A clear shoulder platform that can be easily identified by doctors and technicians or machines (mouth scan and warehouse scan) is important to obtaining a good long-term and stable fixed prosthesis treatment effect. At present, the pre-paration of the shoulder platform is usually based on free hands, and the practical operation is mainly guided by experience. Moreover, no comprehensive and objective preoperative design, intraoperative verification, and final test are available. Thus, the accuracy of shoulder platform preparation needs to be improved. In this study, the clinical pathway of "three determination, three selection, and three steps" with high accuracy of preparation and the precise shoulder preparation method of "bur-tip guidance" are proposed in detail.
Critical Pathways ; Shoulder ; Tooth ; Tooth Preparation ; Tooth Preparation, Prosthodontic

OBJECTIVETo investigate the effects of different tooth preparations on three-dimensional adaption of computer aided design and computer aided manufacturing (CAD/CAM) crowns based on the reverse engineering.

METHODSThe tooth preparation model of the left maxillary first molar was scanned to build five different tooth preparations using the NX Imageware 13.2 software. The resin cores (n=8) were designed with the exocad software. The scanning data of the inner surface of each resin core were used to analyze the three-dimensional adaption with the Geomagic Qualify 12 software.

RESULTSAccording to the color-coded deviation images, the deviation of the heavy chamfer shoulder was the smallest and the most uniform, whereas the other groups with sharp lines showed large deviation. After statistical analysis, the total deviation of the heavy chamfer shoulder, 135° shoulder, feather shoulder, 90° shoulder with lipped margins, and sharp marginal ridges preparation were (16.88±2.83), (26.88±3.61), (53.56±4.30), (51.38±4.46), and (47.19±4.62) μm. A statistical significance was observed between the heavy chamfer and 135° shoulders (P<0.05). The other groups fitted poorly, without statistical significance between each group (P>0.05).

CONCLUSIONThree-dimensional analysis using a computer is a preferable method to study the three-dimensional adaption of crowns. The heavy chamfer shoulder and round line preparation are clinically recommended. However, feather shoulder, 90° shoulder with lipped margins, and sharp marginal ridge preparation should be avoided.

Composite Resins ; Computer-Aided Design ; Crowns ; Dental Marginal Adaptation ; Dental Prosthesis Design ; Humans ; Molar ; Tooth Preparation ; Tooth Preparation, Prosthodontic

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 5^th preparation to the 13^th preparation (P > 0.05). The predicted score of the 14^th 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.
Humans ; Tooth Preparation, Prosthodontic/methods* ; Incisor ; Learning Curve ; Crowns ; Tooth Preparation ; Ceramics ; Dental Porcelain ; Dental Prosthesis Design

PURPOSE: The purpose of this study was to evaluate the intra-rater reliability and inter-rater reliability of three different methods using a drawing protractor, a digital protractor after tracing, and a CAD system. MATERIALS AND METHODS: Twenty-four artificial abutments that had been prepared by dental students were used in this study. Three dental students measured the convergence angles by each method three times. Bland-Altman plots were applied to examine the overall reliability by comparing the traditional tracing method with a new method using the CAD system. Intraclass Correlation Coefficients (ICC) evaluated intra-rater reliability and inter-rater reliability. RESULTS: All three methods exhibited high intra-rater and inter-rater reliability (ICC>0.80, P<.05). Measurements with the CAD system showed the highest intra-rater reliability. In addition, it showed improved inter-rater reliability compared with the traditional tracing methods. CONCLUSION: Based on the results of this study, the CAD system may be an easy and reliable tool for measuring the abutment convergence angle.
Computer-Aided Design* ; Dental Abutments ; Humans ; Students, Dental ; Tooth Preparation, Prosthodontic

OBJECTIVETo study the effect of tooth preparation design on fitness of CAD/CAM all-ceramic coping crown.

METHODSThe tooth preparation comprised 2 types of occlusal convergence (10 degrees, 20 degrees), 2 margin forms (shoulder, chamfer). The MC coping were milled by Cerec 2 CAD/CAM system, cemented, embedded, sectioned, and measured at 10 sites to obtain the data of margin, shoulder, axial surface, occlusal surface fitness.

RESULTSThe coping's fitness was influenced by convergence angle and margin form. The coping's fitness was very nice (101.7 approximately 127.9) microm when the coping with 20 degrees occlusal convergence angle. Those coping with 20 degrees occlusal convergence and chamfer margin in tooth preparation provided the best fitness, its cement film thickness in margin was (40.1 +/- 11.8) microm.

CONCLUSIONSThe 20 degrees occlusal convergence and chamfer margin can be used for CAD/CAM all-ceramic crown in clinical application.

Computer-Aided Design ; Crowns ; Dental Porcelain ; Dental Prosthesis Design ; Humans ; Tooth Preparation, Prosthodontic

OBJECTIVETo evaluate the clinical performance of the two configurations of gingival margin preparation of tooth.

METHODSThe cases in this study were divided into two groups according to different tooth defects. Each group consisted of 40 cases. One group's gingival margin configuration was 90 degree shoulder, the other was under-gingival non-shoulder. The clinical performance of these restorations was followed up for 1 year and 2 years. The evaluators examined the restorations for plaque index, gingival index, marginal discolor and marginal fit.

RESULTSThere was no significant difference in the evaluators between the two groups.

CONCLUSIONThe under-gingival non-shoulder margin configuration of porcelain fused to metal should be used for clinical application compared with the 90 degree shoulder one in certain circumstance.

Dental Porcelain ; Dental Prosthesis Design ; Humans ; Metal Ceramic Alloys ; Tooth Preparation, Prosthodontic ; methods

Finite element stress analysis has been widely used in stomatology. In this article, we summarized the stress distributions of all-ceramic crowns, post crowns, fixed partial dentures and implant support fixed dentures; and with the use of finite element method, we investigated the stress levels of the periodontal ligament of abutment. The results showed: the tensile stress and compressive stress concentrated at the cervical margin of all-ceramic crown and post crown; the stress at the surface of the crown was the highest; the stress concentration exhibited at the connector of fixed parital denture, the molar was an ideal abutment tooth for the fixed bridge; the largest stress appeared around the neck of the implant abutment. These results have provided a theoretical basis for clinical dentistry in terms of restoration design and manufacture. It is suggested that clinical dentists should be careful to avoid the horizontal laoding applied on the prostheses so as to improve the resistance of abutment tooth to fracture.
Crowns ; trends ; Dental Stress Analysis ; Denture, Partial, Fixed ; trends ; Humans ; Principal Component Analysis ; Prosthodontics ; methods ; Tooth Preparation, Prosthodontic ; methods ; trends

OBJECTIVETo investigate the effect of camera control devices of Cerec 2 on the fit of CAD/CAM all-ceramic copyings of posterior tooth.

METHODS24 all-ceramic copyings were made by Cerec 2 with camera control devices and that without camera control devices. Copyings were embed and sectioned, then SEM and image analyzer was used to measure the space between the copyings and dies at the marginal opening, the axial wall, and the occlusal adaptation at the measurement locations.

RESULTSThe marginal fit at buccal space of copyings with camera control devices group was smaller than that without camera control devices group (P < 0.05). The internal fit of of copyings had statistically significant difference at mesio-axial, disto-axial, bucco-axial, bucco-occlusal, linguo-occlusal and disto-occlusal space between camera control device group and without camera control devices group (P < 0.05). There was no statistical difference on the marginal fit and internal fit of copyings between Vita MK II and porous alumina oxide (P < 0.05).

CONCLUSIONThe Cerec 2 with camera control devices reduced effectively the inaccuracy of inner space of copyings which contributed from the technical errors of the operator, and provided well-proportioned space for adhesive. Both the fit of copyings made of Vita MK II and porous alumina oxide satisfied the clinical demand.

Aluminum Oxide ; Ceramics ; Computer-Aided Design ; Dental Marginal Adaptation ; Dental Porcelain ; Dental Prosthesis Design ; Humans ; Molar ; Tooth Preparation, Prosthodontic

OBJECTIVETo determine the infinite optical thickness of dentine porcelain of IPS E.max A color series.

METHODSCylindrical dentine porcelain specimens of the IPS E.max A color series were prepared with a diameter of 13 mm and thickness of 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, and 5.0 mm. The chromatic value of all the specimens was determined with CM-5 spectrometer against standard black and white background. The chromatic aberration (deltaE) was calculated by regression equation.

RESULTSThe infinite optical thickness of dentine porcelain of the IPS E.max A color series ranged from 2.341 to 3.333 mm for a deltaE of 1.0, and from 2.064 to 2.904 mm for a deltaE of 1.5. As the chromaticity or thickness increased, the influence by the background color decreased, and the color of specimens became gradually close to the intrinsic color.

CONCLUSIONThe thickness of the background dentine porcelain specimens must exceed its infinite optical thickness to represent the intrinsic color and avoid the influence by the extrinsic color.

Coated Materials, Biocompatible ; chemistry ; Crowns ; Dental Porcelain ; chemistry ; Dental Prosthesis Design ; Humans ; Prosthesis Coloring ; Tooth Preparation, Prosthodontic ; methods

OBJECTIVETo evaluate the clinical application value of minimal prepared ceramic veneer in anterior teeth, by analyzing the esthetic effects and success rates.

METHODSForty-four anterior teeth in 30 patients with minor esthetic defect were included in this study. Less than 0.5 mm preparation or no preparaion technique was used in the clinical procedure. Glass ceramics veneers were delivered and 3M Relyx Veneer were used as the adhesive. The final appearance of each restoration was evaluated by patients on visual analogue scales (VAS) and by professional prosthodontists. Evaluation criteria included margin effects, color, shape and translucency. The success rate of all the restoration were analyzed in 6, 12 and 24 month after the treatment.

RESULTSThe patients' degree of satisfaction was 9.2 ± 0.4, while the excellent rate of esthetic effect of margin effect, color, shape and translucency was 89% (39/44), 91% (40/44), 98% (43/44) and 93% (41/44) by professional prosthodontist. The success rate of 6, 12 and 24 month were 100% (44/44), 98% (43/44) and 91% (40/44).

CONCLUSIONSThe minimal prepared venneers have a good esthetic effect and a satisfactory success rate, and is a suitable technique in esthetic treatment under the critical indications.

Ceramics ; Dental Restoration, Permanent ; methods ; Dental Veneers ; Esthetics, Dental ; Humans ; Incisor ; Patient Satisfaction ; Tooth Abnormalities ; therapy ; Tooth Preparation, Prosthodontic ; methods ; Tooth Wear ; therapy