Ultrastructural changes of bovine tooth surfaces under erosion in presence of biomimetic hydroxyapatite

Kathia Fabritius-Vilpoux,David Mayweg,Helge-Otto Fabritius,Dierk Raabe,Michael Herbig,Joachim Enax,Frederic Meyer

doi:10.1680/jbibn.21.00017

Abstract

Enamel and dentin are susceptible to acids from food sources leading to dental erosion, a global problem affecting millions of individuals. Particulate hydroxyapatite (HAP) on the tooth surface can influence the effects of acid attacks. Standardized bovine enamel and dentin samples with artificial saliva are used in an in vitro cyclic demineralization–remineralization protocol to analyze the structural changes experienced by tooth surfaces using high-resolution scanning electron microscopy and to evaluate the potential of a HAP-based oral care gel in the protection of teeth from erosive attacks. The interfaces between HAP particle and enamel HAP crystallites are investigated using focused ion beam preparation and transmission electron microscopy. The results show that erosion with phosphoric acid severely affects enamel crystallites and dentin tubules, while artificial saliva leads to remineralization effects. The HAP-gel forms a microscopic layer on both enamel and dentin surfaces. Upon acid exposure, this layer is sacrificed before the native tooth tissues are affected, leading to significantly lower degrees of demineralization compared to the controls. This demonstrates that the use of particulate HAP as a biomaterial in oral care formulations can help protect enamel and dentin surfaces from erosive attacks during meals using a simple and effective protection principle.

Highlights

Human teeth are a fascinating biological material, a constant concern regarding public health, and an an economically relevant factor of global importance for human society.[1,2] Structurally, they consist of a dentin core covered by an enamel layer in the crown area
We investigate the potential of an HAP-based oral care gel in protecting tooth surfaces from erosive attacks in vitro using high-resolution field-emission scanning electron microscopy (SEM) and analyze the interfaces formed between synthetic HAP crystallites and crystallites from the enamel surface using focused ion beam (FIB) milling and transmission electron microscopy (TEM)
Using an in vitro approach simulating erosive processes in the oral cavity, we show for the first time how acidic erosion and storage in artificial saliva affects the ultrastructure of bovine enamel and dentin surfaces on the crystallite level and how this is influenced by the application of biomimetic HAP particles in an oral care gel formulation

Summary

Introduction

Human teeth are a fascinating biological material, a constant concern regarding public health, and an an economically relevant factor of global importance for human society.[1,2] Structurally, they consist of a dentin core covered by an enamel layer in the crown area. The macroscopic architecture of dentin is characterized by the presence of numerous parallel dentin tubules with diameters of ~1 μm, which are surrounded by a thin layer of collagen-free peritubular dentin and embedded in radially oriented, mineralized collagen fibril bundles.[8] Both enamel and dentin do not heal or remodel after eruption of the tooth, and their structure is optimized to sustain lifelong cyclic mechanical stress induced by chewing activities without suffering critical damage.[9] In healthy teeth, the dentin is not exposed to the relatively harsh conditions prevailing in the oral cavity such as extreme fluctuations of temperature and pH. This natural remineralization process is slow and not sufficient to

Methods

Results

Discussion

Conclusion