Effects of non-thermal atmospheric plasma treatment on dentin wetting and surface free energy for application of universal adhesives.

OBJECTIVES: The study aims to evaluate the effects of non-thermal atmospheric plasma (NTAP) treatments on dentin wetting and surface free energy (SFE) and compare the effects of NTAP treatment, etch-and-rinse, and self-etch protocols for application of universal adhesives. MATERIALS AND METHODS: Mid-coronal dentin of intact third molars was used to measure contact angles of distilled water, ethylene-glycol, and diiodomethane and calculate SFE following different NTAP preset treatments (feeding gas consisting of pure He, He + 1% O2, He + 1.5% O2), power input (1 or 3 W), and tip-to-surface distance (2, 4, or 8 mm). Contact angles of reference liquids and SFE of dentin following He + 1.5% O2 at 3-W and 4-mm treatment was compared to phosphoric acid etching. Contact angles of Single Bond Universal (SBU; 3M ESPE) and Clearfil Universal Bond (CUB; Kuraray Noritake) were measured following NTAP, etch-and-rinse, and self-etch protocols. RESULTS: NTAP significantly reduced contact angles of reference liquids and increased dentin SFE compared to untreated dentin (p < 0.05). O2 intensified the effect of He NTAP (p < 0.05). NTAP and phosphoric acid increased dentin polarity and Lewis base surface characteristics. Phosphoric acid increased contact angles of adhesives compared to the self-etch protocol (p < 0.05). NTAP resulted in lower adhesive contact angles than phosphoric acid, the difference being statistically significant for CUB (p < 0.05). Compared to the self-etch protocol, NTAP slightly reduced CUB contact angle but not that of SBU (p > 0.05). CONCLUSIONS: He NTAP with and without O2 increased dentin wetting and SFE, surpassing the effect of phosphoric acid and lowering adhesive contact angles. NTAP produced no apparent micro-morphological changes on dentin surface comparable to acid etching. CLINICAL SIGNIFICANCE: NTAP treatment of dentin prior to adhesive application increases dentin wetting and surface free energy facilitating better adhesive distribution on dentin surface compared to phosphoric acid etching and similar to the "self-etch" application protocol.

Color stability of bulk-fill and universal composite restorations with dissimilar dentin replacement materials.

OBJECTIVE: To determine color changes in bulk-fill composite and universal composite restorations with dissimilar dentin replacement materials in extracted teeth after staining in red wine. MATERIALS AND METHODS: Cylindrical, 4 mm deep, class I cavities were prepared in 140 human molars. Bottom 2 mm was restored with Biodentine (Septodont), everX posterior (GC) or experimental HAP inserts. Each dentin replacement material was covered with a 2-mm layer of a universal composite Filtek Z250 or Z550 (3M ESPE) or Gradia Posterior (GC). Groups combining top composite layer and the underlying dentin replacement were designated as "composite_dentin replacement." Filtek Bulk Fill (3M ESPE) and Tetric EvoCeram Bulk Fill (Ivoclar Vivadent) were placed as a single 4-mm layer. Color measurements were performed using Vita Easyshade 4.0 (Vita Zahnfabrik) initially and after 48-hours storage in red wine at 37°C. RESULTS: Color differences (ΔEoo ) ranged between 2.1 ± 0.7 (Z250_HAP) and 7.8 ± 1.1 (Z550_everX). EverX resulted in higher ΔEoo of the overlying composite than HAP (P < .001) and Biodentine (P = .006). Generally, ΔEoo was affected more by decreasing lightness (ΔL') than changes in chroma (ΔC'). CONCLUSIONS: EverX resulted in higher ΔEoo of the restoration than Biodentine and experimental HAP after staining in red wine. No significant differences in ΔEoo may be expected in different composites with the same underlying dentin replacement material. The same was generally true for bulk-fill and universal composites. CLINICAL SIGNIFICANCE: Similar extent of color changes may be expected in bulk-fill and universal composites. Highly translucent everX might exhibit greater color differences irrespective of the capping composite than non-translucent materials. Clinicians have a wider choice of composite materials to cover a particular dentin replacement material, for example, everX or Biodentine, as similar color differences may be expected in various overlying composite brands.

Novel composite scaffolds based on alginate and Mg-doped calcium phosphate fillers: Enhanced hydroxyapatite formation under biomimetic conditions.

In the present study, we synthesized hydroxyapatite (HAP) powders followed by the production of alginate based macroporous scaffolds with the aim to imitate the natural bone structure. HAP powders were synthesized by using a hydrothermal method, and after calcination, dominant phases in the powders, undoped and doped with Mg2+ were HAP and ß-tricalcium phosphate, respectively. Upon mixing with Na-alginate, followed by gelation and freeze-dying, highly macroporous composite scaffolds were obtained with open and connected pores and uniformly dispersed mineral phase as determined by scanning electron microscopy. Mechanical properties of the scaffolds were influenced by the composition of calcium phosphate fillers being improved as Ca2+ concentration increased while Mg2+ concentration decreased. HAP formation within all scaffolds was investigated in simulated body fluid (SBF) during 28 days under static conditions while the best candidate (Mg substituted HAP filler, precursor solution with [Ca + Mg]/P molar ratio of 1.52) was investigated under more physiological conditions in a biomimetic perfusion bioreactor. The continuous SBF flow (superficial velocity of 400 µm/s) induced the formation of abundant HAP crystals throughout the scaffolds leading to improved mechanical properties to some extent as compared to the initial scaffolds. These findings indicated potentials of novel biomimetic scaffolds for use in bone tissue engineering.

Optical properties of composite restorations influenced by dissimilar dentin restoratives.

OBJECTIVES: To evaluate optical properties (color and translucency) of 'sandwich' restorations of resin-based composites and esthetically unfavorable dentin restoratives. METHODS: Cylindrical 'dentin' specimens (8mm in diameter and 2mm thick, N=5/group) were prepared using EverX Posterior (GC), Biodentine (Septodont), experimental hydroxyapatite (HAP) or conventional composites (Gradia Direct Posterior, GC; Filtek Z250 and Filtek Z500, 3M ESPE). Capping 'enamel' layers were prepared using composites (Gradia Direct Posterior, Filtek Z250 or Z550) of A1 or A3 shade and the following thickness: 0.6, 1 or 2mm. Color (ΔE) and translucency parameter (TP) were determined using a spectrophotometer (VITA Easyshade Advance 4.0, VITA Zahnfabrik). Data were statistically analyzed using analysis of variance with Tukey's post-hoc tests (α=0.05). RESULTS: TP was greatly affected by layer thickness, whilst ΔE depended on shade and layer thickness of the capping composite. HAP and Biodentine showed significantly lower TP and higher ΔE (deviation from 'ideal white') than composites (p<0.05). Greater TP was seen in EverX_composite groups than in corresponding control groups of the same shade and thickness. TP of composites combined with Biodentine or HAP was below 2, lower than the corresponding control groups (p<0.05). Within-group differences of ΔE were greatest in HAP_composite groups. EverX_Gradia and EverX_FiltekZ250 combinations showed the most comparable ΔE with the control groups. SIGNIFICANCE: A 2mm thick layer of composite covering dentin restoratives with unfavorable esthetics is recommended for a final 'sandwich' restoration that is esthetically comparable to a conventional, mono-composite control restoration.

Effect of hydroxyapatite spheres, whiskers, and nanoparticles on mechanical properties of a model BisGMA/TEGDMA composite initially and after storage.

This study investigated the effect of shape, size, and surface modification of hydroxyapatite (HAP) fillers on the degree of conversion (DC) and mechanical properties of a model BisGMA/TEGDMA composite initially and after 4 weeks of storage. Ten percent of conventional glass fillers were replaced by HAP spheres (Sph), silicon-doped spheres (SphSi), whiskers (Wh), silicon-doped whiskers (WhSi), and nanosized HAP particles (Nano). Spheres were specifically structured agglomerates consisting of a central void and radially orientated primary particles, whereas whiskers were compact monocrystals. DC, Vickers hardness (HV), flexural strength (Fs), flexural modulus (Ef), compressive strength (Cs), and compressive modulus (Ec) were tested. There were no significant differences in the DC between all tested groups. HV decreased by 5.4-17% with the addition of HAP, while Fs increased by 13.9-29% except in Nano group (decrease by 13%). After storage, Sph and SphSi groups showed similar HV, Ef, Cs and Ec and higher Fs than the control. The fracture mode of HAP spheres was through the central void whereas whiskers showed longitudinal delamination, transverse, and mixed fractures. HAP spheres with or without silicon- doping have a potential to be part of the filler content of dental composites.