BACKGROUND:Chroming can improve the corrosion resistance of soft magnetic aloys. OBJECTIVE:To identify the optimal chroming conditions of two soft magnetic aloys, Fe-Cr-Mo and Fe-Ni, so as to improve their corrosion resistance. METHODS:Twelve pieces of square-shaped Fe-Cr-Mo and Fe-Ni soft magnetic aloys were casted in the size of 20 mm×20 mm×2 mm. After sanding and polishing, chrome plating was performed on these specimens and the coating thickness and hardness were measured. The selection factors included electroplate type (hexavalent chromium and trivalent chromium), current density (15, 20, 25, 35, 40, 45 A/dm2) and electroplating time (30, 40, 60 minutes). The optimal chroming conditions were determined by one-factor experimental method and the chrome plating was observed under a scanning electron microscope. RESULTS AND CONCLUSION:Cr6+ coating was significantly better than Cr3+ coating in the aspects of hardness, thickness and uniformity, indicating Cr6+ coating can significantly improve the corrosion resistance of Fe-Cr-Mo and Fe-Ni aloys. For Fe-Cr-Mo soft magnetic aloy, the optimal conditions of Cr6+ coating were as folows: current density of 45 A/dm2 and electroplating time of 60 minutes; the optimal conditions of Cr3+ coating were as folows: current density of 20 A/dm2 and electroplating time of 30 minutes. For Fe-Ni soft magnetic aloys, the optimal conditions of Cr6+ coating were as folows: current density of 35 A/dm2 and electroplating time of 60 minutes; the optimal conditions of Cr3+ coating were as folows: current density of 20 A/dm2 and electroplating time of 40 minutes.

BACKGROUND:In the comprehensive treatment of cracked teeth, the temporary protection using the orthodontic band and resin temporary crown can effectively prevent tooth fracture and protect the cracked teeth with a higher clinical success rate. OBJECTIVE:To evaluate the differences in clinical efficacy of orthodontic band and resin temporary crown on the temporary protection of cracked teeth. METHODS: Totaly 189 patients (97 males and 92 females, aged 19-65 years) with cracked teeth were selected, randomly divided into two groups and respectively underwent the temporary protection to cracked teeth with the orthodontic band (n=93) and resin temporary crown (n=96) in the comprehensive treatment. Retention effect, periodontal status and patient satisfaction were observed. RESULTS AND CONCLUSION:There were three cases with loose band and one case with faling band in the group of orthodontic band; there were two cases with faling band in the group of resin temporary crown. No significant difference between two groups in the retention effect was found. There were 11 cases of gingivitis or exploring hemorrhage in the group of orthodontic band and 2 cases in the group of resin temporary crown, indicating the periodontal status in the group of resin temporary crown was better than that in the group of orthodontic band (P< 0.05). There were 18 cases of lower satisfaction for poor color, expand feeling caused by the rubber band and discomfort caused by the band protruding from tooth surface in the group of orthodontic band; there were 3 cases of lower satisfaction in the group of resin temporary crown, and the patient satisfaction in the group of resin temporary crown were higher than that in the group of orthodontic band (P < 0.05). There is a better clinical effect in the temporary protection to cracked teeth by using the resin temporary crown, especialy in the terms of retention effect, periodontal status and patient satisfaction.

BACKGROUND:Temporary crown has been used widely in clinic. The physical properties and biological safety of temporary crown and cement materials are more superior along with the development of material science. OBJECTIVE:To summarize clinical application, physical properties and biological safety of the temporary crown and cement materials. METHODS:PubMed database was searched by the key words of temporary crown, provisional crown, temporary restoration, provisional restoration, interim restoration in English to retrieve relevant articles published from January 2004 to December 2014. Literatures addressing the temporary crown and cement materials were included, and the repetitive researches were excluded. RESULTS AND CONCLUSION:Through the clinical evaluation and experimental study, the physical properties (polymerization shrinkage, polymerization heat production, polymerization monomer release) and biological safety (cytotoxicity, irritation to the soft tissue) of the temporary crown and cement materials are the key problems needed to overcome. With the appearance of new materials and new fabrication methods, the temporary crown and adhesive materials have great application prospect and higher clinical value, but in the exploration process of the laboratory research and clinical application, there are many problems to be solved.

BACKGROUND:In the deep caries treatment, the pulp capping agent used in indirect pulp can induce the formation of dentin bridge (the complex of dental pulp and dentin), to protect the pulp tissue from stimulus and save the pulp vitality, completely avoid the occurrence of complications, with a higher clinical success rate. OBJECTIVE:To evaluate the differences in clinical efficacy of five kinds of calcium hydroxide preparations. METHODS:Totaly 236 patients with deep caries were selected and randomized to undergo indirect pulp with the double-component calcium hydroxide powder (n=46), Metapex with one-component injection dosage form and the chemical curing calcium hydroxide preparation (n=47), Dycal with the chemical curing calcium hydroxide preparation (n=45), Ionosit-Baseliner (n=49) and Calcimol LC (n=49) with one-component and the light curing calcium hydroxide preparation. The status of the dental pulp, the restoration and the root tip were observed at 1, 6, 12 and 24 months after operation. RESULTS AND CONCLUSION: There was no significant difference between the five groups in the success rate of indirect pulp capping at 1, 6 and 12 months (P> 0.05). At 24 months, the success rate of indirect pulp capping in the double-component calcium hydroxide powder group was lower than that in the other four groups (P < 0.05), but there was no significant difference between the latter four groups (P > 0.05). Metapex, Dycal, Ionosit-Baseliner and Calcimol LC al have a good effect on indirect pulp capping to deep caries, which can be used as agents for long-term pulp protection.

BACKGROUND:Studies have demonstrated that implantation of pile and different amount of residual tooth can change the stress distribution patterns of the tooth dentin within the residual root, and have an effect on the fracture mode of post-core restoration. OBJECTIVE:To evaluate the effects of the different amount of residual tooth on the fracture mode under oblique loading conditions in fiber pile composite resin core ful crown restoration. METHODS:Forty single rooted premolars extracted from orthodontic patients were divided into four groups after root canal preparation and filing. The plane going through buccal and lingual enamel cementum border midpoint and perpendicular to the long axis of the tooth was taken as the reference plane, so that the remaining amount of the tooth were 0, 1, 2, 3 mm. Fiber pile composite resin core metal ful restoration was conducted. After the repair, the oblique loading at 45° and at the rate of 1 mm/min was conducted. Fracture mode and load-displacement curve when root fracture occurred were recorded. RESULTS AND CONCLUSION:The tooth neck fracture usualy occurred in the 0 mm group, and central root fracture usualy occurred in the remaining three groups. There was a significant difference in the total fracture mode between 0 mm group and the remaining three groups (P < 0.05). There was no significant difference in the total fracture mode between 1, 2 and 3 mm groups (P> 0.05). In oblique loading conditions, when the remaining tooth structure was smal, the prosthesis was prone to have dental neck fracture. Fiber posts played a protective role in the tooth root, but the clinical probability of failure increased. The fracture mode was changed with the increase of residual tooth amount, transferring from the neck edge to the root. These results demonstrate that we must retain more tooth tissue from the crown in the restoration of residual root with fiber post-core crown.

BACKGROUND:Preparation of calcium hydroxide paste for apexification of immature permanent teeth has recently achieved satisfactory clinical efficacy because of its advantages including simple-to-use, being wel proportioned and ful contact with dentin and root apical periodontal tissues after being guided into root canal. OBJECTIVE: To validate the clinical efficacy of apexification of immature permanent teeth with calcium hydroxide paste. METHODS:Thirty-four patients with periapical periodontitis caused by fracture of abnormal central cusp, consisting of 18 males and 16 females, aged 8-12 years, were included and they received apexification with calcium hydroxide paste. X-ray observation of the tooth apex was performed at 1, 3, 6, 12 and 24 months after operation. RESULTS AND CONCLUSION:Among the 34 cases, 32 cases were successful and 2 cases failed in apexification of immature permanent teeth with calcium hydroxide paste, the success rate was 94%. 16 cases had apical closure at 9-12 months, 15 cases finished apexification at 12-15 months, 1 case with severe infection finished induction at 18-21 months, and two cases could not finish induction at 24 months. During 2 years of folow-up period, there were no recurrence of periapical periodontitis, tooth loose and shedding, tooth fracture, root progressive absorption and other complications. Al the teeth had type II apical closure, and there were no type I and IV apical closure, and the rare cases had the type between II and III which was difficult to distinguish. Apexification with calcium hydroxide paste for immature permanent teeth with incomplete developed root can preserve the affected teeth, aleviate inflammation, and show good induction effects.

BACKGROUND:Studies have demonstrated that Fe-Cr-Mo soft magnetic aloy has desired magnetic properties and machining properties. Surface Cr6+ plating treatment can significantly enhance the corrosion resistance in oral environment, but its biosecurity needs further testing. OBJECTIVE: To evaluate the biocompatibility of Fe-Cr-Mo soft magnetic aloy with chromium plating. METHODS:Logarithmic growth phase L929 cel suspension was obtained and seeded in 96-wel plates at a cel concentration of 6×107/L. Pure titanium extract, Fe-Cr-Mo soft magnetic aloy original extract, Cr6+-plated Fe-Cr-Mo soft magnetic aloy and PVC extract were added respectively. After 5 days of culture, cel morphology and adherent circumstances were observed. The absorbance value was detected using cel counting kit-8 assay. The relative growth rate of cels in each group was calculated. The cytotoxicity grades of materials were evaluated. RESULTS AND CONCLUSION:In the pure titanium extracts group, the cels with normal morphology showed good adherent growth and no cytotoxicity. In the Fe-Cr-Mo soft magnetic aloy original extract group, the cel morphology and growth status were both good, with occasionaly individual cel lysis. Scattered reddish brown particles were visible in the culture solution, showing no or very mild cytotoxicity. In Cr6+-plated Fe-Cr-Mo soft magnetic aloy extract group, the cels grew wel and showed no or very mild cytotoxicity. In PVC extract group, more than 70% of cels were vacuole-shaped and presented with pyknosis or dissolution, there was a large number of cel debris, and cel growth was inhibited in over 50% cels, showing moderate cytotoxicity or above. The cytotoxicity of Cr6+-plated Fe-Cr-Mo soft magnetic aloy extract was grade 0-1. These results demonstrate that Fe-Cr-Mo soft magnetic aloywith chromium plating has good biocompatibility.

Objective: To explore the relationship between family cohesion, psychological resilience and non-suicidal self-injury among middle school students. Methods: By using the stratified random cluster sampling method, 2 065 students from 4 middle school from Fujian province were investigated with family cohesion scale, adolescent psychological resilience scale and adolescent self-injury behavior questionnaire. Results: The report rate of self-injury was 40.34%, which differed by childhood migration experiences, parenting style as well as academic pressure (χ2=11.66，29.45，12.48，P<0.01). Total scores and dimensional scales in family cohesion and psychological resilience showed significant differences in students with or without self-injury (t=-8.33，-12.08，-7.29，-11.53，-3.38，-7.37，-7.68，P<0.01). The family cohesion was positively correlated with the psychological resilience and each dimension (r=0.27-0.56, P<0.01), but negatively correlated with non-suicidal self-injury (r=-0.18, P<0.01). The psychological resilience and each dimension were negatively correlated with non-suicidal self-injury (r=-0.24--0.14, P<0.01). Psychological resilience had a partial mediating effect between family cohesion and non-suicidal self-injury, with mediating effect accounting for 61.11% of the total effect. Conclusion Psychological resilience played a mediating role between family cohesion and non-suicidal self-injury. By promoting family cohesion to improve psychological resilience, it is helpful to prevent non-suicidal self-injury among middle school students.

BACKGROUND:Computer-assisted implant surgery can improve implantation accuracy,but the use of implant template in the posterior tooth area is limited for patients with small opening and small interocclusal distance.Therefore,the digital guide has been improved. OBJECTIVE:To study the effect of modified implant template on the accuracy of assisted implantation in missing second molars. METHODS:From July 2020 to July 2023,40 patients who received digital guide plate implantation or free hand implantation to repair missing second molars were selected from First Affiliated Hospital of Guangzhou Medical University.According to the coin toss method,patients were randomly divided into a trial group(n=22;modified digital guide assisted implantation)and a control group(n=18;free hand implantation).The data of neck deviation,tip deviation,depth deviation,and angle deviation were compared between groups for preoperative and postoperative cone beam CT overlap analysis.One week after the operation,the patients'satisfaction with the operation was assessed by visual analog scale score. RESULTS AND CONCLUSION:(1)The trial group included 25 implants(12 in the upper jaw and 13 in the lower jaw);the control group included 23 implants(8 in the upper jaw and 15 in the lower jaw).The neck deviation,tip deviation,depth deviation,and angle deviation of the trial group were all smaller than those of the control group(P<0.05,P<0.001).There was no significant difference in accuracy between the maxillary and mandibular implant site in the trial group(P>0.05).(2)There was no significant difference in satisfaction with the operation between the two groups(P>0.05).(3)The results showed that improving the digital guide plate for assisted implantation for missing second molar can improve surgical accuracy and is suitable for patients with small opening and small interocclusal distance in the posterior tooth area.