An in vitro investigation of the effect and retention of bioactive glass air-abrasive on sound and carious dentine

Air-Abrasion in Dentistry: A Short Review of the Materials and Performance Parameters

The selection of abrasive material and parameters of the Air-Abrasion device for a particular application is a crucial detail. However, there are no standard recommendations or manuals for choosing these details; the operator must depend on his experience and knowledge of the procedure to select the best possible material and set of parameters. This short review attempts to identify some of the effects that the selection of material and parameters could have on the performance of the Air-Abrasion procedure for a particular application. The material and parameter data are collected from various studies and categorized according to the most popular materials in use right now. These studies are then analyzed to arrive at some inferences on the performance of Air-Abrasion materials and parameters. This review arrives at a few conclusions on the effectiveness of a material and parameter set, and that there is potential for developments in the area of standardizing parameter selection; also, there is scope for further studies on Bio-Active Glass as an alternative to the materials currently used in Air-Abrasion.

Comparison of different bioglass applications on root caries – A laboratory-based study

The aim of this in-vitro study was to assess the effect of bioglass with different concentrations on root caries.

Ninety freshly-extracted teeth with root caries were randomly assigned to a single-use prophylaxis paste containing 15 % bioglass for 30 s with 1,450 ppmF toothpaste (15 % bioglass, n = 30), 1,450 ppmF toothpaste with 5 % bioglass (5 % bioglass, n = 30), and toothpaste containing 1,450 ppmF (Control, n = 30). Each sample received a standard brushing procedure for 10 s twice a day using the toothpastes. Teeth were immersed in remineralising solution with pH of 7 at 37 °C for 720 h. Surface roughness (Ra) was measured at baseline and after the application of the products at 0.5, 1, 4, 12, 24, 48, 168, 336 and 720 h. Subsequently, three samples from each group were randomly selected to measure calcium ion release over 15 h immersion in deionised water. These samples were then analysed using the SEM for the qualitative assessment of lesion topography. Repeated measures ANOVA, Wilcoxon paired tests and percentage changes were carried out to assess Ra. Calcium ion release data was analysed using one-way ANOVA and Tukey post-hoc tests.

After 720 h, 15 % bioglass had the highest decrease in Ra (Mean-difference = 1.502 µm, p = 0.001), then 5 % bioglass (Mean-difference = 0.723 µm, p = 0.09) whereas the control had the lowest Ra decrease (Mean-difference = 0.518 µm, p = 0.55). The differences in Ra between the groups were highly significant (p < 0.001). The cumulative calcium ion release was significantly high for the 5 % bioglass in comparison to the 15 % bioglass, whilst the control had the lowest release (p < 0.001). SEM analysis showed the presence of bioglass particles only on 15 % bioglass samples.

The use of prophylaxis paste with 15 % bioglass and 1,450 ppmF toothpaste was promising to reverse/arrest root caries when compared to the toothpaste containing 1,450 ppmF with 5 % bioglass for a period of 30 days.

An investigation into the cutting efficiency of a novel degradable glass as an alternative to alumina powder in air abrasion cutting of enamel

Objectives

To develop and test the cutting efficiency of a novel degradable glass as an alternative media to alumina powder for air abrasion.

Materials and methods

A zinc-based glass (QMZK2) was designed, produced, and evaluated with a multi-modality imaging analysis. The glass dissolution study was carried out in three acids, using ICP-OES (inductively coupled plasma optical emission spectroscopy) at 5 different time points: 2.5, 5, 10, 60, and 240 min. The cutting efficiency of both materials was tested under the same parameters on slabs of elephant enamel. A stained fissure of a molar tooth was air abraded with the glass and evaluated with X-ray micro-tomography before and after air abrasion.

Results

The particle size distribution of the glass was similar to that of alumina 53 µm but with a slightly greater dispersion of particle size. The shape of the particles was angular, appropriate for cutting purposes. The dissolution study showed that the glass dissolved rapidly in acidic conditions at all time points. Between the two variables, pressure and powder flow, pressure was found to influence the cutting speed to a greater extent than powder flow.

Conclusions

Alumina powder was found to perform significantly better in 4 of the 9 conditions tested on elephant enamel, QMZK2 in one, and no significant differences were found for the rest of the 4 conditions. The QMZK2 seems to offer promising results as an alternative material to alumina.

Clinical relevance.

QMZK2 glass has the potential for replacing aluminum oxide as a degradable material in air abrasion technology.

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

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.

The effect of dentine pre-treatment using bioglass and/or polyacrylic acid on the interfacial characteristics of resin-modified glass ionomer cements

OBJECTIVE

To evaluate the effect of load-cycle aging and/or 6 months artificial saliva (AS) storage on bond durability and interfacial ultramorphology of resin-modified glass ionomer cement (RMGIC) applied onto dentine air-abraded using Bioglass 45S5 (BAG) with/without polyacrylic acid (PAA) conditioning.

METHODS

RMGIC (Ionolux, VOCO) was applied onto human dentine specimens prepared with silicon-carbide abrasive paper or air-abraded with BAG with or without the use of PAA conditioning. Half of bonded-teeth were submitted to load cycling (150,000 cycles) and half immersed in deionised water for 24 h. They were cut into matchsticks and submitted immediately to microtensile bond strength (μTBS) testing or 6 months in AS immersion and subsequently μTBS tested. Results were analysed statistically by two-way ANOVA and Student-Newman-Keuls test (α = 0.05). Fractographic analysis was performed using FE-SEM, while further RMGIC-bonded specimens were surveyed for interfacial ultramorphology characterisation (dye-assisted nanoleakage) using confocal microscopy.

RESULTS

RMGIC applied onto dentine air-abraded with BAG regardless PAA showed no significant μTBS reduction after 6 months of AS storage and/or load cycling (p > 0.05). RMGIC-dentine interface showed no sign of degradation/nanoleakage after both aging regimens. Conversely, interfaces created in PAA-conditioned SiC-abraded specimens showed significant reduction in μTBS (p < 0.05) after 6 months of storage and/or load cycling with evident porosities within bonding interface.

CONCLUSIONS

Dentine pre-treatment using BAG air-abrasion might be a suitable strategy to enhance the bonding performance and durability of RMGIC applied to dentine. The use of PAA conditioner in smear layer-covered dentine may increase the risk of degradation at the bonding interface.

CLINICAL SIGNIFICANCE

A combined dentine pre-treatment using bioglass followed by PAA may increase the bond strength and maintain it stable over time. Conversely, the use of PAA conditioning alone may offer no significant contribute to the immediate and prolonged bonding performance.

The effect of air-abrasion on the susceptibility of sound enamel to acid challenge

OBJECTIVE

To evaluate the effect of air-abrasion using three abrasive powders, on the susceptibility of sound enamel to an acid challenge.

METHODS

40 human enamel samples were flattened, polished and assigned to 4 experimental groups (n=10); a: alumina air-abrasion, b: sodium bicarbonate air-abrasion, c: bioactive glass (BAG) air-abrasion and d: no surface treatment (control). White light confocal profilometry was used to measure the step height enamel loss of the abraded area within each sample at three stages; after sample preparation (baseline), after air-abrasion and finally after exposing the samples to pH-cycling for 10 days. Data was analysed statistically using one-way ANOVA with Tukey's HSD post-hoc tests (p<0.05). Unique prismatic structures generated by abrasion and subsequent pH cycling were imaged using multiphoton excitation microscopy, exploiting strong autofluorescence properties of the enamel without labelling. Z-stacks of treated and equivalent control surfaces were used to generate non-destructively 3-dimensional surface profiles similar to those produced by scanning electron microscopy.

RESULTS

There was no significant difference in the step height enamel loss after initial surface air-abrasion compared to the negative control group. However, a significant increase in the step height enamel loss was observed in the alumina air-abraded samples after pH-cycling compared to the negative control (p<0.05). Sodium bicarbonate as well as BAG air-abrasion exhibited similar enamel surface loss to that detected in the negative control group (p>0.05). Surface profile examination revealed a deposition effect across sodium bicarbonate and BAG-abraded groups.

CONCLUSION

This study demonstrates the importance of powder selection when using air abrasion technology in clinical dentistry. Pre-treating the enamel surface with alumina air-abrasion significantly increased its susceptibility to acid challenge. Therefore, when using alumina air-abrasion clinically, clinicians must be aware that abrading sound enamel excessively renders that surface more susceptible to the effects of acid erosion. BAG and sodium bicarbonate powders were less invasive when compared to the alumina powder, supporting their use for controlled surface stain removal from enamel where indicated clinically.

Comparing the Air Abrasion Cutting Efficacy of Dentine Using a Fluoride-Containing Bioactive Glass versus an Alumina Abrasive: An In Vitro Study

Air abrasion as a caries removal technique is less aggressive than conventional techniques and is compatible for use with adhesive restorative materials. Alumina, while being currently the most common abrasive used for cutting, has controversial health and safety issues and no remineralisation properties. The alternative, a bioactive glass, 45S5, has the advantage of promoting hard tissue remineralisation. However, 45S5 is slow as a cutting abrasive and lacks fluoride in its formulation. The aim of this study was to compare the cutting efficacy of dentine using a customised fluoride-containing bioactive glass Na0SR (38-80 μm) versus the conventional alumina abrasive (29 μm) in an air abrasion set-up. Fluoride was incorporated into Na0SR to enhance its remineralisation properties while strontium was included to increase its radiopacity. Powder outflow rate was recorded prior to the cutting tests. Principal air abrasion cutting tests were carried out on pristine ivory dentine. The abrasion depths were quantified and compared using X-ray microtomography. Na0SR was found to create deeper cavities than alumina (p < 0.05) despite its lower powder outflow rate and predictably reduced hardness. The sharper edges of the Na0SR glass particles might improve the cutting efficiency. In conclusion, Na0SR was more efficacious than alumina for air abrasion cutting of dentine.

Resin bonding using etch-and-rinse and self-etch adhesives to decalcified deciduous enamel after bioactive glass air abrasion

PURPOSE

Bioactive glass air abrasion is a conservative technique for removal of initial decalcified enamel superficial layer and caries vs alumina air abrasion. This study evaluated shear bond strength of composite resin to sound and decalcified deciduous enamel using etch-and-rinse and self-etch adhesives after alumina and bioactive glass air abrasion.

MATERIALS AND METHODS

Ninety-six fat enamel surfaces, mounted in acrylic resin, were prepared from 48 deciduous molars. Half of the specimens were decalcified with a demineralizing solution. Both intact and decalcified specimens were assigned to two groups for alumina and bioactive glass air abrasion. In each group, the specimens were subdivided into two groups for application of Clearfil SE Bond or Optibond FL adhesives (n = 12). After composite resin bonding, the specimens underwent shear bond test. Data were analyzed using three-way analysis of variance (ANOVA), linear regression model and independent-sample t-test (α = 0.05).

RESULTS

No significant differences were noted in bond strength of composite resin after alumina or bioactive glass air abrasion (p = 0.272). Optibond FL adhesive and enamel decalcification produced higher bond strength (p = 0.000, p = 0.001 respectively).

CONCLUSION

In this study, bioactive glass air abrasion produced bond strength comparable to the conventional method. This technique might be an alternative method for preparation of normal and/or decalcified enamel of deciduous teeth for resin bonding.

In Vitro Effect of Air-abrasion Operating Parameters on Dynamic Cutting Characteristics of Alumina and Bio-active Glass Powders

Minimally invasive dentistry advocates the maintenance of all repairable tooth structures during operative caries management in combination with remineralization strategies. This study evaluated the effect of air-abrasion operating parameters on its cutting efficiency/pattern using bio-active glass (BAG) powder and alumina powder as a control in order to develop its use as a minimally invasive operative technique. The cutting efficiency/pattern assessment on an enamel analogue, Macor, was preceded by studying the powder flow rate (PFR) of two different commercial intraoral air-abrasion units with differing powder-air admix systems. The parameters tested included air pressure, powder flow rate, nozzle-substrate distance, nozzle angle, shrouding the air stream with a curtain of water, and the chemistry of abrasive powder. The abraded troughs were scanned and analyzed using confocal white light profilometry and MountainsMap surface analysis software. Data were analyzed statistically using one-way and repeated-measures analysis of variance tests (p=0.05). The air-abrasion unit using a vibration mechanism to admix the abrasive powder with the air stream exhibited a constant PFR regardless of the set air pressure. Significant differences in cutting efficiency were observed according to the tested parameters (p&lt;0.05). Alumina powder removed significantly more material than did BAG powder. Using low air pressure and suitable consideration of the effect of air-abrasion parameters on cutting efficiency/patterns can improve the ultraconservative cutting characteristics of BAG air-abrasion, thereby allowing an introduction of this technology for the controlled cleaning/removal of enamel, where it is indicated clinically.

Influence of sodium content on the properties of bioactive glasses for use in air abrasion

Air abrasion is used in minimally invasive dentistry for preparing cavities, while removing no or little sound dentine or enamel, and the use of bioactive glass (rather than alumina) as an abrasive could aid in tooth remineralization. Melt-derived bioactive glasses (SiO2-P2O5-CaO-CaF2-Na2O) with low sodium content (0 to 10 mol% Na2O in exchange for CaO) for increased hardness, high phosphate content for high bioactivity and fluoride content for release of fluoride and formation of fluorapatite were produced, and particles between 38 and 80 µm in size were used for cutting soda-lime silicate glass microscope slides and human enamel. Vickers hardness increased with decreasing Na2O content, owing to a more compact silicate network in low sodium content glasses, resulting in shorter cutting times. Cutting times using bioactive glass were significantly longer than using the alumina control (29 µm) when tested on microscope slides; however, glasses showed more comparable results when cutting human enamel. The bioactive glasses formed apatite in Tris buffer within 6 h, which was significantly faster than Bioglass® 45S5 (24 h), suggesting that the hardness of the glasses makes them suitable for air abrasion application, while their high bioactivity and fluoride content make them of interest for tooth remineralization.

Influence of air-abrasion executed with polyacrylic acid-Bioglass 45S5 on the bonding performance of a resin-modified glass ionomer cement

The aim of this study was to test the microtensile bond strength (μTBS), after 6 months of storage in PBS, of a resin-modified glass ionomer cement (RMGIC) bonded to dentine pretreated with Bioglass 45S5 (BAG) using various etching and air-abrasion techniques. The RMGIC (GC Fuji II LC) was applied onto differently treated dentine surfaces followed by light curing for 30 s. The specimens were cut into matchsticks with cross-sectional areas of 0.9 mm(2). The μTBS of the specimens was measured after 24 h or 6 months of storage in PBS and the results were statistically analysed using two-way anova and the Student-Newman-Keuls test (α = 0.05). Further RMCGIC-bonded dentine specimens were used for interfacial characterization, micropermeability, and nanoleakage analyses by confocal microscopy. The RMGIC-dentine interface layer showed no water absorption after 6 months of storage in PBS except for the interdiffusion layer of the silicon carbide (SiC)-abraded/polyacrylic acid (PAA)-etched bonded dentine. The RMGIC applied onto dentine air-abraded with BAG/H(2)O only or with BAG/PAA-fluid followed by etching procedures (10% PAA gel) showed no statistically significant reduction in μTBS after 6 months of storage in PBS. The abrasion procedures performed using BAG in combination with PAA might be a suitable strategy to enhance the bonding durability and the healing ability of RMGIC bonded to dentine.

Bioactive Glass: A Material for the Future

Bioactive glasses are novel dental materials that are different from conventional glasses and are used in dentistry. Bioactive glasses are composed of calcium and phosphate which are present in a proportion that is similar to the bone hydroxyapatite. These glasses bond to the tissue and are biocompatible. They have a wide range of medical and dental applications and are currently used as bone grafts, scaffolds and coating material for dental implants. This article reviews various properties of bioactive glasses and their applications and also reviews the changes that can be made in their composition according to a desired application.

How to cite this article

Farooq I, Imran Z, Farooq U, Leghari A, Ali H. Bioactive Glass: A Material for the Future. World J Dent 2012;3(2):199-201.

Effects of common dental materials used in preventive or operative dentistry on dentin permeability and remineralization

The aim of this study was to evaluate the dentin remineralization induced by bioactive substances contained in common dental materials used in preventive and operative dentistry. Several materials were applied on human dentin segments. Dentin permeability was quantified using a fluid filtration system working at 20 cm H(2)O. Micro-Raman, SEM-EDX, and microhardness calculation were used to evaluate changes in the mineralization of dentin. Dentin treated with the prophylactic materials showed different dentin permeability values, in particular subsequent to immersion in remineralizing solutions (RSS). The bioactive glass (Sylc) was the only substance able to reduce dentin permeability after immersion in remineralizing solution and to show hydroxyapatite precipitation as a sign of dentin remineralization. The reduction in dentin permeability obtained after the application of the other prophylactic materials used in this study was due to the presence of the remnant material in the dentinal tubules, with no remineralization effect after storage in remineralizing solution. In conclusion, the results indicated that bioactive glass prophy powder may induce immediate remineralization of dentin.