Increased Scale Novel Glass Production Effect on Composite Flexural Properties

Objectives: When developing new glasses for resin composites it is important to confirm that scaling up from lab-scale to industrial-scale does not deleteriously effect properties. Here, we compare a lab-made glass with an industrially made glass in terms of composite flexural properties.
Methods: A fluoride glass (37.5 SiO₂: 20.4 CaO :20.4 Na₂O :5 P₂O₂ :16.7 NaF, sieved particle size <45μm) was made at <50g scale in our lab and in three batches of 250g scale industrially (GTS, Glass Technology Services, UK). 50:50 urethane dimethacrylate:triethylene glycol dimethacrylate composites (Sigma Aldrich,UK) were made with 20v% our glass and 40v% barium-alumino-borosilicate glass (0,7μm particle size,SCHOTT^® UltraFine). Five composites were made, one for each batch and a fifth from the three GTS batches combined.

Degree of conversion (DC) was measured using ATR-FTIR (Spectrum One, Perkin Elmer) (n=5, 6×1mm) exposed to 40s of light (intensity=1000 mW/cm2, Elipar DeepCure, 3M ESPE, UK). Three-point bend test flexural strength (FS) and modulus (FM) specimens (n=10, 5 overlapping 20s light exposures, 25×2×2mm) were stored in distilled water at 37^○C and properties measured at day 1, 7, 14 and 28 using a universal test machine (model 5567, Instron, UK).
Results: No significant differences in DC were measured (P>0.05, range = 60-69%). Similar behaviour was found for the FS and FM. Initially, all composites had FS above 80MPa and FM above 7.1 GPa, with no significant difference measured (P>0.05). Both parameters then decreased for all composites over time, significantly so for the lab-made glass composites (p<0.05), while no significant differences were found for the scaled-up glass composites (p>0.05).
Conclusions: All composites showed high DC% and good initial mechanical properties. While properties decreased over storage time, the scaled-up glass composites showed superior flexural properties to the lab-based glass composites, suggesting this glass could be suitable for use in an ion-release dental composite.