Abrasive wear of enamel by bioactive glass-based toothpastes

Introduction

The 45S5 bioactive glass sold under the tradename NovaMin has a hardness of approximately 4.68GPa which is considerably harder than enamel at about 3.5 GPa.  The focus of the study is on enamel wear from brushing which may cause dentin to be exposed and cause dentine hypersensitivity.

Findings and Discussion

Under a typical tooth brushing cycle of 20 strokes per tooth about 10 microns would be removed from abrasion every 3 years which would take 300 to 600 years for the dentine on the crown to be eroded.  In contrast, the enamel at the cervical margins is much thinner which would take only 15 years to abrade away, ignoring the fact the enamel close to the dentin-enamel junction is softer and is likely to be abraded away at a much faster rate.  An action that has been observed experimentally.  The erosion can also be increased if the tooth was met with an acid challenge prior to washing which removed the hard apatite phase and resulted in softer enamel.

Whilst the abrasivity of the bioglass toothpaste is not a major concern, it would be desirable to reduce the toothpaste abrasivity, since the outermost enamel layer which becomes fluoridated is very thin and the removal of this protective barrier is likely to promote caries and acid erosion. It has been suggested that toothpaste abrasivity is a contributor in dentine hypersensitivity.

Results suggest reduced D90 sized particles would reduce abrasivity towards enamel. As will the grinding process that is used.  Alternatively, the inclusion of fluoride into the glass results in softer glass that also produces fluorapatite. Incorporating fluoride into the glass also speeds up apatite formation and results in localised fluoride release.

Authors :

Asad Mahmood, Mohammed Mneimne, Li Fong Zou, Robert G. Hill, & David G. Gillam

Journal :

Am J Dent 2014;27:263-267.