1. Topic: Implant therapy outcomes, surgical aspects
Onlay bone grafting to reconstruct the atrophied mandible. A retrospective study with long-term follow up.
G.C. Boven1, H.J.A. Meijer1,2, A.Vissink1, G.M. Raghoebar1 1 University of Groningen, University Medical Center Groningen, Department of Oral and Maxillofacial Surgery, Groningen, the Netherlands
2 University of Groningen, University Medical Center Groningen, Department of Fixed and Removable Prosthodontics, Dental School, Groningen, the Netherlands
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Background and Aim
After an uncompromised healing period of 4 months, the grafted area was exposed under local anesthesia and the screws used for fixation of the onlay graft were removed. Subsequently, two endosseous Straumann standard implants with a diameter of 4.1 mm and a length of at least 10 mm were inserted in a one-stage procedure.
No studies have yet been published about the long-term treatment outcome of onlay grafting of the severely resorbed mandible to facilitate implant placement. Therefore, a retrospective observational study was performed to assess the treatment outcome of lower dentures on two endosteal implants placed in the severely atrophied mandible reconstructed with bone grafts from the iliac crest (delayed approach). The study was done in consecutive patients with a follow up of at least five years.
Figure 7. Height of the interforaminal area of the mandible in mm at various time points.
Materials and Methods
Discussion
All consecutive patients were invited by letter to visit the clinic between September and November 2012 for a recall visit.
Our results about bone height of the augmented mandible and peri-implant bone loss are even better than those reported by Vermeeren et al (1996) which might be due to delayed placement of implants in our study. As depicted in figure 7, bone loss is severe directly after augmentation of the mandible, but very mild later on. Thus delayed implant placement is preferred.
The only major surgical complication encountered was damage to the mental nerve. Fortunately, the area of sensory disturbances on the chin is small and patients experience little to no problems by this.
A favorable aspect of this procedure is that the position of the floor of mouth to the alveolar crest is relatively lowered. This allows comfortable seating of the denture.
Although the results of our study are rather favorable, the surgical method applied is still a method with a considerable morbidity. Especially when compared to the use of short implants. Therefore, on an individual basis, it has to be decided whether a patient should be indicated for a prosthetic rehabilitation on short implants or for reconstructive surgery followed by the placement of longer implants.
Figure 4. Two endosseous implants were placed in the reconstructed area.
After a 3-month osseointegration period, a mandibular overdenture retained by a milled titanium bar and gold retentive clips attached to it, was made.
Figure 1. Severely resorbed mandible.
Under general anesthesia, a block of corticocancellous bone was harvested. Next to this, a low vestibular incision was made. A mucoperiostal flap was raised towards the top of the alveolar ridge. Subsequently, the iliac bone graft was cut with a saw. The resulting corticocancellous bone block was fitted as an inter-foraminal onlay graft and fixed with two screws. The remaining cancellous bone was milled and used to fill the created subperiostal tunnel distal from the mental foramen.
Figure 5. A milled titanium bar was attached to the implants.
Figure 6. Clinical view of the milled titanium bar attached to the implants five years after prosthodontic rehabilitation of the patient.
Conclusions
Two endosseous implants placed in an augmented mandible provide a solid base for the support of an overdenture. The method described combines the benefits of two techniques: onlay bone grafts providing sufficient bone volume and inserting endosseous implants of maximal length to provide retention and stability for the lower denture. Four months after augmentation bone resorption seems to be stabilized.
Our evaluation shows that conservation of the gain in bone height seems possible by placing implants in the reconstructed area.
Results
Forty patients were included. Temporary lip and chin dysaesthesia were reported by about a quarter of the patients, permanent dysaesthesia was present in five patients (12,5%). One implant was lost after 5.5 years due to peri-implantitis. The mean height in the mandibular symphysis region was 8.9±2.2, 16.4±2.7, 15.7±2.7, 15.4±2.5 mm at intake, after augmentation, after implantation and at the last recall visit, respectively. Mean loss of marginal bone around implants between implant placement and the last recall visit was 0.6±0.7 mm. The scores of clinical indices were low and patient satisfaction was high.
Figure 2. The resorbed mandible was reconstructed with a bone graft from the anterior iliac crest.
References
Vermeeren JI, Wismeijer D, van Waas MA. One-step reconstruction of the severely resorbed mandible with onlay bone grafts and endosteal implants. A 5-year follow-up. Int J Oral Maxillofac Surg 1996:25:112-5.
Figure 3. Operative view just before insertion of the implants. Three months before, the interforaminal mandibular region had been reconstructed with a corticocancellous bone block. The graft was fixed with two screws.
Presented at the 22nd Annual Scientific Meeting of the European Association of Osseointegration
17-19 October 2013, Dublin, Ireland