Shelf-life effect of silane-containing universal adhesive on bonding effectiveness to glass-ceramic

Objective

To evaluate the shelf-life effect of a silane-containing universal adhesive (UA) on its shear bond strength (SBS) to lithium disilicate glass-ceramic (LiSi₂).

Methods

SBS to mirror-polished (‘MP’) and hydrofluoric acid-etched ground (‘HF’) lithium disilicate glass-ceramic (Initial LiSi, GC) with/without prior separate ceramic primer application (G-Multi Primer, GC: ‘G-MP’) was measured. Scotchbond Universal Plus (‘SBUp’) (3M Oral Care) was used 33 (‘fresh’) and 6 (‘expiring’) months before the expiration date. ‘MP’ specimen preparation involved (1) ‘G-MP’ priming (or not), (2) ‘SBUp’ application, (3) composite (Clearfil AP-X, Kuraray Noritake) placement, and (4) 20 s light-curing (SmartLite Pro, Dentsply Sirona). ‘HF’ specimen preparation involved (1) HF (Porcelain Etch, Ultradent) etching, (2) phosphoric acid (K-Etchant, Kuraray Noritake) post-etching, with (3) and (4) being the same as for ‘MP’. Upon light-curing, all specimens were stored in 37 °C water for either 1 week (‘immediate’) or 3 months (‘aged’) prior to SBS measurement. Statistics involved Linear Mixed-Effects modelling (α = 0.05).

Results

SBS was not significantly affected by SBUp's shelf life, except for a significantly higher SBS recorded for ‘fresh’ SBUp applied on HF-etched and separately silane-primed LiSi₂. Aging did not significantly decrease SBS. In fact, a significant increase in SBS upon aging was recorded for HF-etched LiSi₂ that was not separately silane-primed. The significantly highest bond strength was measured when LiSi₂ was HF-etched followed by separate silane-priming.

Significance

Despite the UA investigated has silane in its formulation, the most effective and durable bonding to LiSi₂ was achieved by HF-etching followed by separate silane-priming, irrespective of the UA's shelf life.