Equivalence study of the resin-dentine interface of internal tunnel restorations when using an enamel infiltrant resin with ethanol-wet dentine bonding

Abstract

This preregistered ex vivo investigation examined the dentinal hybrid layer formation of a resinous infiltrant (Icon), with reference to both thickness (HLT) and homogeneity when combined with modified tunnel preparation (occlusal cavity only) and internal/external caries infiltration. The adhesives Syntac and Scotchbond MP were used as controls (Groups 1 and 3) or in combination with Icon (Groups 2 and 4). A split-tooth design using healthy third molars from 20 donors resulted in 20 prepared dentine cavities per experimental group. The cavity surfaces (n = 80) were etched (37% H₃PO₄), rinsed, and air-dried. Rewetting with ethanol was followed by application of the respective primers. After labeling with fluorescent dyes, either Syntac Adhesive/Heliobond or Scotchbond MP Adhesive was used alone or supplemented with Icon. HLT, as evaluated by scanning electron microscopy, did not significantly differ (P > 0.05), and confocal laser scanning microscopy revealed homogeneously mixed/polymerized resin-dentine interdiffusion zones in all groups. Icon can be successfully integrated into an ethanol-wet dentine bonding strategy, and will result in compact and homogeneous hybrid layers of comparable thickness considered equivalent to the non-Icon controls, thus allowing for preservation of the tooth's marginal ridge and interdental space in the case of internal/external infiltration of proximal caries.

Keywords: Confocal laser scanning microscopy; Dental adhesives; Dentine bonding; Ethanol-wet bonding; Hybrid layer; Icon; Resin infiltration; Scanning electron microscopy; Scotchbond multi-purpose; Split-tooth design; Syntac.

Figure 1

Flowchart presenting the group assignment/randomization and experimental setup.

Figure 2

Scanning electron microscopic (SEM) characterization revealing the bonded interfaces under various conditions (magnification factor of 400×). (a) Group 1 (control, Syntac Primer/Adhesive plus Heliobond); (b) Group 2 (Syntac Primer/Adhesive plus Icon plus Heliobond); (c) Group 3 (control, Scotchbond MP Primer plus Scotchbond MP Adhesive); and (d) Group 3 (Scotchbond MP Primer plus Icon plus Scotchbond MP Adhesive). With each specimen, the restoration (with filler particles), the adhesive layer, the (partially etched) hybrid layer, and the dentinal tubules (along with resin tag formation) are clearly visible. SE secondary electron mode.

Figure 3

Box-and-whisker plots presenting the outcome referring to scanning electron microscopy (SEM) assessments of the widths of the 4 groups’ resin-dentine interdiffusion zones (hybrid layer thickness). Horizontal lines splitting the boxes indicate medians/second quartiles ($\tilde{\text{x}}$/Q2), and boxes define upper and lower quartiles, while the ends of the whiskers are set at 1.5× interquartile range above the third quartile (Q3) and at 1.5× interquartile range below the first quartile (Q1). Minimum or maximum values lying outside this range are shown as outliers (○), and crosses (×) denote means ($\overline{\text{x}}$). Given P values indicate non-significant differences after t testing between groups, and upper (Δ_U) and lower (− Δ_L) equivalence bounds representing ± 25% and ± 10% of the controls’ means are indicated as transparent grey and green areas, respectively.

Figure 4

Representative confocal laser scanning microscopy (CLSM) image (using an oil-immersion objective with a magnification factor of 63×) of a Group 2 specimen (Syntac Primer/Adhesive plus Icon plus Heliobond). A well mixed resin-dentine interdiffusion zone (composed of FITC-labeled Syntac Adhesive and RITC-labeled caries infiltrant resin) was clearly visible by means of optical sectioning, thus revealing a homogeneous hybrid layer (HL), along with an adhesive layer (AL). Due to imaging restrictions to the thin z-plane, only resin tags (RT) occluding the dentinal tubules are partially portrayed. Mag magnification, NA numerical aperture, WD free working distance.

Figure 5

Illustrative scanning electron microscopy (SEM) micrograph, run in secondary electron (SE) imaging mode, of a representative Group 2 specimen (Syntac Primer/Adhesive plus Icon plus Heliobond) observed at a magnification factor of 650×. Note the only partially preserved adhesive–dentine interface, along with the completely dissolved dentine, now unveiling numerous noninterrupted resin tags revealing the excellent penetration capacity. AL adhesive layer, HL hybrid layer, RT resin tags.

Figure 6

Graphical representation of the present study’s rationale. (a) Proximal caries lesion revealing demineralized (but noncavitated) enamel (illustrated by means of a reflected-light microscope); after preparation of a small but adequate occlusal access cavity, the dentine caries will be excavated using a rose-head bur (or, alternatively, with a PolyBur [Komet]). (b) Polarized light microscopy image of the same tooth’s thin section (modified from, with permission); after etching and using the ethanol-wet dentine bonding technique, the resin infiltrant will be applied using a microbrush, thus allowing for both internal resin infiltration (IRI) of the enamel lesion and dentine bonding (DB). (c) Confocal laser scanning microscopy image (dual fluorescence mode) revealing the adhesive layer, hybrid layer, and resin tag formation. Treatment will be finished by means of an adhesive Class I (occlusal) composite resin restoration as well as by external resin infiltration (ERI), thus stabilizing and protecting the enamel lesion.