FLUORIDE RELEASE OF SIX RESTORATIVE MATERIALS IN WATER AND pH-CYCLING SOLUTIONS

The fluoride release of restorative materials in deionized water has been the subject of many studies, but the behavior of these materials under conditions of acid challenge that simulates the oral cavity, needs to be further explored. Therefore, the aim of this study was to evaluate the fluoride release of restorative materials in two storage protocols: deionized water and pH- cycling system (demineralizing solution-pH 4.3 and remineralizing solution-pH 7.0) for 15 days. Eight disks of each material (Vitremer™-positive control, Dyract AP, Ariston pHc, Definite®, Tetric®Ceram and Z100-negative control) were prepared (11.0 mm x 1.5 mm) and suspended individually in 4.0 mL of each solution, which were daily changed. Daily fluoride release was analyzed with an ion specific electrode (Orion 9609) by the direct method or after HMDS-facilitated diffusion, following 1, 7 and 15 days. The values obtained were converted into μgF/mm² and the data analyzed by ANOVA and Tukey''s test (p< 0.05). The results showed that all materials released more fluoride in the pH-cycling system, except for Ariston pHc which maintained a constant release during the experiment. The highest fluoride release was presented by the positive control, Vitremer™ in pH- cycling and by Ariston pHc, in deionized water. The negative control Z100 and the resins Definite® and Tetric®Ceram did not present statistically significant differences.     

EFFECT OF ACID ETCHING OF GLASS IONOMER CEMENT SURFACE ON THE MICROLEAKAGE OF SANDWICH RESTORATIONS

The purposes of this study were to evaluate the sealing ability of different glass ionomer cements (GICs) used for sandwich restorations and to assess the effect of acid etching of GIC on microleakage at GIC-resin composite interface. Forty cavities were prepared on the proximal surfaces of 20 permanent human premolars (2 cavities per tooth), assigned to 4 groups (n=10) and restored as follows: Group CIE – conventional GIC (CI) was applied onto the axial and cervical cavity walls, allowed setting for 5 min and acid etched (E) along the cavity margins with 35% phosphoric acid for 15 s, washed for 30 s and water was blotted; the adhesive system was applied and light cured for 10 s, completing the restoration with composite resin light cured for 40 s; Group CIN – same as Group CIE, except for acid etching of the CI surface; Group RME – same as CIE, but using a resin modified GIC (RMGIC); Group RMN – same as Group RME, except for acid etching of the RMGIC surface. Specimens were soaked in 1% methylene blue dye solution at 24°C for 24 h, rinsed under running water for 1 h, bisected longitudinally and dye penetration was measured following the ISO/TS 11405-2003 standard. Results were statistically analyzed by Kruskal-Wallis and chi-square tests (α=0.05). Dye penetration scores were as follow: CIE – 2.5; CIN – 2.5; RME – 0.9; and RMN – 0.6. The results suggest that phosphoric acid etching of GIC prior to the placement of composite resin does not improve the sealing ability of sandwich restorations. The RMGIC was more effective in preventing dye penetration at the GIC-resin composite- dentin interfaces than CI.     

PERFORMANCE OF BRAZILIAN AND IMPORTED GLASS IONOMER CEMENTS USED IN ATRAUMATIC RESTORATIVE TREATMENT (ART) REGARDING MICROLEAKAGE IN PRIMARY MOLARS

With the aim of assessing the performance of Brazilian and imported glass ionomer cements (GIC) with regard to microleakage, 40 primary molars received two standard class II cavity preparations with margins in enamel. Twenty cavities were filled with Brazilian materials (Vidrion® R and Vidrion® R_Caps) and the other 20 cavities were filled with imported materials (Fuji® IX and Fuji® IX_GPFast capsule). All fillings were performed by a single operator according to the manufacturer''s instructions. Teeth were immersed in 0.5% methylene blue and half-sectioned. Three independent calibrated examiners assessed microleakage using scores (0-3). Data were submitted to the Kruskal-Wallis statistical test and Wilcoxon analysis. High microleakage indexes were verified for all ionomer cements: 59.5% of the samples restored with Vidrion® R or Vidrion® R_Caps and 83.4% of the samples restored with Fuji® IX or Fuji® IX_GpFast capsule obtained the maximum score (3). The Brazilian ionomer cements presented less microleakage than imported cements, although this difference was only significant (p=0.003) among the encapsulated materials.     

六种牙齿充填修复材料的释氟与再充氟性能研究

目的 评价6种牙齿充填修复材料的释氟和再充氟性能,以期为临床选择和应用提供参考.方法 选择材料A(FujiⅦ玻璃离子水门汀)、材料B(FujiⅡLC光固化玻璃离子水门汀)、材料C(Beautifil离子体复合树脂)、材料D(Compoglass F复合体)、材料E(Charisma普通复合树脂)及材料F(实验Ⅰ型释氟性复合树脂)作为实验材料,制备直径10 mm、厚1 mm的圆片,每组10个试样.每个试样浸于5 ml去离子水中,用氟离子选择电极测定浸出液氟离子量,浸泡1～7d每天测定,8～28d3d测定1次,计算每日释氟量.于浸泡28 d后用氟化泡沫对试样充氟4min,继续测定试样每日释氟量,连续测定7d;再充氟并测定氟释放7d,重复3次.结果 浸泡1d后所有材料均表现最大的释氟量,材料A释氟量最大[(99.68±15.21) μg·cm-2·d-1],其次为材料B[(37.12±1.67) μg·cm-2·d-1],再次为材料F和D[分别为(22.93±1.53)和(15.28±0.70) μg·cm-2·d-1],材料C和E释氟量较小[分别为(2.40±0.52)和(0.11±0.02) μg·cm-2· d-1],各组间差异有统计学意义(P＜0.05).浸泡2d后释氟量显著下降,随后(7～ 28 d)释氟量下降缓慢;浸泡1～28 d内,材料A和B的释氟量始终大于其他材料(P＜0.01),其次是材料D和F,显著大于材料C和E(P＜0.01).所有材料充氟1d后的释氟量均较充氟前显著增加,形成释氟高峰,充氟2d后的释氟量又显著下降.充氟1d后材料A的释氟量超过40 μg· cm-2·d-1,大于其他材料(P＜0.01);其次是材料B,释氟量超过25 μg· cm-2·d-1,大于除A外的其他材料(P＜0.01);材料C、D、F释氟量相近,在15～ 20μg·cm-2·d-1之间;材料E释氟量较小,＜1.5 μg· cm-2·d-1.结论 玻璃离子水门汀类材料的释放及再充氟能力最强,其次是复合体和释氟性复合树脂,离子体复合树脂释氟能力小,但其再充氟能力与复合体和释氟性复合树脂相当,普通复合树脂的释氟及再充氟能力均较小.     

The effect of glass ionomer cement or composite resin bases on restoration of cuspal stiffness of endodontically treated premolars in vitro

The purpose of the present study was to decide whether composite resin or conventional glass ionomer cement should be preferred as a base material in endodontically treated premolars. Twelve extracted human maxillary premolars were mounted in a universal testing machine at a 35° angle. Cuspal stiffness was determined by applying a load of 75 N to the buccal cusp and recording the displacement of the cusp using inductive displacement transducers. In the same teeth, different cavity preparations and restorations were performed sequentially. Standard MOD cavities were enlarged to allow endodontic access. In addition, the cusps were undermined. Half of the teeth were restored to the level of the previous shallow cavities using conventional glass ionomer cement (Ketac Fil), in the rest of the teeth dentine bonding agent (Syntac) and composite resin (Tetric) were used instead. Finally, composite resin fillings (Tetric) were placed. All restorations were removed and the experiments were repeated twice. For each replication, the assignment of the base materials to the experimental groups was reversed, and ceramic inlays (Empress) were used as final restorations for the last replication. Improvement of cuspal stiffness achieved by conventional glass ionomer bases was very small, whereas composite resin bases increased cuspal stability by more than a factor of two. After placement of the final restorations, however, there was no longer a difference between teeth with different base materials. Nevertheless, composite resin bases might be preferred for two reasons. Firstly, deterioration of adhesive restorations will probably start at the cavosurface margins. The incidence of margin gaps, however, will not only compromise marginal seal but also the stabilizing effect of the restoration. In this situation, the resin base may still stabilize the tooth. Moreover, resin bases may reduce the risk of cusp fracture during the time between cavity preparation and the insertion of adhesive inlays. Received: 19 February 1998 / Accepted: 5 May 1998     

TOXICITY TESTING OF RESTORATIVE DENTAL MATERIALS USING BRINE SHRIMP LARVAE (ARTEMIA SALINA)

This study investigated the effect of extracts of different composites, glass ionomer cement (GIC)s and compomers on the viability of brine shrimp larvae. Ethanolic extracts of four dental composites (Z-100; Solitaire 2; Filtek P60 and Synergy), a conventional GIC (Ketac-Fil), a resin-modified glass ionomer cement (Vitremer), two compomers (F2000; Dyract AP), and a flowable compomer (Dyract Flow) were prepared from each material. Following evaporation of the ethanol, the extracts were resuspended in distilled water, which was then used to test the effects on the viability of brine shrimp larvae. For the composites, the extract of Synergy was the least toxic (88% viability) followed by the extracts of Solitaire 2, Z100 and P60 (75%, 67.5% and 50% viability, respectively). One-way ANOVA revealed highly significant differences between the resin composite materials (p<0.001). Follow-up comparison between the composite groups by Tukey''s pairwise multiple-comparison test (α =0.05) showed that the extract of Synergy was significantly less toxic than the extracts of all the other materials except that of Solitaire 2. The compomers showed 100% lethality, while the percentage of viable larvae for the extracts of Ketac-Fil, and Vitremer were 32.3%, and 37.0%, respectively. One-way ANOVA revealed highly significant differences between the groups of materials (p<0.001). Follow-up comparison between the groups by Tukey''s test (α = 0.05) showed that the toxic effect of the extracts of the compomers were significantly greater than that of Ketac-Fil, and Vitremer. The differences in the toxic effects of Vitremer and Ketac-Fil were not statistically significant. In conclusion, the toxicity of composite materials varied according to their chemical composition. Compomers were the most lethal materials to brine shrimp larvae followed by GICs and then composites.     

EFFECT OF DIFFERENT POLISHING SYSTEMS ON THE SURFACE ROUGHNESS OF MICROHYBRID COMPOSITES

The use of composite resins in dentistry is well accepted for restoring anterior and posterior teeth. Many polishing protocols have been evaluated for their effect on the surface roughness of restorative materials. This study compared the effect of different polishing systems on the surface roughness of microhybrid composites. Thirty-six specimens were prepared for each composite [Charisma^® (Heraeus Kulzer), Fill Magic^® (Vigodent), TPH Spectrum^® (Dentsply), Z100^® (3M/ESPE) and Z250^® (3M/ESPE)] and submitted to surface treatment with Enhance^® and PoGo^® (Dentsply) points, sequential Sof-Lex XT^® aluminum oxide disks (3M/ESPE), and felt disks (TDV) combined with Excel^® diamond polishing paste (TDV). Average surface roughness (Ra) was measured with a mechanical roughness tester. The data were analyzed by two-way ANOVA with repetition of the factorial design and the Tukey-Kramer test (p<0.01). The F-test result for treatments and resins was high (p<0.0001 for both), indicating that the effect of the treatment applied to the specimen surface and the effect of the type of resin on surface roughness was highly significant. Regarding the interaction between polishing system and type of resin used, a p value of 0.0002 was obtained, indicating a statistically significant difference. A Ra of 1.3663 was obtained for the Sof-Lex/TPH Spectrum interaction. In contrast, the Ra for the felt disk+paste/Z250 interactions was 0.1846. In conclusion, Sof-Lex polishing system produced a higher surface roughness on TPH Spectrum resin when compared to the other interactions.     

Pulp response after application of two resin modified glass ionomer cements (RMGICs) in deep cavities of prepared human teeth

Objectives: This study evaluated the human pulp response to the application of two RMGICs in deep cavities in vivo. Methods: The cavity floor prepared on the buccal surface of 34 premolars was lined with VBP (VBP), Vitrebond (VB) or Dycal^® (DY), and restored with composite resin. Additional teeth were used as an intact control group. After 7 or 30-60 days, the teeth were extracted and processed for histological evaluation. The following histological events were scored: inflammatory response, tissue disorganization, reactionary dentin formation and presence of bacteria. Results: At 7 days, VBP and VB elicited a mild inflammatory pulpal response in about 70% of specimens and in 1 specimen for DY. Only 1 specimen of each RMGICs exhibited moderate tissue disorganization. Bacteria and reactionary dentin formation were not found. At 30-60 days, about 20% of specimens lined with RMGICs showed a persistent mild inflammatory pulp response while no inflammatory reaction was observed for DY. Moderate tissue disorganization occurred with both materials. Bacteria were found only in 1 VBP specimen. The mean remaining dentin thickness (RDT) in specimens lined with VBP, VB or DY ranged from 342.3 to 436.1 μm, and no statistically significant differences in RDT were found among materials or periods (two-way ANOVA, p > 0.05). Comparison of the two RMGICs tested for the histological events at each period showed statistically similar results (Kruskal-Wallis, p > 0.05). Significance: The use of the new Vitrebond formulation (VBP) in deep cavities in vivo caused mild initial pulp damage, which decreased with time, indicating acceptable biocompatibility.     

INFLUENCE OF THE CURING METHOD ON THE POSTPOLYMERIZATION SHRINKAGE STRESS OF A COMPOSITE RESIN

The aim of this study was to evaluate the effect of different curing methods on the stress generated by the polymerization shrinkage of a restorative composite in two moments: immediately after light exposure and after 5 min. Photoactivation was performed using two different light sources: (1) xenon plasma arc (PAC) light (1,500 mW/cm² – 3s) and (2) a quartz-tungsten-halogen (QTH) light with three light-curing regimens: continuous exposure (40 s at 800 mW/cm² – CL); soft-start (10 s at 150 mW/cm² and 30 s at 800 mW/cm² - SS) and intermittent light [cycles of 4 s (2 s with light on at 600 mW/cm² and 2 s of light off), for 80s – IL]. The composite resin was applied between two 5-mm diameter metallic rods, mounted in a servohydraulic machine. The maximum stress was recorded immediately after light exposure (FF) and after 5 min (5F). The results were submitted to ANOVA and Tukey''s test (5%). For each method, the results obtained in FF and 5F were, respectively: CL (3.58 and 4.46 MPa); SS (2.99 and 4.36 MPa); IL (3.11 and 4.32 MPa) and PAC (0.72 and 3.27 MPa). The stress generated by the polymerization shrinkage during light exposure can be associated with the photoactivation method used. A significant increase in the stress level was observed during the post-curing period up to 5 min, for all evaluated methods.     

Effect of ionizing radiation on properties of restorative materials

Objective

To evaluate the effect of ionizing radiation from high energy X-ray on properties of restorative materials.

INFLUENCE OF ENERGY DENSITY OF DIFFERENT LIGHT SOURCES ON KNOOP HARDNESS OF A DUAL-CURED RESIN CEMENT

The purpose of this study was to evaluate the Knoop hardness of a dual-cured resin-based luting cement irradiated with different light sources as well energy density through a ceramic sample. Three light-curing unit (LCUs) were tested: tungsten halogen light (HAL), light-emitting diode (LED) and xenon plasma-arc (PAC) lamp. Disc-shaped specimens were fabricated from a resin-based cement (Enforce). Three energy doses were used by modifying the irradiance (I) of each LCU and the irradiation time (T): 24 Jcm^-2 (I/2x2T), 24 Jcm^-2 (IxT) and 48 Jcm^-2 (Ix2T). Energy doses were applied through a 2.0-mm-thick ceramic sample (Duceram Plus). Three groups underwent direct irradiation over the resin cement with the different LCUs and a chemically-activated group served as a control. Thirteen groups were tested (n=10). Knoop hardness number (KHN) means were obtained from cross-sectional areas. Two-way ANOVA and the Holm-Sidak method were used for statistical comparisons of activation mode and energy doses (α=5%). Application of 48 J.cm^-2 energy dose through the ceramic using LED (50.5±2.8) and HAL (50.9±3.7) produced significantly higher KHN means (p<0.05) than the control (44.7±3.8). LED showed statistically similar performance to HAL. Only HAL showed a relationship between the increase of LCU energy dose and hardness increase.     

EFFECT OF LIGHT-CURING UNITS AND ACTIVATION MODE ON POLYMERIZATION SHRINKAGE AND SHRINKAGE STRESS OF COMPOSITE RESINS

The aim of this study was to evaluate the polymerization shrinkage and shrinkage stress of composites polymerized with a LED and a quartz tungsten halogen (QTH) light sources. The LED was used in a conventional mode (CM) and the QTH was used in both conventional and pulse-delay modes (PD). The composite resins used were Z100, A110, SureFil and Bisfil 2B (chemical-cured). Composite deformation upon polymerization was measured by the strain gauge method. The shrinkage stress was measured by photoelastic analysis. The polymerization shrinkage data were analyzed statistically using two-way ANOVA and Tukey test (p≤0.05), and the stress data were analyzed by one-way ANOVA and Tukey''s test (p≤0.05). Shrinkage and stress means of Bisfil 2B were statistically significant lower than those of Z100, A110 and SureFil. In general, the PD mode reduced the contraction and the stress values when compared to CM. LED generated the same stress as QTH in conventional mode. Regardless of the activation mode, SureFil produced lower contraction and stress values than the other light-cured resins. Conversely, Z100 and A110 produced the greatest contraction and stress values. As expected, the chemically cured resin generated lower shrinkage and stress than the light-cured resins. In conclusion, The PD mode effectively decreased contraction stress for Z100 and A110. Development of stress in light-cured resins depended on the shrinkage value.     

INFLUENCE OF POST-CURE TREATMENTS ON HARDNESS AND MARGINAL ADAPTATION OF COMPOSITE RESIN INLAY RESTORATIONS: AN IN VITRO STUDY

Objectives:

The purpose of this study was to evaluate the Vickers hardness number (VHN) and the in vitro marginal adaptation of inlay restorations of three hybrid composite resins (Filtek Z250, Opallis and Esthet-X) subjected to two post-cure treatments.

Material and Methods:

For the microhardness test, three different groups were prepared in accordance with the post-cure treatments: control group (only light cure for 40 s), autoclave group (light cure for 40 s + autoclave for 15 min at 130°C); and microwave group (light cure for 40 s + microwave for 3 min at 450 W). To assess the marginal adaptation, the composite resin was inserted incrementally into a mesial-occlusal-distal cavity brass mold and each increment light-cured for 40 s. A previous reading in micrometers was taken at the cervical wall, using a stereomicroscope magnifying glass equipped with a digital video camera and image-analysis software. Subsequently, the specimens were subjected to the post-cure treatments (autoclave and microwave) and a reading was taken again at the cervical wall. Data were compared using ANOVA for the hardness test, split-plot ANOVA for the adaptation assessment and Tukey''s test for multiple comparisons. A significance level of 5% was adopted for all analyses.

Results:

The post-cure treatments increased the hardness of conventional composites (p<0.001) and the gap values of inlay restorations (p<0.01). Filtek Z250 showed higher hardness (p<0.001) and lower gap values than Opallis and Esthet-X (p<0.05). Gap values did not exceed 90 μm for any of the experimental conditions.

Conclusion:

The post-cure treatments increased the VHN and the gap values on the cervical floor of composite resin inlays. Moreover, Filtek Z250 showed the best results, with higher hardness and lower gap values.     

温度循环老化对复合树脂间粘接强度的影响

目的 探讨复合树脂和粘接界面老化后树脂间粘接强度的变化,以期为临床工作提供实验依据.方法 纳入甲基丙烯酸酯类复合树脂(Clearfil AP-X,树脂A)及其配套粘接剂(Clearfil SEBond,粘接剂a)和环氧树脂(Filtek P90,树脂B)及其配套粘接剂(Filtek P90 System Adhesive,粘接剂b).将树脂A、B分别制作基底树脂块各24块,各分为3组,每组8块:①对照组,基底树脂块表面涂布粘接剂,充填固化新树脂后切成条状试样;②粘接界面老化组,基底树脂块粘接新树脂后切成条状试样,行温度循环老化;③基底树脂老化组,将基底树脂块行温度循环老化后打磨表面,再粘接新树脂,最后切成条状试样.每组中由基底树脂(A、B)-粘接剂(a、b)-新树脂(A、B)构成8种粘接组合,每一组合设2个平行样.体视显微镜下筛选条状试样,每个粘接组合获得15条微拉伸试样,用微拉伸测试仪检测微拉伸强度,对不同粘接组合中粘接界面老化组与对照组、基底树脂老化组与对照组的微拉伸强度行独立样本t检验.结果 粘接界面老化组中,由粘接剂a粘接新树脂A或B的粘接组合[A-a-A:(45.0±3.2)MPa,B-a-A:(41.7±3.3) MPa,A-a-B:(28.6±3.9) MPa,B-a-B:(47.7±6.6) MPa],及由粘接剂b粘接新树脂A的粘接组合[A-b-A:(44.2±4.7) MPa,B-b-A:(38.0±3.2) MPa],微拉伸强度均显著低于各自对照组[A-a-A:(70.7±5.5) MPa,B-a-A:(60.3±5.1) MPa,A-a-B:(44.2±1.6) MPa,B-a-B:(54.1±3.2) MPa,A-b-A:(65.6±7.2) MPa,B-b-A:(59.1±4.1) MPa](P＜0.05);而由粘接剂b粘接新树脂B的粘接组合A-b-B及B-b-B的微拉伸强度与各自对照组相比差异均无统计学意义(P＞0.05).基底树脂老化组中,各粘接组合的微拉伸强度均显著低于各自对照组(P＜0.05).结论 复合树脂和粘接界面的老化均可对复合树脂间的粘接强度产生影响.     

MARGINAL ADAPTATION AND PERFORMANCE OF BIOACTIVE DENTAL RESTORATIVE MATERIALS IN DECIDUOUS AND YOUNG PERMANENT TEETH

Objective:

The aim of this study was to investigate the adaptation of different types of restorations towards deciduous and young permanent teeth.

Materials and Methods:

Class V cavities were prepared in deciduous and young permanent teeth and filled with different materials (a conventional glass-ionomer, a resin-modified glass-ionomer, a poly-acid-modified composite resin and a conventional composite resin). Specimens were aged in artificial saliva for 1, 6, 12 and 18 months, then examined by SEM.

Results:

The composite resin and the polyacid-modified composite had better marginal adaptation than the glass-ionomers, though microcracks developed in the enamel of the tooth. The glass-ionomers showed inferior marginal quality and durability, but no microcracking of the enamel. The margins of the resin-modified glass-ionomer were slightly superior to the conventional glass-ionomer. Conditioning improved the adaptation of the composite resin, but the type of tooth made little or no difference to the performance of the restorative material. All materials were associated with the formation of crystals in the gaps between the filling and the tooth; the quantity and shape of these crystals varied with the material.

Conclusions:

Resin-based materials are generally better at forming sound, durable margins in deciduous and young permanent teeth than cements, but are associated with microcracks in the enamel. All fluoride-releasing materials give rise to crystalline deposits.     

OPTICAL DENSITY AND CHEMICAL COMPOSITION OF MICROFILLED AND MICROHYBRID COMPOSITE RESINS

This study evaluated the optical density of two microfilled and two microhybrid resins, as well as the composition of these materials with regard to their optical density. Cavities prepared in 12 2-mm- or 4-mm-thick acrylic plastic plates were filled with Z250 (3M-ESPE), A110 (3M-ESPE), Charisma (Heraeus-Kulzer) and DurafillVS (Heraeus-Kulzer). The resin increments (2-mm-thick) were light-cured for 40 s. Three 0.12-s radiographic exposures were made of each #2 acrylic plastic plate. DenOptix system optical plates were used to obtain the digital images. Three readings of the composite resin surface were made in each radiograph, totalizing 216 readings. The mean of highest and lowest grey-scale values was obtained. Two specimens of each composite resin were prepared for SEM analysis of the chemical elements related to optical density, using energy dispersive x-ray analysis (EDX). The results were subjected to Shapiro-Wilk''s test, ANOVA, Tukey''s test at 1% level of significance and Pearson''s correlation. The mean grey-scale values at 2 mm and 4 mm were: Z250 = 154.27a and 185.33w; A110 = 46.77b and 63.05y; Charisma = 163.40c and 200.46z; DurafillVS = 43.92b and 58.99x, respectively. Pearson''s test did not show any positive correlation between optical density and percentage weight of optical density chemical elements. It was concluded that the microhybrid resins had higher optical density means than the microfilled resins; among the evaluated resins, Charisma had the highest optical density means.     

Mechanical performance of encapsulated restorative glass-ionomer cements for use with Atraumatic Restorative Treatment (ART)

The Atraumatic Restorative Treatment (ART) approach was suggested to be a suitable method to treat enamel and dentine carious lesions in patients with disabilities. The use of a restorative glass-ionomer with optimal mechanical properties is, therefore, very important.

Objective:

To test the null-hypotheses that no difference in diametral tensile, compressive and flexural strengths exists between: (1) The EQUIA system and (2) The Chemfil Rock (encapsulated glass-ionomers; test materials) and the Fuji 9 Gold Label and the Ketac Molar Easymix (hand-mixed conventional glass-ionomers; control materials); (3) The EQUIA system and Chemfil Rock.

Material and Methods:

Specimens for testing flexural (n=240) and diametral tensile (n=80) strengths were prepared according to standardized specifications; the compressive strength (n=80) was measured using a tooth-model of a class II ART restoration. ANOVA and Tukey B tests were used to test for significant differences between dependent and independent variables.

Results:

The EQUIA system and Chemfil Rock had significantly higher mean scores for all the three strength variables than the Fuji 9 Gold Label and Ketac Molar Easymix (α=0.05). The EQUIA system had significant higher mean scores for diametral tensile and flexural strengths than the Chemfil Rock (α=0.05).

Conclusion:

The two encapsulated high-viscosity glass-ionomers had significantly higher test values for diametral tensile, flexural and compressive strengths than the commonly used hand-mixed high-viscosity glass-ionomers.     

GLASS IONOMER CEMENTS AND THEIR ROLE IN THE RESTORATION OF NON-CARIOUS CERVICAL LESIONS

Glass ionomer based materials are clinically popular in several areas of restorative dentistry, but restoration of cervical lesions has proven particularly successful. Various etiologies, conformations, locations and structural characteristics make non-carious cervical lesions more challenging to adhesive restorative procedures and marginal seal in the long run. Due to their characteristics, glass ionomer cements (GICs) have precise indication for these cases. Moreover, the use of a GIC base underneath composite resin, the so-called "sandwich" or mixed technique, allows associating the good characteristics of composite resins and GICs, and has been considered quite useful in the restoration of non-carious cervical defects. The aim of this paper is to critically review the literature and discuss peculiar features of GICs regarding their role in the restoration of non-carious cervical lesions.     

Shear bond strength vs interfacial fracture toughness — Adherence to CAD/CAM blocks

ObjectiveTo compare shear bond strength (SBS) and interfacial fracture toughness (IK_IC) results when assessing the effect of surface roughness and thermocycling on the adherence of a resin composite luting agent (RCLA) to a CAD/CAM resin composite block (RCB).MethodsTetric CAD HT along with the recommended bonding system, Adhese Universal and Variolink Esthetic LC, were used. Surface roughness was achieved with 600/320/60 grit SiC papers. Samples were stored 24 h in 37 °C water or thermocycled 10000× (5 °C–55 °C) prior to testing. Results were analyzed by univariate ANOVA and Scheffé modified t-tests (α = 0.05). Fractured specimens were viewed with a stereo microscope and selected specimens with a scanning electron microscope.ResultsSBS results showed a significant difference between the 60 grit group and the other groups, both after 24 h and thermocycling. A large number of SBS samples showed cohesive fracture or subsurface damage in RCB. Thermocycling led to a significant decrease in SBS in all groups. IK_IC results showed no significant differences due to surface preparation after 24 h storage in 37 °C. After thermocycling, there was a significant difference between the 60 and the 600 grit groups. All K_IC samples fractured adhesively at the RCB surface. K_IC of the RCLA was significantly higher than IK_IC of all groups.SignificanceThe results endorse the use of fracture mechanics methodology for the assessment and characterization of adherence, while identifying difficulties in its implementation. The results suggest also that adherence to CAD/CAM RCB may be limited by the strength of the resin composite block — adhesive interface.