Research progress on the application of Er: YAG laser removing all-ceramic restorations / 口腔疾病防治

@#All-ceramic restorations are widely used in oral restoration because of their beauty and high strength. Glass ceramics and zirconia all-ceramic materials are the two most widely used all-ceramic materials in the clinic. However, when all-ceramic restorations need to be removed due to marginal microleakage and secondary caries, its high strength and high bonding strength greatly increase the difficulty of removal. In recent years, clinicians have tried to use Er: YAG lasers to remove all-ceramic restorations. The Er: YAG laser can be safely and efficiently applied to the removal of glass restorations, and it can also play a role in thinner zirconia restorations. Various factors, such as the material and thickness of the all-ceramic restoration, the type of cement, and the laser power, can affect the speed of removal of the Er: YAG laser. However, the current research is limited to case reports and in vitro studies, lacking systematic clinical research. The specific mechanism of Er: YAG laser removal of all-ceramic restorations and the influence of laser frequency, adhesive type, and abutment on the removal speed need to be further demonstrated by follow-up research.

The Effect of GaAlAs Laser, Sandblasting, and Primers on Bond Strength between Zirconia Ceramic and Direct Resin Composite after Thermocycling / O efeito do laser de GaAlAs, jateamento e primers na resistência de união entre cerâmica de zircônia e resina composta direta após termociclagem

Objective: This study was conducted to evaluate the shear bond strength (SBS) of resin composite on zirconia ceramic after different surface treatments and thermocycling. Material and Methods: Two hundred and seven zirconia specimens were divided into 9 groups and treated as follows: Group C­no treatment (served as the control); Group PC­Clearfil Ceramic primer (CP); Group PZ­Z-Prime Plus primer (ZP); Group A­sandblasted with 50 µm Al2O3 at 0.25 MPa for 20 s at a distance of 10 mm; Group AC­sandblasted and coated with CP; Group AZ­sandblasted and coated with ZP; Group L­GaAlAs diode laser with 808 ± 5 mm wavelength, 3 watts power, and 10 Hz frequency; Group LC­GaAlAs diode laser coated with CP; and Group LZ­GaAlAs diode laser coated with ZP. All specimens were directly bonded with a resin composite cylinder using Adper Scotchbond Multi-purpose. Specimens were stored at 37ºC for 30 days and subjected to 2,500 thermocycles from 5ºC and 55ºC before the SBS was performed. One-way ANOVA and Tukey's HSD test (α = 0.05) were performed. Surface topography changes were evaluated with a scanning electron microscope (SEM). Results:Sandblasting combined with CP or ZP (25.08 ± 0.86 and 24.78 ± 0.13 MPa, respectively) yielded the highest SBS and was significantly different from other methods (p < 0.05). SEM showed various degrees of changes depending on different surface treatments. Conclusion: Surface treatment by sandblasting combined with a CP or ZP significantly provide the highest SBS between zirconia and resin composite (AU)

Objetivo: Este estudo foi conduzido para avaliar a resistência ao cisalhamento (SBS) de resina composta em cerâmica de zircônia após diferentes tratamentos de superfície e termociclagem. Material e Métodos:Duzentos e sete espécimes de zircônia foram divididos em 9 grupos e tratados da seguinte forma: Grupo C­ sem tratamento (serviu como controle); Grupo PC­Clearfil Ceramic primer (CP); Grupo PZ­Z-Prime Plus primer (ZP); Grupo A - jateado com 50 µm de Al2O3 a 0,25 MPa por 20 s a uma distância de 10 mm; Grupo AC - jateado e revestido com CP; Grupo AZ - jateado e revestido com ZP; Grupo L ­ Laser de diodo GaAlAs com comprimento de onda de 808 ± 5 mm, potência de 3 watts e frequência de 10 Hz; Grupo LC ­Laser de diodo GaAlAs revestido com CP; e Grupo LZ ­ Laser de diodo GaAlAs revestido com ZP. Todos os espécimes foram diretamente colados com um cilindro de resina composta usando Adper Scotchbond Multi-purpose. As amostras foram armazenadas a 37ºC por 30 dias e submetidas a 2.500 termociclos de 5ºC e 55ºC antes da realização do SBS. ANOVA unilateral e teste HSD de Tukey (α = 0,05) foram realizados. As mudanças na topografia da superfície foram avaliadas com um microscópio eletrônico de varredura (MEV). Resultados:O jato de areia combinado com CP ou ZP (25,08 ± 0,86 e 24,78 ± 0,13 MPa, respectivamente) rendeu o maior SBS e foi significativamente diferente dos outros métodos (p < 0,05). SEM mostrou vários graus de mudanças dependendo dos diferentes tratamentos de superfície. Conclusão: O tratamento de superfície por jato de areia combinado com um CP ou ZP fornece significativamente o maior SBS entre a zircônia e a resina composta (AU)

Bond Strength Between Resin Cement to High-Translucency Zirconia Following Sandblasting And Non-Thermal Plasma Treatment / Resistência de união entre cimento resinoso e zircônia de alta translucidez após tratamento de jateamento e plasma não térmico

Objective: The aim of this study was to compare the bond strength of High-Translucency zirconia (HT) and lithium disilicate dental ceramics, under different surface treatments. Material And Methods: For this, ceramics were divided into groups: Control Group (C) (n = 5), lithium disilicate sheets, conditioned with 10% hydrofluoric acid, followed by application of 37% phosphoric acid, silane and universal adhesive application; Group HTAI (n = 5), HT zirconia sheets were blasted with silica oxide, followed by the application of universal adhesive; Group HTPAI (n = 5), HT zirconia sheets were blasted with silica oxide, followed by the application of non-thermal plasma and universal adhesive and the HTP Group (n = 5), HT zirconia received only the application of non-thermal argon plasma. Subsequently, the specimens of each group were subjected to a cementation process with resin cement, obtaining cylinders. After 24 h of storage, in distilled water, at 37°C, the specimens were subjected to a mechanical micro-shear test. The data obtained were submitted to ANOVA One-way followed by the Tukey test (5%). Results: The HTP Group was excluded from the statistical analysis, as adhesions failed within the storage period. In addition, it was not possible to verify a statistical difference between the control group C and the experimental groups HTAI and HTPAI. Conclusion: The results showed that the applicability of high translucency zirconia can potentially be compared to the lithium disilicate bond strength, when submitted to the same surface treatments, except for the plasma application, which alone was not effective (AU)

Objetivo: O objetivo deste estudo foi comparar a resistência adesiva das cerâmicas dentárias de zircônia de alta translucidez e dissilicato de lítio. Materiais e Métodos: Para isso, cerâmicas foram divididas em grupos: Grupo Controle (C) (n = 5), lâminas de dissilicato de lítio, condicionadas com ácido fluorídrico 10%, seguido de aplicação do ácido fosfórico 37%, aplicação de silano e aplicação do adesivo universal; Grupo HTAI (n = 5), lâminas de zircônia HT foram submetidas ao jateamento com óxido de sílica, seguido da aplicação do adesivo universal; Grupo HTPAI (n = 5), lâminas de zircônia HT foram submetidas ao jateamento com óxido de sílica, seguido da aplicação do plasma não térmico e do adesivo universal e o Grupo HTP (n = 5), lâminas de zircônia HT receberam apenas a aplicação do plasma não térmico de argônio. Posteriormente, os espécimes de cada grupo foram submetidos a um processo de cimentação com cimento resinoso, obtendo-se cilindros. Após 24h, de armazenamento em água destilada a 37°C, os espécimes foram submetidos a ensaio mecânico de microcisalhamento. Os dados obtidos foram submetidos à ANOVA 1-fator seguido pelo teste de Tukey (5%). Resultados: O Grupo HTP foi descartado da análise estatística, pois as adesões falharam dentro do período de armazenamento. Além disso, não foi possível verificar diferença estatística entre o grupo controle C e os experimentais HTAI e HTPAI. Conclusão: Os resultados mostraram que a aplicabilidade das zircônias de alta translucidez pode potencialmente ser comparada à resistência adesiva da cerâmica de dissilicato de lítio, quando submetidas aos mesmos tratamentos de superfície, com exceção da aplicação de plasma, que isoladamente não foi efetiva (AU)

Effects of universal adhesives and resin cement on the shear bond strength of zirconia / 华西口腔医学杂志

OBJECTIVE@#To study the effects of universal adhesives and resin cement on the shear bond strength and durability of zirconia ceramics.@*METHODS@#Zirconia ceramics were sintered into 20 mm×10 mm×10 mm and 10 mm×10 mm×10 mm specimens. The experiment was divided into 12 groups. The two types of specimens were bonded using two variants of resin cement (RelyX Ultimate and Clearfil SAC self-adhesive resin cement), universal adhesives (non-adhesive, Scotchbond uni-versal adhesive, and Clearfil SE One adhesive), and storage conditions (water bath and water bath-thermal cycling). The shear bond strengths were tested, and the fracture morphologies were analyzed.@*RESULTS@#The cement (F=8.41, P<0.01) and adhesive (F=30.34, P<0.01) exerted a significant effect on the shear bond strength of zirconia, whereas storage condition showed no significant effect on this property (F=1.83, P=0.18). The lowest shear bond strength (14.02 MPa±6.86 MPa) was exhibited by the group treated with RelyX Ultimate resin cement, non-adhesive, and water bath-thermal cycling, whereas the highest shear bond strength (54.12 MPa±8.37 MPa) was displayed by the group treated with RelyX Ultimate resin cement, Scotchbond universal adhesive, and water bath-thermal cycling.@*CONCLUSIONS@#Universal adhesives can improve the durability of the bonding of resin cement to zirconia. If non-self-adhesive resin cement is used without a universal adhe-sive, the durability of the bond will be greatly reduced.

The effects of gingival biotype on the aesthetics of anterior teeth with all ceramic crown / 实用口腔医学杂志

56 teeth in 48 patients were divided into thick gingiva group (28 teeth)and thin gingiva group (28 teeth) and repaired with zirconia ceramic crown.Before 1 and 2 years after repair,gingival index,gingival margin recession and edge color satisfaction were evaluated.1 and 2 years after,repair gingival index was increase in thick group (P ＜ 0.05),but other indices were not (P ＞ 0.05);in thin gingiva group 2 years after repair the gingival margin recession index was increased(P ＜0.05),the other indices were not(P ＞ 0.05).

Reliability of flexural strength and subcritical crack growth of two kinds of zirconia ceramics / 实用口腔医学杂志

Objective:To evaluate the reliability of flexural strength and subcritical crack growth(SCG)of WL and HT zirconia ce-ramics under cyclic loading.Methods:Bar-shaped speciments of WL(n =30)and HT(n =30)were fabricated and loaded in three-point bending and cyclically fatigued.The flexural strength and the number of cycles to fracture were obtained from three-point flexural test and cyclic fatigue test respectively.Data were examined using Weibull statistics.Pairs law was used to analysize the subcritical crack growth(SCG),the behavior of which was described in terms of crack velocity as a function of maximum stress intensity factor (KImax ).Results:The Weibull module(m)of WL and HT was 10.64 and 12.04,the stress corrosion cracking susceptive indexes(n) 23.71 and 32.87,the SCG 90% and 76.7%,the KImax 49.6% and 50.9% of its maximum stress intensity factor(KIC ),respectively. Conclusion:WL and HT produce pronounced SCG.The minimum fatigue crack growth rate of HT is lower than that of WL(νHT <νWL ).

Analysis of linearity between light transmittance and color value of three different brands of zirconia ceramics / 第二军医大学学报

Objective To analyze the relationship between the light transmittance and the color value of 3 different brands of zirconia dental ceramic materials of various thicknesses and colors, so as to provide evidence for a new indicator to the Colorimetric system to better simulate the natural dentin color. Methods X-rite color i7 spectrophotometer was used to measure the transmittance and reflectance (L*, a*, b*) of three brands (Lava, Upcera, Doceram) of zirconia ceramic materials of different colors and different thicknesses (0.9, 0.6 and 0.3 mm). The results were analyzed by SPSS18.0 software to investigate the linearity of transmittance with thickness and color values of the materials. Results The transmittance was not significantly different among the three brands of zirconia ceramic materials (P>0.05); the transmittance ranges of different thicknesses of zirconia ceramic (0.9, 0.6 and 0.3 mm) were 13.63%-27.47%, 18.05%-33.96%, and 25.24%-39.73%, respectively, showing significant difference (P<0.05). There was a linear relation of the transmittance with the thickness and color values of the three brands of zirconia ceramic materials: Upcera:TT=0.366×L*-thickness×0.661-0.280×b*; Doceram: TT=0.524×L*-0.536×thickness-0.237×b*; Lava: TT=0.210×L*-0.610×thickness-0.164×b*. Conclusion The transmittance ranges of the three brands of zirconia ceramic material are similar. The transmittance decreases with increase of its thickness and increases with luminance increase. Bluer zirconia ceramic has higher transmittance. Therefore, introduction of transmittance value for ceramic restoration process is important to redefine the natural tooth color perception and representation.

An in vitro cytotoxicity study of colorized zirconia by immersion method / 实用口腔医学杂志

Objective:To evaluate the cytotoxicity of colorized zirconia ceramics.Methods:Zirconia ceramic 3Y-TZP blocks were colorized by NH4 VO3 ,FeCl3 ,Co(NO3 )3 ,Ni(NO3 )3 and MoCl3 respectively.The cytotoxicity of colorized zirconia to L-929 cells was examined by immersion method and MTT assay.Results:During 3 days culture,L929 cells in all groups showed similar prolifera-tion and normal morphology.The toxicity gradation of all groups was 0 -I.Conclusion:Zirconia ceramics colorized with the 5 kinds of colorants has no cytotoxicity.

Evaluation of shear-bond strength between different self-adhesive resin cements with phosphate monomer and zirconia ceramic before and after thermocycling / 대한치과보철학회지

PURPOSE: This study compared shear bond strengths of five self-adhesive cements with phosphate monomer to zirconium oxide ceramic with and without airborn particle abrasion. MATERIALS AND METHODS: One hundred zirconia samples were air-abraded (50 microm Al2O3). One hundred composite resin cylinders were fabricated. Composite cylinders were bonded to the zirconia samples with either Permacem 2.0 (P), Clearfil(TM) SA Luting (C), Multilink(R) Speed (M), RelyX(TM) U200 Automix (R), G-Cem LinkAce(TM) (G). All bonded specimens were stored in distilled water (37degrees C) for 24 h and half of them were additionally aged by thermocycling (5degrees C, 55degrees C, 5,000 times). The bonded specimens were loaded in shear force until fracture (1 mm/min) by using Universal Testing Machine (Model 4201, Instron Co, Canton, MA, USA). The failure sites were inspected under field-emission scanning electron microscopy. The data was analyzed with ANOVA, Tukey HSD post-hoc test and paired samples t-test (alpha=.05). RESULTS: Before and after thermocycling, Multilink(R) Speed (M) revealed higher shear-bond strength than the other cements. G-Cem LinkAce(TM) (G) showed significantly lower bond strengths after thermocycling than before treatment (P.05). CONCLUSION: Most self-adhesive cements with phosphate monomer showed high shear bond strength with zirconia ceramic and weren't influenced by thermocycling, so they seem to valuable to zirconia ceramic bonding.

Degree of conversion of two dual-cured resin cements light-irradiated through zirconia ceramic disks

PURPOSE: The aim of this Fourier transform infrared (FTIR) spectroscopic study was to measure the degree of conversion (DC) of dual-cured resin cements light-irradiated through zirconia ceramic disks with different thicknesses using various light-curing methods. MATERIALS AND METHODS: Zirconia ceramic disks (KT12) with three different thicknesses (1.0, 2.0, and 4.0 mm) were prepared. The light transmittance of the disks was measured using ultraviolet visible near-infrared spectroscopy. Four different light-curing protocols were used by combining two curing light modes (Elipar TriLight (standard mode) and bluephase G2 (high power mode)) with light-exposure times of 40 and 120 seconds. The DCs of the two dual-cured resin cements (Duo-Link and Panavia F2.0) light-irradiated through the disks was analyzed at three time intervals (3, 7, and 10 minutes) by FTIR spectroscopy. The data was analyzed using repeated measures ANOVA (alpha=.05).Two-way ANOVA and Tukey post hoc test were used to analyze the 10 minute DC results. RESULTS: The 1.0 mm thick disk exhibited low light transmittance (<25%), and the transmittance decreased considerably with increasing disk thickness. All groups exhibited significantly higher 10 minute DC values than the 3 or 7 minute values (P<.05), but some exceptions were observed in Duo-Link. Two-way ANOVA revealed that the influence of the zirconia disk thickness on the 10 minute DC was dependent on the light-curing methods (P<.001). This finding was still valid even at 4.0 mm thickness, where substantial light attenuation took place. CONCLUSION: The curing of the dual-cured resin cements was affected significantly by the light-curing technique, even though the additional chemical polymerization mechanism worked effectively.

A systematic review of zirconia as an implant material.

The purpose of this systematic review was to assess the published data concerning zirconia dental implants from various aspects. To identify relevant literature an electronic search was performed of PubMed. Titles and abstracts were screened and articles that fulfilled the inclusion criteria were selected for a full-text reading. Articles were divided into four groups: 1) studies evaluating the mechanical properties of zirconia implants, 2) studies on osseointegration of zirconia, 3) studies on peri-implant tissue response to zirconia implant, and 4) studies on plaque accumulation with zirconia. Review of the selected articles showed that zirconia implants are reliable for placement in the jaw bone. Furthermore, zirconia implants present a material surface that is compatible with the peri-implant tissue and relatively less attractive to plaque. Based on the reviewed literature, it appears that zirconia has the potential to become the dental implant material of choice, especially for aesthetic restorations; however, some issues need to be studied further.

Evaluation of push-out bond strength of surface treatments of two esthetic posts.

Objectives: To evaluate the push-out bond strength of two surface treatments of a glass fiber and zirconia ceramic post. Materials and Methods: Sixty samples were fabricated and divided into two main groups according to the type of esthetic post indicated for maxillary central incisor: glass fiber post and zirconia ceramic post. Each group was subdivided to two subgroups according to the type of bond strength test either between post and root or between post and core. Each subgroup was further subdivided into three classes according to surface treatment: no treatment (control), sandblasting in conjunction with silica particles then silane coating (SB+SIC+SC), etching using hydrofluoric acid then silane coating (E+SC). For the subgroups of the bond strength between post and root, each class was subdivided into two subclasses according to the location of the sample (cervical or apical). Results: Bond strength to root canal or resin core were affected by the type of post, glass fiber post recorded significant higher bond strength than zirconia ceramic. Surface treatment recorded higher values for bond strength, SB+SIC+SC gave higher bond strength than E+SC. Cervical section recorded significant higher bond strength than apical section. Conclusions: Glass fiber posts recorded higher bond strength than glass ceramic post to both root canal and resin core. Surface treatments increase bond strength for glass fiber and zirconia ceramic posts to both root canal and resin core. SB+SIC+SC gave higher bond strength than E+SC. Bond strength at the cervical section is higher than at the apical section.

A comparative study on the fracture behavior of zironia, glass infiltrated alumina and PFM full crown system / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the fracture behavior of Zironia, glass infiltrated Alumina and PFM full crown system. MATERIALS AND METHODS: Fifteen crowns for each of 3 experimental groups (Zironia, glass infiltrated Alumina and PFM full crown) were made by the conventional method. The crowns mounted on the testing jig were inclined in 30 degrees to the long axis of the tooth and the universal testing machine was used to measure the fracture strength. RESULTS: 1. The mean fracture strengths were 588.3 +/- 49.6 MPa for zirconia system, 569.1 +/- 61.8 MPa for PFM system and 551.0 +/- 76.5 MPa for glass-infiltrated alumina system (P>.05). 2. The mean shear bond strengths were 25.5 +/- 5.6 MPa for zirconia system, 38.9 +/- 5.0 MPa for Ni-Cr alloy system and 39.4 +/- 5.1 MPa for glass-infiltrated alumina system. 3. The chemical bonding was observed at interfaces between PFM or glass-infiltrated alumina and veneering porcelain, however, no chemical bonding was observed at interface between zirconia and veneering porcelain. CONCLUSION: With the study, the fracture strengths of PFM crown system had a higher fracture strength than conventional zirconia system crown and glass-infiltrated alumina crowns. and than the shear bond strengths glass-infiltrated alumina system had a higher shear bond strength than conventional PFM system and zirconia system.

Zirconium for esthetic rehabilitation: An overview.

The demand for esthetic restorations has resulted in an increased use of dental ceramics for anterior and posterior restorations. A few decades ago, all-ceramic restorations were restricted to treatment in the anterior region, but now all-ceramic restorations can be made anywhere in the dentition. The properties of traditional ceramic materials, however, have limited their use to single crowns; larger restorations have been inadvisable because of insufficient strength. In attempts to meet the requirements for dental materials and improve strength and toughness, several new ceramic materials and techniques have been developed during the past few decades The paper reviews the current literature on dental zirconia with respect to survival, properties, marginal fit, cementation, esthetics and suggests clinical recommendations for their use.

Influence of porcelain veneering on the marginal fit of Digident and Lava CAD/CAM zirconia ceramic crowns

PURPOSE: Marginal fit is a very important factor considering the restoration's long-term success. However, adding porcelain to copings can cause distortion and lead to an inadequate fit which exposes more luting material to the oral environment and causes secondary caries. The purpose of this study was to compare the marginal fit of 2 different all-ceramic crown systems before and after porcelain veneering. This study was also intended to verify the marginal fit of crowns originated from green machining of partially sintered blocks of zirconia (Lava CAD/CAM system) and that of crowns obtained through machining of fully sintered blocks of zirconia (Digident CAD/CAM system). MATERIAL AND METHODS: 20 crowns were made per each system and the marginal fit was evaluated through a light microscope with image processing (Accura 2000) at 50 points that were randomly selected. Each crown was measured twice: the first measurement was done after obtaining a 0.5 mm coping and the second measurement was done after porcelain veneering. The means and standard deviations were calculated and statistical inferences among the 2 groups were made using independent t-test and within the same group through paired t-test. RESULTS: The means and standard deviations of the marginal fit were 61.52 +/- 2.88 micrometer for the Digident CAD/CAM zirconia ceramic crowns before porcelain veneering and 83.15 +/- 3.51 micrometer after porcelain veneering. Lava CAD/CAM zirconia ceramic crowns showed means and standard deviations of 62.22 +/- 1.78 micrometer before porcelain veneering and 82.03 +/- 1.85 micrometer after porcelain veneering. Both groups showed significant differences when analyzing the marginal gaps before and after porcelain veneering within each group. However, no significant differences were found when comparing the marginal gaps of each group before porcelain veneering and after porcelain veneering as well. CONCLUSION: The 2 all-ceramic crown systems showed marginal gaps that were within a reported clinically acceptable range of marginal discrepancy.

Fracture strength of zirconia ceramic crowns according to tooth position / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the fracture strength of the zirconia ceramic crowns according to tooth position. MATERIAL AND METHODS: After 10 metal dies were made for each group, the zirconia ceramic crowns were fabricated using CAD/CAM system (Lava(TM) All-Ceramic System) and each crown was cemented on each metal die with resin cement (Rely X(TM) Unicem). The cemented zirconia ceramic crowns mounted on the testing jig were inclined with 30 degrees to the long axis of the tooth and the universal testing machine was used to measure the fracture strength. RESULTS: 1. The fracture strength of the zirconia ceramic crown in the lower 1st molar (2963 N) had the highest and that in the lower central incisor (1035 N) had the lowest. 2. The fracture strength of zirconia ceramic crown was higher than that of the IPS Empress crowns in all tooth position. 3. The fracture mode of the crowns was similar. Most of fracture lines began at the loading area and extended through proximal surface perpendicular to the long axis of the crowns. 4. There were no significant differences on the fracture strength of the zirconia ceramic crowns according to tooth position except in premolar group. CONCLUSION: Within the limitations of this study, the results suggested that strength of zirconia ceramic crown is satisfactory for clinical use.

Shear bond strength of veneering porcelain to zirconia and metal cores

STATEMENT OF PROBLEM: Zirconia-based restorations have the common technical complication of delamination, or porcelain chipping, from the zirconia core. Thus the shear bond strength between the zirconia core and the veneering porcelain requires investigation in order to facilitate the material's clinical use. PURPOSE: The purpose of this study was to evaluate the bonding strength of the porcelain veneer to the zirconia core and to other various metal alloys (high noble metal alloy and base metal alloy). MATERIAL AND METHODS: 15 rectangular (4x4x9mm) specimens each of zirconia (Cercon), base metal alloy (Tillite), high noble metal alloy (Degudent H) were fabricated for the shear bond strength test. The veneering porcelain recommended by the manufacturer for each type of material was fired to the core in thickness of 3mm. After firing, the specimens were embedded in the PTFE mold, placed on a mounting jig, and subjected to shear force in a universal testing machine. Load was applied at a crosshead speed of 0.5mm/min until fracture. The average shear strength (MPa) was analyzed with the one-way ANOVA and the Tukey's test (alpha= .05). The fractured specimens were examined using SEM and EDX to determine the failure pattern. RESULTS: The mean shear strength (+/- SD) in MPa was 25.43 (+/- 3.12) in the zirconia group, 35.87 (+/- 4.23) in the base metal group, 38.00 (+/- 5.23) in the high noble metal group. The ANOVA showed a significant difference among groups, and the Tukey's test presented a significant difference between the zirconia group and the metal group. Microscopic examination showed that the failure primarily occurred near the interface with the residual veneering porcelain remaining on the core. CONCLUSION: There was a significant difference between the metal ceramic and zirconia ceramic group in shear bond strength. There was no significant difference between the base metal alloy and the high noble metal alloy.

Fracture load and marginal fitness of zirconia ceramic coping by design and coloration / 대한치과보철학회지

PURPOSE: The purpose of this study was to compare the marginal fitness and fracture load of the zirconia copings according to the design with different thickness and coloration. MATERIAL AND METHODS: The evaluation was based on 80 zirconia copings. Zirconia copings were fabricated in design with different thicknesses using CAD/CAM system (Everset, KAVO dental GmbH, Biberach, Germany). The designs of copings were divided into four groups. The first group consisted of copings with uniform thickness of 0.3 mm. The thickness in the second group was 0.3 mm on the buccal surface and 0.6 mm on the lingual surface. The third group consisted of coping with uniform thickness of 0.6 mm. The thickness in the fourth group was 0.6 mm on the buccal surface and 1mm on the lingual surface. Each group consisted of 10 colored and 10 uncolored copings. Half of the copings (40) processed with a milling system according to the specific design were sent to be given a color (A3) through saturation in special dye by a manufacturing company. Just after sintering, the marginal discrepancies of copings were measured on the buccal, lingual, mesial and distal surfaces of metal die, under a Video Microscope System (sv-35, Sometech, Seoul, Korea) at a magnification of x100. It was remeasured after the adjusting of the inner surface. Next, all copings were luted to the metal dies using reinforced cement {GC FujiCEM (GC Corp. Tokyo, Japan)} and mounted on the testing jig in a Universal Testing Machine (Instron 4467, Norwood, MA, USA). The results were analyzed statistically using the one-way ANOVA test. RESULTS: The obtained results were as follow: 1. The measured value of marginal discrepancy right after sintering was the greatest in the contraction of the buccal area in all groups, except for group I2. 2. There was no significant difference of marginal fitness among the groups in the colored zirconia group (P.05), with no significance. CONCLUSION: There was difference in the marginal fitness according to the design and coloration of zirconia copings right after sintering, but it was decided that the copings may well be used clinically if the inner surface are adjusted. The copings should be thick enough for the reinforcement of fracture strength. But considering the esthetics of the visible surfaces (labial and buccal surface), the thickness of copings may be a little thin, without giving any significant effect on the fracture strength. This type of design may be considered when giving priority to preservation of tooth or esthetics.

Finite element analysis of maxillary central incisors restored with various post-and-core applications / 대한치과보존학회지

The purpose of this study was to investigate the effect of rigidity of post core systems on stress distribution by the theoretical technique, finite element stress-analysis method. Three-dimensional finite element models simulating an endodontically treated maxillary central incisor restored with a zirconia ceramic crown were prepared and 1.5 mm ferrule height was provided. Each model contained cortical bone, trabecular bone, periodontal ligament, 4 mm apical root canal filling, and post-and-core. Six combinations of three parallel type post (zirconia ceramic, glass fiber, and stainless steel) and two core (Paracore and Tetric ceram) materials were evaluated, respectively. A 50 N static occlusal load was applied to the palatal surface of the crown with a 60degrees angle to the long axis of the tooth. The differences in stress transfer characteristics of the models were analyzed. von Mises stresses were chosen for presentation of results and maximum displacement and hydrostatic pressure were also calculated. An increase of the elastic modulus of the post material increased the stress, but shifted the maximum stress location from the dentin surface to the post material. Buccal side of cervical region (junction of core and crown) of the glass fiber post restored tooth was subjected to the highest stress concentration. Maximum von Mises stress in the remaining radicular tooth structure for low elastic modulus resin core (29.21 MPa) was slightly higher than that for high elastic modulus resin core (29.14 MPa) in case of glass fiber post. Maximum displacement of glass fiber post restored tooth was higher than that of zirconia ceramic or stainless steel post restored tooth.

Cellular attachment and gene expression of osteoblast-like cells on zirconia ceramic surfaces / 대한치과보철학회지

STATEMENT OF PROBLEM: Zirconium oxide can be a substitute to titanium as implant materials to solve the esthetic problems of dark color in the gingival portion of implant restorations. PURPOSE: This study was performed to define attachment and growth behavior of osteoblast-like cells cultured on grooved surfaces of zirconium oxide and evaluate the genetic effect of zirconium oxide surfaces using the reverse transcriptase-polymerase chain reaction (RT-PCR). MATERIAL AND METHODS: MC3T3-E1 cells were cultured on (1) commercially pure titanium discs with smooth surface (T group), (2) yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) with machined surface (ZS group), and (3) Y-TZP with 100micrometer grooves (ZG group). Cell proliferation activity was evaluated through MTT assay and cell morphology was examined by SEM. The mRNA expression of Runx2, alkaline phosphatase, osteocalcin, TGF-beta 1, IGF-1, G3PDH in E1 cells were evaluated by RT-PCR. RESULTS: From the MTT assay, after 48 hours of adhesion of MC3T3-E1 cells, the mean optical density value of T group and ZG group significantly increased compared to the ZS group. SEM images of osteoblast-like cells showed that significantly more cells were observed to attach to the grooves and appeared to follow the direction of the grooves. After 24 hours of cell adhesion, more spreading and flattening of cells with active filopodia formation occurred. Results of RT-PCR suggest that T group, ZS group, and ZG group showed comparable osteoblast-specific gene expression after 24 hours of cell incubation. CONCLUSION: Surface topography and material of implants can play an important role in expression of osteoblast phenotype markers. Zirconia ceramic showed comparable biological responses of osteoblast-like cells with titanium during a short-time cell culture period. Also, grooves influence cell spreading and guide the cells to be aligned within surface grooves.