Search

Aim/Purpose: The primary aim of this study was to examine the clinical performance of posterior monolithic single crowns in terms of failure or complications and the secondary aim was to assess the quality of these restorations according to the United States Public Health Service (USPHS) criteria. Methods: Ιn a private dental clinic, 65 patients with need of posterior crowns were restored with monolithic zirconia crowns. All the restorations were evaluated 6 and 12 months after their cementation. The modified United States Public Health Service (USPHS) criteria and periodontal parameters were applied for the clinical evaluation of the crowns. Restorations with Alpha or Bravo rating were considered a success. Results: Descriptive statistics and nonparametric tests were used for statistical analysis. Sixty-five patients (mean age: 49.52) were restored with 65 monolithic zirconia crowns. No fracture of the restorations was recorded. The overall success rate was 98.5%. The clinical quality of all crowns was acceptable except for the marginal discoloration of one crown at the 6- and 12-month follow-up examination. Conclusions: In this study, no fracture of single-tooth monolithic crowns occurred and the success rate was high. Monolithic zirconia restorations fabricated is a viable option for the restoration of single posterior teeth.

Purpose: To investigate the effects of evaluator fatigue and level of expertise on the grading of preclinical tooth crown preparations, by global and analytical methods of evaluation., Materials and Methods: The study had a double-blind design. Two faculty members, each with more than 10 years of clinical and teaching experience, and two demonstrators with no teaching experience evaluated tooth preparations on maxillary central incisors and mandibular first molars. As a test of the effect of fatigue, preparations were globally (subjective grading) and analytically (criteria-based grading) graded on day 1 (after evaluators had been on duty continuously for 8 hours) and day 2 (in the morning after evaluators had sufficient sleep). Evaluators worked under the same circumstances and did not communicate with each other. The assigned textbooks were used to develop the criteria for grading (rubric) and the predefined exclusion criteria. Grades were recorded and statistically analyzed using statistical software. The paired-sample t-test and Mann-Whitney U test were used for multiple comparisons. Level of significance was set at p ˂ 0.05., Results: An inconsistency in preclinical tooth preparation evaluation was found to exist by both global and analytical methods. Junior faculty tended to award higher grades than senior faculty did. Furthermore, higher grades were scored by the analytical method. More clinical and academic experience did not guarantee intra- and interexaminer reliability. Younger faculty appeared to tolerate fatigue better than older faculty. Likewise, global evaluation appeared to be more influenced by fatigue than was the analytical method., Conclusion: There were variations in grading, with no consistently preferred grading method. Evaluator performance after continuous 8-hour duty had no significant effect on preclinical tooth preparation evaluation. Level of expertise did not affect preclinical evaluation regardless of the grading method used., (© 2016 by the American College of Prosthodontists.)

Objective: To further study the most suitable parameters for automatic full crown preparation using oral clinical micro robot. Its purpose is to improve the quality of automated tooth preparing for the system and to lay the foundation for clinical application. Methods: Twenty selected artificial resin teeth were used as sample teeth. The micro robot automatic tooth preparation system was used in dental clinic to control the picosecond laser beam to complete two dimensional cutting on the resin tooth sample according to the motion planning path. Using the laser scanning measuring microscope, each layer of cutting depth values was obtained and the average value was calculated. The monolayer cutting depth was determined. The three-dimensional (3D) data of the target resin teeth was obtained using internal scanner, and the CAD data of full-crown tooth preparation was designed by CAD self-develged software. According to the depth of the single layer, 11 complete resin teeth in phantom head were automatically prepared by the robot controlling the laser focused spot in accordance with the layer-cutting way. And the accuracy of resin tooth preparation was evaluated with the software. Using the same method, monolayer cutting depth parameter for cutting dental hard tissue was obtained. Then 15 extracted mandibular and maxillary first molars went through automatic full crown tooth preparation. And the 3D data of tooth preparations were obtained with intra oral scanner. The software was used to evaluate the accuracy of tooth preparation. Results: The results indicated that the single cutting depth of cutting resin teeth and in vitro teeth by picosecond laser were (60.0±2.6) and (45.0±3.6) μm, respectively. Using the tooth preparation robot, 11 artificial resin teeth and 15 complete natural teeth were automatically prepared, and the average time were (13.0±0.7), (17.0±1.8) min respectively. Through software evaluation, the average preparation depth of the occlusal surface of 11 resin teeth was approximately (2.089±0.026) mm, the error was about (0.089±0.026) mm; the average convergence angle was about 6.56°±0.30°, the error was about 0.56°±0.30°. Compared with the target preparation shape, the average shape error of the 11 resin tooth preparations was about 0.02-0.11 mm. And the average preparation depth of the occlusal surface of 15 natural teeth was approximately (2.097±0.022) mm, the error was about (0.097±0.022) mm; the average convergence angle was about 6.98°±0.35°, the error was about 0.98°±0.35°. Compared with the target preparation shape, the average shape error of the 15 natural tooth preparations was about 0.05-0.17 mm. Conclusions: The experimental results indicate that the automatic tooth preparation for resin teeth and the teeth were completed according to the specific parameters of the single cutting depth by the micro robot controlling picosecond laser respectively, its preparation accuracy met the clinical needs. And the suitability of the parameter was confirmed.

The aim of this pilot study was to evaluate the feasibility of a new tooth preparation assessment software, Preppr, as an educational tool for dental students in achieving optimal parameters for a crown preparation. In February 2015, 30 dental students in their fourth year in a five-year undergraduate dental curriculum in New Zealand were randomly selected from a pool of volunteers (N=40) out of the total class of 85. The participants were placed into one of three groups of ten students each: Group A, the control group, received only written and pictorial instructions; Group B received tutor evaluation and feedback; and Group C performed self-directed learning with the aid of Preppr. Each student was asked to prepare an all-ceramic crown on the lower first molar typodont within three hours and to repeat the exercise three times over the next four weeks. The exercise stipulated a 1 mm finish line dimension and total convergence angles (TOC) between 10 and 20 degrees. Fulfillment of these parameters was taken as an acceptable preparation. The results showed that Group C had the highest percentage of students who achieved minimum finish line dimensions and acceptable TOC angles. Those students also achieved the stipulated requirements earlier than the other groups. This study's findings provide promising data on the feasibility of using Preppr as a self-directed educational tool for students training to prepare dental crowns.

Objectives: To evaluate teeth preparation designs for metal-ceramic crowns in private dental practice in Jordan., Materials and Methods: One-hundred and seventy two dies were included. Different aspects of tooth preparations were quantified, analyzed and compared with the recommended guidelines., Results: Almost 64% of preparations finish lines were positioned subgingivally. Shoulder finish lines were observed in 74.4% where-as 22.7% showed chamfer finish lines. Total occlusal convergence angles were 29.8 degrees in BL plane, 247 degrees in MD plane., Conclusions: Dental practitioners in private practice in Jordan did not fully adhere to the recommendedguidelines for tooth preparations for MCRs.

Statement of Problem: Controlling tooth reduction for porcelain laminate veneers (PLVs) in fractions of millimeters is challenging., Purpose: The purpose of this study was to assess an automated robotic tooth preparation system for PLVs for accuracy and precision compared with conventional freehand tooth preparation., Material and Methods: Twenty maxillary central incisor tooth models were divided into 2 groups. Ten were assigned to a veneer preparation with a robotic arm according to preoperative preparation design-specific guidelines (experimental group). Ten were assigned to conventional tooth preparation by a clinician (control group). Initially, all tooth models were scanned with a 3- dimensional (3D) laser scanner, and a tooth preparation for PLVs was designed on a 3D image. Each tooth model was attached to a typodont. For the experimental group, an electric high-speed handpiece with a 0.9-mm-diameter round diamond rotary cutting instrument was mounted on the robotic arm. The teeth were prepared automatically according to the designed image. For the control group, several diamond rotary cutting instruments were used to prepare the tooth models according to preoperative preparation design guidelines. All prepared tooth models were scanned. The preoperative preparation design image and scanned postoperative preparation images were superimposed. The dimensional difference between those 2 images was measured on the facial aspect, finish line, and incisal edge. Differences between the experimental and the control groups from the 3D design image were computed. Accuracy and precision were compared for all sites and separately for each tooth surface (facial, finish line, incisal). Statistical analyses were conducted with a permutation test for accuracy and with a modified robust Brown-Forsythe Levene-type test for precision (α=.05)., Results: For accuracy for all sites, the mean absolute deviation was 0.112 mm in the control group and 0.133 mm in the experimental group. No significant difference was found between the 2 (P=.15). For precision of all sites, the standard deviation was 0.141 mm in the control group and 0.185 mm in the experimental group. The standard deviation in the control group was significantly lower (P=.030). In terms of accuracy for the finish line, the control group was significantly less accurate (P=.038). For precision, the standard deviation in the control group was significantly higher at the finish line (P=.034)., Conclusions: For the data from all sites, the experimental procedure was able to prepare the tooth model as accurately as the control, and the control procedure was able to prepare the tooth model with better precision. The experimental group showed better accuracy and precision at the finish line., (Copyright © 2015 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.)

The problems associated with intra- and interexaminer reliability when assessing preclinical performance continue to hinder dental educators' ability to provide accurate and meaningful feedback to students. Many studies have been conducted to evaluate the validity of utilizing various technologies to assist educators in achieving that goal. The purpose of this study was to compare two different versions of E4D Compare software to determine if either could be expected to deliver consistent and reliable comparative results, independent of the individual utilizing the technology. Five faculty members obtained E4D digital images of students' attempts (sample model) at ideal gold crown preparations for tooth #30 performed on typodont teeth. These images were compared to an ideal (master model) preparation utilizing two versions of E4D Compare software. The percent correlations between and within these faculty members were recorded and averaged. The intraclass correlation coefficient was used to measure both inter- and intrarater agreement among the examiners. The study found that using the older version of E4D Compare did not result in acceptable intra- or interrater agreement among the examiners. However, the newer version of E4D Compare, when combined with the Nevo scanner, resulted in a remarkable degree of agreement both between and within the examiners. These results suggest that consistent and reliable results can be expected when utilizing this technology under the protocol described in this study.

The use of computers to aid in instruction and help decrease the subjective component of assessment is steadily increasing. One of the potential barriers to the effective utilization of CAD/CAM technology for assessment purposes is the efficient scanning of the teeth being used for comparison. The purpose of this pilot study was to determine if the use of different typodonts, of the same make and model, has any significant effect on the percent comparison results when using E4D Compare. Tooth #30 was prepared by a faculty member to represent what dental students at Georgia Regents University are taught as the ideal preparation for a full gold crown. Ten typodonts of the same make and model were selected for comparison. Three different examples of students' preparations were scanned and compared to the ideal preparation. Each of the three student preparations was subjected to ten trials (occasions), one for each typodont, at five tolerance levels: 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm, and 0.5 mm. The intraclass correlation coefficient (ICC) was used to measure the intrarater agreement among the typodonts at the various tolerance levels. The agreement coefficients (0.971-0.984) indicated very little variability attributable to the use of a different typodont. The high agreement coefficients achieved using different typodonts of the same make and model provide evidence for the interchangeability of typodonts when assessing a student's performance in the preclinical simulation environment.

Purpose: To evaluate the effect of two putty-wash impression techniques on the long-term accuracy and dimensional stability of poly(vinyl siloxane) (PVS) in the gingival sulcus area., Materials and Methods: Impressions were taken from a master cast to simulate molar crown preparation. A space around the abutment served as the gingival sulcus. Fifteen impressions using the one- and two-step impression techniques were taken using Express Regular, Express Fast, and President impression materials with custom trays. Using a Toolmaker's microscope, the long (LD) and short distances (SD) of the abutment and the planar distance between two parallel lines (PL) at the circumference of the cast were taken at 0.5, 2, 24, 48, 72, 96, 120, and 144 hours after mixing. ANOVA was performed, with the discrepancy between the distances of the impressions and the master cast as the dependent variable., Results: The differences when different materials and impression techniques were used were significant (p < 0.001) for LD, SD, and PL, as was the interaction between the material, time, and technique (p < 0.001). SD discrepancies were higher than those of LD for all materials and times. The two-step impression technique was more accurate, with smaller discrepancies than the one-step impression technique. For all materials, the PL discrepancy was deemed acceptable (less than 0.5%) for all tested times. President had higher discrepancies than the other materials., Conclusions: When using the two-step putty-wash impression technique, pouring of the impressions may be postponed up to 30 hours; however, when using the one-step impression technique, pouring should be performed within 2 hours., (© 2013 by the American College of Prosthodontists.)

Introduction: Preparation of teeth is a basic technique for dental treatment and plays an essential role in pre-clinical education. The purpose of this study was to evaluate whether undergraduate students' evaluations of prepared teeth were consistent with faculty assessments and correlated with students' performance in test preparations., Materials and Methods: Thirty four of 52 dental students having attended a pre-clinical course on basic prosthodontic topics including tooth preparation volunteered to participate in this study. The students were given 10 casts each containing one tooth with an intentionally applied preparation fault of a certain type prepared by an experienced clinician. The students were asked to mark on a list the fault type found in every tooth. The association of students' ratings with their performance during the course was analysed by means of a contingency table, and a generalised linear model was used to compare students' and faculty ratings (α = 0.05)., Results: No significant difference between students' and faculty ratings could be found by analysis of deviance (P = 0.953). Significant deviations of fault detection probabilities from their group mean were found for six of ten fault types. No significant association between students' performance in test preparations and students ratings could be found (P = 0.564)., Discussion: It was possible to achieve a level of calibration within the group of students, which was comparable to that in the group of faculty members., Conclusions: Calibration of both students and examiners remains to be an issue with the teaching concepts applied in this study., (2010 John Wiley & Sons A/S.)

The purpose of this study was to determine the reliability of the data acquisition and modeling process of laser and white light scanners by evaluating the reproducibility of digitized simulated crowns with different convergences. A secondary purpose was to analyze the influence of die preparation by testing this hypothesis with a set of dies without ditching compared with a set with well-defined margins. Ditching or trimming the die defines the position of the margin and acts as a guide to gingival contour when the restoration is being waxed. Two light scanners (a white light optical scanner [Steinbichler Gmbh, Neubeuern, Germany] and red laser light scanner [TurboDent System, Taichung, Taiwan]) were evaluated. Two sets of simulated crowns were fabricated as cone frustrum models with a total occlusal convergence (TOC) of 0°, 5°, 10°, 15°, 20°, and 25° and a 9-mm base and 3-mm height using a precision milling machine and computer-aided design/computer-aided manufacturing (CAD/CAM) technique. One set of the dies was ditched immediately below the finish line to enhance marginal definition. Each die was optically digitized five times directly with the two different measuring systems. The area of each triangle in the scan that is occlusal to the margin line was calculated and summed to produce the final surface area measurement provided. The digitizing error was compared with the computed surface area of the original master die sets and compared with a paired t-test (df=4; 95% CI). There was no difference in accuracy of the untrimmed dies between the two systems evaluated. We also did not find any difference in the 0° (p=0.12) and 5° degree (p=0.21) groups among the ditched dies. However, when the TOC exceeded 5°, there was a significant difference between the two groups, with the laser groups having a smaller error percentage. Three-dimensional light scanning was not affected by the convergence angle except in the 0°-5° range. Trimming the dies greatly affected the accuracy of scanning.

Objectives: To investigate if general dental practitioners (GDPs) in private practice in Jordan follow universal guidelines for preparation of anterior teeth for resin bonded all-ceramic crowns (RBCs)., Material and Methods: A sample (n=100) of laboratory models containing 208 tooth preparations for IPS Empress and In Ceram, featuring work from different GDPs, was obtained from 8 commercial dental laboratories. Aspects of preparations were quantified and compared with accepted criteria defined following a review of the literature and recommendations of the manufactures' guidelines., Results: Subgingival margins on the buccal aspect were noticed in 36% of the preparations, 54% demonstrated overpreparation with a tendency to overprepare the teeth on the mesiodistal plane more than buccolingual plane. Twenty percent of samples presented a shoulder finish line while a chamfer margin design was noticed in 39%. Twenty-nine percent and 12% of samples had either a feathered or no clear margin design respectively. Incisal underpreparation was observed in 18% of dies of each type. Only 17% of all preparations were found to follow the recommended anatomical labial preparations while 29% of the RBC preparations were found to have the recommended axial convergence angle. In total, 43% of preparations were found to have the recommended depth of the finish line., Conclusions: It was found that relevant guidelines for RBC preparations were not being fully adhered to in private practice in Jordan.

Objective: To compare clinically practiced convergence angle values of tooth preparation with recommended values, and also the effect of tooth position and operator experience on convergence angle., Study Design: Analytical study., Place and Duration of Study: The study was carried out at the Dental clinic, The Aga Khan University Hospital, Karachi, from January to June 2007., Methodology: A minimum of 75 crown preparation dies including 25 dies in each group of teeth (anterior, premolars and molars) were collected retrospectively which were prepared by residents and specialists of operative dentistry. AutoCAD 2007 software was used for measurement of convergence angle. One sample t-test was applied to compare the mean practiced convergence angle values with its recommended values. Two way ANOVA was applied to measure difference in convergence angle values with respect to operator experience and tooth type with the level of significance being α=0.050., Results: Mean reported convergence angle value was 22.72°, which was significantly greater (p < 0.001) than the recommended values. Statistically significant difference in convergence angle was found between anterior vs. molar teeth and between premolars vs. molar teeth (p=0.0001 and p=0.002, respectively)., Conclusion: There was a considerable disparity between the convergent angles values recorded in this study and the recommended guidelines. Measured convergence angle values were greater for posterior teeth as compared to the anterior teeth.

Adequate tooth reduction is a prerequisite for function, esthetics, and longevity of fixed restorations. A tooth reduction guide may be useful for establishing the proper angulation of the tooth and maximizing periodontal health and restorative success. This article describes a simple and versatile technique for an accurate evaluation of tooth reduction for fixed restorations by using a color-contrasting positive guide of a silicone occlusal registration material processed inside a vacuum-formed clear thermoplastic matrix.

A structured literature review aimed to elucidate test parameters for in vitro testing of post-endodontic restorations. The literature was digitally searched using MEDLINE, EMBASE, MedPilot and an additional hand search was performed. Two independent researchers assessed the articles in relation to the defined inclusion and exclusion criteria. The literature search revealed 125 abstracts. Sixty-nine studies were included. Fifty-seven per cent of the studies investigated maxillary incisors only. The restorative stage as complex of tooth, post, core, and crown and post-and-core restored specimens without crowns were used most frequently. Fifty-nine per cent of the studies used static loading. Only 15% of the studies performed thermocycling and mechanical loading (TCML). However, the number of thermo- and load cycles varied. The cross-head speed of linear loading after TCML ranged from 0.01 to 150 mm min(-1). The reviewed studies were heterogeneous in test design regarding the used test parameters. A methodological standardization of in vitro testing of post-endodontic restorations is recommended.

The preparation of acrylic teeth in a simulated clinical environment (phantom head) plays an essential role in pre-clinical dental education where evaluation is performed visually by instructors. The aim of this investigation was to verify the quality criteria of a tooth preparation for a metal-ceramic crown (tooth No. 21) with the help of digital measurement. Thirty-six acrylic teeth were prepared by students and one tooth was prepared ideally by a trained dentist: These were examined and compared. Five experienced instructors independently assessed the quality criteria with the use of a criterion list. Afterwards, the teeth were scanned with the 3D-laser scanner 'es1' (Etkon Company, Munich, Germany). The calculation of the correlation coefficient demonstrated a satisfactory correlation between visual and digital rating concerning convergence angle, shoulder width and occlusal reduction. Greater differences between experimental groups were observed with regards to other criteria on the applied criterion list. A directed calibration of the evaluators and a re-evaluation of some measurements would be necessary to gain more precise results.

The evaluation of pre-clinical technical achievement in fixed prosthodontics cannot be objective when using visual examination of dental preparations. This is, however, still the main method used in dental schools. The present study introduces a new method, based on a mathematical formula, to reduce the problem. The idea emerged when using the Kavo PrepAssistant system (software version 1.05). This system is a 3D-scanner with software that can quantify geometrical differences between an instructor and student dental preparation in model teeth. Therefore, a mathematical formula was created, integrating selected clinically relevant geometric characteristics of dental preparations measured by the system. In this new formula, 70% of the evaluation parameters were computer analysed, whilst 30% were visually evaluated. This new method was compared with the traditional visual evaluation system during a pre-clinical practical examination, with the participation of 25 students. Using both methods to evaluate the 25 preparations, results showed similar grading for both methods (K-S test = 0.16; P < 0.05). Although this method does not provide overall clinical evaluation of student performance these results suggest that it can be helpful accessing technical achievement. In this method, the student has the guarantee that 70% of his/her grade results from an objective computer evaluation, with the possibility to visualise the mistakes with the software. It also reduces problems related to the calibration between different examiners. The Kavo PrepAssistant is a powerful tool in pre-clinical teaching, but has some drawbacks. It has to be developed towards the actual needs of pre-clinical departments, in order to achieve its full potential, as described in this study.

To evaluate the cumulative survival (CS) rates of fixed partial dentures (FPDs) retained by full-veneer retainers, and those of resin-bonded FPDs provided by graduating dental students for the replacement of a single missing tooth. In 168 patients, 61 3-unit fixed-fixed FPDs and 25 2-unit cantilevered FPDs retained by full-veneer retainers, and 77 3-unit fixed-fixed resin-bonded FPDs and 47 2-unit cantilevered resin-bonded FPDs, were examined for their retention and integrity. The periodontal health, endodontic status and coronal tissues of all abutment teeth were also evaluated. The survival rates of these various designs were analysed with the Kaplan-Meier method. The mean age of all FPDs was 31 months. At 48 months after their insertion, 3-unit FPDs retained by full-veneer retainers had a CS rate of 82%, followed by 2-unit resin-bonded FPDs at 81%, 2-unit FPDs retained by full-veneer retainers at 77%, and 3-unit resin-bonded FPDs at 63%. No significant difference was found between the four designs (P>0.05). Up to both 48 and 60 months, the most common causes of failure were endodontic for FPDs retained by full-veneer retainers, and dislodgement for resin-bonded FPDs. The 3-unit fixed-fixed FPDs retained by full-veneer retainers had the most favourable prognosis after 48 months for replacing a single missing tooth, but the difference between designs was not statistically significant.

This study compares the convergence angle of preparations for posterior gold crowns made by fourth/ fifth year undergraduate dental students, clinical teaching staff and general dental practitioners. Sixty dies were cast from impressions previously taken of clinical preparations by clinicians within each of the four groups. Each die was trimmed and sectioned in both mesio-distal and bucco-lingual planes before being projected using an overhead projector, thereby enabling the convergence angle silhouette to be measured. The results show the greatest convergence angle range to be produced by the least experienced students (10 degrees - 82 degrees). However, no significant difference (p > 0.05) was found when students with one further year of experience were compared to experienced staff. The degree of conformity to the ideal taper (4 degrees - 14 degrees) was no greater than 50% for any of the groups.

Statement of Problem: One of the most important criteria for the clinical acceptability and longevity of cast restorations is marginal adaptation. However, there is limited information on the accuracy of commonly practiced evaluation techniques., Purpose: This study assessed the effect of preparation design on marginal adaptation. In addition, sensitivity and specificity of clinical evaluations of marginal adaptations of cast restorations were assessed and compared to stereomicroscopy., Material and Methods: Three Ivorine molar teeth of differing designs were prepared: (1) a complete crown preparation with a chamfer finish line, (2) a complete crown preparation with a buccal shoulder and beveled finish line, and (3) a three-quarter crown preparation with proximal boxes and beveled finish line. Twenty-four castings (n = 8) were prepared (Ney technique casting metal). Twelve circumferential sites were identified for examination on each casting using a stereomicroscope, which was interpreted using software (Bioquant 98). The clinical examinations included explorer examination to detect marginal gap by tactile feel, followed by examination with a disclosing media (GC FitChecker). Chi-square tests of independence were used to evaluate the effect of preparation design and compare agreement between examination methods for detection of marginal gap size of greater than or equal to 30 microm (alpha=.05)., Results: The overall marginal adaptation of preparation designs was not significantly different. Results of explorer examination at 30-microm sensitivity and specificity were 46% and 97%, respectively. Similar values for disclosing media at 30 microm were 12% sensitivity and 97% specificity. The overall percent agreement with the stereomicroscope using the explorer was 58.3%, with 23.6% correct acceptance rate and 34.7% correct rejection rate. With respect to detection of marginal fit, the combination of disclosing material with explorer data did not yield significantly improved results (59.4%), as compared to explorer alone. A receiver operator characteristic curve yielded satisfactory sensitivity (0.8) and specificity (0.9) at a gap size value of 124 microm., Conclusion: Within the limitations of this study, the preparation design did not significantly affect the marginal adaptation. Clinical detection, with similar sensitivity and specificity as the stereomicroscope, occurred at marginal openings greater than or equal to 124 microm. Therefore, commonly used clinical evaluation techniques using an explorer and disclosing media may be inadequate for assessments of marginal accuracy.

Purpose: To evaluate, in a clinical field-test, the implementation of manufacturer's preparation guidelines for the all-ceramic CICERO system., Methods: General dental practitioners from the northwest region of The Netherlands were asked to make complete crown preparations in accordance with the specific guidelines of the CICERO system. 3,446 tooth preparations were evaluated with regard to shoulder angle, shoulder width and top angle. They were quantified using a special software program. The results were compared with criteria defined in the manufacturer's preparation guidelines., Results: On a multivariate level all (main and interaction) effects were significant (P < 0.05) excluding the interaction effect of the location of measurement on the tooth by the upper or lower jaw. The value of the shoulder angle showed a strong relation with the tooth position in the mouth as well as with the location of measurement on the tooth. The shoulder width in the lower jaw was significantly smaller when compared to the width in the upper jaw. The shoulder width of the lower incisors was the smallest and also showed the largest variance per tooth. On a group level (incisor, cuspid, premolar, molar), except for the shoulder width of the lower incisors, the average values of all preparation parameters were within the borders as defined in the preparation guidelines of the manufacturer. However, on an individual tooth level nearly all preparations showed to have one or more locations with imperfections.

Use of a digital preparation assistant system may improve considerably the quality of preclinical dental education, provided the system works reliably. Thus, the purpose of this pilot study was to quantitatively assess the reliability of a new preclinical digital preparation assistant system (PREPassist, KaVo, Germany). The system was used to repeatedly scan four different unprepared and four different prepared teeth both with and without repositioning. Corresponding measurements were made to quantify accuracy, repeatability, and reproducibility. This was done by estimating the measurement error. Based on this estimation, respective limits of agreement were calculated. We used these ranges, along with assessments of the measurement's accuracy, to judge whether the results satisfy our expectations for clinically acceptable measurements. For preclinical laboratory instruction, the results indicate an acceptable accuracy (mean accuracy of 89 microm) of the measurements. This assessment applies as well to repeatability, given by the range of the respective limits of agreement (range <200 microm). However, in the case of reproducibility, the limits revealed discrepancies of practical importance (range >200 microm). Reproducibility of tooth repositioning in the available mounting device is unacceptable for preclinical laboratory instruction because of the observed range >200 microm. Thus, there is a need for the manufacture of new and more reliable mounting devices because reproducibility procedures are mostly encountered in preclinical instruction in restorative techniques. In contrast to reproducibility, accuracy and repeatability are acceptable for practical purposes. Balancing advantages and disadvantages, we conclude that, in general, the PREPassist system delivers reliable results.

Objective: To assess the quality of dental casts used in crown and bridge construction., Design: Observational cross-sectional study of dental casts., Setting: Commercial dental laboratories and a university dental hospital laboratory in the UK., Materials and Methods: A sample (n = 150) of working and opposing casts used for crown and bridgework prescribed by general dental practices and a dental hospital were sampled from two commercial dental laboratories and an 'on-site' university dental hospital laboratory respectively. A simple '3 point' assessment scale of quality (good, fair and poor) was used to categorise the casts depending on the clarity of reproduction of soft and hard tissues., Results: The quality of opposing casts used for articulation purposes was significantly better (P<0.001) than that of the working casts. In addition it was found that for working casts the quality in the preparation area(s) was significantly better (p<0.001) than that in areas remote from preparation(s) in the same arch. In general, the quality of casts in the incisal or occlusal surfaces was better than the buccal and lingual surfaces., Conclusions: This study has demonstrated that variation exists in the quality of casts used in crown and bridgework, specifically those used in the construction of indirect restorations and also those used for articulation purposes. This study highlights the need for clinicians to exercise continued vigilance with crown and bridge impressions, and casts, particularly in areas away from the prepared teeth.

Objective: To investigate variations in tooth preparations for resin-bonded all-ceramic crowns (RBCs) in general dental practice (GDP)., Design: Laboratory-based retrospective analysis of dies for RBCs., Setting: General dental practices in the UK and Ireland (2000)., Methods: A sample (n = 132) of laboratory models containing 180 tooth preparations for RBCs, featuring work from different general dental practitioners was obtained from four commercial dental laboratories. Aspects of the preparations were quantified and compared with accepted criteria defined following a review of the literature., Results: The teeth found to be most frequently prepared for RBCs were maxillary incisors (41%). Margin positions were variably positioned with 29% of the preparations on the buccal aspect having subgingival margins. There were many tooth preparation dies for low fusing RBCs (47%) and Chameleon Fortress RBCs (62%) demonstrating overpreparation in the mesiodistal plane. The majority of the margins (84% buccally and 79% lingually) of the dies examined exhibited appropriate shoulder or chamfer finishes. Of the Chameleon Fortress preparations analysed, 86% had been underprepared occlusally. 42% of the teeth had been prepared with no regard to tooth morphology and demonstrated just one plane of reduction. The majority (93%) of the clinicians failed to provide any information regarding the shade of the prepared tooth stump., Conclusions: On the evidence of this survey of this sample of general dental practitioners' work, it was found that relevant guidelines for the preparations of RBCs are not being fully adhered to.

Objective: The purpose of this study was to determine the effect that two guides to tooth preparation had on an operator's ability to appropriately and consistently prepare teeth for porcelain laminate veneers., Study Design: In-vitro study., Materials and Methods: Thirty typodont central incisor teeth were randomly allocated into three groups and a general dental practitioner was asked to prepare the teeth for porcelain laminate veneers. Group A were prepared freehand while Groups B and C were prepared with the assistance of a silicone index and depth preparation bur respectively. Images of the prepared teeth were used to calculate the mean labial depth of preparation and incisal reduction of teeth in each group., Results: The mean labial reduction for Groups A, B and C was 0.37 mm (SD 0.13), 0.62 mm (SD 0.17) and 0.61 mm (SD 0.15) and the mean incisal reduction for Groups A, B and C was 1.0 mm (SD 0.28), 1.0 mm (SD 0.38) and 1.03 mm (SD 0.26) respectively., Conclusion: It is suggested that consideration be given to the use of a silicone index or depth gauge bur when teeth are prepared for porcelain laminate veneers.

Previous work by the authors indicates a tendency for academic clinicians to under prepare and over angle shoulder preparations for metal ceramic crowns. This has implications for the final restoration in terms of contour, appearance and strength. This study analysed ninety six preparations, forty eight in vitro and forty eight in vivo, performed by six clinicians. The results show a mean shoulder width of 0.804 +/- 0.274 mm and a mean shoulder angle of 116 +/- 18 degrees for preparations performed in vitro; and 0.892 +/- 0.337 mm and 121 +/- 24 degrees for preparations performed in vivo. Thus, despite recommendations that such crowns should have 1-1.5 mm, 90 degrees shoulders, many of the preparations studied here fell short of this, indicating a lack of consistency in preparation geometry and adherence to the perceived 'ideal' preparation for a metal ceramic crown.

Statement of Problem: A precise preparation is required to develop resistance form resulting in mechanical stability of the framework for resin-bonded prostheses (RBPs)., Purpose: The effects of 4 methods of tooth preparation (freehand, guiding pin, extraoral parallelometer, and intraoral parallelometer) on the deviation of proximal grooves from a preestablished path of insertion (guide planes) were investigated under clinical conditions., Material and Methods: Tooth preparation of proximal grooves was performed by 32 dentists on resin substitutes of posterior segments intraorally with a single test patient. A Latin-square randomized cross-over design was selected as the experimental design., Results: The significant least angular deviation of proximal grooves from path of insertion was achieved with an intraoral parallelometer (mean +/- SD 3.15 +/- 1.67 degrees). Compared with freehand tooth preparations (4.37 +/- 2. 11 degrees), neither use of a guiding pin (4.10 +/- 1.62 degrees) nor an extraoral parallelometer (5.06 +/- 2.33 degrees) improved the results., Conclusion: Divergence of guiding grooves from path of insertion was reduced with the use of an intra-oral parallelometer. This should improve mechanical stability of posterior RBPs.

Purpose: This study was conducted to assess the quality of impressions and tooth preparations sent to dental laboratories in Jordan and to determine the technical capabilities of these laboratories to construct fixed partial dentures., Materials and Methods: A sample of 136 impressions and stone casts were examined for clinical errors in 35 laboratories that construct fixed partial dentures. They were sorted into unusable, unsatisfactory, acceptable, or satisfactory categories. The type of impression material and tray, opposing arch impressions, and occlusal records were noted. Instructions to technicians were assessed for completeness and clarity. Information regarding laboratory staff and equipment were collected., Results: Half of the specimens inspected were categorized as unusable or unsatisfactory; these were found in commercial laboratories. They showed at least one clinical error such as drags or indefinite finishing lines in impressions and inadequate reduction, undercuts, or obvious taper on stone casts. Alginate impression material was used for 65% of the cases. Only 27% of specimens were accompanied with instructions; of these 22% were graded poor. No occlusal records were available with 54% of the specimens and no articulators were used except in dental school laboratories. The dental schools and some commercial laboratories had the best staff and equipment and were more capable of fabricating fixed partial dentures than those of the Ministry of Health and the Royal Med cal Services., Conclusion: The quality of abutment preparation and impressions were unsatisfactory or unusable in 50% of cases. Of the 37 available instructions 8 were not clear. The dental schools and some commercial laboratories were technically capable of producing good quality fixed partial dentures.

Dental students at Tokyo Medical and Dental University are taught to prepare teeth for full cast crowns with a wall taper of 2 to 5 degrees and an occlusal clearance of 1.2 to 1.5 mm. However, it is difficult to achieve such an ideal taper. The objective of this study was to examine the abutment taper and height of teeth prepared for crowns by final-year dental students under clinical supervision. To evaluate the degree of taper and height of the prepared teeth, shadowgraphs of 63 working stone dies were traced. The angles and height of the abutments were then measured on the same tracing. Only 12.7% (8 out of 63 abutments) of the prepared teeth fell within the ideal range of 2 to 5 degrees, and the average taper was 9.5 degrees (19.0 degrees convergence angle). The average abutment height varied from 4.8 mm to 6.9 mm and showed a close relationship with the abutment taper. The average taper, 9.5 degrees, of the present study was larger than the ideal taper; however, it was thought to be clinically acceptable as it is difficult to achieve the ideal taper intraorally.

Objective: To investigate variations in preparations for porcelain laminate veneers (PLVs) in general dental practice., Design: Laboratory-based retrospective analysis of dies for PLVs., Setting: General dental practice in England and Wales (1994)., Methods: A sample (95 cases) of laboratory models from general dental practice featuring preparations for PLVs was randomly selected from a full service commercial dental laboratory. Aspects of the preparations were quantified and compared with accepted preparation criteria distilled from a review of the literature., Results: The teeth found to be most frequently prepared for PLVs were maxillary incisors (48%). The majority of cases investigated were for one veneer only (56%). The margins of the preparations were variably positioned with more than half of the preparations (55%) having no clear margin. In accordance with current guidelines the incisal edge tended to have been reduced during preparation (47%). In contrast, most teeth were underprepared with an average depth of preparation of 0.16 mm (SD 0.60 mm, 95% CI-0.1, 0.42)., Conclusions: There was little evidence that established guidelines for the preparation of teeth for PLVs had been applied in full.

Objective: To determine the quality of impressions for crown and bridge work made in general dental practice., Design and Setting: All impressions for crown and bridge work which had been sent to four commercial dental laboratories in the UK were assessed by two examiners, each laboratory being visited on two occasions., Materials and Methods: 290 cases which had been received by the laboratories on the days of the visits were assessed for a number of factors related to quality. There was no selection or rejection--all impressions received were examined., Results: Flexible plastic trays were used for the majority of working impressions for crown and bridge work in general dental practice (72%), many had been re-used (> 13%), defects in the recording of the prepared teeth were common, and cross infection control was not routine., Conclusions: Quality standards for impressions for crown and bridge work in general dental practice in the UK are a cause for concern if the sample of cases seen in this study is typical.

The reflex metrograph was used to measure preparation depth for a sample (21) of preparations for porcelain laminate veneers obtained from a large commercial laboratory. Eight (38%) of the teeth investigated were found to be unprepared with 13 (62%) teeth prepared to varying degrees. Five (24%) of the teeth were over prepared with the depth of two preparations exceeding 1.0 mm. There was little evidence that widely advocated guidelines for the preparation of teeth for porcelain laminate veneers had been used. The effect of dentine exposure on the clinical longevity of porcelain laminate veneers remains to be investigated.