This systematic review confirms that both OLP and OLL, the latter with a slightly higher TR, may be considered potentially malignant disorders and suggest that erosive type, female gender and tongue site should be considered as risk factors for OLP transformation. Major efforts should be done to establish strict clinical and histological criteria to diagnose OLP and to perform sounder methodological observational studies.

A novel, direct and independent association between sleep duration and the prevalence of periodontitis was found. However, it needs to be investigated how the factors influencing the sleep duration affect this association.

The head and neck region is an anatomical heterogeneous area that comprises numerous specialised tissues of all lineages, which can give rise to different malignancies, among which squamous cell carcinomas are the most frequent. For this malignancy, a new staging system based on TNM classification was recently published (Lydiatt et al., 2017). These cancers represent the seventh most common malignancy worldwide, accounting for 750,000 new cases per year and causing approximately 340,000 deaths annually (Bray et al., 2018). Radiotherapy (RT) has gained a fundamental role in the treatment of head and neck cancers, and nearly 75% of all these patients undergo this therapy, either with curative, adjuvant or palliative indication (Ratko, Douglas, de Souza, Belinson, & Aronson, 2014).

Osteoporosis (OP) is a bone disease consisting of a progressive loss of bone mineral density (BMD) and therefore resulting in greater susceptibility to fractures. OP shares a number of risk factors and demographic characteristics with periodontitis (PD), a bacteria-induced chronic inflammation of periodontal structures that leads to loss of alveolar bone and teeth. In the last decade, with the advent of gut and oral microbiome studies and profiling, a growing diagnostic and prognostic significance has been attributed to dysbiosis associated with various systemic and organ-specific pathologies. This evidence has inspired research on modulating the microbiota to restore health by the use of prebiotics and probiotics. The aim of this work is to overview the bidirectional interrelationships between OP and PD, reporting the most recent evidence on triggering factors and, mainly, the role of gut and oral dysbiosis in the onset and progression of both OP and PD, with the perspective in their therapy.