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Increasing the Service Life of Dental Resin Composites

Dental Materials and Biomaterials Program
Integrative Biology and Infectious Diseases Branch, DER



OBJECTIVE

The intent of this initiative is to stimulate research that will develop methods to assess the clinical success of dental resin composite materials as a restorative material and to encourage research for improving this material and/or for the development of new restorative materials.  Photocurable composite materials have become increasingly utilized for dental restorations. However, longevity and survival studies show that dental resin composites have an average replacement time of 5.7 years and such failures are mainly due to secondary decay and fracture of the restoration. The long range goal of this initiative is to increase the service life of dental resin composites and to understand the factors causing the decrease in durability as it relates to the oral biofilm and environmental mechanisms of fracture.  The objective of this initiative is to better understand how degradation due to either physical and environmental factors and/or the composition of dental resin composites interacting with the biofilm in the oral cavity facilitates the development of secondary decay. This new knowledge will help to devise better materials for longer lasting dental resin composites and reduce the need for multiple restorative replacements.

Multidisciplinary approaches are strongly encouraged for in vitro, in vivo, animal or clinical studies.  Examples of research include, but are not limited to: 1) identification and characterization of the local microbial composition at the tooth-composite interface and how this profile might compare with native sites; 2) detection of degradation products at the tooth-composite interface and how these products might alter the local microbial composition; 3) development of imaging or sensing modalities for the early detection of tooth-composite interface breakdown; 4) development of novel approaches to modulate the tooth-composite interface including modification of current materials, development of new materials and or resin systems, or delivery of bioactive agents to confer caries resistance, and 5) elucidation of mechanisms of restorative material failure in a physiologically and clinically relevant oral cavity environment.

BACKGROUND

Dental composites consist of a polymerizable resin matrix, a reinforcing glass particle filler, and silane coupling agents. These glass particle/resin matrix composites have good aesthetic properties and strength, making them the most widely used materials for restorations of anterior teeth and increasingly for posterior teeth. The key evaluation of resin composite restoratives is clinical survival.  Although these restorative materials have been reasonably successful for both anterior and posterior restorations, studies have indicated a wide range of failures. The main reason for replacement of dental restorations is secondary decay. A study of posterior composite restorations summarized data published between 1996 and 2002 and concluded that failure of composite restorations between 0-5 years of placement was improper placement technique or material selection followed by secondary decay. Between 6-17 years of placement, secondary caries was the reason to replace the restoration.  As expected, the longer a restoration is in use, the higher the failure rate.  Another study showing that after 10 years for one surface restorations, only approximately one-half survived.

The current research focus has been on the mechanical properties of dental resin composites with numerous publications on fracture toughness, flexure strength and elastic modulus.  However, research addressing the mechanisms of failure is lagging.  Dental composite materials used for restorations are subjected to a harsh chemical and mechanical environment in the mouth. Acids from food, plaque-forming bacteria and ingested liquids contribute to the erosion of dental restorations. Mastication subjects the tooth and any associated fillings to a series of cyclic wear-and-tear forces.  The in vitro results indicate a decrease in mechanical properties with material aging in solutions, especially for ethanol and artificial saliva and cyclic loading (fatigue). The enzymes in saliva degrade dental composites and may enhance tooth decay.  Furthermore, dental resin composites confront a complex oral microbiological environment composed of hundreds of different strains of bacteria.  There is strong evidence to suggest that biofilm formation contributes to the chemical and mechanical degradation of dental composites. On the other hand, there is a lack of evidence to indicate that polymerization shrinkage is the primary cause of secondary decay and that micromorphological margin deterioration and clinical gap formation do not necessarily result in a higher risk for secondary decay.

Private practitioners placed 122.7 million dental resin composites in 2006.  The reasons for the failure of many of these dental restorations remain to be investigated.  Therefore, the development of new longer lasting dental resin composites is an urgent dental and orofacial health need. The use of these new materials will have a significant impact on the oral health of the US population. This Initiative will focus future research towards a better understanding of the interactions of dental resin composites and the surrounding oral environment. In concert with this priority, there will be a focus on the need to develop a new resin system for dental resin composites and on continuing to modify and improve the existing resin systems.  Importantly, what is needed is a better understanding of dental resin composites with respect to mechanical properties and the interaction with the microbial environment as related to clinical success.

 

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This page last updated: February 26, 2014