Effect of deproteinization treatments on the structure and mechanical properties of dental enamel

Abstract

To investigate and quantify the influence of the proteins in dental enamel on the mechanical behavior different deproteinization treatments were carried out and their effect on the mechanical properties was studied. Dental enamel samples were deproteinized chemically using KOH solution and H O containing bleaching agent and by heat-treatment in a temperature range of 200–600°C in air and N atmosphere. The organic content was measured by TGA mass loss. Additionally, FTIR, NCHS elemental analysis and HPLC were used to confirm the removal of organic material. The chemical treatments resulted in a smaller mass loss during TGA (decrease by 0.55 w% for KOH) as well as a lower amount of total organic carbon (TOC) and amino acids (about 50% less TOC for both) compared to the untreated sample, thereby confirming successful deproteinization. The structure of the treated samples was investigated by SEM and TEM and compared to untreated samples. While chemical treatments leave the hierarchical structure of the enamel intact, temperatures >300°C lead to sintering of the enamel crystallites. This change in structure correlates with an increased hardness and elastic modulus of heated samples (up to 58% and 17% respectively for 300°C compared to the untreated sample). The removal of the proteins by chemical means has no major effect on the elastic modulus and hardness. As previous studies have suggested, the main influence on the mechanical properties of dental enamel is the intertwining structure of the enamel crystallites. 2 2 2