Biomimetic dentin desensitizer based on nano-structured bioactive glass
Introduction
It has been stated 8–35% of the population in the U.S. at any one time suffers from dentin hypersensitivity [1], but there are estimates as high as 74% [2]. It also has been reported that root sensitivity increases from 9 to 15% pre-periodontal surgery, to 55% post-surgery [3]. In vivo studies provide strong evidence that the sensitivity originates from the exposure of open dentinal tubules at the surface of the tooth [4] and is caused by changes in the local environment, including temperature, pressure, osmolality, and chemical agents. These local environment changes cause fluids in the dentinal tubules to move quickly, stimulating the nerves surrounding the odontoblasts and giving rise to pain as postulated in the hydrodynamic theory [5]. Typical methods to alleviate the effects of dentin hypersensitivity include occluding the open tubules with organic or inorganic chemicals and compounds, as well as applying chemical agents that suppress pain expression [6], [7]. The general consensus is that the most effective and durable method for achieving relief would be to seal the dentin surface through tubule occlusion, thereby eliminating or minimizing movement of fluids in the tubules [8].
Various agents have been packaged as both in-office, as well as over-the-counter medicaments for treating tooth hypersensitivity [6]. However, there currently is no ideal system for performing this task. Potassium oxalate, potassium chloride, glutaraldehyde, resin monomers, and other materials have been used either in dentifrices or as single or multiple application agents to occlude dentinal tubules. While these materials have been shown to provide some relief, none have been proven to be completely effective. Recently, a bioactive glass has been added to a dentifrice for this express purpose [1]. Tubule occlusion was examined by scanning electron microscopy, and shown to be enhanced to some extent with certain formulations. However, no attempt was made to study the ability of the agent to reduce dentin permeability. The durability of the surface layer also was not studied, though it was suggested that it is easily washed off with water.
Bioactive glasses have been shown to promote the crystallization of new mineral on their surfaces [9], [10], [11], [12]. Other studies have verified the precipitation of a calcium phosphate ceramic on the surface of a tooth after application of a bioactive glass (Bioglass®), providing evidence for the potential of this form of treatment [13]. Bioactive glasses can be formulated by the sol–gel process such that they have varying rates of dissolution and mineral formation in biologic environments [14].
The objective of this study was to examine in vitro the dentinal tubule sealing ability of a nano-structured sol–gel bioactive glass preparation delivered on exposed dentinal tubules and its effects on hydraulic conductance of human dentin. Furthermore, we assessed the physical durability of this sealing, as measured by its resistance to aggressive solutions and toothbrushing, and identified appropriate vehicles and delivery systems for its application. It was hypothesized that this novel material may potentially be used as a dental desensitizing agent.
Section snippets
Materials
We synthesized bioactive glass (BAG), using a sol–gel method. The composition of this glass was 65 mol% SiO2, 31 mol% CaO, and 4 mol% P2O5.
To maintain the highest homogeneity possible, all starting compounds were high-purity metal alkoxides. Tetraethyl orthosilicate (TEOS, C8H20O4Si) was used as the precursor for silica (SiO2) in the final glass; calcium methoxyethoxide (CMOE, C6H14O4Ca) was the precursor for lime (CaO); and triethyl phosphate (TEP, C6H15O3PO) was used to yield phosphate (P2O5).
Results
The FT-IR results from immersing the original BAG particles in SBF showed the appearance of peaks indicative of new carbonate apatite formation on the soaked BAG, specifically the P–O stretch at 960 cm−1 and the P–O bend vibrations at 565 cm−1 and 598 cm−1 (Fig. 3) [16]. The presence of these new peaks is a necessary and sufficient condition to demonstrate bioactivity of the BAG starting materials [17], [18].
All of the carriers were easy to mix with the BAG powder, and the particles remained fully
Discussion
Bioactive glasses have been increasingly studied for their ability to aid in the regeneration and remineralization of tissues throughout the human body, including both orthopedic as well as dental tissues [19], [20], [21]. These materials are relatively inexpensive and are easy to synthesize. They spontaneously produce a carbonate apatite layer on their surface when immersed in physiologic fluids. This aspect of the material was demonstrated in this study using FTIR to show the formation of a
Conclusion
Application of the nano-structured sol–gel bioactive glass with the carrier fluids tested in the study showed a significant reduction in fluid conductance through dentin at each time period vs. the carrier alone. Furthermore, it was shown that the application of non-bioactive particles in a carrier did not further reduce the conductance beyond that obtained with the carrier alone. Application of the BAG mixed into a slurry with glycerol was effective at producing an immediate reduction in fluid
Acknowledgement
This study was supported in part by an IADR/GSK Innovation in Oral Care Award.
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Formerly Department of Restorative Dentistry, Division of Biomaterials and Biomechanics, Oregon Health & Science University, 611 SW Campus Drive, Portland, OR 97239, United States, now in Private Practice.