Smear-Layer Integrity and the Role of Surfactants

Objectives: It is a common observation that hypersensitive dentine is devoid of a smear-layer and that dentine tubules are open at the tooth surface and patent to the pulp. The smear-layer is composed of a mixture of organic and inorganic materials and in its own right is thought to attenuate the so-called transduction mechanism responsible for propagating the pain response. Several investigators have studied the effects of various irrigants on the smear-layer and concluded that elimination required both organic and inorganic solvents. The objective of this study was to utilise atomic force microscopy and nanoindentation to investigate the influence of various surfactants on the physical properties of an artificially generated dentine smear-layer.

Methods: Dentine roots slabs were prepared from human third molars. Dentine slabs were polished successively using 600 to 2400 grit paper. Polishing was carried out using an artificial proteinaceous saliva as a polishing lubricant in order to generate an artificial smear-layer. A pellicle was allowed to form on the smear-layer/dentine surface prior to treatment. Surfactant treatments consisted of 0.5% w/w surfactant/water solutions of either SLS (anionic), Tego Betain (zwitteronic), Adinol CT95 (anionic), Pluronic F108 (non-ionic) or water. Treatment consisted of placing the slabs into the surfactant solutions (held at 37^oC) for up to 30 minutes with agitation. Tapping mode AFM and nanoindentation was carried out on the samples.

Results: The various surfactants removed the smear-layer and smear-plugs (smear-layer materials within the tubule opening) to varying degrees: Notably, SLS removed both the smear-layer and smear-plugs where as Tego Betain only removed the smear-layer did not remove smear-plugs.

Conclusion: Tego Betain had a minimal influence on dentinal tubule patency compared with the other surfactants and may therefore be considered one of the most suitable surfactants for use in antisensitivity dentifrices.