journal of dentistry 43 (2015) 440–449
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Effectiveness of various toothpastes on dentine tubule occlusion W.H. Arnold *, M. Prange, E.A. Naumova Department of Biological and Material Sciences in Dentistry, Witten/Herdecke University, Witten, Germany
article info
abstract
Article history:
Objective: Dentine hypersensitivity is an increasing problem in dentistry. Several products
Received 22 December 2014
are available that claim to occlude open dentine tubules and to reduce dentine hypersensi-
Received in revised form
tivity. The aim of this study was to investigate the effectiveness of several different products
29 January 2015
on dentine tubule occlusion using qualitative and quantitative methods.
Accepted 31 January 2015
Materials and methods: Dentine discs were prepared from extracted human premolars and molars. The dentine discs were brushed with 6 different experimental toothpastes, 1 positive control toothpaste and 1 negative control without toothpaste; the brushing simu-
Keywords:
lated a total brushing time of 1 year. Half of the discs were etched with lemon juice after
Toothpaste
toothpaste application. Standardized scanning electron microphotographs were taken and
Dentine
converted into binary black and white images. The black pixels, which represented the open
Dentine tubules
dentine tubules, were counted and statistically evaluated. Then, half of the dentine discs
Root dentine
were broken, and the occlusion of the dentine tubules was investigated using energy
Hypersensitivity
dispersive X-ray spectroscopy (EDS). Results: The number of open dentine tubules decreased significantly after brushing with 5 of the 6 tested toothpastes. A significant effect was observed after acid erosion for 3 of the 6 tested toothpastes. EDS revealed partly closed dentine tubules after brushing with 3 toothpastes; however, no partly closed dentine tubules were observed after acid erosion. Conclusions: Some toothpastes are capable of partial dentine tubule occlusion. This occlusion is unstable and can be removed with acid erosion. Clinical significance: Desensitizing toothpastes are the most common products that are used against dentine hypersensitivity, and these toothpastes affect dentine tubule occlusion. # 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1.
Introduction
As the demographics of the human population change and as the human population ages, more teeth remain in the mouths of elderly people due to effective caries prevention and periodontal disease management. Thus, dentine hypersensitivity is becoming an increasing problem in dentistry.1,2
Dentine hypersensitivity and a possible cause for this condition were described first by Gysi in 1900.3 Since then, the mechanisms causing this type of pain have remained controversial. Pulpal nerves from the plexus of Raschkow extend into approximately 15% of the dentine tubule length.4 These nerves do not innervate the peripheral dentine. Odontoblast processes may function as sensory receptors; however, odontoblast destruction does not cause insensitive
* Corresponding author at: Department of Biological and Material Sciences in Dentistry, Alfred Herrhausenstrasse 44, 58455 Witten, Germany. Tel.: +49 2302926658; fax: +49 2302926661. E-mail address: [email protected] (W.H. Arnold). http://dx.doi.org/10.1016/j.jdent.2015.01.014 0300-5712/# 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
journal of dentistry 43 (2015) 440–449
dentine.5,6 In addition, no synaptic contacts exist between the somatic nerves and odontoblasts.7 In 1968, Brannstrom postulated the hydrodynamic theory, which hypothesizes that fluid movement from the pulp towards the outer dentine within the dentine tubules causes dentine sensation.8–10 The hydrodynamic theory is now widely accepted as the cause of dentine sensitivity. Open dentine tubules may be the reason for the increased fluid movement that causes dentine hypersensitivity.2,11–13 This possibility is supported by the observation that dentine hypersensitivity directly correlates with the number of open dentine tubules.14 Numerous home-use desensitizing products for the treatment of dentine hypersensitivity are currently available. These products are divided into two categories: products that block the pulp nerve response and products that occlude open dentine tubules.1 The first group is composed of products that contain potassium salts. Potassium is thought to diffuse inside the dentine tubules and lower the excitability of the pulpal nerve fibres. Several arguments oppose this theory. One is that the diffusion distance in human teeth is greater than that in tested animals. Another argument is that the flow of dentinal fluid is outward from the pulp towards the tooth surface, which would hinder diffusion towards the pulp.16 The majority of home-use desensitizing products belong to the second group and contain a wide variety of active components. These active components can be divided into several subgroups, which are summarized in Table 1. The effect of strontium salts is thought to be attributable to their ability to absorb onto the connective tissue of dentine and to form strontium apatite, which may occlude the dentine tubules.17–19 However, dentine tubule occlusion by strontium salts has not been proven. Clinical studies have demonstrated a reduction of pain perception in patients who used strontium salts.20–22 Recent investigations have demonstrated that arginine combined with calcium carbonate occlude dentine tubules and that this deposit converts to calcium phosphate.13,23 However, many calcium phosphates are soluble in acidic environments and, therefore, unstable upon dietary acid challenge. Several randomized controlled clinical trials have demonstrated clear treatment effects of arginine and calcium carbonate toothpastes immediately and up to 8 weeks after treatment.24–28 In vitro studies have shown that stannous fluoride produces precipitates onto dentine; this precipitate is waterand acid-resistant.29 These in vitro studies are supported by
Table 1 – Summary of substances that occlude dentine tubules. Substance Strontium (chloride, acetate) Stannous fluoride Calcium sodium phosphosilicate Oxalates Fluorides Arginine and calcium carbonate Nanoparticles with various functionalizing agents
Literature
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randomized controlled clinical trials that demonstrated the effective treatment of dentine hypersensitivity using stannous fluoride.30,31 Calcium sodium phosphosilicates precipitate onto dentine collagen as calcium phosphate and silicate, forming deposits on the dentine surface and in dentine tubules.32–36 These precipitates are water- and acid-resistant. Randomized controlled clinical studies of calcium sodium phosphosilicates have shown the effective treatment of dentine hypersensitivity compared to controls.37–40 Oxalates form calcium oxalate crystals within the dentine tubules and act as desensitizing agents.41 This effect is enhanced when combined with calcium chloride.42 Some studies have demonstrated decreased hydrodynamic fluid flow within the dentine tubules upon oxalate treatment, thus reducing pain sensations.41,43–46 Another study demonstrated that oxalates block dentinal fluid flow by forming precipitates within the dentine tubules.47 However, a systematic review regarding the effectiveness of oxalates in the treatment of dentine hypersensitivity determined that that single treatments of oxalates had no effect on dentine hypersensitivity compared to placebos.48 The mechanisms of the action of fluorides in desensitizing dentine hypersensitivity remain unclear. Although most toothpastes contain fluorides in some form, the incidence of dentine hypersensitivity remain high. Fluorides, similar to other desensitizing agents, may block the dentine tubules. Fluorides enhance the mineralization of hydroxyapatite49 and may enhance hydroxyapatite formation within the dentine tubules, which blocks fluid movement and reduces pain. However, this enhancement has not been demonstrated. A novel approach in the development of desensitizing agents is the use of various combinations of nanoparticles.50– 52 The idea behind this approach is that nanoparticles may easily penetrate into dentine tubules and that these nanoparticles could act as mineralising agents that block fluid movement within the dentine tubules when combined with various agents. Considering that almost all desensitizing agents claim to occlude open dentine tubules, the aim of this study was to investigate quantitatively the effectiveness of various substances on dentine tubule occlusion.
2.
Material and methods
Seventy-eight caries-free extracted human molars were used for this experimental study. The collection of the teeth was approved by the ethical committee of Witten/Herdecke University (116/2013). Informed verbal consent was obtained from the patients before the use of the teeth. The teeth were stored in 0.9% NaCl containing 0.1% thymol until use.
18,29,61 30,31
2.1.
Experimental design
32,33,35,36 41,42,48 41 2,15,23,24 50–52,59,60
Dentine discs with a thickness of 3 mm were cut from the teeth using a saw microtome (Leica 1600, Leitz, Wetzlar, Germany). Twelve dentine discs were used for each brushing experiment with the different toothpastes. The discs were
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Table 2 – Active ingredients of the desensitizing toothpastes used. Toothpaste # 1 2 3 4 5 6
Product name
Active ingredient
Company
Elmex Sensitive Professional Sensodyne Rapid Sensodyne Repair BioRepair Colgate Total Sensitive Dontodent Sensitive
Pro-Argin, calcium carbonate Strontium acetate Stannous fluoride Zinc-carbonate hydroxyapatite New silica Tetrapotassium pyrophosphate, hydroxyapatite
GABA Glaxo Smith Kline Glaxo Smith Kline Dr. K. Wolff Colgate-Palmolive DM Dogeriemarkt
mounted on specimen holders, and the dentine surface was polished. Before the experiment, the dentine surface was eroded with lemon juice (Hitchcock, Mo¨nchengladbach, Germany) for 30 s. Then, the discs were placed in a tooth brushing machine, and a tooth brushing time of six months was simulated (2 h of continuous brushing, assuming 28 teeth in an oral cavity and 2 3 min tooth brushing per day). Slurries were prepared in a dilution of 1:3 toothpaste/water mixture. The dentine discs were brushed with the Dr. Best classic (medium) toothbrush at 120 spm and a slurry flow rate during tooth brushing of 10 ml per minute. The toothbrush load was 2 N. Six discs were prepared directly for scanning electron microscopic (SEM) investigation, and the six remaining discs were eroded with lemon juice for 30 s and then prepared for SEM investigation.
2.2.
Toothpastes
Five different commercially available toothpastes against hypersensitivity were used. All toothpastes had different active components, which are summarized in Table 2. The following toothpastes were used: Elmex toothpaste (CPGABA, Hamburg, Germany; toothpaste 0), which served as the positive control; Elmex Sensitive Professional (CP-GABA, Hamburg, Germany; toothpaste 1); Sensodyne Rapid (Glaxo Smith Kline, Brentford, Middlesex, United Kingdom; toothpaste 2); Sensodyne Repair (Glaxo Smith Kline, Brentford, Middlesex, United Kingdom; toothpaste 3); BioRepair Sensitive (Dr. K. Wolff GmbH, Bielefeld, Germany; toothpaste 4); Colgate Total Sensitive (Colgate-Palmolive, Hamburg, Germany; toothpaste 5); and Dontodent Sensitive (DMDrogerie Markt, Karlsruhe, Germany; toothpaste 6). Six dentine discs were only brushed with artificial saliva as the negative controls.7
2.3.
SEM investigation
All specimens were dehydrated in graded acetone, critical point dried and sputter-coated with gold palladium. Then, the specimens were examined under a scanning electron microscope (Zeiss Sigma VP, Zeiss, Oberkochen, Germany) at 20 kV acceleration voltage. Standardized images of the dentine discs were acquired at a magnification of 1000. Twenty images were acquired per disc. In addition, energy dispersive X-ray spectroscopy (EDS, EDAX Ametec; Mahwah, NJ, USA) and the accompanying product software were used to observe the penetration of the toothpaste into the dentine tubules. The X-ray signal for silicon served as evidence for the toothpaste. Surface scans were made to study the covering of the discs. Then, the specimens were frozen in liquid N2, fractured and the penetration of silica from the toothpastes into the open dentine tubules was studied.
2.4.
Quantitative analysis of dentine tubule occlusion
The standardized SEM microphotographs were imported into ImageJ software (NIH, USA) and converted into binary images. The black (open dentine tubules) and white (occluded dentine tubules and dentine) pixels (Fig. 1) were counted, and the numbers were transferred into a Microsoft Excel worksheet.
2.5.
Statistical analysis
The mean of all black pixels of each disc was calculated. These mean values were compared between the different toothpastes using the Wilcoxon–Mann–Whitney test for independent variables and post hoc Bonferroni adjustment, which resulted in a final p value of 0.0083. Descriptive statistics are presented as boxplots. All calculations were performed with
Fig. 1 – Preparation of microphotographs for the quantitative determination of closed dentine tubules. (a) SEM image and (b) converted binary black and white image.
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SPSS (IBM Corporation, Armonk, NY, USA; Rel. 21) statistical software.
3.
Results
3.1.
Quantitative evaluation
After tooth brushing, significant differences were found between the brushed only negative control (#7) and toothpastes 2 and 5. No differences were found between the negative control and toothpastes 1, 3, 4 and 6 (Fig. 2). A significant difference was found between the positive control toothpaste (#0) and test toothpastes 2, 3, 4, 5 and 6 (Fig. 3). After erosion with lemon juice, significant differences were found between the negative control (#7) and toothpastes 2, 4 and 6 but not between the negative control and toothpastes 1, 3 and 5 (Fig. 4). After erosion with lemon juice, the number of open dentine tubules was significantly different between the positive control toothpaste and test toothpastes 3, 5, and 6 (Fig. 5).
3.2.
SEM investigation combined with EDS analysis
The surface scans of the discs demonstrated irregular coverage of the dentine surfaces by silica. No evidence of silicon was found near the dentine surface within the open dentine tubules of both controls (Fig. 6/0 and 6/7). A scattered thin layer of silicon covered the dentine surface after the
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application of toothpaste 1 (Fig. 6/1). A clear thin layer of silicon covered the dentine surface and the openings of the dentine tubules after the application of toothpaste 2 (Fig. 6/2). No clear silicon layer was observed after the application of toothpaste 3 (Fig. 6/3). Several occluded dentine tubules were found after the application of toothpaste 4 (Fig. 6/4). Neither a silicon layer on the dentine surface nor occluded dentine tubules were observed after the application of toothpastes 5 and 6 (Fig. 6/5 and 6/6).
4.
Discussion
Gingival recession results in exposed dentine, which is the primary cause of dentine hypersensitivity and which is an increasing problem in dentistry. Consequently, several different strategies have been developed for the treatment of dentine hypersensitivity. These strategies emphasize the application of various types of desensitizing dentifrices, which are recommended as appropriate treatments in most cases.53 In principle, two alternative dentine hypersensitivity treatment methods exist. The first method is the blockage of the nerve transmission in the pulp, and the second method is dentine tubule occlusion to block the hydrodynamic mechanism in the dentine tubules. Potassium ions block the nerve response of the A-beta and A-delta nerve fibres1 and diminish the pain caused by external stimuli. Several different potassium-containing toothpastes are available. Potassiumbased toothpastes are often combined with other ingredients
Fig. 2 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing. Comparison with the negative control (without toothpaste). Significant differences were observed between the controls and toothpastes 2 and 5.
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Fig. 3 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing. Comparison with the reference toothpaste (positive control). Significant differences were observed between the controls and toothpastes 2, 3, 4, 5 and 6.
Fig. 4 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing and acid etching. Comparison with the negative control (without toothpaste). Significant differences were observed between the control and toothpastes 1, 2, 4, and 6.
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Fig. 5 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing and acid etching. Comparison with the reference toothpaste (positive control). Significant differences were observed between the control and toothpastes 3, 5, and 6.
to increase the benefits, and numerous clinical studies regarding potassium-based toothpastes have been performed, with differing results. Some of these studies reported no difference between potassium-based toothpastes and regular fluoridated toothpastes,54,55 whereas other studies raised some doubts regarding the clinical evidence of the effectivity of potassium-containing toothpastes.11,56–58 One toothpaste that was used in this study contained potassium and hydroxyapatite for the occlusion of dentine tubules; however, occlusion could not be verified. Dentine tubule occlusion is achieved in two different ways, by either the deposition of an occluding layer on top of the dentine or the introduction of occluding material into dentine tubules. Insoluble salts usually form a thin deposition on the dentine. Hydroxyapatite; arginine, in combination with calcium carbonate (Pro-Argin technology)2,15,23,24; or various nanoparticles with different functionalised agents50,59,60 are used for the induction of intratubular mineralisation. Several different active ingredients are available and are summarized in Table 2. In vitro studies have shown that strontium acetate or strontium chloride (SrCl2) treatment forms small crystalline deposits on the dentine surface, which can easily be washed away.29,61 Controversial reports regarding the clinical effects of strontium exist. Several studies have reported positive effects of SrCl2 or Sr acetate on dentine hypersensitivity relief.17,19,28,36,62 One study found that SrCl2 is less effective than conventional fluoride-containing products.21 Another
study found no significant differences between SnCl2-containing toothpastes and conventional fluoride-containing toothpastes.55 However, only one study that reported a positive effect of SrCl2 and that fulfilled the criteria for evidence-based dentistry has been identified.63,64 Sr acetate was shown to form a thin occluding layer on the dentine surface in the present in vitro study; however, no tags could be found in the tubule openings. Another active ingredient is SnF2. Several studies regarding the clinical efficacy of SnF2 have been published, with controversial results. Some studies reported positive effects of SnF2,30,31,65 whereas another study was neutral and found no difference between SnF2-containing toothpastes and conventional toothpastes.66 No dentinal occlusion of the cross-sections of dentine could be observed after treatment with SnF2-containing toothpaste in the present study. The top view demonstrated single occluded tubules. Oxalates were introduced for the treatment of dentine hypersensitivity in the early 1980s. Some studies reported good effectiveness of oxalates in reducing dentine hypersensitivity.41,44–46 This effectiveness may be due to the precipitation of oxalates within the dentine tubules and to their relative insolubility, which reduces hydraulic conductivity in the dentine tubules.47,67 However, a meta-analysis of the published papers regarding oxalates found little evidence regarding a positive clinical effect of oxalates.48 No oxalate-containing toothpaste was tested in the present study.
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Fig. 6 – Cross-sections of dentine discs with dentine tubule occlusion. The toothpastes are identified by EDS silicon mapping (pink). Ca is mapped in blue. A weak positive signal for silicon is visible on the surface but not in the tubule openings after treatment with toothpastes 1, 2 and 7. No signal could be detected after treatment with toothpastes 3, 5, and 6. Several dentine tubules were occluded after treatment with toothpaste 4.
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A relatively new method is arginine-calcium carbonate technology (Pro-Argin technology), which was introduced in 2002.68 Several in vitro studies demonstrated a good occluding effect of Pro-Argin technology on open dentine tubules.34,69–72 Clinical studies of Pro-Argin technology supported the in vitro results and showed instant relief of dentine hypersensitivity.24,73 Currently, no in vitro or in vivo studies regarding the occluding effects of zinc-carbonate hydroxyapatite on dentine tubules are available; only reports regarding the effects of zinc-carbonate hydroxyapatite on enamel have been published. Several occluded dentine tubules could be found in the dentine cross-sections after zinc-carbonate hydroxyapatite treatment (toothpaste # 4) in the present study. This finding was supported by the surface scan results, and this occluding effect was not resistant to acid challenge with lemon juice.
5.
Conclusion
Taken together, these results indicate that certain toothpastes occlude dentine tubules. This occlusion is superficial and may be dissolved with acids. Dentine tubule occlusion is dependent on the active ingredient and is not complete in any of the tested toothpastes.
Acknowledgments The authors would like to thank Mrs. Susanne Haußman for her technical assistance preparing the SEM specimens. Elmex toothpaste was provided by CP Gaba, Hamburg, Germany.
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43. Addy M, Dowell P. Dentine hypersensitivity: effect of interactions between metal salts, fluoride and chlorhexidine on the uptake by dentine. Journal of Oral Rehabilitation 1986;13:599–605. 44. Pashley DH, Galloway SE. The effects of oxalate treatment on the smear layer of ground surfaces of human dentine. Archives of Oral Biology 1985;30:731–7. 45. Pashley DH, Livingston MJ, Reeder OW, Horner J. Effects of the degree of tubule occlusion on the permeability of human dentine in vivo. Archives of Oral Biology 1978;23:1127–33. 46. Pashley DH, O’Meara JA, Kepler EE, Galloway SE, Thompson SM, Stewart FP. Dentin permeability. Effects of desensitizing dentifrices in vitro. Journal of Periodontology 1984;55:522–5. 47. Cuenin MF, Scheidt MJ, O’Neal RB, Strong SL, Pashley DH, Horner JA, et al. An in vivo study of dentin sensitivity: the relation of dentin sensitivity and the patency of dentin tubules. Journal of Periodontology 1991;62:668–73. 48. Cunha-Cruz J, Stout JR, Heaton LJ, Wataha JC. Dentin hypersensitivity and oxalates: a systematic review. Journal of Dental Research 2011;90:304–10. 49. Naumova EA, Gaengler P, Zimmer S, Arnold WH. Influence of individual saliva secretion on fluoride bioavailability. The Open Dentistry Journal 2010;4:185–90. 50. Kovtun A, Kozlova D, Ganesan K, Biewald C, Seipold N, Gaengler P, et al. Chlorhexidine-loaded calcium phosphate nanoparticles for dental maintenance treatment: combination of mineralising and antibacterial effects. RSC Advances 2012;2:870–5. 51. Tian L, Peng C, Shi Y, Guo X, Zhong B, Qi J, et al. Effect of mesoporous silica nanoparticles on dentinal tubule occlusion: an in vitro study using SEM and image analysis. Dental Materials Journal 2014;33:125–32. 52. Wang R, Wang Q, Wang X, Tian L, Liu H, Zhao M, et al. Enhancement of nano-hydroxyapatite bonding to dentin through a collagen/calcium dual affinitive peptide for dentinal tubule occlusion. Journal of Biomaterials Applications 2014;29:268–77. 53. Canadian Advisory Board on Dentin Hypersensitivity. Consensus-based recommendations for the diagnosis and management of dentin hypersensitivity. Journal of the Canadian Dental Association 2003;69:221–6. 54. Gillam DG, Bulman JS, Jackson RJ, Newman HN. Comparison of 2 desensitizing dentifrices with a commercially available fluoride dentifrice in alleviating cervical dentine sensitivity. Journal of Periodontology 1996;67:737–42. 55. West NX, Addy M, Jackson RJ, Ridge DB. Dentine hypersensitivity and the placebo response. A comparison of the effect of strontium acetate, potassium nitrate and fluoride toothpastes. Journal of Clinical Periodontology 1997;24:209–15. 56. Orchardson R, Gillam DG. Managing dentin hypersensitivity. The Journal of the American Dental Association 2006;137:990–8. quiz 1028–9. 57. Pashley DH, Tay FR, Haywood VB, Collins MC, Drisco CL. Dentin hypersensitivity: consensus-based recommendations for the diagnosis and management of dentin hypersensitivity. Inside Dentistry 2008;4:1–35. 58. Poulsen S, Errboe M, Lescay Mevil Y, Glenny AM. Potassium containing toothpastes for dentine hypersensitivity. Cochrane Database of Systematic Reviews 2006;3:CD00176. 59. Lee SY, Kwon HK, Kim BI. Effect of dentinal tubule occlusion by dentifrice containing nano-carbonate apatite. Journal of Oral Rehabilitation 2008;35:847–53. 60. Tschoppe P, Zandim DL, Martus P, Kielbassa AM. Enamel and dentine remineralization by nano-hydroxyapatite toothpastes. Journal of Dentistry 2011;39:430–7. 61. Addy M, Mostafa P. Dentine hypersensitivity. II. Effects produced by the uptake in vitro of toothpastes onto dentine. Journal of Oral Rehabilitation 1989;16:35–48.
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62. Mason S, Hughes N, Sufi F, Bannon L, Maggio B, North M, et al. A comparative clinical study investigating the efficacy of a dentifrice containing 8% strontium acetate and 1040 ppm fluoride in a silica base and a control dentifrice containing 1450 ppm fluoride in a silica base to provide immediate relief of dentin hypersensitivity. Journal of Clinical Dentistry 2010;21: 42–8. 63. Karim BF, Gillam DG. The efficacy of strontium and potassium toothpastes in treating dentine hypersensitivity: a systematic review. International Journal of Dentistry 2013;2013:573258. 64. Minkoff S, Axelrod S. Efficacy of strontium chloride in dental hypersensitivity. Journal of Periodontology 1987;58:470–4. 65. He T, Barker ML, Biesbrock AR, Miner M, Qaqish J, Sharma N. A clinical study to assess the effect of a stabilized stannous fluoride dentifrice on hypersensitivity relative to a marketed sodium fluoride/triclosan control. Journal of Clinical Dentistry 2014;25:13–8. 66. Sharma N, Roy S, Kakar A, Greenspan DC, Scott R. A clinical study comparing oral formulations containing 7.5% calcium sodium phosphosilicate (NovaMin), 5% potassium nitrate, and 0.4% stannous fluoride for the management of dentin hypersensitivity. Journal of Clinical Dentistry 2010;21:88–92. 67. Pereira JC, Segala AD, Gillam DG. Effect of desensitizing agents on the hydraulic conductance of human dentin subjected to different surface pre-treatments – an in vitro study. Dental Materials 2005;21:129–38.
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68. Kleinberg I. SensiStat. A new saliva-based composition for simple and effective treatment of dentinal sensitivity pain. Dentistry Today 2002;21:42–7. 69. Cummins D. The efficacy of a new dentifrice containing 8.0% arginine, calcium carbonate, and 1450 ppm fluoride in delivering instant and lasting relief of dentin hypersensitivity. Journal of Clinical Dentistry 2009; 20:109–14. 70. Parkinson CR, Butler A, Willson RJ. Development of an acid challenge-based in vitro dentin disc occlusion model. Journal of Clinical Dentistry 2010;21:31–6. 71. Parkinson CR, Willson RJ. An in vitro investigation of two currently marketed dentin tubule occlusion dentifrices. Journal of Clinical Dentistry 2011;22:6–10. 72. Patel R, Chopra S, Vandeven M, Cummins D. Comparison of the effects on dentin permeability of two commercially available sensitivity relief dentifrices. Journal of Clinical Dentistry 2011;22:108–12. 73. Nathoo S, Delgado E, Zhang YP, DeVizio W, Cummins D, Mateo LR. Comparing the efficacy in providing instant relief of dentin hypersensitivity of a new toothpaste containing 8.0% arginine, calcium carbonate, and 1450 ppm fluoride relative to a benchmark desensitizing toothpaste containing 2% potassium ion and 1450 ppm fluoride, and to a control toothpaste with 1450 ppm fluoride: a three-day clinical study in New Jersey, USA. Journal of Clinical Dentistry 2009;20:123–30.
Available online at www.sciencedirect.com
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Effectiveness of various toothpastes on dentine tubule occlusion W.H. Arnold *, M. Prange, E.A. Naumova Department of Biological and Material Sciences in Dentistry, Witten/Herdecke University, Witten, Germany
article info
abstract
Article history:
Objective: Dentine hypersensitivity is an increasing problem in dentistry. Several products
Received 22 December 2014
are available that claim to occlude open dentine tubules and to reduce dentine hypersensi-
Received in revised form
tivity. The aim of this study was to investigate the effectiveness of several different products
29 January 2015
on dentine tubule occlusion using qualitative and quantitative methods.
Accepted 31 January 2015
Materials and methods: Dentine discs were prepared from extracted human premolars and molars. The dentine discs were brushed with 6 different experimental toothpastes, 1 positive control toothpaste and 1 negative control without toothpaste; the brushing simu-
Keywords:
lated a total brushing time of 1 year. Half of the discs were etched with lemon juice after
Toothpaste
toothpaste application. Standardized scanning electron microphotographs were taken and
Dentine
converted into binary black and white images. The black pixels, which represented the open
Dentine tubules
dentine tubules, were counted and statistically evaluated. Then, half of the dentine discs
Root dentine
were broken, and the occlusion of the dentine tubules was investigated using energy
Hypersensitivity
dispersive X-ray spectroscopy (EDS). Results: The number of open dentine tubules decreased significantly after brushing with 5 of the 6 tested toothpastes. A significant effect was observed after acid erosion for 3 of the 6 tested toothpastes. EDS revealed partly closed dentine tubules after brushing with 3 toothpastes; however, no partly closed dentine tubules were observed after acid erosion. Conclusions: Some toothpastes are capable of partial dentine tubule occlusion. This occlusion is unstable and can be removed with acid erosion. Clinical significance: Desensitizing toothpastes are the most common products that are used against dentine hypersensitivity, and these toothpastes affect dentine tubule occlusion. # 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
1.
Introduction
As the demographics of the human population change and as the human population ages, more teeth remain in the mouths of elderly people due to effective caries prevention and periodontal disease management. Thus, dentine hypersensitivity is becoming an increasing problem in dentistry.1,2
Dentine hypersensitivity and a possible cause for this condition were described first by Gysi in 1900.3 Since then, the mechanisms causing this type of pain have remained controversial. Pulpal nerves from the plexus of Raschkow extend into approximately 15% of the dentine tubule length.4 These nerves do not innervate the peripheral dentine. Odontoblast processes may function as sensory receptors; however, odontoblast destruction does not cause insensitive
* Corresponding author at: Department of Biological and Material Sciences in Dentistry, Alfred Herrhausenstrasse 44, 58455 Witten, Germany. Tel.: +49 2302926658; fax: +49 2302926661. E-mail address: [email protected] (W.H. Arnold). http://dx.doi.org/10.1016/j.jdent.2015.01.014 0300-5712/# 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).
journal of dentistry 43 (2015) 440–449
dentine.5,6 In addition, no synaptic contacts exist between the somatic nerves and odontoblasts.7 In 1968, Brannstrom postulated the hydrodynamic theory, which hypothesizes that fluid movement from the pulp towards the outer dentine within the dentine tubules causes dentine sensation.8–10 The hydrodynamic theory is now widely accepted as the cause of dentine sensitivity. Open dentine tubules may be the reason for the increased fluid movement that causes dentine hypersensitivity.2,11–13 This possibility is supported by the observation that dentine hypersensitivity directly correlates with the number of open dentine tubules.14 Numerous home-use desensitizing products for the treatment of dentine hypersensitivity are currently available. These products are divided into two categories: products that block the pulp nerve response and products that occlude open dentine tubules.1 The first group is composed of products that contain potassium salts. Potassium is thought to diffuse inside the dentine tubules and lower the excitability of the pulpal nerve fibres. Several arguments oppose this theory. One is that the diffusion distance in human teeth is greater than that in tested animals. Another argument is that the flow of dentinal fluid is outward from the pulp towards the tooth surface, which would hinder diffusion towards the pulp.16 The majority of home-use desensitizing products belong to the second group and contain a wide variety of active components. These active components can be divided into several subgroups, which are summarized in Table 1. The effect of strontium salts is thought to be attributable to their ability to absorb onto the connective tissue of dentine and to form strontium apatite, which may occlude the dentine tubules.17–19 However, dentine tubule occlusion by strontium salts has not been proven. Clinical studies have demonstrated a reduction of pain perception in patients who used strontium salts.20–22 Recent investigations have demonstrated that arginine combined with calcium carbonate occlude dentine tubules and that this deposit converts to calcium phosphate.13,23 However, many calcium phosphates are soluble in acidic environments and, therefore, unstable upon dietary acid challenge. Several randomized controlled clinical trials have demonstrated clear treatment effects of arginine and calcium carbonate toothpastes immediately and up to 8 weeks after treatment.24–28 In vitro studies have shown that stannous fluoride produces precipitates onto dentine; this precipitate is waterand acid-resistant.29 These in vitro studies are supported by
Table 1 – Summary of substances that occlude dentine tubules. Substance Strontium (chloride, acetate) Stannous fluoride Calcium sodium phosphosilicate Oxalates Fluorides Arginine and calcium carbonate Nanoparticles with various functionalizing agents
Literature
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randomized controlled clinical trials that demonstrated the effective treatment of dentine hypersensitivity using stannous fluoride.30,31 Calcium sodium phosphosilicates precipitate onto dentine collagen as calcium phosphate and silicate, forming deposits on the dentine surface and in dentine tubules.32–36 These precipitates are water- and acid-resistant. Randomized controlled clinical studies of calcium sodium phosphosilicates have shown the effective treatment of dentine hypersensitivity compared to controls.37–40 Oxalates form calcium oxalate crystals within the dentine tubules and act as desensitizing agents.41 This effect is enhanced when combined with calcium chloride.42 Some studies have demonstrated decreased hydrodynamic fluid flow within the dentine tubules upon oxalate treatment, thus reducing pain sensations.41,43–46 Another study demonstrated that oxalates block dentinal fluid flow by forming precipitates within the dentine tubules.47 However, a systematic review regarding the effectiveness of oxalates in the treatment of dentine hypersensitivity determined that that single treatments of oxalates had no effect on dentine hypersensitivity compared to placebos.48 The mechanisms of the action of fluorides in desensitizing dentine hypersensitivity remain unclear. Although most toothpastes contain fluorides in some form, the incidence of dentine hypersensitivity remain high. Fluorides, similar to other desensitizing agents, may block the dentine tubules. Fluorides enhance the mineralization of hydroxyapatite49 and may enhance hydroxyapatite formation within the dentine tubules, which blocks fluid movement and reduces pain. However, this enhancement has not been demonstrated. A novel approach in the development of desensitizing agents is the use of various combinations of nanoparticles.50– 52 The idea behind this approach is that nanoparticles may easily penetrate into dentine tubules and that these nanoparticles could act as mineralising agents that block fluid movement within the dentine tubules when combined with various agents. Considering that almost all desensitizing agents claim to occlude open dentine tubules, the aim of this study was to investigate quantitatively the effectiveness of various substances on dentine tubule occlusion.
2.
Material and methods
Seventy-eight caries-free extracted human molars were used for this experimental study. The collection of the teeth was approved by the ethical committee of Witten/Herdecke University (116/2013). Informed verbal consent was obtained from the patients before the use of the teeth. The teeth were stored in 0.9% NaCl containing 0.1% thymol until use.
18,29,61 30,31
2.1.
Experimental design
32,33,35,36 41,42,48 41 2,15,23,24 50–52,59,60
Dentine discs with a thickness of 3 mm were cut from the teeth using a saw microtome (Leica 1600, Leitz, Wetzlar, Germany). Twelve dentine discs were used for each brushing experiment with the different toothpastes. The discs were
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Table 2 – Active ingredients of the desensitizing toothpastes used. Toothpaste # 1 2 3 4 5 6
Product name
Active ingredient
Company
Elmex Sensitive Professional Sensodyne Rapid Sensodyne Repair BioRepair Colgate Total Sensitive Dontodent Sensitive
Pro-Argin, calcium carbonate Strontium acetate Stannous fluoride Zinc-carbonate hydroxyapatite New silica Tetrapotassium pyrophosphate, hydroxyapatite
GABA Glaxo Smith Kline Glaxo Smith Kline Dr. K. Wolff Colgate-Palmolive DM Dogeriemarkt
mounted on specimen holders, and the dentine surface was polished. Before the experiment, the dentine surface was eroded with lemon juice (Hitchcock, Mo¨nchengladbach, Germany) for 30 s. Then, the discs were placed in a tooth brushing machine, and a tooth brushing time of six months was simulated (2 h of continuous brushing, assuming 28 teeth in an oral cavity and 2 3 min tooth brushing per day). Slurries were prepared in a dilution of 1:3 toothpaste/water mixture. The dentine discs were brushed with the Dr. Best classic (medium) toothbrush at 120 spm and a slurry flow rate during tooth brushing of 10 ml per minute. The toothbrush load was 2 N. Six discs were prepared directly for scanning electron microscopic (SEM) investigation, and the six remaining discs were eroded with lemon juice for 30 s and then prepared for SEM investigation.
2.2.
Toothpastes
Five different commercially available toothpastes against hypersensitivity were used. All toothpastes had different active components, which are summarized in Table 2. The following toothpastes were used: Elmex toothpaste (CPGABA, Hamburg, Germany; toothpaste 0), which served as the positive control; Elmex Sensitive Professional (CP-GABA, Hamburg, Germany; toothpaste 1); Sensodyne Rapid (Glaxo Smith Kline, Brentford, Middlesex, United Kingdom; toothpaste 2); Sensodyne Repair (Glaxo Smith Kline, Brentford, Middlesex, United Kingdom; toothpaste 3); BioRepair Sensitive (Dr. K. Wolff GmbH, Bielefeld, Germany; toothpaste 4); Colgate Total Sensitive (Colgate-Palmolive, Hamburg, Germany; toothpaste 5); and Dontodent Sensitive (DMDrogerie Markt, Karlsruhe, Germany; toothpaste 6). Six dentine discs were only brushed with artificial saliva as the negative controls.7
2.3.
SEM investigation
All specimens were dehydrated in graded acetone, critical point dried and sputter-coated with gold palladium. Then, the specimens were examined under a scanning electron microscope (Zeiss Sigma VP, Zeiss, Oberkochen, Germany) at 20 kV acceleration voltage. Standardized images of the dentine discs were acquired at a magnification of 1000. Twenty images were acquired per disc. In addition, energy dispersive X-ray spectroscopy (EDS, EDAX Ametec; Mahwah, NJ, USA) and the accompanying product software were used to observe the penetration of the toothpaste into the dentine tubules. The X-ray signal for silicon served as evidence for the toothpaste. Surface scans were made to study the covering of the discs. Then, the specimens were frozen in liquid N2, fractured and the penetration of silica from the toothpastes into the open dentine tubules was studied.
2.4.
Quantitative analysis of dentine tubule occlusion
The standardized SEM microphotographs were imported into ImageJ software (NIH, USA) and converted into binary images. The black (open dentine tubules) and white (occluded dentine tubules and dentine) pixels (Fig. 1) were counted, and the numbers were transferred into a Microsoft Excel worksheet.
2.5.
Statistical analysis
The mean of all black pixels of each disc was calculated. These mean values were compared between the different toothpastes using the Wilcoxon–Mann–Whitney test for independent variables and post hoc Bonferroni adjustment, which resulted in a final p value of 0.0083. Descriptive statistics are presented as boxplots. All calculations were performed with
Fig. 1 – Preparation of microphotographs for the quantitative determination of closed dentine tubules. (a) SEM image and (b) converted binary black and white image.
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SPSS (IBM Corporation, Armonk, NY, USA; Rel. 21) statistical software.
3.
Results
3.1.
Quantitative evaluation
After tooth brushing, significant differences were found between the brushed only negative control (#7) and toothpastes 2 and 5. No differences were found between the negative control and toothpastes 1, 3, 4 and 6 (Fig. 2). A significant difference was found between the positive control toothpaste (#0) and test toothpastes 2, 3, 4, 5 and 6 (Fig. 3). After erosion with lemon juice, significant differences were found between the negative control (#7) and toothpastes 2, 4 and 6 but not between the negative control and toothpastes 1, 3 and 5 (Fig. 4). After erosion with lemon juice, the number of open dentine tubules was significantly different between the positive control toothpaste and test toothpastes 3, 5, and 6 (Fig. 5).
3.2.
SEM investigation combined with EDS analysis
The surface scans of the discs demonstrated irregular coverage of the dentine surfaces by silica. No evidence of silicon was found near the dentine surface within the open dentine tubules of both controls (Fig. 6/0 and 6/7). A scattered thin layer of silicon covered the dentine surface after the
443
application of toothpaste 1 (Fig. 6/1). A clear thin layer of silicon covered the dentine surface and the openings of the dentine tubules after the application of toothpaste 2 (Fig. 6/2). No clear silicon layer was observed after the application of toothpaste 3 (Fig. 6/3). Several occluded dentine tubules were found after the application of toothpaste 4 (Fig. 6/4). Neither a silicon layer on the dentine surface nor occluded dentine tubules were observed after the application of toothpastes 5 and 6 (Fig. 6/5 and 6/6).
4.
Discussion
Gingival recession results in exposed dentine, which is the primary cause of dentine hypersensitivity and which is an increasing problem in dentistry. Consequently, several different strategies have been developed for the treatment of dentine hypersensitivity. These strategies emphasize the application of various types of desensitizing dentifrices, which are recommended as appropriate treatments in most cases.53 In principle, two alternative dentine hypersensitivity treatment methods exist. The first method is the blockage of the nerve transmission in the pulp, and the second method is dentine tubule occlusion to block the hydrodynamic mechanism in the dentine tubules. Potassium ions block the nerve response of the A-beta and A-delta nerve fibres1 and diminish the pain caused by external stimuli. Several different potassium-containing toothpastes are available. Potassiumbased toothpastes are often combined with other ingredients
Fig. 2 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing. Comparison with the negative control (without toothpaste). Significant differences were observed between the controls and toothpastes 2 and 5.
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Fig. 3 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing. Comparison with the reference toothpaste (positive control). Significant differences were observed between the controls and toothpastes 2, 3, 4, 5 and 6.
Fig. 4 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing and acid etching. Comparison with the negative control (without toothpaste). Significant differences were observed between the control and toothpastes 1, 2, 4, and 6.
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Fig. 5 – Boxplot graphics of the quantitative determination of open dentine tubules after tooth brushing and acid etching. Comparison with the reference toothpaste (positive control). Significant differences were observed between the control and toothpastes 3, 5, and 6.
to increase the benefits, and numerous clinical studies regarding potassium-based toothpastes have been performed, with differing results. Some of these studies reported no difference between potassium-based toothpastes and regular fluoridated toothpastes,54,55 whereas other studies raised some doubts regarding the clinical evidence of the effectivity of potassium-containing toothpastes.11,56–58 One toothpaste that was used in this study contained potassium and hydroxyapatite for the occlusion of dentine tubules; however, occlusion could not be verified. Dentine tubule occlusion is achieved in two different ways, by either the deposition of an occluding layer on top of the dentine or the introduction of occluding material into dentine tubules. Insoluble salts usually form a thin deposition on the dentine. Hydroxyapatite; arginine, in combination with calcium carbonate (Pro-Argin technology)2,15,23,24; or various nanoparticles with different functionalised agents50,59,60 are used for the induction of intratubular mineralisation. Several different active ingredients are available and are summarized in Table 2. In vitro studies have shown that strontium acetate or strontium chloride (SrCl2) treatment forms small crystalline deposits on the dentine surface, which can easily be washed away.29,61 Controversial reports regarding the clinical effects of strontium exist. Several studies have reported positive effects of SrCl2 or Sr acetate on dentine hypersensitivity relief.17,19,28,36,62 One study found that SrCl2 is less effective than conventional fluoride-containing products.21 Another
study found no significant differences between SnCl2-containing toothpastes and conventional fluoride-containing toothpastes.55 However, only one study that reported a positive effect of SrCl2 and that fulfilled the criteria for evidence-based dentistry has been identified.63,64 Sr acetate was shown to form a thin occluding layer on the dentine surface in the present in vitro study; however, no tags could be found in the tubule openings. Another active ingredient is SnF2. Several studies regarding the clinical efficacy of SnF2 have been published, with controversial results. Some studies reported positive effects of SnF2,30,31,65 whereas another study was neutral and found no difference between SnF2-containing toothpastes and conventional toothpastes.66 No dentinal occlusion of the cross-sections of dentine could be observed after treatment with SnF2-containing toothpaste in the present study. The top view demonstrated single occluded tubules. Oxalates were introduced for the treatment of dentine hypersensitivity in the early 1980s. Some studies reported good effectiveness of oxalates in reducing dentine hypersensitivity.41,44–46 This effectiveness may be due to the precipitation of oxalates within the dentine tubules and to their relative insolubility, which reduces hydraulic conductivity in the dentine tubules.47,67 However, a meta-analysis of the published papers regarding oxalates found little evidence regarding a positive clinical effect of oxalates.48 No oxalate-containing toothpaste was tested in the present study.
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Fig. 6 – Cross-sections of dentine discs with dentine tubule occlusion. The toothpastes are identified by EDS silicon mapping (pink). Ca is mapped in blue. A weak positive signal for silicon is visible on the surface but not in the tubule openings after treatment with toothpastes 1, 2 and 7. No signal could be detected after treatment with toothpastes 3, 5, and 6. Several dentine tubules were occluded after treatment with toothpaste 4.
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A relatively new method is arginine-calcium carbonate technology (Pro-Argin technology), which was introduced in 2002.68 Several in vitro studies demonstrated a good occluding effect of Pro-Argin technology on open dentine tubules.34,69–72 Clinical studies of Pro-Argin technology supported the in vitro results and showed instant relief of dentine hypersensitivity.24,73 Currently, no in vitro or in vivo studies regarding the occluding effects of zinc-carbonate hydroxyapatite on dentine tubules are available; only reports regarding the effects of zinc-carbonate hydroxyapatite on enamel have been published. Several occluded dentine tubules could be found in the dentine cross-sections after zinc-carbonate hydroxyapatite treatment (toothpaste # 4) in the present study. This finding was supported by the surface scan results, and this occluding effect was not resistant to acid challenge with lemon juice.
5.
Conclusion
Taken together, these results indicate that certain toothpastes occlude dentine tubules. This occlusion is superficial and may be dissolved with acids. Dentine tubule occlusion is dependent on the active ingredient and is not complete in any of the tested toothpastes.
Acknowledgments The authors would like to thank Mrs. Susanne Haußman for her technical assistance preparing the SEM specimens. Elmex toothpaste was provided by CP Gaba, Hamburg, Germany.
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