Comparison of Treatment Strategies for Implant Overdentures
Implants can be used to restore the edentulous mandible in different ways. For many patients, a fixed prosthesis can be placed on four or more dental implants, and long-term results for implant-retained fixed prostheses have been documented in the literature by various authors.1-4 Implant-supported removable overdentures using two or more implants are also a possible treatment option for patients who have problems with conventional dentures.5-14
Overdentures obtain support and retention from a superstructure attached to the implants. This superstructure defines the character of the denture that can be created. One can differentiate between tissue-supported, tissue-implant-supported, and mainly implant-supported overdentures. In the tissue-supported overdenture on two implants, the retentive mechanism is a magnet or a ball attachment.The denture rests on the mucosal tissues and the attachments ensure retention only during lateral and extrusive movements.
A tissue-implant-supported overdenture provides retention via a superstructure on two implants interconnected by a bar attached to two gold caps that are screwed onto the implants. This denture rests on the mucosal tissues on the dorsal denture-bearing areas and on the bar and implants in the anterior regions; the bar is the axis over which the denture can rotate Retention is ensured during lateral and extrusive forces. During “intrusive” forces, the implants carry the occlusal loading of the denture in the anterior region, but in the dorsal region of the denture-bearing area, the mucosal tissues are loaded.
An implant-supported overdenture placed on four implants rests primarily on the superstructure connected to the implants. In most situations, the superstructure is placed on four interconnected implants. During occlusal function the mucosal denture-bearing areas are minimally loaded.
There are several arguments in the literature to indicate a preference for one of the three treatment strategies. Challenges are discussed such as pain caused by denture pressure, the amount of available bone, the expected level of oral hygiene, patient expectations of the new appliance, and the maxillomandibular relationship, as well as therapy cost effectiveness. 10,14 While many studies have been published on implants and overdentures, only a few have compared the above-mentioned treatment options. The only study design that allows for a comparison of different types of treatment for patients with the same problem is a randomized controlled clinical trial.15,16 Several randomized clinical trials on implant overdentures can be found in the literature.17-26
Treatment success is determined by more factors than the survival of the implants alone. An important factor in patient treatment is patient satisfaction. When there are multiple treatment options for edentulous patients, it is important to determine how the patient perceives the treatment and how satisfied he or she is after treatment. It also is important to consider the clinical perfo rmance of the entire treatment strategy. Next to peri-implant and radiographic parameters, problems concerning prosthetic maintenance must be taken into consideration. Another important consideration is the efficacy of the treatment. Evaluation of the total results of patient satisfaction, costs, and treatment aftercare provides insight into the total treatment result and can be compared for the three different treatment strategies.
This chapter describes the patient satisfaction, type and amount of prosthetic aftercare, and clinical perfo rmance associated with mandibular overdentures on dental implants. Overdentures on four interconnected implants are significantly more expensive to provide than are overdentures on two implants, and both types of denture are equally acceptable to patients. This means that mandibular overdentures on two implants is the more favorable option in implant overdenture treatment. Furthermore, the two-implant overdenture with bar retention is more cost-effective than the two-implant overdenture with ball retention, mostly because patients were more satisfied with the fo rmer while the long-term costs involved with the aftercare of both is about the same.
The Breda Implant Overdenture Study
The Breda Implant Overdenture Study (BIOS) was set up as a randomized controlled clinical trial to compare three different treatment options for edentulous patients using the ITI dental implant system (Straumann, Waldenburg, Switzerland). One hundred ten edentulous patients with atrophic mandibles and persistent conventional complete denture problems who were refe rred by their dentist to the Department of Oral and Maxillofacial Surgery and/or the Department of Special Dental Care and Maxillofacial Prosthodontics of the Ignatius Teaching Hospital, in Breda, The Netherlands, during the years 1991 to 1993 were treated with one-stage ITI dental implants and implant-retained overdentures. During the consultation, the medical status and dental history of each individual patient was recorded, followed by an oral and radiological examination.
Patients with a history of preprosthetic surgery (eg, augmentation procedures, vestibuloplasty), patients who previously had been treated with dental implants, and patients who were not suitable for dental implant treatment because of their medical condition, were excluded from this study. One third of patients received a mainly tissue-supported overdenture on two implants with ball attachments (21BA); one third received a combined implant-tissue-supported overdenture on two implants with a single bar (21SB); and one third received a mainly implant-supported overdenture on four implants with a triple bar (41TB). If a mandibular implant overdenture was the indicated treatment, patients were info rmed of the three possible implant-based treatment strategies. They also were informed of the treatment’s expected benefits as well as the theoretical risks. The patients were asked if they would agree to undergo any of the three treatment modalities without prior knowledge of the chosen treatment, which would be revealed after the computed treatment allocation. The treatment allocation was calculated using a balancing procedure15 aimed at ensuring an equal distribution of the patients over the treatment groups with regard to the administered balancing criteria: age, gender, the longevity of mandibular edentulousness, the number of previously wo m mandibular dentures, the age of the present mandibular denture, the morphology of the maxilla and mandible, and the symphyseal bone height of the mandible measured on a lateral head plate.
These criteria were used in a computerized random allocation procedure with a group controller; the randomization procedure was carried out by a third party at an independent location. In this controlled manner, three statistically comparable randomized groups were created.The pretreatment comparability of the treatment groups was examined by an analysis of variance (one-way ANOVA). The surgeons and the prosthodontists were bound by the results, and the patients were treated accordingly.
All implants were placed by an oral and maxillofacial surgeon using local anesthesia. No bone augmentation procedures or bone regeneration procedures were used.The sutures were removed 10 days postinsertion. During this period patients were not allowed to wear their mandibular dentures. Two weeks postinsertion, the existing mandibular denture was adapted to the mucosal tissues with a tissue conditioning material (Softliner, GC, Tokyo, Japan). In some cases this was repeated during the osseointegration phase due to wear of the tissue-conditioning material. Three months postinsertion, the maxillofacial prosthodontist began the manufacture of a new complete maxillary denture and a mandibular overdenture on either two or four implants; this phase was designated as primary prosthetic treatment. For an overdenture with ball attachments, a Dalla Bona matrix (Cendres et Métaux, Bienne, Switzerland) was used. The bars connecting the two or four implants in the other two groups were egg-shaped Dolder bars (Cendres et Métaux). In the case of two interconnected implants, one matrix (Cendres et Métaux) was used, and three corresponding matrices were used for a triple bar (Cendres et Métaux) and were incorporated into the overdenture. The dentures were marufactured for an optimal fit and balanced occlusion. None of the dentures were fitted with a precast metal reinforcement.
A minimum of six visits, including one recall visit, was required to complete treatment. For the treatment evaluation it was arbitrarily stated that primary prosthetic treatment ended 3 months after insertion of the new dentures. Visits to the clinic after this period (including the six monthly recalls) were defined as aftercare.
Since the ITI dental implant system is a one-stage system, part of the implant is exposed to the oral flora at gingival level during osseointegration. Immediately after suture removal, p a tients received instructions on basic />