A laboratory study using a split-tooth design to analyze the micromorphology of the resin-dentin interface when combining the internal/external resin infiltration of proximal caries lesions and the internal tunnel technique v1
Authors: Dr med dent Dr h c Andrej M. Kielbassa Prof , Summer Sabrina , not provided Julia_batzer 
Published: February 2024

Introduction Previously, both the development and the introduction of the resin infiltration technique1-3 have resulted in a non-invasive treatment regimen of proximal enamel caries, aimed to close the gap between preventive and restorative dentistry, and, thus, obviating any sacrifice of dental tissues, and improving oral health4. In case the low-viscous resin used with this treatment regimen has been applied on de-proteinized enamel lesions5, through capillary forces, major parts of the porous volume of these lesions will be occluded, thereby building a 3D network1 consisting of the infiltrant resin enwrapping the demineralized enamel remnants,re-hardening and stabilizing the lesion6, andparalyzing any progressof the latter. Meanwhile, several independent meta-analyses with acceptable quality7-12 (including an umbrella review13) have consistently revealed that resin infiltration of enamel lesions will be effective in reducing further clinical increase of white-spot lesions in both dentitions, thus providing prompt and acceptable aesthetic outcomes4. However, this refers to lesions restricted to enamel, and it should be highlighted that lesions extending beyond the dentin-enamel junction have never been assessed with the initial developments1,2. Not astonishingly, some studies have revealed a poor outcome of the infiltration technique when used with treating proximal lesions extending into the outer third of the dentin, with a therapeutic efficacy of resin infiltration considered not significantly different from the controls10. Consequently, radiographic lesions extending to outer dentin lesions do constitute either a contra-indication of the resin infiltration technique, or would call for a modified treatment regimen. The latter has been introduced recently14,15, and combines the modified (internal) tunnel technique with both internal and external resin infiltration of the carious enamel lesion. By means of an occlusal approach, the dentin caries can be removed, and the enamel caries can be infiltrated both from inside the cavity and from the proximal site, thus obstructing the porous enamel lesion areas by a doubled infiltration through capillary forces. This leads to a stabilization of the weakened proximal enamel14,15 and should result in increased success rates. When reflecting on the finalrestoration of the occlusal access cavity, an adhesively bonded filling would seem recommendable. However, up to now, no information regarding the morphology of the bonding interface between dentin, dentin bonding agent, caries infiltrant, and resinous restoration is available from the literature. Consequently, the aim of the present laboratory study was to analyse various aspects of the resin-dentin interface after the use of a resin infiltrant (Icon Infiltrant; DMG, Hamburg, Germany) when applied in combination with two commercially available etch-and-rinse adhesive systems (Syntac [Ivoclar Vivadent, Schaan, Liechtenstein] and Adper Scotchbond Multi-Purpose [3M/ESPE, St. Paul, MN, USA]). Primary aim was to study hybrid layer formation, and our null hypothesis stated that neither the thickness of the hybrid layer nor the homogeneity of the latter would differ between test and control groups when evaluated by means of scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM), respectively. Secondary aims pertained to aspects concerning both adhesive layer thickness and resin tag formation.