Effect of dental bleaching on caries resistance of human enamel : in vitro study

الملخص EN

Objective: To evaluate the effect of two different bleaching agents on surface microhardness of dental enamel and its influence on the susceptibility of the bleached enamel to acidic attack and hence the possibility of development of dental caries or not.

METHODS: A total of 80 freshly extracted sound human incisors were used.

The labial surfaces were ground flat and then divided into two halves in which the right half was bleached and the left half was unbleached (Control side).

The specimens were divided into two equal groups according to the bleaching agent used, group A1: bleached wit Opalescence PF 10% carbamide peroxide bleaching agent applied for thirty minutes /day for four days, group A2: bleached with Opalescence–Boost PF 38% hydrogen peroxide applied for fifteen minutes /day for only one application.

Following bleaching, the specimens were stored for fourteen days in the storage medium whether distilled water (B1)or artificial saliva (B2), then half of the specimens was subjected to pH cycling (C1) and the other was not subjected (C2).

Microhardness was measured on both halves using a Vicker’s microhardness tester.

Three indentations were made on each half and the mean of the three readings was calculated as the mean microhardness value for each side.

Results: Groups treated with Opalescence-Boost PF 38% HP showed lower microhardness values than that treated with Opalescence PF 10% CP in all groups.

Storage in artificial saliva without subjection to pH cycling has resulted in increased microhardness values of bleached enamel treated either with Opalescence PF 10% carbamide peroxide or with Opalescence-Boost PF 38% hydrogen peroxide.

Subjection to pH cycling has resulted in decreased micro hardness of bleached enamel relative to unbleached one in all groups, even in groups stored in artificial saliva.

Conclusions: 1.

In-office bleaching agents with high concentrations of hydrogen peroxide are capable of causing reduction in surface microhardness relative to at-home bleaching agents with low concentrations .

2.

Artificial saliva is capable of minimizing the possible adverse effects of bleaching agents.

3.

Bleaching did not improve enamel resistance to demineralization.