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Bone Reduction Guide

Placing implants when the bone is limited could require bone grafting or bone remodeling before implant insertion. In this case study bone remodeling is selected for a patient with an edentulous mandible that has a crest with a 'pyramid' morphology classified as a Misch B-w Division bone.


Usually a case like this one would require an osteoplasty to remodel the crest into a Misch A Division bone. Later implant insertion would be set according to the crest after remodeling. However this conventional technique has its limitations. The technique involves a low accuracy of positioning the implants. On the other hand, using the SimPlant bone reduction guide, you can plan bone remodeling and the position of the implants at sub- millimeter accuracy in the virtual 3D mandible in respect to the prosthetic restoration. Later you can place the implants exactly in the desired location, where the bone has a sufficient thickness. Thus, the primary retention of the implants is optimized for the patient. 

Case history

A 74 years old male, socially involved as a past mayor, requests a lower prosthesis supported by implants. He is complaining about an ill-fitting lower partial denture.

Phase I

Diagnosis

This patient has been wearing a conventional upper and lower partial prosthesis for over 50 years. He has less than half a dozen teeth and residuals roots in his mandible. Parodontisis, ill-fitting upper and lower prosthesis, malocclusion and aesthetic unappealing prosthesis were observed.

Planning & Surgery

A two phase treatment plan was established in order to eliminate any pathology in the projected implant area allowing a good prognosis for potential immediately loaded prosthesis and a larger keratinised soft tissue secondary to the dental socket healing. Residual roots and decayed teeth were removed because of severe parodontisis. The panoramic radiography of the edentulous mandible revealed uneventful healing with sufficient bone height. No sign of pathology or teeth fragments were observed after teeth and root extractions. A scanographic template for a CT SimPlant protocol is prepared according to the prosthetic plan. The patient was then sent for the a CT scan.

Phase II

Diagnosis

Evaluation of the bone reduction and the bone density around the implant on a cross section of the mandible at mid implant site. The green color represents the softest bone type and will be eliminated by the bone reduction osteoplasty.

Thickness and density were evaluated for the anticipated osteoplasty and immediate implant loading procedures.

Study of the CT reconstruction radiography reveals the following: 

  • Residual root tips in the anterior mandible are identified with the density tool that were initially not seen on the traditional panoramic radiography 
  • A pyramid bone morphology (div B-w) in the projected implants location
  • Unfavorable bone density for immediate loading in the position A implant
  • Adequate bone length between both mental foramen to fit 5 implants
  • Favorable bone thickness for good implant to prosthesis angulations 

Planning

Planning of the implant placement in SimPlant.

Mandible osteoplasty for a conversion of a div B-w to a div A was planned with SimPlant software. The vertical bone reduction line between both foramens is determined. Five implants of 4mm diameter are planned in the anterior mandible. Angulations and emergence profile were guided by the template. Minor autogenous bone grafts will be required for implants in position A and E, therefore a two stage approach is indicated. Overall density distributions indicate a four month healing period before proceeding to the prosthetic protocol.

An axial cut of the 3D model is performed to evaluate the osteotomy reduction.

A bone reduction guide, along with the corresponding stereolithographic model of the reduced mandible, was ordered. SurgiGuide drill guides were made for the selected osteotomy protocol.

Surgery

Bone reduction guide installed on the anterior mandible to guide the osteotomy leveling in order to set the SurgiGuide.

Leveled osteotomy completed

Surgery is performed with local anesthesia. First stage procedure allows minimal flap opening which is limited to the designed bone reduction guide. Being less iatrogenic reduces healing time and lowers the risk of incision line opening and unnecessary mental foramen exposure.

After bone reduction completion, fitting of the first SurgiGuide is verified with respect to intimate contact with the crest. Fixation of the bone SurgiGuide was done with two fixation screws. A D1-D2 osteotomy protocol was performed with all three guides and implants were placed as planned to sub millimeter precision.

Bone grafting with autogenous bone

Bone grafting was done with the autogenous bone collected from the osteoplasty reduction.

Computer milled Biomet-3i hybrid screw retained titanium bar

At second stage surgery, an open tray impression is made at the implants level and a 3i hybrid fixed titanium bar (computer milled) was selected for this case.

Conclusions

Conventionally, after a bone reduction is performed, one can insert the implants with a free hand setting, but that may not allow ideal 3D implant positioning in the mandible.

A stereolithographic bone reduction guide and SurgiGuide drill guides facilitate the bone osteoplasty and enable the surgeon to place the implants according to the prosthetic plan. This technology allows a true prosthetically driven implantology. Overall benefits include:

  • predictability and precision of surgical procedures 
  • aesthetic improvements 
  • less surgical operation time 
  • less healing time
  • improved patient post-operative comfort giving the patient a prosthetically planned smile.

Biography

Dr Gilbert Tremblay B.Sc., D.M.D. Dipl. ICOI, Fellow MIII

Founder of the Quebec Implant Dental Institute, Dr Tremblay works in his private practice in Montreal Canada. He devotes his time between his practice, teaching and private research. He is also a SimPlant Academy certified provider for teaching and training participants for this software.
www.e-dentalimplants.com

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