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.