The negative impact of diabetes on bone quantity and quality can lead to an increased risk of fractures and severe gum disease. Dana Graves from the University of Pennsylvania in Philadelphia and colleagues reviewed the mechanisms behind bone loss in people with diabetes and the link to severe gum disease (periodontitis). Diabetes reduces bone-forming cells and bone turnover, while enhancing the number of cells that break down and absorb bone tissue back into the body. These changes in bone metabolism increase the risk of fracture and severe periodontitis. Diabetes is one of the main risk factors for periodontitis, people with diabetes being three to four times more likely to have the disease. This higher risk is most likely due to an exaggerated immune and inflammatory response to the bacteria responsible for gum disease.

Embryonic bone development and bone remodeling throughout life both rely critically on the Hedgehog signaling pathway. A team led by Ling Ye from Sichuan University in China and Ying-Zi Yang from the National Human Genome Research Institute in Maryland, USA, review how this key regulatory pathway of animal development affects bone health and disease. During early limb development in vertebrates, for example, one protein in the pathway, Sonic Hedgehog, acts to regulate patterning and growth. Another protein, Indian Hedgehog, later helps convert cartilage into bone in the developing skeleton. The authors discuss how the disruption of Hedgehog signaling can cause severe bone disorders, while enhancing Hedgehog activity can help repair fractured bones. A better understanding of Hedgehog signaling should improve bone disease prevention, diagnosis and treatment.

Researchers in Germany and Egypt have identified a cell population in the gum margins with regenerative potential. A team led by Karim Fawzy El-Sayed, from the Christian Albrechts University in Kiel, Germany, and Cairo University in Egypt, magnetically sorted human gum tissue using antibodies that bind STRO-1, a surface protein that marks cells as mesenchymal stem cells. Cells expressing STRO-1 showed more molecular characteristics of stem cells, had greater proliferative capacity and could differentiate into more cell types than cells without STRO-1 on their surface. The study is the first to directly compare the two gum cell populations. STRO-1-positive cells in the gum margin could provide a renewable source of multipotent stem cells for the treatment of gingivitis and other types of periodontal disease.

Expression of a regulator of tooth mineralization starts late during embryonic development in mice, continuing until four weeks after birth. Jian-Jun Hao and his colleagues at the University of Connecticut Health Center in the USA created a mouse model for tracking when and where the protein Fam20C is expressed in the body. The researchers engineered mice to make green fluorescence protein, a visible marker, in any tissues where Fam20C would normally be found. They saw the green glow in the dentin-forming cells of the teeth and in bone-forming cells of the craniofacial and alveolar bones starting at day 17.5 of embryonic development. The green signal decreased after the mice reached four weeks of age. The findings — and the mouse model itself — could lead to therapies for dentin and bone defects.

Researchers have clarified the molecular interactions that underpin the formation and regeneration of dentin in human teeth. Dentin is the layer of calcified tissue directly beneath the surface enamel of a tooth. It is formed and sustained by the differentiation of cells in the tooth pulp that lies beneath the dentin layer. Chenglin Wang and co-workers at Sichuan University in China, with colleagues at Columbia University, New York, USA, studied human dental pulp cells in vitro. They demonstrated that bone morphogenetic protein 2 (BMP2) promotes the differentiation of pulp cells to form dentin by affecting signaling pathways known to be involved. Identifying the links between the growth factor BMP2, and β-catenin and p38, proteins in these pathways, will improve understanding of dentin formation and repair after injury.

A new protein-repelling dental composite prevents bacterial attachment and plaque build-up while retaining its mechanical strength. Secondary tooth decay following tooth restoration is responsible for the replacement of almost half of all dental restorations within 10 years. An international team led by Hockin HK Xu at the University of Maryland now show that incorporating up to 3% 2-methacryloyloxyethyl phosphorylcholine (MPC) into a dental resin significantly repelled the deposit of salivary proteins that act as anchor points for bacterial attachment. After 48-h exposure to a solution that simulates the oral environment, the MPC resin had less bacterial coverage than controls, and its load-bearing capability was unaffected. MPC has already been incorporated successfully into several medical devices. This study suggests a promising new use in dental composites with the potential to prevent secondary tooth decay.

The strength of dental resin-based adhesives could be improved by adding light-activated riboflavin (RF, also known as vitamin B₂). Amr Fawzy and his team at the National University of Singapore, analysed the resin–dentin interface of human molars in which dentin was restored with adhesives containing different concentrations of RF. Following storage of the restored teeth for up to nine months in artificial saliva, they found that the strongest bonds formed with adhesives containing 3% RF. Scanning electron microscopy showed that this was due to RF’s crosslinking effect on dentin collagen fibrils. This is consistent with their previous findings that dentin pre-treatment with RF strengthens the collagen network. Adding 3% light-activated RF to dentin adhesives could make dental composite restorations more long-lasting without increasing the number of clinical steps required.

The success of replanting vertically fractured teeth depends on crown restoration and healthy periodontal tissues. Using 40 upper first premolar teeth that had been extracted from adolescents for orthodontic reasons, a team led by Wen-Mei Wang from Nanjing University Medical School, China, split each tooth in two, creating vertical fractures. The researchers rejoined the halves with a bonding resin and applied metal crowns to half the teeth. To simulate the two kinds of replantation that can occur, they either attached a layer of silicone rubber to mimic periodontal ligaments or attached epoxy resin as a stand-in for bone. The researchers then applied cyclic forces to reproduce the repeated stress of chewing and found that crown restoration and repaired periodontal fibers are both important for the long-term health of vertically fractured teeth.