An in vivo and in vitro Study of the Loss of Plasticizer from Soft Polymer-gel Materials

Abstract

Polymer-gel materials used as short-term denture soft linings are blended with plasticizers to lower the glass transition temperature (Tg). A lower Tg allows for greater polymer chain mobility, thus producing a more flexible material. The present work evaluated the loss of plasticizers due to leaching both in vivo and in vitro. Two commercial denture soft-lining materials (A and B) were tested. These were both poly(ethyl methacrylate) polymers, blended with alcohol and phthalate esters. A clinical study was conducted in which patients wore, sequentially, dentures bearing (on separate occasions) each of the two soft-polymer lining materials. The two materials A and B were randomly assigned for each of ten patients and were worn for 14 and 30 days, respectively. With one exception, patients wore dentures with both lining materials, for a total of 19 clinical evaluations. The plasticizer loss occurring during the clinical trial was determined by GC analysis from the initial and terminal day sampling of plasticizer content of the soft polymer-gel materials. The results of this analysis were compared with results obtained from an in vitro leachability study by use of sink conditions in water at 37°C for the same two commercial soft polymers conducted over the same time periods of 14 and 30 days. The results indicated that a higher loss of plasticizer occurred in vivo, compared with the in vitro tests for 17 of the 19 clinical evaluations. The average plasticizer lost in vivo from material A at 14 days was 122 ± 58 mg/g, and for material B at 30 days it was 33 ± 27 mg/g. This can be compared with the in vitro loss that was 13.41 ± 1.11 mg/g for material A at 14 days, and 8.47 ± 0.73 mg/g for material B at 30 days. It is not known how much of the plasticizer lost from the denture soft lining in the in vivo trial was ingested by the patient. Patients were cautioned against soaking the denture in any liquid; however, it is not known how much was lost due to cleaning of the denture by the patients.