Australian Dental Journal

Australian Dental Journal The official journal of the Australian Dental Association Australian Dental Journal 2015; 60: 96 103 doi: 10.1111/adj.12241 Effect of a novel bioactive glass-ceramic on dentinal tubule occlusion: an in vitro study Y Zhong,#* J Liu,# X Li,* W Yin,* T He,* D Hu,* Y Liao,* X Yao, Y Wang** *State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China. Department of Preventive Dentistry, West China Hospital of Stomatology, Sichuan University, Chengdu, Sichuan, China. Chongqing Key Laboratory for Oral Diseases and Biomedical Sciences, Chongqing, China. Department of Preventive Dentistry, The Affiliated Hospital of Stomatology, Chongqing Medical University, Chongqing, China. College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan, China. **Department of Oral Implantology, Tianjin Stomatological Hospital of Nankai University, Tianjin, China. ABSTRACT Background: This in vitro study aimed to assess the ability and efficacy of HX-BGC, a novel bioactive glass-ceramic (SiO 2 -P 2 O 5 -CaO-Na 2 O-SrO), to reduce dentine tubule permeability. Methods: Dentine discs from human third molars were etched and randomly allocated into five groups: Group 1 distilled water; Group 2 Sensodyne Repair toothpaste (containing NovaMin ); Group 3 HX-BGC toothpaste (containing 7.5% HX-BGC); Group 4 control toothpaste (without HX-BGC); and Group 5 HX-BGC powder. Specimens were treated daily by brushing with an electric toothbrush for 20 seconds. Between daily treatments (7 days total), specimens were immersed in artificial saliva for 24 hours. Dentine permeability was measured at baseline, after the first treatment, after the first 24-hour immersion in artificial saliva and at the end of day 7. Dentine morphology and surface deposits were observed by scanning electron microscopy after one day and 7 days of treatment, respectively. Results: Sensodyne Repair and bioactive glass-ceramic toothpaste significantly and immediately lowered dentine permeability. The HX-BGC powder group showed the highest reduction in dentine permeability after 7 days of treatment. Conclusions: The novel bioactive glass-ceramic material HX-BGC is effective in reducing dentine permeability by occluding open dentine tubules, indicating that HX-BGC may be a potential treatment for dentine hypersensitivity. Keywords: Bioactive glass-ceramic, dentine hypersensitivity, dentine permeability, desensitizing toothpastes, toothbrushing. Abbreviations and acronyms: HCA = hydroxycarbonate apatite; SEM = scanning electron microscopy. (Accepted for publication 26 March 2014.) INTRODUCTION Dentine hypersensitivity (DH) is a common dental problem. 1 The most widely accepted theory for explaining DH is the hydrodynamic theory proposed by Br annstr om and colleagues. 2 This theory postulates that the exposure of open dentine tubules to thermal, evaporative, tactile, osmotic or chemical stimuli causes fluid movement within them, which in turn activates mechanoreceptors that elicit pain and discomfort. 3 Based on this theory, two methods have been proposed to desensitize dentine. One is reducing fluid movement in dentine by occluding the tubules, the other is decreasing the activity of dental sensory nerves. 4,5 The basis of hydrodynamic theory is that the fluidfilled dentinal tubules are open to the oral cavity at #Y Zhong and J Liu contributed equally to this work. the dentine surface and within the pulp. 6 A histology study determined that an increase in the number and width of patent dentine tubules is related to the severity of DH. 7 According to the Hagen-Poiseuille equation, the movement of dentine fluid in a tubule is proportional to the 4th power of the tubular radius and the pressure difference between the two ends of a tubule. 8 Thus, occluding the exposed tubules and reducing the fluid flow are believed to be efficacious strategies for treating DH. 6 Several physical and chemical agents have been used to treat DH, such as cavity varnishes, calcium compounds, oxalates, strontium chloride, fluoride-based interventions and lasers. Although these treatments have been shown to be successful in relieving DH, no single desensitizing agent is considered ideal. Bioglass was originally developed to stimulate new bone formation. Scanning electron microscopy (SEM) has revealed that bioglass application forms an apatite 96 2015 Australian Dental Association

Effect of a novel bioactive glass-ceramic on dentinal tubule occlusion layer that occludes dentine tubules. 9 NovaMin, which is based on the original 45S5 Bioglass, is the active ingredient in Sensodyne Repair dentifrice, and it occludes dentine tubules by precipitating hydroxycarbonate apatite (HCA) onto the tooth surface. 10 16 The clinical effectiveness of NovaMin for relieving DH has been proven in a small number of clinical studies. 17 Another bioglass material, DP-Bioglass, also treats DH by producing a 60 lm deep sealant on dentine tubules. 13 A novel bioactive material, Nano- CaO@mesoporous silica, has been developed based on DP-Bioglass, and it contains calcium oxide nanoparticles mixed with 30% phosphoric acid. Nano-CaO can efficiently occlude dentine tubules and significantly reduce dentine permeability even in the presence of pulpal pressure. 18 However, it is desirable to improve the effectiveness of bioglass to manage DH because of the limited effectiveness of current bioglass products. Bioactive glasses degrade in aqueous environments to release calcium (Ca 2+ ), sodium (Na + ) and phosphate ions (PO 4 3- ). Ca 2+ and PO 4 3- ions along with mineral ions in saliva are able to form a calcium phosphate layer on dentine surfaces or inside tubules. Cations such as Na + or Ca 2+ from bioglass can substitute H + or H 3 O + and raise the ph of the environment, favouring apatite deposition. 16,19,20 The Materials Laboratory at the State Key Laboratory of Oral Diseases, West China Hospital of Stomatology, Sichuan University recently developed a novel bioactive glass-ceramic (SiO 2 -P 2 O 5 - CaO-Na 2 O-SrO) called HX-BGC, which contains sodium calcium phosphate (NaCaPO4) and hydroxylapatite as its ceramic phase. Preliminary work has shown that when 0.075 g of HX-BGC was mixed in 100 ml distilled water, the ph of the solution raised to above 8.0 (measured using ph instrument 710A, Orion Research Company, USA) and released phosphorus, calcium and strontium ions (measured using plasma spectrometer Optima 5300V/2000DV, PerkinElmer, USA). This study aimed to compare, both quantitatively and qualitatively, the ability of glass ceramic in the form of HX-BGC in reducing dentine permeability with that of a commercial desensitizing bioglass (NovaMin ). It was hypothesized that HX- BGC would occlude dentine tubules as effectively as NovaMin. MATERIALS AND METHODS Specimen preparation All protocols were reviewed and approved by the Ethics Committee of the School and Hospital of West China Stomatology of Sichuan University, and informed consent was obtained to collect teeth for this study. Human third molars extracted for surgical reasons were collected and stored in 0.5% thymol at 4 C for less than a month prior to use. Dentine discs with a thickness of approximately 1.0 mm were obtained by cutting perpendicularly to the long axis of the tooth above the cemento-enamel junction using a low-speed watercooled diamond saw. After preparing the specimens, a homogeneous smear layer was created on the upper dentine surface of each specimen using 500-grit abrasive paper for 30 seconds. The smear layer was subsequently removed by treating the upper dentine surface using 6% citric acid for 3 minutes. 21 The specimens were gently rinsed with distilled water and maintained wet to evaluate the maximum permeability (Lp1), which was assumed to be 100% (baseline value). Experimental design After baseline permeability measurements were taken, the specimens were randomly allocated into five groups, each containing 10 specimens. Specimens in different groups were treated with different regimens: Group 1 (control 1) distilled water; Group 2 Sensodyne Repair toothpaste (containing NovaMin ); Group 3 HX-BGC toothpaste (containing 7.5% HX-BGC); Group 4 control toothpaste (without HX-BGC); and Group 5 HX-BGC powder. All treatments were applied to the upper dentine surface of etched specimens in a humid environment. After initial brushing of the specimens with remineralizing agents (i.e. a pea-sized amount of undiluted toothpaste in Groups 2, 3 and 4, and 0.015 g HX-BGC powder in Group 5) for 20 seconds, the agents were left on the surface for a total of 4 minutes. The specimens were rinsed with distilled water for 4 seconds to remove visible traces of toothpaste or powder. A power toothbrush (Actibrush, Colgate, New York, USA) was used to brush and apply a constant force of 150 g 14 at an inclination of approximately 90 to the dentine surface. Immediately after the treatment, the second dentine permeability values (Lp2) were obtained. The specimens were then stored in artificial saliva (AS, ph 7.4) at 37 C for the rest of the day. The composition of the artificial saliva was as follows: 1.5 mm CaCl 2, 0.9 mm KH 2 PO 4, 130 mm KCl, 5 mm NaN 3 and 20 mm HEPES with ph 7.4 (stabilized with NaOH). After 24 hours, a third permeability value (Lp3) was obtained. The procedure of brushing, rinsing, and storing each specimen in artificial saliva was repeated once daily for 7 days, followed by the fourth permeability measurement (Lp4) after the last treatment. The experimental design is summarized in Fig. 1. Dentine permeability measurement The dentine permeability measuring system is shown in Fig. 2. Each specimen was connected to a waterfilled system working at a simulated pulpal pressure 2015 Australian Dental Association 97

Y Zhong et al. Fluid flow was measured by the movement of an air bubble trapped within a horizontal microcapillary tube (internal diameter 0.1 cm and external diameter 0.6 cm). The linear displacement of the air bubble was converted into volume displacement (fluid flow, ll) that was transformed into dentine permeability (Lp) value (ll min 1 cm 2 H 2 O 1 ), calculated by Lp = Q/At, where Q is the fluid flow (ll), A is the area of the dentine disc (cm 2 ) and t is the time (min). Fig. 1 The experimental design showing dentine disc preparation and permeability measurements in different treatment groups. Statistical analysis All permeability data (Lp2, Lp3, Lp4) were transformed into the percentage of the original maximum permeability values (Lp1) to reduce the baseline differences. These per cent values were adopted in the following statistical analysis. Means and standard deviations of the per cent Lp values were calculated for each group. Using SAS 8.0 for Windows (SAS Institute Inc., Cary, NC, USA), the normality of all scores was verified using the Shapiro Wilk test (p > 0.05). The homogeneity of variance was verified using the Levene s test (p > 0.05). Because the data could be classified as repeated measurements and the time intervals were unequal, the differences across groups were analysed using a mixed linear model considering treatment and measured time as the main effect factors. Using five types of covariance structures to select the smallest value of AIC index, autoregression (1) was finally identified to fit the autoregressive structure of covariance. The mean per cent reduction was computed and compared across groups at each observation point using one-way ANOVA. The mean per cent reduction was compared between groups at each observing point using Student-Newman-Keuls test. Differences were considered significant at a < 0.05. Fig. 2 Schematic illustration of dentine disc preparation and dentine permeability measurement under 20 cm H 2 O pressure. of 20 cm H 2 O. A fluid filtration system and a modified split-chamber unit were used to measure fluid transudation through the dentine disc. Each specimen was held tightly by a pair of rubber O rings with an internal diameter of 0.6 cm (area: 0.38 cm 2 ). SEM analysis Three dentine discs were randomly collected from each group after acid etching, after immersion in artificial saliva for 24 hours and at the end of the 7 days treatment, corresponding to the Lp1, Lp3 and Lp4 stages. The specimens were air dried at room temperature (20 C 1 C) for 24 hours before being coated with gold and subjected to morphological analysis using a scanning electron microscope (FEI, Eindhoven, The Netherlands) at 20 kv. RESULTS Quantitative assessment of dentine permeability (permeability test) Table 1 shows the results of the mixed linear model that confirmed the main effects of treatment and time 98 2015 Australian Dental Association

Effect of a novel bioactive glass-ceramic on dentinal tubule occlusion Table 1. Results of mixed linear model: tests of fixed effects Effect Num DF Pr >F Group 4 0.0002 Time 1 <0.0001 Time*time 1 0.0002 DF: the degree of freedom; Group: the differences in mean dentine permeability (Lp) values between different treatment groups; Time: the effect of time in Lp measurements across different time points; Time*time: the interactions among the different time points of Lp stages. on dentine permeability (p < 0.01). The data showed that there were significant differences across the groups and across different time points within each group. Table 2 shows a continuous decrease in dentine permeability (i.e. changes in Lp %) after the application of different products. Dentine permeability decreased significantly by 43.4% and 51.0% immediately after the first treatment with Sensodyne Repair and HX-BGC toothpastes, respectively. No significant difference was observed between these two groups (p > 0.05), and mean permeability values were significantly greater than those of distilled water (p < 0.05). In comparison, there was lower reduction in dentine permeability in the other three groups (12.0% 26.8%, p > 0.05). After 24 hours of immersion in artificial saliva, dentine permeability decreased further by approximately 7.3% to 15.6% in different treatment groups, except in the HX-BGC powder-treated group where permeability decreased by 39.4% (from 79.7% to 40.3%). No significant differences were observed among the groups treated with Sensodyne Repair toothpaste, HX-BGC toothpaste and HX-BGC powder (p > 0.05). After 7 days of treatment, specimens brushed with distilled water or the control toothpaste had higher dentine permeability (72.0% and 59.8%, respectively) than those treated with HX-BGC toothpaste (21.3%), Sensodyne (28.3%) and HX-BGC powder (21.0%) (p < 0.05). No significant differences were observed among the latter three treatments (p > 0.05). Qualitative assessment of dentine permeability Eroded dentine surfaces (at baseline) were free of a smear layer and nearly all dentine tubules were completely open (Figs. 3A and 3B). After the eroded dentine discs were brushed with distilled water and immersed in artificial saliva for one day, nearly all dentine tubules were completely open (Figs. 4A and 4B). These tubules were still open even after repeated brushing once daily for 7 days (Figs. 4C and 4D). Application of Sensodyne Repair toothpaste to eroded dentine discs and storage in artificial saliva for one day produced irregular crystal-like deposits that covered the dentine surface and occluded dentine tubules (Figs. 4E and 4F). After repeated brushing once daily for 7 days, the dentine surfaces were covered by surface deposits and only a few dentine tubules were open (Figs. 4G and 4H). Application of HX-BGC toothpaste to these dentine discs prior to storage in artificial saliva created granular deposits both on the surface and inside tubules (Figs. 4I and 4J). After brushing once daily for 7 days, the amount of deposits inside the dentine tubules increased, and the diameters of the dentine tubule orifices were reduced (Figs. 4K and 4L). In addition, crystal-like deposits were observed inside dentine tubules (Fig. 5A). Brushing the eroded dentine surface with control toothpaste (without active ingredients) and storage in artificial saliva for one day resulted in small deposits that occluded only a few tubules (Figs. 4M and 4N). Repeated brushing once daily for 7 days resulted in a slight increase in deposits inside the dentine tubules, but they were still patent (Figs. 4O and 4P). Brushing the eroded dentine discs with HX-BGC powder and immersion in artificial saliva for one day created small crystal-like deposits on the surface Table 2. Permeability data after treatments at different times Lp% Distilled water Sensodyne Repair HX-BGC contained toothpaste Control toothpaste HX-BGC powder Citric acid etching (Lp1/Max Lp) 100 100 100 100 100 Immediately after treatments (Lp2) 88.0 11.8 A 56.6 10.1 BC 49.0 8.8 C 73.2 10.8 ABC 79.7 + 11.9 AB 1 day of AS immersion (Lp3) 72.4 14.1 AB 46.1 20.1 BC 41.7 16.1 BC 64.0 11.9 ABC 40.3 + 15.8 C 7 days treatments (Lp4) 72.0 10.7 A 28.3 14.0 B 21.3 10.1 B 59.8 14.6 A 21.0 + 9.3 B Changes in dentine permeability, expressed as per cent of maximum Lp values (means +/ SD), with different treatment regimes over a 7-day period. The maximum dentine permeability after etching with 6% citric acid was expressed as 100% Lp value. The mean percentage of reduction was compared between groups at each observation point using Student-Newman-Keuls test. Means with the same letter were not significantly different at the same time point (p > 0.05). 2015 Australian Dental Association 99

Y Zhong et al. (a) (b) Fig. 3 SEM images showing patent tubules on the dentine surfaces after erosion with 6% citric acid at 50009 (a) and 20 0009 (b) magnifications. (Figs. 4Q and 4R). These deposits occluded most tubule orifices and narrowed their diameters. After repeated brushing once daily for 7 days, a layer of crystal-like deposits completely covered the dentine surface (Figs. 4S and 4T). In addition, small granular crystals were noted to form on the dentine surface at a high magnification (Fig. 5B). Given that bioactive glasses and glass-ceramics induce osteogenesis in physiological systems, 19 they are likely to be capable of regenerating enamel and dentine. HX-BGC is anticipated to have similar characteristics but further studies are needed to investigate the detailed mechanism behind HX-BGC s occluding effect. The mechanisms of action of HX-BGC are likely to be similar to those of other bioactive glasses and glass-ceramics. When HX-BGC particles are exposed to an aqueous environment, its ceramic phase (NaCa- PO 4 ) dissolves and raises the ph of the fluid. 37 Once the ph rises above 4.0, CaP nucleation occurs on the hydroxyapatite wall of the dentine tubules (i.e. heterogeneous nucleation), where the interfacial energy is lower than that in aqueous solution (i.e. homogeneous nucleation). 38 When the ph increases above 7.0, components of HX-BGC toothpaste or the HX-BGC powder are likely to adhere to dentine tubular walls. Mineral salts from saliva may create crystal precipitates on the dentine surface, thereby decreasing dentine permeability. 39 In the present study, SEM images showed that the control specimens (distilled water brushing treatment and control toothpaste treatment) immersed in artificial saliva maintained their baseline appearances, i.e. most dentine tubules remained open. Meanwhile, the dentine surfaces after treatment with HX-BGC toothpaste or HX-BGC powder or Sensodyne Repair toothpaste were covered with newly deposited crystalline substitutes. Differences in micrographic appearances of specimens treated with control toothpaste and HX-BGC toothpaste indicate that the additional active ingredients in HX-BGC toothpaste may have created better tubule occlusion. The result of Sensodyne Repair toothpaste is similar to that of a previous study. 35 Overall, HX-BGC toothpaste, HX-BGC powder and Sensodyne Repair toothpaste were capable of occluding open dentine tubules under a simulated oral enviroment. HX-BGC also contains a small amount of strontium. Strontium is used as an active component in toothpaste for treating DH. Dedhiya et al. 40 suggested DISCUSSION In vitro studies of the efficacy of desensitizing agents use a fluid filtration system for hydraulic conductance measurement. 14,22 28 This model was developed by Pashley et al. 29 and evaluates the ability of potential desensitizing agents to reduce fluid flow due to tubule occlusion. Although 70 cm H 2 O or higher pressure 21,26,30 was used in previous studies, 20 cm H 2 O pressure 14,31 33 was selected in the present study to simulate physiological pulpal pressure. When dentine is subjected to toothbrush abrasion or tooth grinding (from opposing enamel specimen) in the presence of distilled or deionized water, chipped tooth particles and debris cover its surface and occlude dentine tubules. 14,34 A reduction of 12.0% dentine permeability by brushing with distilled water in the present study was less than the almost 70.0% reduction reported by Wang et al. 14 In fact, all permeability values obtained in the present study were much higher than those reported by Wang et al., 14 probably due to the different brushing methods used. In the present study, the specimens were brushed for 20 seconds while maintaining contact with toothpaste for 4 minutes to simulate daily behaviour, whereas the brushing time was 2 minutes in the study by Wang et al. 14 The occlusion effect may have been due to formation of more abraded dentine particles induced by a longer brushing time. In the present study, the novel bioactive glass-ceramic, in the form of HX-BGC toothpaste or powder, was effective in reducing dentine permeability. HX-BGC compared positively with the desensitizing effect of NovaMin in Sensodyne Repair toothpaste. 14,15,17,35,36 100 2015 Australian Dental Association

Effect of a novel bioactive glass-ceramic on dentinal tubule occlusion (a) (b) (c) (d) (e) (f) (g) (h) (i) (j) (k) (l) (m) (n) (o) (p) (q) (r) (s) (t) Fig. 4 (i) Immersion in artificial saliva for 1 day for the first two columns (Figs. a and b; e and f etc.) and (ii) After 7 days of treatment for the last two columns (Figs. c and d; g and h etc.). (i) 95000 for the first column (e.g. a, e etc); (ii) 920 000 for the second column (e.g. b, f etc.), (iii) 95000 for the third column (e.g. c, g etc.) and (iv) 920 000 for the fourth column (e.g. d, h etc.). Group 1 (distilled water): Images showing patent dentine tubules after treatment with distilled water and immersion in artificial saliva for 1 day (a and b) and after 7 days of treatment (c and d). Group 2 (Sensodyne Repair toothpaste): Images showing occluded dentine tubules after treatment with Sensodyne Repair toothpaste and immersion in artificial saliva for 1 day (e and f) and after 7 days of treatment (g and h). Group 3 (HX-BGC toothpaste): Images showing occluded dentine tubules by a large amount of surface deposits after treatment with HX-BGC toothpaste and immersion in artificial saliva for 1 day (i and j). After 7 days of treatment, most of the opened dentine tubules were occluded. Surface deposits covered the intertubular dentine, and small granular crystals were visible inside the dentine tubules (k and l). Group 4 (control toothpaste): Images showing patent dentine tubules, which were partially covered with surface deposits, after treatment with control toothpaste and immersion in artificial saliva for 1 day (m and n) and after 7 days of treatment (o and p). Group 5 (HX-BGC powder): Images showing occluded tubules by crystalline debris after treatment with HX-BGC powder and immersion in artificial saliva for 1 day (q and r). After 7 days of treatment, surface deposits completely covered the dentine surface (s and t). 2015 Australian Dental Association 101

Y Zhong et al. (a) (b) Fig. 5 SEM images showing crystal-like deposits inside the dentine tubules and on the dentine surface from the HX-BGC toothpaste (a) and the HX-BGC powder (b) after 7 days of treatment at 80 0009 magnification. The application of HX-BGC toothpaste formed different sized crystal-like structures inside dentine tubules and narrowed them (a). The application of HX-BGC powder formed small granular crystals that completely blocked the tubules (b). that the formation of a calcium-strontium apatite complex at the apatite crystal surface inhibits the acidic dissolution of hydroxyapatite. This suggestion is supported by the observation that incorporation of strontium, together with fluoride, retards synthetic hydroxyapatite dissolution from acetate acid. 41 Strontium can also replace calcium in activating secretory mechanisms and may also affect or modulate the pulpal adrenergic and cholinergic mechanisms involved in DH. 42 In addition, strontium has a well-documented anti-caries effect, 43,44 and it is believed to play a synergistic role with fluoride in caries inhibition. Therefore, the strontium release from this novel biomaterial is a desirable characteristic. CONCLUSIONS The present study demonstrated that the novel bioactive glass-ceramic (SiO 2 -P 2 O 5 -CaO-Na 2 O-SrO) HX-BGC is effective in reducing dentine permeability under a simulated oral environment. Therefore, HX-BGC may be a potential treatment for DH. Further clinical studies are needed to prove the clinical effectiveness of HX-BGC in relieving DH. REFERENCES 1. Amarasena N, Spencer J. Dentine hypersensitivity Australian dentists perspective. Aust Dent J 2010;55:181 187. 2. Br annstr om M, Johnson G, Nordenvall KJ. Transmission and control of dentinal pain: resin impregnation for the desensitization of dentin. J Am Dent Assoc 1979;99:612 618. 3. Br annstr om M, Linden LA. The hydrodynamics of the dental tubule and of pulp fluid. A discussion of its significance in relation to dentinal sensitivity. Caries Res 1967;1:310 317. 4. Markowitz K, Pashley DH. Personal reflections on a sensitive subject. J Dent Res 2007;86:292 295. 5. Br annstr om M. Sensitivity of dentine. Oral Surg Oral Med Oral Pathol 1966;21:517 526. 6. Bartold PM. Dentinal hypersensitivity: a review. Aust Dent J 2006;51:212 218; quiz 276. 7. Ishikawa S. A clinico-histological study on the hypersensitivity of dentin. Kokubyo Gakkai Zasshi 1969;36:278 298. 8. Wylie SG, Wilson PR. An investigation into the pressure transmitted to the pulp chamber on crown cementation: a laboratory study. J Dent Res 1994;73:1684 1689. 9. Forsback AP, Areva S. Mineralization of dentin induced by treatment with bioactive glass S53P4 in vitro. Acta Odontol Scand 2004;62:14 20. 10. Vollenweider M, Brunner TJ. Remineralization of human dentin using ultrafine bioactive glass particles. Acta Biomater 2007;3:936 943. 11. Gillam DG, Tang JY. The effects of a novel Bioglass dentifrice on dentine sensitivity: a scanning electron microscopy investigation. J Oral Rehabil 2002;29:305 313. 12. Tai BJ, Bian Z. Anti-gingivitis effect of a dentifrice containing bioactive glass (NovaMin) particulate. J Clin Periodontol 2006;33:86 91. 13. Burwell AK, Litkowski LJ. Calcium sodium phosphosilicate (NovaMin): remineralization potential. Adv Dent Res 2009;21:35 39. 14. Wang Z, Sa Y. Effect of desensitising toothpastes on dentinal tubule occlusion: a dentine permeability measurement and SEM in vitro study. J Dent 2010;38:400 410. 15. Pradeep AR, Sharma A. Comparison of clinical efficacy of a dentifrice containing calcium sodium phosphosilicate to a dentifrice containing potassium nitrate and to a placebo on dentinal hypersensitivity: a randomized clinical trial. J Periodontol 2010;81:1167 1173. 16. Wefel JS. NovaMin: likely clinical success. Adv Dent Res 2009;21:40 43. 17. Pradeep AR, Agarwal E. Comparison of efficacy of three commercially available dentifrices [corrected] on dentinal hypersensitivity: a randomized clinical trial. Aust Dent J 2012;57:429 434. 18. Chiang YC, Chen HJ. A novel mesoporous biomaterial for treating dentin hypersensitivity. J Dent Res 2010;89:236 240. 19. Burwell AK, Litkowski LJ. Calcium sodium phosphosilicate (NovaMin): remineralization potential. Adv Dent Res 2009;21:35 39. 20. Reynolds EC. Calcium phosphate-based remineralization systems: scientific evidence? Aust Dent J 2008;53:268 273. 21. Cherng AM, Chow LC. Reduction in dentin permeability using mildly supersaturated calcium phosphate solutions. Arch Oral Biol 2004;49:91 98. 22. Pashley DH. Mechanisms of dentin sensitivity. Dent Clin North Am 1990;34:449 473. 23. Sauro S, Gandolfi MG. Oxalate-containing phytocomplexes as dentine desensitisers: an in vitro study. Arch Oral Biol 2006;51:655 664. 102 2015 Australian Dental Association

Effect of a novel bioactive glass-ceramic on dentinal tubule occlusion 24. Sauro S, Watson TF. Prevention of water contamination of ethanol-saturated dentin and hydrophobic hybrid layers. J Adhes Dent 2009;11:271 278. 25. Kuroiwa M, Kodaka T. Dentin hypersensitivity. Occlusion of dentinal tubules by brushing with and without an abrasive dentifrice. J Oral Rehabil 1994;65:291 296. 26. Prati C, Montebugnoli L. Permeability and morphology of dentin after erosion induced by acidic drinks. J Periodontol 2003;74:428 436. 27. Sauro S, Watson TF. Dentine desensitization induced by prophylactic and air-polishing procedures: an in vitro dentine permeability and confocal microscopy study. J Dent 2010;38: 411 422. 28. Sales-Peres SH, Carvalho FN. Effect of propolis gel on the in vitro reduction of dentin permeability. J Appl Oral Sci 2011;19: 318 323. 29. Merchant VA, Livingston MJ. Dentin permeation: comparison of diffusion with filtration. J Dent Res 1977;56:1161 1164. 30. Elgalaid TO, Creanor SL. The permeability of natural dentine caries before and after restoration: an in vitro study. J Dent 2007;35:656 663. 31. Sauro S, Pashley DH. Effect of simulated pulpal pressure on dentin permeability and adhesion of self-etch adhesives. Dent Mater 2007;23:705 713. 32. Hiraishi N, Yiu CK. Effect of pulpal pressure on the microtensile bond strength of luting resin cements to human dentin. Dent Mater 2009;25:58 66. 33. Sauro S, Mannocci F. Influence of the hydrostatic pulpal pressure on droplets formation in current etch-and-rinse and selfetch adhesives: a video rate/tsm microscopy and fluid filtration study. Dent Mater 2009;25:1392 1402. 34. Ranjitkar S, Narayana T. The effect of casein phosphopeptideamorphous calcium phosphate on erosive dentine wear. Aust Dent J 2009;54:101 107. 35. Earl JS, Topping N. Physical and chemical characterization of the surface layers formed on dentin following treatment with a fluoridated toothpaste containing NovaMin. J Clin Dent 2011; 22:68 73. 36. Greenspan DC. NovaMin and tooth sensitivity an overview. J Clin Dent 2010;21:61 65. 37. Saldana L, Sanchez-Salcedo S. Calcium phosphate-based particles influence osteogenic maturation of human mesenchymal stem cells. Acta Biomater 2009;5:1294 1305. 38. Ishikawa K, Eanes ED. The effect of supersaturation on apatite crystal formation in aqueous solutions at physiologic ph and temperature. J Dent Res 1994;73:1462 1469. 39. Suge T, Kawasaki A. Ammonium hexafluorosilicate elicits calcium phosphate precipitation and shows continuous dentin tubule occlusion. Dent Mater 2008;24:192 198. 40. Dedhiya MG, Young F. Mechanism for the retardation of the acid dissolution rate of hydroxapatite by strontium. J Dent Res 1973;52:1097 1109. 41. Featherstone JD, Shields CP. Acid reactivity of carbonated apatites with strontium and fluoride substitutions. J Dent Res 1983;62:1049 1053. 42. Foreman JC, Hallett MB. Movement of strontium ions into mast cells and its relationship to the secretory response. J Physiol 1977;271:233 251. 43. Athanassouli TM, Papastathopoulos DS. Dental caries and strontium concentration in drinking water and surface enamel. J Dent Res 1983;62:989 991. 44. Thuy TT, Nakagaki H. Effect of strontium in combination with fluoride on enamel remineralization in vitro. Arch Oral Biol 2008;53:1017 1022. Address for correspondence: Dr Xue Li State Key Laboratory of Oral Diseases West China Hospital of Stomatology Sichuan University No. 14, 3rd Section of Ren Min Nan Road Chengdu, Sichuan 610041 China Email: gardonlixue@sina.com 2015 Australian Dental Association 103