Improving the Setting Time and Strength of Glass-Ionomer Cements
Research indicates that the use of heat from curing lights to command cure these materials does not result in pulpal damage
Asha Patel, DDS
Glass-ionomer cements (GICs), which were invented in 1969 and first described in 1972 by Wilson and Kent, are materials that are made up of finely ground fluoroaluminosilicate glass powder that is combined with a polyacrylic acid solution. When compared with other commonly used restorative materials, the coefficient of thermal expansion of GICs most closely mimics that of dentin, making them an ideal dentin replacement. Most notably, GICs release fluoride ions over time, which helps to strengthen the adjacent tooth structure and inhibit the progression of secondary caries.1
Due to these benefits, GICs can be excellent choices for restoring caries in pediatric patients. However, the original GICs failed to gain widespread adoption because of their long setting times, poor wear resistance, and low fracture strength. Some manufacturers attempted to improve their physical properties by including a light-polymerized liquid resin component, which resulted in the creation of resin-modified GICs. Manufacturers also developed high viscosity GICs. To accelerate the setting time and strength of high viscosity GICs, the heat from a curing light can be used; however, this raises concerns about the potential for pulpal damage. Previous studies have established that a temperature increase of 5.5°C could damage the pulp.2-5
At the University of Alabama at Birmingham, we conducted an experiment to determine the intrapulpal temperature increase associated with 40 seconds of thermo-curing to command set high viscosity GICs. Four GICs (ie, EQUIA Forte®, GC America; IonoStar® Plus, VOCO; Riva Self Cure HV™, SDI; and Ketac™ Universal Aplicap™, 3M) were tested. For the experiment, Class I preparations were created with a 557 bur in groups of extracted, noncarious permanent molars (n=6/group). These were filled with the GICs and then set either by light-curing for 40 seconds or by self-curing following the manufacturer's instructions, which took approximately 2 minutes. To measure any temperature changes, a K-type thermocouple probe was inserted from the roots of each tooth into the pulp chamber. All of the tested GICs demonstrated a temperature increase of less than 5°C. Therefore, we can conclude that thermo-curing may be safely used to command set conventional GICs to shorten treatment times.
Further research is required to test the flexural and compressive strength of the GICs that were command set in this experiment. However, we can hypothesize that an increase in strength occurred because a similar study conducted by Kleverlaan and colleagues using similar materials (ie, Fuji IX®, GC America; Fuji IX GP® Fast, GC America; Ketac™ Molar, 3M; and Ketac™ Molar Quick, 3M) found that GICs cured in this manner showed an increase in strength.6 In a separate 5-year randomized clinical trial conducted by Wafaie and colleagues, the clinical performance of high viscosity glass ionomers in small Class II restorations was evaluated.7 This study concluded that, although there were drawbacks in surface luster and color match, the clinical performance was similar to that of microhybrid resin composite restorations.
With the introduction of high viscosity glass ionomer formulations and the use of heat to accelerate their curing times and increase their compressive and flexural strength, we are overcoming the limitations of traditional GICs. These advancements hold the potential to reshape the field of pediatric dentistry, providing practitioners with solutions that are patient-friendly and effective.
About the Author
Asha Patel, DDS, is a pediatric dentist who maintains a private practice in Austin, Texas.
References
1. Kent BE, Lewis BG, Wilson AD. Glass ionomer cement formulations: I. the preparation of novel fluoroaluminosilicate glasses high in fluorine. J Dent Res. 1979;58(6):1607-1619.
2. Zach L, Cohen G. Pulp response to externally applied heat. Oral Surg Oral Med Oral Pathol. 1965;19:515-530.
3. Khajuria R, Madan R, Agarwal S, et al. Comparison of temperature rise in pulp chamber during polymerization of materials used for direct fabrication of provisional restorations: An in-vitro study. Eur J Dent. 2015;9(2):194-200.
4. Gavic L, Gorseta K, Borzabadi-Farahani A, et al. Influence of thermo-light curing with dental light-curing units on the microhardness of glass-ionomer cements. Int J Periodontics Restorative Dent. 2016;36(3):425-430.
5. Ridha AM, Aidinis K, Suliman AH. Temperature rise at the pulp-dentin junction for a multi-layered composite restoration using the finite element method. Open Dent J. 2021;15:487.
6. Kleverlaan CJ, van Duinen RN, Feilzer AJ. Mechanical properties of glass ionomer cements affected by curing methods. Dent Mater. 2004;20(1):45-50.
7. Wafaie RA, Ali AI, El-Negoly SAER, Mahmoud SH. Five-year randomized clinical trial to evaluate the clinical performance of high-viscosity glass ionomer restorative systems in small class II restorations. J Esthet Restor Dent. 2022;35(3):538-555.
