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Mouse Model Sheds Light on Dental Defects

Scientists at the National Institute of Dental and Craniofacial Research have created an animal model that mimics two human hereditary dental defects — dentinogenesis imperfecta type II and dentin dysplasia. Their studies of the mouse model offer clues to how these disorders arise.

Dr. Ashok Kulkarni and his colleagues genetically engineered mice that make extra amounts of TGF-ß1 (transforming growth factor beta-1) in their teeth. The animals were born with no apparent defects, but at two weeks their teeth became discolored and eventually fractured, leaving behind small stumps. Detailed study of the animals revealed reduced activity of the dspp gene, which produces a protein that is critical for dentin formation. The scientists reported their findings in the Apr. 6 issue of the Journal of Biological Chemistry.

"Our mouse model sheds light on the role of TGF-ß1 in tooth development and points to a reduced functioning of the dspp gene as a possible cause of dentinogenesis imperfecta type II and dentin dysplasia," said study author Kulkarni from the NIDCR functional genomics unit and gene targeting facility. "Additionally, this animal model gives us a new tool for developing and testing treatments."

Dentinogenesis imperfecta type II, which affects approximately 1 in 6,000 newborns, is characterized by blue-gray or amber brown opaque teeth. The teeth have narrow roots, are fragile and fracture easily. In dentin dysplasia, tooth color can be normal, or slightly bluish or brownish and opaque. The teeth are shorter and more pointed than normal teeth, and may become loose and fall out because of inadequate root formation. The tooth's dentin is abnormal in both hereditary defects. Dentin, which is a hard material similar to bone, makes up about three-fourths of an adult tooth. It lies between the outer enamel and the innermost core of the tooth called the dental pulp.

Beehive Product May Inhibit Caries

By Jody Dove

Centuries of folk medicine have made use of nature's bounty of plants, herbs and other natural substances to combat diseases and infections. Now scientists are confirming in laboratory studies that one of these substances — propolis, a resinous product collected from beehives — may inhibit the development of tooth decay.

NIDCR-supported investigators at the University of Rochester, working collaboratively with researchers at the University of Campinas, Brazil, found that propolis significantly reduces dental plaque formation. Propolis is a potent inhibitor of glucosyl-transferase enzymes, enzymes that synthesize glucans from sucrose and promote the binding of cariogenic bacteria to teeth, critical steps in the development of decay. Interestingly, the investigators also discovered that the effectiveness of propolis depends on the geographic area from which it was collected in Brazil.

Since early times, man has used propolis in a variety of ways. The word comes from the Greek and means "defender of the city." Ancient Greek texts refer to the substance as a cure for wounds and diseases. Hippocrates prescribed propolis for the healing of sores and ulcers, both internal and external. Records from 12th century Europe show that medical preparations using propolis were employed for mouth and throat infections.

This natural substance is actually used by bees to strengthen and protect their hive from germs and foreign invaders. Worker honeybees collect propolis from the buds of various poplar and conifer trees and bark lesions. The bees pack the propolis on their hind legs and carry it back to their colony where it is combined with beeswax and salivary secretions. Worker bees then use the substance to fill cracks in their hives and as a cleanser for cells prior to placing honey or pollen in them. Before the queen will lay her eggs in a cell, the bees clean it out and line it with a microscopic coating of propolis. Only then will the queen deposit her eggs in this sterile environment. Propolis also has antibacterial and antifungal effects that protect the colony against disease. It has been shown to kill Bacillus larvae, a bacterial disease that attacks bees.

Further characterization of the structure and function of the active component of propolis may lead to a new anti-caries product. Findings from the study appeared in Caries Research.


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