Cerium- and samarium-nitrate interaction and accumulation on human dentin

Objective To investigate the accumulation of cerium-nitrate and samarium-nitrate on dentin without or with smear-layer and to test their antibacterial activity. Design 24 dentin-enamel slices were cut from 24 extracted molars. 12 slices underwent smear-layer creation (320grit, 200g, 5s), the other 12 smear-layer removal (20%EDTA, 300s). Slices were halved to 48 semilunar-shaped specimens. One specimen per tooth was treated with either Ce(NO3)3 (50wt% aqueous solution; pH=1.29; n=6) or Sm(NO3)3 (50wt% aqueous solution; pH=1.88; n=6). The other specimen served as control (A. demin). After water rinsing, elemental composition (Ce,Sm,Ca,P,O,N,Na,Mg,C) was measured (EDX; EDAX Octane-Elect, APEX v2.5, low-vacuum) in dentin. Atomic percent (At%), Ca/P- and Ca/N-ratios were calculated and analyzed non-parametrically (α=0.05, error rates method). Additionally, antibacterial activity (2min exposure) of Ce(NO3)3 and Sm(NO3)3 against Streptococcus mutans, Actinomyces naeslundii, Schaalia odontolytica, and Enterococcus faecalis was determined (colony forming units) after anaerobic incubation at 37°C for 24h (control: 0.2%CHX). Results At% (median) of Ce and Sm were as follows: Ce(NO3)3 3.4 and 0.9At%Ce with and without smear-layer, respectively; Sm(NO3)3 2.4 and 1.3At%Sm with and without smear-layer, respectively. Ce(NO3)3 and Sm(NO3)3-application significantly decreased Ca/P-ratios (1.22-1.45; p≤0.02) compared to controls (1.47-1.63). With smear-layer, significantly higher Ca/N-ratios (5.1-29.3) could be detected across all groups (p≤0.004) compared to specimens without smear-layer (0.37-0.48). Ce(NO3)3 and Sm(NO3)3 showed reduction rates of up to ≥ 5 log10 steps for S. mutans, A. naeslundii, and S. odontolytica. Conclusions Cerium and samarium nitrate showed accumulation on dentin and certain antibacterial activity and could therefore be identified as potential compounds to treat and prevent dentin and root caries and dentin hypersensitivity.