Papers by Author: Long Quan Shao

Abstract: Objective: To study the relative translucency of 4 veneered and glazed all-ceramic systems core material, including Vita In-Ceram Alumina, Vita In-Ceram Zirconium, Ivoclar Vivodent Empress and Colored Zirconia. Methods: Under standard black and write background, the surface light reflectivity of 4 veneered all-ceramic systems core material was determined with contact color difference meter, and the ratio of Yb /Yw was calculated. Results: After veneered, the relative translucency of 4 core materials all declined, and ranged from 0.8015 of Colored Zirconia to 1.00 of In-Ceram zirconia, among of that Empress II and Colored Zirconia were most transparent. Conclusion: Among the groups, there is no significant difference between Empress II and Colored Zirconia(IL1,IL2,IL3). Compared with Vita In-Ceram Alumina and Vita In-Ceram Zirconium, Vita In-Ceram Alumina(AL1) has significant difference. There is no significant difference between Vita In-Ceram Zirconium and Vita In-Ceram Alumina(AL2,AL3,AL4).

Abstract: The aim of this study were to compare the color value of four kinds of dental all-ceramic cores (IPS e.max Press,Zenostar,Lava Zirconia and Upcera Zirconia) on three different post-core materials.All-ceramic core materials were made into samples at the diameter of 10mm and the thickness of 0.50.02mm.Their color value on the post-core material of noble metal,Co-Cr alloy and resin were respectively determined with chromatism instrument.It was showed that the color value of four all-ceramic cores were statistically different.IPS e.max Press was most obviously affected by post-core materials,while Upcera Zirconia the weakest.Lava Zirconia and Zenostar were influenced to a certain degree.In conclusion,non-mental post-core was preferable for IPS e.max Press,Upcera Zirconia was fit for any post-core materials.

Abstract: The aim of this invitro study was to evaluate the fracture resistance of endodontically treated canines restored with one-piece milled zirconia post and core in the varying ferrule modes. Fifty recently extracted human maxillary canines were endodontically treated and randomly divided into 5 groups of 10 specimens each. According to the defect degree of ferrule, intact ferrule was classified as group A and served as control, 2 mm ferrule height without buccal ferrule was classified as group B, 2 mm ferrule height without mesial and buccal ferrule was classified as group C, 2 mm ferrule height without mesial, buccal and lingual ferrule was classified as group D, no ferrule preparation was classified as group E. All of the teeth were restored with one-piece milled zirconia post and core, and zirconia crowns. The teeth were prepared to standardized specifications. The restored teeth were loaded to fracture at a 135° angle to their long axis, at a cross-head speed 0.5 mm/min, and the load (N) at failure was recorded. Statistical analysis was performed by SNK pairwise multiple comparisons (α=0.05). The mean fracture resistance of five groups as follows: 1019.30±139.01N for group A, 861.20±105.67N for group B, 833.70±100.56N for group C, 733.20±96.91N for group D, 698.00±99.90N for group E. The fracture resistance of restored teeth between group B and group C, group D and group E had no statistically significant difference(P>0.05). The fracture resistance of the rest pairwise group comparisons had statistically significant difference(P<0.05). Increasing the absence degree of ferrule, it was found that the fracture resistance decrease. The buccal and lingual ferrule were more important than mesial ferrule for enhanced fracture resistance. This in vitro study supports evidence that reserving the buccal and lingual ferrule is a key point to increase the fracture resistance of canines restored with one-piece milled zirconia post and core.

Abstract: Objective. To investigate the flexure strengths and elastic modulus of four types of dental fiber posts. Methods. The flexure strengths of ParaPost Taper Lux, Tenax Fiber White, Luxa Post and Rebilda Post fiber post were measured. The rupture modes were analyzed with SEM. Results. There was no significant difference between ParaPost Taper Lux (591.47±35.15MPa) and Rebilda Post (614.67±58.36MPa) in flexure strength (P>0.05), and Tenax Fiber White (846.62±71.15MPa) had significantly higher flexure strength than the other groups. There was no significant difference between Tenax Fiber White (23.93±2.14GPa) and Luxa Post (22.67±1.39GPa) in elastic modulus (P>0.05), and Tenax Fiber White and Luxa Post had significantly lower elastic modulus than other groups. It could be observed by transverse SEM that the combine of fiber and resin was even and compact and plenty of resin fragment adhered to the surface of fiber in Tenax Fiber White group, multitudinous cracks were observed by lengthwise SEM. Conclusion. The flexural properties and rupture modes of four kinds of dental fiber posts were significantly different.

Abstract: Aim To explore pigmented glass for infiltration and investigate its physical and mechanical properties. Methods The pigmented glass was prepared by melting glass components in an alumina crucible at 1400°C for 2h. The thermal properties were tested using a Setaram-TGDTA 92 analyzer; three point bending strength and fracture toughness were also tested; the microstructure of the glass was studied using a scanning electron microscope. Results The thermal expansion coefficient over the range 20–600 °C was 6.2 × 10-6 °C -1, Tg was about 690 °C, the density, bending strength, fracture toughness and Vickers hardness were 2.23 g/cm3, 118 MPa, 1.22 MPam1/2, and 7.4 GPa respectively. Conclusion The pigments have no detrimental effects on the physical and mechanical properties; thus the pigmented glass for infiltration has favorable physical and mechanical properties and also good compatibility with presintered porous alumina.

Abstract: The purpose of this study was to study effects of the mechanical properties of veneering porcelain on stress distribution of dental zirconia layered structure by three-dimensional finite element analysis. A 3-D geometric model of the first maxillary molar was established, a tooth preparation was simulated by the Imageware software. A crown was designed and divided into three layers: core, middle layer and outer veneer layer. The elasticity modulus of the middle layer was 70GPa for the control model up to 175GPa for the tested models. Loads of 200N were applied over a 1 mm diameter area beneath the tip of the mesial-distal cusp, simulating typical occlusal contact areas, the stress distribution of the crown systems were analyzed. Results show that within the geometry of the crown configuration, one concentration district of maximum principal stress occurred on the occlusal surface closely proximal to the loading position, several sub-maximum principal stress area were observed, such as margin regions of the mesial face, lingual face, distal faces, buccal face and occlusal fossa. Middle layer with higher modulus can effectively disperse the stress concentration in the layered zirconia all-ceramic crown system.

Abstract: To compare thickness of veneering ceramics dependence of the stress profile in veneering ceramic layered on zirconia and metal frameworks. Cylindrical core materials dentine ceramic specimens whose diameter is 20.0mm, thickness is 0.5mm were made with customized method, and then Upcera zirconia and metal plate were veneered, the thickness of the veneering ceramics respectively were 1.25mm, 1.50mm and 1.75mm, a total of six groups (n=10). An CAD-CAM machine was used for the drilling procedure and residual stress profile of all-ceramic crowns and metal-ceramic crowns was calculated. The mean residual stress of zirconia all-ceramic restorations were: respecitively, 60.15±5.54MPa for 1.25mm thickness of veneering; 53.37±5.12MPa for 1.50mm thickness of veneering; 45.64±4.53MPa for 1.75mm thickness of veneering. The mean residual stress of glass infiltrated alumina all-ceramic restorations were: respectively, 61.32± 5.76MPa for 1.25mm thickness of veneering; 52.45±5.35MPa for 1.50mm thickness of veneering; 45.89±4.26MPa for 1.75mm thickness of veneering. Residual stress profile of all-ceramic restorations was significantly different among specimen groups of Y-TZP and Metal plate (P>0.05). There was also significantly different among specimen groups which had same thickness of the veneering ceramics but not belonged to same frameworks (P<0.01). As the depth increases, the stress gradually increases, reaching the maximum at the interface of MV or CV. The residual stress of frameworks was tensile stress, but the residual stress of veneering porcelain interior was compress. With the veneer porcelain thickness, the residual stress of the interface gradually reduce.

Abstract: To evaluate the masking ability of IPS e.max all-ceramics system of HO series. IPS e.max Press HO ingots were fabricated into twenty cylindrical specimens (n=5) with the diameter of 13mm and four different thinknesses (0.4mm, 0.6mm, 0.8mm, 1.0mm). All specimens after veneered, gazed and cemented to metal substrate disks (thickness 3mm, diameter 13mm) were measured on both the white background and metal substrate disks background using a spectrophotometer and values of L, a and b were calculated to compare color differences among four groups. Meanwhile ΔE with the preselected required color (A2 color) were calculated. ΔE<1.5 was considered a clinically acceptable color match. In the 0.4mm thickness specimens group, the values of L, a and b significantly increased (-1.36±0.05, -0.15±0.06, -1.46±0.02, respectively) between the white background and abutment background. But there were no significant color differences in the other three groups (P<0.05). In the 0.6mm and 0.8mm thicknesses specimens groups, the color difference values (0.71±0.04, 1.14±0.06, respectively) with A2 color were less than the defined value. Thus the cylindrical specimens with the thickness of 0.6mm, 0.8mm and 1.0mm could mask the metal substrate disks background sufficiently and the thickness of 0.6mm and 0.8mm had an acceptable color match compared with the target color. IPS e.max all-ceramics system of HO series can produce clinically acceptable color match and have the capacity to mask a dark background such as a dark tooth or core buildup material.

Abstract: Despite the expanded application for zirconia in restoration dentistry, there is less clear recommendation in the literature regarding the relation between zirconia surface roughness and its shear bond strength to resin cements. The aim of this study was to assess the effect of surface roughness of Cercon zirconia on its shear bond strength to resin cements. 66 Zirconia rectangular specimens (10 mm×10 mm×3 mm) were prepared from Cercon zirconia blocks, finished using a diamond rotary cutting instrument, sintered, and then assigned into 6 groups. The specimens in the first group without polishing were used as control. Other groups were polished against 120#, 240#, 360#, 500# and 600# sand paper after sintered, respectively. Ceramic surface were analyzed by scanning electron microscopy (SEM) and Surface profilometer. 10 samples of each group were bonded with Variolink N resin cements respectively and submitted to shear bond strength test. Shear bond strength was measured and statistically analyzed. The results showed that the population means of 6 groups of samples were not equal. There was no significant difference between control group and 600# sand paper treated group, 500#, 360# and 240# sand paper treated groups (P>0.05), but a significant difference among the other groups (P<0.05). Findings of this study revealed that the shear bond strength might be raised by increasing the surface roughness of Cercon zirconia. Therefore, the surface roughness of Cercon zirconia has an effect on the shear bond strength, but is not the determining factor in clinical use.

Abstract: To investigate the influence of alveolar bone loss and post design on stress distribution of a severely damaged canine. The residual canal dentin wall in the cervical region was standardized at 0.5mm in thickness. Twelve two-dimensional finite element models were created. The models were varied in their alveolar bone loss. The post systems include computer-aided design/computer-aided manufacturing zirconium post, prefabricated glass fiber post, cast stainless steel post, and cast gold post. The numerical models were considered to be restored with an all-ceramic crown. A load of 100N was applied to the crown at an angle of 45 degree on the lingual surface, and Mises stresses were calculated. Finite element analysis revealed that cast stainless steel post system showed the lowest maximum Mises stress in the dentine at 86.46 MPa, while, glass fiber post resulted in the highest stress concentration in the dentin at 174.3 MPa. Stresses were reduced by increasing alveolar height. Loss of alveolar bone loss may lead to an increased risk of failure.