The number of people in the United States requiring removable prosthodontic therapy has increased dramatically over the past twenty years.1-3 Current predictions suggest that over the next two decades, the declining incidence of edentulism4,5 will be more than compensated by a 79% increase in adults over 55 years of age.6 Demographic trends for adults 80 years and older suggest an increase from 9.3 million in 2000 to 19.5 million in 2030.7 Though only 10% of adults18 years and older are edentulous, this rate increases to approximately 33% for adults 65 years and older.8 In the United States alone, the number of adults requiring complete denture therapy is expected to increase from 33.6 million in 1991 to 37.9 million in 2020.6 Considering a projected decrease in edentulism, an expected increase in the number of older individuals, and the need for complete denture therapy by many patients, it has been estimated the 56.5 million complete dentures made in the United States in 2000 will increase to more than 61 million complete dentures in 2020.6
Marked atrophy of alveolar bone following tooth loss9-11 complicates prosthodontic rehabilitation. This phenomenon has been termed “reduction of residual ridges” by Atwood9, who considered it a major oral disease entity. Resorptive changes in residual edentulous ridges appear to be influenced by a multitude of poorly defined factors and the volume and rate of osseous changes vary dramatically between patients. Although consensus regarding etiology is lacking,12-18 alveolar bone and oral soft tissue changes observed in denture wearers may be an inevitable consequence of the loss of natural teeth, tissue remodeling, occlusal factors, and/or prolonged denture wear.18-28 Alveolar bone loss subsequent to long-term edentulism may be severe and the process may progress throughout life.21,22,27,29,30 Although generally more pronounced in the mandible and characterized by individual variability in volume and rate,9,17,22,23,26,28,31,32 advanced residual ridge resorption presents a significant prosthodontic challenge. This oral condition complicates both the dentists’ ability to fabricate adequate complete dentures, and the patients’ ability to successfully manage their dental prostheses. In the authors’ experience, after 5 to 7 years of clinical service, a significant percentage of conventional complete dentures require re-adaptation to the denture bearing tissues using standard reline or remake procedures.
Over 50 years ago it was suggested local factors are primarily responsible for edentulous ridge resorption. Schlosser33 implicated ill-fitting dentures and the associated trauma to oral tissues as the primary causes of rapid deterioration of the denture bearing structures. He lists faulty impressions, excessive occlusal vertical dimension, inaccurate centric jaw relationships, and occlusal disharmony as major contributing factors. Lammie34 suggested a detrimental external molding force may adversely impact the residual bony ridges as overlying oral soft tissues contract or atrophy with time. This molding force may, in turn, accelerate resorption of the edentulous ridges.
In a review of 18 complete denture patients, Atwood35 remarked the deterioration of edentulous ridges is a complex biophysical process involving functional factors (i.e., the intensity and duration of applied forces), prosthetic factors (i.e., techniques and materials used in denture construction), and metabolic factors (i.e., systemic influences on bone formation and resorption). For example, occlusal parafunction may adversely affect the denture bearing tissues. It is likely many complete denture wearers limit both separation of the denture teeth and mandibular movement in order to avoid unintentional prosthesis movement or dislodgement.36 If this habit occurs over extended periods of time and with sufficient force, damage to the denture bearing hard and soft tissues may result.
Others37,38 support Atwood’s conclusions suggesting that despite careful prosthodontic management and apparent short-term success, aggressive reduction of residual edentulous ridges may still occur. Consequently, the impact of systemic factors must be considered when deciphering the etiology of alveolar resorption. Though difficult to substantiate, an association may exist between residual ridge reduction and osteoporosis.9,39-41