Influence of enamel and dentin thicknesses on the esthetic outcome and cytotoxicity of different tooth bleaching protocols

Author(s)

Carla Caroline de Oliveira Duque

• Document type: Master's Dissertation
• Press: Araraquara. 2016-05-23.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Odontologia. Araraquara
• Defense date: 2016-03-23
• Advisor: Carlos Alberto de Souza Costa

Abstract

The susceptibility of pulp-dentin complex to the adverse effects of tooth bleaching therapies has a direct relationship with the thickness of dental substrate. Therefore, the aim of this study was to assess the biologic and esthetic effect of a 10% hydrogen peroxide (H2O2) bleaching gel applied for different periods onto enamel/dentin discs simulating the thickness of low incisors (LI) and upper pre-molars (PM). Enamel/dentin discs from bovine incisors measuring 2.3 and 4.0 mm were adapted to artificial pulp chambers and distributed into the IC Group (low incisors) and PM Group (upper premolars), respectively. The enamel surface was bleached with a 10% H2O2 gel for 3x15, 1x15 or 1x5 minutes. The 35% H2O2 gel applied for 3x15 minutes was used as positive control (traditional therapy) and no treatment was performed on negative control group. The culture medium immediately after bleaching (extract) was applied for 1 hour on human dental pulp cells. Cell viability and morphology were evaluated immediately after bleaching (T1) and 72 h thereafter (T2). Oxidative stress and the amount of H2O2 in culture medium were also quantified at T1. The ALP activity and mineralized nodule (MN) deposition were assessed 14 and 21 days after bleaching, respectively. The color change (ΔE) of enamel was analyzed throughout six bleaching sessions. Overall, the experimental protocols with the 10% H2O2 gel minimized significantly the negative effects of traditional therapy to cultured pulp cells. The protocol 10% 3x15 promoted significant cell viability reduction in comparison with negative control at T1, in both, IC and PM Groups; however, the cells of IC Group did not feature proliferative capability at T2. The morphologic alterations, oxidative stress intensity and reduction on phenotype markers (ALP and NM) expression were also more intense on IC Group for this bleaching protocol. Regarding the protocols 10% 1x15 and 1x5, no significant cell viability reduction related to negative control was observed regardless of the thickness of dental substrate. Nevertheless, significant oxidative stress was observed on cells from IC Group. These protocols caused significant reduction of ALP activity in comparison to negative control, which intensity being proportional to enamel/dentin thickness; however, no reduction on NM was detected at 21 days post-bleaching. Similar ΔE values as positive control were found for the 10% 3x15 and 1x15 protocol on IC Group after 4 and 6 sessions, respectively. For PM Group, this feature was reached out after 6 bleaching sessions for the 10% 3x15 protocol. It was concluded that the enamel/dentin thickness of dental substrate played a significant role on the trans-enamel and trans-dentinal cytotoxicity of a 10% H2O2 bleaching gel on human dental pulp cells in vitro. Application of gel during 45 or 15 minutes onto thin dental substrate minimizes significantly the cell toxicity in comparison to high concentrated gels (35%) associated with similar esthetic outcome by increasing the number of bleaching sessions. (AU)

• FAPESP's process: 14/07229-6 - Effects of enamel and dentin thicknesses on the esthetic outcome and cytotoxicity of different tooth bleaching protocols
• Grantee: Carla Caroline de Oliveira Duque
• Support Opportunities: Scholarships in Brazil - Master