Methods: Four silicone-based soft liners (GC Soft(GS), GC Extrasoft (GXS), Silagum Comfort (SC) and Mollosil Plus (MP)) were processed to PMMA (IMPACT, Dental exports of london, England) and UDMA (ECLIPSE, DENTSPLY, USA) denture base polymers following the manufacturers' recommended relining method. For each soft liner-denture base combination group, 10 specimens were prepared using a custom-made brass mould. The bonding area was 10 mm in diameter and 3mm in thickness. The specimens were stored in distilled water (37ºC)for 24 hours before testing. The specimens were tested for T.B.S using universal testing machine (Shimatzu, Japan)and mode of failure was determined using stereomicroscope at X 10 magnification (Kyowa SD-2PL, Japan). Data were analyzed using Kruskal-Wallis and Mann-Whitney tests.
Results: for PMMA group, there were significant differences in TBS amongst soft lining materials (p<0.05), except, between GS (1.94 MPa) and GXS (2.04 MPa). While,in UDMA group, there was non-significant difference in TBS between all soft liners except, for MP which showed significant lower TBS (0.08 MPa).
All soft lining materials showed a significantly higher TBS to PMMA then to UDMA (p<0.05), except for SC which showed no significant difference (P>0.05). The mixed mode of failure was the most common in PMMA group. While, Adhesive was the most common in UDMA group, except for Silagum Comfort was mostly adhesive in both groups.
Conclusions: The silicone-based soft lining materials showed different T.B.S when used to reline PMMA compared when relined UDMA denture base polymer.
Soft lining materials showed lower TBS to UDMA then to PMMA denture base polymer.