Heat transfer properties and thermal cure of glass-ionomer dental cements

Abstract

Under clinical conditions, conventional glass-ionomer dental cements can be cured by application of heat from dental cure lamps, which causes acceleration in the setting. In order for this to be successful, such heat must be able to spread sufficiently through the cement to enhance cure, but not transmit heat so effectively that the underlying dental pulp of the tooth is damaged. The current study was aimed at measuring heat transfer properties of modern restorative glass-ionomers to determine the extent to which they meet these twin requirements. Three commercial glass ionomer cements (Ionofil Molar, Ketac Molar and Equia™ Fill) were used in association with three different light emitting diode cure lamps designed for clinical use. In addition, for each cement, one set of specimens was allowed to cure without application of a lamp. Temperature changes were measured at three different depths (2, 3 and 4 mm) after cure times of 20, 40 and 60 s. The difference among the tested groups was evaluated by ANOVA (P < 0.05) and post hoc Newman-Keuls test. All brands of glass-ionomer showed a small inherent setting exotherm in the absence of heat irradiation, but much greater temperature increases when exposed to the cure lamp. However, temperature rises did not exceed 12.9 °C. Application of the cure lamp led to the establishment of a temperature gradient throughout each specimen. Differences were typically significant (P < 0.05) and did not reflect the nominal power of the lamps, because those lamps have variable cooling systems, and are designed to optimize light output, not heating effect. Because the thermal conductivity of glass-ionomers is low, temperature rises at 4 mm depths were much lower than at 2 mm. At no time did the temperature rise sufficiently to cause concern about potential damage to the pulp.

Intrapulpal temperature changes during curing of different bulk-fill restorative materials

“…These findings are in agreement with those of Gavic et al 15) , which showed that a much greater temperature increase was observed when glass ionomer cements were exposed to curing lamps. Within the bulk-fill composite resin groups, Fill-up!…”

“…in dual-cure (5.00±0.68°C) or self-cure (5.31±0.69°C) modes showed the lowest temperature rise due to its setting reaction. Briefly, all of these also indicate that the differences of setting reaction and material compositions are important factors inducing the intrapulpal temperature rise 15,24,33) . In previous studies, the temperature increase during the curing of different restorative materials has been measured with a calorimeter 41) , differential thermal analysis 42) , infrared cameras 40) , and thermocouples.…”

“…The poor mechanical properties of the present glass ionomer cements make them unsuitable for posterior teeth restorations in high stress-bearing areas 14) . However, the application of heat from dental curing lamps for one minute can accelerate the setting of the material and improve its early mechanical properties 15) . In recent years, glass ionomer cement products have become more developed and new systems are becoming available in the market.…”

Evaluation of Surface Microhardness and Abrasion Resistance of Two Dental Glass Ionomer Cement Materials after Radiant Heat Treatment

“…Thermal energy providing by the LED light-curing unit increased surface hardness of the tested GIC materials by thermocatalysis. More specifically, radiant heat transfer from a dental LED unit to the surface of the GIC specimens leads to increased ion mobility during the initial stage of setting, decreasing the viscosity of the material which further leads to enhanced reactivity between Ca ions of the glass particles (powder) and carboxylate groups of the polyalkenoic acids (liquid), and resulting in an improved and accelerated setting reaction [10]. Consequently, increase of surface hardness of GIC materials after the radiant heat treatment expresses the improved formation of polycarboxylate network due to thermocatalysis of the setting reaction attributed to the provided thermal energy [8].…”

“…In previous studies various techniques have been suggested in order to increase the surface hardness of the GIC 2 Advances in Materials Science and Engineering materials, which include radiant heat transfer by use of dental light-curing units such as light emitting diodes (LEDs) [9][10][11] or lasers [12], ultrasonic energy transfer to enhance the motivation and interaction of the reacted components of the GIC [9,13,14], and application of calcium chloride (CaCl 2 ) solutions in order to enhance the acid-base reaction between carboxylate groups (-COO − ) of the polyalkenoic acids and calcium cations (Ca +2 ) of the glass particles of the cement [15,16]. Among the above techniques the most common one for improving the physical and mechanical properties of the GIC materials is the radiant heat treatment using dental LED curing units.…”