Effect of sodium hypochlorite and Tooth Mousse™ on hypomineralised enamel in Molar Incisor Hypomineralisation

Abstract

Although Molar Incisor Hypomineralisation (MIH) is being investigated in various parts of the world but our understanding of this entity is still quite limited. The hypomineralised enamel in MIH is weaker than normal enamel and may present with white chalky spots, yellow or brown areas. The surface may be rough with missing enamel due to post-eruptive breakdown. Teeth affected by MIH may be sensitive to cold air and foods, and mechanical stimuli like tooth brushing. Children avoid brushing the affected teeth leading to plaque accumulation which may make these teeth more susceptible to dental caries. Post-eruptive enamel breakdown also contributes to dentine exposure with increasing severity of sensitivity (Weerheijm et al, 2001a).

In addition, management strategies for treating teeth affected by MIH are limited with a high failure rate of restorations. As a result of issues of sensitivity and poor long term success rate of restorations many MIH molar teeth are extracted.

Saroglu et al (2006) and Venezie et al (1994) have recommended the use of sodium hypochlorite (NaOCl) to remove proteins from enamel in order to improve bonding. However, this was based on case reports without any scientific evidence of the efficacy of this pre-treatment with NaOCl.

The remineralisation potential of Tooth Mousse™ (Casein Phosphopeptide-Amorphous Calcium Phosphate) has been investigated in dental caries but its efficacy in altering hypomineralised enamel has only been investigated in one study (Baroni et al, 2011).

The objective of this research was to investigate the potential improvement in mechanical properties of Molar Incisor Hypomineralisation (MIH) enamel following application of Tooth Mousse™ with and without pre-treatment with NaOCl.

It was hypothesised that NaOCl might remove some of the excessive organic content from MIH enamel which might improve the uptake of minerals by hypomineralised enamel.

Brief study outline: Seven extracted first permanent molar teeth affected by MIH were collected from different dental practitioners around New Zealand after ethics approval from the Multi-region ethics committee. These teeth were sectioned and a total of twelve samples were obtained.

All samples were subjected to three tests; laser fluorescence (LF), nanoindentation (NI) and confocal microscopy (CM).

This was followed by division into four groups: Group I: Sodium hypochlorite (NaOCl) pre-treatment group Group II: Sodium hypochlorite (NaOCl) and Tooth Mousse™ treatment group Group III: No treatment group Group IV: Tooth Mousse™ treatment group

The NaOCl (5 percent NaOCl for 5 minutes) pre-treatment was done in the first two groups followed by LF, NI and CM tests.

All the samples were then stored for 30 days following which LF, NI and CM were repeated. The Tooth Mousse™ application was done daily and the Hank‟s solution was replenished every day.

The results of this in vitro study showed based on nanoindentation and laser fluorescence that surface organic was removed from hypomineralised enamel following a single application of five percent NaOCl for five minutes. This resulted in reduction of mechanical properties of hypomineralised enamel as shown by nanoindentation testing (surface H and E reduction of upto 41% and 30% respectively). Confocal microscopy showed mixed results after NaOCl use; protein content appeared to be slightly increased after NaOCl pre-treatment in Group I whereas it was decreased in Group II.

Daily application of Tooth Mousse™ for thirty days and storage in Hank‟s solution without prior NaOCl pre-treatment improved the mechanical properties of hypomineralised enamel (surface H and E improved by 258% and 226% respectively).

Storing the hypomineralised teeth in Hank‟s solution also resulted in improved mechanical properties of enamel (surface H and E increased by 49% and 34% respectively). Therefore, it is not clear how much improvement in mechanical properties of hypomineralised enamel was due to Tooth Mousse™ alone.

In conclusion, further investigation is needed to study the longer term effects of Tooth Mousse™ in MIH. This would be improved by investigating the enamel in an in situ design study. Also, future investigations should aim at a larger sample size as the present study only involved three samples in each group.