The long-term goal of this project is to increase the service life of dental resin composite restorations by obtaining a fundamental understanding of the development of secondary caries. Our more immediate goal is to test the hypothesis that oral biofilms contribute to the degradation of the margin, leading to more frequent instances of secondary caries. That might occur because composite materials select for a more cariogenic flora at the margin, or because products of bacterial metabolism contribute to the breakdown of the composite itself. Neither mechanism is mutually exclusive, so each question will be addressed in complementary clinical and laboratory studies, as described in the Specific Aims: 1.) Compare the bacterial species composition of biofilms collected from the enamel interface of sound amalgam restorations, sound composite restorations, composites with early secondary caries, and composites with frank secondary caries. Human Oral Microbe Identification Microarrays will be used to provide biofilm profiles incorporating 272 species. We will be testing the hypothesis that composite-enamel interfaces are colonized by distinctive bacterial species, compared to amalgam-enamel interfaces. Such ecological selection could account for an increase in virulence of the biofilm at the tooth-composite interface. Near-infrared optical computed tomography (OCT) will be used as an important adjunct to our clinical caries diagnosis, by detecting caries earlier than conventional methods, and confirming sound interfaces. 2.) Bridge our clinical and laboratory studies by optimizing a biofilm reactor system for growing multi-species oral biofilm microcosms at the composite-enamel interface of restorations placed in extracted teeth and coated with saliva. This system will provide the basis for testing the hypothesis that products of bacterial metabolism contribute to composite breakdown. Plaque samples from the clinical study will be used to establish microcosms corresponding to composite-enamel interfaces with no caries, early caries, or frank caries. The HOMIM system will be used to monitor the species composition of microcosms, and determine the conditions needed to reproduce the major species profiles of biofilms from patient samples. 3.) Use the Minnesota Artificial Mouth to incorporate load cycling into the biofilm reactor model. Composite restorations placed in extracted teeth will be subjected to repeated cycles of saliva coating, biofilm growth in the reactor, and loading in the artificial mouth. Teeth restored with composites that generate different levels of shrinkage stress will be exposed to the different types of microcosm, and also to sterile saliva medium alone, with or without loading. Both OCT and micro-CT imaging will be used to monitor the loss of minerals in the tooth tissues, while microhardness testing and Fourier-transform infrared spectrometry will be performed to assess changes in the composites. This in vitro model system will be used to test the hypothesis that defined bacterial microcosms and mechanical loading exert individual and combined effects on the material properties of composite restorations, degradation of the tooth-restoration margin and the time to restoration failure.

Public Health Relevance

Replacing failed dental restorations takes up 70% of a dentist's effort and contributes $5 billion to health care costs in the US. Among the different types of restorations, composite restorations have been shown to have a higher failure rate than amalgam restorations, with the main cause of failure being secondary or recurrent caries. The knowledge gained from this and future projects will help guide the design of the next generation of dental composite materials, which are likely to require reduced shrinkage stress, improved bond strengths, as well as antibacterial and cariostatic capabilities.

Agency
National Institute of Health (NIH)
Institute
National Institute of Dental & Craniofacial Research (NIDCR)
Type
Research Project (R01)
Project #
5R01DE021366-02
Application #
8141300
Study Section
Special Emphasis Panel (ZDE1-JH (19))
Program Officer
Drummond, James
Project Start
2010-09-10
Project End
2014-08-31
Budget Start
2011-09-01
Budget End
2012-08-31
Support Year
2
Fiscal Year
2011
Total Cost
$366,175
Indirect Cost
Name
University of Minnesota Twin Cities
Department
Dentistry
Type
Schools of Dentistry
DUNS #
555917996
City
Minneapolis
State
MN
Country
United States
Zip Code
55455
Zhu, Laikuan; Li, Yuping; Chen, Yung-Chung et al. (2018) Comparison between two post-dentin bond strength measurement methods. Sci Rep 8:2350
Zhu, Laikuan; Li, Yuping; Carrera, Carola A et al. (2017) Calibration of a lactic-acid model for simulating biofilm-induced degradation of the dentin-composite interface. Dent Mater 33:1315-1323
Carrera, Carola A; Li, Yuping; Chen, Ruoquiong et al. (2017) Interfacial degradation of adhesive composite restorations mediated by oral biofilms and mechanical challenge in an extracted tooth model of secondary caries. J Dent 66:62-70
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Isfeld, Darren M; Aparicio, Conrado; Jones, Robert S (2014) Assessing near infrared optical properties of ceramic orthodontic brackets using cross-polarization optical coherence tomography. J Biomed Mater Res B Appl Biomater 102:516-23

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