Objective: Progress Archimedes method to obtain a better reproducibility of the continuous recording giving informations about stress between charges and matrix, during and after photopolymerization process.
Materials and method: Four composite resins have been used, Gradia Direct (GC); Clearfil Majesty™ Posterior (KURARAY); Clearfil Majesty™ Esthetic (KURARAY); Grandio® (VOCO). Samples (sphere of 5 mm diameter) made by an holder are weighted with a balance XS205DU with a tenths of a milligram precision and the LabX software (Mettler Toledo LTd, UK) in the dry air and then in the auxiliary liquid. The sample is held in suspension in the auxiliary liquid and stay between two LED lights (GC). After 30 seconds (needed time to obtain stable measurement) the two LED lights are both simultaneously switched on during 20 seconds. The weight is computed during 480 seconds by the software every second. This method allows a better understanding of the behavior of composite resin during curing process.
Results: From 30 to 60 seconds, there is an exothermic peak due to the rise of temperature of the auxiliary liquid. Results give the volumetric contraction as shown in the table below:
Product | Average weight in the dry air | Average contraction at 50sec | Average contraction at 480sec | Exothermic peak |
Gradia Direct | 0.1081±0.0027 | 1.2099±0.0069 | 1.8827±0.0016 | 0% |
Clearfil Majesty™ Posterior | 0.1817±0.0024 | 0.8157±0.0030 | 1.3777±0.0024 | 0.42% |
Clearfil Majesty™ Esthetic | 0.1252±0.0022 | 1.1954±0.0018 | 1.4531±0.0018 | 0% |
Grandio® | 0.1621±0.0031 | 0.7911±0.0069 | 0.7911±0.0068 | 0.43% |
The analysis of graphics reveals different stress evolutions between charges and matrix of each resin in relation with their density. A 40 seconds polymerization time (higher rate polymerization) could be of course realized to quantify the final contraction.
Conclusion: With the improvement of methodology, results show a good reproducibility and explain materials behavior regarding shrinkage. There are differences between each composite resin, which demonstrate the interest of this continuous registration technique