Evaluation of three different remineralizing agents on artificially demineralized enamel lesions Using scanning electron microscopy-energy dispersive X-ray and magic-angle spinning nuclear magnetic resonance - An in vitro study

Aim: Demineralization can be arrested or reversed when remineralization agents are applied to incipient carious or noncavitated carious lesions. A large number of therapeutic agents, including nonfluoridated products, have been developed to promote enamel remineralization. This study aims to evaluate the efficacy of different remineralizing agents on artificially demineralized enamel lesions. Materials and Methods: The present in vitro study was conducted on 75 sound premolars divided into three groups of normal, demineralized (n = 15 each), and remineralized teeth (n = 45). The remineralized teeth were further subdivided into three groups (n = 15) as remineralized with 2% sodium fluoride (NaF), 2% NaF, and Psoralea corylifolia (bakuchi) and white mineral trioxide aggregate. Specimens of each group were treated with the above-mentioned remineralizing agents and then subjected to Vickers hardness number (VHN), scanning electron microscopy–energy dispersive X-ray (SEM-EDX), and magic-angle spinning nuclear magnetic resonance (MAS-NMR) for further evaluation. Results: The test results showed significantly the highest VHN and the emission peak of elements under the EDX test, such as calcium, phosphorous, oxygen, and fluorine with remineralized with NaF + bakuchi. MAS-NMR spectra showed fluorine and phosphorous peak in a group with NaF + bakuchi indicative of the increase in remineralization. NaF + bakuchi showed effective results in VHN, SEM-EDX, and MAS-NMR with no antagonist interaction. Conclusion: Thus, P. Corylifolia presents an advantage in enhancing remineralization and inhibiting demineralization for early carious lesions and can be used as a herbal extract for effective reduction in pathogenic bacteria.

Efecto de la exposición a bebidas carbonatadas en la dureza superficial de resinas acrílicas / Effect of Exposure to Carbonated Beverages on the Surface Hardness of Acrylic Resins

ABSTRACT: The purpose of this study was to evaluate and compare the effect of carbonated beverage on the surface microhardness of two acrylic materials used to fabricate temporary restorations. The study was experimental in vitro. Forty blocks of acrylic resins used in provisional restorations were made, 20 from Alike® (GC AMERICA INC., Lot 1712161) and 20 from Acryptemp® (Zhermack S.P.A., Lot 302334). After that, the blocks were immersed in distilled water for 24 hours. After this time, the initial surface microhardness was measured. Then the 20 samples of the experimental group were immersed in a carbonated drink (coca cola - soda) for 12 minutes per day, for 5 days. Finally, the final surface microhardness was measured using the Vickers microdurometer. Measures of central tendency and dispersion were used, and the Student's t test and ANOVA were performed. A mean surface microhardness of 8.8 and 7.2HV was found for the PMMA resin group (Initial and final respectively), and 9.5 and 8HV for the bisacrylate group. Statistically significant differences were found when comparing the beginning and end of each group and when comparing the two materials. The acrylic resin of polymethylmethacrylate (Alike® GC AMERICA INC.) Presented higher surface microhardness compared to the bis acrylic resin (Acrytemp® Zhermack S.P.A), after being exposed to a carbonated drink.

RESUMEN: El propósito de este estudio fue evaluar y comparar el efecto de la bebida carbonatada en la microdureza superficial de dos materiales acrílicos utilizados para confeccionar restauraciones provisionales. El estudio fue experimental in vitro. Se confeccionaron 40 bloques de resinas acrílicas utilizadas en provisorios, 20 de Alike® (GC AMERICA INC., Lote 1712161) y 20 de Acryptemp® (Zhermack S.P.A., Lote 302334). Posterior a ello, se sumergió los bloques en agua destilada por 24 horas. Pasado este tiempo se procedió a medir la microdureza superficial inicial. Luego las 20 muestras del grupo experimental se sumergieron en una bebida carbonatada (coca cola-gaseosa) durante 12 minutos por día, durante 5 días. Por último se midió la microdureza superficial final mediante el microdurómetro de Vickers. Se utilizaron medidas de tendencia central, dispersión y se realizaron la prueba t de Student y ANOVA. Se encontró una microdureza superficial media de 8,8 y 7,2HV para el grupo de resina PMMA (Inicial y final respectivamente), y 9,5 y 8HV para el grupo de bisacrilato. Se halló diferencias estadísticamente significativas al comparar el inicio y final de cada grupo y al comparar los dos materiales. La resina acrílica de polimetilmetacrilato (Alike® GC AMERICA INC.) presentó mayor microdureza superficial en comparación con la resina bis acrílica (Acrytemp® Zhermack S.P.A), después de ser expuestas a una bebida carbonatada.

An investigation of the microstructure and mechanical properties of dental zirconia manufactured by digital light processing 3D printing / 华西口腔医学杂志

OBJECTIVES@#This study was performed to investigate the microstructure and mechanical properties of dental zirconia manufactured by digital light processing (DLP) 3D printing and the clinical application prospects of this material.@*METHODS@#The experiment (DLP) group was zirconia manufactured by DLP 3D printing, and the control (MILL) group was milled zirconia. The density, grain size, and phase composition were measured to study the microstructure. Flexural strength was measured by using three-point bending tests, while Vickers hardness was determined through a Vickers hardness tester. Fracture toughness was tested using the single-edge V-notched beam method.@*RESULTS@#Zirconia density of the DLP group was (6.019 8±0.021 3) g·cm@*CONCLUSIONS@#Zirconia manufactured by DLP 3D printing had microstructure and mechanical properties similar to those of the milled zirconia. Only the flexural strength and the Vickers hardness of the experimental zirconia were slightly lower than those of the milled zirconia. Therefore, DLP-manufactured zirconia has a promising future for clinical use.

In Vitro evaluation of remineralization potential of novamin on artificially induced carious lesions in primary teeth using scanning electron microscope and vickers hardness

Aims: The objective of this in vitro study was to find out the efficacy of Novamin in remineralizing enamel surface on which artificial caries lesion had been created. The changes were analyzed using Vickers Hardness Testing Machine and Scanning electron microscope (SEM). Settings and Design: A total of 40 primary teeth were selected and divided into two groups: Control group and SHY NM (Novamin). All the samples were subjected to ph cycle protocol and assessed using Vickers Hardness Testing Machine and Scanning electron microscope. Each demineralized sample was randomly divided into two groups: Gp I –Control group, Gp II – Novamin (SHY NM). After 10-day period of ph cycle, the obtained data was analyzed statistically. Statistical Analysis Used: Pre and post groups were compared by paired t test. The significance of mean difference between the groups was done by Tukey's post hoc test after ascertaining normality by Shapiro-Wilk (W) test and homogeneity of variance by Levene's test. A two-tailed P value less than 0.05 (P < 0.05) was considered statistically significant. All analyses were performed on SPSS software (Windows version 17.0). Results: Statistical analysis showed that bioactive glass (novamin) remineralizes artificially induced carious lesion in primary teeth. Conclusions: SHY NM (Novamin) exhibited superior remineralization potential.

Effects of aging on the surface roughness, composition and hardness of veneering ceramics for zirconia frameworks / 医学研究生学报

Objective Few studies are reported on the aging of veneering ceramics. This study was to investigate the effects of aging on surface roughness, composition and hardness of veneering ceramics for zirconia frameworks.Methods Twenty specimens were fabricated with each of the five types of veneering ceramics for zirconia frameworks － Vintage ZR (ZR), Cerabien ZR (CZR), VitaVM9 (VM9), Cercon ceram KISS (KISS) and IPS e.max ceram (e.max). The specimens were randomly divided into an aging and a control group of equal number, the former subjected to accelerated aging at 200 ℃ and 2 atm for 5 hours while the latter left untreated. The surface roughness and Vickers hardness of the specimens were measured using laser profilometry and Vicker's indentation test machine and their surface topography and chemical composition examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Results Compared with the control group, the aged specimens fabricated with ZR showed significantly increased surface roughness parameters Ra (\[0.157±0.009\] vs \[0.197±0.008\] μm, P=0.000), Rp (\[0.356±0.031\] vs \[0.446±0.036\] μm, P=0.000) and Rv (\[0.411±0.034\] vs \[0.498±0.036\] μm, P=0.000), and so did those fabricated with CZR, VM9 and KISS (P=0.000). The Ra, Rp and Rv parameter values of the aged specimens with CZR were remarkably higher than those with VM9, KISS and e.max (P < 0.001), but those of the aged specimens with e.max markedly lower than those with ZR, CZR, VM9 and KISS (P<0.01). The RSm value was significantly higher in all the aged specimens than in the control (P<0.001), and so was the oxygen content (P<0.05), but the levels of sodium and potassium were lower in the former than in the latter group (P<0.05). Compared with the control group, the silicon content was significantly decreased in the aged specimens with ZR, KISS and e.max (P<0.01), and so was that of calcium in those with ZR and VM9 (P<0.05). The Vickers hardness of the aged specimens with ZR was remarkably lower than that of the control (\[5.01±0.28\] vs \[6.91±0.51\] GPa, P=0.000), and so was that of the other aged specemens (P=0.000).Conclusion Accelerated aging can significantly alter the surface properties, enhance the stability and prolong the working life of veneering ceramics for zirconia frameworks.

Evaluation of the Changes in Polymerization of TheraCal LC with Various Light-curing Time and Distance / 대한소아치과학회지

The purpose of this study was to evaluate polymerization of TheraCal LC, one of the tricalcium silicate cements. To measure the Vickers hardness number (VHN), the specimens were cured at different light curing time and distance.As a result, the VHN of the upper surface was significantly higher than the lower surface's in all groups (p < 0.05). The VHN of the lower surface was increased significantly with the increase of the light curing time in all distance (p < 0.05). When the distance was more than 4.0 mm at all light curing time, the VHN of lower surface was significantly decreased (p < 0.05). When the specimen was light cured for 20 seconds, the VHN of the lower surface did not exceed 2, which corresponds to 10% of the upper surface's.These results suggested that the 20 second light curing time was not sufficient to polymerize the lower surface under specific conditions and that light-curing time should be increased.

Chemical and Microscopy Characterization of Trans-Endodontic Implants / Caracterización química y microscópica de implantes trans-endodónticos

Abstract Trans-endodontic implants are an artificial extension through root apex anchored in periradicular bone tissue. The aim is to improve the crown-root ratio and to provide stability to dental organ present. Zirconium oxide (ZrO2) is a material of great technological importance, having good natural color, high strength, high toughness, high chemical stability, does not suffer any corrosion, chemical and microbial resistance and excellent esthetic properties. Objective: The aim of this study was to evaluate chemical and microscopy of surface conditions of ZrO2 trans-endodontic implant. Materials and Methods: A blocks of ZrO2 were manufactured for produce trans-endodontic implants and divided in two groups: monoclinic and tetragonal phase. They were evaluated using Scanning Electroning Microscope (SEM), EnergyDispersive X-ray Spectroscopy (EDS), and Atomic Force Microscope (AFM) and Vickers Micro hardness. Results: The Monoclinic phase through AFM analysis showed roughness Ra = 0.320μm, whereas in the Tetragonal phase was 0.126μm, SEM/EDX indicated that the phases are not properly uniform and the addition of the Yttrium to favor the stabilization of the Tetragonal phase. The Vickers hardness analysis showed a value of 1500HV. Conclusion: The characterization of the surface of trans-endodontic zirconium oxide implants provides a guideline to know the surface characteristics of the material, since a greater roughness on the surface of the implant will favor the Osseo-integration capacity.

Resumen Los implantes trans-endodónticos son una extensión artificial a través del ápice radicular anclado en el tejido óseo periradicular. El objetivo es mejorar la relación corona-raíz y proporcionar estabilidad al órgano dental presente. El óxido de zirconio (ZrO2) es un material de gran importancia tecnológica, con buen color natural, alta resistencia, alta tenacidad, alta estabilidad química, no sufre corrosión, resistencia química y microbiana y excelentes propiedades estéticas. Objetivo: El objetivo de este estudio fue evaluar las condiciones superficiales de ZrO2 para su aplicación clínica a los implantes transendodónticos. Materiales y Métodos: se trituraron bloques de ZrO2 en implantes trans-endodónticos y se dividieron en: monoclínico y tetragonal. Luego se evaluaron mediante microscopía electrónica de barrido (SEM), espectroscopia de rayos X de energía dispersiva (EDS) y microscopio de fuerza atómica (AFM) y microdureza vickers. Resultados: La fase monoclínica a través del análisis AFM presenta Ra = 0.320 μm, mientras que en la fase Tetragonal es 0.126 μm, SEM / EDS muestra que las fases no son adecuadamente uniformes y la adición del Ytrio para favorecer la estabilización de la fase tetragonal. El análisis de microdureza mostro un valor de 1500HV. Conclusión: La caracterización de la superficie de los implantes trans-endodónticos de óxido de zirconio, brinda una pauta para conocer las características superficiales del material, ya que al haber una mayor rugosidad en la superficie del implante se verá favorecida la capacidad de oseointegración.

The effect of different fluoride application methods on the remineralization of initial carious lesions

OBJECTIVES: The purpose of this study was to assess the effect of single and combined applications of fluoride on the amount of fluoride release, and the remineralization and physical properties of enamel. MATERIALS AND METHODS: Each of four fluoride varnish and gel products (Fluor Protector, FP, Ivoclar Vivadent; Tooth Mousse Plus, TM, GC; 60 Second Gel, A, Germiphene; CavityShield, CS, 3M ESPE) and two fluoride solutions (2% sodium fluoride, N; 8% tin(ii) fluoride, S) were applied on bovine teeth using single and combined methods (10 per group), and then the amount of fluoride release was measured for 4 wk. The electron probe microanalysis and the Vickers microhardness measurements were conducted to assess the effect of fluoride application on the surface properties of bovine teeth. RESULTS: The amount of fluoride release was higher in combined applications than in single application (p < 0.05). Microhardness values were higher after combined applications of N with FP, TM, and CS than single application of them, and these values were also higher after combined applications of S than single application of A (p < 0.05). Ca and P values were higher in combined applications of N with TM and CS than single application of them (p < 0.05). They were also increased after combined applications of the S with A than after single application (p < 0.05). CONCLUSIONS: Combined applications of fluoride could be used as a basis to design more effective methods of fluoride application to provide enhanced remineralization.

The Effect of McInnes Solution on Enamel and the Effect of GC Tooth Mousse on Bleached Enamel: An In Vitro Study

The aim is to evaluate the effect of McInnes bleaching agent on the microhardness of enamel before and after bleaching and to evaluate the effect of G C Tooth Mousse on the bleached enamel surface for its microhardness. The materials and methods used are McInnes bleaching solution, Casein phosphopeptide-amorphous calcium phosphate CCP-ACP (G C Tooth mousse) artificial saliva (Dept. of Oral Pathology, GDC Bellary), deionized water, Vickers’ Micro Hardness tester (Zwick/ZHV, Germany), freshly extracted teeth, cold cure acrylic, Diamond disc (Horico–PFINGST New Jersey, USA, KAVO-Germany), straight handpiece (kavopecareta) and plastic moulds (6.5 × 2 mm2). The purpose of this study was to evaluate and compare microhardness of the sound enamel surface by Vickers’ Hardness Number (VHN) before and after bleaching with McInnes solution, and to evaluate the effect of casein phosphopeptide amorphous calcium phosphate (G C Tooth Mousse) on the bleached enamel surface for its microhardness. The data obtained from the test were subjected for statistical analysis and are presented as range, mean and standard deviation. P value of 0.05 or less was considered for statistical significance. The changes in microhardness at different times of assessment were analyzed using the paired ‘t’ test. The results of all the samples showed decrease in the microhardness after two cycles of bleaching, though immediately after bleaching the decrease in the microhardness was not significant (P = 0.34). However, after the second cycles, it showed a significant decrease (P<0.01) in the microhardness. After application of remineralization solution (GC Tooth mousse), the samples showed a marginal increase in the microhardness (P<0.05) after seven days and a marked increase after fourteen days (P<0.001).McInnes bleaching agent does decrease the microhardness of enamel by causing enamel demineralization and GC Tooth mousse used in the study causes an increase in the microhardness of bleached enamel by maintaining a high gradient of calcium and phosphate ions at the enamel subsurface.

The effect of thermocycling on fracture toughness and hardness of different core build up materials.

Introduction: Core build up materials are routinely used to restore grossly decayed teeth and in the oral environment they are subjected to changes in the temperature due to consumption of hot and cold food. Aims: The purpose of this study was to determine the effect of thermocycling on the fracture toughness and hardness of 5 core build up materials. Materials and Methods: Fifteen specimens were prepared for each of the following materials: DPI alloy, Miracle‑mix, Vitremer, Fuji II LC and Photocore. American Standard for Testing Materials guidelines were used for the preparation of single‑edge notch, bar‑shaped specimens. Ten specimens of each material were thermocycled for 2000 cycles and the other 5 specimens were not thermocycled (non‑thermocycled group). All specimens were subjected to 3-point bending in a universal testing machine. The load at fracture was recorded and the fracture toughness (KIC) was calculated. Vickers hardness test was conducted on the thermocycled and non‑thermocycled group specimens. Results: Photocore had the highest mean KIC in both thermocycled and non‑thermocycled groups. Miracle‑mix demonstrated the lowest mean fracture toughness (KIC) for both thermocycled and non‑thermocycled groups. By applying Mann Whitney ‘U’ test the Vickers hardness value in all materials used in the study is highly superior in non‑thermocycled group as compared to thermocycled group (P < 0.01). Non‑thermocycled Photocore showed highest hardness values of 87.93. Vitremer had lowest hardness of 40.48 in thermocycled group. Conclusion: Thermocycling process negatively affected the fracture toughness and hardness of the core build‑up materials.

Avaliação in vitro da dureza, da resistência adesiva e do índice de adesivo remanescente de três resinas ortodônticas / In vitro evaluation of hardness, adhesive resistance and adhesive remnant index of three orthodontic resins

Este estudo avaliou a Dureza Vickers (HV), a resistência adesiva (RA) e o índice de adesivo remanescente (IAR) de três resinas ortodônticas: Concise (CO), Transbond XT (TB) e a Aqualite (AQ). Para a análise da HV foram confeccionados 30 corpos de prova em matrizes metálicas pré-fabricadas com diâmetro de 0,5 mm e 0,2 mm de espessura. Os valores de HV foram CO = 43,29 ± 1,66, TB = 43,69 ± 1.37 e AQ = 43,51 ± 1,30. Os resultados para HV foram analisados pelo teste ANOVA one-way e pós-teste de Tukey, onde não foram encontradas diferenças estatísticas significativas (p>0,05). Para a RA foram utilizados 60 pré-molares e confeccionados corpos de prova, os quais foram divididos em 3 grupos (n= 20) para a colagem de bráquetes metálicos com as resinas Concise (CO), Transbond XT (TB) e Aqualite (AQ). Os bráquetes após a colagem foram submetidos aos ensaios mecânicos de cisalhamento em máquina de ensaio universal SHIMADZU, com velocidade de carga de 0,5 mm/min. A avaliação dos resultados do cisalhamento foram analisados pelo teste de variância ANOVA, e mostraram RA médias para CO de 18,21 ± 6,21 MPa; para TB de 25,02 ± 9,29 MPa e para AQ de 14,31 ± 8,25 MPa. A ANOVA demonstrou diferença estatística entre AQ/TB e CO/TB (p<0,05) e sem diferença estatística significante entre AQ/CO. Para avaliação do IAR utilizou-se o teste não paramétrico de Kruskal-Wallis, seguido do teste de Dunn, sem diferenças estatísticas significativas (p>0,05). Conclui-se que a resina TB apresentou maior RA em relação à CO e AQ. Não existe diferença entre a HV e o IAR entre as resinas.

This study evaluated Vickers hardness (HV), adhesive resistance and adhesive remnant index (ARI) on three orthodontic resins: Concise (CO), Transbond XT (TB), and Aqualite (AQ). For the HV analysis, 30 specimens were prepared with pre-manufactured matrixes with a 0.5 mm width and 0.2 mm thick. HV values were CO = 43.29 ± 1.66, TB = 43.69 ± 1.37 e AQ = 43.51 ± 1.30. Those values were evaluated by the one-way ANOVA test following Tukey test, and no significant statistical differences (p>0.05) were observed. For the RA evaluation, 60 pre-molar specimens were used, divided in 3 groups (n=20) and the metallic brackets were bonded with Concise (CO), Transbond XT (TB), and Aqualite (AQ). After bonding the brackets were submitted to shear bond strength mechanic trials with a SHIMADZU universal testing machine, with a cross-head speed of 0.5 mm per minute. The results of the shear bond strength were evaluated by the ANOVA and revealed RA means for CO values of 18.21 ± 6.21 MPa; 25.02 ± 9.29 MPa for TB, and 14.31 ± 8.25 MPa for AQ. ANOVA showed statistical differences between AQ/TB and CO/TB (p<0.05) while no statistical differences were observed between AQ/CO. For the ARI evaluation, the Kruskal-Wallis non parametric test was performed following the Dunn’s test, without any statistical significant differences (p>0.05). It was concluded that the TB resin presented higher RA values in relation to CO and AQ. There are no differences between the HV and IAR in the studied resins.

Inhibitory effect on Streptococcus mutans and mechanical properties of the chitosan containing composite resin

OBJECTIVES: This study evaluated the antibacterial effect and mechanical properties of composite resins (LCR, MCR, HCR) incorporating chitosan with three different molecular weights (L, Low; M, Medium; H, High). MATERIALS AND METHODS: Streptococcus (S). mutans 100 mL and each chitosan powder were inoculated in sterilized 10 mL Brain-Heart Infusion (BHI) solution, and was centrifuged for 12 hr. Absorbance of the supernatent was measured at OD660 to estimate the antibacterial activities of chitosan. After S. mutans was inoculated in the disc shaped chitosan-containing composite resins, the disc was cleansed with BHI and diluted with serial dilution method. S. mutans was spread on Mitis-salivarius bacitracin agar. After then, colony forming unit (CFU) was measured to verify the inhibitory effect on S. mutans biofilm. To ascertain the effect on the mechanical properties of composite resin, 3-point bending and Vickers hardness tests were done after 1 and 3 wk water storage, respectively. Using 2-way analysis of variance (ANOVA) and Scheffe test, statistical analysis was done with 95% significance level. RESULTS: All chitosan powder showed inhibition effect against S. mutans. CFU number in chitosan-containing composite resins was smaller than that of control resin without chitosan. The chitosan containing composite resins did not show any significant difference in flexural strength and Vickers hardness in comparison with the control resin. However, the composite resin, MCR showed a slightly decreased flexural strength and the maximum load than those of control and the other composite resins HCR and LCR. CONCLUSIONS: LCR and HCR would be recommended as a feasible antibacterial restorative due to its antibacterial nature and mechanical properties.

Comparative Evaluation of Compressive Strength, Vickers Hardness And Modulus of Elasticity of Hybrid And Packable ( Condensable ) Posterior Composites - An In- Vitro Study.

Background. The authors evaluated the compressive strength, Vicker`s hardness and modulus of elasticity of two hybrid composites, comparing them to two packable resin composites in order to determine differences that occur with respect to specific restorative materials. Methods. The authors studied the following resin-based restorative materials: two hybrid composites (Z-100, CHARISMA) and two packable resin composites (SUREFIL, SOLITAIRE- 2) The objective of the present study was to test compressive strength, Vicker`s hardness and modulus of elasticity. Specific sized moulds were prepared for each restorative material, which were then photopolymerized. Following this, the moulds were stored in physiologic saline. Compressive strength was evaluated using universal testing machine and Vicker’s hardness was determined using Vicker`s indenter. The test for modulus of elasticity was conducted using a three point bending technique and universal testing machine.Results. Results calculated by one-way ANOVA and Tukey`s test indicated that the hybrid composite (Z-100) was superior in all the three physical properties evaluated, followed by SUREFIL, SOLITAIRE- 2, and CHARISMA.Conclusion. The hybrid composite Z-100 is the material of choice for restoration in high stress bearing areas, but further clinical research is still needed in order to substantiate these results. Clinical Implications. Packable composites may be easier for clinicians to handle than conventional resin-based composites; however, their physical properties were not superior to those of the conventional hybrid resin-based composite.

Surface hardness of the dental composite cured by light that penetrate tooth structure according to thickness of tooth structure, light intensity and curing time / 대한치과보존학회지

In this study we measured the amount of light energy that was projected through the tooth material and analyzed the degree of polymerization by measuring the surface hardness of composites. For polymerization, Optilux 501 (Demetron, USA) with two types of light guide was used: a 12 mm diameter light guide with 840 mW/cm2 light intensity and a 7 mm diameter turbo light guide with 1100 mW/cm2. Specimens were divided into three groups according to thickness of penetrating tooth (1 mm, 2 mm, 0 mm). Each group was further divided into four subgroups according to type of light guide and curing time (20 seconds, 40 seconds). Vickers'hardness was measured by using a microhardness tester. In 0 mm and 1 mm penetrating tooth group, which were polymerized by a turbo light guide for 40 seconds, showed the highest hardness values. The specimens from 2 mm penetrating tooth group, which were polymerized for 20 seconds, demonstrated the lowest hardness regardless of the types of light guides (p < 0.05). The results of this study suggest that, when projecting tooth material over a specified thickness, the increase of polymerization will be limited even if light intensity or curing time is increased.

Mechanical proprieties of four cements at different mixing ratios / 实用口腔医学杂志

To investigate the influence of mixing ratios on the hardness,wear resistance and compressive strength of the cements clinically used,Zinc Oxide Eugenol cement,Glass ionomer cements,Zinc Phosphate Cement,and Dual-curing composite cement were mixed at different ratios separately,then made into test pieces.Vickers hardness,wear resistance and compressive strength of these test pieces were measured by related machines.The results showed that vickers hardness,wear resistance and compressive strength of Zinc Oxide Eugenol cement,Glass ionomer cements and Zinc Phosphate Cement reduced with the decrease of powder/liquid ratios.As to Dual-curing composite cement,Vickers hardness,wear resistance and compressive strength decreased with the difference between A/B ratio and 1∶1 increase.Conclusively,mixing ratios could influence the mechanical proprieties of the cements clinical used,so the use of cements should be under the instructions of the product.