Influence of Hydroxyapatite Nanospheres in Dentin Adhesive on the Dentin Bond Integrity and Degree of Conversion: A Scanning Electron Microscopy (SEM), Raman, Fourier Transform-Infrared (FTIR), and Microtensile Study.

Rana S Al-Hamdan,Basil Almutairi,Fahim Vohra,Hiba F Kattan,Tariq Abduljabbar,Noura A Alsuwailem,Imran Farooq

doi:10.3390/polym12122948

Abstract

An experimental adhesive incorporated with different nano-hydroxyapatite (n-HA) particle concentrations was synthesized and analyzed for dentin interaction, micro-tensile bond strength (μTBS), and degree of conversion (DC). n-HA powder (5 wt % and 10 wt %) were added in adhesive to yield three groups; gp-1: control experimental adhesive (CEA, 0 wt % HA), gp-2: 5 wt % n-HA (HAA-5%), and gp-3: 10 wt % n-HA (HAA-10%). The morphology of n-HA spheres was evaluated using Scanning Electron Microscopy (SEM). Their interaction in the adhesives was identified with SEM, Energy-Dispersive X-ray (EDX), and Micro-Raman spectroscopy. Teeth were sectioned, divided in study groups, and assessed for μTBS and failure mode. Employing Fourier Transform-Infrared (FTIR) spectroscopy, the DC of the adhesives was assessed. EDX mapping revealed the occurrence of oxygen, calcium, and phosphorus in the HAA-5% and HAA-10% groups. HAA-5% had the greatest μTBS values followed by HAA-10%. The presence of apatite was shown by FTIR spectra and Micro-Raman demonstrated phosphate and carbonate groups for n-HA spheres. The highest DC was observed for the CEA group followed by HAA-5%. n-HA spheres exhibited dentin interaction and formed a hybrid layer with resin tags. HAA-5% demonstrated superior μTBS compared with HAA-10% and control adhesive. The DC for HAA-5% was comparable to control adhesive.

Highlights

Dentin is a calcified tissue that forms the majority of the tooth structure; it is comprised of microscopic channels called dentinal tubules and an intra-tubular matrix [1,2]
The purpose of the study was to synthesize an experimental adhesive incorporated with different n-HA particles concentrations and analyze its dentin interaction, micro-tensile bond strength, and degree of conversion (DC)
The intergroup DC result comparisons were significantly different (p < 0.01), for groups control experimental adhesive (CEA) and HAA-10%; and HAA-5% equated with HAA-10% respectively (Table 2)

Summary

Introduction

Dentin is a calcified tissue that forms the majority of the tooth structure; it is comprised of microscopic channels called dentinal tubules and an intra-tubular matrix [1,2]. Dentin hypersensitivity (DH) results from the exposure of these tubules due to erosion, abrasion, attrition, abfraction, and dental caries [3,4,5]. Polymers 2020, 12, 2948 composites are among the most popular and widely indicated [6]. These dental composites are polymers combined with inorganic fillers that mimic natural teeth aesthetically, their long-term mechanical and chemical stability is debatable [7]. It is suggested that while bonding to enamel is achieved due to mechanical interlocking, the bonding of adhesive with dentin is more puzzling (due to the lower inorganic content) [9]. The depth of dentin tissue has a direct impact on the bond strength, and decreased bond strength could be observed in deeper dentin compared with superficial dentin [10]

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