Effect of storage media on the fluoride release and surface microhardness of four polyacid-modified composite resins ("compomers").

OBJECTIVES: The aims of this investigation were to measure the surface microhardness (Vickers) as well as the release of fluoride from four polyacid-modified composite resins (PMC) ("compomers") (Compoglass F, F 2000, Dyract AP, experimental compomer) after storage in various artificial saliva (buffers) including one esterase-buffer. METHODS: Samples were stored for 6 days in de-ionized water, acidic buffer I (pH 4.2), neutral buffer II (pH 7.0), or neutral buffer III (pH 7.0) containing porcine esterase. The specimens were transferred into fresh media every 48 h. Fluoride release was measured every 48 h. Vickers hardness of each five samples of every group was determined before storing the samples in media (baseline) as well as after storage for 24, 48, and 144 h in the various solutions. Dry-stored specimens served as control. RESULTS: The surface microhardness of all PMCs significantly decreased after storage in the various media. No significant differences, however, were found between samples of the same material stored in the various media for 6 days. In general, the highest fluoride quantity was released into the acidic buffer I except for Dyract AP, which segregated similar quantities of fluoride into buffer I and into de-ionized water. More fluoride was released into de-ionized water than into neutral buffers. Further, esterase treatment increased fluoride release from three PMCs. SIGNIFICANCE: Our results suggest that the action of salivary esterases may weaken the surface of polyacid-modified composite resin restorations. As a clinical consequence, wear may be enhanced and load resistance may be reduced. In addition, fluoride release from PMCs may be increased by hydrolytic enzymes in saliva and under acidic conditions.