Three-dimensional microscopic comparison of wear behavior between immature and mature enamel: an in vitro study

Posteruptive Loss of Enamel Proteins Concurs with Gain in Enamel Hardness

Tooth enamel maturation requires the removal of proteins from the mineralizing enamel matrix to allow for crystallite growth until full hardness is reached to meet the mechanical needs of mastication. While this process takes up to several years in humans before the tooth erupts, it is greatly accelerated in in the faster developing pig. As a result, pig teeth erupt with softer, protein-rich enamel that is similar to hypomineralized human enamel but continues to harden quickly after eruption.Proteins, such as albumin, that bind to enamel crystals and prevent crystal growth and enamel hardening have been suggested as cause for hypomineralized human enamel that does not naturally harden after eruption. However, albumin is abundant in pig enamel. It is unclear whether fast posteruptive enamel hardening in pigs occurs despite the high protein content or requires a facilitated protein loss to allow for crystal growth. This study asked how the protein content in porcine enamel changes after eruption in relation to saliva. Based on previous data demonstrating the high albumin content in erupted porcine enamel, we hypothesize that following pre-eruptive maturation, enamel and saliva derived enzymes facilitate protein removal from porcine enamel after eruption. We analyzed enamel and the saliva proteome at three critical timepoints: at the time of tooth eruption, 2 weeks after eruption, and enamel 6 weeks after eruption. We used only fourth deciduous premolars and saliva samples from animals sacrificed at the respective time points to determine the organic content in tooth enamel, saliva, and saliva proteins within enamel. We found a decrease in the number of proteins and their abundancy in enamel with posteruptive time, including a decrease in serum albumin within enamel. The rapid decrease in the first two weeks is in line with previously reported rapid increase in mineral density of porcine enamel after eruption. In addition to the enamel proteases KLK-4 and MMP-20, we identified serine-, cysteine-, aspartic-, and metalloproteases. Some of these were only identified in enamel, while almost half of the enzymes are in common with saliva at all timepoints. Our findings suggest that the fast posteruptive enamel maturation in the porcine model coincides with saliva exchange and influx of saliva enzymes into porous enamel.

In-vitro evaluation of wear characteristics, microhardness and color stability of dental restorative CAD/CAM materials

The aim of this study was to demonstrate the vertical and volumetric wear characteristics of CAD/CAM materials. The microhardness and color stability were evaluated. A polymer infiltrated ceramic network CAD/CAM block, resin nanoceramic CAD/CAM blocks, a resin composite, and enamel tissue were investigated. Samples were loaded in a chewing simulator. Other samples were aged and immersed in coffee. Color change was evaluated using the digital image analysis and a spectrophotometer. The data were analyzed using Kolmogorov-Smirnov, Kruskal Wallis, Mann Whitney U, Friedman, Spearman's rho tests (p<0.05). The lowest level of wear was obtained in enamel tissue group 0.20 (Q1:0.14; Q3:0.27μm). Resin composite group 2.48 (Q1:2.12; Q3:2.92) showed lower level of discoloration. No agreement was obtained between the digital image analysis and spectrophotometer data (Spearman's rho -0.314, p=0.014). Similar wear rate to the natural enamel tissue was obtained for Vita Enamic. Digital image analysis was considered a promising technique for monitoring the color change.