The susceptibility of occlusal surfaces to dental caries has been recognized for more than two centuries and remains a subject of continuous clinical and scientific interest. The complex morphology of pits and fissures on molars promotes plaque retention and creates conditions favorable for cariogenic biofilm development, rendering these surfaces particularly vulnerable despite advances in preventive dentistry.^[1]

Early attempts at occlusal caries prevention date back to the beginning of the 20th century. In 1905, Willoughby Miller reported the antibacterial properties of silver nitrate and proposed its application to occlusal surfaces to reduce microbial colonization.^[2] Subsequently, in 1921, Hyatt introduced the concept of prophylactic Class I cavity preparation followed by amalgam restoration on sound permanent molars as a preventive measure against occlusal caries development.^[3] For several decades, preventive strategies were largely based on mechanical alteration of pits and fissures aimed at reducing plaque retention. However, these approaches were characterized by questionable preventive efficacy and often resulted in unnecessary removal of healthy tooth structure, while simultaneously contributing to artificially increased DMF index values.^[3,4]

A decisive shift toward conservative prevention occurred with the advent of adhesive dentistry. The development of the acid-etch technique by Buonocore in 1955, followed by the introduction of resin-based materials such as bisphenol A-glycidyl methacrylate (Bis-GMA) in the late 1960s, enabled the concept of sealing rather than removing susceptible tooth structures.^[4,5,14] Pit and fissure sealants emerged as a minimally invasive and evidence-based method for occlusal caries prevention, demonstrating superior clinical outcomes compared with earlier invasive approaches.^[6]

Over subsequent decades, preventive materials have undergone continuous development. Resin-based sealants evolved through multiple generations with improvements in polymerization, filler content, and wear resistance.^[6,7] Glass ionomer cements introduced chemical adhesion and sustained fluoride release, expanding preventive options in patients with high caries risk or compromised moisture control.^[8] More recently, hybrid materials such as compomers and giomers have been developed to combine the mechanical properties of resin composites with the fluoride-releasing and bioactive characteristics of glass ionomer-based systems.^[9-11]

By definition, a sealant is an organic polymer applied to the occlusal surface after acid etching of enamel.^[11] Until the mid-1960s, the most common prophylactic occlusal sealant material was methyl cyanoacrylate.^[12,13] One-year outcomes showed 71% material retention and an 87% reduction in caries. However, long-term use revealed poor resistance to bacterial invasion and compromised performance.^[2]

Sealants developed over time are classified based on various criteria. In 1965, Bowen introduced a Bis-GMA-based sealant characterized by bacterial resistance and stable bonding to etched enamel.^[12] Composite sealants consist of an oligomeric Bis-GMA matrix and inorganic silica filler, linked via a coupling agent such as silane.^[15] The first commercially introduced sealant, Nuva-Seal (LD Gaulk, Milford, DE), appeared in 1971.^[16-18]

Based on polymerization mechanism, sealants are grouped into four generations:

To enhance wear resistance, fillers such as glass beads, quartz particles, sodium fluoride, zirconia, or silica were added to sealants.^[25,26] Sealants can thus be categorized as either filled or unfilled. Notably, adoption of filler increases viscosity, which inversely affects penetration and retention—unfilled sealants exhibit deeper fissure penetration and stronger adhesion.^[27-29]

Sealants may be clear, opaque, or colored.^[30] White or tinted sealants facilitate evaluation of application accuracy and material wear during follow-up.^[31]

The preventive and therapeutic efficacy of sealants is enhanced by fluoridation. Two mechanisms have been identified for the introduction of fluoride ions: (1) adding soluble fluoride salts into the unset sealant, which release ions post-application, although this may compromise mechanical properties; and (2) incorporating organic fluoride compounds into the sealant structure, where ions are released via anion exchange without weakening the matrix.^[32]

Most dental materials elevate enamel surface energy and tend to retain bacterial biofilm at restoration margins. Fluoride reduces surface energy and inhibits enamel demineralization during acid attacks. Additionally, fluoride inhibits bacterial growth and may exhibit lytic effects on cariogenic strains like S. mutans.^[54]

Fluoridated sealants thus provide both a mechanical barrier and facilitate remineralization. The long-term fluoride-release capacity of composite sealants and glass-ionomer cements correlates with reduced caries incidence in children.^[32] For instance, the glass-ionomer cement Fuji Triage releases a high initial burst of fluoride in deionized water during the first week, followed by sustained lower-level release.^[32] Composite sealants exhibit a pronounced 24-hour “burst effect,” followed by gradual decline.^[33,34]

The reservoir capability of a material depends on its type, permeability, frequency of fluoride exposure, and fluoridating agent concentration.^[32] Glass-ionomers have superior reservoir properties compared to composites^[35], likely due to loosely bound water and soluble components that permit ion exchange via diffusion. Materials with high permeability can absorb fluoride deeply, while less permeable ones absorb it only superficially.^[35] Consequently, the modest increase in fluoride release from composite sealants after exogenous fluoride exposure is attributed to surface adsorption. Overall, variants with high initial fluoride release exhibit greater recharge capacity.^[32]

These materials combine composite and GIC properties. Polyacid-modified composite resins (compomers) were introduced as restorative materials in 1990.^[52] They offer lower viscosity and good flowability, enabling excellent penetration. Compared to conventional GICs, compomers demonstrate improved adhesion to tooth structures and lower solubility in water.^[52,53] However, their fluoride release is lower and less effective than that of conventional or resin-modified GICs.^[54]

Giomers are urethane-based materials containing pre-reacted glass-ionomer filler particles, which impart fluoride release, although at significantly lower levels than GICs.^[50,55,56] They represent a class of composites offering caries protection and favorable functional and esthetic outcomes via incorporation of pre-reacted glass fillers.^[57] Marginal adaptation and postoperative sensitivity are comparable to those of composites and giomers, but the risk of secondary caries is reduced with newer materials.^[57] Bioactive glass in giomers dissolves upon contact with biological fluids, enabling therapeutic release of phosphate, fluoride, and calcium ions, thereby enhancing apatite formation.^[10,58] Their use is recommended across all restoration classes, particularly in high-risk caries patients, for correct restorative of gingival esthetics in cervical areas using existing gingival-shade liners and sealants.^[57]

The bioactive glass components in giomers dissolve upon contact with biological fluids, enabling therapeutic release of phosphate, fluoride, and calcium ions that may enhance apatite formation and remineralization.^[9] A randomized clinical study comparing giomer‑based sealants versus conventional resin‑based sealants found similar retention rates and caries preventive effects over a 12‑month period in permanent molars with non‑cavitated fissures, suggesting that giomer capture of caries risk reduction may be on par with resin when adequately applied.^[11] This indicates that, despite material differences, both giomer and resin sealants can be clinically effective in short‑term caries prevention. Another randomized clinical trial specifically evaluated giomer S‑PRG pit and fissure sealants with or without preparatory enamel etching over one year and demonstrated that performing an etching step significantly enhanced retention rates, with etched giomer sealants showing higher survival than unetched application.^[11] These findings underscore the importance of clinical technique in optimizing hybrid sealant performance. While direct long‑term randomized data comparing compomers and giomers are limited, a clinical comparative study of multiple sealant materials including compomer demonstrated that compomer sealants can achieve intermediate retention levels between resin‑based and GIC sealants over 24 months, with no new caries formation observed in both compomer and resin groups throughout follow‑up.^[4,6] This supports the concept that compomers provide a balance between mechanical performance and cariostatic benefit, though retention declines over time. Although not focused exclusively on hybrid sealants, broader clinical evidence consistently shows that retention rates vary substantially by material type and that resin‑based sealants generally outperform other categories in long‑term retention, whereas differences in caries incidence across materials tend to diminish when sealants are properly maintained.^[1,3]

The available clinical evidence includes randomized trials and comparative studies with follow‑up periods ranging from 12 to 24 months. While these provide useful insights, limitations exist due to heterogeneity in study designs, sealant application methods, and outcome measures. Longitudinal data beyond 2 years remain relatively sparse, and systematic reviews indicate that further high‑quality trials with standardized retention and caries outcomes are needed to strengthen clinical recommendations, particularly for hybrid sealant classes.^[1,3]

Recent systematic reviews provide robust evidence supporting the clinical effectiveness of pit and fissure sealants in caries prevention, while simultaneously highlighting material-dependent differences in retention, fluoride release, and handling characteristics (Table 1). According to the comprehensive review by Ng et al.^[1], resin-based sealants consistently demonstrate superior retention compared with glass ionomer-based materials, which is largely attributed to their micromechanical bonding to etched enamel. This finding is further corroborated by clinical meta-analyses showing that retention remains a key determinant of long-term caries prevention when optimal isolation is achieved.^[2,6]

Conversely, systematic reviews focusing on fluoride dynamics emphasize the distinctive advantage of glass ionomer-based sealants. Dobrzyński et al.^[3] reported that glass ionomer materials exhibit significantly higher fluoride release and recharge capacity compared with resin-based sealants, which may compensate for their comparatively lower retention in high caries-risk populations. This cariostatic potential has been identified as particularly relevant in pediatric dentistry and in clinical scenarios where moisture control is compromised, as also discussed in ART-based systematic evaluations.^[5]

Hybrid materials such as compomers and giomers represent an attempt to combine the mechanical advantages of resin-based sealants with the bioactive properties of glass ionomers. However, recent systematic evidence suggests that these materials generally exhibit intermediate behavior rather than a true synergistic effect. Fluoride release from compomers and giomers is consistently lower than that of conventional glass ionomers, while their retention performance remains variable and product-dependent.^[3,4,9] Importantly, long-term meta-analytical data on giomer sealants remain limited, restricting the strength of clinical recommendations regarding their routine use.

Overall, the current body of systematic reviews and meta-analyses supports a risk-based and context-specific approach to material selection. Resin-based sealants remain the material of choice in low caries–risk patients under ideal isolation conditions, whereas glass ionomer sealants offer a clinically justified alternative in high caries-risk settings and pediatric populations where fluoride release and moisture tolerance are prioritized.^[3,5,6] Future high-quality meta-analyses with standardized outcome measures are needed to clarify the long-term clinical performance of hybrid sealant materials and to strengthen evidence-based guidelines.

Contemporary prevention of occlusal carious lesions is based on minimally invasive, adhesive, and fluoride-releasing materials supported by clinical evidence. Resin-based sealants provide the most predictable long-term retention under optimal isolation conditions, whereas glass ionomer cements represent a suitable alternative in high caries-risk patients and in situations with compromised moisture control due to their fluoride release. Hybrid materials demonstrate intermediate clinical performance, but current evidence is limited by short follow-up periods. Preventive material selection should be individualized according to caries risk and clinical conditions, and further long-term clinical studies are required to clarify the role of hybrid sealants.