Ultrastructural Alterations and Physical Changes on Bovine Dentin After Internal Bleaching with 35 % Hydrogen Peroxide / Alteraciones Ultraestructurales y Cambios Físicos en la Dentina Bovina Después del Blanqueamiento Interior con un 35 % de Peróxido de Hidrógeno

ABSTRACT: The aim of the study was to investigate the effect of internal bleaching on physical proprieties and ultrastructure of the bovine dentin.40 bovine incisors were used, divided in four experimental groups: control group, composed by teeth that did not receive the bleaching agent (G1); teeth submitted to a single internal bleaching session (G2); teeth submitted to two internal bleaching sessions (G3); teeth submitted to three internal bleaching sessions (G4). In each of the sessions, 35 % hydrogen peroxide was applied for 45 minutes on the dentin surface. Tests were performed (microhardness and roughness) and were analyzed using one-way analysis of variance (ANOVA) and Tukey's post-hoc test (p≤0.05). Electromicrographs were captured for quality analysis. In the analysis of the superficial microhardness of the dentin, the internal bleaching reduced the Knoop microhardness since the first session, being observed statistically significant differences between the experimental groups and the control. The surface roughness gradually increased in the G2, G3 and G4 groups, but only G4 presented a statistically significant difference from the others. The qualitatively evaluated electromicrographs showed damage to the dentin ultrastructure, with areas of erosion and greater involvement of the intertubular when compared to peritubular dentin. Internal bleaching with 35 % hydrogen peroxide caused injuries in bovine dentin from the first treatment session. Both modifications in physical properties and dentin ultrastructure have been identified. These changes were intensified the higher the number of dentin internal bleaching sessions was exposed.

RESUMEN: El objetivo de este estudio fue investigar el efecto del blanqueamiento interno sobre las propiedades físicas y la ultraestructura de la dentina bovina. Se utilizaron 40 incisivos bovinos, divididos en cuatro grupos experimentales: grupo de control, compuesto por dientes que no recibieron el agente blanqueador (G1); dientes sometidos a una única sesión interna de blanqueamiento (G2); dientes sometidos a dos sesiones internas de blanqueamiento (G3); dientes sometidos a tres sesiones internas de blanqueamiento (G4). En cada una de las sesiones, se aplicó peróxido de hidrógeno al 35 % durante 45 minutos en la superficie de la dentina. Se realizaron pruebas (microdureza y rugosidad). Los datos se analizaron mediante análisis de varianza de una vía (ANOVA) y prueba post-hoc de Tukey (p≤0,05). Las electromicrografías fueron capturadas para el análisis cualitativo. En el análisis de la microdureza superficial de la dentina, el blanqueamiento interno redujo la microdureza de Knoop desde la primera sesión, observándose diferencias estadísticamente significativas entre los grupos experimentales y el control [NF2]. La rugosidad superficial aumentó gradualmente en los grupos G2, G3 y G4, pero solo G4 presentó una diferencia estadísticamente significativa con respecto a los otros [NF3]. Las electromicrografías evaluadas cualitativamente mostraron daño a la ultraestructura de la dentina, con áreas de erosión y una mayor participación de la dentina intertubular en comparación con la dentina peritubular. El blanqueamiento interno con peróxido de hidrógeno al 35 % causó lesiones en la dentina bovina en la primera sesión del tratamiento. Ambas modificaciones, en propiedades físicas y en la ultraestructura dentinaria, han sido identificadas. Estos cambios se intensificaron a medida que se expuso a mayor número de sesiones de blanqueamiento interno en la dentina.

Choice of toothpaste for the elderly: an in vitro study

Hyposalivation and dental root exposure in the elderly are problems that require special oral care. In this context, the characteristics of certain toothpastes are of particular importance. Thus, the aim of this study was to evaluate the cytotoxicity and dentin wear caused by seven different toothpastes. For dentin wear analysis, 40 root dentin specimens were submitted to 20,000 brushing cycles with the different toothpastes and distilled water (control group-CG), using a brushing machine. Dentin surface loss (SL) was measured by contact profilometer. The cytotoxicity of each toothpaste was tested using cultured fibroblasts submitted to a cell-culture-conditioned medium. Fresh medium served as the control. Cell viability was assessed by MTT assay after 24 h of contact with the conditioned media. The data were analyzed statistically by ANOVA, followed by Tukey’s test (p < 0.05). The SL of the CG was minimal and significantly lower than that of the Oral B Pro Health (OBPH) group (p < 0.05). All other groups presented SL in between that of the CG and the Oral B Pro Health OBPH group, except for the Sensodyne (SEN) group, which presented SL similar to that of CG (p = 0.05). The SEN group presented a percentage of viable cells similar to that of CG: between 60-89%. All the other toothpastes showed high cytotoxicity, with cell viability less than 50% of the CG. Considering study limitations, we concluded that only one of the seven tested toothpastes exhibited the most desirable toothpaste characteristics for the worldwide growing elderly population (e.g. low cytotoxicity and low-abrasive potential).

Wear of depth perception and shade matching outcome in the pre-clinical setting / Percepção da profundidade de desgaste e compatibilidade de cor no ambiente pré-clínico

O presente estudo investigou se a percepção de profundidade de desgaste dental por alunos de graduação tem influência sobre a cor final de restaurações anteriores diretas, realizadas em dentes artificiais. Material e Métodos: Oitenta e um participantes foram divididos em três grupos (n = 27): G1, estudantes do início do curso de odontologia; G2, estudantes de odontologia de nível intermediário; e G3, estudantes de odontologia de nível avançado. Para investigar a percepção de profundidade desgaste dental, cada aluno de graduação recebeu um manequim que continha um incisivo central superior intacto e instruções sobre a técnica de preparação do dente para faceta direta. Todos os grupos foram instruídos a realizar os preparos com 1 mm de profundidade. A profundidade de desgaste dentário foi analisada utilizando um espessímetro. Posteriormente, os dentes foram restaurados com resina composta opaca ou translúcida utilizando-se uma matriz de pré-moldada. A cor foi medida por meio de um espectrofotómetro (L * a * b *). Os dados foram analisados estatisticamente pelo teste KruskalWallis e post hoc de Dunn (α = 5%). Resultados: A profundidade do desgaste dental foi diferente entre todos os grupos (p < 0,05). G1, G2 e G3 obtiveram uma média de 1, 0,5 e 0,8 mm, respectivamente. G3 apresentou maior precisão na profundidade de desgaste dental. Os valores de cor não variaram de acordo com a profundidade de desgaste dental ou para o tipo de resina utilizada na restauração (p > 0,05). Conclusão: A formação técnica e experiência clínica contribuiu para uma melhor percepção de desgaste dental em profundidade por estudantes de graduação em Odontologia. Na configuração pré-clínica, a profundidade de desgaste dental teve pouca ou nenhuma influência sobre a cor final de restaurações anteriores diretas. Além disso, independentemente do tipo de resina composta usada, todas as restaurações realizadas em dentes artificiais tiveram resultado estético similar...

The present study investigated whether the perception of dental wear depth by undergraduate students has influence on the final color of direct anterior restorations performed on artificial teeth. Material and Methods: Eighty-one participants were assigned to one of three groups (n = 27): G1, beginning dental students; G2, intermediate dental students; and G3, advanced dental students. To investigate dental wear depth perception, each undergraduate student received one manikin containing an intact upper central incisor and a flyer instructing the technique of tooth preparation for veneer. All groups were required to prepare 1mm in depth. Dental wear depth was analyzed using a thickness gauge. Subsequently, teeth were restored with opaque or translucent composite resin using a pre-shaped matrix. Color was measured by means of a spectrophotometer (L*a*b* system). Data were statistically analyzed by the Kruskal-Wallis and Dunn’s post hoc tests (α = 5%). Results: Dental wear depth was different among all groups (p < 0.05). G1, G2 and G3 obtained a median of 1 mm, 0.5 mm and 0.8 mm, respectively. G3 presented more accuracy in the dental wear depth. Color values did not vary according to the dental wear depth or to the type of resin composite used in the restoration (p > 0.05). Conclusion: Technical training and clinical experience contribute to the better dental wear depth perception of undergraduate dental students. In the pre-clinical setting, dental wear depth has little or no influence on the final color of direct anterior restorations. Moreover, regardless to the type of resin composite used, all restorations performed on artificial teeth had similar aesthetic outcome...

Left-handed dental students / O estudante de odontologia canhoto

Objectives: to evaluate the frequency of left-handed students and to investigate their difficulties in Operative & Restorative Dentistry, first preclinical discipline of the School of Dentistry, University of São Paulo. Materials and methods: 82 students from both genders participated, who were attending the second year of the course, to whom were applied the Edinburgh Handedness Inventory measurements and a questionnaire about the difficulties encountered by lefty students. Results: in the study sample, we found 6 left-handed students (7%). The greater difficulty reported by them during their laboratorial practice was working in the quadrants on the right side of the manikin’s mouth. Conclusion: therefore, it is clear that Dentistry Schools should be aware of this minority, with regard to the material and equipment availability for lefties, as well as recognition of their difficulties and to orient them to obtain the best performance with minimum discomfort.

Objetivos: Avaliar a frequência de alunos canhotos e investigar suas dificuldades em Dentística Operatória Direta, primeira disciplina pré-clínica da Faculdade de Odontologia da Universidade de São Paulo. Materiais e métodos: Participaram 82 estudantes de ambos os sexos que estavam cursando o segundo ano do curso. Foram aplicados Inventário de Lateralidade de Edimburgo e um questionário sobre as dificuldades encontradas pelos estudantes canhotos. Resultados: Na amostra do estudo foram identificados seis canhotos (7%). A maior dificuldade relatada por eles, durante a prática laboratorial, foi trabalhar nos quadrantes do lado direito da boca do manequim. Conclusão: As Escolas de Odontologia devem estar cientes desta minoria, em relação ao material e disponibilidade de equipamentos para os canhotos, bem como o reconhecimento das suas dificuldades e orientá-los para obter o melhor desempenho com o mínimo desconforto.