Abstract
The aim of this study was to present and evaluate a modified technique to inferior alveolar nerve lateralization (IANL) that allows the placement of longer implants in the posterior mandibular region. One hundred and forty-three consecutive patients were enrolled in this study; these patients had between 1.8 and 8 mm residual crestal height above the mandibular canal. Vertical splitting of the mandibular body was performed using piezoelectric surgery followed by bone expansion and insertion of special conical implants of 10 and/or 12 mm in length. Two hundred and sixty-nine osteotomies were performed and 636 implants were inserted, with a survival rate of 99% at the end of 12 months. Immediately postoperative there was an alteration of sensation in the lip/chin area in 8.5% of cases; 4.1% regained full sensation within 10–14 days, 2.6% after 8 weeks, and 0.7% had persistent paresthesia that did not affect their daily activities. Progressively increasing pain and numbness was present in 1.1%; the implants were removed 6 months postoperatively. This is a relatively simple procedure that has no limitations in clinical situations with minimal bone height. It allows for greater implant stability, and the risk of neurological disturbance is minimal.
Dental rehabilitation of partially or totally edentulous patients with dental implants has become common practice in recent decades, with reliable long-term results. However, clinical situations where low bone quantity and quality are present require therapy prior to implant placement.
Several surgical techniques have been employed in an attempt to allow implant placement in regions of inadequate bone height and thickness. These include bone grafting, distraction osteogenesis, ridge-splitting technique, inferior alveolar nerve transposition or lateralization (IANL), and placement of fixtures in a lingual position to the neurovascular bundle.
Bone grafting techniques are associated with major inconveniences as a result of the need to harvest the graft (generally from an extraoral location). This is a procedure that usually involves general anaesthesia, hospital admission, and a prolonged duration of treatment. The two-stage approach also results in considerable resorption of the bone graft before implant insertion and difficulty in the management of soft tissues, which have a high risk of dehiscence and subsequent infection and necrosis of the graft.
Distraction osteogenesis is a technique described in the literature for alveolar ridge augmentation, thus gaining vertical height in the posterior region of the mandible. However, a minimum height of approximately 8 mm of remaining bone above the mandibular canal is required.
The alternative treatment that has been suggested and researched is the lateralization of the IAN (IANL), which allows placement of longer implants, gives better initial stabilization, and reduces the treatment time. However, nerve repositioning is a complex procedure, with a high risk of complications. This has caused some clinicians to express concern about the routine use of these procedures. The major clinical difficulties associated with IANL are temporary or permanent dysfunction of the nerve and mandibular fractures associated with the placement of endosseous implants following IANL.
The ridge-splitting/expansion technique is aimed at the creation of a new implant bed by longitudinal osteotomy of the alveolar bone. The buccal cortex is repositioned laterally by green stick fracture. This technique is usually performed simultaneously with implant placement and significantly shortens the treatment time.
The aim of this study was to present and evaluate vertical ridge-splitting as an alternative technique to IANL for the rehabilitation of severely atrophic posterior mandibles.
Materials and methods
This study was designed prospectively and was started in 1998. One hundred and forty-three consecutive patients (97 females and 46 males) aged between 45 and 70 years (mean 53 years) were included in this study. The patients received a total of 636 implants in the posterior region and were recruited between June 1998 and September 2011. Any patient with unilateral or bilateral partial or total mandibular edentulism, with a residual bone height over the mandibular canal of between 1.8 mm and 8 mm (mean height 4.17 mm) was included in this study. Patients with immunologic diseases, uncontrolled diabetes mellitus, osteoporosis, or other contraindicating systemic conditions were excluded from participation. The position of the IAN and the mental foramen were assessed radiographically using orthopantomograms and computerized tomography (CT) scans, and the distance between the IAN and the crest of the alveolar ridge was measured at relevant points in order to perform the osteotomies ( Figs. 1 and 2 ). All patients were informed about the risks and benefits of the procedure and they provided written informed consent for the treatment.
All patients received an injection containing 1 vial of methylprednisolone sodium succinate (Solu-Moderín ® 125 mg; Pfizer, Spain) and 1 vial of lincomycin HCl (Lincocin ® 600 mg; Pfizer, Spain) 1 h preoperatively, and they were asked to rinse with 0.2% chlorhexidine gluconate antiseptic solution immediately prior to surgery. All patients were operated on under local anaesthesia: articaine HCl 4% and epinephrine 1:100,000 (Septocaine ® , Septodont, France). The anaesthetic technique used was infiltration anaesthesia at the alveolar crest, the lingual nerve, and the buccal nerve.
A midcrestal incision, centred in the keratinized tissue, was designed through the edentulous span and retromolar pad to allow a minimum of 1–2 mm keratinized gingiva on both sides of the flap. In most cases, this was slightly shifted to the lingual side. A full-thickness mucoperiosteal lingual flap was reflected with extreme caution to prevent tears in the periosteum. The buccal aspect of the alveolar ridge was then exposed via subperiosteal dissection to visualize the mental neurovascular bundle.
In the mental foramen zone, the osteotomy was performed lingual to the crest of the alveolar ridge, using the osteotomy inserts of NSK VarioSurg ® , increasing the depth slowly and gradually until the inferior mandibular cortex was reached. Threaded bone expanders (Microdent System, Barcelona, Spain) were then used sequentially up to expander number 3. This served to displace the buccal wall (containing the neurovascular bundle) buccally, without injuring the nerve, and to prepare the implant bed. Special conical implants of 3.8 mm or 4.2 mm diameter and 10 mm or 12 mm length (MV implants, Microdent System) were then threaded in place. These implants are specially fabricated to be used with threaded bone expanders. The tapered design of these implants with a 2 mm diameter towards the apex allows bone displacement without injuring the nerve.
A modification of the procedure was performed in the second and third molar zone. The osteotomy was done buccally in the area corresponding to the distal root of the second molar and the roots of the third molar, until the inferior cortex was reached. This was followed by the use of the expanders to displace the buccal cortex away from the lingual wall containing the neurovascular bundle. This allowed the placement of another one or two implants without injuring the nerve. Conical implants of 3.8 mm or 4.2 mm diameter and a length of 10 mm or 12 mm (MV implants) were then threaded in place engaging the inferior cortex, aiming towards a tricortical anchorage (buccal, lingual, and inferior) to achieve primary stability ( Fig. 3 ).
The mucoperiosteal flap was then closed using polypropylene monofilament sutures. An orthopantomogram was carried out immediately after surgery to check the direction and position of the implants. Provisional restorations were delivered at the same visit in most cases.
The postsurgical therapy protocol consisted of injecting the patient with the methylprednisolone sodium succinate 125 mg and lincomycin 600 mg mixture for two days after surgery, together with ibuprofen 600 mg twice daily for 3 days. A soft diet and appropriate oral hygiene were prescribed for 2 weeks, including rinsing with 0.2% chlorhexidine gluconate twice daily. The sutures were removed 10 days after the operation, and definitive restorations were delivered to the patients 3–6 months postoperatively ( Fig. 4 ).
The postoperative control period was standardized for all patients; they were followed up weekly during the first month following surgery, and monthly thereafter for a period of 6 months, and then attended for a regular annual follow-up (up to 13 years for some patients). Neurosensory alterations of the lower lip and/or chin and radiographic controls were periodically monitored. Impaired sensitivity in an affected area was recorded as hypoesthesia, and a complete loss of sensation as anaesthesia or dysesthesia, while itching, tingling, or a prickly sensation was recorded as paresthesia. In addition, patients underwent objective assessment of the outcome in the form of a static light touch test with cotton-tipped applicator. A pin prick sensation test was also performed using a sharp and blunt dental probe for the lip and chin area, with the patient’s eyes closed.
Results
One hundred and forty-three patients were enrolled in this study and underwent 269 osteotomies between June 1998 and September 2011. Among them, 126 patients underwent bilateral surgeries and 17 unilateral surgeries. A total of 636 implants were inserted in these patients: 371 implants in the molar region and 265 implants in the premolar region. The implants were all conical of 3.8 mm diameter (221 implants of 10 mm length and 22 implants of 12 mm length) or 4.2 mm diameter (168 implants of 10 mm length and 225 implants of 12 mm length).
In one osteotomy, the buccal cortical bone was fractured while screwing the implant, and this was treated immediately by creating perforations in the cortical bone for mechanical retention of the corticocancellous bone block, which was then covered by a collagen membrane (Osteobiol Tecnoss ® Dental, Italy) ( Fig. 5 ). Healing was uneventful and the implants were stable 12 months postoperatively.
Recovery of the surgical site was uneventful in all but seven osteotomies (2.6%), in which wound dehiscence developed at the surgical site 9–14 days postoperatively. All cases were treated by local debridement and irrigation using warm saline and chlorhexidine 0.2% daily until complete healing was achieved.
Regarding the neurosensory assessment, impaired sensation in the lip and/or chin region in the form of hypoesthesia or paresthesia was reported in 23 IAN osteotomies (8.5%) postoperatively; of those, 4.1% had recovered full sensation within 10–14 days, while 2.6% reported paresthesia in the lower lip, which disappeared 6–8 weeks following intramuscular injections of vitamin B complex every other day for a month. Persistent hypoesthesia at the end of the follow-up period was reported by 0.7%, although the altered sensation was neither annoying nor interfered with daily activities. Upon objective testing of these patients, the only complaint was not being able to differentiate between sharp and blunt objects. A progressively increasing numbness and tingling sensation in the lip and chin region occurred in 1.1% at 6 months postoperatively due to encroachment of the implants on the mental nerve; these implants were removed.
Eight implants were removed (1.3%) at 2–4 months after insertion. Three implants were mobile due to the absence of primary stability at the time of implant insertion and were replaced with 5 mm diameter conical implants, which were successfully osseointegrated. Three implants were removed due to persistent annoying feelings of pain and paresthesia that had not subsided at 6 months after surgery. Two implants were found to be mobile at the time of uncovering the implants and were removed without affecting the stability of the final prosthesis.
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