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Studies on the effects of titanate and silane coupling agents on the performance of poly (methyl methacrylate)/barium titanate denture base nanocomposites

Elshereksi NW, Ghazali MJ, Muchtar A, Azhari CH

J Dent, 2017 Jan;56:121-132.
PMID: 27916635 DOI: 10.1016/j.jdent.2016.11.012

OBJECTIVES: This study aimed to fabricate and characterise silanated and titanated nanobarium titanate (NBT) filled poly(methyl methacrylate) (PMMA) denture base composites and to evaluate the behaviour of a titanate coupling agent (TCA) as an alternative coupling agent to silane. The effect of filler surface modification on fracture toughness was also studied.
METHODS: Silanated, titanated and pure NBT at 5% were incorporated in PMMA matrix. Neat PMMA matrix served as a control. NBT was sonicated in MMA prior to mixing with the PMMA. Curing was carried out using a water bath at 75°C for 1.5h and then at 100°C for 30min. NBT was characterised via Fourier transform-infrared spectroscopy (FTIR), Transmission Electron Microscopy (TEM) and Brunauer-Emmett-Teller (BET) analysis before and after surface modification. The porosity and fracture toughness of the PMMA nanocomposites (n=6, for each formulation and test) were also evaluated.
RESULTS: NBT was successfully functionalised by the coupling agents. The TCA exhibited the lowest percentage of porosity (0.09%), whereas silane revealed 0.53% porosity. Statistically significant differences in fracture toughness were observed among the fracture toughness values of the tested samples (p<0.05). While the fracture toughness of untreated samples was reduced by 8%, an enhancement of 25% was achieved after titanation. In addition, the fracture toughness of the titanated samples was higher than the silanated ones by 10%.
CONCLUSION: Formation of a monolayer on the surface of TCA enhanced the NBT dispersion, however agglomeration of silanated NBT was observed due to insufficient coverage of NBT surface. Such behaviour led to reducing the porosity level and improving fracture toughness of titanated NBT/PMMA composites. Thus, TCA seemed to be more effective than silane.
CLINICAL SIGNIFICANCE: Minimising the porosity level could have the potential to reduce fungus growth on denture base resin to be hygienically accepTable Such enhancements obtained with Ti-NBT could lead to promotion of the composites' longevity.
Fulltext Review of titanate coupling agents and their application for dental composite fabrication

Elshereksi NW, Ghazali M, Muchtar A, Azhari CH

Dent Mater J, 2017 Sep 26;36(5):539-552.
PMID: 28652551 DOI: 10.4012/dmj.2016-014

Silane is a dominant coupler that is widely used in dentistry to promote adhesion among the components of dental composites. Silica-based fillers can be easily silanized because of their similarly ordered structure. However, silane is hydrolytically degraded in the aqueous oral environment and inefficiently bonds to non-silica fillers. Thus, the development of hydrolytically stable dental composites is an important objective in the research on dental materials. Titanate coupling agents (TCAs) exhibit satisfactory interfacial bonding, enhanced homogeneous filler dispersion, and improved mechanical properties of the composites. Titanates also provide superior hydrolytic stability in wet environments, which should be considered in fabricating dental composites. The addition of a small amount of titanates can improve the resistance of the composites to moisture. This paper reviews the effects of the instability of silanes in moisture on the performance of dental composites and presents TCAs as alternative couplers to silanes for fabricating dental composites.

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