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Objective To explore new method to improve the teaching effects of complete denture prosthetics.Methods Totally 49 students were divided into 6 groups randomly.Lecture-based learning (LBL) combined with problem-based learning (PBL) methods were tried in complete denture prosthetics teaching.LBL teaching was made up of 18 class hours,in which teachers' teaching in the form of lecture was given priority to and introduction to basic theory of complete denture was focused on.PBL teaching was made up of 6 class hours in the form of small class ； the teaching plan ' new dentures of uncle Wang' compiled by the teaching and research section was taken as the blueprint；students searched for the references and discussed on the upcoming problems,relevant reasons and processing methods for wearing new dentures ； students made the final report.The effects were estimated by denture prosthodontics examination and PBL teaching feedback form.Data were described by percentage.Results 93.88％ students passed the exam,67.35％ students got good results.Feedback showed that 77.55％ students hold a positive attitude to PBL teaching.Conclusion Combining LBL with PBL in complete denture prosthetics teaching can achieve satisfactory results.
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Objective To investigate the effects of the thickness of the adhesives(3 M ESPE RelyX ARC)on the internal stress distribution of the IPS Empress Ⅱ full-ceramic crowns by using Finite Element Analysis(FEA).Method A dummy Empress Ⅱ ceramic crown restoration of the mandible right first molar was prepared according to standard dental process.Followed by micro-CT scanning,four 3D numerical models with cement thickness 60,90,120 and 150 μm were established respectively.The models were subjected to four loading conditions and stresses in veneer and core layers were presented.Result Numerical results indicate that when adhesive thickness increases from 60 μm to 90 μm,the maximum principal stress either in veneer or core decreases.However,when thickness increases to 150 μm,stress variation trends differ from adhesives.Conclusions The normal stresses in adhesives remain a low level when the thickness varies from 90 μm to 120 μm,while the shear stress is less sensitive to the thickness when it exceeds 90 μm.There is an optimal thickness which can reduce the tensile stress in the core and veneer.Attention should be paid to the shear strength of the adhesives since the shear stress could cause failure in the adhesive layer.
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<p><b>OBJECTIVE</b>This study was about the influence of porcelain thickness on crack at interface.</p><p><b>METHODS</b>The effect of porcelain thickness on the flaw at the interface between porcelain and metal was studied in three groups with porcelain thickness of 0.5 mm, 1.5 mm and 2.5 mm (metal thickness of 0.5 mm) by means of moire interferometre and interfacial fracture mechanics. The parameter Jc was compared among the three groups and the growing of the flaw was observed.</p><p><b>RESULTS</b>Jc and the extreme strength of group with porcelain thickness of 0.5 mm (2.813 N/m and 9.979 N) were lower than those of the groups with porcelain thickness of 1.5 mm and 2.5 mm (5.395 N/m, 19.134 N and 5.429 N/m, 19.256 N). Flaws extend along the interface in the groups with porcelain thickness of 1.5 mm and 0.5 mm.</p><p><b>CONCLUSIONS</b>(1) Fracture resistance of the interface in the groups with porcelain thickness of 1.5 mm and 2.5 mm is similar and it decreases in the group with 0.5 mm thick porcelain. (2) When porcelain is 1.5 mm or 0.5 mm thick, flaws will extend along the interface. When porcelain is 2.5 mm thick, flaws will extend into the porcelain layer.</p>
Subject(s)
Humans , Dental Porcelain , Dental Stress AnalysisABSTRACT
Objective:To evaluate the masking ability of the Rely XTM Veneer try-in pastes. Methods: 100 discolored teeth, including 50 nonvital ones and 50 vital ones, has been collected and restored respectively with all-ceramic crowns and veneers. Five try-in pastes including A1, A3, Translucent (Trt), White opaque(WOT) and B0.5 Opaque(B0.5),which were different in shade, were used to try in before adhesion. The color was measured by a digital colorimeter, and expressed in terms of 3 coordinate values(L*、a*、b*) of the CIE1976- L*a*b* system.Then the color differences of crowns and veneers ?E=[(?L*)2+(?a*)2+(?b*)2]1/2 as well as the value of Light (L= L*)、Chroma[C=〔(a*)2+(b*)2〕1/2] and Hue [H=arctan(b*/a*)] were calculated. The thickness of the measurement point was also measured and recorded. A one-way ANOVA was used to analyze ?E as well as L, C and H. Results:The chromatism of the veneers after try-in was higher than that of the crowns(P