Study of mineral and matrix maturation in dentin

Spectroscopic analysis was used to study the patterns of changes in the mineral and matrix properties of dentin during maturation of the tissue. Fourier Transform Infrared Imaging (FTIRI) analyses on undecalcified semi-thin sections from fetal bovine incisors and developing mouse molars were performed. In addition, fetal bovine microdissected mantle and circumpulpal dentin specimens of successive tissue age were analyzed by Fourier Transform Infrared (FTIR) analysis and by amino acid and matrix phosphate assays. In the initial studies, the formation of mantle and circumpulpal dentin as two distinct dentin compartments in the developing fetal incisors was established through analysis of distribution of mineral:matrix and mineral crystallinity values. Changes in the mineral:matrix, mineral crystallinity, acidic phosphate substitution and carbonate substitution in the mineral of mantle and circumpulpal dentin during maturation were subsequently quantitatively analyzed from FTIRI results. In this study, separate patterns of changes in mineral properties were found for mantle and circumpulpal dentin, in terms of initial and final levels and rates of increase or decrease of mineral properties values. Spectroscopic analysis of different maturation stages microdissected mantle and circumpulpal dentin specimens showed a great decrease in the dentin relative water content, affecting the dentin matrix conformation. Chemical analyses of similar microdissected specimens showed a significant increase in the organic phosphate of dentin matrix occurring during maturation. This increase was associated with continuing phosphorylation of existing phosphoproteins without further changes in the protein density. Finally, the study of dentin maturation using 6 day-old mouse molars by FTIRI was validated. Reproducibility in the pattern of changes in the mineral properties examined was found to be highly dependent on the sectioning orienation of molars. It is likely that higher resolution analytical methods and/or slightly older animal age would enhance the analytical outcome in such studies

Changes in matrix phosphorylation during bovine dentin development

Phosphorylation of the organic matrix proteins of dentin is important for the initiation of mineralization, but its relevance in later mineralization stages is controversial. The objective of this study was to analyze changes in the total matrix phosphate content during dentin development and to identify their origin. Amino acid and total matrix phosphate analyses of microdissected developing mantle and circumpulpal fetal bovine dentin specimens were performed. The amino acid composition showed few changes during mantle and circumpulpal dentin maturation. However, the total matrix phosphate content showed a significant, positive correlation with tissue maturation in both mantle and circumpulpal dentin, with a two- and a three-fold increase, respectively, being observed. The data indicate that changes occur in the pattern of phosphorylation of matrix proteins during dentin maturation, which we suggest may play a functional role in later stages of tooth mineralization

Effect of HIP/ribosomal protein L29 deficiency on mineral properties of murine bones and teeth

Mice lacking HIP/RPL29, a component of the ribosomal machinery, display increased bone fragility. To understand the effect of sub-efficient protein synthetic rates on mineralized tissue quality, we performed dynamic and static histomorphometry and examined the mineral properties of both bones and teeth in HIP/RPL29 knock-out mice using Fourier transform infrared imaging (FTIRI). While loss of HIP/RPL29 consistently reduced total bone size, decreased mineral apposition rates were not significant, indicating that short stature is not primarily due to impaired osteoblast function. Interestingly, our microspectroscopic studies showed that a significant decrease in collagen crosslinking during maturation of HIP/RPL29-null bone precedes an overall enhancement in the relative extent of mineralization of both trabecular and cortical adult bones. This report provides strong genetic evidence that ribosomal insufficiency induces subtle organic matrix deficiencies which elevates calcification. Consistent with the HIP/RPL29-null bone phenotype, HIP/RPL29-deficient teeth also showed reduced geometric properties accompanied with relative increased mineral densities of both dentin and enamel. Increased mineralization associated with enhanced tissue fragility related to imperfection in organic phase microstructure evokes defects seen in matrix protein-related bone and tooth diseases. Thus, HIP/RPL29 mice constitute a new genetic model for studying the contribution of global protein synthesis in the establishment of organic and inorganic phases in mineral tissues

Effect of expertise on TF adaptive system instrumentation quality in simulated mandibular molar canals

The aim of the study was to examine the effect of operator experience on the quality of instrumentation of molar canals using the TF Adaptive file system (SybronEndo, Orange, CA) on a 3D‐printed molar replica model. Three novice and two expert operators instrumented the root canals of three replicas each and resulting pre‐ and postinstrumentation 12 micron voxel size‐microCT volumes of each replica were digitally registered. Relative modified canal wall surface fraction and canal transportation (1–9 mm from the apex) were calculated and analysed by anova. Instrumentation by expert operators resulted in overall higher (P = 0.002) modified wall surface fraction in the distal but not the mesial and higher (P = 0.002) combined from all canal level transportation in the mesiobuccal canals but not the mesiolingual and distal canals. Instrumentation efficiency but also transportation using the TF Adaptive file system can be higher among expert, compared to novice, operators, depending on the canal type