Different jaw positions and condylar positions in oral therapy / 口腔疾病防治

@#In the stomatognathic system, a stable jaw position is influenced by occlusion, the temporomandibular joint and neuromuscular stability. The condylar position in the glenoid fossa is closely related to the jaw position, while no consensus has been reached on the optimum jaw position and its corresponding condylar position in oral therapy. This paper summarizes the controversial opinions regarding the selection of jaw position and the corresponding condylar position in prosthetics and orthodontics, including antero-superior, antero-inferior, and therapeutic positions. Their indications, theoretical bases and clinical applications are also included. The literature review results suggest that, the antero-superior position, in other words, centric relation, should be chosen when the patient has a stable jaw position without TMD. In cases where finding an ideal antero-superior position is difficult due to hyperplasia or deformation or disarrangement of the articular disc, the antero-inferior position is recommended to alleviate symptoms and facilitate reconstruction of the TMJ to obtain good stability. Moreover, for high-angle patients with Class Ⅱ malocclusion or for patients with mild skeletal malocclusion, camouflaged orthodontic treatment combined with antero-inferior jaw repositioning through the potential of condyle remodeling can be an alternative to orthognathic surgery and can simplify the treatment plan. While the therapeutic position is specifically proposed for coping with complicated situations related to cranio-mandibular dysfunction, such as maximal intercuspal position abnormalities or deflection, muscle and TMJ dysfunction, unstable jaw position, in which changes in the original occlusion or abnormal TMJ guidance are induced, and a new intercuspal position can be established and stabilized on the basis of occlusal support and modified guidance. The therapeutic position put aside the debate regarding condylar position, however, the specific position of the condyle has not been reported in this case. This review suggests that different jaw positions and condylar positions have different scopes of application, and their clinical selection should be based on based on whether the patient′s joints have organic changes and the stability of the jaw positions should be comprehensively considered. However, the long-term effects of oral therapy based on different jaw positions need to be further verified by controlled clinical trials in the future.

Influence of different heat treatments on the corrosion behavior of a new type of high palladium dental alloy / 口腔疾病防治

Objective@#To evaluate the influence of different heat treatments on the corrosion behavior of a new Pd-Ag-In-Ga alloy. @*Methods @#The corrosion of a new Pd-Ag-In-Ga alloy was tested according to ISO 10271：2001/cor.1:2005(E). Taken as comparison, a commercial high-palladium alloy (Spartan® Plus) was also employed in the study. For electrochemical corrosion test, the open-circuit potential (Eocp) and potentiodynamic polarization curve were recorded and then the electrochemical parameters, namely corrosion potential (Ecorr) and corrosion current density (Icorr) calculated. The surfaces of the specimens that before and after corrosion test were observed by scanning electron microscopy (SEM). @* Results @#Both of the high-palladium alloys had lower corrosion tendency and higher corrosion resistance by heat treatment in the ISO 10271 electrochemical corrosion test. For both alloys, heat treatment at 500 ℃ was found to be effective in improving the corrosion resistance as the best datas of electrochemical parameters (Eocp, Ecorr, Icorr) were detected among the four temperature groups. However, no evidence showed that there was significant difference in corrosion resistance between the two alloys. Comparison of surface morphology of the specimens before and after electrochemical experiments by SEM demonstrated that all groups of the two alloys were visible of pitting corrosion and crevice corrosion phenomenon that gradually became less with increasing heat treatment temperature. Horizontal comparing among the groups of the two alloys, no apparent differences in the distribution of pitting and crevice corrosion was found. @*Conclusin @#The variation in compositions of high-palladium alloys did not cause significant difference in corrosion behavior due to the identical palladium matrix. The similarity in corrosion behavior among the two high-palladium alloys might be attributed to the predominant palladium content.

Study on electrical measurement stress analysis of root attachment overdenture of three different mechanisams / 口腔疾病防治

Objective@#To analyze the stress difference of alveolar bone around the abutment and alveolar ridge of edentulous of three different kinds of root-attachment-supported overdenture under different load conditions, in order to provide a reference for the choice of clinical root attachment. @*Methods @#The occlusal force of overdenture was simulated by electrical resistance strain measurement in vitro. The stress of the alveolar bone, the central part of the mandibular arch and the first molar correspond to the alveolar ridge were measured. The stress difference of 3 kinds of attachment overdenture under different loading conditions were compared and analyzed.@*Results@#Under the same loading condition, all three kinds of overdentures had a certain degree of slip of the denture (magnetic attachment denture) or rotation (3 kinds of attachment dentures). The abutment neck in different parts of the dental arch and alveolar bone, anterior free end edentulous alveolar ridge stress distribution was significantly different. @*Conclusion@# ERA attachment overdenture was the most preferable, followed by the magnetic attachment overdenture. Suitable attachment should be selected based on specific clinical cases.

Three-dimensional finite element analysis of different designs of residual posterior root restored with a new titanium alloy post / 口腔疾病防治

Objective @#To compare the stress distribution of residual posterior root restored with a new titanium alloy post of different diameter and taper, and discuss the rational design of posterior tooth post by the three-dimensional finite element method. @*Methods @#Mandibular second premolar image data was obtained by CBCT, and the mandibular second premolar post models with different diameter and taper were established with the help of Mimics data conversion, Geomagic Studio image processing technology and Creo/Parametric software. Then Abaqus was used to simulate the load condition of prosthesis and analyze the Von Mises stress of the cervical and apical regions.@*Results@#With the same diameter, the influence of the different post tapers on the peak stress of the root cervical area was irregular. When the taper was the same, the peak stress of the root apex area decreased firstly and then increased as the diameter increased. When the diameter was 1 mm, the peak stress of the root cervical and apex area was the lowest.@*Conclusion @#The effect of diameter on the stress distribution of dentin is more important than that of taper. To select the reasonable diameter and taper of the post is helpful to reduce the peak stress of the root cervical and apex area.