More research is needed to assess whether all-ceramic crowns accelerate the rate of tooth wear in molars and premolars, conclude two dentists in Germany who systematically reviewed the dental literature. Rim Hmaidouch and Paul Weigl from the Johann Wolfgang Goethe University in Frankfurt, searched for published studies that investigated whether a causal relationship exists between the insertions of ceramic crowns and increased wear in the posterior dental region. They found only five studies that examined the issue, including three that evaluated tooth wear in the exact same patient population. From the three independent pools of study subjects, the authors determined that some ceramic materials are wear-friendly. However, the published studies suffered from many design flaws, so they believe that additional, more rigorous clinical trials are still warranted.

Expanded preventative and therapeutic efforts will be critical to maintaining the momentum in the fight against human immunodeficiency virus (HIV), concludes Fariba Younai of the University of California at Los Angeles, USA. Younai has reviewed the scientific and medical advances that help HIV patients in controlling their disease, as well as assist patients and health-care workers in containing the spread of this virus. She noted that existing treatments control but do not eliminate infection. Younai also listed causes for concern, including high disease burdens and mortality rates in the developing world. She explored the value of preventative strategies, such as drug prophylaxis to prevent HIV transmission by pregnant mothers to their children, and male circumcision. She also examined experimental efforts to eradicate latent viral reservoirs that might eventually give rise to AIDS.

A protein that regulates bone development may offer a useful target for promoting stem cell-mediated dental regeneration, report dental scientists in the US and China. The jaw contains multiple mesenchymal stem cell (MSC) populations that have the capacity to develop into a variety of mature cell types. Scientists see great potential in using these cells to repair dental damage, but they require a thorough understanding of how MSC’s development is coordinated. Christine Hong and Cun-Yu Wang of the University of California at Los Angeles have identified a protein that directly facilitates bone formation in dentally derived MSCs. They demonstrated that the enzyme KDM6B activates several genes that facilitate the transformation of MSCs into mature bone tissue. They also showed that this process is essentially blocked in the absence of KDM6B, confirming this protein’s critical role in stem cell based dental repair.

Nicotine increases the bacterium Streptococcus mutans’ cavity-causing ability by interacting with the enzyme sortase A, Richard Gregory of the Indiana University School of Dentistry, USA, and colleagues have shown. Sortase A modifies surface proteins in S. mutans. Scientists knew that nicotine increases cavity formation, but not how. Gregory and colleagues focused on the role played by sortase A because it controls the secretion and anchoring of the bacterium’s virulence proteins. Using S. mutans’ cultures of wild-type or sortase-deficient strains, the researchers investigated the effect of nicotine on biofilm formation ­— difficult-to-remove bacterial aggregates that trigger cavity formation. As they increased nicotine levels in the cultures, the researchers found that the wild-type strains produced significantly more biofilm than the sortase-deficient strains. These results indicate that sortase A plays a key role in nicotine-induced cavity formation.

Different diseases of the specialized tissues that surround and support teeth, the periodontium, result in different expression levels of the gene that encodes a key structural component, the glycoprotein cellular fibronectin (cFn). Guo-Min Ou and colleagues at Sichuan University in Chengdu, China, measured expression levels of cFn RNA in 30 people: 10 with periodontitis, inflammation around the teeth; 10 with peri-implantitis, inflammation around dental implants; and 10 with no periodontal problems. The researchers found that transcription of cFn in the periodontitis group was significantly lower than that in the healthy group. In contrast, the mRNA expression of cFn in the peri-implantitis cohort was higher than that in the healthy individuals. Although both inflammatory diseases of the periodontium share many features, the findings indicate that the underlying pathology is driven, at least partially, by unique molecular mechanisms.

Treatment with botulinum toxin A (BTXA) brings overactive salivary glands under control by restraining fluid secretion. Although several clinical studies have demonstrated that BTXA can inhibit glandular activity, its mechanism was poorly defined. Peking University researcher Zhi-Gang Cai and colleagues in China examined how BTXA affects production of saliva in the rabbit submandibular gland. Within a week of injection, they observed a considerably reduced saliva output and noted that the effects of BTXA persisted after 12 weeks. Some of these effects appear to be attributable to localized toxicity to secretory cells, but the researchers also observed selective inhibition of particular signaling pathways that control fluid production. As the effects of BTXA are relatively long-lasting but also reversible, the researchers conclude that it should offer effective treatment for medical conditions associated with excessive drooling.

A comparative study suggests that fluoride toothpaste is as effective at promoting cavity repair as more expensive alternative treatments. Tooth demineralization accelerates the formation of dental caries, and consumers can now choose between several calcium- and phosphate-rich compounds that were developed to augment the reparative properties of conventional fluoride toothpastes. Somkamol Vanichvatana and Prim Auychai of Chulalongkorn University in Thailand studied the effectiveness of two of these products, CPP-ACPF and f TCP, with a group of volunteers. They confirmed that both compounds promoted remineralization in tooth enamel with artificially induced caries. However, neither product meaningfully outperformed fluoride toothpaste alone. In contrast to previous studies that have suggested some additional benefit, the researchers had volunteers use CPP-ACPF and f TCP directly according to manufacturer's specifications. Therefore, fluoride toothpaste may generally offer a more economical approach to treating caries.

A small chemical compound can have a big impact on the stability of polymers for denture bases, according to Turkish scientists. Acrylic polymers such as polymethyl methacrylate (PMMA) find wide use in dental restoration because they are easy to fabricate and feel comfortable in the mouth. Their less-than-ideal mechanical properties, however, make PMMA dentures prone to fracture. Elif Aydogan Ayaz and Rukiye Durkan from Karadeniz Technical University compared traditional PMMA denture bases to ones incorporating varying amounts of acrylic acid, a reactive molecule that can cross-link polymer fibers together. Tests that simulated chewing motions showed that acrylic acid additions significantly reduced polymer fatigue by improving the material’s resistance to bending. Their quantitative chemical analysis revealed that efficient co-polymerization between PMMA and acrylic acid provides much-needed reinforcements to the denture base.

Choosing the right combination of materials for false tooth cores and veneers could help to reduce chipping, research from Europe indicates. Zirconia ceramics are a popular alternative to metal cores in dental prosthetics because, once colored and veneered, they closely resemble natural enamel. However, chipping can occur in zirconia prosthetics after a short time. Güliz Aktas at Hacettepe University, Turkey, together with co-workers in Finland and Switzerland, analyzed the effect that the coloring of zirconia has on veneer bond strength. They also studied the different thermal expansion rates of the veneers and their adhesion to zirconia. Although coloring had no discernible effects, using a veneer with a different thermal expansion coefficient to that of the core weakened the bond between the two.

This case report is to present a maxillary first molar with one O-shaped root, which is an extended C-shaped canal system. Patient with chronic apical periodontitis in maxillary left first molar underwent replantation because of difficulty in negotiating all canals. Periapical radiographs and cone-beam computed tomography (CBCT) were taken. All roots were connected and fused to one root, and all canals seemed to be connected to form an O-shape. The apical 3 mm of the root were resected and retrograde filled with resin-modified glass ionomer. Intentional replantation as an alternative treatment could be considered in a maxillary first molar having an unusual O-shaped root.