Role of enamel and dentin on color changes after internal bleaching associated or not with external bleaching

Objective: To evaluate the effect of the association between external and internal tooth bleaching on color changes in dentin and enamel, individually or recombined, previously stained with triple antibiotic paste (TAP). Methodology: Forty enamel-dentin specimens from bovine incisors were separated into ten blocks according to similarity in their whiteness index (WID). Three specimens within each block were stained by dentin exposure to TAP, and the remaining specimen was used as control to estimate color changes. Specimens were sectioned to separate tissues, and dentin and enamel colors were measured individually and after being recombined. Alterations in color (CIEDE2000 - ΔE00) and translucency parameter (TP) resulting from staining were estimated by color difference between stained and control specimens. The contribution of each tissue to the color change (CTCC) was also calculated. Non-sectioned stained specimens were bleached by applying sodium perborate on dentin, associated or not with 35% hydrogen peroxide on enamel. Color changes caused by bleaching procedures were estimated and data were analyzed using the paired t-test or Two-way repeated measures ANOVA. Results: TAP caused more pronounced changes in dentin, but enamel color was also affected. Both protocols presented a similar ΔE00, and dentin showed the greater color change. After exposure to TAP, we observed a reduction in WID; WID values were the same for bleached and control specimens regardless of protocol. We found no significant effect of substrate and bleaching technique on TP. Enamel played a more critical role in color changes caused by either staining or bleaching procedures. Conclusion: Enamel color played a greater role on tooth color changes than dentin. External and internal bleaching association did not improve bleaching effect on specimens stained with TAP

Study of the repeatability of centric relation registration techniques after the application of ULF-TENS by means of Electronic Position Analysis (EPA)

A relação cêntrica (RC) é uma posição de grande importância no diagnóstico e tratamento em diversas áreas odontológicas. Durante a manipulação em RC, é importante impedir que a memória neuromuscular conduza a um registro incorreto. A neuroestimulação elétrica transcutânea de ultra baixa frequência (ULF-TENS) reduz a atividade eletromiográfica de músculos da mastigação. Desta forma, o presente estudo avaliou a influência da ULF-TENS no deslocamento da cabeça da mandíbula e na repetibilidade das técnicas de manipulação em RC (Bimanual de Dawson, tiras de Long e sistema R.O.C.A), além de verificar qual destas técnicas apresenta maior variabilidade. Para isso, 25 participantes sem Disfunção Temporomandibular (DTM) foram submetidos à duas etapas do estudo realizadas por meio da análise eletrônica de posição (EPA), que permite a avaliação da posição condilar em três eixos (X, Y e Z). Na primeira (ST), foram feitas três sequências com três registros de RC cada, um por técnica de manipulação. Na segunda (CT), foi aplicada a ULF-TENS por 30 minutos antes das sequências de registros, também realizada por três vezes. Utilizou-se o Mann-Whitney (p ≤ 0,05) para verificar a influência da ULF-TENS no deslocamento total para as técnicas Bimanual de Dawson, tiras de Long e sistema R.O.C.A e o ICC e 1-tailed F test a fim de avaliar a repetibilidade e a variância, respectivamente, dessas técnicas. A utilização da ULF-TENS não influenciou no deslocamento total da cabeça da mandíbula, independentemente da técnica de registro de RC utilizada (p>0,05). Apenas a técnica Bimanual apresentou uma melhora na repetibilidade com o uso da ULF-TENS, que foi restrita aos eixos X e Y direitos. Na comparação da variância entre as técnicas, a Bimanual demonstrou menor variação no eixo X, a de Long e R.O.C.A variaram menos no eixo Y e a de Long novamente teve menor variação no eixo Z. Pode-se concluir que o uso da ULF-TENS não altera o posicionamento condilar e melhora, embora discretamente, a repetibilidade apenas da técnica Bimanual. No geral, a técnica de Long apresentou menor variabilidade entre os participantes.Centric relation (CR) is a position of great importance in diagnosis and treatment for several dental specialties. When guiding the jaw to CR, it is important to prevent the neuromuscular memory to mislead the record. Ultra low frequency-transcutaneous electrical nerve stimulation (ULF-TENS) reduces the electromyographic activity of masticatory muscles. Thus, the current study evaluated the influence of ULF-TENS in the displacement of the mandibular condyle and in the repeatability of centric relation registration techniques (Bimanual manipulation, Long technique, R.O.C.A. wires). In addition it was verified which of these techniques presents greater variability. For this purpose, 25 participants without Temporomandibular disorder (TMD) underwent two study stages conducted via electronic position analysis (EPA), which allows the evaluation of condylar position in three axes (X, Y e Z). In the first stage (NT), three sequences were made with three CR records each, one for manipulation technique. In the second stage (WT), the ULF-TENS was applied for 30 minutes before the record sequences, also performed for three times. Mann-Whitney test (p ≤ 0.05) was used to check the ULF-TENS influence on total displacement for Bimanual manipulation, Long technique and R.O.C.A. wires. ICC and 1-tailed F test were applied to assess the repeatability and variance, respectively, of these same techniques. Application of ULF-TENS did not influence the condyle total displacement, regardless of RC recording technique used (p> 0.05). Only Bimanual technique showed an improvement in repeatability with the use of ULF-TENS, which was restricted to the X and Y right axes. Concerning the variance comparison between the techniques, Bimanual manipulation showed less variation in the X axis, Long technique and R.O.C.A. wires varied less in the Y axis and Long technique was again less variable in the Z axis. It could be concluded that the use of ULF-TENS does not affect the condylar positioning and improved, although slightly, only the repeatability of Bimanual manipulation. Overall, Long technique presented lower variability among participants