The aging population: demographics and the biology of aging.

Epidemiologic studies show that 11% of the world's population is over 60 years of age; this is projected to increase, by 2050, to 22% of the population. Oral aging is a current focus of several organizations including the Federation Dentaire Internationale, the World Health Organization and the American and Japanese Dental Associations. In their Tokyo Declaration, the Japanese Association identified the elderly population as one of its main target groups. One of the WHO goals is for each person to retain more than 20 teeth by age 80, despite the fact that the prevalence of periodontal disease is continuously rising as the population is aging. Every species has its own characteristic lifespan, which is determined by its evolutionary history and is modified by multiple diverse factors, including biological mechanisms. In humans, the gradual accumulation of products of cellular metabolism and extensive DNA damage contribute to the aging process. Aging is thought to be associated with a low-grade inflammatory phenotype in mammals, called 'inflammaging', and is the result of autophagic capacity impairing so-called 'housekeeping activities' in the cells, resulting in protein aggregation, mitochondrial dysfunction and oxidative stress. Delayed stem-cell proliferation, associated with aging, may impact the maintenance and survival of a living being, but excessive proliferation could also result in depleted reserves of stem cells. Studies are needed to address the association of delayed cell proliferation and wound healing with the onset of periodontal diseases and response to treatment. The effects of systemic diseases, medications, psychological effects and decreased interest or ability in performing oral-hygiene practices are thought to result in periodontal diseases, and ultimately in tooth loss, in aged individuals. Together with an aging population comes a responsibility for 'healthy' and 'successful' aging. This article describes the changing global demographic profile and the effects of an aging society on the prevalence and incidence of periodontal diseases. We review the definitions of normal and successful aging, the principles of geriatric medicine and the highlights of biological aging at cellular, tissue and systems levels.