Fluoride release from glass ionomer restorative materials and the effects of surface coating

Objectives. This in vitro study on fluoride (F) release from conventional a nd metal-reinforced glass ionomer investigated the following: (1) the relea se of F in deionized water compared to artificial saliva, (2) the effect of various surface coatings on F release, (3) the uptake of released F by hyd roxyapatite, (4) the expression of the: release data in a mathematical mode l, (5) F content in the powders and set materials, and (6) surface morpholo gy of varnished and resin-coated specimens. Methods. Glass ionomer Ketac-Fi l (KF), Fuji II (FJ), and Ketac-Silver (KS) were mixed according to the man ufacturers instructions, and prepared into specimens of 137.8 mm(2) surface area. All three specimens were suspended in 50 ml of deionized water, arti ficial saliva, or aqueous solution of hydroxyapatite and submitted to const ant agitation at 37 degreesC. In a separate experiment, the specimens were coated with varnish or light-cured bonding resin and tested For F release i n solutions similar to those fur uncoated specimens. The release off occurr ed for 28 days, The concentration of F was measured with F-ion-specific ele ctrode, Results. All tested products showed a strong initial rate of F rele ase which decreased with time until it reached a relatively steady rate aft er two weeks. The F released from KF and FJ was comparable in both pattern and magnitude. They released approximately four times more F than KS. In al l cases, the release of F in artificial saliva was significantly (p < 0.001 ) less than in deionized water. Surface coating the specimens significantly reduced the F release ( p < 0.05 to p < 0.001, depending on the product an d type of coating). The inhibitory effect of coating markedly decreased wit h time. Resin coating reduced F release more than varnish in KF and KS, but not for FJ. Essentially, all F released in aqueous solution was taken up b y the hydroxyapatite, with FJ ranking the highest in increasing hydroxyapat ite F concentration. Over the 28 days, the quantities of F released from FJ , KF, and KS were, respectively, 3.8, 2.3, and 1.0% of the total F content in the specimens. The F concentration in the set KS was 53.9 and 72.5% of t hat found in KF and FJ, respectively. The release data as a function of tim e were best described by the power curve. Micromorphological examinations r evealed remnants of surface coatings on specimens after 14 days storage in artificial saliva. Conclusions. Glass ionomer cements released significantl y less F in artificial saliva than in deionized water. Surface coating the specimens substantially reduced F release. These clinically relevant Factor s were not considered by many in vitro release studies which overestimate t he F availability from glass ionomers. A recall appointment 23 h after the placement of glass ionomer restoration should be given for surface finishin g. (C) 2001 Elsevier Science Ltd, All rights reserved.