White adhesive filling materials bond variably to teeth. Teeth are mainly composed of a hard outer enamel shell that surrounds dentine, a mineralised collagenous scaffold. While enamel structure and composition is predictable, dentine mineral and collagen composition and distribution may vary with patient age as well as tooth depth and site. We investigated the mineral distribution and composition across different dentin depths and sites in young and mature teeth by using backscattered electron images collected in a scanning electron microscopy (SEM) combined with energy dispersive x-ray spectroscopy (SEM-EDS). SEM-EDS and SEM work was complemented by examining patient age, depth and site related effects on the three-dimensional dentine tubule structure by using Xenon plasma focussed ion beam scanning electron microscopy (FIB-SEM).
SEM photomicrographs were first segmented using machine learning before using a custom, automated analytical script to measure segmented regions of interest before performing suitable statistical analyses on each group. Dentin mineral content and distribution changed with patient age, depth and site. Specifically, the peritubular cuff mineral intensity increased with age irrespective of location within the teeth. Although, this increase in intensity may not reflect an increase in mineral content. Analysis from SEM-EDS indicates that Calcium and Phosphorus peaks were greatest in intertubular dentine regardless of age and site, with the exception of young shallow dentine, where the peritubular mineral peaks were relatively higher as determined by SEM-EDS measurements.
Human dentine mineral characteristics vary with patient age and site. These findings indicate that physical variation in dentine is fundamental for the development and use of white adhesive filling materials to repair or restore teeth.