The stage at which tooth precursor cells in suspension form tooth-like structures has been determined in rat cells. Xue-Dong Zhou of Sichuan University, China, and colleagues created single-cell preparations from tooth precursor cells at different stages of development, and assessed their ability to form tooth structures when removed from the normal surroundings of tooth development. The results showed that cells 16.5 days old or more formed distinct tooth-like structures including pulp and dentin, while younger cells formed disordered tissue. Cells aged 18.5 days before isolation went on to exhibit partially formed enamel. The researchers suggest the TGF-beta signaling pathway, identified in previous studies as a mediator of tooth formation, may play a role in this setting. The findings warrant further investigation into tooth bioengineering, which may ultimately yield therapies to replace defective teeth in humans.

A fatty substance called globoside triggers the developing tooth to create the cells that deposit dental enamel. Takashi Nakamura from the Tohoku University Graduate School of Dentistry, Sendai, Japan, and colleagues looked for the expression of globoside in teeth from three-day-old mouse pups and showed that it was highly active in cells known as ameloblasts, which secrete the hard enamel that coats the tooth crown. Adding globoside to cultured rat dental cells led to an increase in proteins involved in making enamel. The substance also stimulated the expression of receptors that drive ameloblast formation, while repressing others that help keep dental cells in an undifferentiated state. The findings reveal a novel developmental pathway that could help inform future treatments of enamel defects.

Research shows that stem cells isolated from adult teeth can develop into tendon tissue and could be used for tendon repair. Tendon injuries are difficult to treat and require long healing periods and/or surgery. Adult stem cells have the potential to improve tissue repair, and they assessed whether stem cells from the teeth could be used. They isolated dental pulp stem cells (DPSCs) from the permanent teeth and showed that they express some tendon-related proteins. When they grew DPSCs on polyglycolic acid scaffolds under mechanical stress on nude mice back, the cells formed tendon tissue that expressed all the crucial tendon-related proteins. The findings show that DPSCs have potential for engineering of tendon-like tissues.

Interaction between developing blood vessel and bone marrow cells may improve the quality of engineered bone grafts. Florian Böhrnsen and Henning Schliephake at Germany’s University of Göttingen cultured bone marrow stem cells and cells from blood vessels together and separately, and analyzed how they differentiated. Even when grown together, cells retained their ability to differentiate into bone marrow and blood vessels, respectively. The expression of differentiation markers was increased in the co-cultures, suggesting that the two cell types reinforce each other’s differentiation. Furthermore, the presence of bone marrow cells encouraged structured growth of the blood vessels. Understanding the beneficial interactions between these two cell types is important in efforts to engineer bone grafts with a blood vessel network, and will improve our ability to successfully engineer and implant bone tissue.

An enzyme found to be crucial to the growth and survival of a bacterium found in the mouth could be targeted to prevent tooth decay. The Streptococcus mutans bacterium is a major cause of tooth decay; fed by high sugar intake, it generates acid that leads to tooth demineralization. Ming-Yun Li and co-workers at Sichuan University in Chengdu, China, have demonstrated that an enzyme called alanine racemase (Alr) is crucial to the growth and maintanance of S. mutans cell wall structure. The team created alr mutant strain of the bacterium, and discovered that without the enzyme the bacterium cell wall tore easily, leading to cell disintegration. They also found that deleting Alr significantly reduced the bacterium's ability to compete effectively with other oral bacteria. The manipulation of the enzyme in oral biofilm could help reduce tooth decay.

A novel antibacterial agent shows promise for use in dental bonding agents and other restorative materials. To preserve tooth structure for successful long-term restorations, dentists are now encouraged to remove as little decayed dentin as possible, but this requires new materials and techniques. Hockin HK Xu at the University of Maryland, USA, Xue-Dong Zhou at Sichuan University in China, and co-workers tested dental primers (chemicals that are applied before adhesive to increase bonding strength) made with an antibacterial agent called dimethylaminododecyl methacrylate (DMADDM). After treatment with 10% DMADDM primer, dentin infected with the bacterium Streptococcus mutans, a leading cause of decay, showed a far larger bacterial inhibition zone, and a much lower bacterial count than dentin treated with a control primer. DMADDM also outperformed a primer containing an existing antibacterial agent.

Clear orthodontic braces can still be improved to avoid coloration changes resulting from coffee drinking. Clear aligners are an alternative to traditional teeth braces, often chosen because they are more cosmetically pleasing. Patients are advised to remove them while eating and drinking by drinking, but many do not comply. Zhi-He Zhao, Jun Liu and colleagues from Sichuan University in China tested clear aligners made of three different materials from three companies (Invisalign®, Angelalign®, and Smartee™) for coloration changes after immersion in coffee, black tea, red wine and water. The three types of devices showed color stability after 12 hours of immersion, except for the Invisalign®aligners immersed in coffee. These were more prone to pigmentation and had a rougher surface after seven days of immersion in coffee than the other aligners.

Common developmental cues probably underlie both premolar tooth agenesis and the shape of the jawbone. About 3% of the population never develop a lower second premolar tooth. What is the relationship between missing teeth and jawbone shape? To find out, a team led by Michael Bertl from the University Clinic of Dentistry in Vienna, Austria, measured anatomical landmark coordinates in the jawbones of 150 patients. They found that people missing a lower second premolar, whether or not their primary second molars had been extracted, had morphological differences that extended across the whole jawbone, pointing to genetic and epigenetic effects affecting the growth of both craniofacial bones and teeth.