[Three dimensional finite element stress analysis in the vertical fractured first premolar after bonding and replantation].

PURPOSE: To evaluate the change of stress distribution after bonding and replantation of vertical fractured first maxillary premolar. METHODS: The stress distribution in two types of loading and different treatments on the vertical fractured first maxillary premolar were analyzed by three dimensional finite element. The gap was respectively filled with Clearfil SE Bond and Super Bond C & B; and vertical and lateral stress force was calculated. RESULTS: The result of the FEM study of adhesive fracture tooth indicated that the stress distribution was similar to the normal tooth, Clearfil SE Bond was better than Super Bond C & B. CONCLUSION: The treatment of bonding and replantation for vertical fractured tooth is effective.

[Analysis the effect on the stress of root canal wall of pulpless teeth by different degree of root canal preparation].

OBJECTIVE: To analyze the stress variations of wall of root canal of pulpless teeth that resulted from different diameters of root canal. METHODS: On the basis of the finite-element model of the mandibular first molar that modified by routine, diameter of root canal was modified and enlarged so as to the diameter of root canal was 1/3 and 1/2 of root diameter, then modified models were loaded and the maximal stress of each part of teeth and wall of root canal was calculated. RESULTS: The results revealed that enlargement of root canal diameter will bring on increase of stress of root canal wall at the orifice and coronal 1/3. The stress difference of lateral loading was greater than that of vertical loading. CONCLUSION: The principle of root canal preparation should be infected material removed and good shape of root canal gained. Over-preparation is unnecessary and harmful.

[Analysis of the effect on the stress of root canal wall by vertical and lateral condensation procedures].

OBJECTIVE: To analyse the stress variations of root canal wall that resulted from vertical and lateral condensation. METHODS: On the basis of the finite-element model of the mandibular first molar that modified by step-back technique, mesial-buccal root canal was chosen as tested root canal and simulated the procedure of vertical and lateral condensation. The maximal stress of root canal wall and its position were calculated by special software upon different loading condition. RESULTS: Stress of root canal wall caused by vertical condensation was higher than that by lateral condensation on the same loading condition. Maximal stress of vertical condensation was located on loading section and one of lateral condensation was located on coronal and middle 1/3 of root. The lower the position that was loaded, the higher the stress of wall of root canal. CONCLUSION: Lateral condensation will not bring on vertical root fracture directly,but over-force and improper operation are both dangerous that gives rise to vertical root fracture with whichever method.

[Analysis the effect on the stress of wall of root canal by different proportion between crown and root].

OBJECTIVE: Use FEM to observe the relationship between the change of alveolar ridge's height and the stress change of wall of root canal. METHODS: Modify the model on the basis of the set up model of the mandibular first molar, simulating the height of alveolar ridge and reducing 1/4, 1/3, 1/2 of the height to set up modified model, and load on the modified model by vertical and lateral forces. Then calculate the maximum mises stress of each part of teeth and wall of root canal. RESULTS: The stress-changing tendency of each part of wall was similar to the changing tendency of each part of teeth, but the stress of wall was fewer than the stress of teeth. The stress value of original model was close to the modified model at the orifice. Then the stress of original model obviously reduced, and the stress of the modified model reached maximum in the coronal thirds, and when the fixed height was lower, the stress was larger, the stress reduced more slowly. The lateral stress was larger than the vertical stress, and when the fixed height was lower, the difference was more obvious. CONCLUSION: The change of alveolar ridge's height will affect the stress change of wall of root canal, and which is in an inverse proportion.

[Analysis the stress variations of the root canal wall of pulpless tooth by different root canal preparation with finite-element method].

OBJECTIVE: To analyze the stress variations of the root canal wall of pulpless tooth by different root canal preparations. METHODS: On the basis of the set up model of the mandibular first molar, modified model was established by simulation of the routine or step-back root canal preparation and filling in. Then the maximum mises stress of each part of teeth and wall of root canal were calculated by special finite-element software. RESULTS: The stress-changing tendency is similar between two modified models but the maximum mises stress of the model by step-back technique is a little greater than one by routine. The stress of wall of mesial-buccal root canal was the greatest and one of mesial-lingual root canal was the least at three root canals. The stress-changing tendency of modified models was similar to original model. The maximum mises stress of modified models was near or less than one of original model except that of amalgam layer because of material property alteration. CONCLUSION: Not only routine but step-back technique is an effective and safe method. Dentist can choose them in practice.

[Three dimensional finite element stress analysis in various class II cavity design on first maxillary premolar].

OBJECTIVE: To evaluate the stress influence in different contour of class II cavity with different filling materials on first maxillary premolar. METHODS: The stress distribution in two types and all three contours of class II cavity in maxillary premolar were analyzed by three dimensional finite element. The cavity was respectively filled with amalgam and composite resin; and the vertical and lateral stress force was calculated. RESULTS: In the different contours, the stress of composite restoration by slot design was close to that by dovetail design, and the stress of amalgam restoration by slot design, especially in vertical force, descended respectively at 41%,29% and 27%. CONCLUSION: When class II lesions is only limited in proximal region of the premolar, the filling of composite resin with slot design is recommended.