An assessment of patients treated with implant retained mandibular overdentures

Abstract

Literature Review The loss ofteeth has been a common dental experience for man since the earliest times. Historically, the loss was partial rather than complete, and if treated, the rationale tvas aesthetic rather than functional. Beginning in the late 1700's and continuing through to the late 1900's the incidence of edentulism has increased dramatically. Through a combination of dental disease, aggressive surgery, and a longer life span, the rate of complete edentulism has climbed to between l0 to 20 per cent of the adult population in most developed societies. The restoration of function, in addition to form, became increasingly important with the loss of all teeth. Improvements in materials, particularly the advent of porcelain and acrylic, largely solved the problem of providing an aesthetic restoration. Improvements in technique, such as impression taking and the use of articulators, led to better fabricated prostheses. Functionally, however, dentures remained a barely adequate replacement for the natural dentition. The changes that occur on the loss of teeth impact profoundly on form and oral function. Changes in extra- and intra-oral form are due principally to residual ridge resorption (RRR), which is the outstanding feature of the post-extraction milieu. RRR can result in dramatic morphological changes in the edentulous jaw with changes in the maxilla-mandibular relationship, and changes in muscle attachments and sulcus depth. Changes in form may be due to RR& but changes in function are derived mainly from loss of the periodontal ligament. The periodontal ligament has a pivotal role in supporting and retaining the natural dentition in bone, as well as having important neurosensory inputs into masticatory control. Hence, ligament loss results in a very significant functional deficit. This deficit is most obvious in the mandible. Here the denture bearing area is approximately half that of the maxilla and continuing bone loss produces a dramatic decrease in denture support and retention and superficial muscle attachments undermine denture stability. Thus, the successfi.¡l restoration of the edentulous mandible presents one of the great challenges in clinical dentistry. The rationale for treatment of the edentulous mandible is the restoration of form, essentially by compensating for the loss of teeth and the ravages ofRR& and the restoration of function, essentially by compensating for the loss of the periodontal ligament. Whereas the loss of form can largely be restored with porcelain and acrylic, the restoration of function has proven to be much more problematic. Contemporary treatments of the edentulous mandible which seek to restore function may be classified into three categories: conventional removable denture treatment on an existing tissue foundation, conventional removable denture treatment on a surgically improved tissue foundation, and removable and fixed denture treatment on an implant foundation. Conventional removable denture treatment on an existing tissue foundation relies heavily on denture support, stability and retention for satisfactory function. Unfortunatel¡ two factors militate against this triad of denture elements so important to function. The first factor is ongoing RRR. Regardless of how well a denture is fabricated ongoing RRR will insidiousþ undermine the denture foundation. The second factor is the mucosa. In the dentate, the medium by which bone provides support, stability and retention is the periodontal ligament, whereas in the edentulous it is the mucosa. Where the ligament is resilient enough to withstand the functional load, very often the mucosa is not. Hence, conventional denture therapy may restore adequate form but often it cannot restore adequate function. Although clinical experience demonstrates that most patients can cope with conventional removable dentures, this is more a testament to their stoicism than to the adequacy of their prostheses. All edentulous patients realise the functional deficiencies of their dentures and many remain actively dissatisfied with conventional therapy. The desire to overcome the functional deficit has seen major developments in preprosthetic surgery, particularly in the use of implants. Augmentative treatment whether relative, absolute or both can improve the denture foundation but does not change the load bearing status of the mucosa. Although augmentation can improve ridge form, jaw relations and soft tissue profiles, a number of problems especially relapse and neurosensory loss limit its routine prescription. Augmentation can restore form by compensating for bone loss but does not address the problems of continuing RRR and loss of the periodontal ligament. Hence, functional improvements after enlargement of the denture foundation are generally marginal. Implant therapy can largely compensate for the loss of the periodontal ligament and help prevent ongoing RRR. Complication and failure rates are much lower than for reconstructive preprosthetic surgery and generally the surgery is less traumatic. Dental implants have a long and controversial history and it is only in recent times that this treatment modality has been accepted into the mainstream of dental practioe. The acceptance of implants as an efficacious prosthodontic therapy has in large part been due to the discovery and development of osseointegration by Professor P. I. Branemark. Based on 30 years of clinical research osseointegration does appear to provide predictable and long term implant success. The use of implants overcomes the two fundamental problems of conventional denture treatment. RRR is stabilized by implant use and so intra- and extra- oral form are preserved. Secondly, the implant becomes the means by which bone supports the functional load and so the mucosa is unloaded. Further, because the implant is fixed in bone it can provide the necessary prosthetic stability and retention required for satisfactory and comfortable function. Although the implant cannot compensate for the neurosensory deficit caused by ligament loss, studies on masticatory efficiency have shown that the chewing ability of patients with implant supported prostheses approaches that of the dentate and is much superior to that of complete denture wearers. Hence, the implant is a very adequate replacement for the periodontal ligament providing the necessary prosthetic support, stability and retention for satisfactory function. - There are two broad categories of prosthesis available for use with implants in the treatment of the edentulous: the implant borne prosthesis and the implant and tissue borne prosthesis. Totally implant borne prostheses, whether fixed or removable, completely unload the mucosa. The success of implant borne prostheses is well substantiated in the literature with minimal bone loss in the underlying jaw after loading, considerable improvements in function, and importantly, high patient satisfaction. Although these treatments are very successful, they are also complex and expensive. For a large proportion of the edentulous grouP, i.e. the economically disadvantaged, such treatments are often out of reach. For this group a simpler and less expensive implant option is required. The simplest and perhaps least expensive option for the troublesome edentulous mandible is the two implant retained overdenture. This is an implant and tissue borne prosthesis. Present Study The efücacy of the implant and tissue-borne mandibular prosthesis is not well established in the long-term. Reports on efficacy, simplicity and cost-effectiveness of the treatment are somewhat contradictory with some studies noting good clinical success for a simple and relatively inexpensive restoration, whereas others record reservations about longterm effrcacy and cost-effectiveness considering ongoing bone resorption and maintenance problems. The objectives of this study were to assess the efficacy of mandibular overdentures retained by two endosseous implants and to compare three overdenture retention systems' The efficacy of implant overdenture treatment was evaluated by a patient and clinical assessment of denture function, comfort and retention, and an assessment of peri-implant tissue health including: plaque, calculus and gingival bleeding indices; crevice depth; implant mobility and radiographic changes in bone. The three retention systems \¡/ere compared with respect to patient and clinical assessments of denture function, comfort and retention. The null hypothesis for the study states that, "There is no perceived improvement in mandibular denture function, comfort and retention provided by the use of two Integral implants and overdenture attachments, and that there is no difference in using either clip, Oring or ball attachment systems". Within the constraints of a study with a sample size of 24 patients followed up for l8 months only the results demonstrate that a two-implant retained overdenture can provide significant improvements in denture function, comfort and retention. Of the attachments systems used (clip, O-ring and ball) no one was superior to any other. The study also demonstrated that overdenture treatment can result in high levels of prosthetic maintenence due to ongoing ridge resorption and support problems. Twenty th¡ee of the 24 implants placed were still functioning at the end study and were generally in good health with favourable gingival bleeding, crevice depth and tissue height indices, negligible mobility and minimal bone loss.