DENTAL-2512; No. of Pages 12

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

Available online at www.sciencedirect.com

ScienceDirect journal homepage: www.intl.elsevierhealth.com/journals/dema

Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization Hussam Milly a,b , Frederic Festy a , Manoharan Andiappan c , Timothy F. Watson a,d , Ian Thompson a , Avijit Banerjee a,d,∗ a

Tissue Engineering & Biophotonics Research Group, King’s College London Dental Institute at Guy’s Hospital, King’s Health Partners, London, UK b Restorative Dentistry, Dental Institute, Damascus University, Syria c King’s College London Dental Institute at Guy’s Hospital, King’s Health Partners, London, UK d Conservative & MI Dentistry, King’s College London Dental Institute at Guy’s Hospital, King’s Health Partners, London, UK

a r t i c l e

i n f o

a b s t r a c t

Article history:

Objective. To evaluate the effect of pre-conditioning enamel white spot lesion (WSL) surfaces

Received 19 May 2014

using bioactive glass (BAG) air-abrasion prior to remineralization therapy.

Received in revised form

Methods. Ninety human enamel samples with artificial WSLs were assigned to three WSL

28 October 2014

surface pre-conditioning groups (n = 30): (a) air-abrasion with BAG-polyacrylic acid (PAA-BAG)

Accepted 7 February 2015

powder, (b) acid-etching using 37% phosphoric acid gel (positive control) and (c) uncondi-

Available online xxx

tioned (negative control). Each group was further divided into three subgroups according to

Keywords:

(100 wt.% BAG) and (III) de-ionized water (negative control). The average surface roughness

the following remineralization therapy (n = 10): (I) BAG paste (36 wt.% BAG), (II) BAG slurry Enamel white spot lesion

and the lesion step height compared to intra-specimen sound enamel reference points were

Remineralization

analyzed using non-contact profilometry. Optical changes within the lesion subsurface com-

Air-abrasion

pared to baseline scans were assessed using optical coherence tomography (OCT). Knoop

Bioactive glass (BAG)

microhardness evaluated the WSLs’ mechanical properties. Raman micro-spectroscopy

Polyacrylic acid (PAA)

measured the v-(CO3 )2− /v1 -(PO4 )3− ratio. Structural changes in the lesion were observed

OCT

using confocal laser scanning microscopy (CLSM) and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX). All comparisons were considered statistically significant if p < 0.05. Results. PAA-BAG air-abrasion removed 5.1 ± 0.6 ␮m from the lesion surface, increasing the WSL surface roughness. Pre-conditioning WSL surfaces with PAA-BAG air-abrasion reduced subsurface light scattering, increased the Knoop microhardness and the mineral content

∗ Corresponding author at: King’s College London Dental Institute, Floor 26, Tower Wing, Guy’s Dental Hospital, London Bridge, London SE1 9RT, UK. Tel.: +44 0207 188 1577; fax: +44 0207 188 7486. E-mail address: [email protected] (A. Banerjee).

http://dx.doi.org/10.1016/j.dental.2015.02.002 0109-5641/© 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

2

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

of the remineralized lesions (p < 0.05). SEM–EDX revealed mineral depositions covering the lesion surface. BAG slurry resulted in a superior remineralization outcome, when compared to BAG paste. Significance. Pre-conditioning WSL surfaces with PAA-BAG air-abrasion modified the lesion surface physically and enhanced remineralization using BAG 45S5 therapy. © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

1.

Introduction

The optimal goal of minimal invasive (MI) dental caries management is to prevent and “heal” the incipient lesion by inhibiting the demineralization process, preventing any further mineral loss and enhancing the remineralization repair process [1]. The enamel white spot lesion (WSL) results from the physical changes occurring in enamel due to the caries process before it has reached the enamel–dentin junction (EDJ) [2]. Different protocols have been described to remineralize enamel WSLs including bioactive glass (BAG) 45S5 [3–7]. BAG 45S5 is an inorganic amorphous, calcium, sodium phosphosilicate material which contains fivefold ratio of Ca/P [8]. It interacts with aqueous solutions such as saliva to form a hydroxycarbonate apatite (HCA) layer, attached chemically to the treated surfaces [9,10]. In vitro and in vivo studies demonstrated that BAG 45S5 allowed close contact of the living cells at its surface and did not contain leachables which produce inflammation [11]. It has been shown that BAG 45S5 mixture prepared to treat dentin hypersensitivity and incipient enamel caries is a biocompatible material concluded by assessing the viability and the morphological alternations of pulp cells [12]. The remineralization of enamel WSL is a complex physicochemical process where the remaining mineral crystals are less reactive, covered by salivary proteins and the limited diffusion of ions lessens the net mineral gain [13–15]. In order to promote the WSL remineralization process, an additional stage of pre-conditioning the lesion surface using phosphoric acid prior to the remineralization therapy has been described and shown to increase the remineralization of WSLs [16–18]. In the present study, air-abrasion with PAA-BAG powder was used to pre-condition the lesion surface as opposed to cutting it, in order to promote remineralization using different topical therapies including mixtures of BAG 45S5. Polyacrylic acid (PAA) altered the hydroxycarbonate apatite (HCA) induced by BAG 45S5, with smaller structures deposited on the surfaces of enamel WSLs, remineralized using PAA-BAG slurry and assessed using Raman micro-spectroscopy and SEM [7]. The ( COOH) functional group of PAA may bind the calcium and phosphate ions to form nano-precursors small enough to penetrate the carious lesion more effectively [19,20]. The objectives of this study were to assess the physical effects of this WSL surface pre-conditioning and to study the impact of this modification on overall lesion remineralization. The physical changes were assessed using non-contact white light confocal profilometry and optical coherence tomography (OCT). The mineral content at the lesion surface following the application of the remineralization therapies was evaluated using Raman micro-spectroscopy used in a StreamLineTM

scanning technique to map the lesion surface measuring the v-(CO3 )2− /v1 -(PO4 )3− ratio of 2880 spectra per sample. The biomechanical properties of the WSLs were assessed using Knoop microhardness testing. Confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectrometry (EDX) were used to study the ultra-structural changes within remineralized artificial WSLs created using a bi-layer demineralization protocol. The two null hypotheses investigated in this study were that pre-conditioning the WSL using PAA-BAG air-abrasion had no effect on lesion surface characteristics and that this pre-conditioning had no effect on the following remineralization therapy using BAG 45S5.

2.

Materials and methods

2.1.

Sample preparation

Caries-free human molars were collected using ethics approval reviewed by the East Central London Research Ethics Committee (Reference 10/H0721/55), stored in refrigerated deionized water and used within a month from the extraction. One buccal enamel slab from each tooth was sectioned using a diamond wafering blade (XL 12205, Benetec Ltd., London, UK). The slab’s initial surface integrity was inspected using a confocal tandem scanning microscope (TSM) (Noran Instruments, Middleton, WI, USA), with an 20× air objective in reflection scanning mode. Ninety samples were included in this study. The samples were included face down in acrylic resin using a hard-anodized aluminum and brass sample former (Syndicad Ingenieurbüro, München, Germany). The superficial enamel layer was removed to create more consistent, reproducible artificial enamel lesions [14,21], using a water-cooled rotating polishing machine (Meta-Serv 3000 Grinder-Polisher, Buehler, Lake Bluff, IL, USA) with a sequential standard polishing protocol started from 600- to 4000-grit silica carbide disks, followed by 3 min of ultrasonication to remove the smear layer. Dental wax was applied to protect part of the enamel leaving an exposed window of 3 mm × 1 mm in the central area of the exposed enamel slab. The specimens were submitted to a previously documented bi-layer demineralization protocol of 8% methylcellulose gel buffered with a layer of lactic acid solution (0.1 mol/L, pH 4.6) for 14 days at 37 ◦ C, to create artificial WSLs with an average depth of 70–100 ␮m [22,23]. The sound enamel areas around the WSL were covered with polyvinyl chloride tape throughout the experimental procedures, and removed at the end of the remineralization therapies. The samples were assigned into nine experimental groups according to the

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

ARTICLE IN PRESS 3

d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

Table 1 – The experimental groups according to the procedures (n = 10), showing the means and their standard errors (␮m) of average surface roughness (Sa ). Group (n = 10)

Experimental procedures

Before surface pre-conditioning

After surface pre-conditioning

0.18 ± 0.02 0.17 ± 0.01 0.16 ± 0.01 0.19 ± 0.01 0.21 ± 0.02 0.20 ± 0.01 0.19 ± 0.02 0.29 ± 0.07 0.16 ± 0.15

0.71 ± 0.15 0.57 ± 0.15 0.49 ± 0.09 0.90 ± 0.07 0.70 ± 0.04 0.80 ± 0.07 0.20 ± 0.01 0.25 ± 0.04 0.20 ± 0.02

After remineralization therapy

Surface pre-conditioninga Remineralization therapyb 1 2 3 4 5 6 7 8 9

PAA-BAG air-abrasion PAA-BAG air-abrasion PAA-BAG air-abrasion Acid-etching (+ve control) Acid-etching (+ve control) Acid-etching (+ve control) Unconditioned (−ve control) Unconditioned (−ve control) Unconditioned (−ve control)

BAG paste (36 wt.% BAG) BAG slurry (100 wt.% BAG) De-ionized water (−ve control) BAG paste (36 wt.% BAG) BAG slurry (100 wt.% BAG) De-ionized water (−ve control) BAG paste (36 wt.% BAG) BAG slurry (100 wt.% BAG) De-ionized water (−ve control)

0.80 0.60 0.59 1.14 0.82 0.82 0.24 0.31 0.25

± ± ± ± ± ± ± ± ±

0.13 0.06 0.08 0.10 0.05 0.05 0.02 0.06 0.03

The underlined cells represent the significance (p < 0.05) within the same experimental group (before) vs. (after) surface pre-conditioning. Applied once at the beginning of the experiment. b Applied twice daily (5 min per application) for 21 days. a

surface pre-conditioning and remineralization therapies (n = 10; Table 1).

2.2.

Surface pre-conditioning

The surface pre-conditioning was conducted once before initiating the remineralization therapy. PAA-BAG abrasive powder (2–8–17 ␮m) was prepared by mixing 60 wt.% BAG 45S5 powder with 40 wt.% PAA powder (MW: 1500, Sigma Chemicals, Gillingham, Dorset, UK) for 5 min at 300 rpm. The homogeneity of the mixed powders was validated using Fourier-transform infrared spectroscopy (FTIR) (Perkin-Elmer, Beaconsfield, UK) to detect the vibration of C O (PAA) at 1710 cm−1 and of Si O (BAG) at 1030 cm−1 . An AquacutTM (Velopex, Harlesden, UK) dental air-abrasion unit was used to pre-condition the lesion surface using the following operating parameters: air pressure, 20 psi; powder flow rate dial, 1 g/min; nozzle angle, 90◦ ; nozzle-lesion distance, 5 mm and the internal nozzle diameter, 900 ␮m [24]. The air-abrasion was conducted for 10 s in wet abrasion mode fulfilled by shrouding the air stream with a curtain of de-ionized water. For acid-etching treatment, 35% phosphoric acid gel (3 M ESPE Dental Products, St Paul, MN, USA) was applied onto the lesion surface for 30 s followed by 1 min rinsing with de-ionized water and 5 s drying with a gentle oil-free air stream using the three in one syringe of a dental unit. The negative control samples in the surface preconditioned groups remained untreated (Table 1).

2.3.

Post-conditioning remineralization therapy

The remineralization therapy included the application of a BAG paste or a BAG slurry twice daily (5 min per application) for 21 days. The remineralization agent was applied onto the exposed WSL surface using a microbrush with hand-agitation by a single operator blinded to the surface pre-conditioning procedure. Following each application, the samples were rinsed thoroughly with de-ionized water and incubated at 37 ◦ C in de-ionized water, which was refreshed at each application for all of the nine experimental groups. The BAG slurry was prepared using de-ionized water (L/P ratio of 1 g/ml) prior to the treatment using BAG 45S5 particles (2–6–12 ␮m) [7]. The

BAG paste was prepared using the following formula: 36 wt.% BAG 45S5 powder, 25.70 wt.% chalk (CaCO3 ) and 38.3 wt.% glycerine and stabilizers. In order to prevent any premature BAG chemical reaction, the paste did not include water in its composition. Therefore, the de-ionized water was introduced into the paste at the lesion surface to initiate the reaction kinetics of BAG particles. The negative control of the remineralization agent was de-ionized water, while the positive control was a BAG slurry (100 wt.% BAG particles) relying upon the results of a previous study where this formula was shown to remineralize enamel WSLs when compared to a “standard” remineralization solution [7].

2.4.

Profilometry analysis

The samples’ surface topography was scanned three times: before surface pre-conditioning, after the surface preconditioning and finally, post-remineralization therapy, using non-contact white light confocal profilometry (XyrisTM 4000 WL, TaiCaanTM Technologies Ltd., Southampton, UK) with a 10 ␮m step-over distance and 10 nm vertical resolution. A standard scan area of (3 mm × 2 mm) was chosen over the center of the surface including the lesion in the middle surrounded by sound enamel from each side acting as internal sample reference levels. The resulting 3D images were analyzed using a manufacturer’s software supplied by leveling the reference sound enamel areas to a “zero” plane. The step height of the lesion surface in relation to the sound enamel level was obtained by averaging five measurements within each sample. In order to obtain the average roughness (Sa ) of the lesion surface, further three areas of 250 ␮m × 250 ␮m were scanned within the lesion surface and analyzed for each sample.

2.5.

Optical coherence tomography (OCT)

The specimens were scanned prior to surface pre-conditioning and again after remineralization therapy was complete using OCT (VivoSight, Kent, UK) operating at 1305 nm central wavelength, 10 kHz rate and 15 mW energy power. This system uses XY mirror sets with multi-beam Z technology in order to

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

ARTICLE IN PRESS

DENTAL-2512; No. of Pages 12

4

d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

maintain the axial resolution over an extended range of depth [25,26]. The lateral resolution is 7.5 ␮m and the axial resolution is 10 ␮m in air which corresponds to 6.1 ␮m in enamel assuming a refractive index (n) of 1.63. The OCT beam was oriented perpendicularly and set at a fixed distance over the sample surface by means of a moving stage. For each sample, 50 bscan images were acquired at 5 ␮m intervals covering an area of 3000 ␮m × 250 ␮m with a pixel size of 3.36 ␮m × 4.06 ␮m. The multi-beam scan creates a scan depth of approximately 2 mm. The 16-bit TIFF file b-scan images were imported into a purpose-written ImageJ macro (ImageJ, MD, USA) which analyzed individual o-scans using a polynomial fitting function. Both the air/lesion interface reflection and the average subsurface scattering, up to 40 ␮m in depth, were recorded for each X and Y sample positions (Fig. 2). The subsurface light scattering was normalized to the surface reflection within each sample to be analyzed statistically, measuring the reduction (%) of the subsurface light scattering at the end of remineralization therapies in comparison with baseline scans.

2.6.

Lesion Knoop microhardness

A Struers Duramin microhardness tester (Struers Ltd., Denmark) with a Knoop diamond indenter (50 g load applied for 10 s) produced elongated diamond-shaped indentations which were imaged with an 40× air objective and the Knoop values were calculated from measurements of each longaxis indentation, using the manufacturer’s software supplied. Three measurements, 500 ␮m apart, were recorded and then averaged to measure the lesion surface microhardness of each sample at the end of remineralization therapies. Prior to each measuring session, the instrument was calibrated using a calibrated transfer-standard block (N 0441, UKAS calibration, UK).

2.7.

Raman micro-spectroscopy

The lesion surfaces were scanned using a Renishaw inVia Raman microscope (Renishaw Plc, Wotton-under-Edge, UK), running in StreamLineTM scanning mode, using a 785-nm diode laser (100% laser power) focused into the samples through a 20× air objective. The signal was acquired using a 600 lines/mm diffraction grating centered at 800 cm−1 and a CCD exposure time of 2 s. The Raman map was set at the center of the lesion surface covering an area of 700 ␮m × 500 ␮m and including 2880 spectra acquired with 2.7 ␮m resolution across the lesion. The demineralized enamel produced a slight background autofluorescence (AF), and to take this slowly varying background signal into account, the resultant spectra were exported into an in-house curve-fitting software to fit the spectra using a linear combination of a Gaussian function and a first order polynomial using the following fitting function:



−(X − D) F(X) = AX + B + C Exp (2E2 )

2



The intensity of the peak was given by the fitting parameter C from the above equation. The intensity of phosphate peak at 959 cm−1 and that of carbonate peak at 1085 cm−1 were measured to obtain the ratio of v-(CO3 )2− /v1 -(PO4 )3− per spectrum.

The measurements of 2880 spectra were averaged to obtain one value from each sample.

2.8.

Microscopy imaging

Imaging was conducted for three selected experimental groups including, air-abrasion + BAG paste, air-abrasion + BAG slurry and unconditioned + de-ionized water (negative control). For CLSM imaging, three samples from each experimental group were sectioned vertically across the lesion and ground with carborundum paper up to 1200 grit. The samples were soaked in a freshly prepared 0.1 mM Rhodamine-B solution (R6626-Sigma–Aldrich, Dorset, UK) for 24 h, without further rinsing [27]. A confocal laser scanning microscope (CLSM) (Leica Microsystems, Heidelberg GmbH, Germany) was used to image the samples with an 63× oil objective lens in conjunction with 540 nm excitation wavelength and 625 nm emission wavelength for the Rhodamine-B. Samples were scanned between 10 and 50 ␮m below the sectioned surface to avoid the smear layer, created during the cutting procedures [27]. For SEM scanning, three samples from each group were fractured across the WSL to provide a sagittal view without surface grinding or polishing artifact, secured to aluminum stubs and sputter coated with gold (Emitech K550, UK). The fractured surfaces were imaged using an FEI Quanta 200F field emission scanning electron microscope (FEI Co. Ltd., Cambridge, UK), with accelerating voltage of 10 kV, working distance of 10 mm. For EDX mapping of the lesion top surface, further three samples from each group were carbon sputter-coated and scanned using energy-dispersive X-ray spectroscopy (EDAX Inc., 91 McKee Drive, Mahwah, NJ 07430, USA), with accelerating voltage of 10 kV and working distance of 12 mm.

2.9.

Statistical analysis

Statistical analysis was carried out using Stata statistical package (Stata-CorpLP v 11.2, TX, USA) at p = 0.05 significance. Data were tested for normality, and the non-normal data were transformed into the normal using appropriate transformation prior to further analysis. The profilometry data were tested using two-way analysis of variance (ANOVA) and Tukey’s HSD as post hoc including significant interactions, while those of Raman micro-spectroscopy, microhardness and OCT were analyzed using linear modeling by including the interaction term for pre-conditioning and remineralization therapy.

3.

Results

3.1.

Profilometry analysis

The means and standard errors of the step height measurements at three measurement points are shown in Fig. 1, while data for surface roughness (Sa ) are presented in Table 1. The baseline measurement showed no statistically significant differences in step height and roughness measurements between the nine experimental groups prior to

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

5

commencing any experimental procedure (p > 0.05). Preconditioning the lesion surface using air-abrasion and acid-etching significantly increased the surface roughness (p < 0.001) and the step height values compared to unconditioned control groups (p < 0.001 and p = 0.01 respectively). Here, PAA-BAG air-abrasion removed significantly more substrate (5.1 ± 0.6 ␮m, mean ± SE) from the lesion surface compared to that removed by acid-etching (2.2 ± 0.1 ␮m) (p < 0.001) (Fig. 1B), but this difference was deemed not to be clinically significant. The surface roughness measurements after remineralization therapy were similar to those after surface preconditioning. However, there was a significant increase in the step height measurements within the acid-etch groups at this stage. The acid-etching groups in Fig. 1C show that samples treated with BAG paste and slurry exhibited significantly higher step height values (5.4 ± 0.4 ␮m and 5.8 ± 0.3 ␮m respectively) (p < 0.001) compared to those treated with deionized water, the negative control of remineralization therapy in acid-etching groups (2.3 ± 0.1 ␮m).

3.2.

Optical coherence tomography (OCT)

Fig. 2 represents the means and the standard errors of the reduction (%) in the subsurface light scattering in relation to the baseline scans. Pre-conditioning the lesion surface using PAA-BAG air-abrasion and acid-etching reduced significantly the subsurface light scattering when compared to unconditioned groups (p < 0.001 and p = 0.01 respectively). BAG paste remineralization therapy reduced significantly the light scattering compared to BAG slurry (p = 0.0042) and de-ionized water (p = 0.001). The use of BAG slurry exhibited similar subsurface light scattering to the de-ionized water, regardless to the surface pre-conditioning procedure (p > 0.05). Representative OCT images with their signal intensity profiles from the unconditioned + de-ionized water (negative control) and the air-abrasion + BAG paste groups are shown in Fig. 3. There was a reduction in the OCT signal intensity within the depth profiles following the remineralization therapy using BAG paste.

3.3.

Fig. 1 – Bar graphs represent mean ± SE of step height measurements before surface pre-conditioning (A), after surface pre-conditioning (B) and after remineralization therapy (C). Air-abrasion and acid-etching significantly increased the measurements compared to unconditioned group (p < 0.05).

Lesion Knoop microhardness

The means and standard errors of lesion microhardness measurements are shown in Fig. 4. The microhardness data were not normally distributed and hence the analysis was carried out on the transformed data. According to the effect of pre-conditioning on the microhardness, both PAA-BAG air-abrasion and acid-etching increased the microhardness values significantly, compared to unconditioned control groups (p = 0.002 for air-abrasion and p = 0.035 for acid-etching). No statistically significantly differences were observed between the microhardness of air-abrasion and acid-etching groups. As regards the remineralization effect, both BAG paste and BAG slurry exhibited significantly higher (p < 0.001) microhardness values compared to the de-ionized water groups (negative control) regardless to the surface pre-conditioned state. Within pre-conditioned groups, WSLs treated with the BAG slurry showed statistically significant higher microhardness compared to those treated with BAG paste (p = 0.014).

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

6

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

Fig. 2 – Representative OCT-image of WSL and the depth OCT-signal intensity showing the two values measured in this study (arrows). The bar graph presents the mean ± SE of the reduction (%) in the subsurface light scattering comparing to baseline scans.

3.4.

Raman micro-spectroscopy

Fig. 5 shows representative Raman spectra of scanned lesion surface in treated (air-abrasion + BAG slurry) and untreated (unconditioned + de-ionized water) groups. The heights peak along both spectra was that of v1 -PO4 3− at 959 cm−1 , relating to the enamel HA. All the phosphate peaks of enamel HA were detected within both spectra at 433 cm−1 , 579 cm−1 , 959 cm−1 and 1043 cm−1 [28]. A new peak appeared within the spectra

following the remineralization therapies using BAG 45S5 at 1085 cm−1 assigned to (CO3 )2− of HCA that forms on reacted BAG 45S5 [29]. The means and the standard errors of the v-(CO3 )2− /v1 (PO4 )3− ratio are presented in Fig. 5. The interaction between treatment and conditioning was statistically significant (p < 0.001). The measured ratio in BAG paste and BAG slurry was significantly higher than that of de-ionized water (negative control) (p < 0.001). The remineralization therapy using

Fig. 3 – Representative OCT images of the negative control: (unconditioned + de-ionized water) and the treated: (air-abrasion + BAG paste) groups, before and after 21 days treatment. The depth profiles related to the OCT signal intensity within the WSL (dashed white rectangles). There was a reduction in the intensity at the subsurface level (the black star) in the treated sample when compared to the baseline intensity profile of the same sample. The TIFF analysis images (the gray-scale images) represent the reduction in the OCT signal intensity at the subsurface level measured to the surface reflection of the same sample. Note the difference in the gray-scale image of treated sample after 21 remineralization therapy (the white star). Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

ARTICLE IN PRESS

DENTAL-2512; No. of Pages 12

7

d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

remineralized using BAG paste or slurry (p = 0.004 and p < 0.001 respectively). Pre-conditioning the lesion surface using PAABAG air-abrasion or acid-etching reduced significantly the measured ratio compared to the unconditioned samples when the lesions were only immersed in the de-ionized water, the negative control of remineralization therapy (p < 0.001 for airabrasion and p = 0.04 for acid-etch).

ionized

3.5.

Fig. 4 – Mean ± SE of lesion Knoop microhardness. There was significantly increase in the Knoop microhardness in air-abrasion and acid-etching groups compared to unconditioned group. The remineralization therapies using BAG 45S5 showed improved lesion microhardness values (p < 0.05).

BAG slurry significantly increased the ratio at the lesion surface compared to that observed using BAG paste when the lesions were pre-conditioned using PAA-BAG air-abrasion (p < 0.001), while there were no statistically significant differences between BAG slurry and BAG paste therapies when the lesions were unconditioned or pre-conditioned using acidetch (p > 0.05). Using PAA-BAG air-abrasion to pre-condition the lesion surface increased significantly the v-(CO3 )2− /v1 -(PO4 )3− ratio compared to the unconditioned groups when the lesions were

Microscopy imaging

Representative CLSM fluorescence images are shown in Fig. 6 presenting the lesion depth (approximately 80 ␮m), the enamel prism outlines and the Rhodamine-B distribution. More Rhodamine-B permeating was observed within the nontreated group implying that the Rhodamine-B penetrated and was retained more within the depth of lesion. In contrast, in the CLSM-micrographs of the treated samples, less dye distribution was observed as a band-like area at the outer third of the cross-sections. Representative SEM micrographs of the experimental groups are presented in Fig. 7. The cross-sectional views of fractured non-treated lesions showed the partially demineralized enamel prisms, with no external mineral precipitation evident. In contrast, plate-like structures were observed at the lesion edge and could be differentiated from the original lesion structure (enamel prisms) in the treated groups. The external mineral precipitation was more pronounced in the BAG slurry than BAG paste. The lesion top surface in the non-treated group exhibited porosities resulting from the demineralization process. This porosity was covered completely by a “newly” formed layer of mineral within the treated groups (Fig. 6). The elemental analysis of the lesion top surface using EDX mapping presented an addition peak of Si (1.73 keV) relating to the reacted BAG particles in the remineralized lesions (Fig. 7).

v1 PO4

Intensity (a.u.)

ionized

Untreated v CO 3 Treated

400

600

800 1000 Raman shift (cm-1)

1200

Fig. 5 – Representative Raman spectra of WSL surface in untreated and treated samples. The arrows indicate to the measured peaks in the analysis. Bar graph represents mean ± SE of v-(CO3 )2− /v1 -(PO4 )3− ratio. PAA-BAG air-abrasion statistically increased the ratio value in the remineralized groups. BAG slurry increased the peak ratio when compared to BAG paste and de-ionized water (p < 0.05). Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

8

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

Fig. 6 – Representative CLSM images show the Rhodamine-B distribution in the cross-sectional views of the untreated WSL (A) and remineralized WSL using air-abrasion and BAG slurry (B). The enamel prism outline can be observed along the lesion depth. A band-like area (arrow) with less Rhodamine-B permeating is observed at the outer-third of the cross-section in the treated WSL.

4.

Discussion

4.1.

Profilometry analysis

Using PAA-BAG air-abrasion prior to remineralization therapy removed approximately 5 ␮m from the lesion surface, which is insignificant clinically. This pre-conditioning also increased the average surface roughness and consequently the surface area providing more sites for mineral deposition. The pre-conditioned WSL surface offered more sites for remineralization and showed increased remineralization [18]. PAA-BAG air-abrasion modified physically the lesion surface employing the kinetic energy of the abrasive particles, whereby a thin superficial layer is irregularly chipped away from the lesion surface increasing the surface roughness and exposing the WSL subsurface structure. Indeed, two aspects should be considered when pre-conditioning WSL using air-abrasion: the abrasive powder and the system’s operating parameters. Here, PAA-BAG has been selected due to its reduced cutting efficiency when compared to the standard BAG abrasive powder (30–60–90 ␮m) [30], while the operating parameters used in the current study have been shown to promote the ultraconservative application of this technology [24]. The profilometry data showed that the use of BAG paste or BAG slurry increased the step height values in the acidetch groups. It has been shown that conditioning WSL with 30% phosphoric acid for 30 s removed 3–6 ␮m from the lesion surface and increased the subsurface porosity up to 21 ␮m, detected using polarized light microscopy when the etched surface zone exhibited higher birefringence [31]. When the WSL was etched with 36% phosphoric acid, the surface layer of the lesion was completely decalcified [32]. The subsurface micro-porosities and the demineralization effect of phosphoric acid itself, may explain the slight reduction (approximately 3 ␮m) in the lesion surface following the physical remineralization therapy in acid-etching groups (Fig. 1C).

4.2.

Optical coherence tomography (OCT)

In OCT, the measurement of subsurface light scattering represents the degree of porosity within the lesion body.

This depends upon light scattering whereby the scattering increases in porous demineralized enamel [33]. Different factors can affect the light scattering in the remineralized WSLs such as the pores size/number, the mineral content and the natural of the enamel repair [33–35]. The remineralization therapy using BAG paste reduced significantly the subsurface light scattering implying that more penetration of the remineralization agent occurred filling more subsurface micro-porosities. Pre-conditioning the lesion surface using PAA-BAG air-abrasion or acid-etching promoted this penetration. The main differences between BAG paste and BAG slurry, which may had an effect on remineralization outcomes, were the concentration of BAG particles (36 wt.% in paste and 100 wt.% in slurry) and the additional chemical components of the paste. Raman micro-spectroscopy and microhardness testing detected a higher remineralization rate within WSLs treated with the slurry as discussed later. On the other hand, the OCT measurement showed more reduction in subsurface light scattering using the BAG paste. According to the results of the other analytical methods used in this study, it might appear that the OCT analysis highlighted mainly the pore size/number within treated lesions rather than the formation of new mineral. The presence of glycerine in the paste might increase the penetration of the paste components into lesion body to fill more pores.

4.3.

Lesion Knoop microhardness

Pre-conditioning the lesion surface with PAA-BAG air-abrasion and acid-etching promoted the subsequent remineralization therapy with BAG slurry, evaluated using microhardness testing. BAG slurry contained more BAG particles compared to the BAG paste and that may explain the improved microhardness detected for lesions treated with BAG slurry. Previous studies reported an increase in enamel microhardness following the remineralization therapy using BAG 45S5 [5,6,36]. The increase in the Knoop microhardness reflects a net mineral gain and an improved crystalline structure [37,38].

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

9

Fig. 7 – Representative SEM images of the fractured cross-sections and the lesion top surface. The lesion shows the partially demineralized enamel prisms (*). The fractured cross-sections of treated samples show mineral precipitations with plate-structures (white arrows), more pronounced in BAG slurry. The SEM micrographs of the top surface in non-treated sample exhibit a surface porosity resulted from demineralization process. The lesion surfaces in treated group present a layer of mineral completely blocked the surface porosity. The EDX spectra of treated samples show an additional peak at (1.73 keV) related to Si of reacted BAG particles (black arrow).

4.4.

Raman micro-spectroscopy

Quantitative information about the mineral concentration within a substrate can be obtained using Raman microspectroscopy, dependent upon the peak intensity being proportional to the number of molecules within the volume of the scanned area [39,40]. The phosphate peak at 959 cm−1 represented the hydroxyapatite (HA) of enamel, and its intensity relates to the amount of HA mineral within the scanned area [41,42]. The C O Raman peak of hydroxycarbonate apatite (HCA) layer formed on the reacted BAG particles at 1085 cm−1

clearly detectable during HCA formation [29]. In the current study, the v-(CO3 )2− /v1 -(PO4 )3− ratio was analyzed statistically to assess the mineral content at the lesion surface. The results showed that air-abrasion pre-conditioning increased significantly the peak ratio compared to acid-etching and to the unconditioned groups. This might result from the increased surface area and surface roughness which might enhance the HCA deposition within the superficial layer of lesion. Conditioning WSLs prior to remineralization therapy using phosphoric acid has been shown previously to improve the mineral gain of the treated lesion [16,17]. In the current study,

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

10

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

the Raman dataset revealed that pre-conditioning WSLs using phosphoric acid prior to remineralization therapy exhibited similar mineral content measurements to those of the unconditioned groups. Assessing the remineralization of enamel WSLs pre-treated with phosphoric acid revealed that the recovery of the mineral had occurred within the lesion body, but not within the etched surface level [43]. This might explain the reduced mineral content observed within the acid-etching groups using Raman micro-spectroscopy since this analytical method is considered a surface assessment method. In contrast, microhardness measurement showed that the etched WSLs exhibited an improved remineralization rate compared to the equivalent unconditioned groups. This can be considered subsurface assessment method since the Knoop indenter penetrates the lesion depth by 5 ␮m in depth [44], and the indentation is not only affected by the immediate contact areas, but also by areas at a distance of approximately 10 times the dimensions of the indenter [45,46].

4.5.

Microscopy imaging

The use of CLSM imaging in the present study was based on the fact that imbibition of a fluorescent dye into the WSL porosities decreased following remineralization treatment [27]. It has been shown that Rhodamine-B fluorescent dye penetrates enamel micro-porosities created through the demineralization process and that less of this dye penetrates the lesion following the remineralization therapy [47]. This was observed within the treated samples in the current study where a band-like area, with a reduced Rhodamine-B penetration, was observed at the outer edge of the cross-sectional views. However, the deeper part of the cross-sections showed a Rhodamine-B distribution similar to that observed in the untreated sample implying that the remineralization therapy was not involved that part of the lesion, and the complete repair had not occurred. A layer of newly precipitated mineral was detected covering the lesion surface in the BAG paste and slurry groups. The chemical analysis of this layer using EDX analysis showed an additional silicon peak confirming that this layer consisted of HCA structures of reacted BAG 45S5 [48]. The SEM micrographs of fractured cross-sections permitted the observation of interior lesion structures showing plate-like structures attached firmly to the lesion surface and penetrated into the lesion’s outer edge. The plate-like structures have been reported when the HCA of reacted BAG 45S5 was examined using SEM [49]. The use of BAG in WSL remineralization provides an external ion source with the intention of promoting and accelerating enamel remineralization in vivo. Treating BAG particles with de-ionized water causes leaching and exchanging of BAG ions with those of the water and that in turn, increases the interfacial pH followed by breaking Si O Si bonds and forming a Si(OH)4 layer. Calcium and phosphate ions are released from BAG at this stage, to form an amorphous CaP layer, which is crystallized to HCA [50]. The HCA crystal induced by BAG 45S5 exhibited approximately 50 nm thickness [51], and therefore these crystals could penetrate the pores of WSL surfaces which are approximately 200–300 nm wide (Fig. 7). In addition, the ions released form the BAG particles during the reactivity process might penetrate into the

lesion pores to form a mineral reservoir for the remineralization process. The remineralization of WSLs reported in the present study is expected to be improved within the biological oral environment due to the presence of fluoride and salivary calcium/phosphate ions, and this hypothesis requires further in situ study. The subsurface porosity of enamel WSLs, detected using OCT and CLSM, promoted the diffusion and the micro-mechanical fixation of minerals within the WSL depth. Erosive-like lesions do not exhibit the subsurface porosity, but irreversible enamel surface loss. A method has been described recently to treat erosive-like lesions where applying a 45S5 BAG-phosphoric-acid gel onto the enamel surface followed directly by placing a layer of bonding agent, preserves the 45S5 gel in contact with enamel surface for 24 h until the bioactive process matures [4]. An additional beneficial effect of using BAG 45S5 in WSL remineralization is that BAG particles exhibit an antibacterial effect against certain oral bacteria, including those associated with caries and periodontal disease [52,53]. The clinical translation of biomimetic remineralization strategies is still required since most in vitro studies included the immersion of specimens in remineralization solutions containing biomimetic analogs, which is inapplicable clinically [54]. Using air-abrasion technology to seed the early carious lesion surface with bioactive particles prior to remineralization therapy could be an appropriate clinical delivery system to apply biomimetic remineralization strategies in vivo. Previous studies reported that BAG particles were retained on the treated surface after BAG air-abrasion in spite of the post-treatment cleaning regimen [55,56]. The methodology of this study was designed to develop a clinical remineralization protocol whereby a single preconditioning lesion surface procedure carried out by the operator (dentist or therapist) would be followed by the home application of the remineralization therapy twice daily (5 min per application) for 21 days by the patient. This approach removes an ultra-thin layer from the lesion surface, which would not be clinically significant. Since enamel surface is polluted/covered by saliva proteins and impurities in vivo, the physical modification of WSL surface can expose more reactive subsurface structures which in turn, may improve the seamless adhesion of repairable layer with lesion structure when followed directly by HA formation [57,58]. Using PAABAG air-abrasion for this purpose also increased the lesion surface area and may seed the lesion surface with bioactive materials potentially aiding the further remineralization therapy.

5.

Conclusions

The two null hypotheses investigated in this study were rejected. Pre-conditioning WSL surface using PAA-BAG airabrasion removed an ultra-thin layer which would not be clinically significant, increased the lesion surface area and exposed subsurface structures. This pre-treatment enhanced the remineralization of WSL treated with BAG 45S5 slurry assessed by the increased mineral content, improved mechanical properties and the ultrastructural changes and therefore,

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

maybe recommended clinically to promote the mineral uptake during remineralization therapy.

references

[1] Banerjee A. Minimal intervention dentistry: Part 7. Minimally invasive operative caries management: rationale and techniques. Br Dent J 2013;214:107–11. [2] Gustafson G. The histopathology of caries of human dental enamel with special reference to the division of the carious lesion into zones. Acta Odontol 1957;15:13–55. [3] Gjorgievska ES, Nicholson JW, Slipper IJ, Stevanovic MM. Remineralization of demineralized enamel by toothpastes: a scanning electron microscopy, energy dispersive X-ray analysis, and three-dimensional stereo-micrographic study. Microsc Microanal 2013;19:587–95. [4] Bakry AS, Takahashi H, Otsuki M, Tagami J. Evaluation of new treatment for incipient enamel demineralization using 45S5 bioglass. Dent Mater 2014;30:314–20. [5] Deng M, Wen HL, Dong XL, Li F, Xu X, Li H, et al. Effects of 45S5 bioglass on surface properties of dental enamel subjected to 35% hydrogen peroxide. Int J Oral Sci 2013;5:103–10. [6] Burwell AK, Litkowski LJ, Greenspan DC. Calcium sodium phosphosilicate (NovaMin): remineralization potential. Adv Dent Res 2009;21:35–9. [7] Milly H, Festy F, Watson TF, Thompson I, Banerjee A. Enamel white spot lesions can remineralise using bio-active glass and polyacrylic acid-modified bio-active glass powders. J Dent 2014;42:158–66. [8] Hench LL, Splinter RJ, Allen WC, Greenlee TK. Bonding mechanisms at the interface of ceramic prosthetic materials. J Biomed Mater Res 1971;5:117–41. [9] Hench LL, Paschall HA. Histochemical responses at a biomaterial’s interface. J Biomed Mater Res 1974;8:49–64. [10] Thompson ID, Hench LL. Mechanical properties of bioactive glasses, glass–ceramics and composites. Proc Inst Mech Eng H 1998;212:127–36. [11] Wilson J, Pigott GH, Schoen FJ, Hench LL. Toxicology and biocompatibility of bioglasses. J Biomed Mater Res 1981;15:805–17. [12] Bakry AS, Tamura Y, Otsuki M, Kasugai S, Ohya K, Tagami J. Cytotoxicity of 45S5 bioglass paste used for dentine hypersensitivity treatment. J Dent 2011;39:599–603. [13] ten Cate JM. In vitro studies on the effects of fluoride on deand remineralization. J Dent Res 1990;69(Spec No.):614–9, discussion 34–6. [14] White DJ, Chen WC, Nancollas GH. Kinetic and physical aspects of enamel remineralization – a constant composition study. Caries Res 1988;22:11–9. [15] Larsen MJ, Pearce EIF. Some notes on the diffusion of acidic and alkaline agents into natural human caries lesions in vitro. Arch Oral Biol 1992;37:411–6. [16] Al-Khateeb S, Exterkate R, Angmar-Mansson B, ten Cate JM. Effect of acid-etching on remineralization of enamel white spot lesions. Acta Odontol Scand 2000;58:31–6. [17] Flaitz CM, Hicks MJ. Role of the acid-etch technique in remineralization of caries-like lesions of enamel: a polarized light and scanning electron microscopic study. ASDC J Dent Child 1993;61:21–8. [18] Peariasamy K, Anderson P, Brook AH. A quantitative study of the effect of pumicing and etching on the remineralisation of enamel opacities. Int J Paediatr Dent 2001;11:193–200. [19] Tay FR, Pashley DH. Guided tissue remineralisation of partially demineralised human dentine. Biomaterials 2008;29:1127–37.

11

[20] Qi YP, Li N, Niu LN, Primus CM, Ling JQ, Pashley DH, et al. Remineralization of artificial dentinal caries lesions by biomimetically modified mineral trioxide aggregate. Acta Biomater 2012;8:836–42. [21] ten Cate JM, Duijsters PP. Alternating demineralization and remineralization of artificial enamel lesions. Caries Res 1982;16:201–10. [22] ten Cate JM, Exterkate RA, Buijs MJ. The relative efficacy of fluoride toothpastes assessed with pH cycling. Caries Res 2006;40:136–41. [23] Ingram GS, Silverstone LM. A chemical and histological study of artificial caries in human dental enamel in vitro. Caries Res 1981;15:393–8. [24] Milly H, Austin RS, Thompson I, Banerjee A. In vitro effect of air-abrasion operating parameters on dynamic cutting characteristics of alumina and bio-active glass powders. Oper Dent 2014;39:81–9. [25] Ring HC, Mogensen M, Banzhaf C, Themstrup L, Jemec GBE. Optical coherence tomography imaging of telangiectasias during intense pulsed light treatment: a potential tool for rapid outcome assessment. Arch Dermatol Res 2013;305:299–303. [26] Wang KX, Meekings A, Fluhr JW, McKenzie G, Lee DA, Fisher J, et al. Optical coherence tomography-based optimization of Mohs micrographic surgery of basal cell carcinoma: a pilot study. Dermatol Surg 2013;39:627–33. [27] Fontana M, Li Y, Dunipace AJ, Noblitt TW, Fischer G, Katz BP, et al. Measurement of enamel demineralization using microradiography and confocal microscopy – a correlational study. Caries Res 1996;30:317–25. [28] Spizzirri PG, Cochrane NJ, Prawer S, Reynolds EC. A comparative study of carbonate determination in human teeth using Raman spectroscopy. Caries Res 2012;46: 353–60. [29] Rehman I, Hench LL, Bonfield W, Smith R. Analysis of surface layers on bioactive glasses. Biomaterials 1994;15:865–70. [30] Sauro S, Watson TF, Thompson I, Banerjee A. One-bottle self-etching adhesives applied to dentine air-abraded using bioactive glasses containing polyacrylic acid: an in vitro microtensile bond strength and confocal microscopy study. J Dent 2012;40:896–905. [31] Hicks MJ, Silverstone LM. Acid-etching of caries-like lesions of enamel: a polarized light microscopic study. Caries Res 1984;18:315–26. [32] Van Dorp CSE, Exterkate RAM, ten Cate JM. Mineral loss during etching of enamel lesions. Caries Res 1990;24:6–10. [33] Kang H, Darling CL, Fried D. Nondestructive monitoring of the repair of enamel artificial lesions by an acidic remineralization model using polarization-sensitive optical coherence tomography. Dent Mater 2012;28:488–94. [34] Jones RS, Darling CL, Featherstone JD, Fried D. Remineralization of in vitro dental caries assessed with polarization-sensitive optical coherence tomography. J Biomed Opt 2006;11:014016. [35] Hariri I, Sadr A, Shimada Y, Tagami J, Sumi Y. Effects of structural orientation of enamel and dentine on light attenuation and local refractive index: an optical coherence tomography study. J Dent 2012;40:387–96. [36] Dong ZH, Chang JA, Zhou Y, Lin KL. In vitro remineralization of human dental enamel by bioactive glasses. J Mater Sci 2011;46:1591–6. [37] Featherstone JDB, Ten Cate JM, Shariati M, Arends J. Comparison of artificial caries-like lesions by quantitative microradiography and microhardness profiles. Caries Res 1983;17:385–91. [38] Kielbassa AM, Wrbas KT, Schulte-Mönting J, Hellwig E. Correlation of transversal microradiography and microhardness on in situ-induced demineralization in

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

DENTAL-2512; No. of Pages 12

12

[39]

[40]

[41]

[42]

[43]

[44]

[45] [46]

[47]

[48]

ARTICLE IN PRESS d e n t a l m a t e r i a l s x x x ( 2 0 1 5 ) xxx–xxx

irradiated and nonirradiated human dental enamel. Arch Oral Biol 1999;44:243–51. Penel G, Leroy G, Rey C, Bres E. MicroRaman spectral study of the PO4 and CO3 vibrational modes in synthetic and biological apatites. Calcif Tissue Int 1998;63:475–81. Tramini P, Pelissier B, Valcarcel J, Bonnet B, Maury L. A Raman spectroscopic investigation of dentin and enamel structures modified by lactic acid. Caries Res 2000;34:233–40. Mohanty B, Dadlani D, Mahoney D, Mann AB. Characterizing and identifying incipient carious lesions in dental enamel using micro-Raman spectroscopy. Caries Res 2012;47:27–33. Santini A, Pulham CR, Rajab A, Ibbetson R. The effect of a 10% carbamide peroxide bleaching agent on the phosphate concentration of tooth enamel assessed by Raman spectroscopy. Dent Traumatol 2008;24:220–3. Hidaka K, Nishimura K, Miyazawa K, Miwa H, Goto S. Effects of acid etchants used for bonding orthodontic brackets on the remineralization of enamel white-spot lesions. Orthod Waves 2011;70:125–35. Schlueter N, Hara A, Shellis RP, Ganss C. Methods for the measurement and characterization of erosion in enamel and dentine. Caries Res 2011;45:13–23. Barbour ME, Rees JS. The laboratory assessment of enamel erosion: a review. J Dent 2004;32:591–602. de Jong EdJ, van der Linden A, Ten Bosch JJ. Longitudinal microradiography: a non-destructive automated quantitative method to follow mineral changes in mineralised tissue slices. Phys Med Biol 1987;32:1209. González-Cabezas C, Fontana M, Dunipace A, Li Y, Fischer G, Proskin H, et al. Measurement of enamel remineralization using microradiography and confocal microscopy. Caries Res 1998;32:385–92. Hench LL, Pantano CG, Buscemi PJ, Greenspan DC. Analysis of bioglass fixation of hip prostheses. J Biomed Mater Res 1977;11:267–82.

[49] Zhong JP, Greenspan DC, Feng JW. A microstructural examination of apatite induced by Bioglass in vitro. J Mater Sci: Mater Med 2002;13:321–6. [50] Hench LL. The story of Bioglass. J Mater Sci: Mater Med 2006;17:967–78. [51] Wen H, Moradian-Oldak J, Zhong J, Greenspan D, Fincham A. Effects of amelogenin on the transforming surface microstructures of Bioglass® in a calcifying solution. J Biomed Mater Res 2000;52:762–73. [52] Hu S, Chang J, Liu MQ, Ning CQ. Study on antibacterial effect of 45S5 Bioglass. J Mater Sci: Mater Med 2009;20: 281–6. [53] Allan I, Newman H, Wilson M. Antibacterial activity of particulate bioglass against supra- and subgingival bacteria. Biomaterials 2001;22:1683–7. [54] Niu LN, Zhang W, Pashley DH, Breschi L, Mao J, Chen JH, et al. Biomimetic remineralization of dentin. Dent Mater 2014;30:77–96. [55] Koller G, Cook RJ, Thompson ID, Watson TF, Di Silvio L. Surface modification of titanium implants using bioactive glasses with air abrasion technologies. J Mater Sci: Mater Med 2007;18:2291–6. [56] Paolinelis G, Banerjee A, Watson TF. An in vitro investigation of the effect and retention of bioactive glass air-abrasive on sound and carious dentine. J Dent 2008;36: 214–8. [57] Onuma K, Yamagishi K, Oyane A. Nucleation and growth of hydroxyapatite nanocrystals for nondestructive repair of early caries lesions. J Cryst Growth 2005;282: 199–207. [58] Robinson C, Hallsworth AS, Shore RC, Kirkham J. Effect of surface zone deproteinisation on the access of mineral ions into subsurface carious lesions of human enamel. Caries Res 1990;24:226–30.

Please cite this article in press as: Milly H, et al. Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization. Dent Mater (2015), http://dx.doi.org/10.1016/j.dental.2015.02.002

Surface pre-conditioning with bioactive glass air-abrasion can enhance enamel white spot lesion remineralization.

To evaluate the effect of pre-conditioning enamel white spot lesion (WSL) surfaces using bioactive glass (BAG) air-abrasion prior to remineralization ...
3MB Sizes 0 Downloads 9 Views