RESUMO
Polymer networks are considered to be largely affected by water and chemical absorption from environment. Objective: The aim of this study was to evaluate the hygroscopic expansion of bulk-fill composite. Material and Methods: Fifteen disks (5 in each group) with different thickness(4mm/2mm) of Tetric N-Ceram Bulk Fill composite(TB) and Tetric N-Ceram composite(TN) were made according to the manufacturer's instruction and stored in deionized water. The length of each specimen was recorded using a digital micrometer at baseline and at the end of 24 h, 1, 2, 4, 12 weeks intervals. Repeated measure ANOVA and Tukey HSD were used to determine the effect of variables. At 12 weeks, the mean hygroscopic expansion after water immersion ranged between 0. 33±0.09mm for TN to 0.41±0.07mm for TB with 2mm thickness. Repeated measure ANOVA revealed a significant increase in hygroscopic expansion over time (P <0.05). Results: The results indicated that at 24hours and 2weeks there was a significant difference among TN and TB with 4mm thickness (p=0.007 and p=0.023, respectively). The other differences were not significant. Hygroscopic expansion affected by the type of composite and the passing of time. Conclusion: The results showed that the time taken to reach stabilization in hygroscopic expansion was shorter for TN in comparison with TB. For 2mm thickness equilibrium was attained earlier. (AU)
Considera-se que as redes de ligações intrínsecas de polímeros são amplamente afetadas pela absorção de água e produtos químicos do meio ambiente. Objetivo: O objetivo deste estudo foi avaliar a expansão higroscópica do compósito bulk-fill. Material e Métodos: Quinze discos (5 em cada grupo) com diferentes espessuras (4mm / 2mm) de compósito Tetric N-Ceram Bulk Fill (TB) e Tetric N-Ceram (TN) foram confeccionados de acordo com as instruções do fabricante e armazenados em água deionizada. O comprimento de cada espécime foi registrado usando um micrômetro digital no início e no final de 24 h, 1, 2, 4, 12 semanas de intervalo. O teste de medidas repetidas ANOVA e Tukey foram usados para determinar o efeito das variáveis. Às 12 semanas, a expansão higroscópica média após imersão em água variou entre 0,33 ± 0,09mm para NT a 0,41 ± 0,07mm para TB com 2mm de espessura. ANOVA revelou um aumento significativo na expansão higroscópica ao longo do tempo (P <0,05). Resultados: Os resultados indicaram que às 24h e 2 semanas houve diferença significativa entre TN e TB com 4mm de espessura (p=0,007 e p=0,023, respectivamente). As outras diferenças não foram significativas. A expansão higroscópica foi afetada pelo tipo de compósito e pelo tempo. Conclusão: Os resultados mostraram que o tempo necessário para alcançar a estabilização na expansão higroscópica foi menor para TN em comparação com TB. Para 2 mm de espessura o equilíbrio foi atingido mais cedo. (AU)
Assuntos
Resinas Compostas , Polimerização , ÁguaRESUMO
Objective: Zirconia cores have limited light transmittance and data are scarce on light transmission through zirconia cores with and without the veneering ceramic
Methods: In this in vitro study, Disc-shaped specimens [11.5 mm in diameter and 0.4 [0.05] mm in thickness] were fabricated of three types of zirconia namely Mamut, Heany and ZirkonZahn [n=5]. A disc-shaped specimen [11.5 mm in diameter and 0.65 [0.05] mm in thickness] of veneering ceramic [Cerabien ZR, Kuraray, Noritake, Japan] was also fabricated. The intensity of light transmitted through the zirconia specimens with and without the veneering ceramic was recorded using a light curing unit [LED, SDI Radii Plus, Australia] and its respective radiometer [LED Radiometer, SDI, Australia]. Data were analyzed using repeated measures ANOVA and Tukey's HSD test
Results: A significant difference was noted in light transmission among different types of zirconia before and after veneering. After veneering, light transmission decreased in all specimens and the reduction in light transmission in Zirkonzahn group was significantly greater than that in Heany and Mamut groups [p<0.001]
Conclusion: Veneered zirconia systems have limited translucency and ceramic veneering significantly decreases light transmission through zirconia
RESUMO
Objective: Bulk-fill composites are a group of composite resins designed for easy and fast filling of large cavities. This study aimed to assess the color stability of bulk-fill composites subjected to xenon radiation and evaluate their color change [[delta]E] following polymerization
Methods: In this in vitro experimental study, 30 specimens [4mm in height and 8mm in diameter] were fabricated of x-traFil and Tetric N-Ceram universal color bulk-fill composites and A2 shade of Grandio composite [as control]. Bulk-fill composites were placed in the mold in 4mm thickness according to the manufacturers' instructions. In the control group, composite was applied to the mold in two layers each with 2mm thickness. Tetric and Grandio composites were cured for 20 seconds and x-traFil was cured for 10 seconds with a LED light-curing unit. A total of 15 specimens [five of each composite] were used for each test. For assessment of color change due to polymerization, L[asterisk], a[asterisk] and b[asterisk] color parameters were measured before and immediately after polymerization and also 30 days after immersion in distilled water in an incubator at 37[degree sign] and 70% humidity using a spectroradiometer. For xenon test, the specimens were subjected to color analysis after 48 hours of storage in distilled water. Next, they were subjected to xenon lamp radiation in xenon environment chamber for 122 hours at 22[degree sign] and 25% humidity and then the color parameters were measured again. The mean and standard deviation [SD] of all values were calculated. One-way and repeated measures ANOVA were used to compare [delta]E and [delta]L among the groups. Tukey's HSD test was used for pairwise comparisons
Results: The value of [delta]E immediately after polymerization was the lowest for Grandio [4.91] and the highest for Tetric [9.44]. Thirty days after the polymerization, [delta]E was the lowest in Grandio [3.07] and the highest in Tetric [9.27]; [delta]E showed a decreasing trend over time in all specimens. Under xenon light radiation, Grandio showed the lowest [1.50] and Tetric showed the highest [delta]E [11.15]
Conclusion: Following polymerization and under xenon lamp radiation, [delta]E of conventional composite was less than that of bulk-fill composites
RESUMO
Objective: Numerous studies have emphasized on the importance of developing an ideal educational system for high-quality dental education. The present study sought to assess the perception of dental students on operative dentistry education in Department of Restorative Dentistry, Shahid Beheshti Dental School, Tehran, Iran
Methods: In this descriptive cross-sectional study, 220 students were selected and given a questionnaire including demographic , grades in operative dentistry clinical and didactic courses, the efficacy of preclinical courses in preparing students for clinical practice, ways to improve competency and expertise of students for clinical setting, student's opinion on relating the assessment tests with the taught topics, required instructional resources for assessment of students' proficiency in restorative dentistry and satisfaction rate of students with clinical courses offered in the current curriculum. Data were analyzed using descriptive statistics [SPSS 18]
Results: The Clinical Operative Dentistry 3 and Preclinical Dental Anatomy received a mean satisfaction score of 3.31 and 2.74, respectively. Furthermore, 57.3% of students highly emphasized the necessity of studying textbooks of restorative dentistry. 50.5% of students believe that lectures by instructors along with active participation of students were the best method for didactic operative dentistry courses. In addition, 60.5% were in favor of using a combination of textbooks, lectures, and class notes for the assessment of students' learning
Conclusion: The present study revealed that Department of Restorative Dentistry in Shahid Beheshti Dental School is successful in its teaching and achieving students' satisfaction. However, some revisions need to be made in educational methods and contents and active participation of students in class discussions should be encouraged as well