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OHSU School of Dentistry team finds persistent oral bacterial strains, even one year after treatment for severe early childhood caries

01/07/13  Portland, Ore.

A follow-up study shows dominant genetic strains of highly-cariogenic bacteria and several emergent strains in young patients

In a follow-up to a study conducted one year ago, researchers at the Oregon Health & Science University School of Dentistry have determined that certain genetic strains of bacteria are dominant in children one year after treatment for microbial-caused plaque and tooth decay, and six new previously undetected minor strains were identified. The research team also found that certain bacterial strains in children are resistant to xylitol, a popular product used to reduce plaque and suppress bacterial growth.

The study is published online in the December 2012 issue of the Journal of Oral Microbiology.

Dental caries represents one of the most common chronic diseases affecting young children, and is a multi-factorial disease involving complex interactions of genetic, dietary, environmental, and behavioral risk factors. The most predominant collections of bacteria associated with dental caries are members of the mutans streptococci (MS) group. Individuals who exhibit high caries prevalence, compared to those with low caries prevalence, may have MS strains with distinct differences in virulence and caries-promoting activities. The coexistence and concurrent virulence of multiple MS genotypes in caries-active individuals may be important determinants for increased caries incidence, as well as treatment success or failure.

In the OHSU follow-up study, the team examined the profiles of MS genotypic strains from children initially in the study who had been diagnosed with severe early childhood caries. Children in good health, aged three to five, who underwent full-mouth dental rehabilitation therapy while under general anesthesia in the Pediatric Dental Surgery Clinic at OHSU’s Doernbecher Children’s Hospital were the focus of the study.

Dental rehabilitation therapy for the children included application of chlorhexidine gluconate, followed by amalgam, composite, and stainless steel crown restorations, formocresol pulpotomies, extractions, sealants, dental prophylaxis, and sodium fluoride varnish. Plaque samples were then taken from each participant during the one-year recall visit and compared to specimens collected during three periods: prior to the initiation of dental rehabilitation therapy, within the two-to-four week post-rehabilitation visit, and at the six-month recall visit.

Of the children available for their post-rehabilitation recall visits (seven total), the team identified 37 genotypic strains of S. mutans, two genotypic strains of S. sobrinus, and seven non-MS strains during the entire study, including the appearance of six new MS strains found only at the one-year collection.

“In the follow-up study, we identified caries-active children who possess MS genetic strains with different xylitol resistance properties, with some strains exhibiting increased cariogenic potential,” said Curt Machida, Ph.D., principal investigator and OHSU professor of integrative biosciences and pediatric dentistry. “We hope these studies will provide insight into the use of xylitol treatment for caries preventive maintenance therapy in children with severe early childhood caries, and lead to potential applications in personalized dentistry practices.”

The OHSU team included Machida; Elizabeth A. Palmer, D.M.D. `08, Pediatric Dentistry `10, assistant professor of pediatric dentistry; Alex Vo, D.M.D. `12; Shelby Hiles, D.D.S., Pediatric Dentistry `11; Patricia Peirano, D.D.S., Pediatric Dentistry `12; Samyia Chaudhry, lab assistant, integrative biosciences department and incoming first-year dental student; fourth-year dental students Amy Trevor, Iraj Kasimi; and Jill Pollard; first-year OHSU oral and maxillofacial surgery resident Christopher Kyles, D.M.D. `12; Beth Wilmot, Ph.D., OHSU biostatistician and statistical geneticist; John Engle, D.D.S., chair and assistant professor of pediatric dentistry; John Peterson, D.D.S., professor of pediatric dentistry; and Tom Maier, Ph.D., assistant professor of integrative biosciences and oral pathology and radiology.

The research was funded by the Pediatric Dentistry Resident Fund of the OHSU Foundation, and OCTRI (the Oregon Clinical and Translational Research Institute; grant numbers TL1 RR024159 and UL1 RR024140), which is funded by a grant from the National Center for Research Resources (NCRR), a component of the National Institutes of Health (NIH) and the NIH Roadmap for Medical Research.

Established in September 2006 through the NIH’s Clinical and Translational Science Award (CTSA) program, OCTRI is a unique partnership between OHSU and Kaiser Permanente Center for Health Research – bringing together an academic medical center and an innovative managed care organization. OCTRI’s mission is to improve human health by enhancing clinical and translational research. OCTRI works with institutional partners, community organizations, and industry to engage communities in clinical research efforts and to reduce the time it takes for laboratory discoveries to become treatments for patients.

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Oregon Health & Science University is the state’s only academic health and research university. As Portland's largest employer with nearly 14,000 employees, OHSU's size contributes to its ability to provide many services and community support not found anywhere else in the state. OHSU serves patients from every corner of Oregon and is a conduit for learning for more than 4,300 students and trainees. OHSU is the source of more than 200 community outreach programs that bring health and education services to each county in the state.

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