Effect of low-power laser irradiation on the shear bond strength and thermal changes across different zirconia thicknesses using different irradiation times.

PURPOSE: To investigate the effect of irradiation time and zirconia thickness using low power Er,Cr:YSGG laser irradiation (for debonding purposes) on the thermal changes and shear bond strength of resin-bonded 3% mol yttrium oxide stabilized tetragonal zirconia polycrystal (3Y-TZP) specimens. MATERIALS AND METHODS: 3Y-TZP slices of 0.5, 2, and 3 mm thick were used. The temperature during laser irradiation using single spot irradiation at different times (30, 60, 90, and 120 s) and line scanning irradiation from one spot tanother at three different distances (2-, 4-, and 6- mm) were recorded. Single spot and line scanning irradiation data were analyzed using three-way ANOVA (α: 0.05) and generalized linear mixed model, respectively. Non-irradiated (control) and irradiated resin-bonded 3Y-TZP specimens were shear tested, and the data were analyzed using two-way ANOVA (α: 0.05). RESULTS: Under single spot irradiation, the laser-induced temperature was higher through thin 3Y-TZP at any time compared to thick 3Y-TZP. For the line scanning method, short distances (2 and 4 mm) resulted in a significant increase in temperature in 0.5 mm thick specimens. Laser irradiation significantly decreased the shear bond strength of the 0.5 mm group compared to the non-irradiated group. After irradiation, the bond strength of the 2- and 3-mm thick 3Y-TZP was similar to the non-irradiated group. CONCLUSION: The temperature and bond strength of low-power laser irradiated 3Y-TZP specimens was affected by the specimen thickness but not by the irradiation time tested. Low-power laser irradiation is an effective debonding method for thin Y-TZP restorations.

Functionalized Collagen/Elastin-like Polypeptide Hydrogels for Craniofacial Bone Regeneration.

Critical-sized cranial bone defects fail to re-ossify and require the surgical intervention of cranioplasty. To achieve superior bone healing in such cases, a hydrogel consisting of an interpenetrating network of collagen and elastin-like polypeptide to encapsulate bone morphogenetic protein-2 (BMP-2), doxycycline, and 45S5 Bioglass is developed. This hydrogel has an appropriate elastic modulus of 39 ± 2.2 kPa to allow proper handling during implantation. The hydrogel promotes human adipose-derived stem attachment, proliferation, and differentiation toward the osteogenic lineage, including the deposition of hydroxyapatite particles embedded within a collagenous fibrillar structure after 21 days of in vitro culture. After eight weeks of implantation of the acellular hydrogel in a critical-sized rat cranial defect model, only a small quantity of various pro-inflammatory (< 20 pg mg-1 ) and anti-inflammatory (< 10 pg mg-1 ) factors in the adjacent cranial tissue is noticed, indicating the overall biocompatibility of the hydrogel. Scanning electron microscopy evidenced the presence of new fibrous extracellular matrix and mineral aggregates at the defect site, with calcium/phosphorus ratio of 0.5 and 2.0 by eight and twelve weeks, respectively. Microcomputed tomography (Micro-CT) and histological analyses showed formation of mature mineralized tissue that bridged with the surrounding bone. Taken together, the acellular composite hydrogel shows great promise for superior bone healing after cranioplasty.

Relationship between fracture toughness and fractal dimensional increment in two types of dental glass-ceramics with different fracture surface roughness.

OBJECTIVES: Previous studies have reported the fractal dimensional increment of glass-ceramic fracture surfaces. The objective of this study was to determine the relationship between fracture toughness and fractal dimensional increment of two dental glass-ceramics with different volume fraction of crystals and different fracture surface roughness. METHODS: Bar-shaped specimens were prepared from lithium disilicate (LDS) and nanofluorapatite (NFA) glass-ceramics. One face of each specimen was indented using a Knoop diamond at 25 N (LDS) or 10 N (NFA) followed by loading in 4-point, or 3-point flexure, respectively, until failure. Fracture toughness (Kc) was calculated using the surface crack in flexure (SCF) technique (ASTM C1421). Epoxy replicas of the fracture surfaces were scanned using the atomic force microscope (AFM) followed by noise filtering. The FRACTALS software was used to determine the fractal dimensional increment (D*) by the Minkowski cover algorithm. RESULTS: Median (25%, 75% quartiles) fracture toughness of LDS bars were 1.62 (1.59, 1.69) MPa m1/2 and NFA bars were 0.68 (0.66, 0.74) MPa m1/2, respectively. The median fractal dimension (D) value (25%, 75% quartiles) before noise filtering were 2.16 (2.15, 2.17) and after noise filtering were 2.14 (2.14, 2.15) for LDS and before noise filtering were 2.29 (2.21, 2.38) and after noise filtering were 2.17 (2.17, 2.18) for NFA. Median (25%, 75% quartiles) surface roughness (Ra) before noise filtering were 139 (119, 188) nm and after noise filtering were 137 (118, 187) nm for LDS and before noise filtering were 7 (6, 15) nm and after noise filtering were 7 (6, 15) nm for NFA. SIGNIFICANCE: Noise filtering successfully eliminated noise from the material with smooth fracture surfaces (NFA), decreasing the measured fractal dimension. The NFA data fit a Kc vs. D*1/2 statistical model for fused silica previously tested using a similar technique. The equation relating fracture toughness to the fractal dimension was modified, accounting for the toughening mechanisms. Fractal analysis with noise filtering can be used to estimate the fracture toughness of dental glass-ceramics that do not exhibit crack bridging.

Fractal analysis at varying locations of clinically failed zirconia dental implants.

OBJECTIVES: Previous studies have shown that the fracture toughness of ceramics can be determined from the fractal dimensions (D) of their fracture surfaces and that the surface should be leveled to obtain an accurate D measurement. This study was to determine the effects of leveling operations and distance from the failure origin on the D values. METHODS: Twelve clinically failed zirconia implants from four different manufacturers: Axis Biodental (n=7), Z-Systems (n=3), Straumann (n=1), and Swiss Dental Solutions (n=1) were obtained from one of the authors and thoroughly cleaned. Epoxy replicas were made of three locations along the crack path in the center region of each fracture surface (near origin (O), hackle (H), and near compression curl (CC)) using a light body polyvinyl siloxane impression material. Surfaces were scanned in ScanAsyst mode with a scan size of 5µm×5µm and a scan rate of 0.592Hz using the atomic force microscope. The surface scans were then leveled using 1st order flattening operation in the AFM analysis software. The height data before and after the operation were imported into a custom MathCAD script, and FRACTALS software was used to determine the D value by Minkowski Cover algorithm, which was shown previously to be the algorithm with the highest precision. A Wilcoxon signed-rank test, two-way repeated-measures ANOVA, and one-way repeated-measures ANOVA were performed as detailed below. RESULTS: The data were not normally distributed (S-W p≤0.05), so a non-parametric repeated measures test (Wilcoxon signed-rank test) was selected. The median D values before and after leveling were 2.161 and 2.174, respectively. There was a significant difference before and after leveling (p<0.001). The two-way repeated-measures ANOVA showed no significant difference among the D values for different implant brands (p=0.66) and scanning locations on the fracture surface (p=0.83). After eliminating the implant brand as a factor, the data passed normality and equal variance tests (S-W p=0.88, BF p=0.15). The mean D values and standard deviations from the three locations (O, H, CC) were 2.183±0.031, 2.179±0.024, and 2.175±0.018, respectively. One-way repeated measures ANOVA showed no significant effect of scanning location (p=0.74). SIGNIFICANCE: The leveling operation successfully removed the tilt without decreasing surface tortuosity, as it increased the D values significantly. The fractal dimension was the same at the three locations on the fracture surfaces. This means that hackle and compression curl regions can be used to determine fracture toughness when the failure origin has been lost.

Collagen-Elastin-Like Polypeptide-Bioglass Scaffolds for Guided Bone Regeneration.

The goals of this study are to evaluate the ability of the multicomponent collagen-elastin-like polypeptide (ELP)-Bioglass scaffolds to support osteogenesis of rat mesenchymal stem cells (rMSCs), demonstrate in vivo biocompatibility by subcutaneous implantation in Sprague-Dawley rats, monitor degradation noninvasively, and finally assess the scaffold's ability in healing critical-sized cranial bone defects. The collagen-ELP-Bioglass scaffold supports the in vitro osteogenic differentiation of rMSCs over a 3 week culture period. The cellular (rMSC-containing) or acellular scaffolds implanted in the subcutaneous pockets of rats do not cause any local or systemic toxic effects or tumors. The real-time monitoring of the fluorescently labeled scaffolds by IVIS reveals that the scaffolds remain at the site of implantation for up to three weeks, during which they degrade gradually. Micro-CT analysis shows that the bilateral cranial critical-sized defects created in rats lead to greater bone regeneration when filled with cellular scaffolds. Bone mineral density and bone microarchitectural parameters are comparable among different scaffold groups, but the histological analysis reveals increased formation of high-quality mature bone in the cellular group, while the acellular group has immature bone and organized connective tissue. These results suggest that the rMSC-seeded collagen-ELP-Bioglass composite scaffolds can aid in better bone healing process.

In vitro study of fracture load and fracture pattern of ceramic crowns: a finite element and fractography analysis.

PURPOSE: This in vitro study investigated the null hypothesis that metal-free crowns induce fracture loads and mechanical behavior similar to metal ceramic systems and to study the fracture pattern of ceramic crowns under compressive loads using finite element and fractography analyses. MATERIALS AND METHODS: Six groups (n = 8) with crowns from different systems were compared: conventional metal ceramic (Noritake) (CMC); modified metal ceramic (Noritake) (MMC); lithium disilicate-reinforced ceramic (IPS Empress II) (EMP); leucite-reinforced ceramic (Cergogold) (CERG); leucite fluoride-apatite reinforced ceramic (IPS d.Sign) (SIGN); and polymer crowns (Targis) (TARG). Standardized crown preparations were performed on bovine roots containing NiCr metal dowels and resin cores. Crowns were fabricated using the ceramics listed, cemented with dual-cure resin cement, and submitted to compressive loads in a mechanical testing machine at a 0.5-mm/min crosshead speed. Data were submitted to one-way ANOVA and Tukey tests, and fractured specimens were visually inspected under a stereomicroscope (20×) to determine the type of fracture. Maximum principal stress (MPS) distributions were calculated using finite element analysis, and fracture origin and the correlation with the fracture type were determined using fractography. RESULTS: Mean values of fracture resistance (N) for all groups were: CMC: 1383 ± 298 (a); MMC: 1691 ± 236 (a); EMP: 657 ± 153 (b); CERG: 546 ± 149 (bc); SIGN: 443 ± 126 (c); TARG: 749 ± 113 (b). Statistical results showed significant differences among groups (p < 0.05) represented by different lowercase letters. Metal ceramic crowns presented fracture loads significantly higher than the others. Ceramic specimens presented high incidence of fractures involving either the core or the tooth, and all fractures of polymer crown specimens involved the tooth in a catastrophic way. Based on stress and fractographic analyses it was determined that fracture occurred from the occlusal to the cervical direction. CONCLUSIONS: Within the limitations of this study, the results indicated that the use of ceramic and polymer crowns without a core reinforcement should be carefully evaluated before clinical use due to the high incidence of failure with tooth involvement. This mainly occurred for the polymer crown group, although the fracture load was higher than normal occlusal forces. High tensile stress concentrations were found around and between the occlusal loading points. Fractographic analysis indicated fracture originating from the load point and propagating from the occlusal surface toward the cervical area, which is the opposite direction of that observed in clinical situations.

Effect of bleaching agent on dental ceramics roughness

The aim of this study was to assess the effect of bleaching agents (10% and 16% carbamide peroxide) on the roughness of two dental ceramics in vitro, and to analyze the surface by scanning electronic microscopy (SEM). Two bleaching agents (10% and 16% / Whiteness, FGM Gel) and two microparticle feldspathic ceramics (Vita VM7 and Vita VM13) were used. Forty disks of Vita VM7 and Vita VM13 ceramic were manufactured, measuring 4mm in diameter and 4mm high, in accordance with the manufacturers’ recommendations, and were divided into 4 groups (n=10): (1) VM7 + Whiteness 10%; (2) VM7 + Whiteness 16%; (3) VM13 + Whiteness 10%; (4) VM13 + Whiteness 16%. The bleaching agent was applied for 8 hours a day for 15 days and during the intervals the test specimens were stored in distilled water at 37°C. The roughness (Ra) of the test specimens was evaluated before and after exposure to the bleaching agents using a laser roughness meter and the topographic description was analyzed by SEM. The statistical analysis of roughness data showed significant differences in the VM7 groups, using paired t-test, p=0.05 (VM7 + Whiteness 10%: p=0.002; VM7 + Whiteness 16%: p=0.001) and two-sample t-test (VM7 p=0,047), and no significant difference was found among VM13 groups. The qualitative SEM analysis showed different degrees of surface changes. The results suggest that the roughness of the tested ceramic surfaces increased after exposure to the bleaching agents.

O objetivo do estudo foi avaliar o efeito de agente clareador (10% e 16% de peroxido de carbamida) na rugosidade de duas ceramicas dentais in vitro e analisar a superficie atraves da microscopia eletronica de varredura (SEM). Foram utilizados dois agentes clareadores (10% e 16% / Whiteness, FGM Gel) e duas ceramicas feldspaticas microparticuladas (Vita VM7 e Vita VM13). Foram confeccionados quarenta discos de ceramica Vita VM7 e Vita VM13, com 4mm de diametro e 4mm de altura, de acordo com as recomendacoes do fabricante, sendo divididos em 4 grupos (n=10): G1- VM7 + Whiteness 10%, G2- VM7 + Whiteness 16%, G3- VM13 + Whiteness 10% e G4- VM13 + Whiteness 16%. O agente clareador foi aplicado por 8 horas durante 15 dias e durante os intervalos os corpos de prova (cp) ficavam armazenados em agua destilada a 37°C. A rugosidade (Ra) dos cp foi avaliada antes e apos a exposicao aos agentes clareadores utilizando o rugosimetro a laser Perthomether S8P, e a descricao topografica foi analisada no MEV. A analise estatistica na rugosidade mostrou diferenca significante entre os grupos da VM7, usando o teste pareado, p=0.05 (VM7 + Whiteness 10%: p=0.002; VM7 + Whiteness 16%: p=0.001) e nao foi encontrado diferenca estatistica para os grupos da VM13. A descricao qualitativa no SEM evidenciou alteracao nas superficies em diferentes graus. Os resultados sugeriram que as superficies das ceramicas testadas aumentaram a rugosidade apos a exposicao ao agente clareador.

The effect of carbamide peroxide bleaching agents on the microhardness of dental ceramics.

This study examined the effect of 10% and 16% carbamide peroxide bleaching agents on the surface microhardness of micro-particulate feldspathic ceramics (VM7 and VM13, Vita Zahnfabrik). Forty specimens (8-mm diameter, 2-mm thickness) were divided into four groups (n=10): GI-VM7 + 10% Whiteness, G2-VM7 + 16% Whiteness, G3-VM13 + 10% and G4-VM13 + 16% Whiteness. The home-use bleaching agents were applied for 8 hours on 15 days, and the specimens were stored in distilled water at 37 degrees C. The Vickers hardness number (HV) was determined for each specimen. Data were analyzed by the Wilcoxon and Mann-Whitney tests (p < 0.05). The microhardness values before exposure were: g1-433 (57); g2-486 (22); g3-509 (28); g4-518 (24), and after exposure: G1-349 (32); G2-496 (95); G3-519 (38); G4-502 (81). G2 exhibited a higher and significant difference than GI in VM7 groups, and the effect of bleaching concentration was shown to be significant by the Mann-Whitney test. And for VM13, both the Wilcoxon and Mann-Whitney tests showed no significant differences. When using 10% carbamide peroxide, the microhardness of VM7 ceramic was affected, and there were no effect on the microhardness between VM7 and VM13 ceramics when 16% carbamide peroxide was used.

The effect of carbamide peroxide bleaching agents on the microhardness of dental ceramics

This study examined the effect of 10% and 16% carbamide peroxide bleaching agents on the surface microhardness of micro-particulate feldspathic ceramics (VM7 and VM13, Vita Zahnfabrik). Forty specimens (8-mm diameter, 2-mm thickness) were divided into four groups (n=10): G1- VM7 + 10% Whiteness, G2- VM7 + 16% Whiteness, G3- VM13 + 10% and G4- VM13 + 16% Whiteness. The home-use bleaching agents were applied for 8 hours on 15 days, and the specimens were stored in distilled water at 37°C. The Vickers hardness number (HV) was determined for each specimen. Data were analyzed by the Wilcoxon and Mann- Whitney tests (p<0.05). The microhardness values before exposure were: g1- 433 (57); g2- 486 (22); g3- 509 (28); g4- 518 (24), and after exposure: G1- 349 (32); G2- 496 (95); G3- 519 (38); G4- 502 (81). G2 exhibited a higher and significant difference than G1 in VM7 groups, and the effect of bleaching concentration was shown to be significant by the Mann-Whitney test. And for VM13, both the Wilcoxon and Mann-Whitney tests showed no significant differences. When using 10% carbamide peroxide, the microhardness of VM7 ceramic was affected, and there were no effect on the microhardness between VM7 and VM13 ceramics when 16% carbamide peroxide was used.

Este estudo examinou o efeito do agente clareador peroxido de carbamida a 10% e a 16% na microdureza superficial de ceramicas feldspaticas micro-particuladas (VM7 e VM13, Vita Zahnfabrik). Quarenta corpos-de-prova (8 mm de diametro, 2 mm de espessura) foram divididos em quatro grupos (n=10): G1- VM7 + 10% Whiteness, G2- VM7 + 16% Whiteness, G3- VM13 + 10% e G4- VM13 + 16% Whiteness. Os agentes clareadores foram aplicados por 8 horas durante 15 dias e os cp foram armazenados em agua destilada a 37°C. A dureza Vickers (HV) de cada cp foi determinada. Os dados foram analisados pelos testes de Wilcoxon e Mann-Whitney (p<0.05). Os valores da dureza antes da exposicao ao agente clareador foram: g1- 433 (57); g2- 486 (22); g3- 509 (28); g4- 518 (24), e depois da exposicao: G1- 349 (32); G2- 496 (95); G3- 519 (38); G4- 502 (81). G2 exibiu diferenca significante e microdureza maior comparado ao G1 nos grupos da VM7 e o efeito da concentracao do clareador foi significante, apresentados atraves dos testes Mann-Whitney. Para VM13, ambos testes, Wilcoxon e Mann-Whitney, nao apresentaram diferenca significante. Quando o peroxido de carbamida a 10% foi avaliado, a microdureza da ceramica VM7 foi afetada, e nao houve diferenca na microdureza entre as ceramicas VM7 e VM13 quando o peroxido de carbamida a 16% foi utilizado.

Mechanical strength and subcritical crack growth under wet cyclic loading of glass-infiltrated dental ceramics.

OBJECTIVES: Evaluate the flexural strength (sigma) and subcritical crack growth (SCG) under cyclic loading of glass-infiltrated alumina-based (IA, In-Ceram Alumina) and zirconia-reinforced (IZ, In-Ceram Zirconia) ceramics, testing the hypothesis that wet environment influences the SCG of both ceramics when submitted to cyclic loading. METHODS: Bar-shaped specimens of IA (n=45) and IZ (n=45) were fabricated and loaded in three-point bending (3P) in 37 degrees C artificial saliva (IA(3P) and IZ(3P)) and cyclic fatigued (F) in dry (D) and wet (W) conditions (IA(FD), IA(FW), IZ(FD), IZ(FW)). The initial sigma and the number of cycles to fracture were obtained from 3P and F tests, respectively. Data was examined using Weibull statistics. The SCG behavior was described in terms of crack velocity as a function of maximum stress intensity factor (K(Imax)). RESULTS: The Weibull moduli (m=8) were similar for both ceramics. The characteristic strength (sigma(0)) of IA and IZ was and 466MPa 550MPa, respectively. The wet environment significantly increased the SCG of IZ, whereas a less evident effect was observed for IA. In general, both ceramics were prone to SCG, with crack propagation occurring at K(I) as low as 43-48% of their critical K(I). The highest sigma of IZ should lead to longer lifetimes for similar loading conditions. SIGNIFICANCE: Water combined with cyclic loading causes pronounced SCG in IZ and IA materials. The lifetime of dental restorations based on these ceramics is expected to increase by reducing their direct exposure to wet conditions and/or by using high content zirconia ceramics with higher strength.

Effect of bleaching agent on dental ceramics roughness.

The aim of this study was to assess the effect of bleaching agents (10% and 16% carbamide peroxide) on the roughness of two dental ceramics in vitro, and to analyze the surface by scanning electronic microscopy (SEM). Two bleaching agents (10% and 16%/Whiteness, FGM Gel) and two microparticle feldspathic ceramics (Vita VM7 and Vita VM13) were used. Forty disks of Vita VM7 and Vita VM13 ceramic were manufactured, measuring 4 mm in diameter and 4 mm high, in accordance with the manufacturers' recommendations, and were divided into 4 groups (n = 10): (1) VM7 + Whiteness 10%; (2) VM7 + Whiteness 16%; (3) VM13 + Whiteness 10%; (4) VM13 + Whiteness 16%. The bleaching agent was applied for 8 hours a day for 15 days and during the intervals the test specimens were stored in distilled water at 37 degrees C. The roughness (Ra) of the test specimens was evaluated before and after exposure to the bleaching agents using a laser roughness meter and the topographic description was analyzed by SEM. The statistical analysis of roughness data showed significant differences in the VM7 groups, using paired t-test, p = 0.05 (VM7 + Whiteness 10%: p = 0.002; VM7 + Whiteness 16%: p = 0.001) and two-sample t-test (VM7 p = 0.047), and no significant difference was found among VM13 groups. The qualitative SEM analysis showed different degrees of surface changes. The results suggest that the roughness of the tested ceramic surfaces increased after exposure to the bleaching agents.

Flexural strength of glass-infiltrated zirconia/alumina-based ceramics and feldspathic veneering porcelains.

PURPOSE: To compare the flexural strength of two glass-infiltrated high-strength ceramics and two veneering glass-ceramics. MATERIALS AND METHODS: Four ceramic materials were tested: two glass-infiltrated high-strength ceramics used as framework in metal-free restorations [In-Ceram Zirconia IZ (Gr1) and In-Ceram Alumina IA (Gr2)], and two glass-ceramics used as veneering material in metal-free restorations [Vita VM7 (Gr3) and Vitadur-alpha (Gr4)]. Bar specimens (25 x 5 x 2 mm3) made from core ceramics, alumina, and zirconia/alumina composites were prepared and applied to a silicone mold, which rested on a base from a gypsum die material. The IZ and IA specimens were partially sintered in an In-Ceram furnace according to the firing cycle of each material, and then were infiltrated with a low-viscosity glass to yield bar specimens of high density and strength. The Vita VM7 and Vitadur-alpha specimens were made from veneering materials, by vibration of slurry porcelain powder and condensation into a two-part brass Teflon matrix (25 x 5 x 2 mm3). Excess water was removed with absorbent paper. The veneering ceramic specimens were then removed from the matrix and were fired as recommended by the manufacturer. Another ceramic application and sintering were performed to compensate the contraction of the feldspar ceramic. The bar specimens were then tested in a three-point bending test. RESULTS: The core materials (Gr1: 436.1 +/- 54.8; Gr2: 419.4 +/- 83.8) presented significantly higher flexural strength (MPa) than the veneer ceramics (Gr3: 63.5 +/- 9.9; Gr4: 57.8 +/- 12.7). CONCLUSION: In-Ceram Alumina and Zirconia were similar statistically and more resistant than VM7 and Vitadur-alpha.