Comparative Evaluation of the Microleakage of Two Bonding Systems Pretreated with Chitosan Nanoparticles and Restored with Composite Resin: An In Vitro Study ^†

Abstract

Class II cavity preparation was conducted on 84 recently extracted premolars. Group I consisted of teeth restored with composite and without adhesive, (n = 12). Group II consisted of teeth restored with composite using prime and bond universal adhesive (n = 36). Group III teeth were restored with composites with Scotchbond universal adhesive (n = 36). Group II and III (n = 18 each) were further subdivided into chitosan pretreated and non-pretreated groups and named as II a, II b, III a, and III b, respectively. Microleakage was tested using the fluid filtration model. The mean microleakage was least for the prime and bond universal groups pretreated with chitosan (0.00145 and 0.00205) at both time periods. This was followed by the Scotchbond universal group pretreated with chitosan group (0.00149 and 0.00203). This was followed by the prime and bond without pretreatment with chitosan groups (0.00229 and 0.00225).

1. Introduction

Composite restoration is one of the first materials of choice for patients because of its superior aesthetics, as well as its good strength and wear resistance [1]. Nevertheless, because of the inherent property of polymerization shrinkage, dental composites contribute to microleakage, allowing the movement of oral fluids and microbes from the oral cavity. This can lead to postoperative sensitivity, pulpal inflammation, secondary caries, and marginal staining. To overcome this problem, good bonding between the restoration and the tooth is essential. Developments in adhesive technology and newer bonding systems have considerably improved the bonding of dental composites to the tooth structure [2]. Despite numerous advances in bonding, the failure of the interface between the tooth and restoration continues to be a concern [3].

Bonding to dentin is a complex process due to its diverse structure, comprising mineral-rich inorganic components, collagen-rich organic materials, and dentinal fluid. The deterioration of the bond between the restoration and the dentin, formed using hydrophilic bonding agents, occurs through processes involving hydrolysis, enzymatic action, and fatigue. Once this degradation occurs, a notable quantity of collagen fibrils sparsely embedded into resin can be detected within the hybrid layer, potentially leading to unsuccessful adhesive restorations. This issue underscores the need for innovative bonding techniques focusing on preserving both the stability of resin elements and the integrity of dentin’s organic matrix. Several methods have been proposed to combat enzymatic degradation, namely collagen crosslinking, inhibiting matrix metalloproteinases (MMPs), and employing biomimetic remineralization [4]. Incorporating chitosan has been proposed to enhance the hybrid layer’s resistance to degradation caused by collagenase enzymes [5]. Furthermore, chitosan has the potential to alter the smear layer by removing its inorganic content from the dentin surface, potentially enhancing bonding effectiveness.

A prior investigation focused on a primer incorporating bulk chitosan, assuming its potential to augment bond stability following dynamic aging. Nanodentistry, a domain where nanotechnology has significantly influenced various dental aspects, harnesses nanomaterials known for their mechanical strength, enhanced dimensional stability, and superior bioactivity. Chitosan nanoparticles (CNPs), initially pioneered as a special drug-delivery system by Bodmeier et al. in 1989, are cationic biopolymers derived from chitin through alkaline deacetylation. These nanoparticles find diverse applications in the dental field due to their biocompatibility, lack of toxicity, and chelating action. Research indicates that pretreatment with chitosan nanoparticles can enhance the dentinal surface’s resilience against degradation caused by collagenase, consequently elevating bond strength [5].

Universal adhesives consist of combinations of monomers with mild to moderately acidic properties at reduced concentrations in comparison to their previous forms [6]. They also use traditional dimethacrylates as cross-linking agents, monomer emulsifiers without acidity, light- or dual-curing catalysts, and well-chosen solvents to improve the spread of monomers and the capacity for substrate infiltration. prime and bond universal developed by Dentsply is a one-step universal dental adhesive with a versatile application. The adhesive formulation has a pH of 2.5 containing the recently introduced hydrolysis-stable crosslinker phosphoric acid esters, isopropanolol, and water [7]. Scotchbond universal, developed by 3M ESPE, is a single-bond universal adhesive that is a light-curing adhesive. These adhesives contain a phosphate monomer, i.e., MDP and silane, in addition to conventional functional monomers [8]. There are no known studies, to the best of our knowledge, that evaluate and compare the microleakages of class II preparation pretreated with chitosan nanoparticles and restored with bulk fill composites using two different bonding systems. The null hypothesis was that there would be no difference in the microleakage of Class II cavities restored with composites bonded with prime and bond and Scotchbond universal adhesives, both with and without pretreatment with chitosan nanoparticles.

2. Methodology

Ethical clearance was taken from the institutional ethics committee. In total, 84 caries-free human maxillary premolars recently removed for periodontal or orthodontic reasons were utilized in this study. The debris were cleaned with hand scalers, polished with pumice, and preserved in 0.25% Sodium azide in Ringer solution. They were then mounted in acrylic blocks. In all the teeth, Class II cavity preparation (Mesio-Occlusal) was prepared with 245 bur (Dentsply/Caulk, Milford, DE, USA) with aerator. The buccolingual dimension of the preparation was standardized to 4 mm; the gingival wall was in dentin, just above the CEJ, and the internal angles were rounded. The specimens was randomly divided into 3 groups, as shown in

Table 1. Distribution of the experimental groups.

Groups	Adhesive	Test Time
Group I: Teeth restored with composite (n = 12)	Without adhesive	After 24 h 1 month
Group II: Teeth restored with composite SG1: with chitosan pretreatment (n = 18) SG2: without chitosan pretreatment (n = 18)	Prime and bond universal adhesive	After 24 h 1 month
Group III: teeth restored with composite SG1: with chitosan pretreatment (n = 18) SG2: without chitosan pretreatment (n = 18)	Scotchbond universal adhesive	After 24 h 1 month

.

Teeth in group I were filled with a nanohybrid composite (Filtek Z250, 3M ESPE, St. Paul, MN, USA) without adhesive application. The samples in other two groups were selectively etched in enamel with 3M™ Scotchbond™ Multi-Purpose Etchant, which is 37% orthophosphoric acid, for 10 s, and the respective bonding agents were applied in their respective groups, as per manufacturer’s instructions, and restored using nanohybrid composite. The manufacturers and the composition of the material used are shown in

Table 2. Microleakage score distribution among the test groups with means and standard deviations of either immediate or 1 month.

Subgroups	N		Mean	Std. Deviation
G1:Control	Microleakage-Immediate	12	0.50500	0.07538
	Microleakage-1 month	12	0.50242	0.06743
Prime and bond universal-sg1	Microleakage-Immediate	18	0.00145	0.00022
	Microleakage-1 month	18	0.00205	0.00287
Prime and bond universal-sg2	Microleakage-Immediate	18	0.00229	0.00024
	Microleakage-1 month	18	0.00225	0.00023
Scotch Universal-SG1	Microleakage-Immediate	18	0.00150	0.00057
	Microleakage-1 month	18	0.00203	0.00242
Scotch Universal-SG2	Microleakage-Immediate	18	0.00213	0.00019
	Microleakage-1 month	18	0.00214	0.00019

. Three layers of nail paint were applied to the root crown and surfaces. Subsequently, the teeth underwent a series of thermocycling steps in a water bath, enduring 1000 cycles oscillating between 5 °C ± 2 °C and 55 °C ± 2 °C. Each cycle involved a dwell time of 30 s at each temperature extreme and a transfer time of 10 s.

2.1. Microleakage Testing Using the Fluid Filtration Method

The technique involved assessing microleakage by observing fluid movement in the model, as observed by the movement of bubbles. The system comprises two sections: Section 1, consisting of tubes, syringes, micropipettes, faucet controls, a pressurized buffer system, and experimental samples; Section 2, comprising a bubble displacement recorder integrated with a DSLR camera (Canon 1200D) and AutoCAD software, version 24.1 (Autodesk, Inc. California, U.S.). Firstly, the extracted teeth were affixed to the control faucet. The control faucet was then shut to ensured that it solely connected to the micropipette and syringe. A bubble was created within the micropipette using a syringe. Once the bubble was injected into the micropipette, the control valve was shut to secure the attachment of the micropipette to the tooth sample. Simultaneously, the settings of the digital SLR camera were fine-tuned. Oxygen was then slowly dispensed from the oxygen cylinder via a pressure adjustment apparatus set between 4 and 6 psi [9].

2.2. Statistical Analysis

The data analysis was conducted using IBM Corp’s Statistical Package for the Social Sciences (SPSS), version 21.0, released in 2011, employing ANOVA and the Kolmogorov–Smirnov test. A significance level of p ≤ 0.05 was set for the analysis.

3. Results

The mean microleakage was lowest for the prime and bond universal group pretreated with chitosan (0.00145 and 0.00205) at both time periods. This was followed by the Scotchbond universal group pretreated with chitosan (0.00149 and 0.00203). This was followed by the prime and bond group without pretreatment with chitosan (0.00229 and 0.00225) and the Scotchbond universal group without pretreatment with chitosan (0.00213 and 0.00214). Chitosan pretreatment has significantly reduced the microleakage of teeth restored with composite using the universal adhesive system (Figure 1).

4. Discussion

The microscopic gaps at the dental restoration interface are a major concern, as they cause secondary caries and the penetration of bacterial toxins to the pulp and ultimately lead to restoration failure [10,11]. This study assessed the microleakages of teeth filled with nanohybrid composites using two different universal adhesive systems, each with and without pretreatment with chitosan nanoparticles.

In the present study, the Scotchbond universal adhesive group presented a low microleakage value in comparison to the control group. As per the investigation led by Ghajari et al., the strength and endurance of Scotchbond universal adhesive displayed higher performance when applied using the self-etch method on dentin, in contrast to the etch-and-rinse mode. This aligns with the findings of the current study [8]. The prime and bond universal adhesive developed by Dentsply contains acetone to repel water from the cavity preparation. Contrary to the MDP adhesive monomer’s single vinyl group, PENTA harbors five vinyl groups. The inclusion of PENTA offers an exclusive micromechanical and chemical bond crucial for enduring success [7,12]. In the present study, the prime and bond universal group showed the lowest microleakage at both the time intervals, i.e., immediately and after 1 month. The superior adhesion properties of the prime and bond universal adhesive could be contributed due to the its better degree of conversion due to its hydrophobic nature, which chases water, enforcing a strong bond between the composite resin and the tooth [13,14,15].

Chitosan nanoparticle (CNP) is a natural polysaccharide acquired via the alkaline deacetylation of chitin [16]. In this study, least microleakage is observed with the teeth restored with nanohybrid composite using prime and bond universal adhesive, followed by Scothbond universal adhesive, both with pretreatment with chitosan nanopaticles. In Mohammed et al.’s study [5], chitosan nanoparticles (CNPs) were employed as a biomodifying substance on the smear layer prior to the application of dental adhesive. This modification influenced the smear layer, subsequently enhancing the durability of bond strength [17,18]. A prior investigation was conducted on a primer incorporating chitosan in larger quantities, following the hypothesis that it could improve adhesive durability following exposure to dynamic aging [19,20].

With the oral cavity being complex and dynamic, the in vitro study design used in this study may not completely mimic the natural oral environment. Since this study was performed on extracted teeth, further clinical studies are required in this direction. Nevertheless, the results of the present study can be helpful for dental practitioners in terms of selecting the right type of bonding agent when restoring with composite resin. This study also provides insights to help researchers to further explore chitosan pretreatment prior to restoration with composite resin.

5. Conclusions

In the present study, teeth restored using prime and bond adhesive showed the least microleakage, followed by Scotchbond universal adhesive. In both groups, chitosan pretreatment significantly reduced the microleakage of teeth restored with composite using the universal adhesive system.