Detection of Hydroxyl and Perhydroxyl Radical Generation from Bleaching Agents with Nuclear Magnetic Resonance...

Children/adolescent's orodental structures are different in anatomy and physiology from that of adults, therefore require special attention for bleaching with oxidative materials. Hydroxyl radical (OH^.) generation from bleaching agents has been considered directly related to both its clinical efficacy and hazardous effect on orodental structures. Nonetheless bleaching agents, indirectly releasing hydrogen peroxide (H₂O₂), are considered safer yet clinically efficient. Apart from OH^., perhydroxyl radicals (HO₂^.) too, were detected in bleaching chemistry but not yet in dentistry. Therefore, the study aims to detect the OH^. and HO₂^. from bleaching agents with their relative integral value (RIV) using ³¹P nuclear magnetic resonance (³¹PNMR) spectroscope.

Radicals were generated with UV light in 30% H₂O₂, 35% carbamide peroxide (CP), sodium perborate tetrahydrate (SPT) and; neutral and alkaline 30% H₂O₂. Radicals were spin-trapped with DIPPMPO in NMR tubes for each test agents as a function of time (0, 1, 2, 3min) at their original pH. Peaks were detected for OH^. and HO₂^. on NMR spectrograph. RIV were read and compared for individual radicals detected.

Only OH^. were detected from acidic and neutral bleaching agent (30% acidic and neutral H₂O₂, 35%CP); both HO₂^. and OH^. from 30% alkaline H₂O₂; while only HO₂^. from more alkaline SPT. RIV for OH^. was maximum at 1min irradiation of acidic 30%H₂O₂ and 35%CP and minimum at 1min irradiation of neutral 30%H₂O₂. RIV for HO₂^.was maximum at 0min irradiation of alkaline 30%H₂O₂ and minimum at 2min irradiation of SPT.

The bleaching agents having pH- neutral and acidic were always associated with OH^.; weak alkaline with both OH^. and HO₂^.; and strong alkaline with HO₂^. only. It is recommended to check the pH of the bleaching agents and if found acidic, should be made alkaline to minimize oxidative damage to enamel itself and then to pulp/periodontal tissues.

H₂O₂: hydrogen peroxide CP: carbamide peroxide SP: sodium perborate SPT: sodium perborate tetrahydrate ROS: reactive oxygen species ³¹PNMR: ³¹P nuclear magnetic resonance spectroscope RIV: relative integral value OH₂^.: hydroxyl radical HO₂^.: perhydroxyl radical O₂^.: super oxide radical DIPPMPO: 5-(Diisopropoxyphosphoryl)-5-methyl-1-pyrroline-N-oxide DEPMPO: 5-diethoxyphosphoryl-5-methyl-1-pyrroline-n-oxide DMPO: 5,5-dimethyl-1-pyrroline-N-oxide D₂O: heavy water EDTA: ethylene diamine tetra acetic acid.