Resin Infiltration Technique for Proximal Caries Lesions in the Permanent Dentition: A Contrarian Viewpoint

Minimal intervention dentistry has been promoted as the contemporary science-based paradigm in operative dentistry.¹ The FDI task group reviewing minimal intervention dentistry cautioned in 2012 that one of the procedures, resin infiltration technique, while promising, needed more clinical evidence for conclusive findings.¹ The aim of this brief commentary is to consider the use of resin infiltration technique for proximal caries lesions in the permanent dentition.

Resin infiltration technique was first described in the 1970s for conservative management of noncavitated smooth surface caries lesions but did not find acceptance following preliminary reports indicating dismal clinical application in proximal surfaces of premolars in vivo.^2,3,4 The resin infiltration technique has recently been reinvigorated and suggested for proximal caries “lesions extending radiographically into inner enamel or the outer third of dentin” with the intent to avoid the first restoration and its consequent retreatments.⁵

It has been recently remarked that resin infiltration may not be appropriate for proximal caries lesions in primary molars, the better alternative being remineralization for enamel lesions and conventional restorations for those lesions into dentin.⁶ In a similar vein, promotion of remineralization may be a better option than resin infiltration for proximal lesions in permanent enamel for the following reasons:

1. There is slow progression of enamel caries lesions with “an average of four years for a lesion to progress through the enamel of permanent teeth.”⁷

2. The resin infiltration technique may further undermine the structural underpinning of enamel caries lesions with its relatively intact surface layer and more demineralized subsurface area.⁸ It has been shown that, compared to sound enamel, there are large reductions in elastic modulus (up to 83% lower) and hardness (up to 91% lower) in natural proximal noncavitated caries lesions in premolars, whereas the intact surface layer of enamel of the caries lesion had the least reduction (34%) in mechanical properties.⁹ The surface layer of enamel has, however, been identified as a barrier impeding resin infiltration into the body of the caries lesion.¹⁰ Resin infiltration technique therefore requires acid conditioning (15% HCl for 2 minutes) in order to remove the enamel surface layer and enhance penetration of the resin infiltrant.¹⁰ This acid conditioning thus results in the removal of the residual strongest component of an already weakened tooth structure within the caries lesion. The importance of the surface layer is also alluded to by a study in bovine enamel using 37% phosphoric acid for 5 seconds instead, which found that subsequent infiltration with various resins increased “both microhardness and demineralization resistance of enamel caries lesions.”¹¹

3. Removal of the surface layer of enamel during resin infiltration technique also renders moot the potential for remineralization.¹² Promoting remineralization of the carious enamel without resin infiltration would result in the healed tooth structure being more resistant to acid dissolution than normal enamel.¹³

Definitive restorations in permanent teeth for proximal lesions that are not amenable to remineralization may be a better option than resin infiltration for the following reasons:

1. The dentino-enamel junction may be considered the Rubicon of treatment threshold for surgical intervention since a compilation of data regarding proximal caries lesions in permanent teeth “found an increasing proportion of cavitated lesions with increasing radiographic depth.”¹⁴ It has been reported that in bitewing radiographs of permanent teeth, 11% of the lesions in the inner half of enamel had cavitation, with the proportion of cavitated lesions increasing on breaching of the dentino-enamel junction to 41% for lesions in the outer half of dentin and 100% for lesions in the inner half of dentin.¹⁵ This concept is prudently reflected in clinical practice with ∼90% of dentists in a practice-based research network reporting that regardless of caries risk, they would restore a proximal lesion involving the outer one-third of dentin in a lower premolar tooth.¹⁶

2. Subsequent to 2-minute etch treatment, resin infiltration initially increased the microhardness of caries lesions in bovine enamel; however, there was a reduction in microhardness following acid challenge, likely due to either resin shrinkage or dissolution of the remaining mineral within the body of the lesion.¹⁷ Definitive restorations, though seemingly more drastic, may therefore be more pragmatic than resin infiltration since longitudinal caries data (birth to 32 years of age) have shown caries rate to be constant over the years.¹⁸

Robinson, who pioneered the resin infiltration technique in the 1970s, reported in a 2011 review that the contemporary technique lacked resolution of some methodological concerns and therefore recommended that it be restricted to “accessible and relatively superficial lesions.”¹⁹ Use of the resin infiltration technique for proximal lesions in the permanent dentition therefore warrants further research prior to its application in clinical practice.