Flexural Strength of PMMA/MMA-Based Material Reinforced with Sisal

Objective: This research was to develop the dental restorative material having both biocompatibility and environmental adaptability by using plant fiber as reinforcement. Methods: Sisal hemp (Takasho, Co.LTD., Japan) was used as plant fiber. Sisal fiber was chopped into 10mm length and then dried on oven at 110 °C for 3h to remove moisture. Bend specimen (2.5x10x65 mm) was fabricated according to a conventional heat-cure type denture processing (curing cycle:30min in 70 °C water and then 1h in boiling water).Dough mixture was prepared using Polymer (P) and Liquid (L) of Acron (GC, Japan) as control (P/L=10g/4.5ml).Chopped sisal was formulated to 2.5, 5, and 10 by mass % of P.The specimen surfaces were finished in a wet condition using a SiC abrasive paper up to 2000 grit (CC-Cw, Sankyo Rikagaku Co.LTD., Japan).The specimen was stored in 37 °C distilled water for 3d.Flexural test was carried out at a crosshead speed of 5mm/min using a calibrated universal testing machine with a 500N load cell (EZ Tester, Shimazu, Japan).Bend strength values were statistically analyzed using one-way ANOVA and Fisher's PLSD. Results: Flexural properties (mean and SD, n=6) are presented in the following table.

Sisal/Acron	0/100	2.5/97.5	5/95	10/90
Bend strength MPa	98(2)	69(5)	69(5)	76(12)
Deflection at fracture load mm	6.89(0.23)	4.48(0.50)	4.67(0.46)	4.78(0.97)
Elastic modulus MPa	2397(49)	2407(75)	2329(10)	2248(173)

Bend strength and deflection at fracture load decreased with increasing the incorporation of sisal hemp compared to the control (p<0.01). Elastic moduli of sisal-reinforced materials did not show a significant difference compared to control (p>0.05).Conclusion: Chopped sisal fiber-incorporated composites did not improve bend strength behavior. Further studies regarding surface treatment and aspect ratio of sisal fiber should be performed to improve the bend strength.