Multicenter follow-up study of the transmandibular implant

Prosthetic management of an existing transmandibular implant: A clinical report

This report describes the prosthetic management of a fractured Dolder bar on a transmandibular implant system. The patient declined surgical removal of the implants. Therefore, to repair the superstructure, a cast Dolder bar was fabricated and luted onto the existing transmandibular implants. An implant-retained bar overdenture was then fabricated to rehabilitate the mandibular arch.

Implantology and the Severely Resorbed Edentulous Mandible

Patients with a severely resorbed edentulous mandible often suffer from problems with the lower denture. These problems include: insufficient retention of the lower denture, intolerance to loading by the mucosa, pain, difficulties with eating and speech, loss of soft-tissue support, and altered facial appearance. These problems are a challenge for the prosthodontist and surgeon. Dental implants have been shown to provide a reliable basis for fixed and removable prostheses. This has resulted in a drastic change in the treatment concepts for management of the severely resorbed edentulous mandible. Reconstructive, pre-prosthetic surgery has changed from surgery aimed to provide a sufficient osseous and mucosal support for a conventional denture into surgery aimed to provide a sufficient bone volume enabling implants to be placed at the most optimal positions from a prosthetic point of view. The aim of this paper is to review critically the literature on procedures related to the severely resorbed edentulous mandible and dental implant treatment. The study includes the transmandibular implant, (short) endosseous implants, and reconstructive procedures such as distraction osteogenesis, augmentation of the mandibular ridge with autogenous bone, and bone substitutes followed by the placement of implants. The number of patients participating in a study, the follow-up period, the design of the study, the degree of mandibular resorption, and the survival rate of the dental implants all are considered evaluation parameters. Although numerous studies have described the outcome results of dental implants in the edentulous mandible, there have been few prospective studies designed as randomized clinical trials that compare different treatment modalities to restore the severely resorbed mandible. Therefore, it is not yet possible to select an evidence-based treatment modality. Future research has to be focused on long-term, detailed follow-up clinical trials before scientificaly based decisions in treating these patients can be made. This will contribute to a higher level of care in this field.

Mandibular fractures associated with endosteal implants

PURPOSE

The purpose of this study is to report four cases of mandibular fractures associated with endosteal implants and to discuss prevention and treatment of these types of fractures.

DISCUSSION

To evaluate whether the patient's anatomy allows insertion of implants, radiological exams that demonstrate the height and the labial-lingual width are needed. To reduce the potential fracture problem, the mandible can be restrengthened with bone grafting techniques. The treatment of a fracture in an atrophic mandible is always a challenge because of the diminished central blood supply, the depressed vitality of the bone, and the dependence on the periosteal blood supply. The basic principles in fracture treatment are reduction and immobilization of the fractured site for restoration of form and function.

CONCLUSIONS

If implants are placed in severe atrophic mandible, iatrogenic fracture of the mandible may occur during or after implant surgery because implant placement weakens the already-compromised mandible. A few millimeters of cortical bone should remain on both the labial and the lingual sites after the hole for insertion of an implant has been drilled. A 3-D surgical planning should be recommended at least in severe atrophic mandibles in order to prevent a severe reduction of bone tissue.

Finite element analysis of a transmandibular implant

Finite element analysis (FEA) was used to study the influence of bony height and baseplate effect on the transmandibular implant (TMI). FEA was used to assess the stress distribution in the mandible, with and without a baseplate. Forces were applied to the center of a bar space. The von Mises stress (SEQV) was displayed in bone, and shear stress also was measured. Tensile stress was always seen at the so-called saddle area; compressive stress was seen at the inferior border. Tensile strain at the saddle area of a 6-mm height mandible is always 9.1 times greater (corresponding to more SEQV) than that of an 18-mm mandible. At same bone heights, saddle area stresses are similar with or without a baseplate. However, stress at the lateral transossseous post interface with bone was significantly different between different bone height groups. Shear stress around the lateral transossseous post was smaller than does the SEQV of the same site. Decreased bone height dramatically increases stress at the saddle area independent of the baseplate presence. These data suggest that bone apposition is found in the severely atrophic mandibles. Thus, there is no need for a baseplate in a slight to mild atrophic mandible.

The transmandibular implant: a 5- and 15-year single-center study

PURPOSE

Fifty-eight patients (average age, 60 years) with gross mandibular atrophy had transmandibular implants inserted between 1984 and 1988. This study reports on their progress at 5 and 15 years.

PATIENTS AND METHODS

In both 1991 and 2000, 50 cases were reviewed, with the other 8 lost to follow-up. Detailed surveys, using exactly the same format, were conducted to determine the outcome of transmandibular implant treatment. The records were reviewed and surviving patients with transmandibular implants were examined.

RESULTS

An overall success rate of 80% in 1991 had fallen to 56% by 2000, with a total of 22 implants being removed.

CONCLUSION

Factors involved in failure were age and medical infirmity of the patients, gross mandibular atrophy, and the use of several surgeons, in particular, trainees. This survey shows that the TMI has a progressive long-term failure rate and that extreme care needs to be taken in both patient selection and implant placement.

Implant-retained mandibular overdentures: 6-year results of a multicenter clinical trial on 3 different implant systems

PURPOSE

The goal of this multicenter prospective clinical trial was to compare clinical outcome and post-treatment care and patient satisfaction with different implant systems used for mandibular overdenture treatment during a 6-year follow-up period.

PATIENTS AND METHODS

A total of 87 edentulous patients with a severely resorbed mandible (bone height, 8 to 15 mm) received treatment involving either 2 Intra Mobiele Zylinder implants (IMZ group, n = 41) (Friedrichsfeld AG, Mannheim, Germany), 2 Brånemark implants (Brå group, n = 17) (Nobel Biocare AB, Gothenburg, Sweden) or a Transmandibular Implant (TMI; Krijnen Medical, Beesd, The Netherlands) (TMI group, n = 29). The evaluation involved clinical parameters, radiographs, surgical and prosthetic post-treatment care, clinical implant performance (CIP scale), and patient satisfaction.

RESULTS

After 6 years, there was a significant difference in the mean plaque index:the mean plaque index of the TMI group was significantly higher than that of the IMZ and Brå groups. Other clinical parameters showed no significant differences. The implant survival rate of 97.5% was noted in the IMZ group, 97.1% in the Brå group, and 72.0% in the TMI group. The CIP scale were significantly worse for the TMI group.

CONCLUSION

It was concluded that the IMZ and the Brånemark implant systems have a better survival rate and clinical implant performance than the TMI system. Based on these data, these systems should be the choice for the edentulous mandible with a height between 8 and 15 mm.

Use of short endosseous implants and an overdenture in the extremely resorbed mandible: a five-year retrospective study

PURPOSE

A retrospective study was performed to assess the success of short endosseous implants in combination with an implant-retained overdenture in the extremely resorbed mandible.

PATIENTS AND METHODS

Patients included had a mandible not exceeding a median height of 12 mm measured on a standardized lateral cephalometric radiograph. Seventeen patients (14 women, 3 men; mean age, 65 years) with 68 endosseous implants were clinically and radiographically evaluated.

RESULTS

During the follow-up period (mean, 77 months; range, 60 to 97 months), 8 implants were lost, bringing the cumulative survival rate to 88%. The peri-implant tissues were in good condition, and the bone loss around the implants was minimal.

CONCLUSION

Because of the relative simplicity and low morbidity of this treatment strategy, it is a justified treatment option.

The shift in the therapeutic paradigm: osseointegration

The loss of teeth is an extremely traumatic and upsetting experience. The accompanying feelings of grief and loss are compounded by the inherent inadequacies of complete dentures. It is hardly surprising that many edentulous people and their dentists have searched long and hard for a viable alternative. This article places in perspective the shift that has occurred in the therapeutic paradigm of treatment as a result of osseointegrated implant therapy.

Outcomes and their measurement in clinical trials of endosseous oral implants

The clinical suitability of an oral implant system should be substantiated by well-planned clinical trials that meet the expectations of both the patient and the clinician; i.e., to offer anchorage to a dental prosthesis for one or more decades. The literature often reports on the survival rather than on the success rate, and for the latter a large variety of more or less stringent criteria have been proposed. Although the use of cumulative percentages to assess survival or success on consecutive patients, the so-called Kaplan-Meier statistics, is essential, many publications only report on absolute percentages, thus giving much too optimistic results. Indeed, the large number of recently inserted implants tend to dilute the small fraction that has gone through the maximum observation period. Multi-center studies on consecutive patients who are not selected on the basis of bone quality and volume should be recommended. Otherwise the labeling of the implant should clearly mention which groups; e.g., smokers or patients with limited bone volume are not part of the validated target group. The final outcome measurement would be that an endosseous implant is no longer able to carry out its purpose: to anchor or support successfully a functional dental prosthesis. Like many other clinical evaluations, surrogate parameters have been sought to assess interim success rates. The stability of the marginal bone level is one parameter proposed by many, although bone loss as such is not synonymous with failure. Several implant systems with a roughened surface (plasma sprayed or coated) suffer from progressive marginal bone loss and consequently ongoing loss of implants even after 5 or more years. Those implant systems should be evaluated with cumulative success rates over a period of 10 years. Only those that demonstrated a clustering of both bone and implant loss during the first 1 or 2 years after insertion and subsequently a levelling off for those two parameters-a so-called plateau pattern, should be allowed to draw conclusions after 5 years. Since radiographs reveal only the approximal areas, measurement of the attachment level by means of probing towards a reference point on the abutment should also be performed annually. Intra-oral radiographs can only reveal absence of radiolucency at the bone-implant interface, but do not prove osseointegration. The use of an electronic device offers objective results and reveals even subclinical mobilities of endosseous implants. One can conclude that there is an urgent need for a consensus between health authorities, third parties, and the scientific community to define a set of universally-acceptable success criteria, to impose the use of cumulative success rates, and to ask for observation periods of 10 years for implants that do not demonstrate stable results after one or two years.

In vivo testing of an experimental endosseous implant design

PURPOSE

The purpose of this study was to test a new implant system with apically expanding, double-hinged wing stabilizers in dogs before human testing.

METHODS

Twenty-seven HA-coated endosseous implants were placed in five dog mandibles. The implants were placed into function for 12-weeks after a 12-week healing period. At the end of this period, the implants were evaluated clinically and radiographically. The animals then were killed, allowing for the implants to be evaluated mechanically and histologically.

RESULTS

After the initial healing period, 24 of 27 implants demonstrated osseointegration. Seven of eight implants restored with acrylic resin-fixed partial dentures were stable after the 12-week period of function. However, 17 of 27 implants failed to satisfactorily deploy the apical wing stabilizer system.

CONCLUSION

This new implant system has a number of design flaws that must be addressed before testing in humans.

Functional and cosmetic reconstruction of the facial lower third associated with placement of the transmandibular implant system

PURPOSE

Conventional preprosthetic procedures have typically focused on improvement of denture base stability and retention and have ignore patients' concerns about facial appearance and articulation difficulties. Soft tissue procedures have been developed, combined with insertion of the transmandibular implant (TMI) system through a submental incision, for functional and cosmetic reconstruction of the lower face to improve speech and facial esthetics, and prevent gingival hyperplasia along the lateral posts of the implant.

PATIENTS

The surgical procedure was evaluated in 146 patients with slight, moderate, severe, and extreme mandibular atrophy classified according to the proportion of muscle origin loss on the edentulous mandible. Preoperative, 3-month, and 1-year postoperative full-face and profile photographs were taken. Patients also were questioned about their satisfaction with their facial appearance and speech at these intervals. Gingival hyperplasia along the TMI posts was scored as present or absent.

RESULTS

Satisfaction with the soft tissue reconstruction in 146 patients treated according to this protocol was high, with almost every patient describing the positive comments they had received from their friends and relatives. Postoperatively, none of the patients requested a temporary denture to use during the 12-week incorporation period, although this was a common cosmetic and speech concern preoperatively. Gingival hyperplasia secondary to muscle pull was controlled satisfactorily.

CONCLUSIONS

With the described technique for placement of the TMI system, not only is masticatory function improved, but also the lower third soft tissues of the face are functionally and cosmetically reconstructed to the satisfaction of the patients.

The transmandibular implant: from progressive bone loss to controlled bone growth

PURPOSE

In a prospective study, 146 consecutive transmandibular implant (TMI) patients were treated according to revised surgical and prosthetic protocols to induce and control bone growth. Revisions included 1) placement of transosseous posts and cortical screws between the mental foramina so that two threads extended beyond the alveolar crest of the mandible without protruding through the mucosa and 2) fabrication of an implant-borne prosthesis that rested on the retromolar pads with a gap of 2 mm between the denture base and the mucosal tissues in the saddle areas.

PATIENTS AND METHODS

Measurements of the height of the mandible were made using a digital millimeter calliper and panoramic radiographs, with the enlargement calculated for each radiograph. The follow-up period ranged from 18 to 51 months.

RESULTS

Bone growth was present in 131 of the 146 patients whereas the bone resorption was arrested in the remaining patients. Increase in bony apposition varied from 9 mm in patients with severe mandibular atrophy to 2 mm in patients with mild atrophy.

CONCLUSION

The revised surgical and prosthetic protocols for TMI insertion and rehabilitation are advocated to prevent further alveolar resorption and to promote bone growth in patients with mandibular atrophy.

Dental implants and chemotherapy complications

The cancer patient receiving chemotherapy often suffers severe oral complications related to the administration of antineoplastic drugs. Cancer patients who also have transmucosal or endosseous dental implants pose special problems for medical oncologists and dentists, both when planning for chemotherapy and when providing supportive care during the course of treatment. The relationship between dental implants and cancer chemotherapy is described and complications experienced by implant patients treated with chemotherapy at The University of Texas M.D. Anderson Cancer Center are reviewed. Recommendations on various aspects of management involving implant evaluation and the removal or retention of dental implants are discussed.

The transmandibular implant: prosthodontic treatment considerations

The transmandibular implant (TMI) is a type of transosteal implant designed for use in the edentulous mandible. The implant is composed of a gold-based alloy. The TMI is a loaded implant in that the prosthesis is supported by the implant. A transitional type of prosthesis, for insertion following surgery can be made either by altering the patient's existing mandibular complete denture or by making a new denture. The completed prosthesis is retained by clips held in the mandibular denture with autopolymerizing acrylic resin. The clips engage Dolder bar segments, which are a part of the implant suprastructure, and provide the necessary retention for the mandibular complete denture.

State of the art in oral implants

Uncontrolled oral implant devices are still being widely used. The documentation of most oral implant systems is poorly backed up or not followed up for an adequate time period. Success rates are being quoted without reference to any defined success criteria. Frequently used oral implant designs such as the Core-Vent, IMZ and Calcitek hydroxyapatite coated implants are in neither case supported by any adequate clinical reports from minimally 5-years of follow-up. Other implant systems such as the ITI, some subperiosteal designs and the Tübingen implant demonstrate well-controlled and acceptable 5-year data but are not followed up in a sufficient number or have demonstrated less good results in the 10-year evaluation. The Small transosteal staple has been adequately reported for more than 10 years of follow-up, whereas the Brånemark implant is the only endosseous design that has demonstrated acceptable 15-year success rates.

The transmandibular implant: a 13-year survey of its use

During the period from August 1976 until July 1989 the transmandibular implant was introduced in a total of 31 oral and maxillofacial surgery departments in the Netherlands and 1,466 patients were treated. This study includes 1,356 treated patients from 28 departments. The treatment course of 1,201 patients (89.6%) was uneventful. Of the 157 complications, 58 related to the anatomic contour of the mandible, 49 to the surgery, 25 to the prosthetic reconstruction, 8 to the psychosocial attitude of the patient, 8 to the use of medication, 5 to trauma, and 4 to the presence of a skin graft. Treatment of the complications included removal of the implant in 44 patients; in 106 patients the complication was treated satisfactorily. In the remaining 7 patients, hypesthesia was present. The reasons for the removal of the 44 implants were infection (11), operative error (5), premature loading of the implant (3), insufficient width of the mandible after a visor osteotomy (1), loss of osseointegration caused by the prosthesis (14), psychological problems (4), trauma (3), drug-related gingival hyperplasia (2), and inexplicable pain (1). The present survey shows a consistent success rate of 96.8%.