serves as control while the second group was prepared with an external 30° bevel on the buccal and lingual walls. All samples crowned were exposed to a compressive load at 130° to their long axis until fractures occurred. Fracture resistance loads were recorded and failure modes were also observed. Mann-Whitney test was carried out to compare the two groups. Results. Mean failure loads for the groups were, respectively, 1038.69 N (SD ±243.52 N) and 1078.89 N (SD ±352.21 N). Statistically, there was no significant difference between the two groups (P = 0.7675 > 0.05). Conclusion. In the presence of a ferrule and a crown in the anterior teeth, adding a secondary ferrule to the cast post and core will not increase the resistance to fracture.

Custom total occlusal convergence angle sticker fabrication

This article describes a method of fabricating a custom total occlusal convergence angle sticker with photo editing software and label stickers. The custom total occlusal convergence angle sticker can help clinicians achieve an accurate degree of taper during axial wall reduction of tooth preparation.

Computer-aided evaluation of preparations for CAD/CAM-fabricated all-ceramic crowns

OBJECTIVE

The aim of this study was the evaluation of preparations from general dental practitioners for zirconia crowns and their correlation with clinical recommendations using a digital approach.

MATERIAL AND METHOD

Seventy-five datasets of left first upper molars (FDI 16) prepared for single zirconia crowns by general dental practitioners were analyzed using a computer-aided design software (LAVA(TM) Design; 3M ESPE, Seefeld, Germany) and a 3D-inspection software (COMETinspect®plus version 4.5; Steinbichler Optotechnik, Neubeuern, Germany). Evaluated parameters were convergence angle, undercuts, interocclusal reduction, abutment height, and design of preparation margin.

RESULTS

The mean convergence angle was determined to be 26.7°. The convergence angle in the mesiobuccal to distopalatal dimension was significantly the highest (31.7°), and the abutment height showed a mean value of 4.1 mm. Convergence angle and abutment height showed a negative correlation. Seventy-three percent of the evaluated locations revealed a margin design conforming to ceramic restorations. In over 30 % of the cases, the interocclusal reduction was insufficient. Generally, no preparation fulfilled all recommendations. Five (6.66 %) of the preparations fulfilled four criteria, 16 (21.33 %) preparations fulfilled three criteria, 31 (41.33 %) fulfilled two criteria, 17 (22.66 %) preparations fulfilled one criterion, and 6 (8 %) fulfilled no criterion.

CONCLUSIONS

Within the limitations of this study, most general dental practitioners seem to have difficulties fulfilling all clinical recommendations given for the preparation of zirconia crowns. The presented digital approach seems to be a useful method to evaluate the preparation geometry.

CLINICAL RELEVANCE

The correct preparation geometry represents an important prerequisite for the success of all-ceramic full crowns. As preparations clearly need to be improved, the approach presented could be the basis of a future tool to increase preparation quality in practice and education by direct objective feedback.