Radiopacity and microhardness changes and effect of X-ray operating voltage in resin-based materials before and after the expiration date

Abstract

This study observed alteration in the radiopacity and microhardness of expired resin-based materials compared to non-expired materials and the operating characteristics of the X-ray source used. Five 2 mm-thick cured specimens were prepared for each material: composite resins (P60®, Z100®), and a compomer (Dyract AP®). Radiopacity of the specimens was evaluated comparing the density of the resin-based material to an equivalent (mm) density of a 99.5% pure aluminum step wedge using a transmission densitometer. Surface microhardness measurements were carried out using a calibrated Vickers indenter on three different points of the same surface. ANOVA and Tukey tests (pre-set alpha = 0.05) revealed that expired materials showed no significant change in radiopacity. One material (Filtek P60) demonstrated lower radiopacity with lower KVp. Change in microhardness wa s statistically significant for Z100: for this material, the microhardness after expiration was significantly lower than before the expiration date

Adhesive performance of precoated brackets after expiration

“…8 Others reported reduced microhardness for some expired composites. 9,10 This was attributed to degradation of the photoinitiator, leading to a lower degree of polymerization and thus reduced microhardness. 9 Volatile acetone-based dental adhesives were shown to develop reduced bond strengths due to evaporation of the solvent.…”

“…9,10 This was attributed to degradation of the photoinitiator, leading to a lower degree of polymerization and thus reduced microhardness. 9 Volatile acetone-based dental adhesives were shown to develop reduced bond strengths due to evaporation of the solvent. 17 The shelf life of precoated adhesive, which is more comparable to dental composites than to dental adhesives, is likely primarily determined by the influence of storage on ingredients that affect the polymerization process.…”

“…7 For the few published studies in dentistry investigating expiration date effects on mechanical properties of resin-based materials, the results have been mixed. [8][9][10] In orthodontics, the dilemma of whether to use expired brackets is associated with both the economics of disposing of a potentially useful bracket and the risk of altered bond strength leading to either bracket bond failures and extended treatment times or compromised patients. At the authors' institution, the Department of Orthodontics had approximately 1500 "expired" brackets in its inventory.…”

Improving the Radiopacity of Calcium Aluminate Cement Based Blends

“…Material radiopacity is changed by adding a suitable content of particles containing heavy metals such as bismuth (Z=83), silver (Z=47) or zinc (Z=30) 8,9 . Zinc oxide is used in dental materials for prosthetic and implant purposes and does not present toxicity 10 .…”

Influence of radiopacifier additives on calcium aluminate cement properties

“…The radiopacity of material is changed by adding particles containing heavy metals such as bismuth (Z=83), barium (Z=56), zirconium (Z=40), strontium (Z=38) or zinc (Z=30) 16,17 . Bismuth oxide is a well-known radiopacifying agent.…”