| Endocrown, involving a circular margin and a central retention form in the pulp chamber, is a design particularly for endodontically treated tooth with excessive tooth defect. With decay-orientated tooth preparation, endocrown strictly follows the gold standard of tooth restoration, ie. Minimally invasive cut of tooth structure to preserve a maximum amount of tooth tissue, thus enhances the inner strength and stress distribution patterns of the endocrown-abutment complexes. With the development of bonding technology, endocrown was used successfully in clinical restoration, especially for tooth with serious wear, low occlusal-gingival distance and other tooth defect for elderly patients.CAD/CAM and all ceramic materials are recommended in endocrown design. However, the price was too high to be affordable by many patients. The porcelain fused to metal crown, especially the porcelain fused to cobalt chromium alloy crown, which is of low price and relatively ideal biocompatibility and aesthetic effect, is still the choice in many circumstances of clinical treatment.Yet there’re some disadvantages in the fabrication of the endocrown with the Co-Cr alloy. A key issue is the larger volume of the core and uneven thickness of the inner crown, which may lead to prominant deformation and poor marginal adaptation, as well as poor metal-porcelain combination.The purpose of this study was to explore the influences of the thickness and marginal types of inner crown on of the adaption of porcelain fused to Co-Cr alloy endocrown. Meanwhile, the relationships between the thickness of inner crown and the ceramometal anchoring strength were also studied.Part one:Comparative study of inner crown thickness on marginal adaptation of porcelain fused to Co-Cr alloy endocrownObjective:To investigate influence of inner crown thickness on marginal adaptation of porcelain fused to Co-Cr alloy endocrown by silicone replica method.Methods:According to the molar average anatomical data to get simplified model for mandibular first molar endocrowns(Ⅰ), and collecting vitro teeth to establish a study endocrown model(Ⅱ), each contains inner crown thickness:0.3mm group,0.5mm group,0.8mm group,1.0mm group, eight inner crowns of porcelain fused to Co-Cr alloy endocrowns were fabricated for each thickness group. Under the stereoscopic microscope, silicone replica technique was used to measure the thickness at different locations silicone impression. Datas were statistically analyzed to find the best thickness of the inner crown.Result:The mean thickness of the impression material for part Ⅰwere 62.14-68.27μm at the marginal point, and 61.50-69.33μm at the corner of the occlusal surface and the axial surfacem,31.31-44.25μm at the wall of the chamber,56.02-67.96μm at the bottom of the chamber. And for part Ⅱ, there were 56.99-62.09μm at the marginal point, and 57.18-72.72μm at the corner of the occlusal surface and the axial surfacem,45.42-51.26μm at the wall of the chamber,73.36-98.68μm at the bottom of the chamber. For part Ⅰ, the difference among different inner crown thickness was not statistically significant(P>0.05). But in the axial wall 1, significant difference was calculated between the 0.3mm group and 1.0 mm group(P<0.05). For part Ⅱ, significant differences were calculated among 0.3mm group,0.5mm group and 1.0mm group in the occlusal-axial corner, although there was not statistically significant differences among marginal, axial wall 1 and 2. In the subface, significant differences were calculated among 0.5mm group,0.8mm group and 0.3 mm group.Significant differences were calculated in the axial wall 1 and 2 of 0.3mm group, the subface of 0.5mm group, the subface, the axial wall 1 and 2 of 0.8mm group, the occlusal-axial corner, the subface, the axial wall 1 and 2 of 1.0mm group between part Ⅰ and part Ⅱ (t test).Conclusion:As far as marginal adaption was concerned, inner crown with different thickness were all valid in clinic. Choice should be made according to the different situation in clinical application.Part two:Influence of finish line design on the adaptation of the inner crown of porcelain fused to Co-Cr alloy endocrownsObjective:To evaluate the influence of four different finish line designs on the adaptation of inner crowns of porcelain fused to Cobalt-chromium alloy endocrowns by silicone replica method.Methods:According to molar average anatomical data to get simplified model for mandibular first molar endocrowns with four finish line designs:flat margin,90° shoulder, chamfer shoulder and 135° shoulder. Eight inner crowns of porcelain fused to Co-Cr alloy endocrowns were fabricated for each finish line design group. Adaptations between the inner crowns and the abutment teeth were duplicated by silicone impression method, and the thickness of silicone rubber was evaluated at the margin, the occlusal-axial corner, the axial wall, and the subface by a stereomicroscope. Data among the four different groups were statistically analyzed using one-way ANOVA.Result:Different line designs of porcelain fused to Co-Cr alloy endocrowns met the clinical requirements. The means of universal adaption of different finish line designs were 53.76±23.42μm,59.18±16.33μm,61.19±25.43μm,60.82±30.72μm for flat margin,90° shoulder, chamfer shoulder and 135° shoulder respectively. The difference was no statistically significant (P>0.05). As to the marginal fitness, the mean values were 66.41±18.19μm,56.60±14.95μm,74.62±18.55μm,58.08±13.53μm in sequencing. The difference was no statistically significant. Analysis of variance was statistically significant between 90° shoulder and chamfer, chamfer and 135° shoulder (P<0.05).Conclusion:The adaptation of the inner crowns of porcelain fused to Co-Cr alloy endocrowns affected by finish line design. The metal coping with 90° shoulder led to the most favorite marginal adaption, and the flat margin showed the best average adaption.Part three:The influence of the thickness of inner crown on the bonding strength of porcelain fused to Co-Cr alloy endocrownObjective:To investigate the influence of inner crown thickness on the bonding strength of porcelain fused to Co-Cr alloy endocrown by shear strength test method.Methods:According to the molar average anatomical data to get simplified model for mandibular first molar endocrowns, and collecting vitro teeth to establish a study endocrown model, each contains inner crown thickness:0.3mm group,0.5mm group,0.8mm group,1.0mm group, eight inner crowns of porcelain fused to Co-Cr alloy endocrowns were fabricated for each thickness group. Shear strength test was used to observe the metal-ceramic bonding strength after porcelain, and using SEM and EDS to analyze the interface of metal-ceramic.Result:The bonding strength of difference thickness of inner crown for part Ⅰ were 10.50±2.55MPa,13.21±2.27MPa,14.47±1.46MPa and 15.78±2.81MPa respectively, for part Ⅱ, there were 11.34±1.70MPa,11.55±1.62MPa,13.42±1.41MPa and 15.21±2.85MPa respectively, analysis of variance showed there was statistically significant difference between part Ⅰ and part Ⅱ (P<0.05). For part I, statistically significant difference was calculated among 0.5mm group,0.8mm group,1.0mm group and 0.3mm group,0.5mm group and 1.0mm group. For part II, statistically significant differences were calculated among 0.3mm group,0.5mm group and 1.0mm group.There was no statistically significant difference between part I and part II (P>0.05). And through the linear regression analysis, it was found that with the increase of the thickness of the inner crown, the bonding strength value was also increased. The SEM observation test showed tight bonding, the EDS analysis showed element diffusion phenomenon at the metal ceramic interface.Conclusion:The bonding strength of porcelain fused to Co-Cr alloy endocrown varied according to the different thickness of inner crown and the thicker inner crown was recommended to tooth defect with sufficient prosthodontics space. |
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