Influence of Convergence Angle and Cement Space on Margin and Internal Adaptation of CAD/CAM All-ceramic Crowns / 中国医科大学学报

Objective To study the influence of the convergence angle and cement space on the fit of CAD/CAM all-ceramic crowns.Methods The PMMA resin was produced in two groups,group A (2 degrees) and group B (4 degrees),30 in each group,and each group was divided into 3 sub-groups A 1,A2,A3;or B 1,B2,B3.Each subgroup included 10 patients with a CAD/CAM all-ceramic crown with PMMA resin generation type,but the cement space was 40 μm,60 μm,or 80 μm.The internal clearance edge of the double color silicone rubber impression reproduction technology of the all-ceramic crown was observed under the microscope.Analysis Micro-image software was used to measure the edge gap,and the resulting data were analyzed using SPSS 20.0 software.Results When the cement space is the same,the difference between 2 degrees and 4 degrees was statistically significant.Conclusion The fit is the best when the cement space is 60 μm and the convergence angle space is 4 degrees.

The Effect of Sub-glottal Convergence Angle on the Degree of Glottal Closure / 听力学及言语疾病杂志

Objective To study the effect of sub-glottal convergence angle on the degree of glottal closure, and to analyze the potential mechanism of dysphonia by the incomplete glottal closure.Methods Three vocal fold positions (adduction, intermediate and abduction) were evaluated by the degree of glottal closure, and divided into three groups.The neck CT images of the subjects were gathered.The vocal folds were adduction group when the normal subjects made a sustaining phonation /i:/ during CT scanning;the vocal folds were abduction group when the normal subjects made a deep breathing during CT scanning, and the unilateral vocal folds were incomplete closing group when the unilateral vocal fold paralysis subjects made a deep breathing during CT scanning.3D models of the vocal folds and the airway were reconstructed using Mimics software, through which the sub-glottal convergence angle was measured.Using one-way factor analysis of variance, we compared the angle among three groups.Results The angle changed with degree of glottal closure, with statistically significant differences among the three groups(P<0.01).The means of the angle in three groups were 33.49°±3.75°, 55.03°±2.61° and 75.02°±7.32°.Conclusion The 3D model generation from CT data is an effective method of measuring the sub-glottal convergence angle, while the angle changes with the degree of glottis closure.The angle may affect sub-glottal pressure distribution in the sub-glottal shear or normal direction and influence vocal fold vibration, which would make vibration and vocal fold mucosal wave generation more difficult, and might cause dysphonia.

Measuring abutment convergence angles using stereovision dental image processing system

PURPOSE: The purpose of this study was to develop a dental image processing system using a three-dimensional (3D) camera and stereovision technology. The reliability of the system for measuring axial wall convergence angles was evaluated. MATERIALS AND METHODS: The new system predicted 3D coordinate points from 2D images and calculated distances and angles between points. Two examiners measured axial wall convergence angles for seven artificial abutments using a traditional tracing-based method (TBM) and the stereovision-based method (SVBM). Five wax abutment models of simplified abutment forms were made and axial wall convergence angles of wax models were measured by both methods. The data were statistically analyzed at the level of significance, 0.05. RESULTS: Intraclass correlation coefficients showed excellent intra-examiner and inter-examiner reliabilities for both methods. Bland-Altman plots and paired t-tests showed significant differences between measurements and true values using TBM; differences were not significant with SVBM. CONCLUSION: This study found that the SVBM reflected true angle values more accurately than a TMB and illustrated an example of 3D computer science applied to clinical dentistry.

The reliability of an easy measuring method for abutment convergence angle with a computer-aided design (CAD) system

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.

Comparison of the retention of the full veneer casted gold crowns with varying convergence angle, crown length and dental cements / 대한치과보철학회지

PURPOSE: The aim of this research was to establish the effect and variation in differing convergence angle and length of abutment on the retention of full veneer casted gold crown. MATERIALS AND METHODS: Two different length,5 mm and 10 mm in height with convergence angles of 5, 10, 15 and 25 degrees crowns were fabricated. Cementation was done using cements; zinc phosphate cement (Fleck's zinc phosphate cement), resin-modified glass ionomer cement (Vitremer) and resin cement (Panavia 21). These were tested for tensile force at the point of separation by using Instron Universal Testing Machine. Statistical analysis was done by SAS 6.04 package. RESULTS: In all cements the mean retention decreased with significant difference on increase of convergence angle (P<.05). Increase in every 5 degree-convergence angel the retention rate decreased with resin-modified glass ionomer cement of 15.9% and resin cement of 14.8%. With zinc phosphate cement, there was largest decreasing rate of mean retention of 25.5% between convergence angles from 5 degree to 10 degree. When the crown length increased from 5 mm to 10 mm, the retention increased with the significant difference in the same convergence angle and in all types of cement used (P<.05). CONCLUSION: The retention was strongly dependent on geometric factors of abutment. Much care is required in choosing cements for an optimal retention in abutments with different convergence angles and crown lengths.

Assessment of convergence angle of full-coverage porcelain fused to metal crowns in clinical practice.

Background: Full-coverage porcelain fused to metal crowns is commonly recommended for restoration of extensively damaged teeth. Ability of the dentist to adequately prepare teeth is fundamental to success and longevity of these restorations. Aims: This study was designed to compare recommended convergence angle and taper values of tooth preparation with clinically practiced values and to assess the factors such as tooth position, operator experience, vitality, and restorative status on convergence angle of prepared teeth. Setting and Design: It was a descriptive, cross-sectional study design and held at The Aga Khan University Hospital, Dental Section, for a period of 1 year. Materials and Methods: A minimum of 197 crown preparation models of molar and premolar teeth prepared by residents and specialists were collected in order to achieve the objectives of the study on the basis of convenient sampling technique. Statistical Analysis: One sample t-test used to compare the mean practiced convergence angle values with its recommended values. Independent sample t-test and one-way ANOVA was used to see difference in the convergence angle values of the teeth prepared by different operators, tooth type, vitality status, and restorative status of teeth. Results: Mean reported convergence angle and axial wall taper values were 23.7°±8.9° and 11.3°±7.8°, respectively, which is significantly greater (P<0.001) than the recommended values. Convergence angle values were greater for molars as compared to premolars. Conclusion: There was a considerable disparity between the convergent angles values recorded in this study and the recommended guidelines and are affected by tooth type, vitality, and restorative status of tooth.

Algoritmo matemático para cuantificar directamente el ángulo de convergencia en preparaciones de dientes artificiales / Mathematical algorithm to directly quantify the convergence angle in tooth preparations dyes

El objetivo de este trabajo fue determinar un algoritmo matemático para cuantificar directamente el ángulo de convergencia (AC) en troqueles de preparaciones dentarias. El modelo experimental consistió en preparaciones coronarias simuladas sobre troqueles de yeso, en el cual el AC fue calculado por tres formulas trigonométricas. Las formulas fueron obtenidas de un modelo matemático en el cual la preparación coronaria representa una forma de pirámide truncada, la cual permite una proyección triangular en un plano. Fueron realizadas 60 mediciones in situ sobre las paredes de 15 troqueles. Se obtuvo una imagen de cada troquel usando una cámara digital (Schick® CDR). El AC fue medido usando la herramientas del software (Control). Los datos fueron analizados estadísticamente y se aplicaron test de propagación de errores. Los ángulos calculados con las tres fórmulas matemáticas ([F1], [F2] y [F3]) mostraron un alto nivel de correlación con el grupo control excepto para dos muestras. Dentro de las limitaciones de este estudio podemos concluir que a través de este algoritmo matemático, es posible cuantificar directamente el AC de las preparaciones coronarias en troqueles. Actualmente la evaluación de los AC tanto en preparaciones realizadas por alumnos de pregrado de odontología como por dentistas, se hacen de manera subjetiva. Las tres fórmulas presentadas en el algoritmo tiene una correlación alta para cuantificar el AC en troqueles. La [F3], es la que mas correlación logra en todas las muestras (0,89).

The aim of this study was to determine a mathematical algorithm to directly quantify the convergence angle (AC) dyes tooth preparations. The experimental model system consisted of crown preparations dyes simulated on plaster, which the CA was quantify by three trigonometric formulas. Formulas were obtained from mathematical models representing the crown preparation as a truncated pyramid shape, allowing a triangular projection on the plane. 60 direct measurements were made in situ on the walls of 15 dyes. An image was obtained from each dye using a digital camera (Schick ® CDR). The CA were measured using software tools (Control). The data were statistically analyzed and test data were applied to propagation of errors. The angles calculated with the three math formulas ([F1], [F2] and [F3]) showed a high level of correlation with the control except for two samples. Within the limitations of this study we can conclude that through this mathematical algorithm, it is possible to directly quantify the AC preparation coronary dyes. Currently the evaluation of AC in both preparations made by undergraduate students of dentistry as well as dentists, are made subjectively. The three formulas presented in the algorithm have a high correlation to quantify the AC dyes. The [F3], correlation is the most accomplished in all samples.

Clinical convergence angle and rounding radius on tooth preparation for zirconia all-ceramic crown / 대한치과보철학회지

PURPOSE: This article attempted to examine how teeth for restoration is made in a clinical practice and utilize it as future educational material of teeth formation and basic data for additional research. MATERIALS AND METHODS: This experiment investigated the models sent to milling center for production of zirconia crowns. After scanned with Lava CAD/CAM System (3M ESPE, Seefeld, Germany), they are measured on 'ImageJ (version 1.32j, National Institutes of Health, USA)' program and compared and analyzed. Convergence angle from mesio-distal surfaces and bucco-lingual surfaces of each teeth are measured. Also, bucco-lingual diameter of the region lowered as much as 0.4 mm from incisal edge in anterior teeth except canines.(This measure is defined as the Peak 0.4) The analysis of data between each group was conducted by Windows SPSS statistic program, and was proved significant on 95% confidence level by independent t-test, one-way ANOVA and multiple analysis (Sheffe test). RESULTS: The mean value of convergence angle was 18.67degrees. It is ranked as molar (26.70degrees) > premolar (16.87degrees) > anterior teeth (14.81degrees) in the order of mesio-distal convergence angle; anterior teeth (22.32degrees) > molar (20.93degrees) > premolar (15.41degrees) in the order of bucco-lingual convergence angle. The mean value of Peak 0.4 was 1.18 mm. CONCLUSION: Convergence angle of abutment of zirconia all ceramic crown has difference depending on the location in the arch. Due to the nature of production of zirconia all ceramic crown, convergence angle of abutment and line angle finishing degree can have an effect on internal suitability of restoration.