Resin infiltration revolution in minimal invasive treatment – A review

INTRODUCTION

Dental caries is a multifarious, infectious disease with significant factors as host, bacteria, diet, and time. This process increases demineralization and halts the remineralization of hard tissue over time, leading to negative impacts on children’s oral as well as general health.^[1] White spot lesions (WSLs), also known as early caries lesions, are the first clinical manifestation of enamel caries, having a demineralized porous subsurface layer with a milky opaque white appearance on a smooth surface.^[2] Cavitation is uncommon in early lesions that reach up to the outer half of enamel, that is, E1, but it is likely to occur in lesions that extend into the middle, that is, D2, or inner third, that is, D3, of dentin. For radiolucencies into the outer third of dentin, that is, D1, or inner enamel, that is, E2, uncertainty is common. Therefore, choosing between non-operative and restorative methods at these stages is challenging due to the possibility of either receiving too little or too much treatment.^[3] Therefore, there was a requirement for treatment that lies between prevention and restoration. Restorative therapy is invasive, leading to extensive tooth destruction, evokes dental anxiety toward drilling thus leading to evasive behavior in kids.^[4] Performing operative procedures during restorative treatment in children is quite effortful to carry out and may call for specialized behavior management techniques.^[5] Nowadays, there is a shift in dentistry from an operative to a preventive approach, giving way to non-invasive treatment preventing healthy tooth structure and longer tooth life.^[6]

WSLs have various influences such as hypoplastic enamel, initial enamel caries, demineralization due to orthodontic treatment, and fluorosis. Frosted or whitish appearance of enamel is said to be due to a difference in optical density and loss of mineral content from the inner layer or surface of enamel.^[2] The treatment of choice for initial caries lesion is remineralization, and remineralization of teeth surface is achieved by various methods, like topical fluoride and casein phosphopeptide amorphous calcium phosphate application, bleaching of teeth, veneering of teeth having white spots, and microabrasion. Remineralization of tooth structure is an efficient method but has limited cosmetic impact as it is confined only up to the surface of the lesion. Treatment by remineralization is time investing and shows appreciable result if applied once the lesion develops.^[5] Microabrasion and bleaching methods may cause post-operative discomfort and have less satisfying esthetic outcomes, whereas veneers are a highly invasive procedure.^[7]

To overcome these problems recently, a minimally invasive technique called resin infiltration has been introduced and is intended to fill the gap between restoration and prevention by occluding and strengthening the pores of non-cavitated early caries lesions.^[8] The goal behind the introduction of resin infiltration is to stop the early stages of an enamel caries lesion by allowing a low-viscosity resin to penetrate the enamel and block the diffusion paths for dissolved minerals and acids.^[9] Resin infiltration proves to be a superior alternative due to its microinvasive property, tooth conservation, arrest of lesion progression, deep occlusion in porous demineralized areas, and ability to be completed in a single visit, thus reducing chairside time. In addition, this technique needs no anesthesia, which makes the treatment needle-free and highly acceptable for children.^[10]

Robinson et al., (1976) have among the first to explain the use of resorcinol formaldehyde resin in the infiltration approach for carious lesions.^[11] In 2007, in an effort to create the best resins for infiltrating enamel lesions, bisphenol A-glycidyl methacrylate (BISGMA), urethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), and hydroxylethyl methacrylate (HEMA) monomers in various viscosities and weight proportions were examined.^[12] In September 2009, Sebastian Paris and Hendrik Meyer-Lueckel from Charité Medical University in Berlin introduced the “infiltrant,” and it was marketed by Dental Milestones Guaranteed (DMG) dental Company in Hamburg, Germany, under the Icon brand that became well-liked for cosmetic reasons.^[13] The American Academy of Pediatric Dentistry, in 2017, considered resin infiltration in its reference manual and came to the recommendation that there was evidence for using RI as a treatment for small, non-cavitated interproximal carious lesions in permanent teeth.^[14] In the same year, the American Dental Association (ADA) established a Current Dental Terminology code (D2990) for the use of resin infiltration in smooth surface lesions after obtaining positive research results for this material.^[15] In 2018, new guidelines from the ADA recommended the use of resin infiltration for interproximal incipient carious lesions.^[16]

Resin infiltration is comprised of the following, according to the manufacturer [Table 1].^[17]

• Icon resin infiltrant – Smooth surface [Figure 1]

  

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  Figure 1:

  Smooth icon kit.

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• Icon resin infiltrant – Interproximal surface [Figure 2].

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Figure 2:

Proximal icon kit.

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The idea behind caries arrest with resin infiltration is to clog the micropores developed during the initial caries process and stop further acid dissolution through those micropores. The surface layer of enamel is removed first, as the surface layer of the lesion acts as a barrier to the functioning of resin infiltration.^[5] These are low-viscosity TEGDMA-based resins which are light curable and have low viscosity, low contact angles to the enamel, and a high surface tension that helps the resin to completely penetrate the porous lesion by capillary force. In the second step, after application resin infiltrates into the porous enamel and forms a covalently bound three-dimensional polymer framework that replaces the lost minerals, encapsulates the hydroxyapatite crystals, interlocks the remaining enamel prisms by micromechanical bond, and acts as an effective barrier for hydrogen ions [Figure 3]. These hydrogen ions inhibit further demineralization and arrest subsurface lesion progress. In the process of infiltrating the non-cavitated lesion, an additional benefit is seen, that is, masking of the lesion. This masking of the lesion occurs due to negligible variation in the refractive indices between sound enamel (1.62) and resin infiltration (1.46), resulting in less scattering of light.^[18]

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Figure 3:

(a) Initiation of caries by infiltration of acid (H⁺) of sub-surface porosities (red dots) and leaching of calcium and phosphate ions (yellow lines - dentin, white - enamel, inward arrow - acid infiltration, outward arrow - leaching of calcium and phosphate ions), (b) Post treatment, pores are closed by the occluding resin (green dots), blocking the advancement of caries (green dots -infiltrated resin, revert back yellow arrow - inhibition of infiltration of hydrogen ion). H⁺: Hydrogen ion, Ca²⁺: Calcium ion, PO₄^3-: Phosphate ion.

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PHYSICAL PROPERTIES

Enamel like optical characteristics lead to improvement of esthetics as the pores of carious lesions are incorporated by water and air having refractive index (RI) of 1 and 1.33 which is closer than that of the surface infiltrated by resin (RI = 1.42–1.44) than healthy enamel (RI = 1.62), which makes this material suitable for masking WSL.^[19] Molecular weight is the sum of the atomic weights of all atoms in a molecule. Molecular weight of resin infiltration is lower around 286.32 g/mol due to presence of TEGDMA as a component.^[18] Viscosity is a measure of fluid resistance to flow. It is a low viscosity monomer (0.006) at 25°C. The contact angle is the angle between the liquid and the solid surface where they meet. Resin infiltration has a low contact angle to the enamel and high surface tension. These properties help in better penetration of resin into the body of the lesion.^[18] Permeability coefficient is the rate at which a fluid can move through a porous material. Permeability coefficient of resin infiltration is 273 cm/s, leading to greater penetration depth. [20] It is the physical property of a molecule that causes it to be insoluble in water. Resin infiltration is a hydrophobic monomer; therefore, application of ethanol prior, improves the efficacy of penetration, forming resin-infiltrated layer. Surface micro-hardness for sound human enamel is 352 Hardness Vickers Number (HVN) and for carious enamel is 0.29–3.29 GPa, while after application of resin infiltration, microhardness ranges between 33 HVN and 0.32 GPa.^[21]

FACTORS AFFECTING APPLICATION OF RESIN INFILTRATION

Method of application of resin infiltration has an influential effect on removal of surface layer. In the course of application of acid gel, etching brush applicator removes surface layer 2.7 times greater than sponge applicator, that is, 1.7 times, as mechanical friction caused by the brush applicator is more, and produces significant porous enamel surface.^[22] Depth of non-cavitated lesion has a direct impact on penetration of infiltrant. The likelihood of a full infiltration will decrease with the depth of the carious lesion.^[23] Isolation of the working field also exerts influence on the penetration of resin infiltration. TEGDMA monomer is an active component of resin infiltration which is hydrophobic in nature; therefore, before application resin infiltration requires complete dry field.^[24]

INDICATIONS

• It is advisable in case of sub-surface or porous lesions of enamel and shows good results up to International Caries Detection and Assessment System (ICDAS) codes of 2 and 3. These ICDAS codes can be confirmed by an additional detecting tool bitewing radiograph.^[25]

• It is strongly recommended to be used for the treatment of lesions that are present in the inner enamel (E2) or the outer third of dentin (D1).^[25]

• Resin infiltration has the ability to hide discoloration caused by decalcified carious lesions, developmental defects of enamel, and post-orthodontic decalcification spots.^[25]

• Resin infiltration is used widely to mask WSLs in kids, youngsters, and adults of all ages.^[10]

CONTRAINDICATIONS

• Resin infiltration is contraindicated in a few cases as it can be counterproductive and may have minimal benefit even after application. It is not recommended in case of deep-seated lesions of enamel or cavitated enamel due to a negligible masking effect.

• It should not be used in patients with any known allergy, intolerance to monomer, or any material component.

• Resin infiltration is not advisable in cases of exposed dentin or cementum surface, as it may lead to pain in the patient by interaction with vital tissues, as well as in severe levels of fluorosis, because it reduces the snow white appearance only to a limited extent.^[25]

ADVANTAGES

Resin infiltration, considered as a novel approach toward uncovering new scopes in microinvasive dentistry, offers a number of advantages which make its unique among other restorative materials. It is considered as first intermediate treatment of choice between preventive and restorative therapies, thus leading to preservation and maintenance of sound tooth structure. Resin infiltration mechanically stabilizes demineralized enamel by occluding subsurface porosities permanently. It strengthens the body of the lesion by acidic decalcification and delays restorative intervention for a longer period of time. It leads to easy access to proximal WSL than restoration procedure, thus reduces the risk of periodontitis and gingivitis, as well as lowers down chance of secondary cavities. As this treatment approach is recommended to be used up to the outer layer of dentin, there is no risk of post-operative sensitivity and pulpal irritation. It is user-friendly, convenient with simple application, therefore reducing the chair time. These qualities make resin infiltration a good treatment of choice in children and have high acceptance also. It is highly advised in case of aesthetic concerns, especially for labial surface lesions.^[25]

DISADVANTAGES

Resin infiltration has numerous benefits with few disadvantages, like initial lesion conditioning, which is necessary as early caries lesions have a hypermineralized surface layer that prevents resin from penetrating the demineralized area. After application of resin infiltration, it releases unreacted monomers from TEGDMA and which may cause acrylate allergies and allergic contact dermatitis. Dry working field is necessary for better penetration of resin as it is hydrophobic in nature.^[25]

Resin infiltration is a successful microinvasive approach, even though some short-term potential drawbacks are addressed. Therefore, recently, superior alternatives are now being tried to overcome these drawbacks. For the infiltration of initial proximal lesions, a new glass-based substance called Wroclaw, Poland, is made up of ethanol and 15% hybrid-glass monomer. This hybrid glass material is a transparent, low viscosity, and inorganic-organic hybrid polymer obtained using the sol-gel technique that self-cures quickly after application. Incorporation of silica core with an organic side chain gives the substance particular qualities. Hybrid-glass-based material is acid resistant. It can create a smooth, glassy surface that reduces plaque accumulation and acts as an effective diffusion barrier.^[26]

When nanohydroxyapatite (Sigma-Aldrich) is added to resin in concentrations of 5% and 10%, it has been observed that the artificially created enamel caries surfaces are improved in terms of penetration of resin, smooth surfaces, and mineral density.^[27] Colloidal silica infiltrate is used as another alternative to resin infiltration. It is manufactured by Zephyr Chemicals, Navi Mumbai, Maharashtra, and composed of 29.6 weight percentage suspension of silica in water pH at 25°C, with average particle diameter: 8.3 nm and stabilizing counter ion: Sodium. Colloidal silica nanoparticles exhibit mineralization potential by acting as a scaffold, assisting in the formation of hydroxyapatite crystals, and mineralizing the dentinal collagen matrix at high pH levels. These nanoparticles lower the energy barrier in the collagen’s inter- and intrafibrillar gaps, which ultimately affects the development of inorganic ion clusters. The study showed that colloidal silica nanoparticle-treated demineralized dentin has a significant potential for remineralization, recovering 16% of its mineral volume and restoring over 20% of its phosphate levels.^[28]

CONCLUSION

Infiltration of resins into cavitated micropores has created a novel approach in the treatment of early carious lesions, thus meeting the goals to deliver the least invasive esthetic procedure. In the realm of minimally invasive dentistry techniques, the suppression of caries progression through infiltration is currently being investigated as a substitute for more invasive therapies. Resin infiltration technique nowadays is soaring high, as they not only provide esthetic rehabilitation but also arrest lesion progression as well as allow recovery from hypomineralization. Therefore, it is considered an upcoming microinvasive approach for the management of non-cavitated lesions and opens up more research and scopes in microinvasive dentistry.