The Effect of Silver Diamine Fluoride and Fluoride Varnish on Microhardness of Primary Teeth Enamel (An In Vitro Study)

Aims: This study aims to compare and evaluate the effect of two remineralizing agents: fluoride varnish and silver diamine fluoride solution on the surface microhardness of enamel of primary teeth. Materials and methods: A total of (150) primary anterior teeth were used in the study. Enamel blocks were prepared and divided into three groups: Fluoride varnish n(50), silver diamine fluoride n(50) and the control group of deionized water n(50), then introduced into PH cycle. Microhardness of enamel blocks was measured using Vickers microhardness tester machine (OTTO Wolpert−WERKE GMBH) before and after the PH cycle. Results: There were highly statistically significant differences among study groups after PH cycle and there were a decreasing in surface microhardness in all groups due to the demineralization, but the least reduction in surface microhardness belonged to silver diamine group followed by fluoride varnish group. Conclusions: Silver diamine fluoride was significantly better than fluoride varnish in preserving enamel's hardness and resistant to demineralization.


INTRODUCTION
Early childhood caries is still one of the most prevalent, rapidly progressing microbial disease affecting children worldwide. It is influenced by sugar-rich diet and poor oral hygiene or insufficient dental plaque removal that is not necessarily related to bottle feeding.
It is resulted in dental destruction, pain also placesthe permanent dentition at risk for developing the dental caries. In addition, it can negatively influence the quality of life of children and their caregivers (1) .The enamel of primary dentition is only half as thick as that of permanent dentition (2,3) . It also has a higher organic and lower mineral contents, making it more liable to carious attack than the enamel of permanent dentition (4,3) . Recent treatments focus on the application of remineralizing agents to incipient thecaries to control demineralization and promote remineralization.
Remineralizing agents make a super saturated environment around the decayed lesion, thus, it will prevent mineral loss and concentrate the phosphate and calcium ions in the vacant areas (5) . Fluoride is the most effective measure for the prevention of demineralization which can be used either topically or systemically (6) .
Fluoride also assists to speed remineralization as well as disrupts the acid production in already erupted teeth of both children and adults (7,8) . Fluoride varnish (professional use, typically, 22,600 ppm F) was effective in preventing caries in both primary and permanent teeth (9,10) . Recently published multiple systematic reviews point out that silver diamine fluoride (SDF) application could optimally arrest dental carious lesions in children (11−14) ,and treatment using SDF has been shown to be 89% more effective than other active treatments or placebo in arresting dental caries of primary teeth (14) . SDF application could be widely recommended and promoted as an alternative preventive approach for the conventional invasive caries management, especially among children patients who are too young to receive dental care, those with special care needs, or those with difficulty in attaining and affording the conventional dental care (15) .
The present study aims to compare and evaluate the effect of two remineralizing agents: fluoride varnish and silver diamine fluoride solution on the surface microhardness of enamel of primary teeth in an vitro study. surface of the tooth exposed so that enamel block of 4x4mm window was obtained (19) . The rings with the exposed surfaces of teeth were .

Figure (1):
The crowns were mounted in cylindrical plastic tubes (16mm diameter ×14mm depth) with cold cure acrylic resin with the outer buccal enamel surface exposed

Materials:
The materials used in this study are: Fluoride

The Experimental Design of the Study:
The total number of teeth samples were randomly divided into three main groups, each one contains (50) teeth samples as follows: Group 1(Fluoride Varnish): The teeth were exposed to fluoride varnish for 24 hrs and stored in deionized water, then the layer of varnish was removed with ascalpel blade and cotton soaked with acetone. Being careful not to scratch the surfaces, samples washed with deionized water for 1 min then introduced to PH cycle (19) .
Group 2 (Silver Diamine Fluoride ): the teeth surfaces were exposed to silver diamine fluoride solution with a small brush for 2 min then washed with deionized water for 30 sec and lightly dried with absorbent papers,then introduced to PH cycle (19) .
Group 3 (Control): no agent was applied, only washed with deionized water. Experimental Design of the Study seen in Figure (2).

Solutions preparation
Chemical materials were imported from  (20) .

2.Remineralization solution:
The remineralizing solution consists of 1.5m MCaCl 2 , 0.9 mM NaHPO 4 , 0.15 mM KCl , pH of 7.0, 15 mL/tooth (20) . Distilled water, pH of 7 (concentrations G\L) (21) .The unclear, cloudy liquid of remineralizing solution and artificial saliva had been filtered using filter papers, after that when minerals had been completely stabilized , the PH was measured to be sure that no changes of PH readings will occur days later.

PH−cycling:
The formation of artificial caries occurs by submission of teeth samples to PH cycling. The teeth were introduced to a total of 10 cycles and the duration of each cycle was one day (24 hours). The demineralizing − remineralizing solutions were changed each day, and the artificial saliva was replaced after every treatment (22,23) .

Microhardness Assessment:
The mechanical properties of teeth samples were measured using a Vickers

DISCUSSION
Silver diamine fluoride (SDF) a topical agent, has been considered as an effective, equitable, safe, simple and noninvasive caries preventive agent (28) . It could be applied without the removal of dental caries (12) . Clinical trial declared that SDF is an effective topical agent for preventing and arresting dental caries in primary and permanent dentition (29) . The use of SDF in dentistry has acquired much attention globally due to its approval by the US Food and Drug Administration in August 2014 (30) .  (19) .  (35) . Furthermore, concentrations of silver ions and fluorine, prevent the growth of cariogenic biofilms in multi-species because SDF is highly effective against the cariogenic biofilm of Streptococcus mutans (36) .
On the other hand, Laboratory studies have revealed that following SDF application an insoluble protective layer of silver phosphate and silver chloride is formed on tooth surfaces and this layer will reduce calcium and phosphorus loss from demineralized enamel and dentin, additional investigation in vivo is necessary to know the actual role of this silver compound (37) .