Effects of different tooth preparations on the fracture behavior of teeth with severe wedge-shaped defect restored with post and core crowns / 华西口腔医学杂志

<p><b>OBJECTIVE</b>This study aimed to investigate the effects of different tooth preparations on the fracture strength and pattern of failure of teeth with severe wedge-shaped defect restored with post and core crowns.</p><p><b>METHODS</b>According to whether the teeth above the wedge-shaped defect was removed (represented by B) or not (represented by A), the ferrule next to the wedge-shaped defect was prepared (represented by D) or not (represented by C), the cast post-and-core was chosen (represented by E) or glass-fiber post and resin core was chosen (represented by F). A total of 64 human mandibular premolar teeth were randomly divided into 8 groups: A1-1 (A + C + E), A1-2 (A + C + F), A2-1 (A + D + E), A2-2 (A + D + F), B1-1 (B + C + E), B1-2 (B + C + F), B2-1 (B + D + E), B2-2 (B + D + F), each group 8 teeth. All the teeth were prepared and restored accordingly and then mounted on an electronic pressure universal testing machine. The maximum fracture strength and the patterns of failure were recorded.</p><p><b>RESULTS</b>1) The fracture strength of Group A1-1 > that of Group B1-1, Group A1-2 > Group B1-2, Group B2-1 > Group B1-1, and Group B2-1 > Group B2-2 with significant differences (P < 0.05). 2) The patterns of repairable fracture in Group A1-2 and B1-2 were both 37.5%, and that of the other groups were 0. Furthermore, the difference was significant, and Group A1-2 and B1-2 were higher than other groups.</p><p><b>CONCLUSION</b>The maintenance of the overhang above the severe wedge-shaped defect aid in the improvement of the fracture strength of the tooth restored with post and core crown. The ferrule of the wedge-shaped defect is not recommended to be prepared. Furthermore, the glass-fiber post and resin core is favorable for the re-repair of the teeth than the cast post and core.</p>

Studies on the correlation between the expression of Toll-like receptor 4 and the synovitis of the temporomandibular joint in rats / 中华口腔医学杂志

<p><b>OBJECTIVE</b>To investigate the expression of the Toll-like receptor-4 (TLR-4) in temporo-mandibular joint synovitis in rats, and to discuss the correlation between the expression of TLR-4 and the synovitis.</p><p><b>METHODS</b>Sixty male wistar rats were randomly divided into five groups, 12 each. Group A was the control group in which the rats were given normal diet.In Group B, the rats' bilateral masseter muscles were cut off (masseter resection group). In Group C, An cast metal crown were bonded on the mandibular right first molar of each rat (occlusal interference group). In Group D, occlusal pad were bonded on maxillary molars of each rat (occlusal dimension increase group). In Group E, rats' bilateral masseter muscles were re-sected and occlusal pads were bonded on their maxillary molars (masseter resection and occlusal dimension increase group). Pathological changes of synovium were observed using hematoxylin and eosin (HE) stains and pathology scores were evaluated. The expression of TLR- 4 were determined by immunohistochemical stains, and the expression of TLR-4 mRNA were determined by real-time PCR. The correlation between the expression of TLR-4, TLR-4 mRNA and the pathological score were analyzed using Spearman analysis.</p><p><b>RESULTS</b>The pathological scores of Group A-E were 0.5 ± 0.5, 2.5 ± 1.0, 2.7 ± 1.0, 3.0 ± 0.9, 5.3 ± 1.2 respectively. The expression of TLR-4 were (3.2 ± 1.5)%, (16.± 2.6)%, (15.8 ± 2.1)%, (17.5 ± 2.4)%, (38.2 ± 4.4) %. The expression of TLR-4 mRNA were 1.07 ± 0.09, 2.12 ± 0.33, 2.07 ± 0.29, 2.17 ± 0.34, 4.53 ± 0.46. Compared with group A, groups B- E showed significant higher pathology score (P < 0.05) and increased expression of both TLR-4 (P < 0.05) and TLR-4 mRNA (P < 0.05). An significant positive correlation was found between the expression of TLR- 4 and the pathology score (r = 0.785, P < 0.05), and between the expression of TLR- 4 mRNA and the pathology score (r = 0.720, P < 0.05).</p><p><b>CONCLUSIONS</b>TLR-4 may be closely associated with the development of the synovitis of TMJ of rats.</p>

The effect of fluoride on dental alloys in different concentrations of fluoride artificial saliva / 华西口腔医学杂志

<p><b>OBJECTIVE</b>To study the changes in surface morphology of cobalt-chromium alloy, pure titanium and high-cobalt chromium molybdenum alloy immersed in artificial saliva with different concentrations of fluoride, and to analyze the corrosion resistance of these metals.</p><p><b>METHODS</b>The three kinds of metal were polished and then were immersed in artificial saliva with different concentrations of fluoride (0%, 0.05%, 0.2%). All specimens were immersed for 3 weeks at (37.0 +/- 1.0) degrees C. Metal surface roughness before and after immersion were measured and analyzed by scanning electron microscope (SEM).</p><p><b>RESULTS</b>Metal surface roughness was increased with the concentration of fluoride. The surface roughness of the Co-Cr group and Ti group had a statistically significant difference between before and after immersion at the fluoride concentration of 0.05% (P<0.01), and the difference between Co-Cr group and vitallium2000 group, Ti group and vitallium2000 group were statistically significant difference (P<0.01). The differences of three groups before and after immersion were statistically significant at the fluoride concentration of 0.2% (P<0.01), and the difference among three groups was statistically significant (P<0.01).</p><p><b>CONCLUSION</b>Patients who frequently use fluoride products should not use pure titanium or cobalt-chromium alloy prosthesis. Patients with these three metal prostheses are not advised to use high concentration fluoride products.</p>