Comparative evaluation of shear bond strength of two different chairside soft liners to heat processed acrylic denture base resin: An in vitro study

摘要

Background: Chairside softliners are used more frequently than is reported and studies regarding the bond strength of chairside softliners to heat-polymerized denture base resin are few and limited. Hence, this study was conducted to comparatively evaluate the shear bond strength of two chairside soft relining materials viz., autopolymerizing plasticized acrylic resin liner and a silicone-based liner bonded to heat polymerized polymethyl methacrylate denture base resin and to analyze the mode of interfacial bond failure. Materials and Methods: Forty test specimens ( n = 40) were prepared by bonding plasticized acrylic- and silicone-based soft liner to heat polymerized acrylic resin blocks. Twenty specimens, ten from each group, were subjected to thermal cycling and later to shear bond strength testing. The debonded specimens were then qualitatively analyzed for the mode of failure using scanning electron microscopy. The results obtained were tabulated and statistically analyzed. Results: The mean shear bond strength values obtained for acrylic-based soft liner before and after thermal cycling were 0.3365 ± 0.025 MPa and 0.3164 ± 0.04 MPa, respectively. The mean shear bond strength values obtained for silicone-based soft liner before and after thermal cycling were 0.4159 ± 0.025 MPa and 0.4335 ± 0.02 MPa, respectively. Silicone-based soft liner showed higher shear bond strength than the acrylic-based both before and after thermal cycling ( P = 0.0001). Scanning electron microscopy analysis showed a predominantly mixed mode of failure with silicone-based liner and predominantly adhesive mode of failure with acrylic-based soft liner. Conclusion: The silicone-based soft liner showed higher shear bond strength to heat polymerized acrylic resin than acrylic-based soft liner both before and after thermal cycling. KEY WORDS: Heat polymerized acrylic resin, shear bond strength, softliner, thermal cycling Aconventional removable dental prosthesis relies on the residual alveolar bone and the overlying mucoperiosteum for its support. The condition of these bearing tissues may be adversely affected by high-stress concentrations during function which can cause considerable damage to the supporting tissues resulting in accelerated ridge resorption and soft tissue injury to the denture bearing areas.[ 1 ] Relining of such prostheses is an accepted protocol for limiting the damage to the supporting structures. Relining ill-fitting removable dentures improve their stability, support, and retention.[ 2 ] A denture may be relined as a laboratory procedure or at the chairside in the dental clinic. The chairside relining procedure with a soft denture liner is used extensively in prosthodontics because of the simplicity of the technique, and the good fit of the prosthesis obtained. Soft denture liners have a key role in modern removable prosthodontics because of their ability to restore health to the inflamed and abused mucosa. They are resilient, viscoelastic materials used to form part of the fitting surface of a denture. They act as a cushion for the denture bearing mucosa through absorption, dampening, and redistribution of forces transmitted to the stress-bearing areas of edentulous ridges, provide more equal force distribution, reduce localized pressure, and improve denture retention by engaging undercuts. The ideal properties for a soft liner include resilience, tear resistance, viscoelasticity, biocompatibility, lack of odor and taste, adhesive bond strength, low solubility in saliva, low adsorption in saliva, ease of adjustability, dimensional stability, color stability, lack of adverse effect on denture base material, resistance to abrasion, and ease of cleaning.[ 3 ] There are several problems associated with the use of resilient denture liners, including bond failure between the liner and the denture base, colonization by Candida albicans, porosity, poor tear strength, and loss of softness. One of the most serious problems with these materials is bond failure between the resilient denture liner and denture base. The interfacial bond between the denture base and resilient liner is of much importance since the ability of the liner to effectively absorb and uniformly transmit the masticatory stresses is dependent on the integrity of the bond. Bond failure creates a potential surface for bacterial growth, and plaque and calculus formation. Weakened bond strength promotes the ingress of oral fluids and microorganisms at their interface and finally results in separation of the reline material from the denture base.[ 4 , 5 ] A variety of parameters affects the bond between resilient lining materials and the denture base, including water absorption, surface primer use, denture base composition, and temperature changes.[ 6 , 7 , 8 ] It is, therefore, essential that there is an adequate bond between the denture base and the soft lining material. Failure of soft lining materials is often attributed to a breakdown of this bondin