The three-dimension finite element analysis on mandibular first molar restored with different designed fiber post-core and all ceramic crown / 中国医师杂志

Objective:To evaluate the effect of different numbers and location of fiber post on stress distribution of fiber post-all-ceramic crown restored mandibular first molar, with application of finite element method.Methods:Intact human mandibular first molars were used to build three-dimensional finite element models, restored with fiber post core and all ceramic crown. Three-dimension finite element model with 7 different post designs(according to the numbers and location of fiber post inserted into root canal) were created with soft wares of Mimics, Geomagic and Ansys. The von Mises criterion was applied for comparing the maximum von Mises stress value of dentin and stress concentration areas in 7 models maximum load (F1, 225 N), vertical load (F2, 225 N), inclined load (F3, 225 N) and horizontal load (F4, 225 N).Results:Under maximum load, vertical load, inclined load and horizontal load, the maximum von Mises stress value of dentin were 21.854-22.629 MPa (F1), 20.945-21.369 MPa (F2), 21.637-22.513 MPa (F3) and 37.922-38.277 MPa (F4), when the mandibular first molar defect was restored with fiber post core and all ceramic crown. There was little difference in maximum von Mises stress values and stress distribution among the 7 groups. Increasing the number of Posts has no significant effect on the stress distribution of the original post. The maximal Von Mises stress on dentine increased when the horizontal direct loads increased.Conclusions:The number and location of posts have little influence on maximum stress values and stress distribution, when the mandibular first molar defect was restored with fiber post core and all ceramic crown.

Exercise can promote cognition and memory after molar loss / 中华物理医学与康复杂志

Objective To observe the effect of wheel running and treadmill running on the cognitive functioning of rats after the extraction of a molar.Methods Thirty-two Sprague-Dawley rats were randomly divided into a control group (group C,n =8),a molar extraction group (ML group,n =8),a wheel running pretreatment group (W-ML group,n=8) and a treadmill running pretreatment group (T-ML group,n =8).The rats in the T-ML and W-ML groups practiced wheel running and treadmill running for 1 week,then they and the rats in the ML group received molar extraction surgery.One week later,a passive avoidance test was used to evaluate the cognitive functioning of all of the rats.Results No significant differences were found in the groups' average latency I times,but the average latency II time of the ML group was significantly shorter.There was no significant difference in the average latency II times of the T-ML and W-ML groups.Conclusion Either wheel running or treadmill running can promote learning and memory after molar loss by oral surgery,at least in rats.

A study on establishment of examination criteria for the clinical practice of dental students in the department of prosthodontics by Delphi method / 中华医学教育探索杂志

Objective To establish the examination criteria for the prosthodontic clinical practice using Delphi method,to improve the evaluation level of clinical practice of dental students.Method 15 clinical experts in the department of prosthodontics,Peking University School of Stomatology were selected in this study.The evaluation indicators system of prosthodontic clinical practice was established by two rounds of investigations by Delphi method.Initiative ratio and authority coefficient (Cr) of the experts were used to evaluate the reliability of the new examination criteria.Next,the eight-year program students in class of 2007 (38 students) and 2008 (34 students) were examined by old and new examination criteria respectively and the feedback of the students were collected by the method of questionnaire.SPSS 16.0 was used for data processing.Results In this study,the initiative and the authority of the experts was very high,and the initiative ratio and authority coefficient were 100％ and 0.860 respectively.A new examination criterion of prosthodontic clinical practice was established,including 3 first-level indicators,9 second-level indicators and 19 third-level indicators.Questionnaire analysis revealed that only 12％ (n=4) and 9％ (n=3)of the students in class of 2008 considered the new examination criteria was not comprehensive enough or objective enough,which was obviously less than the students in class of 2007 [45％ (n=17) and 36％ (n=14)].Conclusion A new examination criterion of prosthodontic clinical practice was successfully established by Delphi method.The new examination criterion is more comprehensive and objective than the old one and can promote the educational quality of clinical practice of dental students.The method of this study also provides reference for the educational reform of clinical practice in other fields.

Three-dimensional finite element analysis on half of the structure defect with post core and all-ceramic crown restoration of mandibular first molar / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To make a mechanical analysis on three-dimensional finite element models of the mandibular first molar defect restored with post core and all-ceramic crown, and to provide a guideline for planning restoration for such kind of tooth structure defect.</p><p><b>METHODS</b>Cone-beam CT based three dimensional finite element models of post and core restored first mandibular molars were established, with 6 different ferrule designs (the ferrule with only 180 axial wall on different locations). The von Misses criterion was applied for comparing the maximum von Misses stress value of dentin and stress concentration areas in six models which restored with fiber post or cast NiGr alloy post core or Au alloy post core under the maximum, vertical, inclined and horizontal direct loads.</p><p><b>RESULTS</b>The restoration effects in six models were compared, and the maximum von Misses stress concentration areas were not obviously different. The maximum von Misses stress value of NiCr alloy post core and crown was 62.81 MPa. Under horizontal load, the maximum von Misses stress value of dentin increased remarkably.</p><p><b>CONCLUSIONS</b>The location of residual dentin has little influence on the stress distribution, when restored by post core and crown. Au alloy post core and crown or fiber post core and crown are superior to NiCr alloy post core and crown.</p>

Stability of phonetics to determine the horizontal jaw relation in healthy adults / 华西口腔医学杂志

<p><b>OBJECTIVE</b>The aim of this study was to compare the mandibular position when speaking with the intercuspal position and to check the stability of phonetics when determining the horizontal jaw relation in healthy adults.</p><p><b>METHODS</b>A total of 19 healthy volunteers were recruited. Seven Chinese letters, namely, /xi/, /er/, /yi/, /ci/, /mi/, /ni/, and /ri/, were chosen in the test. O-bite was used to record the mandibular position when speaking these letters. A full-adjusted articulator was used to find the mandibular position during speech, and the mandibular position was measured using a vernier caliper. The mandibular position during speech with intercuspal position was compared in both anterior-posterior and left-right directions of the horizontal plane. Multi-factor analysis of variance was conducted for the statistical analysis of the effect of objects and letters on the mandibular position.</p><p><b>RESULTS</b>1) The mandibular position was in front of the intercuspal occlusion position when speaking all seven letters, and almost no deviation was observed in the left and right directions (the mandibular position value of 82% was in the range of 0.5 mm). 2) Different objects had different mandibular positions during speech, whereas different letters did not. The distance between the centric relation position and the intercuspal position had a positive correlation with the range of the mandibular position during speech.</p><p><b>CONCLUSION</b>The mandibular position was in front of the intercuspal position when speaking all seven words in the test. In the same object, the mandibular position was stable during speech.</p>

Three-dimensional finite element analysis of gold alloy post-core in the repair of structure defects of the mandibular first molar / 中国组织工程研究

BACKGROUND:The location of residual dentin may affect stress distribution of tooth root. ＜br> OBJECTIVE:To make a three-dimensional finite element analysis of gold al oy post-core and al-ceramic crown in the repair of structure defects of the mandibular first molar, and to provide a guideline for planning restoration for such kind of tooth structure defects. ＜br> METHODS:Three-dimensional finite element models of the restored first mandibular molars were constructed by CT image reconstruction technique. Then MIMICS software was used to separate the areas and finish the three-dimensional calculation. GEOMAGIC software was also applied to modify and generate a NURBS surface in each patch. Al components of the models were assembled under the ANSYS preprocessor. The Mohr strength theory was applied for comparing the maximum Mohr stress value of dentin and stress concentration areas in six models under different simulating loads. ＜br> RESULTS AND CONCLUSION:The restoration effects in six models were compared, the maximum Mohr stress value of dentin and stress concentration areas were not obviously different. The location of residual dentin has little influence on the stress value and distribution, when restored by gold al oy post-core and and al-ceramic crown.

Impression technique with a tissue-stop area for type four edentulous jaws / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study aims to develop a mandibular impression technique for type four edentulous jaws.</p><p><b>METHODS</b>Twenty patients with type four edentulous jaws were selected for this study. The mandibular impression for each patient was made using both a traditional impression technique and the impression technique with a tissue-stop area. After the cast was made for each impression, the temporary denture bases were constructed on each cast. When the patients wear temporary denture bases, they must appreciate the degree of comfortability provided by each denture base. Whether the soft tissues that had been pushed away was also recorded. For 10 of the randomly selected patients, a complete denture was made using the traditional impression technique; the remaining ten subjects were given complete dentures constructed by the impression technique with a tissue-stop area. The number of times a review for misfit was recorded. The tissue fitness of each denture was also recorded.</p><p><b>RESULTS</b>A paired t-test showed that the soft tissues that stacked on the residual ridge were more readily pushed away by the impression technique with a tissue-stop area than by the traditional impression technique. However, for all patients, the degree of comfortability did not vary when different techniques were used. The independent t-test results indicated that the differences between the fitness of dentures constructed using different impression techniques were not significant. The number of times a review for misfit conducted by the impression technique with a tissue-stop area was considerably lower than that for patients wearing traditionally dentures.</p><p><b>CONCLUSION</b>Using the impression technique with a tissue-stop area can more readily push away the soft tissues packed on the residual ridge and reduce the times of review for misfit compared with using the traditional technique. However, the degree of comfortability and fitness of denture are not improved.</p>

Relationship of the terminal position of the muscular contraction path and centric relation position in different vertical dimension / 北京大学学报(医学版)

Objective: To investigate the relationship of the terminal position of the muscular contraction path and centric relation position with different vertical dimension.Methods: The terminal position of the muscular contraction path and centric relation position with different vertical dimension were recorded for ten edentulous patients with gothic arch.Results: The mesial distance between the terminal position of the muscular contraction path and centric relation position increased with the vertical dimension.The lateral dimension between the terminal position of the muscular contraction path and centric relation position,the distribution of the terminal position of the muscular contraction path are not correlated to the vertical dimension.The center of the terminal position of the muscular contraction path is 1-4 mm ahead of the centric relation position and(0.42?0.47) mm lateral to the centric relation position.The distribution of the terminal position of the muscular contraction path is(1.36?0.58) mm in the mesial-distal direction,(1.56?0.62) mm in the lateral direction.Conclusion: With the increase of the vertical dimension,the mesial distance between the terminal position of the muscular contraction path and centric relation position increased.