Fibres used in bullet-proof vests can quadruple toughness of dental composites, according to the results of detailed engineering tests on dental composites containing glass fibers as well as the type of polyethylene fibres used in bullet-proof vests.

Polyethylene fibres used in bullet-proof vests can quadruple toughness of dental composites, according to the report.

Vistasp Karbhari, a Professor of structural engineering at University of California San Diego, has developed fibre-reinforced polymer composites as strong, lightweight materials for aerospace, automotive, civil and marine applications. He thought, “If they work so well in highway bridges, why not dental bridges?”

In a paper, available at the Dental Materials website, Professor Karbhari and Howard Strassler, a Professor and Director of Operative Dentistry at the University of Maryland Dental School, found that the toughness of fibre-reinforced dental materials depends on the type and orientation of the fibre used.

Their report shows that braided polyethylene fibres performed the best, boosting toughness by up to 433 percent compared to the composite alone.

Many of the strength and durability tests reported in the paper are not currently required by the US Food and Drug Administration (FDA), which regulates dental composites as class II prescription devices. The agency requires eight minimum tests plus biocompatibility tests to ensure that dental composites are safe and nontoxic.

“Fibre-reinforced composites are now widely used in the aerospace and automotive industries and the experience we've gained in these applications can be applied in a more rigorous way in dentistry and medicine to tailor performance to exacting requirements,” said Professor Karbhari. Dentists began using particle filled composites ten years ago as an alternative to ceramics and mercury-containing metal amalgams. Professor Strassler selected three commercially available fibre-reinforced composites for analysis.

Dental composites made with glass or polyethylene fibres are sold as pliable ribbons that dentists mold into the required shape and then harden with curing lights.

“Many reinforcing fibres can add strength and toughness to dental composites,” Professor Karbhari said, “but if they are improperly aligned they could actually accelerate damage to existing teeth.”

The three products tested were a 3-millimeter-wide ribbon of unidirectional glass fibres, a 3-millimeter-wide ribbon of polyethylene fibres woven in a figure-of-eight stop-stitch leno-weave, and a 4-millimeter-wide ribbon of polyethylene fibres woven in a biaxial braid. The resistance to breakage and various measures of toughness of the three preparations were compared to the dental composite alone.

“All three fibre fabrics dramatically increased the durability and strength of the dental composite, but the polyethylene fibres braided in a biaxial ribbon performed best,” said Professor Karbhari.

“The tests required by the FDA indicate that fibre-reinforced composites are safe, but those tests are only partially informative. Our analyses show that we can optimise these materials to match and improve performance of teeth, for greater durability, toughness, and resistance to breakage.”