Despite the enormous progress in the technology available to preserve the dentition, prosthetic restoration and rehabilitation of the masticatory system is still needed in patients who’ are edentulous or partially ederitulous. Nearly 10% of the American population, including 35%
of those over age 65, are currently totally edentulous, and millions of people have experienced a partial loss of their dentition General systemic and local factors are responsible for the variation in the amount and pattern of alveolar bone resorption.’ General factors include, the presence of  nutritional abnormalities and systemic bone disease, such as osteoporosis, endocrine dysfunction, or any other systemic condition that may affect bone metabolism. Local factors affecting alveolar ridge resorption include alveoloplasty techniques used at the time ‘of tooth removal and localized
trauma associated with loss of alveolar bone. Denture wearing also may contribute to alveolar ridge resorption because of improper ridge adaptation of the denture or inadequate distribution of occlusal forces. Variations in facial structure may contribute to resorption patterns in
two ways: First, the actual volume of bone present in the alveolar ridges varies with facial form.! Second, individuals with low mandibular plane angles and more acute gonia I angles are capable of generating higher bite force, thereby placing greater pressure on the alveolar ridge areas. The
long-term result of combined general and local factors is the loss of the bony, alveolar ridge, increased interarch space, increased influence of surrounding soft tissue, decreased stability and retention of the  prosthesis,  and increased discomfort from improper prosthesis adaptation. In the most severe cases of resorption a significant increase in the risk of-spontaneous mandibular fracture exists. The prosthetic replacement of lost or congenitally absent teeth frequently involves surgical preparation of the
remaining oral tissues to support the best possible prosthetic replacement. Often oral structures, such as frenal attachments and exostoses, have no significance when teeth are present but become obstacles to proper  rosthetic appliance construction after tooth loss. The challenge of prostnepc rehabilitation of the patient includes restoration of the best masticatory function possible, combined. with Maximal preservation of hard and soft tissue during preprosthetic surgical preparation ‘J .ilso mandat-ory. The oral tissues are difficult to replace or. .e they are lost.
The objective of preprosthetic, surgery is to create proper supporting structures for subsequent placement of prosthetic appliances. The best denture support has the following eleven char actertstlcs-: 1. No evidence of intraoral or extraoral pathologic conditions. 2. Proper interarch jaw relationship in the anteroposterior, transverse, and vertical dimensions
3. Alveolar processes that are as large as·possible and of the proper configuration (The ideal shape of the alveolar process is a broad U-shaped ridge, with the verti’cal components as parallel as possible [see Fig. 13-1].)
4. No bony or soft tissue protuberances or undercuts 5. Adequate palatalvault form 6. Proper posterior tuberosity notching 7. Adequate attached keratinized mucosa in the primary denture-bearing area
8. Adequate vestibular depth for prosthesis extension 9. Added strength where mandibular, fracture may occur 10. Protection of the neurov scular bundle 11. Adequate bony support and attached soft tissue covering to fadlitate implant placement when necessary

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