Cells derived from human embryonic stem cells express a similar suite of genes as the precursor cells that eventually deposit tooth enamel. The findings highlight the potential of one day using such stem cells to help regenerate the hard tissue that coats the outside surface of teeth. A team led by Yan Zhang of the University of California, San Francisco, compared the gene expression profiles of embryonic stem cells, coaxed partially down a pathway toward an enamel-producing fate, with true enamel-forming precursor cells taken from human fetal teeth. They showed that both cell types expressed CK76, a gene encoding a fibrous structural protein known as keratin that makes up the bulk of the enamel matrix, in addition to various other genes that affect the deposition of this protective tooth layer.

Human stem cells taken from the connective tissue that attaches teeth to the underlying bone can give rise to new cartilage. Because such tissue can be obtained fairly easily during dental surgery, the findings—reported by Jaejin Cho and his co-workers at the Seoul National University, Korea—suggest that patient-specific dental stem cells could provide a personalized way to treat a number of cartilage and bone disorders. Cho’s team isolated dental stem cells from the connective tissue, or periodontal fibers, attached to an impacted third molar taken from an otherwise healthy donor. They added growth factors to induce a process called ‘chondrogenesis’ and ran a battery of genetic, chemical and histological tests to demonstrate that the cells had taken the first steps toward cartilage formation.

People with the condition known as leukoplakia, which causes thickened, white patches to form inside the mouth, express elevated levels of epidermal growth factor receptor (EGFR) 4, a signaling molecule that has been linked to cancer. The findings, reported by Yoshiki Hamada of Tsurumi University, Japan, and colleagues could explain one of the drivers of this precancerous dental disease and provide a new target for drug therapies. Hamada and his colleagues compared the expression profile of the four EGFR-family genes and their target ligands among 14 people with leukoplakia, 10 people with a separate mouth condition known as oral lichen planus and 14 healthy controls. They showed that only the fourth receptor, sometimes called HER4 or ErbB4, was overexpressed in people with leukoplakia along with two of its activating ligands, Neuregulin 2 and 4.

Radiation therapy for cancer can alter the type and number of microbes in patients’ mouths, research by Zheng-Wei Huang and colleagues of the Ninth People’s Hospital in Shanghai, China has shown. Diverse oral microbial communities play an important role in maintaining human oral health, and changes in composition can contribute to side-effects such as radiation caries and soft tissue necrosis. Huang and colleagues sampled plaque from 8 patients and used high-throughput sequencing to produce detailed microbial maps for 7 time points during the course of radiotherapy. This technique averts the need for inefficient and unreliable culturing. Overall, 50% of all microbes detected belonged to just 5 genera, although many species were present in low numbers. As radiotherapy progressed, the composition of patients’ microbial communities changed. Understanding these community shifts may help researchers design effective therapies.

The new antiseptic alexidine disinfects root canals as effectively as the commonly used chlorhexidine, a study by Kee-Yeon Kum of the Seoul National University School of Dentistry in South Korea and co-workers has shown. The root canal’s complex anatomy is prone to infection following treatment, so is treated with combinations of antiseptics. Chlorhexidine interacts poorly with the ubiquitously used sodium hypochlorite. Kum and co-workers therefore tested the efficacy of alexidine — which interacts well with sodium hypochlorite — against Enterococcus faecalis, a major cause of persistent infections. The researchers soaked blocks of bovine root canal, infected with E. faecalis, in 1% alexidine or 2% chlorhexidine for 5 or 10 minutes. Visualization of intact cells using scanning electron microscopy showed that alexidine and chlorhexidine are equally effective against E. faecalis, and that 5 minutes of soaking is required.

During root canal treatment, disinfection with chlorhexidine — an antimicrobial with long-lasting effect — can help prevent infection, Brazilian research shows. The complex anatomy of the canal, which is comprised of the pulp-containing canal and the microscopic dentinal tubules radiating outward to the tooth’s edge, can harbor harmful microbes after a tooth’s pulp is removed. Effective disinfection is therefore essential. Ronan Delgado and colleagues at the University of São Paulo, Brazil, tested two antimicrobial gels, chlorhexidine and calcium hydroxide, on extracted teeth infected with Candida albicans, a particularly tenacious oral microbe. Using fluorescence techniques to count live and dead cells very accurately, they determined that either alone or paired with calcium hydroxide, chlorhexidine was more effective against C. albicans than calcium hydroxide alone.

Grafting a new biologically derived matrix onto damaged dental tissue may help cell regeneration, research from China and the USA shows. Guo-qiang Guan at the State University of New York, USA, and co-workers at that institute and Shandong University, China, have successfully designed and trialed a matrix scaffold for use in the repair of periodontal tissues, which surround and support the teeth. The team removed cells from sections of pig tissue, while leaving the extracellular framework intact to create so-called ‘porcine acellular dermal matrix’ (PADM) grafts. They then treated the PADMs with hydroxyapatite (HA) — a mineral form of calcium apatite similar to that found in dental enamel and dentin. The HA-PADM provided an excellent, biodegradable scaffold for the regeneration of periodontal tissue cells both in laboratory cultures and in rabbits.

Dental fillings made of nickel—chromium-based alloys appear to increase the levels of these toxic metals excreted in recipients’ urine. A team led by Qing-wu Jiang of Fudan University in Shanghai, China, compared the urinary concentrations of nickel and chromium in 795 people who had metal dental fillings with 198 people who had no such fillings. Nickel concentrations were significantly higher in people who had received the fillings within the past month compared with controls. Elevated chromium levels were detectably higher in people who had received fillings within the past six months. Urinary concentrations of both metals were also greater in people with more than one nickel–chromium alloy fillings. The authors call for follow-up work to investigate the potential health outcomes of having these metals leaching into the body’s circulation system following dental restoration.

Research in China to classify smiles could help guide future oral reconstruction surgery in the world’s most populous country. A team led by Wen-Jie Hu of Peking University analyzed smiles from 188 young adults of Han Chinese ethnicity and categorized them according to overall shape and upper lip curvature. Consistent with studies from other populations, the researchers showed that around 60% of the participants had what’s known as a ‘commissure’ smile, typically shaped like a Cupid’s bow. Another third had a ‘cuspid’ smile, in which the lips are commonly visualized as a diamond, and the final 6% had ‘gummy’ smiles. However, unlike a previously reported Caucasian cohort, the Chinese subjects, like Koreans, had lips that tended to be straight or downward-facing, rather than curving upwards.

One-step apexification using mineral trioxide aggregate (MTA) has been reported as an alternative treatment modality with more benefits than the use of long-term calcium hydroxide for teeth with open apex. However, orthograde placement of MTA is a challenging procedure in terms of length control. This case series describes the sequence of events following apical extrusion of MTA into the periapical area during a one-step apexification procedure for maxillary central incisor with an infected immature apex. Detailed long-term observation revealed complete resolution of the periapical radiolucent lesion around the extruded MTA. These cases revealed that direct contact with MTA had no negative effects on healing of the periapical tissues. However, intentional MTA overfilling into the periapical lesion is not to be recommended.