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

The present investigation assessed the effect of acid etching on marginal adaptation of white- and gray-colored mineral trioxide aggregate (MTA) to apical dentin using microcomputed tomography (micro-CT) and scanning electron microscopy (SEM). Sixty-four extracted single-rooted human maxillary teeth were used. Following root-end resection and apical preparation, the teeth were equally divided into four groups according to the following root end filling materials: (i) white-colored MTA (WMTA), (ii) etched WMTA (EWMTA), (iii) gray-colored MTA (GMTA) and (iv) etched GMTA (EGMTA). After 48 h, the interface between root-end filling materials and the dentinal walls was assessed using micro-CT and SEM. Data were statistically analyzed using the Kruskal-Wallis and Dunn tests. Micro-CT analysis revealed gap volumes between the apical cavity dentin walls and EGMTA, GMTA, EWMTA and WMTA of (0.007 1±0.004) mm(3), (0.053±0.002) mm(3), (0.003 6±0.001) mm(3) and (0.005 9±0.002) mm(3) respectively. SEM analysis revealed gap sizes for EGMTA, WMTA, EWMTA and GMTA to be (492.3±13.8) µm, (594.5±17.12) µm, (543.1±15.33) µm and (910.7±26.2) µm respectively. A significant difference in gap size between root end preparations filled with GMTA and EGMTA was found (P<0.05). No significance difference in gap size between WMTA and EWMTA were found in either SEM or micro-CT analysis. In conclusion, pre-etching of apical dentin can provide a better seal for GMTA but not for WMTA.
Acid Etching, Dental ; methods ; Aluminum Compounds ; chemistry ; Apicoectomy ; methods ; Calcium Compounds ; chemistry ; Dental Bonding ; Dental Marginal Adaptation ; Dental Pulp Cavity ; ultrastructure ; Dentin ; ultrastructure ; Drug Combinations ; Humans ; Materials Testing ; Microscopy, Electron, Scanning ; Oxides ; chemistry ; Retrograde Obturation ; methods ; Root Canal Filling Materials ; chemistry ; Root Canal Preparation ; instrumentation ; methods ; Silicates ; chemistry ; Surface Properties ; Time Factors ; Tooth Apex ; ultrastructure ; X-Ray Microtomography

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.

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

OBJECTIVEThe study was designed to investigate the relationship between the accuracy of Root ZX and the size of apical foramen, when the apical constrictions were intact or not. Methods Lengths were taken when the needle reached the '0.5' mark and 'APEX' mark on the Root ZX. The electronic apex locator (EAL)-measured canal working length (L2) and EAL-measured canal length (L1) were then compared with the actual canal working length (L') and actual canal length (L). Besides, the areas of apical foramens CS) were measured when the apical constriction were intact or not. Then the measurement deviations and the areas of apical foramens were analyzed by linear correlation and linear regression using the software SPSS 12.0. Statistical significance was considered at P < 0.05.

RESULTSThere were no significantly correlations between the area of apical foramen and the accuracy of Root ZX if the apical constriction was intact (P > 0.05). However, the accuracy of Root ZX and the size of apical foramen had significant negative correlation when the apical constriction was destroyed (P < 0.001). Then the linear regression was completed, and the linear regression equation was deltaL2 = -0.623 + 6.5965, so the critical area of the apical foramen was 0.135 mm2 if the tolerant error was set at 0.5 mm according to the statistic control.

CONCLUSIONThe size of apical foramen has little effect on the accuracy of Root ZX if the apical constriction is intact. However the measurements of Root ZX should be used carefully when the apical constriction was destroyed.

The aim of this study was to evaluate the microleakage of teeth according to root canal preparation with & without apical enlargement in various size of apical foramen. 60 extracted one canal roots were cross-cutted at 5 mm from root apex and divided into two groups according to their apical foramen size of large (L) and small (S). Each group was subdivided into two groups accordance with their cross-sectional configuration at 5 mm from apex, round (R) and ovoid (O); SR Group, SO Group, LR Group, LO Group. Each group was shaped in .02 taper by Quantec series Nickel-Titanium (NiTi) rotary file, obturated by lateral condensation method. Leakage was measured using a fluid transport model under 40 cmH2O pressure. After the leakage test, blocks which had showed the leakage retreated with .04 taper and .06 taper and evaluated the degree of fluid filtration in each group. The data was analysed statistically using chi-square test and fisher's exact test. The results obtained were as follows: 1. Significant difference in leakage was found in groups which had different apical foramen size in .02 taper instrumentation (p < 0.05), but not in .04 taper instrumentation (p > 0.05). 2. The difference in microleakage according to the shape of canal was not evident at 5 mm from apex (p > 0.05). 3. There was correlation between .02 taper instrumentation and .04 taper instrumentation in LR group , LO group (p < 0.05).
Filtration ; Root Canal Preparation ; Tooth Apex ; Tooth*

Pulpitis and periapical periodontitis is a type of bacterial infectious disease, and bacteria frequently plant in the entire root canal system during the terminal stage. Main clinical treatment strategy of the disease requires root canal therapy, a key and core procedure for the successful treatment by thoroughly removing the root canal infection. The premise and guarantee of thoroughly removing root canal infection is by determining the accurate root canal working length. However, introduction of the complexity of the apical root anatomical structure, the confusion in determining the position of apical stop, and the method to determine the root canal working length. methods of accurately determining root canal working length, especially determining the position of apical stop, has been a hot topic among endodontic specialists, frequently causing confusion among many clinicians. This review provides a brief
Dental Pulp Cavity ; Periapical Periodontitis ; Pulpitis ; Root Canal Preparation ; Root Canal Therapy ; Tooth Root

OBJECTIVE: To set up near-field microwave detection system, to evaluate the accuracy of measuring water and to compare the effects of different methods on drying root canal. METHODS: Known and quantitative distilled water in Eppendorf tube and root canal was detected by near-field microwave detection system which was set up first. The microwave reflection coefficient was recorded so as to evaluate the accuracy of the measuring water. 12 single-rooted mandibular premolar teeth with apical matureness and a curvature less than 10° were decoronated, leaving roots 14 mm in length. After instrumentation to F3, the root canals were air-dried and injected with 10 μL distilled water each. Then all the root canals were assigned to 4 groups (n=12) according to different methods on root canal drying. Near-field microwave detection system was used to detect the change of water after air-drying and root canal drying so as to evaluate the effects of different root canal drying methods: (1) negative control group, the canals were injected with 10 μL distilled water and no root canal drying method was performed; (2) paper points drying experimental group, four #60 paper points were used to blot-dry the middle and upper part of the canal, followed by #40 paper points blot-drying the apical area. The above step was repeated with the tip of paper point that appeared with no water under microscope as finished; (3) 95% (volume fraction) ethanol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 95% ethanol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal; (4) 70% (volume fraction) isopropyl alcohol drying experimental group, after the distilled water was removed with paper points (similar to paper points experimental group), 10 μL 70% isopropyl alcohol was injected into the canal and was left in place for 10 s, then paper points were used to dry the canal. The linear correlation analysis was used to test the accuracy of the measuring water by near-field microwave detection method and physical measurement. The Pearson correlation coefficient was calculated based on the data. The effects of different methods on drying root canal were analyzed by Chi square test. RESULTS: The R2 for the microwave reflection coefficient and the physical measurement of the water in Eppendorf tube and root canal were 0.991 and 0.970. The microwave reflection coefficient in all the experimental groups showed significant difference (P<0.05). After drying with paper points, the residual water was the most, and the microwave reflection coefficient was the highest: 0.023. While after 70% isopropyl alcohol drying root canal, the residual water was the least with the microwave reflection coefficient 0.006, showing that the effect of drying was the best. CONCLUSION Near-field microwave detection system could detect the change of water in root canal. The effect of root canal drying by 70% isopropyl alcohol was superior to 95% ethanol and paper points.
Dental Pulp Cavity ; Desiccation ; Microwaves ; Root Canal Preparation ; Root Canal Therapy ; Tooth Root

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.