Elsevier

Dental Materials

Volume 37, Issue 11, November 2021, Pages 1734-1750
Dental Materials

An in-vitro study investigating the effect of air-abrasion bioactive glasses on dental adhesion, cytotoxicity and odontogenic gene expression

https://doi.org/10.1016/j.dental.2021.09.004Get rights and content

Highlights

  • Air-abrasion with bioactive glasses do not interfere with the bonding performance of universal adhesives.

  • Air-abrasion with bioactive glasses may prevent excessive degradation at the resin-dentine interface.

  • Bioactive glasses do not interfere with the differentiation of stem cells to odontoblasts.

  • Alumina may interfere with the differentiation of stem cells to odontoblasts.

Abstract

Objective

To assess the microtensile bond strength (MTBS) and interfacial characteristics of universal adhesives applied on dentine air-abraded using different powders. The analysis includes the cytotoxicity of the powders and their effect on odontogenic gene expression.

Methods

Sound human dentine specimens were air-abraded using bioglass 45S5 (BAG), polycarboxylated zinc-doped bioglass (SEL), alumina (AL) and submitted to SEM analysis. Resin composite was bonded to air-abraded or smear layer-covered dentine (SML) using an experimental (EXP) or a commercial adhesive (ABU) in etch&rinse (ER) or self-etch (SE) modes. Specimens were stored in artificial saliva (AS) and subjected to MTBS testing after 24 h and 10 months. Interfacial nanoleakage assessment was accomplished using confocal microscopy. The cytotoxicity of the powders was assessed, also the total RNA was extracted and the expression of odontogenic genes was evaluated through RT-PCR.

Results

After prolonged AS storage, specimens in the control (SML) and AL groups showed a significant drop in MTBS (p > 0.05), with degradation evident within the bonding interface. Specimens in BAG or SEL air-abraded dentine groups showed no significant difference, with resin-dentine interfaces devoid of important degradation. The metabolic activity of pulp stem cells was not affected by the tested powders. SEL and BAG had no effect on the expression of odontoblast differentiation markers. However, AL particles interfered with the expression of the odontogenic markers.

Significance

The use of bioactive glass air-abrasion may prevent severe degradation at the resin-dentine interface. Unlike alumina, bioactive glasses do not interfere with the normal metabolic activity of pulp stem cells and their differentiation to odontoblasts.

Introduction

Operative dentistry has embraced the minimally invasive philosophy with dental restorations based on the development and use of advanced adhesive materials and/or “bioactive” components that are able to remineralise the dental hard tissues [[1], [2], [3], [4], [5]]. Bioactive glasses, which were formerly intended for use as biocompatible materials for bone regeneration [6,7], have been advocated as suitable powders for air-polishing and/or selective caries removal with dental air-abrasion [8,9]. The most common technique for carious tissue removal is based on the use of non-selective rotary burs in air turbine or electric micromotor handpieces. Nevertheless, air-abrasion has been promoted as an alternative method for minimally invasive cavity preparation and/or caries removal [3,10]. Air-abrasion is a kinetic method using a stream of high-speed abrasive particles to remove sound and carious dental tissues via an end-cutting process [[11], [12], [13]]. It is able to create a smooth cavity with indistinct walls and margins [3]. Moreover, air-abrasion does not cause excessive vibrational stress on tooth structures, so resulting in increased comfort and less pain for patients [14,15]. Alumina (aluminium oxide) is the most common abrasive powder used to date [10,16]. Its drawbacks relate to its indiscriminate efficacy in selectively removing caries-affected dental hard tissues [16,17]. Moreover, there are some controversial issues about health and safety, in particular in those patients with severe dust allergies and asthma, chronic lung disease and other respiratory disorders. Studies evidenced early signs of mild fibrosis and emphysema associated to the use of alumina for air-abrasion procedures [[18], [19], [20]]. To the best of the authors’ knowledge, there is no information about the potential cytotoxicity of alumina on dental pulp stem cells and on odontoblast metabolism. Although there may be no direct correlation between cytotoxic activity on dental pulp stem cells and respiratory diseases, it has been observed that during air-abrasion procedures, the abrasive powders can penetrate several microns into patent dentine tubules [2,8]. When used in deep dentine, in close proximity to the pulp, such abrasive particles penetrating the tubules may react with dentine fluid and release ions, which might induce a response on the pulp and/or stem cells. Unfortunately, there is no available information about this possible scenario, thus it is relevant to test if conventional powders such as alumina, or bioactive glasses may have an effect on the metabolism of such type of cells (odontogenic gene expression).

There is a clinical need for more biocompatible air-abrasion powders with greater selective ability in removing caries-infected dentine alongside their bioactive properties, but that do not interfere with the adhesion of modern universal adhesives [17]. Recently, an innovative polycarboxylated zinc-doped bioactive glass has been developed (SELECTA Kinetic, Velopex International, London, UK) as a potential remineralising air-abrasion powder for selective caries removal in dentine and enamel. To date, there is limited information in the literature apart from its capability to induce the formation of apatite-like crystallites when used as a microfiller for resin adhesives and cements [2,5,21]. Carvalho et al. [22] reported that the use of air-abrasion with an experimental niobo-phosphate bioactive glass on dentine had no negative impact on the immediate bond strength of both self-etching and self-adhesive resin-based systems. Moreover, the use of bioglass 45S5 (Sylc™, OSspray Ltd., London, UK) or experimental PAA-doped bioglass 45S5 in air-abrasion procedures was demonstrated to produce a bioactive smear layer characterised by protective/reparative properties, preserving the integrity of the dentine-bonded interface and the bond strength created using self-etch adhesives (SEAs) or resin-modified glass-ionomer cements (RMGICs) [23,24]. Conversely, it was hypothesised that the residual presence of alkaline air-abrasion powders within the smear layer, such as bioglass 45S5 [2,23] or other biomaterials, may affect negatively the bonding performance of simplified self-etching adhesives [22]. Thus, it is necessary to evaluate the residual alkalinity in dentine interferes with the bonding performance of modern universal adhesives (UAS).

Progress in adhesive dental biomaterials development is represented by UAS, which are based on an “all-in-one” approach [21,24], but can be also used in self-etch, etch-and-rinse or selective-enamel etch mode for direct and indirect restorations [[25], [26], [27]]. This is due to the incorporation of mild and ultra-mild functional acidic monomers within the UAS composition, along with conventional cross-linking and non-acidic emulsifying monomers, light- or dual-curing catalysts. Moreover, definite solvents are also employed to enhance monomer diffusion and infiltration in substrates such as alloys and polycrystalline ceramics. In some cases, silanes are also incorporated within the composition of UAS to enhance their chemical interaction with glass-ceramic materials [[28], [29], [30]]. Thus, considering the important roles of UAS in minimally invasive operative adhesive dentistry, further examination of their bonding performance is required, especially when they are applied on dental substrates air-abraded using conventional and innovative powders.

The objective of this study was to evaluate the pH and scanning electron microscopy (SEM) ultramorphology of dentine after air-abrasion performed using Bioglass 45S5 (BAG), a novel polycarboxylated zinc-doped bioactive glass (SEL) or aluminium oxide (AL). The dentine microtensile bond strength (MTBS) at 24 h and after 10 months of storage in artificial saliva (AS), of two universal adhesives applied in self-etch (SE) or etch&rinse (ER) mode to air-abraded dentine, was assessed. The interfacial dye-assisted nanoleakage of the bonded interfaces was analysed using confocal laser-scanning microscopy (CLSM). The biocompatibility and the expression of genes related to odontoblast differentiation (ocn, dspp, dmp1, mepe) were also evaluated.

The first hypothesis was that the air-abrasion powders would not affect the bonding performance of the adhesive applied in SE or ER mode at 24 h. The second hypothesis was that the air-abrasion powders would not affect the bonding performance of the adhesive applied in SE or ER mode after 10-month aging in artificial saliva. The third hypothesis was that there would be no difference in biocompatibility and influence on gene expression between the tested air-abrasion powders.

Section snippets

Preparation of dentine specimens and experimental design

One hundred twenty eight sound human molars extracted for periodontal or orthodontic reasons were collected according to the guidelines of the local ethics committee, under protocol number (CEI20/097) and stored in distilled water at 5 °C for no longer than 3 months. The roots were removed 1 mm beneath the cemento–enamel junction using a diamond blade mounted on a low-speed microtome under continuous water cooling (Remet evolution, REMET, Bologna, Italy). A second parallel cut was made to

Micro-tensile bond strength, failure mode and SEM analysis

The SEM ultramorphological analysis performed on the specimens air-abraded with the tested powders showed that the dentine and enamel surfaces were always characterised by smoother walls and indistinct margins compared to the specimens prepared only with burs (Fig. 1). The storage media of specimens treated with AL and those untreated (SML) of the control group had, after 24 h, an average pH of 6.6 (±0.33) and 7.1 (±0.29), respectively. Conversely, the storage media of the specimens treated

Discussion

The ultramorphological data of all the specimens air-abraded using AL, BAG or SEL, characterised by the presence of smoother dentine walls and indistinct margins compared to the those prepared with burs, are in accordance with those presented by Banerjee A. in 2013 [3], who reported that the most relevant morphological characteristic of a cavity prepared by air-abrasion is a rounded-shape and halo contour; saucer-shaped cavities with indistinct walls and margins were also previously identified [

Acknowledgements

All authors gave their final approval and agree to be accountable for all aspects of the work. They no conflict of interest with respect to the authorship and/or publication of this paper. All the other materials used in this study were regularly purchased from local distributors, and research facilities were supported by grants “Ministerio de Ciencia, Innovación y Universidades (PID2020-120346GB-I00) and Universidad CEU-Cardenal Herrera (Programa FUSP CEU-Santander 2019-2020)” (PI: SS). Paula

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