Long-term stability of dentin matrix following treatment with various natural collagen cross-linkers

Abstract

Objectives: Collagen disorganization is one of the main degradation patterns found in unsuccessful adhesive restorations. The hypothesis of this study was that pretreatment using natural collagen cross-linking agents rich in proanthocyanidin (PA) would improve mechanical properties and stability over time of the dentin collagen and, thus, confer a more resistant and lasting substrate for adhesive restorations.

Methods: PA-based extracts, from grape seed (GSE), cocoa seed (CSE), cranberry (CRE), cinnamon (CNE) and açaí berry (ACE) were applied over the demineralized dentin. The apparent elastic modulus (E) of the treated dentin collagen was analyzed over a 12 month period. Specimens were immersed in the respective solution and E values were obtained by a micro-flexural test at baseline, 10, 30, 60, 120 and 240 min. Samples were stored in artificial saliva and re-tested after 3, 6 and 12 months. Data was analyzed using ANOVA and Tukey test.

Results: GSE and CSE extracts showed a time-dependent effect and were able to improve [240 min (MPa): GSE = 108.96 ± 56.08;CSE = 59.21 ± 24.87] and stabilize the E of the organic matrix [12 months (MPa): GSE = 40.91 ± 19.69;CSE = 42.11 ± 13.46]. CRE and CNE extracts were able to maintain the E of collagen matrices constant over 12 months [CRE = 11.17 ± 7.22;CNE = 9,96 ± 6.11;MPa]. ACE (2.64 ± 1.22 MPa) and control groups immersed in neat distilled water (1.37 ± 0.69 MPa) and ethanol-water (0.95 ± 0.33 MPa) showed no effect over dentin organic matrix and enable their degradation and reduction of mechanical properties.

Significance: Some PA-based extracts were capable of improving and stabilizing collagen matrices through exogenous cross-links induction.

Figure 1

Illustration of experimental steps. A – samples cutting; B – dentin restangular beams; C – dimensions of samples and dimple; D – phosphoric acid demineralization for 5 hours; E – immersion in solutions for time periods; F – schematization of micro-flexural test for apparent elastic modulus assessment.

Figure 2

Influence of proanthocyanidin-based agents on the stiffness of demineralized dentin (MPa) in different incubation times (min). GSE- grape seed extract; CSE- cocoa seed extract; ACE- açaí berry extract; CRE- cranberry extract; CNE- cinnamon extract; DW- distilled water; ETW- ethanol-water.

Figure 3

Elastic modulus of cross-linked dentin for long-term periods. A-Elastic modulus of demineralized dentin treated with GSE (grape seed extract) storage for several time periods. B - Elastic modulus of demineralized dentin treated with CSE (cocoa seed extract) storage for several time periods. C - Elastic modulus of demineralized dentin treated with ACE (açaí berry extract) storage for several time periods. D - Elastic modulus of demineralized dentin treated with CRE (cranberry extract) storage for several time periods. E - Elastic modulus of demineralized dentin treated with GSE (grape seed extract) storage for several time periods. E - Elastic modulus of demineralized dentin treated with CNE (cinnamon extract) storage for several time periods. F - Elastic modulus of demineralized dentin treated with DW (distilled water) storage for several time periods. G - Elastic modulus of demineralized dentin treated with ETW (ethanol-water) storage for several time periods. NOTE: Different scales for each graph.