ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10015-2354
World Journal of Dentistry
Volume 15 | Issue 1 | Year 2024

Shear Bond Strength of Resin-modified Glass Ionomer Cement to Primary Teeth Dentin Pretreated with Silver Diamine Fluoride and Sodium Fluoride Varnish: An In Vitro Study

Mounashree Narayanaswamy¹, Nagarathna Chikkanarasaiah²

^1,2Department of Pedodontics & Preventive Dentistry, RajaRajeswari Dental College & Hospital, Bengaluru, Karnataka, India

Corresponding Author: Mounashree Narayanaswamy, Department of Pedodontics & Preventive Dentistry, RajaRajeswari Dental College & Hospital, Bengaluru, Karnataka, India, Phone: +91 7019662344, e-mail: mounagowda88@gmail.com

Received: 03 December 2023; Accepted: 04 January 2024; Published on: 20 February 2024

ABSTRACT

Aim: To evaluate and compare the shear bond strength (SBS) of resin-modified glass ionomer cement (RMGIC) to primary teeth dentin pretreated with silver diamine fluoride (SDF) and sodium fluoride (NaF) varnish.

Materials and methods: Sixty samples of noncarious human primary molars were collected for the study. Teeth were prepared to expose a flat dentin surface and teeth were randomly divided into two groups. In group I primary teeth dentin surface was pretreated with SDF 38%, while group II samples were pretreated with NaF varnish 5%, then the samples were restored with RMGIC. SBS was evaluated using a universal testing machine.

Results: The results of the study showed that the mean SBS of group I was significantly higher (11.64 ± 6.78) as compared to group II (7.90 ± 4.96) with a mean difference of 3.74 MPa.

Conclusion: Primary teeth dentin surface pretreated with SDF 38% had shown an increase in the SBS to RMGIC when compared to NaF 5% varnish.

Clinical significance: Bonding of restorative material to primary teeth dentin pretreated with caries-preventing agents has shown good adhesion to the dentinal surface. It is a simple, minimally invasive procedure that can be beneficial in the pediatric population.

How to cite this article: Narayanaswamy M, Chikkanarasaiah N. Shear Bond Strength of Resin-modified Glass Ionomer Cement to Primary Teeth Dentin Pretreated with Silver Diamine Fluoride and Sodium Fluoride Varnish: An In Vitro Study. World J Dent 2024;15(1):60–63.

Source of support: Nil

Conflict of interest: None

Keywords: Primary teeth, Resin-modified glass ionomer cement, Shear bond strength, Silver diamine fluoride, Sodium fluoride varnish

INTRODUCTION

Dental caries is one of the most common chronic dental diseases in all populations with varying degrees of severity. International data on caries epidemiology confirm that dental caries remains a significant disease of childhood in both developing and developed countries.¹ The current trend to manage dental caries in children aims to utilize minimally invasive, tissue-preserving, affordable, and safe approaches, while efforts to create more effective anticaries agents and the choice of restoration are still ongoing.

Various methods have been proposed to arrest dental caries in children out of which topical application of fluoride in various forms has been proven to be the most important method in combating the carious lesion.

Silver diamine fluoride (SDF) (38% SDF) has been used for arresting dental caries in children worldwide since the 1970s. It is a minimally invasive, non-aerosolizing approach for the management of dental caries. SDF is a colorless alkaline solution that contains silver and fluoride ions. It inhibits demineralization and preserves the collagen in dentin from destruction. SDF reacts with calcium and phosphate ions to form fluorohydroxyapatite and calcium fluoride, which is considered one of the main factors for arresting caries.²

Sodium fluoride (NaF) varnish (5%NaF) is a non-aqueous based product that contains fluoride in a natural colophony base and adheres longer to tooth surfaces in the presence of saliva. It helps in the prevention, and arrest of dental caries through remineralization.³ A recent systematic review showed that NaF varnish had a modest benefit in preventing new dentin carious lesions.⁴

Restorations are needed for cavitated lesions as their self-cleansing surface will reduce the potential for secondary caries also, they seal out bacteria-harboring plaque and restore esthetics and function. Restorative material makes a huge difference in the clinical success of the restoration. Based on the scientific evidence, resin-modified glass ionomer cement (RMGIC) has been recommended as a restorative material in children due to its superior biocompatibility, esthetics, better bond strength, ease of handling, fluoride release(anticariogenic), less moisture sensitivity thus resulting in low solubility and disintegration.⁵^,⁶ Hence, it is a material of choice in children with high caries risk and also in case of the active carious lesion.

Shear bond strength (SBS) is the resistance to forces that slide restorative material past tooth structure. It assumes much importance to the restorative material clinically because the high SBS of a restorative material implies better bonding of that material to the tooth.

However, any agent applied to the dentin and enamel surfaces before the restorative procedure could potentially interfere with bonding which results in changes in their mechanical properties. So restorative material is considered successful clinically based on its good adhesion with the dentinal surface to resist various dislodging forces that are acting within the oral cavity.

Few in vitro studies have shown no adverse influence on SBS even after the teeth were pretreated with 38% SDF.⁷ Yet, few more studies reported raise in the SBS of RMGIC to primary teeth dentin pretreated with 38% SDF.⁸^,⁹ While the studies on NaF varnish have shown caries arresting effect on a cavitated dentinal lesion. There is no literature to prove the SBS of RMGIC restoration to the primary teeth dentin surface pretreated with NaF varnish.

Hence, to our knowledge, there is insufficient evidence in the literature to understand the adhesion property of RMGIC restoration to the primary teeth dentin surface pretreated with SDF and NaF varnish. Therefore, the present in vitro study was undertaken to evaluate and compare the SBS of RMGIC to primary teeth dentin pretreated with SDF and NaF varnish in children.

MATERIALS AND METHODS

This is an in vitro study done in the department of pediatric and preventive dentistry, it has received approval from the ethical committee of the institution. Sample size estimation was done using the software G*Power v. 3.1.9.4 (Franz Faul, Universität Kiel, Germany). Considering the effect size to be measured (d) at 74% for two-tailed hypotheses, the power of the study at 80%, and the α error at 5%.

A total of 60 sample-size human primary molars which are noncarious with intact buccal and lingual surfaces and those advised for extraction due to exfoliative mobility and orthodontic reasons were taken for this study. Carious, fractured/injured teeth, teeth with restorations, and hypoplastic or developmental defects were excluded from the study.

Tissue debris and calculus were removed from the teeth using an ultrasonic scaler and were stored in 0.02% thymol solution for 1 week and later in normal saline solution at room temperature. The teeth were then embedded in self-cure acrylic blocks of 3 × 2 cm in size such that the occlusal surface of the teeth was parallel to the acrylic resin block surface. Occlusal enamel was removed using a standard high-speed dental handpiece and diamond bur with water coolant until the yellow flat dentin surface was exposed. The surfaces were abraded and smoothened with silicon carbide paper (600 grit). Later a window of 3 × 3 mm was created with vernier calipers and nail varnish to leave only the area of flat dentin to be exposed. All the prepared specimens were then stored in distilled water for 24 hours at room temperature. The teeth were randomly divided into the following groups.

Group I: Silver diamine fluoride (SDF) 38% (FAgamin) solution was dispensed into mixing well, then applied directly onto the primary teeth dentin using a micro applicator tip for 2 minutes, followed by rinsing with water for 30 seconds and gently air dried with oil-free compressed air. Then RMGIC was mixed and applied to the dentin surface as per the manufacturer’s instructions using a plastic filling instrument and the cement was contoured to 2 mm thickness and light cured for 20 seconds.

Group II: Sodium fluoride (NaF) varnish 5% (VOCO Profluorid Varnish) was applied to the primary teeth dentin for 3 minutes using a microbrush and as per manufacturer instructions area of application should be allowed to become wet by gentle rinsing to ensure the setting of fluoride. The restoration was carried out as in group I.

Immediately after restoration, teeth were transferred into separate labeled containers filled with distilled water and subjected to thermocycling for 500 cycles with temperatures varying between 5 and 55°C and a dwell time of 60 seconds and stored in distilled water for 2 days. SBS analysis was done using a universal testing machine (Fig. 1) with a crosshead speed of 1 mm/minute in a compression mode until the dislodgement of restoration.

Fig. 1: Shear bond strength (SBS) evaluation using universal testing machine

Statistical analyses were performed using Statistical Package for Social Sciences (SPSS) for Windows Version 22.0 Released in 2013, Armonk, New York: IBM Corp., Results on continuous measurement are presented as mean ± SD. Mann–Whitney U test was used to compare the mean SBS between the two study groups. The level of significance was set at p < 0.05.

RESULTS

Mann–Whitney U test results demonstrated that the mean SBS of group I was significantly higher (11.64 ± 6.78) as compared to group II (7.90 ± 4.96) with a mean difference of 3.74 MPa [95% confidence interval (CI), 0.67–6.80]. This difference in the mean SBS between the two groups was statistically significant at p = 0.01 (Table 1).

**Table 1:** Comparison of mean SBS (in MPa) between group I and group II using Mann–Whitney U test
Groups	N	Mean	Standard deviation	Mean difference	95% CI of the difference		Z	p-value
Groups	N	Mean	Standard deviation	Mean difference	Lower	Upper	Z	p-value
Group I	30	11.64	6.78	3.74	0.67	6.80	2.491	0.01*
Group II	30	7.90	4.96	3.74	0.67	6.80	2.491	0.01*

*, statistically significant

DISCUSSION

Dental caries is the most prevalent disease seen especially in preschool children. The untreated carious lesion can cause pain and infection which might affect not only children’s oral health but also their general growth and development and quality of life. Young children still showing the development of cognitive and psychological behavior exhibit limitations during restorative treatment. Thus, the traditional approaches are replaced by minimally invasive approaches to arrest the progression of caries involving enamel and dentin. A variety of fluoride-based chemotherapeutic agents are used for preventing and arresting dental caries. In dentinal carious lesions, better results may be achieved using caries arresting agents such as SDF followed by restorations.

Clinically, both SDF and NaF varnish have proven successful in arresting the caries progression, there is still a risk for secondary caries formation if the cavitated lesions are left unrestored, and also it has shown a negative impact on children as it has led to chewing difficulties, food accumulation, difficulty in maintaining oral hygiene and had an unesthetic appearance. Thus, restorations are needed for cavitated lesions.

Resin-modified glass ionomer cement (RMGIC) was used as a restorative material in our study as it is effective in the reduction of microleakage, and incidence of secondary caries formation and provides better retention and seal. Due to their broad use, it is necessary to evaluate the behavior of RMGICs bonded to hard dental tissues and also to assess which surface treatments will produce the best outcome.

In our study, the increase in SBS of SDF (group I) is related to better ionic and micromechanical bonding of dentin to SDF components as well as strengthening of the organic portion such as dentin collagen and surface mineralization. SDF when applied to the dentin surface reacts with calcium hydroxyapatite and forms silver phosphate and calcium fluoride. The silver phosphate formed may react with the carboxylic group of RMGIC increasing the bond between the restoration and the primary dentin. Calcium fluoride is seen plugging the dentinal tubules. Moreover, fixation of the organic content leads to the contraction of organic substance inside the dentinal tubules increasing the interlocking between dentinal tubules. Reduced collagen degradation and promotion of remineralization by antimatrix metalloprotease action of SDF could improve the chemical bonding of glass ionomer cement (GIC) to collagen fibrils.⁵^,⁹^,¹⁰ These results are supported by various studies in the literature, that SDF increases the mineral content of dentin by penetrating the dentinal tubules and collagen fibril network thus leading to an increase in bond strength, and also when silver in SDF occludes the flow of dentinal fluids, it facilitates the micromechanical bonding of resin components of RMGIC.⁵

Rinsing off SDF after the application seems to eliminate the unreacted silver particles and also the excess silver precipitate from peritubular to intertubular dentin favoring the adhesion.⁹^,¹¹^,¹² The dentin surface darkened more when SDF was light cured which indicates more precipitation of metallic silver increasing the ionic interaction between GIC and dentin.⁸^,¹³ On the contrary only a few studies have shown that SDF application had no significant influence on the bond strength of RMGIC.⁵ Another study showed a decrease in bond strength when SDF was left on the tooth surface after the application.¹⁴

Lower SBS to RMGIC associated with NaF varnish pretreatment was due to the formation of fluorapatite which not only occludes dentinal tubules but also fills in the irregular dentin surface. NaF tends to form a spherical calcium fluoride precipitate on the dentin surface which could change tooth surface morphology. The precipitate formed is acid-resistant and may chemically and physically prevent complete penetration of the resin components RMGIC.¹⁵ The same was evaluated using a scanning electron microscope and results showed that deposition of fluoride blocked and reduced the lumen of dentinal tubules which prevented penetration of resin components of the bonding system and also led to loss of mechanical interlocking, thus decreasing the bond strength.¹⁶^,¹⁷ Still bonding between dentin surface pre-treated with NaF varnish to RMGIC occurs, due to component 2-hydroxyethyl methacrylate (HEMA) in RMGIC which is a hydrophilic wetting agent, it helps to reopen the interfibrillar spaces and also depresses the surface tension of water and enhances the monomer diffusion into the dentin.¹⁸

In vitro tests are relatively fast and standardized easily. Though our study provided reliable data and reproducible measurement the above results combined with the antimicrobial nature of SDF will increase the benefits of caries arrest. Thus, require more clinical trials to establish reliability and overcome limitations such as:

Gray discoloration of RMGIC restoration in the SDF group.
The thermocycling procedure does not stimulate change in the pH of the intraoral environment.
Fractured surfaces after SBS were not analyzed under the microscope to know the type of failures like adhesive, cohesive, or mixed type.

CONCLUSION

Considering the limitations of the study, it was concluded that primary teeth dentin surface pre-treated with SDF 38% had shown an increase in the SBS to RMGIC.

ACKNOWLEDGMENTS

The author would like to acknowledge all the staffs of the Department of Pediatric and Preventive Dentistry for helping me in completing this study.

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