Abstract
The height and consistency of the bone tissue located above the inferior alveolar nerve (IAN) represents an important challenge when a patient’s atrophied posterior mandible is rehabilitated with an osseointegrated implant. Usually, the surgical reconstruction of atrophic ridges is performed using several different techniques. The purpose of this study is to demonstrate the effectiveness and safety of the inferior alveolar nerve lateralization (IANL) technique performed with ultrasonic cutting technology (piezotome). To demonstrate this, 38 osseointegrated implants (11–15 mm in length) were performed during 19 procedures on 15 different patients. After 8 weeks, 14 of those 15 patients (18 of 19 sites: 94.73%) showed normal IAN function. The implant success rate was 97.36%.
Posterior or lateral mandibular atrophies in patients who need dental implants are a common issue in oral and maxillofacial departments. These cases present several challenges in terms of dental restoration, such as a minimum bone height above the Inferior Alveolar Nerve (IAN) on which to place suitably sized implants, and a disproportionate implant-crown relationship. Several alternatives have been developed to resolve these problems such as: alveolar distraction ; on-lay versus in-lay autologous bone grafting ; guided bone regeneration with autologous bone particles such as allografts or xenografts, which are then covered with titanium mesh or titanium reinforced membranes ; tilted or ‘all-on-four’ procedures which extract the remaining teeth; and short implants (<8 mm) Grant et al. (2009). Varying methods of Inferior Alveolar Nerve Lateralization (IANL) and immediate implant placements that have used drills, burs or saws, have been reported. Disturbances in postoperative neurosensory function of the IAN are common. The risk of IAN morbidity created some controversy, which resulted in the limited use of this classic technique.
The authors propose the re-use of IANL, because by updating it using the piezotome they have found it to be effective. The aim of this procedure is to lateralize the IAN in order to achieve the required bone height to securely place a suitably sized implant (at least 11 mm in length), while keeping the neurosensory function of the IAN intact. Although the ultrasonic cutting device developed by Tomaso Vercellotti was relatively underutilized immediately following its debut, it has since been found to be useful in much oral and maxillofacial surgery. A few implant placement cases with IANL and case series using piezotome equipment have been published which demonstrated positive neurosensory function and implant survival results. The efficient and selective piezotome cutting ability is based on its 5–16 W ultrasonic power waves (with a functional frequency between 25 and 30 kHz), which generates micro-vibrations of 60–210 μm amplitude that are amplified and transferred to the tip of the handpiece. This feature enables discrimination between mineralized and non-mineralized tissue due to the cavitation phenomenon, thus effectively avoiding soft tissue damage when the device is used. Several tips (inserts) with different shapes, materials and sizes can be attached to the handpiece to carry out different functions. The ‘boosted’ mode is usually utilized in oral and maxillofacial surgery.
Results have shown that the operated tissue responds more favourably to piezosurgical techniques rather than conventional bone cutting techniques, and has been shown to disinfect the surgical site. Pavlíková et al. have recently published a review paper about piezosurgery in oral and maxillofacial surgery.
The aim of the present study is to confirm the effectiveness of IANL performed with the piezotome as an alternative treatment for edentulous patients with severe posterior mandibular alveolar atrophies, as well as to evaluate their postoperative neurosensory function and the survival rates of their implants.
Materials and methods
A prospective cohort study (according to the STROBE Statement guidelines) was carried out in edentulous patients with posterior mandibular atrophies who were treated between 2004 and 2010 at the authors’ Oral and Maxillofacial surgery Department of La Princesa University Hospital department. The key element of this study was to rehabilitate atrophied posterior mandibles through IANLs performed with piezotome and immediately osseointegrated implants. Patients were included if their bone height above the IAN was <5 mm ( Fig. 1 ). Patients were informed about alternative treatments, and were given information regarding the risk of postoperative neurosensory dysfunction both orally and in writing. After receiving this information, and after orally agreeing to the surgery, the patients’ written informed consent was obtained. No patient refused the IANL treatment. Patients who were excluded from this study were treated with other rehabilitative techniques suitable to their case.
The implant sizes, the bone heights above the IAN, the surgical procedures, the results of the neurosensory evaluation, and implant survival rates were taken from the medical records 1 year after the end of the study. The same surgeon carried out all the procedures.
To keep track of the neurosensory function of the IAN and postoperative implant survival rate, follow-up visits were scheduled on the third and eighth weeks, and at 6, 12 and 24 months, during the 2 years immediately following the surgery. Patients were asked about pain and neurosensory disturbance (such as dysaesthesia or hypoesthesia). Neurosensory function was checked by a two point-discrimination test, during which a measurement of <15 mm was considered normal. The distance of <15 mm was chosen as normal, based on previous studies by Rosenquist and Ferrigno. X-rays were taken at 3 months and 1 year after implant loading to check for marginal bone loss (MBL). The degree of osseointegration of the implants was determined by examining whether or not the implants were both painless and immobile when under torque and while loading, and whether or not any pathology was detected in the X-rays during the examination.
Surgical technique
All the patients were operated on under general anaesthesia. A horizontal incision from the canine to the anterior border of the mandibular ramus was made on the alveolar crest. Additionally, a releasing anterior incision and a mucoperiosteal dissection were performed to preserve and to free the mental neurovascular bundle ( Fig. 2 ). The mental foramen and vestibular surface of the mandible were exposed.
The ultrasonic osteotomy safely carved through the cortical and cancellous bone (approximately 5 mm in height and 25–30 mm in length) immediately posterior to the mental foramen until the surgeon felt that he was no longer cutting bone, which meant that the tip of the device was touching the soft tissue of the neurovascular bundle ( Fig. 3 ). The bone window was then luxated and the medullary remainder bone was removed with small curettes or the piezotome insert. The IAN was identified and gently lifted out of the osseous canal using a blunt curette. The implants could then be placed under direct visualization ( Fig. 4 ). 38 Mozo-Grau ® osseous implants, 11–15 mm in length and 3.3–4.25 mm wide, were placed. When necessary, some bicortical anchorage was performed to achieve primary stability.
