Comparative evaluation of the efficacy of bonding agents in cervical cavities after using desensitizing agents: an in vitro study

INTRODUCTION

Caries results from the interaction between dental structure and microbial bio-film. It is characterized by a cyclic process of de-mineralization and re-minerali­zation [1-3]. Over time, the hybrid layer within dental restorations can degrade, leading to a loss of adhesive resistance. This can affect the longevity of restorations [4]. Teeth with open tubules tend to have more numerous and larger tubules, which can exacerbate sensitivity [5]. Dentinal hypersensitivity (DH) was found mostly in adult population, ranging from 4% to 74%, and the highest incidence is in age group of 20 to 40 years and in females. Canines and premolars in either jaw are most frequently involved with commonly affected buccal cervical zones [6]. DH occurs due to loss of protective layer of enamel and removal of cementum from the root, which leads to exposure of dentin. The most common clinical conditions causing DH are abrasion, attrition, erosion, abfraction, and gingival recession. A hydrodynamic theory of dentin sensitivity is widely accepted, and suggests that sensitivity is caused by fluid movement within the tubules [7].
Current treatment protocol aims to reduce the movement of tubular fluid by decreasing dentin permeability, or by reducing the excitability of nerve bundles with neutrally vital agents [8]. To alleviate dentin sensitivity, various materials, such as fluoride iontophoresis, laser irradiation, strontium chloride, and potassium nitrate dentifrices, are employed [9, 10].
Both invasive and non-invasive procedures can be used to treat hypersensitivity. Gingival surgery, adhesive restoration, or pulpectomy, are some of the invasive procedures [11]. However, continuous presence of abrasive, erosive, and tensile stresses at the cervical region makes these restorations susceptible to failure. One concern in this approach is the effect of the adhesive procedure after performing desensitizing steps with agents, which block the tubules [12].
The purpose of this research was to evaluate the impact of desensitizing agents on the pull-out bond strength of 5^th and 7^th generation bonding agents.

OBJECTIVES

This study attempted to evaluate the pull-out bond strength of 5^th and 7^th generation bonding agents after treatment with two desensitizing agents.

MATERIAL AND METHODS

Twenty-four single-rooted, intact non-carious anterior teeth extracted for periodontal or orthodontic reasons were selected for the study, and were stored in saline. Soft tissue and calculi were mechanically removed from the tooth surface. Class V cavities of 1.6 mm depth and 1.4 mm width were prepared on the buccal surface coronal to the cemento-enamel junction, using inverted cone diamond abrasive point (SI-47, Mani, Japan). Surfaces of the prepared cavities were conditioned using a dentin conditioner (GC, Japan) applied with an applicator tip for 20 sec, followed by rinsing with water and drying with a cotton pellet. Samples were then randomly divided into 2 groups depending on desensitizing agent used.
Group A (n = 12): Desensitizing agent (Shield Activ, Prevest DenPro, Jammu, India) was applied using an applicator tip on dentinal surfaces, and left for 30-60 sec. The surface was then dried using a stream of compressed air, until the fluid film was fully dried.
Group B (n = 12): Desensitizing agent (Gluma, Kulzer, Germany) was applied using an applicator tip on dentinal surfaces, and left for 30-60 sec. The surface was then dried using a stream of compressed air, until the fluid dehydrated.
Samples from both the groups were further divided into 2 sub-groups, depending on bonding agent used.
Sub-group 1A (n = 6): Two coats of 5^th generation bonding agent (Single Bond 2, 3M ESPE, USA) was applied according to the manufacturer’s instruction, using an applicator tip for 15 sec with gentle agitation, followed by light curing (Bluephase G2, Ivoclar Vivadent GmbH, Austria) for 20-30 sec, with an intensity of 1,200 mW/cm².
Sub-group 2A (n = 6): One coat of 7^th generation bonding agent (Single Bond Universal Adhesive, 3M ESPE, USA) was used as per the manufacturer’s instruction, followed by air drying for 10 sec. Then, another coat of the bonding agent was applied with gentle agitation, using an applicator tip followed by light curing for 20-30 sec.
Sub-group 1B (n = 6): 5^th generation bonding agent (Single Bond 2, 3M ESPE, USA) was applied with a simi­lar manner as in sub-group 1A.
Group 2B (n = 6): 7^th generation bonding agent (Single Bond Universal Adhesive, 3M ESPE, USA) was applied with a similar protocol as in sub-group 2A.
In sub-groups 1A and 1B, selective etching of cavity enamel margins was done using 37% phosphoric acid (Prime Dental Products, Mumbai, India). In sub-groups 2A and 2B, self-etching property of Single Bond Universal was utilized. The cavities were then restored with incremental placement of nano-hybrid composite (Filtek Z350XT, 3M ESPE, St. Paul, MN, USA) and light-cured for 30 sec. A cylindrical projection of composite from the surface of restoration with 4 mm height and 1.8 mm width was made with silicon molds. A loop was created using 23-gauge stainless steel wire, and fixed around composite cylinder. Load was applied using an universal testing machine (ACME Engineers, India), and values were tabulated.

Statistical analysis

Data were analyzed using IBM SPSS version 21.0, and subjected to descriptive and inferential statistical tests. For continuous data, mean (standard deviation, SD) was calculated, while for maximum load and pull-out bond strength, mean and SD were considered. For inter-group comparison, independent t test was applied. All statistical tests were assessed with confidence interval at 95%, and p < 0.05 was considered statistically significant.

RESULTS

As shown in Table 1, comparison of the pull-out bond strength in sub-groups 1A and 1B (Shield Activ + Single Bond 2, and Gluma + Single bond 2) was done, revealing that sub-group 1B performed significantly better, with the mean pull-out bond strength value of –7.29500 (p < 0.05). As shown in Table 2, comparison of the pull-out bond strength in sub-groups 2A and 2B (Shield Activ + Single Bond Universal, and Gluma + Single Bond Universal) was done, demonstrating that sub-group 2B performed significantly better, with the mean pull-out bond strength value of -8.10833 (p < 0.05). The summary of the results of all the groups is depicted in Figure 1.

DISCUSSION

It is widely accepted that the main cause of DH is the loss of enamel or gingival recession [4]. Dentin is composed mostly of dentinal tubules that stretch from the pulp to the junction of enamel-dentin or cementum-dentin, which can cause exposure of the dentin, resulting in sensitivity [13]. This leads to the exposure of dentinal tubules in the oral cavity, inducing hypersensiti­vity [14]. To manage DH, various therapeutic models and agents are recommended. Salz and Bock suggested that the most effective way to alleviate sensitivity caused by exposed dentinal tubules is to use agents, which form precipitates, such as potassium oxalate and protein coagulants, e.g., glutaraldehyde, chlorhexidine, or fluoride [13]. Sealing and occluding dentinal tubules is a viable treatment option for DH by blocking the hydrodynamic mechanism [8]. The use of various desensitizing agents for treating DH may impact the bond strength during restoration, potentially compromising the longevity of restorations [5]. Desensitizing agents function by obstructing inter-tubular diffusion channels and tubule orifices, thus inhibiting resin infiltration to de-mine­ralized dentin, resulting in reduced bond strength [15].
Gluma desensitizer consists of 5% glutaraldehyde and 35% 2-hydroxyethyl methacrylate (HEMA). The pre­sence of glutaraldehyde and HEMA may contribute to a greater bond strength. Glutaraldehyde acts as a fixative and flocculating agent, forming cross-links with collagenous bio-materials. It intersects with the ε-amino groups of lysine and hydroxylysine residues found in dentin collagen [16-18].
Shield Activ contains 2 HEMA, sodium fluoride, potassium nitrate, and ethanol. HEMA is an important component in dental procedures, because it prevents shrinkage and reacts chemically with the collagen in the dentin. It also helps to create a strong bond between the dentin and resin, and aids in the diffusion of monomer to form a hybrid layer. This makes HEMA a crucial stiffening agent in dental applications [18].
A hybrid layer of resin-infiltrated inter-tubular and peri-tubular dentin is crucial for establishing a strong bond between the dentin and composite resin that depends on resin monomers. This hybrid layer forms the primary bonding mechanism with primed dentin [19]. If resin monomers cannot fully penetrate open dentinal tubules, a weak film of non-encapsulated collagen may persist, reducing bond strength and causing fractures to propagate unevenly [20].
In the current study, Single Bond 2 (5^th generation) and Single Bond Universal (7^th generation) bonding agents were employed to verify the pull-out bond strength. Enamel conditioning with phosphoric acid during total-etch technique for Single Bond 2 leads to the creation of tiny pores, allowing the resin to penetrate and form prism-like resin tags, resulting in creating a predominantly micro-mechanical enamel bonding [21].
In the chemical formulation of self-etch adhesive systems, the functional monomers play an important role for the adhesive’s long-term bonding performance. Single Bond Universal one-bottle dentin bonding agent contains HEMA monomer in order to enhance wettability of the dentin surface. HEMA improves binding of the dentin’s hydrophilic collagen to hydrophobic composite resin material [22].
In the current study, Gluma was used in combination with Single Bond Universal, and showed a higher bond strength when compared with Single Bond 2. This could be due to protein fixation that bonds glutaraldehyde to the collagen fibrils of dentin. This development could possibly stabilize the collagen layer, thus contributing to enhanced bond strengths. This finding is similar to that obtained by Ravikumar et al. [23].
Shield Activ, a newly introduced desensitizing agent, demonstrated reduced bond strengths when used with both 5^th and 7^th generation bonding agents. Shield Activ employed in combination with Single Bond Universal, showed a higher bond strength when compared with Single Bond 2. This could be due to the collapse of collagen network due to the absence of stabilizing agent in Shield Activ, thereby resulting in limited penetration of the resin.

CONCLUSIONS

As the number of elderly patients increases, there is a rise in the prevalence of non-carious cervical lesions and DH. If the use of desensitizing agents do not relieve sensitivity, restorations of these defects should be considered. However, the success of restorative procedures depends heavily on the adhesion to the cavity, making the selection of adhesive system of utmost importance. From the results of this study, it can be concluded that application of desensitizing agents for relief of patients’ symptoms is an acceptable practice, and such teeth can be restored satisfactorily using 7^th generation dentin adhesives.

DISCLOSURES

1. Institutional review board statement: This study was approved by the Ethics Committee of the Dr. D. Y. Patil Dental College, Pimpri, India (Ref. No DYPDCH/DPU/EC/920/11/2023).
2. Assistance with the article: None.
3. Financial support and sponsorship: None.
4. Conflicts of interest: None.

References