[Three-dimensional finite element analysis of the influence of different implant-abutment joint design on abutment and abutment screw stress].

PURPOSE: This experiment studied the influence of different connection designs of the tapered retention and platform transfer implant on the stress of the abutments and abutment screws. METHODS: Implant models (Platform-switching: 0.2, 0.4, 0.6, 0.8, 1.0 mm; Taper:6°,8°,10°) were established, and Von-mises stress and strain of abutment and abutment screw under different loads were analyzed. RESULTS: With the increase of the platform-switching amount, the peak von-Mises stress and strain of abutment and abutment screw increased. The peak von-Mises stress of the model with platform transfer≥0.8 mm was higher than 690 MPa. In addition, the variation amplitude was horizontal loading>oblique loading>vertical loading. The maximum stress of the abutment was concentrated at the neck of the abutment in 81.67% models. The stress of the abutment screw was concentrated at the turning point of the head and body of abutment screw in all models. CONCLUSIONS: The increase of the amount of platform switching makes the abutment and the abutment screws bear more force in the occlusion process. Therefore, in order to reduce the occurrence of mechanical complications after implantation and restoration, the implant system with the minimum amount of platform transfer should be selected within a certain range. The maximum stress on the abutments and screws exceeds the yield strength of pure titanium in implants with platform-switching amount greater than 0.8 mm, indicating that this design should be selected prudently in clinical practice.

[Study on the friction and wear properties of fluorapatite glass ceramics, feldspathic porcelain and natural tooth].

PURPOSE: The purpose of this study was to observe the friction and wear characteristics of dental fluorapatite glass ceramics, feldspathic porcelain and natural tooth in dry friction and saliva lubrication. METHODS: Two kinds of veneering porcelain (IPS-emaxcream and Vita vm9) coated zirconia-decorative porcelain double-layer material sample were prepared (size 20 mm × 20 mm × 4.5 mm), each group had 20 specimens. Friction and wear tests were carried out on 2 kinds of zirconia-decorative porcelain sample under dry friction and saliva accompanying environment respectively by setting different sizes of vertical load and sliding frequency using MMV-1 friction and wear testing machine. SPSS 17.0 software package was used for one-way ANOVA and t test to determine whether there were differences in friction coefficient and wear amount between two groups. RESULTS: The dynamic friction coefficient and wear amount of fluorapatite glass ceramics under saliva lubrication condition were significantly greater than those under dry friction condition. On the contrary to fluorapatite glass ceramics, the dynamic friction coefficient and wear amount of feldspathic decorative ceramics under dry friction condition were significantly greater than those under saliva lubrication condition. Under dry friction and saliva lubrication, the wear amount of fluorapatite glass ceramics was significantly smaller than that of feldspathic decorative ceramics. Scanning electron microscopy showed that under saliva lubrication condition, fluorapatite glass ceramics and the corresponding natural teeth had more severe wear surface than dry friction. Under dry friction condition, feldspathic decorative porcelain and corresponding natural teeth wear more seriously than fluorapatite glass ceramic, and the difference in saliva lubrication condition was relatively small. CONCLUSIONS: Compared with feldspathic decorative porcelain, fluorapatite glass ceramics and natural teeth shows superior wear resistance under dry friction condition. The addition of saliva can reduce the difference between the friction and wear performance of the two decorative porcelains.

[Effect of recombinant human bone morphogenetic protein-7 expressed in prokaryocyte to augment bone formation of alveolar ridge].

OBJECTIVE: To investigate new bone formation of alveolar augmentation with recombinant human bone morphogenetic protein-7 (rhBMP-7) expressed in prokaryocyte. METHODS: To create the model of rabbit extraction socket into which the composites of rhBMP-7 and the gelatin sponge was immediately implanted, then the samples were investigated 2, 4, 8 and 12 weeks postoperatively by gross observation, scanning electron microscope (SEM), quantitative measurement of calcium content and alkaline phosphatase (ALP) activity. RESULTS: There was significant difference in height of alveolar ridge absorpted between the experimental groups and the carrier control groups through gross observation. The result of SEM showed that bone healing in rhBMP-7 groups was 4-6 weeks earlier than that of control groups. ALP activity in rhBMP-7 groups were obviously high compared with that of control groups. CONCLUSION: The BMP-7 has a satisfactory osteoinduction ability to promote new bone formation and prevent alveolar bone absorption.

[Animal experimental study of intra-articular injection of S-methylisothiourea for treatment of temporomandibular joint osteoarthrosis].

OBJECTIVE: To investigate the efficacy of S-methylisothiourea (SMT) for treatment of temporomandibular joint osteoarthrosis (TMJOA) of goats. METHODS: Nine purebred black goats were randomly devided into three groups: Normal control group, control group and experimental group. The upper compartments of both temporomandibular joint of the goats in control group and experimental group were injected with collagenase only once to induce osteoarthrosis. Normal control group received no treatment. The upper compartments of both TMJ were injected with 0.5 mL of normal saline, and experimental group, the upper compartments of both TMJ were injected with 0.5 mL of SMT. The TMJ of goats was examined with scanning electron microscopy and microscopy after sacrificed. RESULTS: Examined in light microscopy and scanning electron microscopy, normal control group showed normal performance, the control group showed severe osteoarthrotic changes in the temporal surface, disk and condyle, while the experimental group showed improvement of different degree. CONCLUSION: On the basis of 3-month following-up study, repeated intra-articular injection of SMT may play a role in inhibiting TMJOA progression.

[Analysis of p53 gene mutation in salivary adenoid cystic carcinoma.].

PURPOSE: The purpose of this study was to investigate the occurrence of p53 gene mutation in salivary adenoid cystic carcinoma, the correlation between the gene and prognostic significance. METHODS: A series of salivary adenoid cystic carcinoma were studied by polymerase chain reaction and single strand conformation polymorphism (PCR-SSCP) analysis to detect p53 mutation, respectively. RESULTS: The result showed that p53 gene mutations in exon 5-8 were detected in 65.8% (25/38) of the salivary adenoid cystic carcinoma. The p53 gene mutation was related to tumor distant metastasis and tumor recurrence (P<0.05) but not related to pathological types, clinical stages (P>0.05).There was a significant correlation between p53 gene mutation and postoperative survival . CONCLUSION: It is suggested that p53 gene mutations were very common in salivary adenoid cystic carcinoma, and might be useful in screening progress and evaluating prognosis of patients.