ABSTRACT
Objective To analyze the effect of different bone defect types on stress distributions of the implant- bone interface and bone-Bio-oss interface under dynamic loads by finite element method. Methods The finite element models for four types of bone defects (fenestrative bone defect, dehiscent bone defect, circular bone defect, vertical bone defect) without the first molars were established, then the models of grafting bone and implants corresponding to each model were established. The vertical load of 100 N and Oblique load of 200 N were used to simulate the dynamic chewing process of 5 stages in a masticatory cycle, and the maximum Von Mises stresses at the implant-bone interface and bone-Bio-oss interface were analyzed. Results In a masticatory cycle, from stage 2 to stage 4, the stresses on implant-bone interface increased by 81.6%, 90.7%, 182%, 106%, respectively, while the stresses on Bio-oss bone and natural bone interface increased by 26%, 13%, 6%, 56.25%, respectively. Conclusions The sequence of bone graft stability for the models with four types of bone defects is: circular bone defect> dehiscent bone defect>fenestrative bone defect>vertical bone defects. In clinic, doctors should screen the high-risk patients according to the sites of the bone grafts, and choose different methods for fixing the bone grafts so as to improve the stability of bone grafting. The axial loading will be more beneficial to the stress distributions on the interface, and the oblique loading should be decreased or avoided in clinical design for the superstructure of implant denture.
ABSTRACT
Objective To establish the model of dentulous mandible and straight wire appliance and investigate the stress and displacement distributions of the roots and periodontal tissues under en masse space closure with sliding mechanics. Methods The three-dimensional finite element model of mandible and teeth was developed from CT images, which consisted of the dentin, enamel, dental pulp, PDL (periodontal ligament), cortical and cancellous bone. The models of Roth straight wire brackets with actual data were also constructed. The dental adhesives were used to stick the brackets on the corresponding teeth. Contact elements were used to simulate the interaction between the stainless steel arch wire and the brackets. Moreover, spring elements were used to connect the brackets and the arch wire. The load with the value of 1 N was applied on the model to close the space. Results The lingual tipping of lateral and central incisors was found, corresponding with the clinical observation of en masse space closure with sliding mechanics. High stress in the teeth and periodontal tissue appeared at the incisors and the distal roots of the first molars. The maximum von Mises stresses in PDL of the central incisors and the distal roots of the first molars were 3.97 kPa and 5.75 kPa, respectively. Conclusions In order to avoid root resorption of incisors, the torque of the brackets could be increased. Less orthodontic forces or orthodontic implant could be used to avoid distal roots of first molars.
ABSTRACT
<p><b>OBJECTIVE</b>To evaluate the abutment periodontium condition after restored with the distal-extension extracoronal attachment dentures.</p><p><b>METHODS</b>20 mandibular distal-extension cases were followed up, to measure the gingival index (GI) and plaque index (PLI) of the distant-abutments before restored with attachment dentures and after restored for one month, six months and one year; to compare the length of distant alveolar bone before restored with that after restored one year by taking digital stomatology tomogram photos.</p><p><b>RESULTS</b>There were not significantly different in the PLI of distant-abutment between before repaired and after repaired one month, six months, one year (P > 0.05). There were not significantly different in the GI of distant-abutment between before repaired and after repaired one month, six months (P > 0.05), but the GI of distant-abutment after repaired one year was significantly higher than that before repaired (P < 0.05). There were no significant differences on the length of distant alveolar bone in distant-abutment before repaired and after repaired one year(P > 0.05).</p><p><b>CONCLUSION</b>It is important to protect the periodontal health of the abutment when restored with distal-extension extracoronal attachment dentures. It is necessary to examine periodically after restored in order to keep the periodontal health of the abutment.</p>