Caries progression in non-cavitated fissures after infiltrant application: a 3-year follow-up of a randomized controlled clinical trial

Abstract Objectives To evaluate the efficacy of a conservative treatment to prevent the progression of caries using an infiltrant on non-cavitated pit and fissures. Material and Methods This controlled clinical trial selected 23 volunteers with clinically and radiographically non-cavitated occlusal caries among patients presenting a “rather low” to “very high” caries risk. Eighty-six teeth were randomly divided into two experimental groups: teeth receiving a commercial pit-and-fissure sealant (Alpha Seal-DFL) and contralateral teeth receiving Icon infiltrant (DMG). Caries progression was monitored by clinical (laser fluorescence caries detection) and radiographic examination at 12-month intervals over a period of 3 years of monitored caries progression. Probing the sealing materials to detect areas of retention was also used to evaluate marginal integrity. Results Statistical analysis showed no difference in caries progression using laser fluorescence caries detection when both materials were compared, regardless of the evaluation times (p>0.05). No significance was observed when the marginal sealant integrity of both materials was compared, regardless of the evaluation time (p<0.05). Marginal integrity significantly reduced after 1 year for both materials (p<0.05), but remained stable after 2 and 3 years of evaluation, compared with 1-year results (p>0.05). SEM analysis exhibited a more homogeneous sealing for the infiltrant than obtained by the sealant. Conclusions The infiltrant was effective to prevent the caries progression in non-cavitated pit-and-fissures after 3 years of clinical evaluation, comparable with the conventional sealant. The infiltrant also presented better results in terms of caries progression at the 3-year evaluation time using the radiographic analysis.


Introduction
The configuration of pits and fissures is clinically relevant to determine the susceptibility for occlusal caries when the factors are present 29 . Sealants prevent caries by reducing available retention sites forming a smooth surface layer and providing the inhibition of bacterial survival by preventing nutrients from reaching microflora in the fissures 29 . Therefore, differently from glass ionomer sealants that can be lost maintaining their anti-cariogenic effect, the clinical effectiveness and success of resin sealants have been related with their retention 30 . If the sealant is fully retained, then possibly recurrent caries or progression of caries beneath the restoration is negligible 19 . To enhance the longevity of pit-and-fissure sealants, several materials and techniques have been developed 11 .
Caries lesions are characterized by demineralization in the lesion body, whereas the surface remains comparably highly mineralized 18 . In an early stage, these lesions can be arrested or even remineralized 9 .
Conventional fissure sealing results only in a superficial resin penetration on the pit and fissure, establishing a preventive mechanical barrier. Therefore, its indication relies on sound and/or slight demineralized superficial surface, which is clinically difficult to define. In this scenario, low-viscosity infiltrant represents a promising alternative approach. A promising alternative therapy to arrest caries lesions relies on the infiltration of lowviscosity, photoactivated resins in their subsurface 17 .
The application of an infiltrant resin has been claimed to improve caries infiltration 17 . It erodes the pseudointact and relatively impermeable surface layer with hydrochloric acid gel, desiccating the lesion with ethanol. Then, a subsequent application of the infiltrant material takes place 24 . In contrast to caries sealing, caries infiltration removes any excessive resin on the lesion surface before the material is light cured 21 . Consequently, caries inhibition comes mostly from occlusion of the pores within the lesion body, which slows down diffusion 27 .
Resin infiltration seems to result in considerably deeper resin penetration whereas pre-treatment with hydrochloric acid seems more suitable compared with the application of phosphoric acid 21 . Regarding clinical practice, this modified etching technique is claimed to reduce the influence of the highly mineralized surface layer on infiltration abilities into fissure caries lesions 21 .
In addition, the ability of the infiltrant to effectively infiltrate the enamel lesions may allow better clinical results 23 . Enamel caries present pores that may act as diffusion pathways for acids and dissolved minerals. Therefore, occluding these pores with photoactivated resins might arrest the progress of the caries lesion and mechanically stabilize the structurally fragile lesion 23 . A systematic review of in vivo studies revealed that resin infiltration seems to be an effective method to arrest the progression of non-cavitated proximal caries lesions extended radiographically at maximum to the outer third of dentin in combination with non-operative measures compared to non-operative measures applied alone 6 .
The rationale that support the use of infiltrant as a sealing material relies on fact that, although the protocol for the application of the former is completely   Most lesions were classified as ICDAS 2 and some were ICDAS 1 or ICDAS 3. They were randomly allocated to two treatment groups ("conventional sealing" and "resin infiltration"). The cariogram model (Bratthall Cariogram) was assessed to estimate the caries risk. In the same way, the contralateral teeth were submitted to prophylaxis using pumice and a photoactivated pit and fissure sealant (Alpha Seal -DFL), was applied according to the manufacturer's instructions, as follows: the enamel surface was etched using 37% phosphoric acid gel for 60 s, waterrinsed thoroughly for 10 s, and dried. The material was applied with a sharp explorer to avoid excessive spreading of sealant, and light cured for 20 s using the same light curing device. In the same way, the fissures were filled about one third to half of them. The excess material was also removed using a microbrush. Visual inspection then evaluated both sealant and infiltrant coverages, using a dental probe to detect any pit or fissure region not covered by the material.
After photoactivation with the same light curing unit, the rubber dam was removed. Then, the occlusion was checked with a carbon marker and premature contacts were relieved to ensure that the materials would not produce occlusal interferences. Finally, polishing cups were used for the surface finish. Patients were then advised regarding oral hygiene. Impressions Caries detection using fluorescence method was performed before the application of both sealing materials and also on the recalls. Although five areas were scored, for statistical reasons, the worst score among all of the points were selected as it provided the real caries risk condition.

Caries detection using radiographic analysis
Radiographs were obtained after 1, 2, and 3 years, using the same equipment and settings, and compared     Figure 1 shows the relationships between results of radiography and laser fluorescence, which included two sets of data (sealant and infiltrant).
Spearman's correlation coefficients showed moderate (infiltrant) and strong (sealant) positive correlation between the two methods ( Figure 1A and 1B). Table 3  Analysis of clinical caries progression (Table 4) showed no association between the condition of the tooth at the end of the study period and group 1=definitely not caries (sound), 2=probably not caries, 3=questionable, 4=probably caries, and 5=definitely caries. *significant (p<0.05) Table 2-Distribution of caries detection using radiographic analysis after 3 years
Concerns have been expressed over the changes in caries pattern and the substantial improvements in the fields of caries diagnosis and caries prevention and treatment. In particular, the use of the dental probe has been continuously criticized as an inappropriate diagnostic tool 14  Thus, the dental probe has turned out to be almost a "useless" tool in the daily basis clinical practice.
Conversely, the great majority of manufacturers generally recommend checking the sealant retention with a probe after polymerization to ensure that all fissures are completely sealed. If not, it should be reapplied, re-etching the exposed fissure. In addition, it has been claimed that an important parameter in the evaluation of the clinical success of sealant materials is marginal adaptation, mainly at the sealant margin 4 .
It is true that the traditional methods of evaluating the integrity of the dental sealants, such as visual and

Conclusions
With the criteria used to evaluate the clinical performance of these materials, it can be concluded that: Similar results in terms of marginal sealant integrity were observed after 3 years; An explorer-probe of the infiltrant presents more regular wear after 3 years of clinical application; Less caries progression occurs after 3 years when the infiltrant is applied on non-cavitated fissures in the radiographic analysis; Resin infiltration seems to be suitable to prevent caries progression when applied to sealing occlusal non-cavitated pits and fissures.