Understanding the mechanical properties of human teeth could enhance artificial tooth development, dental scientists in China conclude in a review of recent research. Artificial teeth are required to make incisions, lacerate and grind food like natural teeth, but the perfect material to make them remains undiscovered. This deficiency is partly because of gaps in current knowledge regarding the structural and mechanical properties of the two main dental tissues, enamel and dentin. After reviewing recent research into both tissues, Xue-Dong Zhou, Hai-Yang Yu and co-workers at Sichuan University, China, recommend further investigations — particularly at the microscopic level — into the elastic mechanics and fracture-resistant qualities of dental tissues. The team believes it is important also to investigate how these properties change as people age, and how the surrounding oral environment affects tooth strength and fracturing.

A protein that alters bone and dental support structures does not affect tooth development, which has been reported by researchers in Austria and Switzerland. A team led by Reinhard Gruber, from both the Medical University of Vienna, Austria, and the University of Bern, Switzerland, analysed the lower jaws of mice engineered to lack a functioning copy of a gene called Sost. This gene encodes the protein sclerostin, which inhibits bone formation. Scientists knew that sclerostin was expressed by bone-resorbing cells called osteocytes and cementocytes, which form the modified bone found around the root of teeth. Gruber and colleagues found abnormalities in the structures surrounding the first molars of the mice lacking sclerostin. However, they found no significant defects in tooth dimensions. The work has implications for periodontal regeneration, implant dentistry and dentin formation.

Dental resins incorporating antibacterial agents could help to destroy the bacterial biofilm responsible for tooth decay, new research shows. By forming a biofilm on surfaces such as teeth, bacterial cells strengthen their chances of survival. To avoid secondary tooth decay following tooth restoration, it is important to minimize the biofilm growth of Streptococcus mutans, bacteria commonly associated with tooth decay. Hockin Xu at the University of Maryland and co-workers across USA and China investigated the effects of new antibacterial dental resins containing various ammonium salts. Their work focused on bacterial survival in different areas of the biofilm. The team found that the most effective resin was that incorporating an ammonium salt with a carbon backbone chain length of 16. This resin killed bacteria throughout the whole thickness of the biofilm.

Bone healing after oral surgery could be enhanced by new biodegradable membranes for reconstruction, according to research from South Korea. The search for non-toxic, biodegradable and hypoallergenic membranes to guide oral bone reconstruction after surgery is on-going. Current membranes are made from collagen. Sang Hun Shin and co-workers at Pusan National University have created a new membrane (named CFB-HAP) incorporating the natural polysaccharide chitosan, a structural protein from silk called fibroin, and hydroxyapatite, a component of natural bone. In a study comparing the effectiveness of CFB-HAP with collagen membranes, the team used microscopic computerized tomography to investigate new bone formation in rats. The images showed that CFB-HAP performed as well as existing membranes in terms of increasing bone volume and mineral density following oral surgery.

A new cement for tooth root repair may offer better biocompatibility and lower risk of inflammation than currently used materials. Mineral trioxide aggregate (MTA) has proven highly effective for endodontic repair procedures, but Ming-You Shie and colleagues at Taiwan’s Chung Shan Medical University have developed a calcium silicate (CS) cement that may prove safer. To simulate conditions in the mouth, they cultured dental pulp cells on both MTA and CS, and exposed them to a toxic compound produced by oral bacteria. Cells cultured on MTA exhibited an elevated and prolonged inflammatory response, possibly arising from silicon released from MTA. In contrast, cells cultured on CS showed improved viability and reduced inflammation over time. The researchers propose that this new cement may offer a useful alternative to MTA.

Zirconia-based ceramic crowns are strong, mechanically reliable and resist loading fatigue over time, according to research from China. Crowns made entirely from ceramics are frequently used as tooth replacements, but repeated stresses can cause cracks to propagate and sometimes lead to total failure of the crown. Dong-Sheng Zhang at Shanghai University and co-workers compared the impact of cyclic loading on two leading types of ceramic crown: one is made from hot-press lithium disilicate and the other from zirconia core materials. The researchers subjected the crowns to two million loading cycles of different magnitudes and measured the changes in the crowns' elasticity, hardness and fracture toughness over time. They found that cyclic loading had no significant influence on zirconia crowns, but the lithium-based crowns had a markedly lower load-bearing capacity.

Porous titanium granules (PTGs) that support growth of new bone could provide a robust scaffold for dental and skeletal repair. As a truly natural replacement, a patient’s own bone tissue seems ideal for such procedures, but bone implants tend to degrade so artificial materials may be more desirable for some applications. PTGs are sturdy and allow colonization by bone cells. Researchers led by Rafael Delgado-Ruiz of Stony Brook University in the USA tested the capacity of PTGs to mediate bone repair in rabbits. Six weeks after implantation, animals that received implants showed closure of bone defects and extensive growth of new bone relative to controls. Recovery was greatly improved by enclosure of the PTGs within a membrane. Unenclosed PTGs tended to exit the bone defect, leading to incomplete repair and an inflammatory response.

By taking regular casts of teeth, dentists could more easily monitor sealant retention over time, according to research from China. Dental sealants gradually deteriorate in the mouth and require careful observation by dentists. Human error and reflections from bright lights, however, can interfere with results during visual clinical examinations. Taking casts of teeth periodically to spot deterioration has proved useful for other dental treatments. To establish whether replica casts are useful for tracking sealant retention, Ming-Wen Fan and co-workers at Wuhan University, together with scientists from the Netherlands, compared the two observation methods in a study of 370 patients with sealed teeth over two years. They found that taking regular casts of the teeth allowed dentists to assess sealant levels more accurately and reliably than by using traditional visual examinations.

Extreme overload stress on cartilage during clenching can lead to significant damage to the jaw joint, researchers in Spain report. Around 85% of people suffer from awake or sleep bruxism —clenching / grinding of the jaw — at some point in their lives. Bruxism can lead to chronic pain and in extreme cases may do irreparable damage to the temporomandibular joint (TMJ). Maria Commisso and colleagues at the University of Seville built a finite element computer model of the TMJ and human mandible to examine the effect of abnormal loading stresses on the TMJ articular disc. The researchers modelled the behavior of the disc under sustained and cyclic loading, as found in awake and sleep bruxism, respectively. They found that sustained clenching in awake bruxism is the most damaging to disc cartilage.