RESUMO

The objective of this study was to evaluate the influence of Er:YAG laser (λ = 2.94 µm) on microtensile bond strength (µTBS) and superficial morphology of bovine dentin bleached with 16% carbamide peroxide. Forty bovine teeth blocks (7 × 3 × 3 mm(3)) were randomly assigned to four groups: G1- bleaching and Er:YAG irradiation with energy density of 25.56 J/cm(2) (focused mode); G2 - bleaching; G3 - no-bleaching and Er:YAG irradiation (25.56 J/cm(2)); G4 - control, non-treated. G1 and G2 were bleached with 16% carbamide peroxide for 6 h during 21 days. Afterwards, all blocks were abraded with 320 to 600-grit abrasive papers to obtain flat standardized dentin surfaces. G1 and G3 were Er:YAG irradiated. Blocks were immediately restored with 4-mm-high composite resin (Adper Single Bond 2, Z-250-3 M/ESPE). After 24 h, the restored blocks (n = 9) were serially sectioned and trimmed to an hour-glass shape of approximately 1 mm(2) at the bonded interface area, and tested in tension in a universal testing machine (1 mm/ min). Failure mode was determined at a magnification of 100× using a stereomicroscope. One block of each group was selected for scanning electron microscope (SEM) analysis. µTBS data was analyzed by two-way ANOVA and Tukey test (α = 0.05). Mean bond strengths (SD) in MPa were: G1- 32.7 (5.9)(A); G2- 31.1 (6.3)(A); G3- 25.2 (8.3)(B); G4- 36.7 (9.9).(A) Groups with different uppercase letters were significantly different from each other (p < .05). Enamel bleaching procedure did not affect µTBS values for dentin adhesion. Er:YAG laser irradiation with 25.56 J/cm(2) prior to adhesive procedure of bleached teeth did not affect µTBS at dentin and promoted a dentin surface with no smear layer and opened dentin tubules observed under SEM. On the other hand, Er:YAG laser irradiation prior to adhesive procedure of non-bleached surface impaired µTBS compared to the control group.

Assuntos

Resinas Compostas/efeitos da radiação , Colagem Dentária , Dentina/efeitos da radiação , Lasers de Estado Sólido , Resistência à Tração , Animais , Peróxido de Carbamida , Bovinos , Esmalte Dentário/efeitos dos fármacos , Esmalte Dentário/efeitos da radiação , Dentina/ultraestrutura , Microscopia Eletrônica de Varredura , Peróxidos/farmacologia , Cimentos de Resina/efeitos da radiação , Clareamento Dental , Ureia/análogos & derivados , Ureia/farmacologia

RESUMO

OBJECTIVE: The objective of this study was to evaluate the influence of different Er:YAG laser (λ = 2.94 µm) energy parameters on the microtensile bond strength (µTBS) and superficial morphology of bovine enamel bleached with 16% carbamide peroxide. BACKGROUND: Laser irradiation could improve adhesion to bleached enamel surfaces. METHODS: Sixty bovine enamel blocks (7 × 3 × 3 mm(3)) were randomly assigned to six groups according to enamel preparation procedures (n = 10): G1-bleaching and Er:YAG laser irradiation with 25.52 J/cm(2) (laser A, LA); G2-bleaching and Er:YAG laser irradiation with 4.42 J/cm(2) (laser B, LB); G3-bleaching; G4-Er:YAG laser irradiation with 25.52 J/cm(2); G5-Er:YAG laser irradiation with 4.42 J/cm(2); G6-control, no treatment. G1 to G3 were bleached for 6 h during 21 days. Afterwards, enamel surfaces in all groups were slightly abraded with 600-grit SiC papers and G1, G2, G4 and G5 were irradiated according to each protocol. Enamel blocks were then restored with an etch-and-rinse adhesive system and a 4-mm thick composite buildup was made in two increments (n = 9). After 24 h, restored blocks were serially sectioned with a cross-section area of ∼1 mm(2) at the bonded interface and tested in tension in a universal testing machine (1 mm/min). Failure mode was determined at a magnification of x100 using a stereomicroscope. One treated block of each group was selected for scanning electron microscopy (SEM) analysis. µTBS data were analyzed by two-way ANOVA and no statistical differences were observed among groups. RESULTS: Mean bond strengths (SD) in MPa were: G1-30.4(6.2); G2-27.9(8.5); G3-32.3(3.9); G4-23.7(5.8); G5-29.3(6.0); G6-29.1(6.1). A large number of adhesive failures was recorded for bleached and irradiated enamel surfaces. CONCLUSIONS: Bleached enamel surfaces µTBS values were not significantly different from those of unbleached enamel. Even though Er:YAG laser irradiation with both parameters had no influence on µTBS for bleached and unbleached enamel, SEM analysis revealed that Er:YAG laser irradiation with 25.52 J/cm(2) should not be recommended, as enamel ablation was observed, whereas irradiation with 4.42 J/cm(2) did not promote any remarkable changes on enamel surface.

Assuntos

Colagem Dentária/métodos , Esmalte Dentário/efeitos dos fármacos , Esmalte Dentário/efeitos da radiação , Adesivos Dentinários/química , Lasers de Estado Sólido , Clareamento Dental , Animais , Bovinos , Microscopia Eletrônica de Varredura , Distribuição Aleatória , Resistência à Tração

RESUMO

BACKGROUND: The understanting of the dental fluorosis process, that begins with enamel maturation, is important to Dentistry students, since fluoride has drastically decreased the incidence of caries in several population groups, with a resultant increase in fluorosis prevalence and severity, as shown in literature. AIMS: The objective of this paper is to report the changes in the level of knowledge about dental fluorosis of undergraduate Dentistry students at Guarulhos University. SUBJECTS AND METHODS: One hundred and twenty-four undergraduate students enrolled in the first and second semester (2008) and seventh semester (2008) were evaluated. The data was obtained through questionnaires with dichotomic questions (true and false) and an alternative to evaluate whether the subject had been presented in the classroom. The data obtained was submitted to statistical analysis using the Chi-square test (α=0.05). RESULTS: When evaluating the first semester students, differences were verified in numbers of the questions assigned with the alternatives true or false, when compared with seventh semester students (p<0.001). However, there were no differences when the same questionnaire was applied to the first semester students after six months (p=0.358). CONCLUSIONS: It is possible to conclude that the six months period was insufficient to increase the level of knowledge about dental fluorosis, and when the students beginning and concluding the dentistry course were compared, there was an increase in the number of correctly assigned true or false questions in the latter group.