BACKGROUND: In clinical practice, the selection of dental implants with different specifications is based on the patient' s mandibular plane angle, and the long-term success rate is different in dental implants with different specifications. Therefore, it is reasonable to assume that the mandibular plane angle could affect the mandibular stress distribution of dental implants, thus affecting the success rate of dental implantation.OBJECTIVE: To perform an orthogonal experimental study on the mechanical effects of different implant specifications, mandibular plane angles and mandibular bone densities on stress distribution of the first mandibular molar implants.METHODS: A L9(33) orthogonal experiment was designed with 3 three-level factors, including mandibular plane angle (14°, 22°, 34°), implant diameter (6.6, 8.2, 9.6 mm), and mandibular bone density (types II, III, IV). Different dental implants with different combinations were implanted into an alveolar bone model, and placed onto a pressure testing machine under 500 N load. Then, strain (stress) data were collected in real-time and analyzed.RESULTS AND CONCLUSION: The optimal combination was as follows: low angle; 4.8 mm in diameter; mandibular bone with type II bone density. The relations of all the three factors were the diameter of dental implant > the mandibular plane angle > mandibular bone density. To conclude, the mandibular plane angle has some certain influences on the stability of dental implants. If the biting force is the same, dental implant bears the largest stress under the high angle,subsequently followed by the average angle and the low angle.

BACKGROUND:In root canal preparation, the clearance effect of sodium hypochlorite for root canal irrigation on the smear layer is associated with the contact time and contact area of irrigation fluid, the amount of irrigation fluid, irrigation fluid temperature, irrigation fluid concentration, flushing methods and so on. OBJECTIVE:To investigate the clearance effect of 3% sodium hypochlorite on the smear layer of root canal under different flushing methods, flushing temperature and flushing time. METHODS:Totaly 180 isolated front teeth with single root were colected and root canal preparation was conducted using motorized ProTaper. The root canal was flushed with 3% sodium hypochlorite. According to different flushing methods, these root canals were randomly and evenly divided into root canal active flushing group, passive ultrasound swished group and side opening flushing needle group. According to the flushing temperature and the flushing time after replacing a file, each group was randomly divided into six subgroups: 20℃ 30 seconds group, 20℃ 60 seconds group, 37 ℃ 30 se group. The clearance effect on the smear layer of root canal was observed using scanning electron microscope. RESULTS AND CONCLUSION:The general clearance effect on the smear layer in the root canal active flushing group was better than that in the passive ultrasound swished group and side opening flush acupuncture group (P< 0.05). At the same time, the clearance effect on the smear layer in the 60℃ group was better that that in the 37 ℃ group and 20℃group (P < 0.05). At a certain temperature, the clearance effect on the smear layer in 60 seconds group was better than that in the 30 seconds group (P < 0.05). The clearance effect on the smear layer in the 1/3 root cap zone was better than that in the 1/3 root and 1/3 apical root zone (P < 0.05). These results show that the best clearance effect on the smear layer can be achieved as folows: 3% sodium hypochlorite irrigation at 60℃ for 60 seconds.

Objective:To study the effect and mechanism of berberine intervention on alveolar bone absorption in diabetic rats.Methods:Diabetes rat model was established by one-time intraperitoneal injection of streptozotocin (35 mg/kg). Sixty healthy female Sprague-Dawley rats without specific pathogens were divided into normal group, diabetic group and berberine group according to the random number table method, 20 rats for each group. The rat models in the berberine group and the diabetic group were given berberine (200 mg/kg) and an equal volume of sodium chloride injection by gavage, once a day, for 4 consecutive weeks. The rat models in the normal group were not treated. Fasting blood glucose (FBG), fasting insulin level (Fins) , hormone resistance index (HOMA-IR) and insulin sensitivity index (ISI), as well as the serum calcium, phosphorus content, alkaline phosphatase activity and osteocalcin content of the rats were measured. The pathological changes of periodontal tissues were detected by HE staining. The expression of BMP-2/Smad pathway (BMP-2, Smad1, Smad4) was detected by RT-PCR and Western blot.Results:Compared with the diabetes group, the FBG level of rats in the berberine group [(9.88±1.23) mmol/L vs. (21.66±2.41) mmol/L], Fins levels [(11.63±3.63) mIU/L vs. (21.64±5.58) mIU/L] , HOMA-IR (7.58±0.96 vs. 20.85±1.95) were reduced, and ISI (-5.10±0.16 vs. 6.15±0.18), serum calcium levels[(1.855±0.125) mmol/L vs. (1.317±0.104)) mmol/L], serum phosphorus levels [(3.087±0.278) mmol/L vs. (2.526±0.226) mmol/L], serum ALP levels [(130.681±18.963) U/L vs. (99.874±31.968) U/L] and osteocalcin levels [(112.368±9.752) ng/ml vs. (78.645±10.973) ng/ml] were all increased, and the differences were statistically significant (all P<0.05). The results of hematoxylin-eosin staining showed that there was no bone resorption in the alveolar bone of the rats in the normal group, bone resorption was found in the alveolar bone of the rats in the diabetes group, and the bone resorption of the alveolar bone in the berberine group was significantly reduced. RT-PCR and Western Blot results showed that compared with the diabetes group, the BMP-2, Smad1, Smad4 gene mRNA and protein in the alveolar bone tissue of the berberine group were significantly increased (all P<0.05). Conclusions:Berberine intervention can reduce FBG levels in diabetic rats and improve insulin resistance, which may reduce alveolar bone resorption in diabetic rats by up-regulating the BMP-2/Smad signaling pathway.