Effect Of Oral Environment On The Bonding Of Two Silicone Denture Liners To Denture Base Polymers

Objective:This in vitro study simulated the oral environment where the soft denture liner actually used. We evaluated the effect of mechanical fatigues, thermal cycles, artificial saliva on the bonding between a denture base resin and two silicone denture liners solidified by different way.Methods:Sofreliner MS polyvinyl siloxane soft denture liner and Silagum automix comfort soft relining were chosen as representatives for self-curing and heat-curing silicone liner material, respectively. Those two soft lining materials were bonded toα-RESIN dentistry-denture base polymers to produce cylindrical specimens (8mm diameter and 10mm high), with 102 specimens for each material. Then the specimens of each material were divided into 17 groups (6 specimens for each group), and subjected to fatigue loading of 66 700, 133 300, 200 000, 266 700, 333 300, 400 000 times simulate 0.5, 1, 1.5, 2, 2.5, 3 years of intraoral conditions, thermal cycles of 5 000, 10 000, 15 000, 20 000, 25 000, 30 000 times simulate 0.5, 1, 1.5, 2, 2.5, 3 years of intraoral conditions, immersing in artificial saliva at 37℃for 7, 30, 90, 180 days, respectively, immersing in distilled water at 37℃for 24 hours as the control group. The tensile strength of specimens of each group was tested and the fracture mode was observed with Stereomicroscope to evaluate the effect of mechanical fatigues, thermal cycles, and artificial saliva on the bonding between a denture base resin and these two silicone denture liners.Results:1. Immersing in distilled water at 37℃for 24 hours(the control group), the tensile strength of Sofreliner MS was (1.4721±0.2802) MPa, the tensile strength of Silagum was (3.2834±0.6091) MPa. Sofreliner MS lining material showed failure of the soft denture liner itself, Silagum lining materials showed failure of cohesive and adhesive while main failure of adhesive.2. With the increase of fatigue loading times, the bonding strength (MPa) of each group for Sofreliner MS was: 1.1748±0.2040, 1.0516±0.1937, 1.1520±0.1699, 0.9761±0.2185, 0.9007±0.1146, 0.8754±0.0809, the tensile strength of each group declined significantly compare to the control group, the tensile strength of 2.5 years group and 3 years group declined significantly compare to the 0.5 year group, the tensile strength of 2.5 years group and 3 years group declined significantly compare to the 1.5 years group(P<0.05); the bonding strength (MPa) of each group for Silagum was: 2.5789±0.5322, 2.1605±0.4046, 1.9676±0.5214, 1.9121±0.4213, 2.0709±0.1229, 1.6570±0.3282, the tensile strength of each group declined significantly compare to the control group, the tensile strength of 1.5 years group, 2 years group and 3 years group declined significantly compare to the 0.5 year group(P<0.05).3. Sofreliner MS lining material and Silagum lining material showed failure of cohesive and adhesive after fatigue loading.4. With the increase of thermal cycles, the bonding strength (MPa) of each group for Sofreliner MS was: 1.5484±0.1709, 1.5861±0.1010, 1.4949±0.0267, 1.4194±0.1277, 1.4182±0.2563, 1.5011±0.0633, the tensile strength of each group had no significant change; the bonding strength (MPa) of each group for Silagum was: 3.0404±0.4502, 3.4269±0.3797, 3.4501± 0.3312, 3.1296±0.5929, 3.1557±0.7625, 3.1561±1.1281, the tensile strength of each group had no significant change.5. The fracture mode of Sofreliner MS lining material and Silagum lining material was cohesive failure after thermal cycles.6. With immersing in artificial saliva for 7, 30, 90, 180 days, the bonding strength (MPa) of each group for Sofreliner MS was: 1.2465±0.0918, 1.3382±0.2412, 1.3290±0.2632, 1.8201±0.4520, the tensile strength of first three group had no significant change. Stored in artificial saliva of 180 days, the bonding strength of Sofreliner MS was significantly increased(P<0.05); the bonding strength (MPa) of each group for Silagum was: 2.8613±0.7741, 3.0151±0.5909, 3.0545±0.6173, 2.6631±0.2809, there had no significant difference of tensile strength between each group of Silagum.7. Sofreliner MS lining material showed failure of the soft denture liner itself after the artificial saliva storing. Silagum lining material showed main failure of the soft denture liner itself after storing.Conclusions:1. With the increase of fatigue loading times, the tensile strength of both soft lining materials significantly declined.2. Thermal cycling had no effect on tensile strength of the two soft lining materials we choose in this experiment in vitro.3. Stored in artificial saliva of 180 days, the bonding strength of the two soft liners we choose had no change except for the last group of Sofreliner MS.4. The tensile strength and tear strength of each group of heat-curing silicone liner material tested in these three studies were higher than each group of the self-curing silicone liner material tested. The bonding property of the two silicone lining materials was acceptable for clinical usage (≥0.44MPa).