Safety Zone to Mandibular Canal for Posterior Mandible Implant Surgeries

Special Article - Dental Implants

J Dent & Oral Disord. 2016; 2(6): 1030.

Safety Zone to Mandibular Canal for Posterior Mandible Implant Surgeries

Garcia Blanco M* and Puia SA

Department of Oral and Maxillofacial Surgery, University of Buenos Aires, Argentina

*Corresponding author: Garcia Blanco M, Department of Oral and Maxillofacial Surgery, School of Dentistry, University of Buenos Aires, Buenos Aires, Argentina

Received: July 04, 2016; Accepted: August 04, 2016; Published: August 05, 2016


Dental implant surgeries are widely used in dentistry due to their numerous advantages. Many articles have focused on local accidents and complications of this treatment. One of the major complications is the injury of the inferior alveolar nerve, which could potentially be damaged permanently. In order to protect clinicians and patients, some authors recommend leaving a safety zone around this nerve. The aim of this article is to review guidelines proposed to avoid this complication, and discuss critical clinical situations when this recommendation could be reappraised.

Keywords: Dental implants; Diagnosis; Nerve injury; Safety zone; Short implants


IAN: Inferior Alveolar Nerve; MC: Mandibular Canal; CT: Computed Tomography; CBCT: Cone Beam CT


Nerve injuries and safety zone

Replacement of teeth through dental implants is a widely accepted technique due to its numerous advantages [1-3]. Although it has many benefits, there may be some unfavorable outcomes. Damage to the Inferior Alveolar Nerve (IAN) is a potential major complication in mandibular dental implant surgeries. Physical harm can occur during anesthesia, flap elevation or advancement, bone graft harvest, osteotomy preparation or implant placement [4-7]. The prevalence of nerve damage that results in altered lip sensations ranges from 0% to 40% in old literature [8-10]. Currently, midcrestal incisions and Computed Tomography (CT) help prevent this type of injury, and recent studies report prevalence below 3% [11,12]. Patients’ symptoms include complete absence of sensation, diminished or increased sensitivity, abnormal sensations which may not be unpleasant and spontaneous or mechanically evoked painful symptoms [13-15]. The IAN enters the mandible in the internal side of the ramus, lies beside the lingual plate and makes a sudden turn in direction towards the buccal plate in the first molar area to the mental foramen, which size and frequency are still controversial [16-19]. Although Cone Beam CT (CBCT) seems to have the best potential efficiency in the identification of the Mandibular Canal (MC) [20], nerve detection maybe difficult in some cases [21].

Recommendations have been proposed to avoid injuring the inferior alveolar nerve. It is especially important to set guidelines in the dental community about how to act prudently to avoid nerve damage, and it is essential for beginners in the discipline. Lack of experience can cause injuries due to not recognizing drill length marks, confusing these marks through poor visualization, extending drilling time and overheating the bone, and other deficiencies in surgical technique (such as vertical incision next to mandibular foramen, or excessive traction of the flap). As some manufacturing companies make implant drills slightly longer to improve drilling efficiency [22,23] drill stops could be used to prevent over-drilling [4,22,24]. It would also be useful to take intra-operative radiographs during implant bed preparation in atrophic mandibles to confirm distance to MC [22,24].

The safety zone to the MC that most authors have proposed is 2 mm [25,26]. Implant length is chosen by making vertical linear measurements, from the top of the alveolar crest to the upper border of the mandibular canal, subtracting 2 mm as a safety zone to the MC. Since the advent of CT, clinicians have begun to reduce this limit, setting a safety zone in the range of 1 to 2 mm to MC [27-29]. This is especially important in some clinical situations, when bone height is reduced, and the safety zone needs to be reappraised. The aim of this article is to review the guidelines proposed to avoid nerve injuries and discuss different clinical situations.

Literature Review

Bone height 12 mm or greater

When patient’s bone height is 12 mm, the clinical situation has a simple, predictable resolution by placing a 10mm long dental implant, maintaining a 2 mm safety zone to the nerve (Figures 1-6). If there is greater bone height, implant length could be increased, improving bone implant contact, although some authors recommend not placing implants longer than 12 mm in posterior mandible, because it would increase the possibility of complications [30].