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A tougher tooth thanks to mussels.

Fewer trips to the dentist may be in your future, and you have mussels to thank. Inspired by the mechanisms mussels use to adhere to Inhospitable surfaces, researchers at the University of California, Santa Barbara, have developed a new type of composite that provides an extra layer of durability to treated teeth. The potential payoff?--longer lasting fillings, crowns, implants, and other work.

"It's as hard as a typical dental restoration, but less likely to crack," Kollbe Ahn, materials scientist at UCSB's Marine Science Institute, says of the composite.

On average, a dental restoration lasts five to 10 or so years before needing replacement. The time frame depends on the type of restoration and how well the patient cares for the treated tooth. However, the continual onslaught of chewing, acidic and hard foods, poor hygiene, nighttime tooth grinding, generally weak teeth, and even inadequate dental work can contribute to early demise.

According to Ahn, one of the primary reasons restorations fall out or crack is brittle failure of the bond with the surrounding tooth. "All dental composites have microparticles to increase their rigidity and prevent their shrinkage during their curing process, but there's a tradeoff: when the composite gets harder, it gets more brittle."

With enough pressure or wear and tear, a crack forms, which then propagates throughout the entire restoration--or the gap between the tooth and the restoration results in restoration failures, including marginal tooth decay.

Having perfected the art of adhering to irregular surfaces under the variable conditions of the intertidal zone--evolving to resist pounding waves, the blazing heat of the sun, and cycles of salt water Immersion and windy dryness--mussels presented the ideal model for more durable dental restoration materials.

The byssal threads they use to affix to surfaces allow them to resist the forces that would tear them from their moorings. "In nature, the soft collagenous core of the mussel's byssal threads is protected by a five-to-10 micrometer thick, hard coating, which is also extensible and thus, tough," Ahn relates.

This durability and flexibility allow the mollusks to stick to wet mineral surfaces in harsh environments that involve repeated push-and-pull stress. Key to this mechanism is what scientists call dynamic or sacrificial bonding--multiple reversible and weak bonds on the subnanoscopic molecular level that can dissipate energy without compromising the overall adhesion and mechanical properties of the load-bearing material.

"Say you have one strong bond --it may be strong but, once it breaks, it breaks," Ahn points out. "If you have several weaker bonds, you would have to break them one by one." Breaking each weak bond, would dissipate energy, so the overall energy required to break the material would be greater than with a single strong bond.

Mussels have a high number of unique chemical functional groups called catechols, which are used to prime and promote adhesion to wet mineral surfaces.

The study shows that using a catecholic coupling agent instead of the conventional coupling agent provides 10 times higher adhesion and a 50% increase in toughness compared to current dental restorative resin composites.

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Title Annotation:Dental Restoration
Publication:USA Today (Magazine)
Geographic Code:1USA
Date:Oct 1, 2017
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