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19: 148-l 52

Dentine hypersensitivity-effects of some proprietary mouthwashes on the dentine smear layer: a SEM study M. Addy, T. Loyn and D. Adams* Departments of Periodontology and *Basic Dental Science, Dental School, University of Wales College of Medicine, Cardiff, South Wales, UK

ABSTRACT Exposed dentine may be sensitive to stimuli depending on the patency of the dentinal tubules. Most abrasive elements tend to produce a smear layer which obturates the dentinal tubules. This layer is easily removed by a number of erosive agents, particularly dietary acids. Mouthwashes are increasingly used and largely

investigated for possible benefits to dental health. Rarely do studies assess potential detrimental activity. The aim of the present study was to examine effects of mouthwashes on dentine. Smear layers artificially produced on dentine sections were exposed, for time periods ranging from 3 to 300 min, to mouthrinses alone, or with subsequent brushing for 2 min using water or a fluoride toothpaste. Assessments were made by scanning electron microscopy. Of the nine rinses tested, six produced no consistently observable changes compared to water treated controls at any time period with or without brushing. A hexetidine rinse and a fluoride/antiseptic rinse both exposed tubules after exposure times of 2 h and longer, an effect enhanced by post-treatment brushing. A phenolic antiseptic rinse consistently removed the smear layer from specimens, an effect enhanced by brushing such that after 10 min exposure and 2 min brushing many tubules were open at the surface. The results indicate that the use of some mouthrinses could predispose to excessive tooth substance loss and dentine hypersensitivity, particularly if used prior to toothbrushing. There is a need to determine whether the intermittent use of some mouthrinses produces cumulative effects on dentine. KEY WORDS: J. Dent. 1991;

Dentine, Dentine smear layer, Dentine hypersensitivity, Mouthwashes 19: 148-l

52 (Received 14 November 1990;

accepted 30 January 1991)

Correspondence should be addressed to: Professor M. Addy, Department University of Wales College of Medicine, Cardiff CF4 4XY, UK

INTRODUCTION Exposure of buccal cervical dentine arising from enamel loss and/or gingival recession is a common observation in adults. Avariety of factors may lead to exposure of dentine in this area. In particular, and for many years, toothbrushing has been considered to play an aetiological role in gingival recession (Hirschfeld, 1939) and indirect evidence supports this opinion (Addy et al., 1986). Once exposed to the oral environment dentine will be impacted by numerous agents, some of which may result in tissue loss by mechanical and/or chemical actions. These agents include toothbrushes and toothpaste ingredients, notably abrasives, and dietary factors particularly acids (Holloway et al., 1958; Pindborg, 1970; Davis, 1978; Touyz, 1983). Such abrasive and erosive influences not only remove @1991 Butterworth-Heinemann 0300-5712/91/030148-05

Ltd.

of Periodontology, Dental School,

dentine but the latter may expose dentinal tubules (Addy er al.. 1987). Indeed, the combination of abrasive and erosive factors markedly accelerates tissue loss (Davis and Winter, 1980) and the opening of tubules at the dentine surface (Absi et al., 1987) may produce symptoms of the condition described as dentine hypersensitivity. Increasingly mouthwashes are used, in addition to toothbrushing with a toothpaste, to provide cosmetic and dental health benefits. Aside from the considerable attention paid to the abrasivity of toothpastes (Davis, 1978) there has been little interest in the possible detrimental chemical effects of oral hygiene products. Thus, both toothpastes and mouthwashes contain substances which could erode dentine. Interestingly, the acidic nature of a number of mouthwashes has been

Addy et a/.: Mouthwashes

Fig. 7. Dentine section soaked in Fluorigard for 10 min. The smear layer is intact with no evidence of dentinal tubules. x 530.

reported (Perdok et al., 1990):The aim of this study was to observe the effects of a number of proprietary mouthwases on dentine alone and together with toothbrushing. The objective was to evaluate removal of the dentine smear layer and exposure of the tubules.

METHOD

AND MATERIALS

The method employed a dentine section model (Greenhill and Pashley, 1981). Freshly extracted and cleaned, caries-free permanent teeth were cut transversely using a diamond cutter (Microslice 2, MR Metals Research Ltd, Cambridge, UK) to produce sections

and dentine

hypersensitivity

approximately 1 mm thick. This produces specimens with a smear layer on both surfaces (Fig. I). All sections were stored in saline until required. A selection of mouthwash products were chosen for study and their pH values recorded with a pH meter (Table I). Water was used as the negative control. Pairs of dentine sections were selected at random and placed individually into 10 ml volumes of the respective mouthwashes for varying time periods-3, 10, 60, 120, 180 and 300 min. Sections were then removed, washed by tumbling in water for 2 min and processed for scanning electron microscopy. The experiment was repeated exactly as before; however, sections removed from the mouthwashes at each time period were washed in water and then manually brushed for a timed 2 min with a single tufted brush (Interspace, Sensodyne, StaffordMiller Ltd, Hatfield, UK) and water. The brushing action used a reciprocal horizontal action. Again the experiment was repeated followed by a postsoaking brushing with a popular commercial fluoride toothpaste (Colgate, Colgate-Palmolive Ltd, London, UK). In an attempt to standardize the force applied, all brushings were performed by one individual. After water or toothpaste brushings, specimens were washed by tumbling in water for 2 min. Specimens were studied on the scanning electron microscope and photomicrographs taken from four arbitrarily chosen fields of each dentine section. Photomicrographs were scored blind for the presence and estimated number of tubules observed: = no tubules + = a few tubules visible + + = moderate numbers of tubules visible + + + = large number of tubules visible

Table 1. Products into which dentine specimens were placed

Product

Manufacturer

Corsodyl

Imperial Chemical Industries PLC, Macclesfield, UK Ashe Laboratories Ltd, Leatherhead, UK Colgate-Palmolive Products, London, UK Warner Lamber-t Health Care, Eastleigh, UK Warner Lambert Health Care, Eastleigh, UK Warner Lambert Health Care, Eastleigh, UK Merrell, Dow Pharmaceuticals Ltd, Staines, UK Pfiezer Unicliffe Ltd. Sandwich, UK Unichem Ltd, Chessington, UK

Double Amplex Fluorigard Listerine

Listermint

Oraldene

Merocet

Plax Thymol (Water)

149

Active ingredients

PH

Chlorhexidine

6.2

Fluoride

5.6

Fluoride

5.6

Phenols

4.4

Cetylpyridinium chloride/fluoride

4.6

Hexetidine

4.2

Cetylpyridinium chloride

7.0

Sodium lauryl sulphate, sodium benzoate Phenol

8.0 7.6 7.0

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Fig. 2. Dentine section soaked in Oraldene for 120 min. The smear layer has disappeared and the openings of dentinal tubules are apparent. x 530.

Fig. 3. Dentine section soaked in Double Amplex for 180 min and brushed with water for 2 min. The smear layer has disappeared and large numbers of dentinal tubules are apparent. X 530.

All of the experiments were duplicated, however, for those products which consistently produced visible changes on the specimens the experiment was repeated a third time. Thus, for all of the mouthwashes and water, at each time period and for each regimen, four specimens were examined. For mouthwashes which produced consistent changes a total of six specimens were examined at each time period for the three regimens.

and Listerine. The results for these products are summarized in Table II. For Double Amplex and Oraldene soaking alone for 120 min partially removed the smear layer to expose moderate numbers of tubules (Fig. 2). This was a consistent feature at all time periods after 120 min for both products, with some specimens scored as exhibiting large numbers of tubules. Postsoaking brushing with water hastened the appearance of tubules, such that few to moderate numbers of tubules were seen at 10 min for Double Amplex, and similarly for Oraldene at 60 min. Brushing specimens with water also produced ‘large numbers of tubules’ scores for specimens at all time periods after 60 min for Double Amplex and Oraldene (Fig. 3). Postsoaking brushings with toothpaste were more difficult to interpret because some surface deposits remained after postbrushing washings on most specimens. Nevertheless, loss of the smear layer with exposure of tubules was apparent at equivalent time periods to postbrushing with water. The most rapid surface changes were produced by Listerine, with the exposure of moderate numbers of tubules after soaking only for 10 min, and moderate to large numbers scored at all time periods thereafter. Brushing with water after soaking for almost all specimens resulted in scores for large numbers of tubules present at time periods after and including 10 min (Fig. 4). Postsoaking brushings with toothpaste created the same difficulties as for other treated specimens, however, tubules were apparent at 10 min and subsequent times after soaking with Listerine although scores were usually for moderate numbers of tubules (Fig. 5).

RESULTS Most of the mouthwashes tested in this study did not produce consistent visible changes to the dentine surface at any time period, with or without post-treatment brushings with water or toothpaste. The smear layer remained intact and tubules were not visible (Fig. 1). Thus, specimens exposed to these products appeared similar to those treated with water. Three mouthwashes did produce visible changes compared to controls, namely Double Amplex, Oraldene Table II. The grade and time of tubule exposure in dentine sections soaked/brushed with mouthwash products Grade (-/+) Soak

Product Corsodyl Double Amplex Fluorigard Listerine Listermint Merocet Oraldene Plax Thymol Water

and time (min) Soak/ Soak/ brush W brush TP

-

_

-

++120

++10 -

++10 -

+10 -

+++10 _ -

++10 -

++120 -

+++120 -

++120 -

-

Grade: -, no tubules visible; +, a few tubules visible; + f, moderate numbers of tubules visible; +++, many tubules visible. W, water; TP. toothpaste.

DISCUSSION This study has demonstrated that some proprietary mouthwashes have the potential to remove the dentine smear layer to expose tubules. The effects are similar to those noted with various organic acids and more importantly acidic foods and drinks (Addy et al., 1987).

Addy et al.: Mouthwashes

and dentine

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151

Fig. 4. Dentine section soaked in Listerine for 10 min and brushed with water for 2 min. The smear layer has disappeared and large numbers of wide dentinal tubules are apparent. X 530.

Fig. 5. Dentine section soaked in Listerine for 1 h and brushed with toothpaste for 2 min. Dentinal tubules are apparent but a surface deposit is apparent and tubules appear partially closed. X 530.

The time taken to produce effects were longer than for dietary acids. but nevertheless these erosive changes were consistently recorded with three mouthwash products. One mouthwash produced changes after 10 min of soaking. Postsoaking 2 min brushings with water enhanced smear layer removal. Thus, for these products tubule exposure was observed sooner and greater numbers of tubules were observed at these earlier times. Toothbrushing with a nylon tilamented brush and water has virtually no abrasive effect on untreated dentine (Absi et al., 1990) and certainly not within 2 min as confirmed in this study. The mouthrinses, therefore, have reduced the abrasive resistance of the smear layer by effects on the inorganic and/or organic components of the dentine. The effects of postsoaking brushings with toothpaste revealed essentially similar changes to water brushing. Observations were made more difficult because of the retention of some toothpaste ingredients, almost certainly the abrasives, on the dentine surface (Addy and Mostafa, 1989). Furthermore, some particulate material was noted in the tubules. It is apparent, therefore, that brushing with a paste could, to a limited degree, reverse the process of opening tubules. The effect could also be enhanced if the toothpaste also abraded and smeared the dentine. The retention of abrasives on dentine in vitro and the smearing of the surface layer have been noted previously (Addy and Mostafa, 1989). Indeed, these effects of toothpaste abrasives were thought to explain the reduced hydraulic conductance of etched dentine following brushing with toothpastein vitro (Pashleyet al., 1984). The effects produced are nevertheless dependent not only on the type of abrasive in the toothpaste but also the formulation of the paste (Addy and Mostafa, 1989). Clearly these findings have implications to the frequent and long-term use of mouthwash products. First, loss of the dentine smear layer and exposure of tubules may in a vital tooth result in dentine hypersensitivity. Secondly,

hard tissue loss, irrespective of tubule opening, is occurring and this erosion may enhance the abrasion produced by subsequent toothbtushing (Davis and Winter, 1980). Prebrushing rinses are now appearing in the marketplace, however, although many of the rinses may be used after toothbrushing this does not remove the likelihood of detrimental action. The erosive action will still occur and may reverse beneficial effects produced by the toothpaste such as dentine smearing and the uptake of ingredients onto or into the tooth surface. The mechanism by which the smear layer was removed by the products is unclear. Many products were acidic but the changes were not totally pH dependent. Since dentine is a calcified collagen matrix either dissolution of the inorganic component and/or destruction of the organic matrix may have occurred. As with all tests in vitro extrapolation of findings to the situation in viva is difficult. The numerous variables in the complex oral environment will determine whether or not the changes observed in vitro actually occur in the mouth. In general mouthwashes are formulated to provide benefit of a cosmetic or health nature. However, these observations indicate that some mouthwashes may, with prolonged use, have deleterious effects on dentine. The effects could include increased tissue loss with time, predisposition to dentine hypersensitivity, or reversal of beneficial effects of toothpastes, Moreover, the detrimental effects may be exaggerated if some of the rinses were used prior to toothbrushing. The method used in the study in vitro was chosen to determine whether, under well-controlled conditions, proprietary mouthrinses produced observable changes to the dentine surfaces. The time periods for exposure were chosen to determine whether effects occurred within short periods of time or required protracted exposure. Clearly effects noted within a few minutes would be of clinical relevance since these time periods represent relatively few rinses with the product. Changes seen after longer time periods suggest, albeit not

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necessarily, that cumulative effects would have to occur from repeated use of a product. Modifications to the method used here could go some way to providing information on the cumulative effects of rinses and the actual quantitative tissue loss caused by rinses alone and when associated with toothbrushing. In conclusion, there is clearly a greater need to study the possible detrimental effects of oral hygiene products in order to balance formulations more advantageously for the benefits provided. References Absi E. G.. Addy M. and Adams D. (1987) Dentine hypersensitivity: a study of the patency of dentine tubules in sensitive and nonsensitive cervical dentine. J. Clin. Periodontal. 14,280-284. Absi E.. Adams D. and Addy M. (1990) Does toothbrushing remove or produce a smear layer on dentine? An S.E.M. study. J. Dent. Res. 69, 965. Abstr. 88. Addy M. and Mostafa P. (1989) Dentine hypersensitivity II. Effects produced by the uptake in vitro of toothpastes onto dentine. J. Oral Rehabil. 16, 35-48. Addy M.. Mostafa P. and Newcombe R. (1986) Dentine hypersensitivity: the distribution of recession, sensitivity and plaque. J. Dent. 15, 242-248.

Addy M.. Absi E. G. and Adams D. (1987) Dentine hypersensitivity: the effects in vitro of acids and dietary substances on root planed and burred dentine. J. Clin. Periodontal. 14, 274-279. Davis W. B. (1978) The cleansing, polishing and abrasion of teeth by dental products. Cosmetic Sci. 1, 39-81. Davis W. B. and Winter P. J. (1980) The effect of abrasion on enamel and dentine after exposure to dietary acid. Br. Dent. J. 148,253-256. Greenhill J. D. and Pashley D. H. (1981) The effects of desensitising agents on the hydraulic conductance of human dentine in vitro. J. Dent. Res. 60, 686-698. Hirschfeld I. (1939) The toothbrush. Its use and abuse. In: Dental Items of Interest. London. Kimpton. p. 180. Holloway P. J., Mellanby M. and Stewart R. J. C. (1958) Fruit drinks and tooth erosion. Br. Dent. J. 104,305-309. Pashley D. H.. O’Meara J. A., Kepler E. E. et al. (1984) Dentine permeability. Effects of desensitising dentifrices in vitro. J. Periodontal. 55, 522-521. Perdok J. F.. Van der Mei H. C. and Busscher H. J. (1990) Physico-chemical properties of commercial mouthrinses. J. Dent 18, 147-150. Pindborg J. J. (1970) Chronic mechanical injuries. In: Pathology of the Dental Hard Tissues. Copenhagen, Munksgaard. chap. 8. pp. 294-3 Il. Touyz L. Z. G. (1983) Fruit induced sensitivity of cervical margins. J. Dent. Assoc. South Afi-. 38, 199-200.

Book Review An Atlas of Glass-ionomer Cements. A Clinician’s Guide. G. J. Mount. Pp. 136. 1989. London, Martin Dunitz. Hardback, E29.95. Dr Mount is an Australian practitioner who has been using glass-ionomer cements since their introduction in 1976. He has already produced numerous papers and some excellent video-tapes on their use and it will not surprise those who are familiar with this work to learn that his new atlas is an excellent guide for the interested clinician. It is beautifully produced, on high quality paper; most of the 258 illustrations are good colour reproductions of clinical photographs expertly taken by the author. Chapter 1 is a readable introduction to this group of restorative materials which summarizes their development, composition and chemistry and explains the potential advantages conferred by their hydrophilic nature, ability to adhere to dentine and release fluoride over long periods. The scientific background to their correct manipulation is clearly explained using clinical photographs to illustrate the effects of mishandling. It is emphasized that both water uptake and loss should be avoided for at least 24 h after placement and light-cured resins are recommended in preference to solvent-based varnishes for this purpose. The use of polyacrylic acid to remove the dentine smear layer and optimize bonding is also recommended. Manufacturers who do not at present provide suitable varnishes and dentine conditioners please note. For the following chapters a classification is used which divides glass-ionomer materials into luting cements,

restorative cements and linings. One chapter is devoted to each group, illustrating and describing operative procedures and explaining how and why these are used to maximize performance. Modified cavity designs for glass-ionomer restorations are considered in a separate chapter which includes no less than three types of tunnel preparation which might be used for the conservative management of proximal lesions in posterior teeth. Throughout the book, the importance of correct mixing is stressed and all the important points are brought together in a useful chapter aimed primarily at dental surgery assistants. The final chapter then gives condensed written instructions for correctly using each type of material, summarizing the detailed information given in preceding chapters. A few minor criticisms: Figure 1.3 is an impressivelooking but incomprehensible graph which is not explained in the text. The author’s frequent use of the term ‘erosion cavity’ is curious since almost all of the cases illustrated as such are in fact toothbrush abrasion cavities: a true erosion lesion is shown in Figure 1 .12. On a more general note, Dr Mount does not make clear which of the many recommended applications of glass-ionomer cements are supported by properly conducted and reported clinical trials. In fact, such evidence is rather meagre. Nevertheless, the atlas illustrates well how they can be used by a skilled and meticulous operator and it is highly recommended to clinicians wishing to make the most of this exciting group of materials. F. J. Hill

Dentine hypersensitivity--effects of some proprietary mouthwashes on the dentine smear layer: a SEM study.

Exposed dentine may be sensitive to stimuli depending on the patency of the dentinal tubules. Most abrasive elements tend to produce a smear layer whi...
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