Modern preventive dentistry advancements, the widespread public acceptance of fluoridation and the greater emphasis on dental hygiene have considerably affected the nature of dental care profession. Nevertheless, caries restoration is still one major activity of Pediatric Dentists. ¹ Although fluoride application has led to significant caries decrease in smooth surfaces of enamel and cementum, it has not been as promising in protecting occlusal pits and fissures and 50% of carious lesions still occurs on the occlusal surfaces. ² The fact that occlusal surface makes only 12% of total dental surfaces suggests that pits and fissures are 8 times more caries-susceptible than smooth surfaces. ² , ³ Therefore, sealant placement is nowadays considered to be an effective means of preventing caries in occlusal surfaces. Since 1975 when the first methyl methacrylate sealant was used, ¹ , ⁴ quite a number of changes have occurred. Yet the main material used in sealants is still BIS-GMA monomers. ¹ The most acute problem with sealants is the leakage problem; none of the restorative materials available are intrinsically resistant to microleakage. ¹ However, the application of acid etching results in better micromechanical binding, which in turn causes less microleakage. ¹ , ⁵ Since marginal leakage interferes with the formation of a protective barrier between the teeth and the oral environment thus, allowing the permeation of mutans streptococci, fermentable carbohydrates and destructive agents, ² , ⁶ this study tried to make an in vitro comparison of the microleakage of two agents used in fissure sealants and introduce the superior technique and agent.

Study design and samples

This experimental, non-directional, in vitro study through using simple random sampling technique was conducted in Torabinezhad Research Center in Isfahan.

Procedures

Fifty-five premolar teeth extracted for orthodontic reasons and assessed to bear no cavity, anatomic abnormality, distinct crack and surface pigment were selected. The teeth were cleaned with the prophylaxis brush and the periodontal fibers were also removed. The teeth were then preserved in thymol solution 0.2% for 24 h and later in distilled water at room temperature. Thus, 2 months before the experiment, 55 teeth were prepared. The teeth were divided into five groups. Before sealant therapy, the teeth were completely cleaned with the prophylaxis brush and sound. Fifty five extracted premolars were assigned randomly to one of the following five groups: Group 1: Acid-etching Ultra Etch Ultradent Products Inc., South Jordan, Utah, USA]) + fissure sealant Helioseal Clear Ivoclar Vivadent Ets, Schaan, Liechtenstein conventional method)], Group 2: Acid etching + bonding agent single bond + fissure sealant, Group 3: Self-etching primer + bonding agent SE bond Kurary Medical Inc. Okayam, Japan + fissure sealant, Group 4: Acid-etching + bonding agent + flowable composite [Filtek Flow (3M Dental Products Inc., St. Paul, Minn, USA)], Grope 5: Self-etching primer + bonding agent + flowable composite. Following sealant placement, the teeth were thermocycled (3000 cycles; 5-55°C) and then immersed in 50% of silver nitrate solution for 24 h and then immersed in photo developing solution for 4 h under fluorescent light. The teeth were then sectioned longitudinal. Microleakage was scored using a stereomicroscope and a 4-criteria ranking/ordinal score. Score 0: Without microleakage, Score 1: Color penetration to 1/3 occlusal thick of sealant, Score 2: Color penetration to 2/3 occlusal thick of sealant, Score 3: Color penetration to the total depth.

Statistical analysis

Data were analyzed statistically using the Kruskal-Wallis and Mann-Whitney test. The minimum P value for being meaningful was assumed 0.05.

Table 1illustrates the frequency distribution of microleakage rate in the study groups and Figure 1shows the general results of the study.

Since the recorded values for microleakage were of ordinal nature, the Kruskal-Wallis test was firstly applied Table 2. The result showed there were significant differences between the study groups (P < 0.05). Then the Mann-Whitney test showed (P < 0.05) that Groups 2 and 4, namely where acid etching and bonding agent had been used, had the highest frequency of score: 0 (no micro leakage) and the lowest frequency of score: 3 (complete microleakage), indicating in these groups complete microleakage had not occurred at all. Figure 1

Comparison of Microleakage Rate in the Study Groups (X axes: Number of group-y axes: Mean Microleakage)

In this study, the microleakages of two material agents used as fissure sealants were compared. Resinous sealants prevent caries development through forming a mechanical barrier between the grooves of teeth and the oral environment interrupting metabolic exchange. Thus, unlike glass ionomers which depend on fluoride uptake for success, the efficacy of resinous sealants is dependent on retention and integrity. ⁷ Hence, in this study, microleakage, as one of the most important indicators of success or failure of sealant therapy has been investigated. Pumice prophylaxis and enameloplasty were avoided. Though a number of studies argue that pumice prophylaxis plays an important role in fissure sealant retention, there is still a controversy over the matter. Although many Dentists apply pumice prophylaxis as the first step in fissure sealants, there has been no significant difference in retention with or without pumice prophylaxis. ⁸ Some researchers propose that pumice may remain in the depths of grooves and interfere with resin infiltration into those parts. ⁹ As for enameloplasty, similarly there is no unanimity. Some of the studies ¹⁰ have found it necessary for reducing sealant microleakage, while others have regarded it unnecessary. However, Celiberti and Lussi ¹¹ argue that although enameloplasty provides better access to the depths of the grooves when etching, which helps resin infiltration, the probability of sealant microleakage increases when a larger region is covered by the sealant. This is due to greater movements of the sealant margins. For this reason and also because this study, like all other similar studies aimed to reach a simpler procedure for sealant therapy, enameloplasty was not applied, to make it possible to observe only the effect of the materials and the techniques used. In our study, no anatomical distinction was made between groove depths. The reason was that some studies have shown that there is no significant difference in microleakage in anatomically different grooves. ¹² The device used for curing was a blue phase LED. Since the device has a built-in radiometer, it makes it possible to make sure all specimens receive the same amount of output energy.

Furthermore, we applied flowable composite only after the application of the bonding material/agent because findings of a study by Kwon and Park in 2006 ¹³ showed that the application of flowable composite on etched surfaces without using bonding agents did not bear favorable results. The results of our study showed that microleakage occurred in all the study groups with varying extents, which is in concordance with other studies on microleakage of fissure sealants. ⁸ , ¹⁴ , ¹⁵ , ¹⁶ , ¹⁷ The Mann-Whitney test showed there was a significant difference between a numbers of the groups in microleakage. The results of the test revealed the least microleakage existed in groups where acid etching and bonding agent had been used. It also showed microleakage was maximum in groups where self-etching primer and bonding agent had been applied. As it is seen, these results are in agreement with the finding of studies which suggest the use of bonding agents following etching positively affects the sealant therapy. ¹⁸ , ¹⁹ , ²⁰ Considering the results, it is seen that in Groups 2 and 4 in which acid-etching and bonding agents were applied, a high percentage of the specimens (81.8%) showed no microleakage and complete microleakage did not occur in any of the specimens. As it was noted earlier, neither enameloplasty nor pumice prophylaxis was applied in this study; therefore, it could be concluded that acid etching by using bonding agents positively affect sealant therapy. Further studies might reveal that enameloplasty and pumice prophylaxis are not required for sealant therapy. ⁸ The application of self-etching primers for preparation of occulusal surfaces (in Groups 3 and 5) was not efficient, which is similar to the findings of other similar studies. ¹¹ , ²¹ Ram et al. ²¹ recommends using conditioners without cleansing only when cleansing is impossible. Furthermore, the findings of a study conducted by Hannig et al. in 2004, ¹¹ in accordance with our findings, suggest the application of self-etching primers does not promote sealant therapy. Findings of a very similar study by Pardi et al. in 2006 shows that microleakage of the flowable composite (Filtek) is similar/equal to that of Delton sealant. ¹⁶ We used 50% of silver nitrate solution for 24 h. As the particles are thinner than in other agents, silver nitrate has the highest infiltration rate among other agents used for dye infiltration technique applied in microleakage studies. ¹⁶ Dye infiltration period was also longer (24 h) in our study. These reasons could possibly explain the difference between the findings of our study. Comparison of microleakage rate in Group 1 (conventional approach) and Group 2 (acid etching + bonding agent + sealant) showed a near-to-significant difference. This may change to a significant difference if the number of specimens is increased. Comparison of microleakage rate in Group 1 (conventional approach) and Group 4 (acid-etching + bonding agent + flowable composite) showed a significant difference. Mean microleakage in Group 4 was significantly lower than in Group 1. Considering the high rate of microleakage in Groups 3 and 5, the application of self-etching primers, even when a simple and short procedure is desired, is not recommended. When it is possible to add a further step, that is, the application of a bonding agent to sealant therapy, our findings suggest that it will decrease the microleakage rate, if the bonding agent is used before sealant placement. Otherwise, when money matters, the conventional sealant therapy approach is recommended. ²² From the results and findings of this study, it could be proposed that under a similar technique the application of both the flowable composite and fissure sealant results in the same microleakage rate. Therefore, the flow able composite could substitute fissure sealants in sealant therapy only if further studies can show it outperforms fissure sealants in term of retention and other properties such as wear resistance.

Based on the findings of this study, it can be concluded that the best sealant therapy technique is acid-etching bonding agent and then application of sealant (conventional sealant or flow able composite). The application of acid-etching and bonding agent together with the flowable composite is recommend.