Indications and Treatment Planning for Mandibular Implant Overdentures
Planning a patient’s mandibular overdenture treatment is a straightforward process that will yield very predictable results if done in a systematic manner. This treatment planning process is reviewed in detail in this chapter.
It is no longer a safe assumption that patients who are treated with implant-supported overdentures were first introduced to the concept by their dentist. As dental implant therapy becomes more common, denture wearers are increasingy aware that there is an alternative to the mucosa-supported complete mandibular denture and frequently seek information about implant alternatives. It is becoming more important for clinicians who offer complete denture services to also offer dental implants as a means of increasing patient satisfaction and improving quality of life. The process of evaluating an edentulous patient for dental implant therapy is straightforward and extremely satisfying to both patient and provider.
At the initial consultation, the clinician can determine whether the patient already has wellconstructed, functional dentures that would serve adequately by the addition of two implants in the anterior mandible to stabilize and retain the denture. Generally it is not advisable for a clinician to undertake the modification of a mandibular complete denture into an overdenture unless the same clinician originally provided the dentures. It is best to avoid working with dentures made by another clinician, particularly when entering into an implant treatment plan.
Initial discussions with a patient regarding a proposed treatment plan that involves the placement of dental implants for overdenture support must take into consideration the patient’s current dental status and concerns. Many times, the patient who has had experience with complete dentures is enthusiastic about any procedure that may improve the comfort and function of a mandibular denture. In other situations, the patient may be satisfied, or nearly so, with a mandibular complete denture, and the possibility of improved comfort and function is not a high priority.The dentist must be aware of patient concerns and approach the treatment planning discussion from a conservative direction.Treatment with an implant-supported denture should not be pursued for patients who are not confident that the process is appropriate for their needs.
For the patient facing edentulism in the mandible for the first time, the decision to proceed immediately to an implant overdenture may be difficult. Frequently,the patient already has had experience with a maxillary complete denture, and the quality of that experience will influence the patient’s decision whether to proceed with conventional complete denture fabrication for the mandibular arch or to place implants at the time of extraction. The latter option minimizes the healing period before an overdenture or a fixed implant-supported prosthesis can be placed. A patient who has been satisfied with a maxillary complete denture may prefer to try the conventional mandibular denture before committing to the additional expense and surgery involved with implant placement. Unlike implant placement in a partially edentulous patient, particularly in esthetic areas of the mouth, delayed implant placement in an edentulous mandible does not compromise the predictability or quality of the result. It can be argued that a moderately resorbed mandible is preferable for implant placement when compared to the newly edentate mandible with a prominent alveolar ridge in the anterior region. Implant placement and fabrication of an overdenture attachment system, either bar or ball type, is much more difficult in the minimally resorbed mandible because of a lack of available space within the profile of the denture. In such instances, the likelihood of denture fracture due to insufficient bulk of denture base material may be problematic.
Another potential argument for deferred implant placement is that it gives the patient the experience of wearing a complete denture without overdenture anchorage. This makes the experience of gaining additional support, retention, and stability with overdenture anchorage a more dramatic and satisfying change.The decision to use immediate or delayed implant placement for overdenture anchorage should be made on a patient-by-patient basis.
The determination of whether a mandibular implant-assisted overdenture is appropriate for a patient must be made regardless of whether a preexisting denture will be modified to receive implants or whether the patient requires fabrication of new maxillary and mandibular denture prostheses in conjunction with dental implant therapy.
Successful implant overdenture therapy is dependent on adherence to basic principles of denture fabrication, as is treatment with conventional complete dentures. Adequate denture base extension and adaptation to the underlying soft tissues are prerequisites for success. The assumption that the additional stability and retention provided by the implants will compensate for less-than-adequate denture base support will likely limit the successful outcome of treatment and may lead to problems with patient acceptance and comfort, as well as chronic denture base irritation and accelerated alveolar resorption. It is important to take time to determine the proper vertical dimension of occlusion, accurate registration of centric relation, and proper tooth position within the arches. Less-than-ideal registration of any of these factors may lead to ongoing denture instability, soreness, and patient dissatisfaction. In short, the use of dental implants to overcome or mask deficiencies in denture fabrication may result in an unsatisfactory outcome and treatment failure.
Consideration of Overall Patient Health for Implant Surgery
There are surprisingly few absolute contraindications for dental implant placement. As a general rule, any medical condition that contraindicates elective surgery of any kind may be considered a contraindication for dental implant surgery. Placement of dental implants, particularly in the edentulous anterior mandible, is a straightforward procedure with few anatomic risks and a low morbidity rate.
Many candidates for dental implant surgery are elderly, and their ove rall medical condition may be complex. Consultation with the patient’s physician is important to ensure that surgical risks are minimized. It cannot be assumed that the physician will be aware of exactly what is involved with surgical placement of dental implants, and physician education may become part of the treatment planning process.The surgical risk of implant surgery in the medically compromised patient may be offset by the potential increase in function, food selection, and quality of life that could result from treatment with an implant overdenture. Adjustment of daily medications that affect hemostasis may by suggested for patients on long-term anticoagulant therapy, which can include the low-dosage aspirin regimen that is routinely prescribed for many older patients.
Medical conditions that are generally considered contraindications for dental implant placement include uncontrolled diabetes or other metabolic diseases that alter the normal healing process, previous radiation therapy to the oral cavity (although with careful management this is not an absolute contraindication), hematologic and immunologic diseases that put the patient at risk for minor surgical procedures, and chronic use of systemic steroids. Systemic steroid use in particular is a substantial risk factor for successful osseointegration of dental implants. Neither age nor osteoporosis have been shown to be contraindications for successful dental implant osseointegration.1 Care should be taken with patients who have severe osteoporosis, due to the increased risk of fracture resulting from the surgical osteotomy and loading of a potentially weakened mandible.
An additional relative contraindication is tobacco use. While the literature is not conclusive as to the effect of smoking on the success of dental implant treatment, there is strong evidence that heavy tobacco use severely compromises dental implant therapy.2 Tobacco use has been implicated in both early (failure to integrate) and delayed (peri-implant infection) implant loss. The question that must be addressed with a patient who smokes is whether that patient is willing to accept complete responsibility for the increased risk of failure to the extent of being willing to pay for and undergo the procedure with no guarantees of success. If the patient understands and accepts the potential increased risk, then implant therapy can proceed as planned. Obviously, a smoking cessation program prior to surgery would likely increase the chances of successful treatment.
Radiographic Examination of the Edentulous Mandible
The panoramic radiograph is the most convenient and readily available radiographic examination tool when considering dental implant placement. Frequently, the clinician who initially evaluates an edentulous patient for possible treatment with an implant-assisted overdenture is a general dentist or prosthodontist. In this situation, a panoramic radiograph will assist planning and is useful to evaluate residual pathologic lesions of the jaws and to judge the amount of residual bone available for implant placement (Fig 9-1).While a panoramic radiograph is subject to substantial distortion of the image, it still is an acceptable film to initially gauge the amount of residual bone. Additional radiographic analysis, when necessary, should be performed at the discretion of the surgeon placing the implants.The lateral cephalometric view gives an excellent cross-sectional view of the anterior mandible in the symphyseal region (Fig 9-2).This view provides information about the labiolingual thickness of the mandible, the presence of concavities in the lower part of the mandible, and the quality of bone present. The lateral cephalometric radiograph is more accurate than the panoramic radiograph for imaging the symphyseal region. It is relatively inexpensive and requires minimal radiation exposure. Similarly, an occlusal radiograph may be useful to determine labiolingual ma/>