Kinetics of fluoride release from and reuptake by orthodontic cements

The purposes of this in-vitro study were to compare the fluoride-release profiles and the fluoride release, reuptake, and rerelease characteristics of orthodontic cements before and after topical fluoride treatment.

The orthodontic cements tested were 2 resin-modified glass ionomers (Vitremer [3M Dental Products, St Paul, Minn] and Fuji Ortho LC [GC Dental, Tokyo, Japan]), a glass ionomer (Ketac-Cem [Espe-Premier Dental Products, Norristown, Pa]), and a composite (Concise [3M Dental Products]). Fifteen specimens of each material were stored in plastic vials containing deionized water at 37 degrees C. Fluoride release was measured daily for the first 15 days and then weekly for a 57-day period. After initial elusion, specimens were exposed to 1.23% acidulated phosphate fluoride gel, and the fluoride release was monitored daily for 7 consecutive days. The fluoridation/elution procedure was repeated once, and the specimen surfaces were then examined with a scannning electron microscope.

Kinetic release profiles of the test materials were deduced. All materials except Concise had similar fluoride-release profiles. Vitremer demonstrated the highest fluoride release, followed by Fuji Ortho LC and then Ketac-Cem in the time period of the study (P <.01). All glass-ionomer cements, but especially Fuji Ortho LC, showed enhanced uptake and release on repeated exposure to the topical fluoride treatment. Nevertheless, Vitremer showed the greatest surface degradation after refluoridation.

All resin-modified and conventional glass ionomers studied exhibited the capacity for fluoride release and reuptake after fluoridation, but the subsequent fluoride release was transitory. Thus, the benefit from fluoride reuptake in these orthodontic cements should be balanced with the risk of weakening them after repeated fluoridation.