Better understanding of tooth root development may hold the key to artificial tooth regeneration, suggest scientists in China and the US. Based on research published during the last decade, Xiao-Feng Huang of Capital Medical University, Beijing, and Yang Chai of the University of Southern California, Los Angeles, reviewed the molecular mechanisms operating during root formation. Following tooth crown formation in the gums, a collection of cells called Hertwig’s epithelial root sheath (HERS) grows around it. HERS triggers the development of dentin and cementum, both vital materials for healthy roots. HERS cells, however, disperse as the root grows. More research is needed to clarify the fate of these cells, as well as the genetic signaling between two types of dental tissue, the epithelium and mesenchyme. Full understanding of these processes could eventually lead to artificially triggered tooth growth in humans.

Tiny movements at the contact area between dental implants and the underlying bone surface can cause wear and tear that threatens the long-term integrity of dental prostheses. This problem of so-called ‘fretting damage’ was long ignored by dentists and dental surgeons. Now, a review by Hai-Yang Yu and colleagues at Sichuan University in Chengdu, China, shows that the micrometer-scale movements at the dental implant–bone interface can actually be subdivided into two types: tangential fretting, which is caused by the direct contact stress of mastication, and radial fretting, which arises from the grinding-like pressure between the two surfaces when they remain in contact. The combination of these stresses leads to small cracks that are a big problem in the replacement of missing teeth by implant-supported prostheses.

Dentin matrix protein 1 (DMP1) protects cells involved in tooth formation against regulated cell death caused by high blood phosphate (Pi). Elevated Pi levels, caused by disorders such as chronic kidney disease, cause abnormal tooth formation. Afsaneh Rangiani and her colleagues from the Baylor College of Dentistry, USA, used mutant mice to dissect the roles of DMP1 and Pi in controlling the formation of dental pulp, enamel and dentin—major components of teeth. DMP1-deficient mice with elevated Pi levels had severe defects in pulp formation and the deposition of enamel and dentin. These defects were correlated with the premature death of ameloblastas and odontoblasts, the cells that produce enamel and dentin, respectively. No defects in tooth formation were found in DMP1-deficient mice with normal Pi levels.

Protective biofilms produced by cariogenic bacteria can be treated effectively with common and inexpensive dental equipment, Korean research shows. Ho-Won Park and colleagues from Gangneung-Wonju National University have shown that, after eight hours of incubation in cell culture, a novel variation of the technique known as photodynamic therapy (PDT) kills 75% of the biofilm-producing bacterium Streptococcus mutans. In cultures containing sucrose, the treatment was less effective at 55%. PDT uses a nontoxic photosensitizer that, when exposed to light, produces reactive oxygen species that kill bacteria. Although previous research had shown that PDT is effective against cariogenic bacteria, the treatments used specialized and expensive equipment. Park and colleagues’ variation of PDT uses only the photosensitizer erythrosine and a halogen curing unit, which are already used widely by dentists. Future research will investigate its efficacy in clinical situations.

Acid etching of tooth root surfaces could improve the adhesion of surgical filling materials, according to research from Saudi Arabia and the United States. Khalid Al-Hezaimi at King Saud University and colleagues studied the adhesion of mineral trioxide aggregate (MTA), which is used to fill the ends of tooth roots after infected tissue has been removed. MTA comes in both white and gray colors. The researchers applied MTA to root cavities in 64 extracted human teeth, half of which had been pre-treated by etching with phosphoric acid. They then used microcomputed tomography and scanning electron microscopy to measure the sizes of gaps between the MTA and the root. This showed that the acid pre-etching helped to improve the adhesion of gray MTA, but not white—a finding the researchers attribute to chemical and structural differences between the two colors.

Bleaching teeth using hydrogen peroxide-based whitening agents damages the molecular structure of enamel, scientists in China report. Researchers have long debated the damage caused by tooth bleaching methods, including ‘cold-light bleaching’ — accelerating acidic hydrogen peroxide activity using blue light. Wei Li and co-workers at Sichuan University evaluated the effects of different bleaching procedures on enamel crystals in a bid to settle this debate. The researchers used X-ray diffraction — a technique used in materials science to examine crystals — to analyze the enamel non-invasively. They found that blue light alone did not affect the enamel, but whitening solutions of 35% hydrogen peroxide in the pH range of 5.2 to 5.8 caused it to demineralize. The enamel crystals decreased in size, the overall crystalline structure was less coherent, and the tooth surface also became rougher.

Clinicians in China report that an alternative surgical procedure to correct retrusion of the lower jaw is safe and effective. Backward displacement of the lower jaw, or mandibular deficiency, can affect an individual’s facial appearance and the ability to chew food, speak, breathe, and sleep normally. Bilateral sagittal split ramus osteotomy (SSRO), the procedure typically used to correct mandibular deficiency, has associated risks of nerve injury and relapse. Jing Hu and his colleagues at Sichuan University, China, therefore assessed the clinical efficacy of the less-established, alternative procedure known as inverted L-osteotomy (ILO). Their early results showed that ILO aligned the upper and lower jaws of 11 adults with mandibular deficiency. The patients’ aesthetic appearances improved, and they had no associated permanent damage to their facial nerves.

Daily chewing has no effect on the fracture toughness of quartz-fiber tooth restoration materials, according to recent research from China. Chun-Yuan Zhang from Sun Yat-Sen University and colleagues investigated how extracted molars — that had been repaired with aligned quartz-fiber ‘posts’ in an epoxy matrix — behave under two kinds of destructive force. They found that molars subjected to five years’ worth of chewing motions through cyclic force loading had identical fracture points and patterns as molars under a static, steadily increasing force. Zhang and colleagues attribute the resilience of the quartz posts to biomechanical movements that allow homogenous transfer of stress into tooth dentin. Chemically enhanced bonding of the quartz posts to teeth and structural reinforcements also contributed to the sturdiness of this novel system.

Gingival fibromatosis is a rare disease, especially its syndromic form. Here, we review the literatures on gingival fibromatosis and briefly summarize some characters on clinical, etiological, genetic and histopathological aspects. We also present a rare case of gingival fibromatosis with multiple unusual findings in a 21-year-old man. And we differentiate it from some well-known syndromes including gingival fibromatosis. Maybe it implies a new syndrome within the spectrum of those including gingival fibromatosis.

Laugier–Hunziker syndrome (LHS) is an acquired pigmentary condition affecting lips, oral mucosa and acral area, frequently associated with longitudinal melanonychia. There is neither malignant predisposition nor underlying systemic abnormality associated with LHS. Herein, we present three uncommon cases of LHS with possibly new feature of nail pigmentation, which were diagnosed during the past 2 years. We also review the clinical and histological findings, differential diagnosis, and treatment of the syndrome in published literature.

This case report describes the diagnosis and endodontic therapy of maxillary fused second and third molars, using cone-beam computed tomography (CBCT). A 31-year-old Chinese male, with no contributory medical or family/social history, presented with throbbing pain in the maxillary right molar area following an unsuccessful attempted tooth extraction. Clinical examination revealed what appeared initially to be a damaged large extra cusp on the buccal aspect of the distobuccal cusp of the second molar. However, CBCT revealed that a third molar was fused to the second molar. Unexpectedly, the maxillary left third molar also was fused to the second molar, and the crown of an unerupted supernumerary fourth molar was possibly also fused to the apical root region of the second molar. Operative procedures should not be attempted without adequate radiographic investigation. CBCT allowed the precise location of the root canals of the right maxillary fused molar teeth to permit successful endodontic therapy, confirmed after 6 months.