Monomer-to-polymer conversion and micro-tensile bond strength to dentine of experimental and commercial adhesives containing diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide or a camphorquinone/amine photo-initiator system

Abstract

Objectives: To compare the degree of conversion (DC) of adhesives initiated by diphenyl(2,4,6-trimethylbenzoyl) phosphine oxide (TPO) or a camphorquinone/tertiary amine system (CQ/Amine) as well as their 'immediate' micro-tensile bond strength (mu TBS) to bur-cut dentine. Methods: DC of Scotch bond Universal('SBU';3MESPE), its experimental counter part containing TPO as photo-initiator system, an experimental G-aenial Bond ('Ga-B'; GC) adhesive formulation, and an experimental LUB-102 adhesive formulation ('LUB', Kuraray Noritake), containing as photo-initiatior system either 2 wt% CQ along with 2 wt% tertiary amine ('SBU_CQ/Amine'; 'Ga-B_CQ/Amine'; 'LUB_CQ/Amine'), or 2 wt% TPO ('SBU_TPO'; 'Ga-B_TPO'; 'LUB_TPO'), was determined using Fourier-transform infrared spectroscopy(FTIR), after being cured with a dual wave length light-curing unit(blue phase 20i, Ivoclar Vivadent). The same adhesive formulations were applied to bur-cut mid-coronal dentine of intact human molars, and subjected to a mTBS test after 1-week water storage. Besides being applied following a self-etch (SE) application mode, the adhesive formulations SBU_CQ/Amine and SBU_TPO were also applied following an etch-and-rinse (E&R) mode, this both for DS and mTBS measurement. Results: No significant difference in DC was found for any of the adhesive formulations, except for SBU_CQ/Amine_SE and SBU_TPO_SE. For both SBU formulations, a significantly higher DC was reached for the E&R than the SE approach. Regarding mTBS, no significant differences were recorded, except for the significantly higher mTBS measured for SBU_CQ/Amine_E&R and SBU_TPO_E&R. Conclusions: In self-etch adhesives, the photo-initiator TPO may be used instead of CQ/Amine. The curing and 'immediate' bonding efficiency depended on the application protocol (E&R versus SE), but not on the photo-initiator system. Clinical significance: The photo-initiator TPO may be used in self-etch adhesives instead of CQ/Amine with similar curing and 'immediate' bonding efficiency.