The efficacy of the novel zinc-containing desensitizer CAREDYNE Shield on dentin hypersensitivity: a study protocol for a pilot randomized controlled trial

Dentin hypersensitivity (DH) is a condition characterized by short and sharp episodes of pain which arise in response to tactile, chemical, thermal, evaporative or osmotic stimuli, and which cannot be ascribed to any other form of dental defect or pathology [1, 2]. A recent systematic review reported the DH prevalence in various population to range from 1.3 to 92.1%, and the estimated DH prevalence analyzed in a random-effects meta-analysis was 33.5% (95% confidence interval 30.2–36.7%) [3]. The painful symptoms cause discomfort in patients and reduce their quality of life [4].

Normally, dentin is covered by enamel or cementum and is not affected by direct stimuli; however, once the dentin has been exposed and dentinal tubules are patent in the oral environment, the painful symptoms of DH arise in response to external stimuli. Dentin exposure results from a loss of enamel or cementum. The loss of enamel can be attributed to erosion, abrasion or abfraction, while the loss of cementum is caused by gingival recession associated with improper tooth-brushing, periodontal disease and periodontal surgery.

A number of theories have been suggested to explain the mechanisms of DH; however, the hydrodynamic theory has been widely accepted [5, 6]. According to this theory, fluid movement in the patent dentinal tubules occurs in response to external stimuli, stimulating sensory nerve endings located at the dentin-pulp interface. Thus, dentinal tubule occlusion, which reduces the fluid movement in the dentinal tubules, is one of the ideal DH treatments and is performed with adhesive systems or desensitizing agents that form insoluble mineral precipitates in the patent dentinal tubules [7].

One of desensitizing agents which form insoluble mineral precipitates in patent dentinal tubules is the fluoroaluminocalciumsilicate-based desensitizer Nanoseal (Nippon Shika Yakuhin, Yamaguchi, Japan). The components are similar to those of silicate cement. Nanoseal acts as a desensitizer by a chemical reaction resulting in insoluble nanoparticles that aggregate on the tooth surface for dentinal tubule occlusion and has been suggested to protect the root surface from demineralization via ions, such as calcium or fluorine, released from Nanoseal [8‐10]. Thus, Nanoseal may act not only as a desensitizer but also as a root caries inhibitor.

Recently, the fluorozinccalsiumsilicate-based desensitizer CAREDYNE Shield (GC Dental Industrial Corporation, Tokyo, Japan) has been developed. It acts as a desensitizer by inducing chemical occlusion of dentinal tubules and contains a novel functional filler that releases not only ions, such as calcium and fluorine, but also zinc. Zinc has been reported to reduce the demineralization of enamel and dentin, and inhibit dentin collagen degradation, plaque growth and biofilm formation [11, 12].

However, the effectiveness of CAREDYNE Shield on DH still remains unclear; therefore, the aim of this study is to investigate the effectiveness of CAREDYNE Shield on DH by comparing with that of Nanoseal. The PICO question of this study is described in Table 1.

Several limitations associated with the present study warrant mention. First, blinding of operators will not be performed; therefore, the risk of bias in this domain may be unavoidable. Second, the data will be collected just after the participant’s training. Thus, VRS which is easier to understand for participants than a visual analog scale (VAS) will be performed; however, VRS is considered to be less sensitive than VAS [18, 19]. Third, it has been recommended that at least three different stimuli, specifically tactile, cold and air stimuli, should be used for clinical assessments of DH because DH may differ among stimuli [2]. However, only air stimuli will be evaluated in the present study because this study is being performed for sample size calculations, which is based on the primary outcome: the reduction of pain intensity in response to air stimuli. Tactile stimuli will be evaluated as a secondary outcome in a future, large-scale study. The GI and PI will be used as secondary outcomes in the present study. If a reduction in either is observed, the effectiveness of CAREDYNE Shield for the reduction of the GI and PI will be investigated in a future clinical study.

Desensitizers like CAREDYNE Shield and Nanoseal that induce chemical occlusion of dentinal tubules are biocompatible and react only with tooth substance; they can, therefore, be casually applied to subgingival areas and proximal surfaces. Furthermore, for several decades, in-vitro studies have investigated the function of zinc and reported that zinc reduced the demineralization of enamel and dentin and inhibited dentin collagen degradation, plaque growth and biofilm formation [20‐24]. Thus, CAREDYNE Shield, which releases zinc ions, may be a useful novel desensitizer that acts not only as a desensitizer but also as a root caries inhibitor.