Year : 2010 | Volume
: 28 | Issue : 2 | Page : 68--72
Comparative evaluation of 2% sodium fluoride iontophoresis and other cavity liners beneath silver amalgam restorations
M Gupta1, IK Pandit2, N Srivastava3, N Gugnani3,
1 Reader, Department of Pedodontics & Preventive dentistry, D.A.V. (C) Dental College, Yamuna Nagar, Haryana, India
2 Professor & head, Department of Pedodontics & Preventive dentistry, D.A.V. (C) Dental College, Yamuna Nagar, Haryana, India
3 Professor, Department of Pedodontics & Preventive dentistry, D.A.V. (C) Dental College, Yamuna Nagar, Haryana, India
Department of Pedodontics & Preventive Dentistry, D.A.V. (C) Dental College, Yamuna Nagar
Background: This study was designed to compare 2% sodium fluoride (NaF) iontophoresis with other cavity liners. Materials and Methods: This study was carried out in 30 patients in the age group 10-14 years with bilateral carious permanent first molars. The study evaluated the use of 2% NaF iontophoresis as a cavity liner and also compared its desensitizing effect with varnish and an adhesive bonded liner. Sensitivity gradings were done on a subjective verbal rating scale. Results: All the liner treatments decreased the sensitivity following liner application. However, decrease of sensitivity in the case of 2% NaF iontophoresis was more compared with that of varnish and adhesive bonded liner. The results were statistically significant. Conclusions: It was found that 2% NaF iontophoresis was more effective in reducing the postoperative sensitivity compared with that of varnish and scotchbond multipurpose.
|How to cite this article:|
Gupta M, Pandit I K, Srivastava N, Gugnani N. Comparative evaluation of 2% sodium fluoride iontophoresis and other cavity liners beneath silver amalgam restorations.J Indian Soc Pedod Prev Dent 2010;28:68-72
|How to cite this URL:|
Gupta M, Pandit I K, Srivastava N, Gugnani N. Comparative evaluation of 2% sodium fluoride iontophoresis and other cavity liners beneath silver amalgam restorations. J Indian Soc Pedod Prev Dent [serial online] 2010 [cited 2021 May 8 ];28:68-72
Available from: https://www.jisppd.com/text.asp?2010/28/2/68/66738
Dental caries is one of the most prevalent chronic dental diseases affecting the human race. It causes progressive mutilation of tooth structure and, if left untreated, it may lead to involvement of the pulp.
Though a lot of materials are available for restoration of dental caries, silver amalgam is a time tested and most widely used material especially for posterior restorations because of its high strength, low cost, and relative ease of handling. In spite of these advantages, one of the main drawbacks of silver amalgam is its high thermal conductivity. The average thermal conductivity of amalgam is 55 Χ 10 -3 cal/second/cm 2 (°C/cm) and that of dentin is 1.5 Χ 10 -3 cal/second/cm 2 (°C/cm). Moreover, the coefficient of thermal expansion of amalgam is different from that of the tooth, leading to percolation of salivary fluid components and bacteria at the tooth restoration interface with a variation in oral temperature.  This often causes postoperative pain and sensitivity to the patients. Therefore, it is mandatory to protect the pulp tissue from thermal shock by giving liners and bases before placing silver amalgam restoration. 
Customarily, various dental cements, viz., zinc phosphate, polycarboxylate, zinc oxide eugenol, calcium hydroxide and cavity varnishes, have been used as cavity bases or liners beneath amalgam restorations. The use of bases requires additional depth for their placement which endangers the pulp and also reduces the bulk of restoration. Though the conventional liners and varnishes form a film on the prepared cavity, they act as semipermeable membranes; therefore, even a continuous coating does not provide complete protection. 
With the introduction of adhesive dentin bonding agents, focus has been shifted toward their use as a liner beneath amalgam restorations. Their use, besides being technique sensitive, is also cumbersome. 
To overcome these difficulties, an alternative to conventional lining system is sought after. Use of sodium fluoride (NaF) iontophoresis is well documented for desensitizing the exposed root surfaces. It employs deposition of the fluoride ions deep into the dentinal tubules, which not only desensitizes but also provides fluoride to exert a cariostatic effect.
The present study explores  the use of 2% NaF iontophoresis as a cavity liner and also compares its desensitizing effect with other conventional cavity liners.
Materials and Methods
The study was carried out in 30 child patients in the age group 10-14 years requiring restoration of bilateral carious permanent first molars. The study was carried out in the Department of Pedodontics and Preventive Dentistry, D.A.V. Dental College, Yamuna Nagar. The criteria for exclusion included sensitivity related to gingival recession, attrition, abrasion and patient on anti-inflammatory drugs that could alter the pain response. Patients with pulpal pathology were also excluded.
Patients were divided into two groups, A and B. These groups were further divided into subgroups A 1 and A 2 and B 1 and B 2, respectively.
Teeth in subgroup A 1 were treated with 2% NaF iontophoresis and those in A 2 were treated with two coats of varnish. Similarly, subgroup B 1 was treated with 2% NaF ionotophoresis and B 2 was given a adhesive bonded liner (Scotch Bond Multipurpose 3M Dental Products, St Paul, MN, USA), according to manufacturer's instructions.
Class 1 cavities were prepared following G.V. Black's principles of cavity preparation. All the cavities were prepared under rubber dam with air rotor and micromotor. On the basis of clinical judgment, deep cavities were sorted out and radiographed, and if the remaining dentin thickness was found to be less than 1.5 mm, those cavities were not included in the study.
In subgroups A 1 and B 1, the iontophoretic application of 2% NaF was accomplished by using a desensitron (Parkell Electronic Division, New York USA). A cotton pellet dampened with 2% NaF was placed in the prepared cavity and the applicator tip of unit was placed over the pellet. The current intensity was gradually increased till the patient felt a tingling sensation and then the current was reduced slightly to make the patient comfortable during the treatment.
The subgroup B 2 was treated with scotchbond multipurpose (SBMP), and to apply this, first acid etching was done using 33% phosphoric acid for 15 seconds followed by rinsing and then scotchbond primer was applied and air dried for 5 seconds. After this, adhesive application was done and was light cured for 15 seconds.
Sensitivity was evaluated by tactile and thermal methods. A sharp explorer was used as tactile stimulus. Thermal method included the use of both air blast and cold water tests. Air blast test was accomplished by a 1-second air blast at 60 psi pressure, whereas cold water test was performed by allowing 1 ml of ice cold water to flow slowly into the prepared cavity with a disposable syringe.
Sensitivity was assessed based on the following verbal rating scale:
0 - No discomfort; 1 - mild discomfort; 2 - moderate discomfort; 3 - pain only during application of stimulus; 4 - severe pain persisting after removal of stimulus.
After the liner treatment, only air blast was used as a stimulus. After this, patients were recalled on 2nd, 7th, 14th, and 30th days to evaluate the postoperative sensitivity using air blast and cold water.
The criteria for evaluation of the degree of sensitivity were based on verbal rating scale. Nearly all the teeth were sensitive in both groups A and B before liner treatment. This, when subjected to statistical analysis, yielded no significant difference among the groups [Table 1] and [Table 2].
It was observed that post-liner treatment, only two teeth were sensitive in subgroup A 1 (2% NaF iontophoresis) and five teeth were sensitive in subgroup A 2 (varnish). Intergroup comparison between the two subgroups A 1 and A 2 was found to be statistically significant (P < 0.05). After silver amalgam restoration, one tooth was sensitive on day 2 in subgroup A 1 (2% NaF) and no sensitivity was found in the same group from the seventh day onward. On the other hand, four teeth were sensitive in subgroup A 2 on day 2 out of which one remained sensitive till the 14th day and no sensitivity was observed in the same group on the 30th day thereafter. The difference in sensitivity between subgroups was statistically significant (P < 0.05) [Table 3].
In subgroup B1 (2% NaF), two teeth showed sensitivity after the liner treatment and the number of sensitive teeth was reduced to five in subgroup B 2 (SBMP) following liner treatment. Intergroup comparison between subgroups B 1 and B 2 using student's 't' test showed significant results (P < 0.05). Post-silver-amalgam restoration, one tooth showed sensitivity on the second day in subgroup B 1 and no sensitivity was found in the same group from the seventh day onward. In subgroup B 2 , five teeth were sensitive on day 2 and 1 tooth remained sensitive till the 30th day.
Statistically significant difference in sensitivity was found between subgroups B 1 and B 2 (P < 0.05) over various periods of time [Table 4].
NaF was first proposed as a desensitizing agent by Lukomsky  in 1941, who suggested that NaF when applied to the exposed dentin forms an effective barrier and results in desensitization of dentin. Using 2% NaF iontophoresis, Carlo et al0.found significant relief from sensitivity in 90% of cases. Gangorosa and Park reported similar results using 2% NaF iontophoresis. The investigators recommended that using 2% NaF is the most economic way to treat dentin hypersensitivity.
Cavity varnish traditionally is the most frequently used liner beneath amalgam restoration. Varnish is believed to reduce postoperative sensitivity by minimizing microleakage. This effect is of particular importance in the case of silver amalgam restoration since gross leakage occurs during the first few days and weeks.
Recently, dentin bonding agents have also been used as liners as they are believed to bond the restorative material to tooth structure. The mechanism by which dentin bonding agents reduce sensitivity probably involves hybrid layer formation and occlusion of tubules by resin tags.
The criteria for sensitivity assessment in this study were subjective, as the subjects were asked to rate tooth sensitivity on a subjective discomfort scale. The stimuli used to elicit sensitivity were air blast, water jet and probing because they appear to involve the dentinal fluid movement which most investigators now believe to be the basis of pain response. ,
In both subgroups A 1 and B 1, NaF was more effective than varnish (A 2 ) and SBMP (B 2 ) [Table 4]. Although the exact mechanism by which fluoride iontophoresis produces desensitization is not known, several hypothesis have been proposed. One mechanism described by Lefkovitz et al.involves the formation of reparative dentin following application of current to dentin. A second hypothesis states that electric current produces parasthesia by altering the sensory mechanism of pain conduction.  A third explanation is that fluoride ions in the dentinal tubules caused microprecipitation of calcium fluoride that may act to block hydrodynamically mediated pain-inducing stimuli. 
Scott,  on the basis of a histologic study, described direct current up to 1 mA as safe causing no injury to pulp and so it has to be recommended so that the patients' sensory threshold is not exceeded during treatment. So, in this study, the direct current used was 0.5 m A.0
In subgroup A 1 (2% NaF) after liner treatment, only two teeth were sensitive, whereas in subgroup A2, five teeth were sensitive. Moreover, in subgroup A1, no teeth were sensitive on day 7, whereas in subgroup A 2 (varnish), one tooth was still sensitive on the 14th day [Figure 1].
This can be attributed to iontophoresis of 2% NaF which drives the fluoride ion deep into the dentinal tubules resulting in effective blockade. The delay in the relief of sensitivity in the varnish group can be attributed to the fact that varnish provides an uneven film with high solubility and to the incapability of completely eliminating the microleakage around amalgam restoration. Chawla, using 2% iontophoroses as an alternative to cavity lining, also found 50-60% decrease in sensitivity after first application and 70-90% decrease on second application.
Similar results were obtained in group B. It was observed that only one tooth was sensitive on 2nd day in patients treated with 2% NaF iontophoresis, whereas five teeth were sensitive in adhesive liner group [Figure 2].
The increased sensitivity in subgroup B 2 can be due to excessive demineralization from etching and incomplete impregnation resulting in a band of dentin that is left unprotected and assessable to the corrosion products of amalgam. Initial sensitivity can also be due to removal of the dentinal smear layer resulting in opening of dentinal tubules. This leads to increased dentinal fluid flow, causing fluid contamination and resultant inflammation and sensitivity. 
Deep cavities were not included in the study as film-forming liners do not provide adequate strength to bear the masticatory forces, and moreover, they do not provide adequate thermal insulation. The added advantage of NaF iontophoresis is that fluoride is provided to the walls and base of the cavity, which is expected to exert a cariostatic effect and prevent marginal and recurrent caries. Simone et al. reported that fluoride concentrations in surface and subsurface enamel layers of iontophoretically treated teeth were significantly higher than those treated by topical fluoride application alone.
NaF iontophoresls could be effectively used as a cavity liner beneath silver amalgam restoration. Teeth treated with 2% NaF iontophoresis showed reduction in dentinal sensitivity much earlier as compared to teeth treated with adhesive liner or varnish. In terms of efficacy, 2% NaF iontophoresis was also found to be most effective, followed by varnish and SBMP.
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