November 1, 2006
by Alan Kwong Hing, DDS, MSc., Rick Danceluzzi, CDT and Keith Mackenzie, DD
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.1
Often in severely resorbed mandibles there is insufficient bone height for the placement of conventional root form implants without extensive bone grafting. A severely resorbed (Class V) mandible was successfully reconstructed with an autogenous bone graft on the inferior border of the mandible and a titanium mesh plate. After the placement of endosseous implants in the mandible, the patient was rehabilitated with an overdenture to restore masticatory function.2 The results of a 10-year follow-up examination show that non-rigid telescopic connectors with two interforaminal implants for overdenture stabilization appear to be an efficient and effective long-term treatment modality in severely resorbed edentulous mandibles. Particularly in geriatric patient treatment this concept may provide advantages in terms of handling, cleaning and long-term satisfaction.3
An alternative to grafting is the use of mini dental implants but this technique does not employ a flap for placement and as a result the true dimension of the bone width cannot be addressed. The issue of severe width loss and the rehabilitation of these patients does not get as much attention as the loss of height. The loss of height is more prevelant in the mandible while in the maxilla, the bone loss is generally more in width.
An approach which utilizes tilted implants and a Procera Implant Bar in combination with implants placed in the symphyseal region is described. This approach is advocated in situations where there is considerable loss of bone width, conventional surgery and prosthetics is desired and to decrease overall treatment time.
The patient was a 59-year-old female who had been edentulous for 13 years. She presented with severely resorbed mandibular bone width which introrally only measured 3mm across including soft tissue from the 35 to 45 area and would be described as knife edged. This thin bone level extended at least 10mm apically. The bone in the midsymphyseal region was measured intraorally to be at least 6mm wide including soft tissue thickness.
The panorex demonstrated 14mm of bone height, but this bone height was determined to be insufficient for osteoplasty and placement of conventional implants due to the severe loss of bone width. The treatment options presented included: mini dental implants, block grafts for increasing bone width or the use of tilted implants and a splinted bar. After a discussion of the treatment options the patient elected to have conventional root form implants placed in tilted positions and then splinted by a Procera implant bar.
The patient had no medical contraindications to surgery. She was provided with local anaesthesia via inferior dental and mental nerve blocks utilizing Marcaine and sedated with halcion (triazolam 0.5 mg) one hour prior to surgery. Post operatively she was given amoxicillin 500mg three times per day for one week and ibuprofen 600mg three times per day for three days as needed for pain.
Upon full thickness flap reflection (Fig. 2) the bone width was 1 – 2mm and in the symphyseal area 3mm wide. Severe undercuts were noted on the buccal and lingual.
In Figure 3 two 3.5 implant drills are shown in place to demonstrate the angulation achieved with the planned midsymphyseal implant placement.
Nobel Tapered Select Implants were placed according to the standard manufacturer’s protocol at no greater than 45Ncm. A standard surgical protocol is followed to place the two anterior implants with a titanium surgical template utilized in the ALL in 4 technique to ensure not greater than a 30 degree divergence in the angulation of the implants relative to the occlusal plane. Two Nobel Select Tapered TiUnite implants 3.5mm wide and 16mm in length were utilized. The implant in the 33 region was tilted towards the lingual and the 43 towards the buccal (Fig. 4.).
As there was insufficient bone width augmentation was performed with autogenous bone from the osteotomy sites and BioOss bone in a 50:50 mix (Fig. 5).
A one stage approach with healing abutments was used and the patient was allowed to heal for a period of three months prior to prosthetic procedures commencing. See Fig. 6 for final healing of the soft tissues.
Impressions are then taken of the implant positions. An open tray approach is used due to the implant angulations (Fig. 7).
Polyvinylsiloxane impression material is utilized to capture the impression posts. The impression has the impression posts inserted into it with attached analogs. A soft tissue model is poured up to transfer the tissue heights and contours from the mouth. A wax rim stabilized to the implants is utilized to establish vertical dimension. Teeth are added to the wax rim for a try in to assess for esthetics and phonetics. Once the correct teeth relationships are established an index is made of the model. A duralay bar is made and then placed on a milling machine. After milling the correct draw, the bar is scanned and processed for a Procera bar. Once the bar is returned from Sweden the final polishing and finishing is completed. The denture is processed and then the attachments are retrofitted to the denture (Figs. 8 & 9).
Final delivery of the bar is completed with removal of the healing abutments and flushing the implant access holes with chlorhexidine. The bar is fit and then the fit is confirmed with x-rays. Once the seating is confirmed the Tiunite screws are torqued to 35Ncm. The denture is delivered and any adjustments that are required are made.
The patient is provided with a comfortable, esthetic, ease of maintenance overdenture that has better ability to carry load and increases function as compared to a conventional two implant overdenture (Fig. 10).
RESULTS AND DISCUSSION
In this clinical application the All on 4 Technique with a titanium surgical guide is utilized to place two anterior implants tilted at no greater than 30 degrees and in the mental symphysis area rather than implants placed conventionally straight up and down and anterior to the mental foramen. The use of tilted or angulated implants has shown good ten year results.4-6 This is done to avoid extensive bone grafting. In a paper by Stellingsma et al7 their prospective clinical study was to compare the clinical and radiographic results of three modes of implant treatment in combination with an overdenture in patients with extremely resorbed mandibles. The three treatment strategies used were a transmandibular implant, augmentation of the mandible with an autologous bone graft followed by placement of four endosseous implants, and the placement of four endosseous implants only.
During the evaluation period significantly more implants were lost in the transmandibular implant and the augmentation groups compared to the group with endosseous implants only. This suggests the use of autogenous grafting and its associated loss of more implants can be avoided by placing the implants in the symphysis alone without extensive reconstruction with grafts prior to implant placement.
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. Procedures related to the severely resorbed edentulous mandible
and dental implant treatment 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.1
In their case presentation Kao et al8 describe a mandible reconstructed with an anterior osteotomy and interpositional sandwich iliac bone graft at the symphysis area, subperiosteally with iliac bone chips mixed hydroxylapatite bilaterally at the posterior atrophic ridge and vestibuloplasty with a split thicknes skin graft. Nine months after the grafting five fixtures were placed and after 3 months the second stage surgery. The final prosthetic reconstruction was an implant supported overdenture with a milled bar. It is proposed the use of the symphyseal technique avoids the use of these grafting procedures and extended time line for treatment.
In a five year retrospective study the use of short endosseous implants and an overdenture in the extremely resorbed mandible, because of the relative simplicity and low morbidity of this treatment strategy, is a justified treatment option.9 Another retrospective study followed the long-term treatment outcome of patients with severely resorbed edentulous mandibles being subjected to oral implant placement with short (6-7mm) Brnemark implants.10 The outcome of the study showed that placement of short Brnemark implants without the use of bone grafting procedures for reconstruction of severely atrophic edentulous mandibles is a highly predictable treatment procedure In the tilted and symphyseal method as described in this paper the use of short implants can be avoided. In this case 16mm implants were utilized as opposed to 6-7mm implants in the study.
In one paper11 a configured titanium mesh with a xenogenic material was utilized for vertical mesh augmentation. The mesh was removed after nine months and then the implants were placed. The resulting time line for final prosthetic reconstruction can be as much as 12 months. Again with the symphyseal technique the time line is shortened to a conventional three month healing period.
In a group of 10 edentulous patients suffering from insufficient retention of their mandibular denture related to a severely resorbed mandible, the anterior segment was augmented as a preimplant surgical procedure using the nonvoluminous Groningen Distraction Device (GDD).12 In all patients that the anterior segment distracted from the mandible body was sufficiently enlarged to enable insertion of endosseous implants with a length of at least 12mm. One implant was lost during the healing phase, but was successfully replaced thereafter. Implant retained overdentures were fabricated three months after implantation. Again in the scenario utilizing the symphyseal approach the time line for treatment is significantly decreased from one year to three months. In addition the very thin ridge of 2mm precludes the use of distraction techniques.
Batenberg13 et al concluded in a literature review of edentulous that patients with a severely resorbed mandible often experience problems with their dentures. Treatment concepts involving two to four implants for the support of an overdenture have been proposed. The aim of this study was to develop a treatment concept for mandibular overdentures supported by endosseous implants based on a review of the literature. It is proposed that two implants supporting a mandibular overdenture (bar construction) are sufficient for most applications. Four implants were indicated in situations involving an edentulous maxilla, a narrow mandibular arch, extreme resorption of the mandible (bone height greater than 12mm), and mandibular soreness and pain. The symphyseal approach allows the treatment of the extremely resorbed mandible with 2 vs. 4 implants. The advantage is less cost and surgery to the patient.
In this clinical case BioOss bone was mixed with autogenous bone from the osteotomy sites and utilized for augmentation of the symphyseal width. Hising et al14 in a study of reconstruction of severely resorbed alveolar ridge crests with dental implants using a bovine bone mineral for augmentation to be a viable treatment modality.
In conclusion, the use of the symphyseal approach with tilted implants and the Procera implant bar allows for conventional surgical techniques with angulated longer implants and with the spread of the implants a larger bar can be fabricated. The advantages are the patient avoids extensive bone grafting procedures, regular prosthetic techniques can be used and conventional time lines for healing can be followed.
Dr. Alan Kwong Hing is Adjunctive Professor, Division of Periodontics, Schulich School of Medicine and Dentistry, University of Western Ontario and Private Practice, Toronto, ON.
Keith Mackenzie, DD, is a practicing denturist in Peterborough, ON.
Rick Daneluzzi is the owner of Bioesthetic Lab located in Woodbridge, ON.
Oral Health welcomes this original article.
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