Comparative In Vivo Study on the Desensitizing Efficacy of Dentin Desensitizers and One-bottle Self-etching Adhesives

Dentin hypersensitivity (DH) is one of the most common problems encountered in daily dental practice. The typical short and sharp tooth pain on exposed dentin arises from a variety of exogenous stimuli, including thermal, evaporative, tactile, osmotic and chemical changes.1–2 The prevalence of DH reported in the literature varies from 4% to 74%,2 depending on differences in the populations studied and the various methods of investigation, such as questionnaires2 or different clinical examinations.3 

Brännström's hydrodynamic theory is most widely accepted as an explanation of tooth sensitivity.4–8 Assumptions of the hydrodynamic theory conclude that exogenous stimuli applied to the exposed dentinal tubules result in the flow of dentinal tubular fluid, activating the intradental nerves to create pain.4–5 Previous research reveals that the dentin tubules of hypersensitive teeth are approximately eight times more open and two times wider than dentin tubules in control teeth.9 

Dentin desensitizers and adhesives are applied to the exposed dentin surfaces to occlude the patent dentinal tubules10–11 or to depolarize the intradental nerves by dentin desensitizers.12–13 

Recently, one-bottle self-etching adhesives have been developed to greatly simplify the multiple steps of application to one step. Self-etching adhesives might be used to desensitize the DH by reducing dentin permeability. 10,14 Many dentin desensitizers do not adhere to the dentin surface, as do self-etching adhesives, and thus, their effects are temporary.3 However, self-etching adhesives applied to the dentin surface produce an acid-resistant hybrid layer.15 This may result in longer-lasting clinical effectiveness. The clinical effectiveness of dentin desensitizers and self-etching adhesives in reducing the DH has not to date been clarified in detail.

The aim of the current study was: 1) to evaluate the clinical effectiveness of two dentin desensitizers, two one-bottle self-etching adhesives and a placebo for DH treatment and 2) to observe the micromorphology of the hypersensitive dentin surface treated with either self-etching adhesives, dentin desensitizers or placebo.

The null-hypothesis tested in the current study was that all the dental materials in this study would significantly reduce the DH to some degree.

This clinical investigation on the efficacy of DH treatment was carried out in the Department of Stomatology, No 1 Hospital Affiliated to Medical College, Zhejiang University, Hangzhou, China.

Thirty-one volunteers (22 females and 9 males) with 55 sensitive teeth were recruited into the clinical study. The volunteers' ages ranged from 18 to 78 years, with the mean age being 42.4 years. A prospective randomized, subject-blinded, placebo-controlled, split-mouth study was performed after informed written consent of the volunteers was obtained. The sensitive teeth were randomly allocated to one of five groups/treatments by drawing lots. Each individual volunteer had only one hypersensitive tooth in one quadrant. The sensitive teeth of the different quadrants were treated using different materials. All the volunteers fasted for two hours after treatment, and they were instructed to eat and drink as usual during the clinical investigation period. The clinical research was conducted in full accordance with ethical principles, including the World Medical Association Declaration of Helsinki (version, 2002 http://www.wma.net/en/20activities/10ethics/10helsinki/index.html) and the study was independently reviewed and approved by the local ethical committee. The medical and dental histories of all the volunteers were recorded. Exclusion criteria for volunteers were: 1) tooth sensitivity due to improper restorations, dental caries, tooth fractures, tooth defects, tooth cracks or pulpitis; 2) use of tooth desensitizing pastes within the past six weeks; 3) surgical or non-surgical periodontal treatment within the past three months; 4) use of medications, including antihistamines, anti-inflammatory drugs, anti-depressants or analgesics; 5) pregnancy or in lactation of the female volunteers.

The detailed treatment materials and methods used in the current study are described in Table 1.

To assess a response to mechanical stimulation, the sensitive area of the tooth was tenderly scratched with a new standard dental explorer by the same investigator (Yu X). To assess a response to thermal stimulation, the sensitive tooth was isolated with cotton rolls and zero-degree water celsius (a mixture of ice and water kept in the refrigerator at 4°C) was dropped onto the tooth's sensitive area.

DIS scores of the sensitive teeth were recorded at three different investigation times (baseline, immediately and one month after treatment). The DIS scores ranged from 0 to 4: 0: no pain; 1: mild pain; 2: moderate pain; 3: severe pain and 4: intolerable pain.16 

All the data were analyzed using the SPSS software package (version 16.0, SPSS Inc, Chicago, IL, USA). The Friedman test procedure was used to analyze the clinical treatment efficacy of all the materials, and the Mann Whitney U-test was used to analyze the clinical efficacy of the different desensitizing materials at the different investigation times (baseline, immediately and one month after treatment). The level of significance was set at p<0.05.

Impressions were taken of the sensitive teeth with an extremely low-viscosity hydrophilic vinyl polysiloxane (Imprint II Garant, 3M ESPE, Seefeld, Germany, Lot #20070809) plus putty rubber (Express STD, 3M ESPE, Lot #20061128) using a two-step impression method at the three different investigation times. The replica models were then made with epoxy resin (EpoFix Lot #6120-7535, Struers A/S, Ballerup, Denmark) for evaluation of the dentin surfaces by SEM (Scanning Electrical Microscopy) (Stereoscan 260, Cambridge, UK). Epoxy resin replicas were gold-sputtered (ion sputter, E-1020, HITACHAI, Tokyo, Japan), and the same locations of interest on the replicas were analyzed with SEM.

DIS scores of the hypersensitive teeth are summarized in Tables 2 and 3. Regardless of the type of stimulus, all dental materials significantly reduced tooth sensitivity immediately after treatment (p<0.05). All the dental materials significantly relieved the thermal sensitivity of the teeth over a month (p<0.05). All the dental materials, with the exception of Bifluorid 12, also significantly decrease mechanical sensitivity of the teeth over a month (p<0.05). The placebo (water) only significantly relieve the tooth thermal sensitivity immediately after treatment (p<0.05). Changes in the thermal/mechanical DIS scores over time by the different treatment materials are presented graphically in Figures 1 and 2.

There were a large variety of patent dentinal tubules on the sensitive areas of the investigated teeth (Figures 3–7). The application of water (placebo) on the sensitive areas did not close the open dentin tubules (Figure 7). In contrast, topical application of the dentin adhesives/desensitizers on the sensitive dentinal areas resulted in occlusion of the patent tubules (Figures 3–6). Some occluded dentin tubules were partly reopened one month after treatment (Figures 3–6).

The placebo response involves conscious and non-cognitive expectancies. The placebo achieved its effects on the DH.17–19 The placebo (water) used in the current study had only an immediate effect on the thermal DH (p<0.05). These findings suggest that the placebo provides an immediate psychological effect on the thermal DH and does not possess a long-lasting clinical effectiveness.

Bifluorid 12 is a fluoride varnish consisting of sodium and calcium fluoride. In the current study, Bifluorid 12 significantly reduced the thermal DH immediately and over a month. However, it significantly relieved the mechanical DH immediately but did not maintain the effect over a month. It created a barrier by precipitating calcium fluoride (CaF2) on the tooth surface and within the tubules' orifices,3,20 as well as by occluding the dentin tubules through the crystallization of sodium fluoride.21 However, most of the fluoride is released within two weeks of the topical application of fluoride,22 due to the lack of bonding between the dentin and the varnish.23 Furthermore, the varnish was easily peeled off the dentin surfaces during the impression procedure during the mechanical stimulus at the clinical investigation. This might be due to the fact that Bifluorid 12 reduced the thermal DH for a longer time, but it could not lessen the mechanical DH throughout the duration of one month. The Gluma desensitizer did not fully mechanically block dentin permeability, but it still possessed some sealing ability to reduce dentin permeability as evidenced in previous research by the authors of this study.10 This is consistent with the current study, revealing that the desensitizer relieved the DH immediately and over one month. The desensitizer achieves its desensitizing effects by the precipitation of dentinal fluid proteins, such as serum albumin, and by reduction of the intratubular fluid flow directed to the exposed dentin surfaces.8,13 

The topical application of dental adhesives is one well-established method to manage the DH.3,10 Single-bottle self-etching adhesives (all-in-one adhesives) have been developed in order to simplify the multiple steps of application into one step. The single-bottle self-etching adhesives (Xeno V and i Bond) could produce an acid-resistant hybrid layer on the dentin surface for DH relief. However, the all-in-one adhesives tested in the current study did not perform better than the dentin desensitizers, with the exception of Bifluorid 12, regarding the decrease of mechanical DH. The reason for this observation might be the fact that single-bottle self-etching adhesives contain mixtures of hydrophilic and less hydrophobic monomers and, thus, are permeable to water after application to the dentinal surface.10,25 Nevertheless, they can reduce the dentin permeability to some degree.

Based on the current data, the null-hypothesis that all the dental materials in this study can significantly reduce the DH to a certain degree is accepted. The clinical desensitizing effectiveness depends on the individual dentin desensitizers/adhesives used.

The one-bottle self-etching adhesives and dentin desensitizers (except Bifluorid 12) involved in the current clinical investigation significantly relieved dentin hypersensitivity immediately and over a period of one month. The fluoride containing varnish Bifluorid 12 reduced the thermal and mechanical sensitivity of dentin immediately and thermal sensitivity over one month, but it failed to relieve the mechanical sensitivity over the course of a month. Water had an immediate effect on thermal dentin hypersensitivity.

This research was financially supported by the Natural Scientific Research Fund of Zhejiang, China (Y2080045) and the National Natural Scientific Research Fund, China (20973152). The authors are grateful to associate professor Xiuyang Li, statistician in the Department of Epidemiology & Health Statistic, Zhejiang University, China, for providing all statistical analysis work for this study.