Physicochemical Effects of Niobic Acid Addition Into Dental Adhesives

Isadora Martini Garcia,Gabrielade Souza Balbinot,Mary Anne S Melo,Susana Maria Werner Samuel,Fabrício Mezzomo Collares,Abdulrahman A Balhaddad,Vicente Castelo Branco Leitune

doi:10.3389/fmats.2020.601078

Abstract

The incorporation of metallic oxides in dental adhesives has been a strategy to confer improved radiopacity and physicochemical properties for polymers. Tailoring the structure of these fillers could contribute to their application in therapeutic strategies for dental restorations. The aim of this study was to evaluate the incorporation of niobic acid into experimental dental adhesives, and compare these adhesives to niobium pentoxide containing adhesives. A control group without Nb2O5·n H2O or Nb2O5 was also used for comparison. Niobium-based particles have been used as a feasible approach, mainly because of their bioactivity. In this study, hydrated niobium pentoxide, also called niobic acid (Nb2O5·n H2O), was incorporated into an experimental dental adhesive as a potential catalyst for monomer conversion. A base resin for dental adhesive was formulated with methacrylate monomers and photoinitiators. Two types of oxides were tested as filler for this adhesive: Nb2O5·n H2O or niobium pentoxide (Nb2O5). Both fillers were added separately into the experimental adhesive at 0, 2.5, 5, and 10 wt.%. One group without Nb2O5·n H2O or Nb2O5 (0 wt.% of filler addition) was used as a control group. The formulated materials were analyzed for radiopacity according to the ISO 4049 and used FTIR analysis to assess the degree of conversion (DC) and the maximum polymerization rate (RPmax). Mechanical properties were analyzed by ultimate tensile strength (UTS) in a testing machine. Softening in solvent was conducted by measuring Knoop microhardness before and after immersion of samples in ethanol. Normality of data was assessed with Shapiro-Wilk, and comparisons between factors were conducted with two-way ANOVA and Tukey at 5% of significance. Both fillers, Nb2O5 or Nb2O5·n H2O, increased the radiopacity of dental adhesives in comparison to the unfilled adhesive (p &lt; 0.05). There were no differences among groups for the ultimate tensile strength (p &gt; 0.05), and all groups containing Nb2O5 or Nb2O5·n H2O improved the resistance against softening in solvent (p &lt; 0.05). The groups with 5 and 10 wt% addition of Nb2O5 showed decreased DC compared to the control group (p &lt; 0.05), while the addition of Nb2O5·nH2O up to 10 wt% did not alter the DC (p &gt; 0.05). The polymerization rate did not change among groups (p &gt; 0.05). In conclusion, Nb2O5·n H2O is a promising filler to be incorporated into dental adhesives providing proper mechanical properties, improved resistance against solvents, and increased radiopacity, without changing the DC.

Highlights

Adhesive systems for dental restoration have undergone several modifications so that their physical and chemical properties could be improved, supporting long-lasting restorative treatments
Nb2O5·n H2O is a promising filler to be incorporated into dental adhesives providing proper mechanical properties, improved resistance against solvents, and increased radiopacity, without changing the degree of conversion (DC)
Bioactive particles have been used to assist in tooth remineralization (Balhaddad et al, 2019; Braga and Fronza, 2020), making bioactive resinbased dental materials to be feasible approaches to prevent dental demineralization and to provide the recovery of hard dental tissues affected by caries (Garcia et al, 2017; Ibrahim et al, 2020a; Ibrahim et al, 2020b)

Summary

Introduction

Adhesive systems for dental restoration have undergone several modifications so that their physical and chemical properties could be improved, supporting long-lasting restorative treatments. Inorganic fillers have been incorporated into dental adhesives aiming to reduce polymeric degradation via increasing hydrolytic stability (Münchow and Bottino, 2017). These particles have been tuning in adhesives formulation to improve polymers’ radiopacity (Garcia et al, 2020a) and mechanical properties (Lohbauer et al, 2010; Belli et al, 2014). Calcium phosphates (Garcia et al, 2017; Braga and Fronza, 2020), calcium silicates (Profeta, 2014), bioactive glasses (Balbinot et al, 2020a; Yao et al, 2020), and zincbased particles (Toledano et al, 2016) were already tested and showed mineral deposition or remineralization effect on dental hard tissues. Niobium-based particles have been highlighted due to their interesting properties for dentistry, such as high radiopacity and bioactivity (Marins et al, 2018)

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