Short, non-coding microRNAs play a critical role in regulating bone remodeling and provide therapeutic targets for treating bone disease. In a review article, Zhi-He Zhao and colleagues from the State Key Laboratory of Oral Diseases at Sichuan University in Chengdu, China, examine the ways in which microRNAs control gene expression in various types of bone cells, including bone-forming osteoblasts and bone-resorbing osteoclasts. Through this regulatory function, microRNAs can help tip the balance toward bone synthesis or degradation to spur disease processes and affect healthy development. After highlighting some of the specific molecules and pathways impacted by microRNAs at various stages of bone remodeling, the authors discuss how microRNAs could be delivered into the body, either directly or through some kind of biomaterial, to correct skeletal disease, trauma, osteoporosis, cancer and other disorders affecting bone.

A method that enables the efficient, effective delivery of genes into human baby teeth cells could aid research into tooth regeneration. Dental pulp cells found inside baby teeth give rise to other cells that make dentin, one of the major components of teeth. Masahiro Sato from Kagoshima University, Japan, and colleagues now show that a gene delivery system called ‘PiggyBac’ can be used to introduce DNA into these pulp cells or stem cells derived from them, yielding modified cells that stably express one or two genes for months at a time. The PiggyBac system greatly outperforms other more conventional gene delivery systems, but because of safety risks is not suited for clinical application. Rather, the system is expected to boost functional studies of genes and proteins related to tooth development.

A rat model offers insights into the bacterially-induced inflammatory response that contributes to the tissue damage in periodontal disease. Several studies have demonstrated that lipopolysaccharide (LPS), a component of the bacterial cell wall, can promote tissue damage in the gums. However, these experiments typically used LPS from bacteria not associated with periodontal disease. Researchers led by Tadashi Saigusa from Nihon University School of Dentistry in Matsudo, Japan, studied the effect of LPS from Porphyromonoas gingivalis, which is linked to periodontal disease, on rats. They identified a specific inflammatory signal that was activated by P.gingivalis, but not by LPS from another bacterial species that typically resides in the gut. These data highlight the importance of using appropriate bacterial species to model periodontal disease, and reveal molecular pathways that might contribute to this pathology.

Surgical removal of apparently normal tissue adjacent to oral squamous cell carcinoma (OSCC) tumors could improve patient outcomes. OSCC is the most common oral cancer and survival rates are only around 50%, mainly due to local recurrence. Long-Jiang Li, at Sichuan University, Chengdu, China, and colleagues, examined 50 biopsy samples from patients treated for OSCC and found that tissues up to 2 cm away from the visible border of the tumor could be pre-cancerous. A gradual decrease in the expression of cancer-related molecules from the tumor to surrounding tissue suggests that some cells, despite their normal appearance, have begun to transform into tumor-forming cells. By determining the molecular boundary of OSCC tumors, these findings help to establish a safer surgical margin which fully removes precancerous tissue and thus lowers the risk of recurrence.

The inheritance patterns of two distinct dental anomalies suggest a common genetic origin. An international team led by Simon Camilleri at Kings College London sought to determine if there is a genetic association between dental anomalies involving tooth displacement (palatally displaced canines, PDC) and tooth transposition (the commonest type being between maxillary canines and premolars, MxCP1). They examined 35 individuals with PDC and 35 with MxCP1 and found no differences in the prevalence of PDC among their first-degree relatives. The fact that over 20% of relatives of individuals with MxCP1 showed PCD suggests that the same genes are likely to be responsible for these dental anomalies. Interestingly, the incidence of MxCP1 was associated with increased maternal age, highlighting the influence of environmental and epigenetic factors on genes involved in dental development.

Higher levels of proteinase 3 (PR3) in saliva are associated with lower levels of dental caries. Other salivary proteins have previously been shown to influence dental health. Ping Zhang, Xue-Dong Zhou and co-workers at the State Key Laboratory of Oral Diseases, Sichuan University, China, analyzed salivary proteins and the pH of saliva collected from 128 healthy six-year-old children. Caries-free children showed significantly higher levels of PR3 than those with caries. Salivary pH was not significantly associated with caries, but a higher pH was significantly associated with higher PR3 levels. The researchers investigated whether PR3 showed activity against Streptococcus mutans, a bacterium commonly associated with cavities. High levels of PR3 inhibited the growth of S. mutans. Further studies will be required to determine whether PR3 can be used to help prevent cavities.

Bacterial lipopolysaccharide (LPS) can accelerate or inhibit the corrosion of titanium implants depending on the acidity of the environment. These contrasting effects were demonstrated by Owen Addison and colleagues from Birmingham University, UK. Titanium and its alloys are used in biomedical implants and are generally resistant to corrosion under normal physiological conditions. Inflammation and bacterial activity can, however, modify the local environment in the biofilms around dental implants. The researchers therefore investigated the effects of LPS from bacterial cell walls on corrosion. At normal acidity levels corrosion increased in the presence of LPS, but in the more acidic conditions associated with inflammation corrosion was inhibited. Increased acidity in the absence of LPS increases corrosion. The effects of LPS may influence the long-term stability of many implants.

Porcelain veneers protect zirconia dental restorations on aging but how the porcelain is applied has little effect on zirconia stability. Porcelain is added to zirconia restorations principally for cosmetic reasons, however, it is prone to chipping. The phase transformation of zirconia from a tetragonal to a monoclinic crystal structure is believed to be a contributing factor to chipping. This transformation may be influenced by the preparation conditions of the restorations and aging within the oral environment. Using X-ray diffraction, Tariq Alghazzawi and Gregg Janowski at the University of Alabama at Birmingham, US, showed that porcelain protected zirconia samples from the structural transformation under accelerated aging conditions. There was no significant difference in the protection offered between manual layering and pressing methods of porcelain application.