Characterisation and optimisation of a three component formulation for bleaching teeth

Abstract

This study investigates a new three-component bleaching formulation, Carbamide Plus, which contains hydrogen peroxide, urea and sodium tripolyphosphate (STPP). In a recent clinical trial, a 5% Carbamide PLUS gel was shown to be as affective at bleaching teeth when compared to a 10% carbamide peroxide gel and also resulted in a decrease in tooth sensitivity. We illustrate that the improved efficiency of Carbamide Plus is due to a distinct pH rise upon dilution. We propose this pH rise catalyses the dissociation of the hydrogen peroxide, resulting in an increased bleaching efficiency for Carbamide Plus when compared to carbamide peroxide. To investigate intermolecular interaction between the three components in solution Nuclear Magnetic Resonance (NMR) spectroscopy was utilised, focusing on the ³¹P nuclei in STPP and the ¹H nuclei in urea. A series of NMR titrations were conducted and using Job’s method of continuous variation, binding stoichiometry was determined and a proposed structure for the adduct was established. The formulation of Carbamide PLUS gels was subsequently optimised by investigating the water-uptake ability of a number of gels prepared with Carbopol 974®, Carbopol 971® and Noveon AA1® as thickening agents, using gravimetric analysis. Cross-link density and polymer concentration was shown to play an important role in the gel’s swelling ability. Rheological characterisation was carried out on all gel formulations to investigate whether the improved water uptake greatly affected the physical properties required to bleach teeth safely. 9.36% w/w Noveon AA1® gels were shown to uptake 52% more water with only a small reduction (14%) in gel stiffness compared to the current benchmark formulation. Finally, the potential of novel thin film composites impregnated with alternative solid peroxide materials which are activated upon contact with water was investigated as a potential method for bleaching teeth. Hydrogen peroxide release from these materials was measured by chemiluminescent imaging. An ex-vivo bleaching study on bovine incisors revealed significant tooth whitening for all three solid peroxides after 7 x 2 h treatments compared to a placebo.

Date of Award	Sept 2014
Original language	English
Sponsors	Department of Education and learning, Northern Ireland CAST award
Supervisor	John Callan (Supervisor), Bridgeen Callan (Supervisor), John Callan (Supervisor) & Paul McCarron (Supervisor)