Bond strength and rupture properties of some soft denture liners

The bond strength and rupture properties of three soft acrylic liners (Coe-Soft, Coe Super-Soft and Vertex Soft) and two silicone liners (Molloplast-B and Flexibase) were tested immediately after processing and following immersion in water at 37 degrees C for 7 and 90 days. The bond test gave variable results, as some materials partly peeled and then stretched until rupture occurred. After saturation the acrylic liners exhibited an increase in tear resistance, whilst silicone materials deteriorated, in the case of Flexibase to approximately 25% of its original value. Vertex Soft was the exception, as tear resistance decreased as water sorption increased. Scanning electron microscopy revealed indefinite demarcation between soft acrylic resins and hard denture base, which was not altered after saturation in water. On the other hand, the interface between denture base and silicone liners was clearly visible before and after saturation. The results indicated that denture soft liners had variable water sorption values depending on their basic structure, and some properties changed after immersion in water, a finding that is of relevance to prosthodontic practice.