2023 ACP ANNUAL SESSION

Accelerated Aging of Dentin-Resin Interface Via Thermomechanical and Biochemical Challenges

Jesse Barker, D.M.D., Yoav Finer, D.M.D., Ph.D., F.R.C.D.(C)

Faculty of Dentistry, University of Toronto, Toronto, Ont. Canada M5G 1G6

Abstract

Current in vitro protocols used to artificially age the hybrid layer interface between dentin and resin composite often require lengthy incubation periods. The effects of exposing hybrid layer specimens to biochemical and thermocycling challenges together in vitro may shorten the time required to induce hybrid layer aging.

A recently developed biochemical and thermocycling aging protocol (BC-TC) was found to accelerate the chemical aging of the adhesive resins, significantly increasing the rate of 2,2-Bis[4(2,3-hydroxypropoxy)phenyl] propane (BisHPPP) and drug release in comparison to samples aged by biochemical challenge (BC) alone. The aim of this study is to test the BC-TC protocol to study the chemical and mechanical degradation of hybrid layer specimens incorporating enhanced total-etch adhesive resin formulations.

Octenidine dihydrochloride (OCT), a highly biocompatible cationic surfactant antiseptic molecule with no known bacterial resistance, exhibits broad efficacy against gram-positive and gram-negative bacteria. OCT has been suggested as a candidate to be incorporated into resin adhesives as an antiseptic within the hybrid layer. This ongoing study investigates whether in-house total-etch resin adhesive containing drug-eluting molecules loaded with OCT imparts a protective effect when exposed to BC-TC protocol.

Dentin-composite specimens are prepared, exposed to BC-TC artificial aging protocol using simulated human salivary esterase (SHSE) with thermocycling, and tested for fracture toughness (K1c) and fracture mode (FM).

Objectives

•Apply a combined biochemical and thermomechanical aging protocol to artificially age in vitro specimens designed to represent the hybrid layer between resin composite and tooth structure

•Investigate whether incorporation of OCT-eluting drug silicone particles into resin adhesive affects fracture toughness at hybrid-layer when exposed to simulated human salivary esterase

•Compare fracture mode of hybrid layer interfaces fabricated using resin adhesive with and without octenidine-eluting particles after exposure to BC-TC aging protocol

Methods

The proposed study will use mini-SR specimens based on a description of mini-SR fabrication from Serkies, 2015. 3 mm x 7 mm dentin slabs are sectioned from extracted molars. Each dentin slab is embedded in a semi-cylinder of composite resin. A thin spacer with a triangle-shaped cut-out is positioned against the exposed dentin face prior to applying adhesive and fabricating the second semi-cylinder of composite resin. Thus, the two halves of the mini-SR specimen are adhered by a triangle-shaped resin-dentin interface. A chevron shaped notch will remain between the two halves. When a force is applied to separate the two semi-cylindrical halves of the mini-SR sample, the tip of the stresses concentrates at the tip of the triangle where the crack will initiate.

The BC-TC protocol was developed to study whether an aging protocol including enzymatic challenge and thermocycling would accelerate aging of mini-SR specimens. To simulate biochemical degradation by saliva, the mini-SR specimens are incubated in 3 ml simulated human salivary esterase (SHSE). To produce SHSE media, a solution consisting of cholesterol esterase (CE) and pseudocholinesterase (PCE) is used.

After aging via the BC-TC protocol, degradation of the specimens is quantified by measuring interfacial fracture toughness (K1c) and failure mode. To determine these values, specimens are individually mounted into a customized jig and fractured using the Electroforce 5500 testing machine (TA instruments, New Castle, Delaware). Immediate fracture toughness and fracture mode aremeasured for four groups without incubation. The 4 immediate fracture groups include specimens fabricated using Scotchbond Multipurpose (SBMP), in-house total etch (TE), TE incorporated with drug-eluting silica particles (DSP-TE), and TE incorporated with calcined heat-deactivated drug-eluting silica particles (CDSP-TE) (total 40 specimens). Specimens incubated using the BC-TC aging protocol will be subjected to the same fracture testing.

During the BC-TC aging protocol, degradation products will be measured using Ultra-performance liquid chromatography (UPLC) to assess rate of 2,2-Bis[4(2,3-hydroxypropoxy)phenyl] propane (BisHPPP) and drug release in three groups of specimens. The three groups exposed to the BC-TC aging protocol are TE, DSP-TE, and CDSP-TE (total 30 specimens)

Results

Fracture toughness of immediate fracture groups reveals no significant difference between groups fabricated using SBMP, TE, DSP-TE, and CDSP-TE. Results are pending for measurement of UPLC measurement of Bis-HPPP degradation products and for measurement of fracture toughness and fracture mode of specimens after 6-month aging using BC-TC protocol.

Discussion

Adhesive formulation containing OCT-eluting particles may protect the hybrid layer against enzymatic degradation. Results have shown that addition of OCT-eluting particles to adhesive does not affect fracture toughness of specimens for specimens that have not undergone BC-TC aging protocol. Data from ongoingaging followed by fracture of aged specimens will be used to determine whether OCT release defends against enzymatic degradation of the hybrid layer

References

Vilde TA. An Accelerated Aging Protocol Based on Thermomechanical and Biochemical Challenges for Dental Bonding Agent Development. 2021

Tam LE, Pilliar RM. Fracture Toughness of Dentin/Resin-composite Adhesive Interfaces. J Dent Res. 1993;72(5):953–9

Serkies KB. The Effect of Simulated Human Salivary Enzymes and Matrix Metalloproteinase (MMP) Inhibition on the Degradation and Fracture Toughness of the Self-etched Resin-dentin Interface. 2015

Huang B, Siqueira WL, Cvitkovitch DG, Finer Y. Esterase from a cariogenic bacterium hydrolyzes dental resins. Acta Biomater. 2018;71:330–8

2023 ACP ANNUAL SESSION

Accelerated Aging Protocol Based on Thermomechanical and Biochemical Challenges for Dental Bonding Agent Development

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