Treatment planning for implant placement includes the prescription and interpretation of an appropriate diagnostic imaging technique in order to determine the quantity of bone available for implants and to assess the morphology of the alveolus. Location of critical anatomic structures, such as the mandibular canal, in three dimensions is critical to successful implant place ment. Panoramic imaging has been traditionally used for this purpose but is limited in that it only provides a two-dimensional view and does not allow evaluation of the alveolus in the cross-sectional plane. Anatomic variations such as narrowing or a depression of the alveolus cannot be evaluated and the buccal-lingual location of the mandibular canal cannot be assessed. Further more, the image is distorted and magnified and in many cases, does not provide all the needed information for treatment planning. CBCT is an ideal imaging technique for this purpose because it delivers an acceptably low patient radiation dose1 and allows reformatting of the alveolus in the cross-sectional plane, providing non-magnified, dimensionally accurate images for measurement and analysis. 2,3 Identification of structures such as the mandibular canal has been shown to be accurate. 4 Conventional tomography was used prior to availability of CBCT but the images were blurred and magnified, occasionally making identification of some anatomic structures difficult.
In the cases presented in this report, the information provided by the earlier conventional tomography was critical in enabling us to plan the buccal-lingual placement of implants relative to the position of the mandibular canal. 120 months post treatment, we were able to follow up the earlier case using CBCT technology.
Four decades ago, during the early history of osseointegrated implant treatment, clinicians looked for adequate available bone as a critical case selection criterion. 5 That requirement excluded many patients who would have benefited from treatment. Implant treatment, while promising, was a mere footnote as an oral reconstruction option. About a decade ago, grafting of deficient potential implant sites began to assume an increasingly important role in generating biologically sound foundations for implant placement. 6 Implant treat ment became the new paradigm in oral reconstruction.
To discover the most effective grafting techniques, a systematic review of 526 refereed journal articles published between 1980 and 2005 divided all papers into maxillary sinus and alveolar ridge sites. 7 The techniques studied included guided bone regeneration, onlay/veneer grafting, combinations of onlay, veneer and interpositional inlay grafting, distraction osteogenesis, ridge splitting, free and vascularized auto-grafts, mandibular interpositional grafts and socket preservation. A total of 7,748 implants were followed up for periods ranging from 12 to 102 months. The review stated that well documented, long term studies support the conclusion that implant placement into grafted maxillary sinuses compares favorably to conventional placement without grafting. For alveolar ridge grafting, with the exception of guided bone regeneration, no such studies existed at the time (2007) and more good documentation over five-year periods was needed to elucidate the subject. In fact, implant survival and success in grafted alveolar ridge sites might well be attributed to the role of native bone rather than grafted bone.
To date, no articles have been published describing implant placement buccally or medially to the mandibular canal without IAN mobilization and primarily within native bone. We report two such cases herewith.
CASE 1 — PRE-TREATMENT IMAGING
Surgery
General, system-specific surgery for the Tenax Implant System® has been described elsewhere. 8 For this particular case, for maximal visibility, flaps were raised to expose the mental foramina (Figs. 4-6).
Prosthodontics
General, system-specific prosthodontic treatment for the Tenax Implant System® has been described elsewhere. 9
Results
The patient returned for follow-up examinations several times with all implants surviving. The pa tient was lost to recall after 48 months.
CASE 2 -PRE-TREATMENT IMAGING
Surgery and Prosthetics Again, system-specific surgery and prosthetics for the Tenax Implant System® have been described elsewhere. 8,9 For this particular case, for maximal visibility during surgery, a large lingual flap was raised to expose the submandibular gland fossa. A Seldon retractor was used during osteotomy preparation to protect the soft tissue from the drills as they penetrated into the submandibular fossa space. For ideal vertical positioning, all three implants were intentionally placed through the lingual cortical plate. Bio active glass graft material (PerioGlas, Nova-Bone Products, Alachua, FL) was placed to surround the apices of the implants. It did not contribute to implant stability, which derived from native bone entirely.
The patient was followed up regularly and was re-imaged 120 months after completion of treatment. All implants are surviving and the prosthetic treatment is successful.
DISCUSSION
The two cases described were treatment planned using conventional tomography, the most reliable imaging technique available at the time. Today, one would use the more accurate CBCT to enhance diagnosis and assist during surgery. CBCT is becoming the new treatment-planning standard in evaluation and preparation of most implant cases.
Additionally, with stents developed from the CBCT data we have entered the era of guided surgery, which increases implant placement accuracy and reduces the risk of complications.
To allow implant placement, severe mandibular ridge deficiencies frequently need correction with ridge augmentation procedures. Cortiocancellous bone grafting is often used to achieve that objective harvesting the bone from intra-oral or extra-oral donor sites. Traumatic surgical intervention additional to implant placement is needed. Asses sing bone augmentation techniques for dental implant treat ment The Cochrane Data base of Systematic Reviews concluded: “Major bone grafting procedures of resorbed mandibles may not be justified.” 10 CONCLUSION
Appropriate diagnostic imaging technique allows the determination of the quantity of bone and morphology of the alveolus available for implants. The two cases described here demonstrate that by using the presented imaging methods, selected patients with severe mandibular ridge vertical deficiencies but adequate width can be successfully treated using implant-supported prostheses without needing cortiocancellous bone grafting.
OH
Tenax Dental Implant System implants were used in all cases illustrated in this article.
Dr. Somborac is in general private practice in Collingwood, Ontario. He is the co-inventor of this implant system and a shareholder in Tenax Implant Inc.
Dr. Weel is an oral and maxillofacial surgeon in private and hospital practice in Barbados, West Indies.
The authors are grateful to Dr. Paula Sikorski and Martin Bourgeois, oral radiologists, Toronto, Ontario, for their contribution of the conventional tomograms used and Dr. Grace Petrikowski, oral radiologist, Barrie, Ontario, for contributing the cone beam computed tomography images and for aid in preparation of this manuscript.
Oral Health welcomes this original article.
REFERENCES
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ABSTRACT
PURPOSE: To describe diagnostic imaging protocols for the placement of endosseous implants lingually or buccally to the mandibular canal. PATIENTS AND METHODS: Following a cross sectional imaging diagnostic protocol described, two patients received seven implants in three posterior sextants each with =7.5mm of bone coronal to the mandibular canal. One patient had adequate bone width buccal to the mandibular canal and received two 15mm. implants in each quadrant as well as one 12mm implant anterior to each mental foramen. The other patient had adequate bone width lingual to the canal and received three 12mm implants. Using cross sectional imaging for patient selection and the surgical methods referred to, neither patient needed inferior alveolar nerve (IAN) mobilization nor block grafting. RESULTS: When examined clinically as well as using conventional imaging after 48 months, the four buccally placed implants were osseointegrated and functional. The three lingually placed ones were osseointegrated and functional after 120 months as shown by cone beam computed tomography (CBCT). There were no complications. CONCLUSIONS: Following the cross sectional imaging and surgical protocols referred to allows successful implant placement into the posterior mandible with adequate bone width but inadequate bone height without block grafting and without IAN mobilization.
