OBJECTIVEThis study was about the influence of porcelain thickness on crack at interface.

METHODSThe 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.

RESULTSJc 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.

CONCLUSIONS(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.

OBJECTIVETo study the precise stress distribution of the apical foramen area of endodontic endosseous implant, in order to improve the prosthetics of endodontic endosseous implant.

METHODSAfter analysis of the two-dimensional endodontic endosseous implants model with finite element method, left and right areas beside the apical foramen were selected as infinite domains to calculate. D-N interactive method was used to connect the finite and infinite domains.

RESULTSUnder 45 degrees axial right oblique loading, the stress concentration occurred in both infinite domains of the apical foramen. The infinite domain nearing the load side was tension stress concentration, but the other side was compressive stress concentration. Two stress concentration points were just at the central points, which were intersections between implant and dentin. The stress reduced in all directions from these two stress concentration points, but in the ligament, the result was contrary.

CONCLUSIONSThe change of the tooth rotational center is helpful to the tooth stability and carrying capacity after restoration. In the implant area, the diameter of implant at the apical foramen of root shall not be reduced to protect root in clinical work. It is very important to preserve the tissue of periodontal ligament for endodontic endosseous implants.

PURPOSE: This study is aimed to assess changes of stress distribution dependent on different connection lengths and placement of the fixture top relative to the ridge crest. MATERIALS AND METHODS: The internal-conical connection implant which has a hexagonal anti-rotation index was used for FEM analysis on stress distribution in accordance with connection length of fixture-abutment. Different connection lengths of 2.5 mm, 3.5 mm, and 4.5 mm were designed respectively with the top of the fixture flush with residual ridge crest level, or 2 mm above. Therefore, a total of 6 models were made for the FEM analysis. The load was 170 N and 30-degree tilted. RESULTS: In all cases, the maximum von Mises stress was located adjacent to the top portion of the fixture and ridge crest in the bone. The longer the connection length was, the lower the maximum von Mises stress was in the fixture, abutment, screw and bone. The reduction rate of the maximum von Mises stress depending on increased connection length was greater in the case of the fixture top at 2 mm above the ridge crest versus flush with the ridge crest. CONCLUSION: It was found that the longer the connection length, the lower the maximum von Mises stress appears. Furthermore, it will help prevent mechanical or biological complications of implants.
Dental Implant-Abutment Design ; Dental Stress Analysis ; Finite Element Analysis

OBJECTIVETo investigate the effects of different implant thread locations on stress distribution in implant and bone under concentrated load, and discuss the best design of location of implant thread.

METHODSThe stress in implant-bone interface of implants with different thread locations (model A, B, C, D), which were loaded in axial and oblique 450 to axle, were analyzed by Solidworks 2005 plus and Cosmos/works 7.0 software.

RESULTSThe stresses in cervical cortical bone of implant with model C were lower than others. But under oblique load, the stresses of implant and cancellous bone in model C were higher than model A. The stresses distribution of model B was obviously concentrated, and under axial load, all kinds of stresses in this model were higher than others. The stress distribution in model A and D were more even, the stress concentrated more on implant neck, upper part of cortical bone and the lowest thread on implant. The stresses in interface under oblique load were much higher than those under axial load.

CONCLUSIONThe location of thread has effect on stress distribution in implant-bone interface. More attention should be paid to it when we design implants, and we should try to avoid oblique load in implant prosthodontics.

OBJECTIVETo investigate the influences of varying lingual traction forces on the space-closing speed in a typodont model.

METHODSForty-two Angle Class I standard typodont models of bimaxillary teeth protrusion were divided into 7 equal groups. Four regions of the model were paired to groups, and in the odd-numbered models, the top left and bottom left regions served as the experimental group and the top right and bottom right regions as the control group; in the even-numbered models, the regions in the model were grouped oppositely. In the experimental group, the space was closed by niti wire extension spring in the buccal ridge combined with lingual elastic traction of 0, 5, 10, 15, 20, 25 and 30 g. In the control group, the space was closed by exclusive niti wire extension spring in the buccal ridge. The space-closing speed were analyzed in all the groups.

RESULTSThe space-closing speed was significantly lower in the control group than in the experimental groups with lingual traction forces of 5, 10, 15, 20 and 25 g (P<0.05), but a traction force of 30 g resulted in a significantly lower speed than that in the control group (P<0.05). The space closing speed was the greatest in the experimental group with a traction force of 15 g (P<0.05).

CONCLUSIONNiti wire extension spring in the buccal ridge combined with lingual elastic traction results in faster space-closing speed than traditional exclusive niti wire extension spring. The speed is the fastest by applying 15 g lingual traction, which is also associated with the lowest slip resistance.

OBJECTIVEIn terms of the problems of now available dental machinable ceramics, a new type of calcium-mica glass-ceramic, PMC-I ceramic, was developed, and its machinability was compared with that of Vita MKII quantitatively. Moreover, the relationship between the strength and the machinability of PMC-I ceramic was studied.

METHODSSamples of PMC-I ceramic were divided into four groups according to their nucleation procedures. 600-seconds drilling tests were conducted with high-speed steel tools (Phi = 2.3 mm) to measure the drilling depths of Vita MKII ceramic and PMC-I ceramic, while constant drilling speed of 600 rpm and constant axial load of 39.2 N were used. And the 3-point bending strength of the four groups of PMC-I ceramic were recorded.

RESULTSDrilling depth of Vita MKII was 0.71 mm, while the depths of the four groups of PMC-I ceramic were 0.88 mm, 1.40 mm, 0.40 mm and 0.90 mm, respectively. Group B of PMC-I ceramic showed the largest depth of 1.40 mm and was statistically different from other groups and Vita MKII. And the strength of the four groups of PMC-I ceramic were 137.7, 210.2, 118.0 and 106.0 MPa, respectively.

CONCLUSIONThe machinability of the new developed dental machinable ceramic of PMC-I could meet the need of the clinic.

OBJECTIVETo investigate the effect of three types of veneering porcelain on the bending strength of KAVO Y-TZP/porcelain layered structure.

METHODSKAVO zirconia ceramics were used as the substructure. To form Y-TZP/porcelain bilayered structure, a leucite-based veneering porcelain was fired on the zirconia substructures by slip-casting technique with dentin washbake, and two nano-fluorapatite-based veneering porcelains were fired on the zirconia substructures by either slip-casting or pressed-on technique with or without liner coverage. The bending strength was tested according to ISO 6872 standard, and the veneered surfaces of the fracture samples were analyzed by scanning electron microscopy (SEM).

RESULTSFor covering KAVO zirconia core material, the conventional veneering slurry-porcelain combined with liner or wash firing had significant higher bending strength than pressed-on porcelain. SEM showed that the main failure type at the interface was adhesive failure.

CONCLUSIONThin layer sintering using washbake program or liner on KAVO zirconia surface increases the surface wettability, and this procedure may be indispensable when veneering on the surface of dental zirconia.

OBJECTIVETo establish anisotropic mandible model with dental implants and to investigate the effect of anisotropy material on stress and strain distribution of implant-bone interface.

METHODSThree-dimensional finite element models of whole mandible with anisotropic and equivalent isotropic material were created by CT scanning and universal surgical integration system (USIS) software developed by the authors. Two ITI threaded implants were implanted in the posterior teeth area. The values of principal stress and principal strain on the bone around dental implants were calculated in two different finite element models with buccolingual load.

RESULTSIn the anisotropic mandible model, nearly all values of the principal stress and principal strain on cortical and cancellous bone increased compared with the equivalent isotropy model, 2.1%-74.1% for principal stress and 4.7%-57.3% for principal strain, but 10. 3%-71.4% for principal stress and 19.5%-63.4% for principal strain on cancellous bone.

CONCLUSIONSIn the three-dimensional finite element analysis, anisotropic mandible model with dental implants has an apparent effect on the stress and strains of the implant-bone interface. Anisotropic mechanical properties of mandible should be emphasized in biomechanical study.

OBJECTIVETo investigate the influence of indenter diameter on fracture strength and fracture mode of IPS e. max all-ceramic crowns using mechanical experiments and three-dimensional finite element (3-DFE) method, to validate the 3-DFE model using mechanical experiments, and to provide a guideline for occlusal surface design for IPS e. max all-ceramic crowns.

METHODSA 3-DFE model of an all-ceramic crown on a molar was established using ANSYS10.0 software. The 3-DFE crown was loaded occlusally at three points to simulate the contact points of a hemispherical indenter loading on the crown. Two indenter diameters (4 mm and 10 mm) were designed by changing loading point, load level and its direction. The stress distribution and the principal stress in the 3-DFE model were calculated. Meanwhile, IPS e. max ceramic crowns were made on a laboratory model and loaded with indenters. The diameters of the indenters were also 4 mm and 10 mm respectively. Fracture mode and fracture-resistance of the crowns were recorded.

RESULTSThe principal stress increased as load increases for both small and large indenters. Stress concentrated in the central fossa of the 3-DFE crown when loaded with the small indenter. Stress concentration appeared in the middle area of the occlusal surface mesio-distally when 3-DFE crown was loaded with large indenter. The fracture-resistance load was 600 N to 700 N for 4 mm diameter indenter, and 2500 N to 2750 N for 10 mm diameter indenter. Mechanical experiments indicated the same results as those from 3-DFE analysis.

CONCLUSIONSBoth the three-dimensional finite element analysis and the mechanical experiment showed the same results. When loaded with 4 mm diameter indenter, fracture occurred in the central fossa of the crown, however, 10 mm diameter indenter usually caused extensive crown damage.

OBJECTIVETo establish three-dimension finite element model of mandible with two kinds of Replace implant, and to study stress of implant and abutment.

METHODSThe data of components of the dental implant was measured, cross section of the mandible was scanned by spiral CT and image reconstruction technique was conducted. Three-dimension finite element analysis software UG and MSC. Marc/Mentat were used to built the conjunction model and bone model of two implant systems. Axial loading (200N) and 30 degrees oblique loading (100N) were applied on the models respectively, the stress distribution patterns of the implant and abutment of two implant systems were analyzed.

RESULTSThe peak stress district was concentrated on the structure of the implant cervix, which was more obviously displayed on the Replace Select implant. The peak stress of oblique loading was higher than that of axial loading. The peak stress on the implant cervix of Replace Select implant was higher than that of Replace External Hex implant in all loadings.

CONCLUSIONTo Replace Select especially, oblique force should be avoided on clinical practice in case of the implant fracture.