Effect of dentin biomodification delivered by experimental acidic and neutral primers on resin adhesion

Abstract

Objectives: Proanthocyanidins (PACs) are biocompounds mimicking native collagen cross-links. The effective and practical delivery of any biocompound is pivotal for clinical usage. The aim was to investigate the dentin biomodification and effective formation of dentin-resin biointerfaces of two highly bioactive PAC-rich extracts, Vitis vinifera (Vv) and Camellia sinensis (Cs), delivered using neutral (NP) or acidic (AP) rinse-out primer approaches.

Methods: The depth of dentin demineralization (optical profilometry), dentin biomodification (apparent modulus of elasticity, collagen auto-fluorescence) and properties of dentin-resin interfaces (microtensile bond strength - μTBS, and micro-permeability) were investigated. NP consisted of either 15% Vv or Cs applied for 60 s after surface etching; while AP contained 15% Vv or Cs in either 35% glycolic acid or tartaric acid applied for 30 s or 60 s. Data were analyzed using ANOVA and post-hoc tests (α = 0.05).

Results: The depth of demineralization was statistically higher when applied for 60 s, regardless of rinse-out primer approach (p < 0.001). Compared to the AP strategy, NP exhibited statistically higher apparent modulus of elasticity, regardless of PAC extract (p < 0.001). Highest μTBS were obtained for NP_Vv, which were statistically similar to AP_GAVv, when applied for 60 s (p < 0.001); both resulted in a dramatic decrease of the interfacial permeability. NP_Cs group showed the lowest μTBS (p < 0.001).

Conclusions: A combination of high bond strength and low micro-permeability can be accomplished using glycolic acid with the mid- and high-PAC oligomer enriched extract (Vv). Cs extract containing mostly catechins and dimeric PACs, was found unsuitable for resin-dentin adhesion despite exhibiting high initial dentin biomodification.

Clinical significance: This study provides a new conceptual delivery of PAC-mediated dentin biomodification and conservative dentin surface etching using rinse-out primers. The strategy requires a specific combination of PAC source, α-hydroxy acid, and application time.

Keywords: Alpha-hydroxy acids; Bond strength; Collagen; Dentin; Mechanical properties; Optical profilometry; Proanthocyanidins.

Figure 1.

Results of the dentin etching depth of acidic primers (AP), glycolic (GA) and tartaric acid (TA) by digital profilometry. (A) Representative digital profilometry images of the depth of dentin demineralization treated with AP applied for 60 s. (B) Results of the demineralization depth (ΔZ, μm) of dentin surface for 30s and 60 s application times. Symbol (δ) depicts statistically significant difference between application times (p < 0.05) Vv: Vitis vinifera, Cs: Camellia sinensis, GA: glycolic acid, TA: tartaric acid. T: treated surface, UT: untreated surface.

Figure 2.

Representative confocal laser scanning microscopy overlapping images of the resin-dentin interfaces show collagen auto-fluorescence (green) and interfacial micro-permeability (red) of experimental groups of neutral (A) and acidic (B) primers. GA: glycolic acid; TA: tartaric acid. Magnification set at 50 μm scale bar.