The Effect of 35% Carbamide Peroxide (CP) Whitening Agent on Physico-chemical Properties of Dentine

Objectives: Determine the effect of tooth whitening on chemical–physical properties of dentine structure using 35%CP applied for 2& 4hours daily /1week. Establish if a correlation exists between any potential effects of this concentration and its different exposure time.

Methods:
A total of 38 intact human premolars and third molars, were collected under ethical approval (11/LO/0939). Following local hard tissue management protocols, the teeth were then assigned to different time-dependent whitening protocols 2& 4hours groups using 35%CP. The experimental protocol was designed to duplicate the conditions of standard clinical application of whitening agent on teeth. The efficacy of the whitening agent was measured colourimetrically using a Spectroshade and its resulting impact on dentinal collagen was characterised spectroscopically by Raman spectroscopy, mechanically by Vickers Hardness and structurally by Electron Microscopy.

Results:
Spectroscopically, the relative intensities of Amide I & III bands from the dentinal collagen were greatly reduced for the 35% when compared with to a lesser extent for the 5% and 10% (Previous study accepted for JDR publication). A gradient of apparent denaturation could be observed from the buccal side (exposure to CP) to the lingual side (not exposed). This deteruration of the internal collagen structure was supported by both EM and mechanical analyses of the samples. Following tooth whitening protocol, the greatest colour change occurred for the 35%CP groups whereas less changes could be observed for the 5% and 10% groups.

Conclusions: A 35% CP concentration applied for 2 & 4houres daily/1week achieved efficient tooth whitening properties but contributed to maximum changes and impact on physico-chemical properties of the teeth when compared to 5% & 10%CP. There was a significant correlation between the concentration of CP, its application time, and its effect on dentine structure .Within the limitation of this in-vitro study, it raises questions about the unknown long-term implications on tooth longevity.