Ting Sun

Load-bearing capacity and the recommended thickness of dental monolithic zirconia single crowns

PURPOSE The aim of this study was to evaluate the load bearing capacity and a reasonable thicknesss of dental monolithic zirconia crowns. MATERIALS AND METHODS Polymethyl methacrylate (PMMA) abutment tooth specimens were made by CAD/CAM technic. Monolithic zirconia crowns (MZC), monolithic lithium disilicate crowns (MLC), layered zirconia crowns (LZC) and metal ceramic crowns(MCC), of which the occlusal thickness was 1.5mm were thereafter fabricated and cemented on the abutment tooth specimens. MCC with occlusal thicknesses of 0.6mm, 0.8mm, 1.00mm, 1.2mm were also made. All specimens underwent load-to-fracture test. Weibull parameters (σ0) and (m) were calculated. Fracture modes were also evaluated. RESULTS The mean fracture load was 1863.16±116.81 for MLC, 2284.77±355.60 for MCC, 2308.0±510.94 for LZC, 4109.93±610.18 for MZC (1.5mm), 3068.31±233.88 for MZC (1.2mm), 2429.88±315.03 for MZC (1.0mm), 1814.60±68.21 for MZC (0.8mm) and 1308.38±111.38 for MZC (0.6mm). The fracture load of MZC was significantly higher than MCC, LZC and MLC (P<0.05). The fracture loads for MCC with different thickness were significantly different (P<0.05). Similar trend was observed for the characteristic strength (σ0) and Weibull modulus (m). For MZC and MLC, the fracture mode was catastrophic failure. The predominant fracture mode for LZC was catastrophic fracture. The fracture loads of MZC(1.0mm) and MCC were not statistically different (P>0.05). CONCLUSIONS Monolithic zirconia crowns exhibit higher fracture loads than monolithic lithium disilicate crowns, layered zirconia crowns and metal ceramic crowns. The fracture resistance of monolithic zirconia crowns with a thickness of 1.0mm can be equal to metal ceramic crowns. Doubling the monolithic zirconia core from 0.6mm to 1.5mm increases the fracture resistance of this restorative system threefold.

The effect of graded glass–zirconia structure on the bond between core and veneer in layered zirconia restorations

OBJECTIVE The aim of this study was to test the hypothesis that a graded glass-zirconia structure can strengthen the core-veneer bond in layered zirconia materials. METHODS A graded glass-zirconia structure was fabricated by infiltrating glass compositions developed in our laboratory into a presintered yttria tetrahedral zirconia polycrystal (Y-TZP) substrate by the action of capillary forces. The wettability of the infiltrated glass and Y-TZP substrate was investigated by the sessile drop technique. The microstructures of the graded glass-zirconia structure were examined by scanning electron microscopy (SEM). The phase structure characterization in the graded glass-zirconia structure were identified by X-ray diffraction (XRD) analysis. The elastic modulus and hardness of the graded glass-zirconia structure were evaluated from nanoindentations. Further, the shear bond strength (SBS) of the graded glass-zirconia structure and veneering porcelain was also evaluated. RESULTS SEM images confirmed the formation of the graded glass-zirconia structure. Glass frits wet the Y-TZP substrate at 1200 °C with a contact angle of 43.2°. Only a small amount of t-m transformation was observed in as-infiltrated Y-TZP specimens. Nanoindentation studies of the glass-zirconia graded structure showed that the elastic modulus and hardness of the surface glass layer were higher than those of the dense Y-TZP layer. The mean SBS values for the graded glass-zirconia structure and veneering porcelain (24.35 ± 0.40 MPa) were statistically higher than those of zirconia and veneering porcelain (9.22 ± 0.20 MPa) (P<0.05). CONCLUSIONS A graded glass-zirconia structure can be fabricated by the glass infiltration/densification technique, and this structure exhibits a strong core-veneer bond.

Evaluation of the effect of time on the distribution of zinc oxide nanoparticles in tissues of rats and mice: a systematic review.

To evaluate the time effect on the distribution of zinc oxide nanoparticles (ZnO NPs) in tissues from rats and mice, a search on the PubMed, Embase, SpringerLink, Scopus, Science Direct, Cochrane, CNKI, Wanfang, and vip databases up to September 2014 was performed, followed by screening, data extraction, and quality assessment. Thirteen studies were included. At 24 h, Zn content was mainly distributed in the liver, kidney, and lung. At ≥7 days, Zn content was mainly distributed in the liver, kidney, lung, and brain. ZnO NPs are readily deposited in tissues. Furthermore, as time increases, Zn content decreases in the liver and kidney, but increases in the brain.

Study of a new bone-targeting titanium implant–bone interface

New strategies involving bone-targeting titanium (Ti) implant–bone interface are required to enhance bone regeneration and osseointegration for orthopedic and dental implants, especially in osteoporotic subjects. In this study, a new dual-controlled, local, bone-targeting delivery system was successfully constructed by loading tetracycline-grafted simvastatin (SV)-loaded polymeric micelles in titania nanotube (TNT) arrays, and a bone-targeting Ti implant–bone interface was also successfully constructed by implanting the delivery system in vivo. The biological effects were evaluated both in vitro and in vivo. The results showed that Ti surfaces with TNT–bone-targeting micelles could promote cytoskeletal spreading, early adhesion, alkaline phosphatase activity, and extracellular osteocalcin concentrations of rat osteoblasts, with concomitant enhanced protein expression of bone morphogenetic protein (BMP)-2. A single-wall bone-defect implant model was established in normal and ovariectomized rats as postmenopausal osteoporosis models. Microcomputed tomography imaging and BMP-2 expression in vivo demonstrated that the implant with a TNT-targeting micelle surface was able to promote bone regeneration and osseointegration in both animal models. Therefore, beneficial biological effects were demonstrated both in vitro and in vivo, which indicated that the bone-targeting effects of micelles greatly enhance the bioavailability of SV on the implant–bone interface, and the provision of SV-loaded targeting micelles alone exhibits the potential for extensive application in improving local bone regeneration and osseointegration, especially in osteoporotic subjects.

An in vitro evaluation of the zirconia surface treatment by mesoporous zirconia coating on its bonding to resin cement

The effect of zirconia surface treatment by mesoporous zirconia coating on the microtensile bond strength (MTBS) between zirconia and resin cement was investigated in this work. 160 zirconia specimens were prepared and divided into four groups according to surface treatments: (1) airborne-particle-abrasion treatment (APA); (2) glass infiltration and hydrofluoric acid treatment (GI+HF); (3) mesoporous zirconia coating (MZ); and (4) no treatment (C). The as-prepared zirconia specimens were bonded using Panavia F2.0 and RelyX Unicem. The MTBS values were tested using a universal testing machine, and data were analyzed using ANOVA and SNK methods (a=0.05). The MTBS values obtained after GI+HF and MZ treatments were significantly higher than those obtained after APA and C treatments (P<0.05), especially for samples cemented with Panavia F2.0. The results reveal that zirconia surface treatments using GI+HF and MZ yield higher bond strength than those using APA or C, regardless of the resin cements.

Graded Nano Glass-Zirconia Material for Dental Applications-Part II Biocompatibility Evaluation

A graded glass/graded zirconia (G/Z) system was previously synthesized via the infiltration of a low modulus nanosized glass into a zirconia surface. The bond strength of G/Z to veneering porcelains was demonstrated to be 3-fold higher than in zirconia-based systems. Nevertheless, biocompatibility testing prior to the possible clinical application of G/Z systems is essential. Herein, such biocompatibility testing was performed with L-929 fibroblasts seeded onto G/Z and yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) for 2-72 h. Assessments included an oral mucous membrane irritation test in conjunction with analyses of cell viability, cell morphology, cell cycle, cell apoptosis, oxidative stress responses, inflammatory cytokine expression, and cellular toxicity. Cell viability tests showed no significant decrease in G/Z- and Y-TZP-treated cells over 72 h. Fluorescence and SEM images demonstrated that cell spreading on Y-TZP and G/Z was similar; cells were flattened and well-spread. Oxidative stress data for G/Z- and Y-TZP-treated cells showed no significant difference in ROS production. Cellular toxicity results for G/Z did not elicit significant differences in LDH release compared with Y-TZP over 72 h. G/Z and Y-TZP had no significant differences in IL-1α, IL-8, PGE2, and TNF-α expression and elicited significantly increased IL-8 expression compared with that of the untreated control group. Cells that were cultured with G/Z showed no significant changes in cell cycle distribution compared with Y-TZP or the untreated control group. Cells that were cultured with Y-TZP and G/Z showed no apoptosis compared to untreated controls at 24 and 48 h. According to the oral mucous membrane irritation test, scores for the macroscopic and microscopic observations for both G/Z and Y-TZP sides were 0, demonstrating no consequent irritation. Therefore, the excellent biocompatibility of G/Z indicates that it has potential for future clinical applications.

Bilingual Teaching Efficiency of Prosthodontics in Different Teaching Methods

Objective to compare bilingual teaching efficiency of expository teaching method and PBL teaching method in Prosthodontics. Methods 120 students were randomly divided into 2 groups (n = 60), one group was taught by expository teaching method and the other group was taught by PBL teaching method. The t test was used to analyze the final scores and Chi square test was used to deal with the questionnaires. Results The average score of expository teaching group was 100.22 ± 7.82, with statistical differences in the score of PBL teaching group, which was 131.28 ± 7.12 (P < 0.05). 45.0 % of students understood the teaching content in expository group and 80.0 % in PBL group; 48.3 % of students were satisfied with the expository teaching method and 75.0 % in PBL group. There were statistical differences between two groups (P < 0.05). Conclusion PBL teaching method is more efficiency than expository teaching method. Students feel easy to understand the teaching content in PBL teaching method and satisfied with the PBL teaching method. PBL teaching method deserves popularization in bilingual class of Prosthodontics.

Influence of mesoporous silica coating treatment on push-out bond strength of zirconia posts.

This study aimed to evaluate the influence of mesoporous silica coating surface treatments on push-out bond strength of zirconia posts. Zirconia posts (Cosmopost) were treated with vehicle (control), sandblasting plus silane application (SB+SI), a combination of sandblasting, mesoporous silica coating and silane application (SB+MSC+SI) (n=10/group). Specimens were cemented with RelyX Unicem (3M ESPE, Germany) then horizontally segmented into three sections and subjected to a push-out test. Surface treatments showed significant higher bond strength than the control group, and SB+MSC+SI group presented higher values than SB+SI group (P<0.05). No significant differences were found in bond strength among root regions (P>0.05). We conclude that the combination of mesoporous silica coating and silane application greatly enhance the push-out bond strength of zirconia posts.

Advances in application of CBCT in diagnosis and guidance of operation designing of mandible fracture

The purpose was to illustrate and discuss the importance of cone beam computed tomography (CBCT) for accurate diagnosis of mandible fracture and designing of surgery. Two cases of mandible fracture were selected in this report. The history of patients revealed traumatic injuries on their faces because of accidents. The patients were primarily examined with 2D panoramic radiography which did not provide adequate information. Both cases were thereafter investigated preoperatively with CBCT. As the results, CBCT showed the displacement of fracture ends clearly which were useful for diagnosis and designing of surgery. We concluded that CBCT allowed accurate diagnosis of mandible fractures and also provided guidance for operational design.

Clinical study of Cone Beam CT imaging and 3D reconstruction aided detection accuracy of impacted tooth

The objective is to explore the efficiency and accuracy of the KODAK 9000C Dental Cone Beam CT imaging and 3D reconstruction to detect the impacted tooth and help decide the orthodontic-surgical treatment. 30 patients who were diagnosed to suffer an impacted tooth were selected to have a Cone Beam CT scan. After scanning, we used the technique of image processing and sharpening to make a clear three-dimensional reconstruction model of the impacted tooth. The three-dimensional reconstruction model had collected these medical information including site, extent, shape, and other characteristic features of the impacted tooth. Then we applied the processing technique which could adjust the color of the impacted tooth and the surrounding bone tissue so as to separate them, as the result, we could get a 3D reconstructed visualization image of the impacted tooth. A clinician could study the precise radiographic information about the segmented impacted tooth which helped to decide the orthodontics treatment to pull the impacted tooth back to its anatomical position. All the patients had accepted the orthodontics treatment aided by processed Cone Beam CT 3D reconstruction image and received a satisfying treatment outcome. It was concluded that the digital image processing technique could separate out the impacted tooth successfully and provide the accurate radiographic information to help the clinician decide an optimal orthodontics treatment plan.