Spectrophotometric assessment of the color stability of composite resins polished with different techniques.

This study aimed to use spectrophotometry to assess the color stability of composite resins polished with different polishing techniques and scanning electron microscopy (SEM) to evaluate the surface micromorphology of the specimens. In this in vitro experimental study, a total of 96 disc-shaped specimens were fabricated from microfilled (Renamel Microfill, shade SB3) and nanohybrid (Estelite Sigma Quick, shade BW) composite resins in bright white shades (n = 48). Each group was randomized into 1 control and 2 experimental subgroups (n = 16): no polishing (control), polishing with aluminum oxide discs (experimental), or polishing with diamond-impregnated spiral wheels (experimental). In each subgroup, half of the specimens were immersed in a coffee solution and the other half in a tea solution for 48 hours after finishing (control) or polishing (experimental). Spectrophotometry was used to measure the color of the specimens at baseline, after finishing, after polishing (experimental groups only), and after immersion in tea and coffee. The surface micromorphology of a randomly selected specimen from each subgroup was assessed under SEM. The color change (ΔE*) of the specimens between measurements was calculated and analyzed using 1-way, 2-way, and 3-way analyses of variance (ANOVAs) and the Tukey test. Both tea and coffee caused significant color change in the composite resin specimens, with specimens immersed in coffee undergoing significantly greater color change than those immersed in tea (P < 0.001; 2-way ANOVA). The nanohybrid composite specimens polished with polishing discs had a significantly greater color change than nanohybrid specimens polished with spiral wheels (P = 0.041). The Tukey test revealed that there was no overall significant difference between the 2 polishing techniques (P = 0.505), but both of these subgroups exhibited a significantly lower color change than the control group (P < 0.001). In general, SEM did not reveal substantial differences between the 2 polishing techniques, but specimens polished by spiral wheels appeared to have a smoother surface. All polished specimens demonstrated clinically acceptable mean color change values (ΔE* < 3.5). The type of coloring agent had a greater effect on color stability than either the polishing technique or type of composite resin, with coffee causing a greater color change than tea.

The effect of atmospheric pressure on the bond strength of composites.

Background: In the current study, we investigated the effect of atmospheric pressure change on the microtensile bond strength of direct and indirect composite restorations to the teeth. Materials and Methods: A total of 16 extracted teeth were prepared after crown cutting and randomly divided into four groups. The study groups included: 1) direct restoration (Filtek™ Z250 Universal Composite Restorative System, 3M, United States) at constant pressure (control); 2) direct restoration in variable pressure; 3) indirect restoration (Z250 composite) at constant pressure (control); and 4) indirect restoration at variable pressure. Then, samples were subjected to thermal cycles. Variable pressure groups were pressurized to 0 to 5 atmospheres for 96 cycles inside the hyperbaric chamber, followed by measuring the microtensile bond strength of the specimens. Results: The mean of microtensile bond strength in both direct and indirect variable-pressure groups was significantly lower than their counterpart control groups. There was no significant difference between direct and indirect restorations in constant and variable pressure. The failure mode of the samples in the control groups was often mixed, while in the pressure groups, it was dominated by adhesive. Also, microscopic examination of restoration interfaces showed that the number and volume of voids in variable pressure groups were much more than the control groups. Conclusion: Regardless of the type of restoration, changing the atmospheric pressure is effective on the bond strength of the restorations to the teeth.

Thermal effect of light irradiation time on the setting time of mineral trioxide aggregate and calcium-enriched mixture cements.

This study aimed to assess the thermal effect of different light irradiation times on the setting time of mineral trioxide aggregate (MTA) and calcium-enriched mixture (CEM) cements. This in vitro experimental study evaluated 40 hydraulic cement specimens, including 20 MTA and 20 CEM specimens, according to the manufacturers'instructions. For each cement, the specimens were divided into 3 test groups light cured with a halogen light-curing unit (n = 5 per group) and 1 control group (n = 5) that was not exposed to irradiation. The specimens in the MTA test groups were light cured for 20, 40, or 60 seconds, and the specimens in the CEM test groups were light cured for 60, 90, or 120 seconds. All test and control groups had 60 seconds of rest time. Setting of the cements was assessed at different timepoints using a Gillmore needle weighing 113.4 g with a 12.2-mm diameter according to ASTM C266-03 standards. The data were analyzed with the Fisher exact test and the Mann-Whitney U test (α = 0.05). The setting of MTA specimens after different curing times was significantly different (P < 0.05). The setting time of MTA control specimens was significantly longer than that of test specimens (P = 0.008). The setting of CEM specimens after different curing times was not significantly different (P > 0.05). However, the setting time for CEM control specimens was significantly longer than that for test specimens (P = 0.008). Light curing with a halogen light-curing unit can significantly decrease the setting time for MTA and CEM cements.

Composite surface roughness and color change following airflow usage.

BACKGROUND: Esthetic dental restorations have gained increasing popularity. The surface of restorations should be smooth enough to achieve maximum esthetics and prevent the adhesion of microorganisms and food particles. This study aimed to assess the surface roughness and color change of composite specimens following airflow usage. METHODS: In this in vitro, experimental study, 30 Tokuyama composite discs were fabricated and randomly divided into three groups (n = 10) for the use of airflow with calcium carbonate/bicarbonate powder and conventional polishing with FlexiDisc. The surface roughness of the specimens was measured by profilometry while the color change was assessed by measuring the L*, a* and b* color parameters using spectrophotometry before polishing (T1). The composite specimens were then polished for stain removal, and their surface roughness as well as color parameters were remeasured after polishing (T2). Paired t-test and Tukey's test were applied for within-group and between-group comparisons. RESULTS: Significant differences were noted in roughness average (Ra) between airflow with calcium carbonate (0.251 ± 0.014 µm) and airflow with sodium bicarbonate (0.421 ± 0.208 µm), and between airflow with sodium bicarbonate and FlexiDisc (0.207 ± 0.076 µm) groups after polishing (P < 0.05). Regarding the correlation of change in surface roughness and color parameters at T1 and T2, an inverse correlation was noted between the change in surface roughness and all color parameters except for L*. In other words, reduction in surface roughness decreased the a* and b* color parameters. CONCLUSIONS: Within the limitations of this study, the results showed that the airflow device used in this study had no significant difference with conventional polishing in terms of reduction in surface roughness and staining. Considering the cost and maintenance of the airflow device, it is not suggested as a suitable alternative to the conventional polishing procedures. TRIAL REGISTRATION NUMBER: This study does not involve human subjects.

Effect of different surface treatment on the repair bond strength of feldspathic porcelain.

BACKGROUND: Considering the use of silane-containing universal adhesives to enhance the repair bond strength of porcelain restorations, a question arises whether the application of these adhesives eliminates the need for a separate application of silane or not. OBJECTIVES: This study aimed to assess the effect of various kinds of surface treatment, including hydrofluoric acid (HF) etching, the application of bis-silane and the use of universal adhesives, on the repair bond strength of feldspathic porcelain. MATERIAL AND METHODS: In this experimental in vitro study, 70 porcelain disks were fabricated and divided into 7 groups (n = 10) for the following types of surface treatment: C (control group) ­ HF etching + silane + Porcelain Bond; HSB ­ HF etching + Single Bond; HSSB ­ HF etching + silane + Single Bond; HAB ­ HF etching + All Bond; HSAB ­ HF etching + silane + All Bond; HFB ­ HF etching + FuturaBond®; and HSFB ­ HF etching + silane + FuturaBond. After applying different kinds of surface treatment, the specimens were light-cured and the Filtek® Z250 composite was bonded to the treated surfaces. The specimens were incubated in distilled water at 37°C for 24 h, and then underwent 5,000 thermal cycles. The repair bond strength of porcelain was measured and the mode of failure was determined under a stereomicroscope. Data was analyzed using the one-way analysis of variance (ANOVA) and Tukey's test. RESULTS: Differences between the groups in the porcelain repair bond strength were significant (p < 0.0001). Bond strength for Single Bond (p < 0.001) and All Bond (p < 0.001) along with silane was significantly higher than for the application of these adhesives without a separate silane application step. This difference was not significant for FuturaBond. Mixed failure was the dominant mode of failure in all groups. CONCLUSIONS: The application of silane, irrespective of the use of universal adhesives with or without silane, increased the porcelain repair bond strength. Thus, a separate silane application step following HF etching and the use of universal adhesives with or without silane can enhance the repair bond strength of feldspathic porcelain.

Nd:YAG Laser Treatment of Bioglass-coated Zirconia Surface and Its Effect on Bond Strength and Phase Transformation.

PURPOSE: To evaluate the morphological properties, phase transformation, and microshear bond strength of composite cement to bioglass-coated zirconia surfaces treated with Nd:YAG laser. MATERIALS AND METHODS: Seventy-five zirconia disks were divided into five groups (n = 15). Group C received no surface treatment (control). Group S was subjected to sandblasting with 50-µm aluminum oxide particles. Group B samples were coated with bioglass 45S5. Groups BL9 and BL5 received bioglass coating and laser irradiation with 9 J/cm2 and 5 J/cm2 energy density. Morphological assessment was done using atomic force microscopy (AFM) and scanning electron microscopy (SEM). Zirconia phase transformation was assessed by XRD. Microhear bond strength testing was performed using a modified microtensile tester. The data were analyzed using the Welch test and the Games-Howell test (p < 0.05). RESULTS: The sandblasted and bioglass-coated groups showed the highest bond strengths compared to other groups (p < 0.05). Group S showed the highest surface roughness and the highest frequency of cohesive failure. In all samples, the tetragonal phase decreased after surface treatment. Groups BL9 and BL5 showed some levels of tetragonal to cubic phase transformation. CONCLUSION: Bioglass coating of zirconia surfaces (using the slurry method) can increase its microshear bond strength comparable to that of sandblasting. Surface roughness of sandblasted zirconia was the highest among all methods. Irradiation of Nd:YAG laser on bioglass-coated zirconia surfaces is not effective and decreases its bond strength compared to sandblasting and bioglass coating. Increasing the Nd:YAG laser energy density cannot increase the surface roughness of bioglass-coated zirconia surfaces. Bioglass coating results in transformation of the tetragonal to the cubic phase.

Surface topography and bond strengths of feldspathic porcelain prepared using various sandblasting pressures.

OBJECTIVE: The purpose of this study was to determine the bond strength of composite resin to feldspathic porcelain and its surface topography after sandblasting at different pressures. METHODS: In this in vitro study, 68 porcelain disks were fabricated and randomly divided into four groups of 17. The porcelain surface in group 1 was etched with hydrofluoric acid. Groups 2, 3, and 4 were sandblasted at 2, 3 and 4 bars pressure, respectively. Surface topography of seven samples in each of the four groups was examined by a scanning electron microscope (SEM). The remaining 40 samples received the same silane agent, bonding agent, and composite resin and they were then subjected to 5000 thermal cycles and evaluated for shear bond strength. Data were analyzed using one-way anova. The mode of failure was determined using stereomicroscope and SEM. RESULTS: The highest shear bond strength was seen in group 4. however, statistically significant differences were not seen between the groups (P = 0.780). The most common mode of failure was cohesive in porcelain. The SEM showed different patterns of hydrofluoric acid etching and sandblasting. CONCLUSION: Increasing the sandblasting pressure increased the surface roughness of feldspathic porcelain but no difference in bond strength occurred.

Effect of Extension and Type of Composite-Restored Class II Cavities on Biomechanical Properties of Teeth: A Three Dimensional Finite Element Analysis.

OBJECTIVES: Controversy exists regarding cavity preparation for restoration of interproximal caries in posterior teeth in terms of preserving the tooth structure and suitable stress distribution. This study aimed to assess the effect of extension and type of class II cavities and the remaining tooth structure in maxillary premolars restored with composite resin on the biomechanical properties of teeth using finite element method (FEM). MATERIALS AND METHODS: Using FEM, eight three-dimensional (3D) models of class II cavities in maxillary premolars with variable mesiodistal (MD) dimensions, variable thickness of the residual wall in-between the mesial and distal cavities and different locations of the wall were designed. Other dimensions were the same in all models. Cavities were restored with composite resin. A load equal to the masticatory force (200N) was applied to the teeth. Finite element analysis (FEA) was used to calculate the von Mises stress. RESULTS: Stress in the enamel margin increased by increasing the MD dimensions of the cavities. Deviation of the residual wall between the mesial and distal cavities from the tooth center was found to be an important factor in increasing stress concentration in the enamel. Increasing the MD dimensions of the cavity did not cause any increase in stress concentration in dentin. CONCLUSION: Increasing the MD dimensions of the cavities, decreasing the thickness of the residual wall between the mesial and distal cavities and its deviation from the tooth center can increase stress concentration in the enamel but not in dentin.

Surface treatment of feldspathic porcelain: scanning electron microscopy analysis.

PURPOSE: Topographic analysis of treated ceramics provides qualitative information regarding the surface texture affecting the micromechanical retention and locking of resin-ceramics. This study aims to compare the surface microstructure following different surface treatments of feldspathic porcelain. MATERIALS AND METHODS: This in-vitro study was conducted on 72 porcelain discs randomly divided into 12 groups (n=6). In 9 groups, feldspathic surfaces were subjected to sandblasting at 2, 3 or 4 bar pressure for 5, 10 or 15 seconds with 50 µm alumina particles at a 5 mm distance. In group 10, 9.5% hydrofluoric acid (HF) gel was applied for 120 seconds. In group 11, specimens were sandblasted at 3 bar pressure for 10 seconds and then conditioned with HF. In group 12, specimens were first treated with HF and then sandblasted at 3 bar pressure for 10 seconds. All specimens were then evaluated under scanning electron microscopy (SEM) at different magnifications. RESULTS: SEM images of HF treated specimens revealed deep porosities of variable sizes; whereas, the sandblasted surfaces were more homogenous and had sharper peaks. Increasing the pressure and duration of sandblasting increased the surface roughness. SEM images of the two combined techniques showed that in group 11 (sandblasted first), HF caused deeper porosities; whereas in group 12 (treated with HF first) sandblasting caused irregularities with less homogeneity. CONCLUSION: All surface treatments increased the surface area and caused porous surfaces. In groups subjected to HF, the porosities were deeper than those in sandblasted only groups.

Psychometric properties of a Farsi version of the authentic assessment perception questionnaire.

The term 'authentic assessment' has recently gained widespread use in education. A five-dimensional questionnaire for authentic assessment was translated into Farsi. The questionnaire which comprises 29 items, divided into 5 subscales (task, physical context, social context, result/form and criteria) was developed in English by Dr. Gulikers and her colleagues in the Netherlands. The questionnaire was translated using a forward-backward method and was pilot tested in terms of translation clarity and applicability. The psychometric properties of the Persian version of the questionnaire were evaluated in terms of face, content, and construct validity in addition to test-retest reliability. A convenience sample of 230 dental students (70 males and 160 females) studying in four dental schools in Tehran city was recruited to evaluate the reliability and construct validity of the Persian version. The quality rating of the translations was favorable, suggesting a high quality of both forward and backward translations. The Content Validity Index (CVI) and Ratio (CVR) for the final Farsi version of the questionnaire were found to be acceptable. Cronbach alpha coefficients for all subscales ranged from 0.78-0.91. These preliminary results suggest that a five dimensional questionnaire in its Farsi version may be a valuable tool in dental education assessment and studies.