Clinical and Radiographic Evaluation of Three Different Modalities for Management of Distal Extension Atrophied Mandibular Ridge: A One Year Prospective Study

Introduction Long span distal-extension removable partial dentures (RPDs) are associated with several problems related to their stability, retention, esthetics, and masticatory efficiency.1,2 The lack of distal dental support in mandibular Kennedy class I distal extension-RPDs results in transmission of vertical, horizontal, and torsional forces to supporting tissues during mastication with subsequent adverse changes in both abutment teeth and edentulous areas. In addition, constant pressure from the denture base gradually causes ridge resorption under the denture base.3-5 Prosthodontic management of long span distal extension partially edentulous patients has expanded with the introduction of Osseo integrated implants.6 The use of implants to support and retain distal extension partial overdentures has been reported to minimize RPD dislodgement, provide additional retention and stability, prevent the development of combination syndrome and improve patient satisfaction in a cost-effective manner.7,8 Moreover, placing bilateral dental implants distal to canine area of the residual alveolar ridges is becoming a popular treatment choice in case of limited height of posterior mandibular ridge7,9,10 Such prostheses can be retained to the implants with different unsplinted anchors such as ball, Locator, and magnetic attachments.1 Although Implant-supported distal extension prosthesis could be an ideal treatment option, alveolar resorption, lack of sufficient bone volume and proximity to the inferior alveolar nerve, presenting a difficult clinical situation for positioning endosseous implants. A bone height of 10-12mm is generally considered to be the minimal amount of bone required to place implants of ''sufficient'' length, 9-11mm long, which are most likely to generate good long-term results and to minimize the risk of permanent damage to the alveolar inferior nerve.11 Often times, however, the amount of residual bone above the mandibular canal is <10mm, and implant placement is considered at a higher risk of failure.11To address a case of reduced bone height in the posterior mandible, either ridge augmentation or placement of short implant could be the proposed approaches.

The development of bone augmentation procedures has allowed placement of dental implants into jawbone areas lacking an amount of bone sufficient for standard implant placement.11 While augmentation procedures can yield favorable outcomes, they can be associated with significant postoperative morbidity and complications.12 On the other hand, short implants could be a simpler, cheaper, and faster alternative to augmentation procedures, even if in some "critical cases" the residual bone crest above the inferior alveolar nerve is only 5-7 mm in height, and therefore the surgical augmentation treatment is mandatory.11,12 However, it is commonly perceived that short implants do not have a good long-term prognosis when compared with longer implants. Although preliminary findings suggest that short implants may be a better alternative to various bone augmentation procedures, long-term follow-up evaluations are indicated to draw definitive conclusion.13-15 Implant-supported removable prostheses improve patients' satisfaction with treatment and quality of life. When canines are the only present abutments, insertion of the implants distal the canine areas can provide support and retention, eliminate the use of unesthetic retentive clasps, and prevent unfavorable horizontal forces that may damage the abutment periodontium. However, some biological and mechanical complications remain. Mechanical complications associated with implant-supported overdentures are loss of retention of attachment systems, the need to replace retention elements and to reline or repair the resin portion of the denture, and implant fracture. Despite their success, implant-supported removable prostheses require periodic maintenance.

Based on the proceeding, three treatment modalities could be the solution for long span distal-extension removable partial dentures (RPDs); implant retained partial overdenture, short implant supported fixed prosthesis, and long implant supported fixed prosthesis after ridge augmentation. Comparing the clinical and radiographic outcomes of the three different treatment modalities are relatively scarce in literature to explore which treatment is more appropriate regarding periodontal tissue health and patient satisfaction.

Aim of the work This study will aim to assess the clinical and radiographic outcomes of three different treatments modalities for management of distal extension atrophied mandibular ridge; A; implant retained partial overdenture, B; short implant supported fixed prosthesis, C; long implant supported prosthesis after ridge augmentation

• Clinical evaluation will be made in terms of: