Bond strengths of composite resin and compomers in primary and permanent teeth

Previous clinical and in vitro studies have shown a higher failure rate of composite resins and conventional glass ionomer cements in primary teeth when compared to permanent teeth. A new generation of light-cured glass ionomer cements (compomers) were suggested to be used as restorative materials for the primary teeth. This study was conducted into two parts. The objective of the first part was to compare shear bond strength of compomers (Compoglass and Dyract) and composite resin (Herculite/Optibond) in both primary and permanent teeth. Buccal and lingual surfaces of extracted sound human primary and permanent molars were ground flat on 600-grit SiC paper and divided into 6 groups of 10 surfaces each. The materials were handled according to the instructions of the manufacturer and placed on to the tooth surfaces via clear plastic tubes of 3 mm in diameter. After light curing for 40 seconds, all samples were thermocycled in water bath of 5 degrees F and 55 degrees F for 500 cycles. The samples were embedded in acrylic resin and sheared with an Instron running at a crosshead speed of 0.5 mm/min. Results (mean shear bond strength) were recorded in MPa. Factorial ANOVA revealed that shear bond strength of Herculite/Optibond in the primary teeth (6.07 +/- 2.63) was significantly lower than that of the permanent teeth (17.61 +/- 4.34) (p < 0.0001), but there was no statistically significant difference of bond strength of Compoglass and Dyract between the primary and the permanent teeth. The results from the first part revealed that no materials tested in the primary teeth could provide a shear bond strength of at least 17.6 MPa as recommended. Thus, the objective of the second part of this study was to evaluate shear bond strength of composite resin (Herculite) using three different dentinal bonding agents (Optibond, One-Step and Amalgambond) in the primary teeth. Methods employed in this part were similar to that of the first part. Results showed that Amalgambond provided significantly higher mean shear bond strength (17.96 +/- 5.77) than One-step (11.79 +/- 4.73) and Optibond (6.07 +/-/- 2.63) as tested by Kruskal-Wallis ANOVA and Mann-Whitney U test (p < 0.0001).