Neurovascular disturbances afterimplant surgeryREINHILDE JACOBS, MARC QUIRYNEN & MICHAEL M. BORNSTEIN

Nowadays, oral implants are routinely used for reha-bilitation of the edentulous jaw bone. In recent years,the surgical procedure has been endorsed as uncom-plicated and therefore often labelled as implant place-ment rather than as true jaw-bone surgery.Nevertheless, the potential risk of neurovascular com-plications should always be taken into account, evenin the symphyseal area, which has traditionally beenpromoted as a safe surgical area. With the steep rise ofimplant placement in oral health care, the number ofreports on neurovascular complications has also beensteadily increasing, with most complications occur-ring in the mandible. Indeed, when analyzing data onneural injuries, it seems that the incidence of lingualnerve injury (mostly related to wisdom tooth surgery)has remained static over the last 30 years, whilst theincidence of inferior alveolar nerve injury has steadilyincreased (88). Those injuries are resulting in anincreasing number of medico-legal claims (61).

In a retrospective study of patient complaints fortransient and permanent neurosensory disturbancesof the inferior alveolar nerve, one insurance companyclassified 382 claims in a decade, one in five (n = 75) ofwhich were related to permanent injuries (61). Third-molar removals were responsible for 47% of the casesexperiencing permanent loss of sensation. Endo-dontic treatments, with their traumatic and chemicaleffects, also seem to be responsible for causing anincreasing number of nerve injuries, accounting for35% of the complaints, with one-fifth of these beingpermanent sensory deficiencies. Overall, implantsaccount for only 3% of all reported cases of neurosen-sory disturbances (61). However, it is striking thatwhen the distribution is recalculated for permanentneurosensory disturbances, implant placement seemsto be responsible for 12% of such injuries (61). Thisimplies that 75% of all neurosensory disturbances fol-lowing implant placement are of a permanent nature.Libersa and coworkers (61) estimated, in a 10-year fol-low-up period, that 0.2% of practitioners may cause a

transient neurosensory deficiency each year, with0.05% causing a permanent deficiency. For implantplacement specifically, risk analysis showed muchlower numbers, with 0.008% of practitioners causing atransient neurosensory deficiency each year and0.006% causing a permanent deficiency. Overall, whenreviewing the literature, the incidence of neuropathicorofacial pain following implant placement variesfrom 0% to 24% for transient damage and from 0% to11% for permanent damage, depending on the regionof the surgery, the presurgical planning, the surgicalact and the postoperative neurosensory evaluationmethod (1, 3, 21, 25, 28, 59, 80, 85, 87, 88, 90). The vari-able results reported in the literature are largelydependent on the evaluation strategy and (lack of)standardization of neurosensory assessment andreporting. For an objective neurosensory follow up,initial presurgical testing should be compared withfurther postsurgical assessment at specific intervals(1 week, 1 month, 6 months and 1 year), by usingsimple, but objective, neurosensory testing tools (35).This type of testing is usually performed for orthogna-tic surgery and maxillofacial trauma (85), but not forthird-molar removal and implant placement.

The aim of the present report is to accomplish a cri-tical review in relation to the neurovascular challengesin the jaw bone, including the potential risks involved.Information will be derived not only from case reportson neurovascular complications, but also primarilyfrom micro- and macroanatomic studies, as well asradiographic studies, on human anatomic variability.

Reducing risks for neurovasculartrauma by preoperative diagnosticsand planning

Of the implant-related neural injuries recentlyreported by Renton et al. (87), only one in 10patients had received presurgical planning following

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Periodontology 2000, Vol. 66, 2014, 188–202 © 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd

Printed in Singapore. All rights reserved PERIODONTOLOGY 2000

assessment including cone beam computed tomogr-aphy. To reduce the peroperative risks, it is there-fore obvious that oral implant placement shouldalways be preceded by careful preoperative radio-graphic planning, paying attention not only to jaw-bone volume and morphology, the mandibularcanal and the maxillary sinus, but also to all otherneurovascular structures and their potential varia-tions (34). The preoperative radiographic planningphase should evidently start with a preplanningdiagnostic phase, considering intraoral radiographyand/or panoramic radiography, depending on theextent of the edentulous areas. If it turns out thatimplants are needed in areas with a potential risk ofdamage to vital structures, a safety margin of 2 mmaway from the neurovascular canal should berespected (109) to avoid (in)direct trauma. But, eventhen, some case reports mention postoperative neu-rovascular complaints (24, 91). If it turns out thatspatial information is essential to prepare the surgi-cal implant placement, one may opt for addition ofa third dimension. More provocative, but probablyalso more effective and even conditionally dose-friendly, the following reasoning could be made:when the consulting patient expresses an obviousneed for implants, with the clinical examinationrevealing not only one or more edentulous areasbut also showing severe periodontal breakdownwith the presence of crown and bridges weakeningthe roots, it could be hypothesized for the initialexamination to be a three-dimensional low-dosecone beam computed tomography scan, meanwhileskipping all other two-dimensional diagnostic imag-ing steps and their related radiation dose (36). Thelatter would then enable the clinician to maximizethe use of the inherent three-dimensional dataderiving from the cone beam computed tomogra-phy. This single data set could generate all neces-sary reformats, and even provide a diagnosticallyuseful cone beam computed tomography-derivedindividualized reconstructed panoramic resliceimage (84). Although a panoramic radiograph isoften advocated for initial treatment planning, thepresent proposal would hypothesize skipping theinitial panoramic radiograph in cases where three-dimensional imaging is clinically justified. Shouldthe clinician still feel the need for a panoramicoverview image, additional exposure can be avoidedby using the existing three-dimensional data sets tocreate a panoramic reslice. This could subsequentlybe used as an orientational reference to indicatewhere to place the implants and where to inspectthe remaining teeth. The use of the three-dimen-

sional cone beam computed tomography data setcould be further maximized by using it as a diag-nostic cast, considering an inherent segmentationaccuracy of up to 200 lm, thus competing with theplaster cast exactitude (5, 27, 60, 107).

Only when this preoperative diagnostic phase ismeticously performed can one proceed to the nextphase, namely the preoperative planning. Here, oneshould consider identification of the neurovascularstructures and their relation to bone volume, mor-phology and bone quality, whilst incorporating pros-thetic demands.

Several imaging options are available for this pre-surgical evaluation (11, 26, 106). As imaging involvesthe use of ionizing radiation, the choice of the propertechnique or combination of techniques is based onthe interplay of obtaining as much additional infor-mation on the jaw bone as possible whilst minimizingcost and the dose of radiation to which the patient isexposed. Imaging should provide not only accuratequantity and quality assessments of the jaw bone butalso necessary information on the location of vitalanatomic structures, such as the inferior alveolarnerve, other neurovascular structures and variations.Various recommendations and indications for theappropriate radiographic method related to pre-implant imaging have been proposed (11, 26, 34, 36,106). One of the first radiographs to be considered isthe panoramic image. This should be consideredmerely as an overview image during the preoperativediagnostic phase. Although it may provide informa-tion on the gross anatomy of the jaws and its neuro-vascularization, its inherent distortion, low resolutionand tomographic effect with substantial anatomicoverlap may hamper reliable and anatomically realis-tic measurements and visualization of the neurovas-cular canals (33, 34, 78, 93, 105). Another frequentlyused two-dimensional image is the intra-oral radio-graph. With optimal projection geometry and aninherently good spatial resolution, this image can beconsidered as valuable during the preoperative diag-nostic phase (to determine the status of the remain-ing teeth) as well as during the planning phase (toprovide a preliminary estimation of the dimensionsof the potential implant). Yet, even then, its limitedfield of view and two-dimensional nature often ham-per visualization of the neurovascular structures. Inorder to detect and critically inspect the neurovascu-lar canal trajectory, a third dimension may beneeded, and this could be achieved using so-calledcross-sectional imaging. At present, this third dimen-sion is achieved most easily using dentomaxillofacialcone beam computed tomography, as this offers

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high-quality images at low radiation dose levels andcosts (36, 55).

In the past, further imaging has sometimes beenadvocated during the perioperative treatment phaseand was originally denoted as image-assisted implantplacement as a result of the use of intra-oral radio-graphs when placing implants (37). Whilst this radio-logic procedure might help to generate perioperativeinformation to display the implant and visualize thepotential distance from vital neurovascular struc-tures, its inherent two-dimensional nature, the cumu-lative dose, inconvenience and increasedcontamination risk have discouraged its widespreadclinical use.

Having stressed the importance of accurate identi-fication of neurovascular structures preoperativelyand recognition of the appropriate techniques toevaluate the neurovascular structures clinically, theneurovascular structures, and the variations, in bothmaxilla and mandible need to be described in greaterdetail.

Neurovascular challenges in the jawbones

The jaws are richly supplied by neurovascular struc-tures and therefore it is of utmost importance to iden-tify these before carrying out a surgical procedure, inan attempt to avoid interference. Anatomic and ra-dioanatomic studies carried out during the last dec-ade reveal that the jaw bones, irrespective of whetherthey are edentulous or dentate, show significant ana-tomic variation in neurovascularization (31, 32, 45,58, 59, 64, 65, 75, 77). Many of these accessory or bifidcanal structures contain a neurovascular bundle, thediameter of which may be large enough to cause clin-ically significant trauma, including sensory distur-bances as well as severe hemorrhage (1, 4, 7, 43, 53,61, 72, 82, 87, 88, 115, 119).

Sensory disturbances can be caused by directtrauma to the nerve, indirect trauma (e.g. pressureby hematoma formation in the neurovascular canalat its exit) or chronic stimulation to the trigeminalnerve or any of its branches (31, 59, 87). If animplant is situated aside, or on top of, the nerve,then the nerve can be stimulated each time the indi-vidual bites or chews. It is likely that such a chronicstimulation will end up as chronic neuropathy (31,46, 59). This situation is expected to occur mostly inthe mandible (80); however, a similar situation mightarise less frequently in the maxilla if the implant isplaced in contact with the canalis sinuosis or thenasopalatine canal (15).

Hypesthesia, anesthesia and paresthesia may mani-fest as a sensory disturbance. In some patients, it ismainly the sense of pain that is disturbed but, inothers, the tactile and temperature senses are alsoaffected (1, 59). All of these changes can be transientor persistent, depending on the degree of damage tothe nerve tissue involved.

Case reports on postimplant injury causing neuro-pathic pain seem to be related more often to ische-mia of the mandibular nerve caused by hemorrhageinto the canal, than by direct mechanical traumacaused by the implant itself (46). ‘Cracking’ the man-dibular canal roof while preparing the implant bedmay indeed result in hemorrhage into the canal orthe deposition of debris, which may compress theneurovascular bundle, resulting in nerve ischemia.This constrictive effect on the nerve may persist ifthe implant is left in situ, even if the implant is‘backed-up’ or replaced with a shorter implant.Intra-operative risk factors may also include a sud-den give or a reported electric shock-type feelingduring preparation. Furthermore, if extensive bleed-ing (e.g. from the inferior alveolar artery) is present,it is occasionally advisable to delay implant place-ment for a few days, also to ensure that no nervedamage has occurred.

Extensive hemorrhage in the floor of the mouthmay occur during or after implant placement in themental interforaminal region (10, 14, 18, 19, 23, 29,39, 42, 48, 49, 67, 69, 74, 79, 81, 83, 102). This mayeven result in a life-threatening acute airwayobstruction (14, 23, 48, 49, 67, 69, 79). The hemor-rhage may be caused by instrumentation, throughperforation of the lingual cortical plate, and also bytouching and damaging the neurovascular bonycanals, such as lingual canals. Vascular suppliesfrom the lingual artery, sublingual artery and sub-mental artery anostomose through superior, inferiorand lateral foramina. These multiple vascular anas-tomoses may lead to profuse bleeding, even from abroken small-size bony canal. Importantly, the vas-cular size and neurovascular canal diameter havebeen identified as being large enough to cause sig-nificant damage and bleeding when touched (29,31, 56–58, 103, 114).

In the maxilla, visualization of pertinent anatomicstructures, such as the nasoplatine canal, nasal fos-sa or maxillary sinus, has received less attention inthe literature (9, 68, 76). Although the presence ofthese structures may impede implant success, it isunclear whether (intentional) violation of thesestructures result in neurosensory side effects (31,77).

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Risks for neurovascular trauma inthe mandible

In the mandible, the limiting factors for implantplacement are definitely the mandibular canal and itsanterior extensions. Unfortunately, many of thesecanal structures are neglected in anatomy handbooks(2, 52, 62, 63, 71, 73, 120), but not in oral radiographicanatomy handbooks, because of their visible cortical-ized contour (44, 50, 51, 117). The intra-osseouscourse of the inferior alveolar nerve is not alwaysstraightforward (16, 17, 77). Hence, the risk for surgi-cal trauma may vary accordingly. A bifid mandibularcanal has been reported to occur with a frequency of1% (Fig. 1) (16, 77). In contrast, mandibles with uni-lateral absence of the mandibular canal are rare,although when they do occur, thay seem to be associ-ated with tooth agenesis. One of the often neglectedand rarely documented canal structures is the re-tromolar foramen (16, 111, 113). von Arx et al. (111)described bilateral foramina in the region of the wis-dom teeth, containing small arteries and venulesbesides myelinated nerve fibers and sometimes aber-rant buccal sensory nerve fibers. When present, thisanatomic variation may sometimes explain failures ofmandibular block anesthesia or postsurgical sensitiv-ity changes in the supply area of the buccal nerve(111). In a retrospective radiographic study, conebeam computed tomography scans of 100 patientswere evaluated (113). In this group of patients, a totalof 31 retromolar canals was identified, and only sevenof these were also seen on the corresponding pano-ramic radiographs. The existence of a retromolar

canal was not statistically significantly related to gen-der or side of the mandible. The authors concludethat clinicans should preserve this anatomic variationwhen performing surgery in the retromolar area.

Another vital structure, more anteriorly located, isdefinitely the mental foramen (8, 17, 77, 97). Whilethe mandibular nerve runs forward through the man-dibular canal, at the level of the mental foramen, it isbranching into the incisive nerve and mental nerve.The latter is typically single in nature. Additionalmental foramina exist, with a reported prevalence of9% (Fig. 2). These foramina are often smaller and arelocated more posteriorly (17). Some of those foraminaare rather accessory in nature and are thereforetermed ‘accessory mental foramina’, yet others doexhibit the same size and functional importance andare thus denoted as ‘double foramina’. The absenceof mental foramina has occasionally been described.Variations in the position of the mental foramen arealso common. Typically, the foramen is located half-way between the alveolar crest and the lower borderof the mandible, between the first and the secondpremolars. However, it may be found as far anterioras the canine, or as far posterior as the first molar(see Fig 2B), sporadically even as far as the secondmolar. The latter definitely holds true for the doubleforamina. When extending anteriorly, the mentalnerve may make a U-turn. In the literature, this isdenoted as ‘anterior looping’ or an ‘anterior loop’ andmay occur in no less than 10% of cases (16, 17, 77,92). The average length of such an anterior loop ofthe mental nerve ranges from 3 to 7 mm. Postsurgicalcomplications may occur when this loop is not identi-fied (59, 87, 88). This type of iatrogenic injury to themental nerve or its anterior looping during surgerymay lead to permanent neurosensory damage or todisturbed sensory feeling and/or pain (21, 25, 28, 59,87, 88, 97) (Figs 3 and 4).

While mostly considering the anterior parts of jawsas safe for oral surgery, the use of volumetric imaginghas allowed visualization of an elaborate neurovascu-larization with many variations (31). Apart from themental nerve, the incisive nerve is often identified asa second terminal branch of the inferior alveolarnerve, which has an intra-osseous course in a so-called mandibular incisive canal (31–33, 65, 66). Thiscanal is located anteriorly to the mental foramenfrom both left and right sides of the mandible. Thiscanal is often neglected, probably because of theaforementioned ignorance of such structures inanatomy textbooks (2, 52, 62, 63, 71, 73). Only Gray’sAnatomy mentions that the mandibular canal givesoff two small canals – mental and incisive; the mental

Fig. 1. Panoramic reslice of a cone beam computedtomography image of the mandible, showing a clear verti-cal bifurcation of the mandibular canal, starting at thelevel of the ramus. The upper canal is therefore positionedmore crestally than would normally be the case.

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canal swerves up, back and laterally to the mentalforamen, whereas the mandibular incisive canal con-tinues below the incisor teeth (118). Conventionalradiographs usually fail to show such canals (33), buthigh-resolution cross-sectional imaging can identifythese canals by viewing and inspecting their coursefrom three dimensions (32). A high-resolution mag-netic resonance imaging study, carried out by Jacobset al. (31), indicates that the mandibular incisivecanal contains a true neurovascular bundle withnerve structures, thus having a sensory function. Thisfinding may confirm the statement that the canal con-tains the intra-osseous extension of the inferior alve-olar neurovascular bundle, supplying the mandibularanterior teeth. In some cases, complaints of postoper-ative pain have been noticed after placement of oral

implants in the incisor region. With the informationobtained above, it seems clear that trauma may occurupon touching the incisive nerve (Fig. 5). Its contin-ued presence in edentulous patients is underlined bythe surgical complications reported. Indeed, sensorydisturbances caused by direct trauma to the mandib-ular incisive canal bundle have been reported afterimplant placement in the interforaminal region (31).As previously mentioned, sensory disorders mightalso be related to indirect trauma caused by a hema-toma in the canal, acting as a closed chamber andthus affecting the mandibular incisive canal bundleand spreading to the main mental branch (75, 77).

An elaborate neurovascularization also exists inthe symphyseal midline. Implant placement inthis region is associated with a high incidence of

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Fig. 3. Implant placement in the left mandible (location35) has resulted in anesthesia of the left lip and chin. Acone beam computed tomography scan does not revealthe problem on a cross-sectional slice (A) of the implant,even though the implant was placed through the mandibu-lar canal. (B) The axial slice indicates the mental foramen

(two stars), the anterior extension (denoted as the incisivecanal) and the mandibular canal (one star). (C) In the pan-oramic slice, the perforation of the implant into the area ofthe mental foramen, splitting the incisive canal from themandibular canal, becomes obvious.

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Fig. 2. Double mental foraminavisualized on a three-dimensionalcone beam computed tomographymodel. (A) The foramina are posi-tioned more vertically, in contrast to(B) where the positioning is ratherhorizontal. The latter is more signifi-cant when it comes to surgical risks.

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Fig. 4. Another patient with mentalnerve trauma at tooth 34, caused byimplant placement through thecanal roof. This may cause bleedingand ischemia of the nerve, in addi-tion to a direct pressure trauma. (A)Cross-sectional, (B) axial and (C)panoramic slices showing theimplant touching the mental nerve.

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postoperative neurosensory disturbances (1, 6–8, 59).Midline neurovascularization can be considered anindividual fingerprint because of the endless varia-tions, making it different in each patient. Superiorand inferior genial spinal foramina in the symphysealmidline are found in 85–99% of the mandibles (56–58,70, 96, 103, 108, 114). The superior genial spinal fora-men is at level of, or superior to, the genial spine; theinferior genial spinal foramen is below the genialspine; and the lateral genial spinal foramen is on theleft or the right side of the midline. These are consid-ered important neurovascular structures, often hav-ing dimensions sufficiently large enough to causeclinically significant trauma (Fig. 6). Lateral lingualforamina are often much smaller in size, with adecreased complication risk (57, 103, 114).

Acquiring the correct knowledge of these foraminaand their variability could be important for presurgi-cal considerations of implant placement in the mid-line of the mandible (31, 56, 58, 114).

In some macro- and micro-anatomic dissectionreports, anatomic variations and anastomosis havebeen discovered. The superior genial spinal foramenhas been found to contain a branch of the lingualartery, vein and nerve (56, 108). Furthermore, abranch of the mylohyoid nerve, together withbranches or anastomoses of sublingual and/or sub-mental arteries and veins, has been identified uponentering the inferior genial spinal foramen. Thesearteries could be of sufficient size to provoke a

hemorrhage intra-osseously or in the connective softtissue. Both might be difficult to control (56, 58, 59).

Again, a high-resolution magnetic resonance imag-ing study (31) clearly demonstrates the neurovascularnature of the canal content. This finding is matchedto histology using qualitative and quantitativehigh-resolution magnetic resonance imaging formicroanatomic assessment. These findings may beconsidered as an important link to case reports onhemorrhage and/or sensory disturbances after ante-rior mandibular surgery. In contrast to visualizationof the mental foramen and the incisive canal on mul-tislice computed tomography images as well as conebeam computed tomography images, the relativelysmall size but, far more importantly, the typical mid-line location, may often prevent clear depiction of thelingual foramina on multislice computed tomographyimages (58). This is not the case for cone beam com-puted tomography, which allows continuous slicesampling along the mandible to thicknesses as low as100–200 lm, without any slice interval (31, 36, 55,114). This permits a 100% depiction of the true mid-line structures and greatly assists in the assessment ofsuch neurovascular structures before anterior man-dibular surgery (31, 59, 77). Ignorance may lead tosevere surgical complications, such as neurologic def-icits caused by direct damage or pressure on the roofof the incisive canal, penetration of the lingual inci-sive canal and severe hemorrhage into the floor of themouth, potentially resulting in life-threateningobstruction of the upper respiratory tract (14, 23, 48,49, 67, 69, 79).

Risks for neurovascular trauma inthe maxilla

Increased risks for neurovascular disturbances arealso noted in the anterior maxilla. The maxillary nerveis a sensory nerve, with its superior nasal and alveolarbranches supplying the maxilla, with branches to thepalate, nasal and maxillary sinus mucosa, maxillaryteeth and their periodontium.

The bony canal on the lateral sinus wall mayhost both branches of the posterior superior alveo-lar and infraorbital arteries. Identification of thebony canal is important, especially before sinus-grafting procedures, not only because of the risk ofarterial bleeding (20, 22, 30, 41, 54, 104, 121) butalso because this canal contains numerous nervefibers that may result in postoperative discomfortand altered sensations after sinus floor-elevationprocedures (94, 121).

Fig. 5. Implant touching the roof of the incisive canal,causing severe chronic neuropathia.

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Furthermore, the anterior superior alveolar nerve issometimes found to run in a clearly defined canal,palatally of the canine. This is denoted as canalis sin-uosus (15, 95) and is only described in the 1973 edi-tion of Gray’s Anatomy (15). If the anterior superioralveolar nerve is clearly visible and large enough, oneshould be able to avoid neurovascular trauma duringinstallation of a canine implant. In fact, it seems thatover 15% of the population has additional foraminain the anterior palate, which are usually between 1and 2 mm wide, with variable locations (15). Thecanals associated with these foramina mostly presentas a direct extension of the canalis sinuosus or coursetoward the nasal cavity floor. When the diameter is≥2 mm, these canals may become clinically relevantwhen traumatized (Fig. 7).

Another branch of importance during implantplacement is the superior nasal branch of the maxil-lary nerve, denoted as the nasopalatine nerve. It des-cends to the roof of the mouth through thenasopalatine canal and communicates with the corre-sponding nerve of the opposite side and with theanterior palatine nerve (76). Typically, it has beendescribed as having a Y-shape with the orifices of twolateral canals, terminating at the nasal floor level inthe foramina of Stenson. It allows the paired nasopal-atine (incisive) nerves and the terminal branch of thedescending palatine artery to pass from the nasalmucosa to the palatal mucosa. The oral entrance ofthe canal lies underneath the incisive papilla.

Occasionally, two additional minor canals transmitthe nasopalatine nerves (foramina of Scarpa). Mraiwaet al. (76) point out significant variability in thedimensions and the morphological appearance of thenasopalatine canal. To avoid disturbance of theseneurovascular bundles and further complications,presurgical planning of implant placement in themaxillary incisor region should consider this impor-tant structure (9). In this region, the esthetic chal-lenge is greater than in any other implant site, whilstexactly here the bone volume and morphology maybe hampered more, considering traumatic tooth andrelated vestibular bone loss and the presence of thenasopalatine canal and its potential enlargementafter tooth extraction. Anatomic evaluation andradiographic visualization of this area might be con-sidered of utmost importance before surgical (e.g.implants) procedures in order to avoid potential com-plications (Fig. 8).

The nasopalatine duct, also called the ‘incisiveduct’, runs within the incisive or nasopalatine canal,but it is a separate anatomic entity, is formed out ofepithelial tissue and is only present during fetal stagesof life. It is located laterally and anterolaterally of thenasopalatine nerves, often separated by an osseousbarrier. In the adult, only obliterated epithelial rem-nants may be seen. The literature describing the pre-natal development of the nasopalatine canal iscontradictory and partly even bizarre. One reason forconfusion in describing the origin of the incisive canal

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Fig. 6. (A) Cross-sectional slice ofthe anterior midline of the mandible,showing the lingual (superior genialspinal) canal. (B) Similar cross-sec-tional image after implant place-ment, with the apex of the implantcompressing the entry of the canal.The latter image was taken when thepatient reported with unbearablepain in the mandible after the localanesthetic had worn off.

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might be the inconsistent use of the nomenclature.Another reason is the difficulty in imagining thethree-dimensional aspects of the development in thisregion. What is clear is that the nasopalatine nerveand the nasopalatine artery exist in the area of thefuture incisive canal before ossification (31, 86). Fur-thermore, the incisive foramen is the orifice of thenasopalatine canal. Considering the complex embry-ologic origin, it is clear that variations in morphologicdescriptions and dimensional differences may occur(9, 12, 13, 68, 76, 112). Yet, reports also focus on nas-opalatine canal pathology (98–100). Anatomic studiesoften do not mention the wide variety of morphologi-es and the related dimensional measurements. Thediameter of the incisive foramen is usually consideredto be less than 6 mm. When more than 10 mm, cysticdegeneration should be considered (76, 98, 100). Oncone beam computed tomography scans of the ante-rior maxilla, periapical radiolucencies and variationsin diameter of the nasopalatine canal can be differen-tiated from cysts of the nasopalatine canal in the ini-tial stages, which usually show a characteristic bulkyenlargement of the nasopalatine canal (98, 99).

Interestingly, it recently became evident that thecanal is generally enlarged by 1.8 mm after extractionin the central incisor area (68). This means that theabsolute bone loss experienced following incisorextraction is potentially superposed on the relativebone loss caused by underlying trauma but evenmore by nasopalatine canal enlargement. This com-bined effect has a definite impact on implant place-ment in an area where esthetic requirements are ofutmost importance. Jacobs et al. (31) described the

nasopalatine canal with its neurovascular bundle onhigh-resolution magnetic resonance imaging, therebyconfirming its presence and significant size onmatching histological images. Regarding the branchesof the nasopalatine canal sprouting out to the left andthe right (31, 86), placing an implant to the left or theright of the canal might also be risky.

A particular anatomic variation concerns anoronasal communication via bilateral canal openingsof the nasopalatine canal on either side of the pala-tal incisive papilla (12, 13, 112). This is much morecommon in pigs, monkeys and dogs – in which suchpatent canals serve as a link from the oral cavity tothe accessory vomeronasal organs of Jacobson,which has some smell and taste function – than inhumans.

Cross-sectional imaging is, in any case, favored, notonly to inspect the canal radiographically in differentdimensions and at various levels, but also to checkwhether implant placement is possible in the alveolarbone anterior to the canal (9, 76).

Neurosensory disturbancesreported

As stated earlier, the incidence of neuropathic orofa-cial pain following implant placement largely variesfor both transient (0–24%) and permanent (0–11%)nerve injuries (3, 61, 80, 85, 87, 88). When studyingclaims for neurosensory disturbances of the inferioralveolar nerve, implant placement was found toaccount for only 3% of all reported cases but was

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Fig. 7. (A) Axial slice showing aprominent canalis sinuosis in the leftcanine area and a more discrete ca-nalis sinuosis at the right side. (B)The prominent canal at the left sideis confirmed on a coronal slice,nicely showing its routing via thenasal floor toward the maxillarysinus wall. (C) Illustration of the ca-nalis sinuosis on a cross-sectionalslice, before (C) and after (D)implant placement. A postoperativeintra-oral image (E) shows a dimen-sional overlap of the implant and thecoronal extension of the canal, visi-ble as an indistinct radiolucent bandat the apical level of the implant andfurther upwards.

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responsible for 12% of all permanent injuries. Thelatter implies that 75% of all neurosensory distur-bances following implant placement are of a perma-nent nature (61). Vazquez et al. (109) evaluatedimplant placement based on preoperative panoramicradiographs of 1527 consecutively treated patients

and showed only two cases of postoperative paresthe-sia, representing 0.08% of implants inserted in theposterior segment of the mandible, or 0.13% ofpatients. In this study, sensory disturbances wereminor, lasted for 3–6 weeks and resolved spontane-ously. However, it is important to realize thatimplants were inserted with a safety zone of at least2 mm in relation to the mandibular canal. Rentonet al. (87, 88) reviewed cases of implant-related nerveinjuries. The most important cause of injury wasproximity of the implant (bed) to the inferior alveolarcanal, with one-fifth of the cases of injury caused byentry into the canal, one-fifth caused by crossing thecanal and almost half caused by contacting the roofof the canal. In one patient only, the injury was pre-sumed to result from a local anesthetic trauma. Manyother case reports describe neurosensory distur-bances of the inferior alveolar nerve, not only in theposterior mandible but also in the symphyseal area(1, 4, 7, 21, 43, 53, 61, 72, 82, 87, 88, 115, 119). Basedon the analysis of questionnaires, Ellies and Hawker(21) showed that 37% of their subjects had an alteredsensation after implantation, with 10–15% still notingsuch changes after 15 months. By using a combina-tion of psychophysical methods, Bartling and col-leagues could identify eight out of 94 subjects havingan altered sensation after mandibular implant place-ment (7). Wismeijer et al. (119) described an alteredsensation in 11% of their subjects 10 days afterimplant surgery, with 10% still reporting this sensa-tion 6 months later. On the other hand, Abarca andcolleagues (1) evaluated neurosensory disturbancesassociated with immediately loaded implants in theedentulous anterior mandible. One-third of theirsubjects reported a neurosensory disturbance aftersurgery, and 15% still complained of neurosensorydisturbance 8–21 months afterwards (1).

Intra-oral hemorrhage

Significant hemorrhages are mostly described afteranterior mandibular implant placement or in sinusaugmentation before or during implant placement.For mandibular implant placement, a review of theliterature shows at least 19 case reports related tohemorrhage in the floor of the mouth (10, 14, 18, 19,23, 29, 38, 39, 42, 48, 49, 67, 69, 74, 79, 81, 83, 102, 116)and potentially life-threatening upper airway obstruc-tion (14, 23, 48, 49, 67, 69, 79). Those hemorrhageswere mostly related to lingual perforations, longimplants (≥15 mm) or deep osteotomy preparations.Most cases were handled adequately by controlling

B

A

C

Fig. 8. Young male patient complaining of hyperesthesiain the area of the nasopalatine canal after implant place-ment at the level of the canal, with the implant in region21 being present with its mesiopalatal side along its entirelength, up to the level of the nose. (A) Axial slice showingthe presence of the implant in a coronal section and (B)another axial slice higher up at the apical implant level,with a continued presence in the canal. (C) Cross-sectionalimage showing the implant present along the course of thenasopalatine canal up to the level of the nose.

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airway passage and stopping the hemorrhage (14, 23,48, 49, 67, 69, 79). Airway control was established, inmost patients, with naso- or oro-tracheal intubationor tracheostomy. To control hemorrhage, surgicalexploration of the floor of the mouth was performedin most of the patients to evacuate and isolate thehematoma. All patients were discharged home after1–12 days and recovered well.

As stated in the previous paragraph, significantbleeding may also occur during sinus-augmentationprocedures. To avoid this complication, detailedknowledge and timely identification of the anatomicstructures inherent to the maxillary sinus are required(121). Because of its location, the intra-osseous arteryhas the potential to cause bleeding complications inapproximately 20% of normally positioned lateralwindow osteotomies. Although anatomic studiesidentify an intra-osseous artery in 100% of cadaverspecimens, it could only be visualized in half thecomputed tomogrpahy scans (20). Yet, current conebeam computed tomography scans have an increasedresolution, and a reduced slice thickness and interval,allowing improved visualization of the canals (41). Amaxillary arterial endosseous anastomosis is observedin more than half of the patients. The perpendiculardistance from the sinus floor to the vascular canal isshortest in the first molar region and longest in thefirst premolar region. Severe bleeding has beenreported after sinus floor elevation (30, 38, 54, 104)and may thus be related to the aforementioned ana-tomic variations. Zijderveld et al. (121) revised 100consecutive maxillary sinus floor elevation proce-dures and found a strong convexity of the lateralsinus wall in 6%. Reported hemorrhages (2% ofthe cases) were related to this anatomic constraintand to compromised visualization of the trapdoorpreparation.

Dealing with postimplantneuropathic pain and neuralinjuries

Even at a preoperative stage, there is already a needfor neurosensory assessment, especially in edentu-lous patients. Indeed, it has been reported that one-quarter of edentulous patients present with a degreeof altered inferior alveolar nerve function (119).Patients with a severely resorbed jaw bone exposingthe mental nerve and/or inferior alveolar nerve cres-tally, may be at risk for an underlying chronic com-pression neuropathy.

To prevent surgical complications during implantsurgery, careful preoperative probing and/or eleva-tion of the periosteum are suggested to provide a suf-ficient and safe view of the anatomy (34, 89).Surgeons normally regard a longer implant as desir-able to ensure primary stability. However, there is noclinically proven advantage for long implants. Brug-genkate and colleagues (101) reported a successfulosseointegration in the rehabilitation of resorbedmandibles following the use of 6- and 8-mm shortimplants. Most of the formerly discussed complica-tions were coupled to placement of long implants.The placement of shorter implants may also help toavoid thermal trauma, for example in the dense sym-physeal area.

Nevertheless, even when careful measures beforesurgery are taken, nerve injuries may occur and oneshould recognize and differentiate these from othermanifestations of postoperative pain to allow timelyaction. The literature seems to indicate that three-quarters of the neural injuries which occur afterimplant placement result in permanent injury (61, 87,88).

In general, damage to sensory nerves can result inanesthesia, dysesthesia, pain, or a combination ofthese factors. The severity and the duration of symp-toms depends on the extent of the anatomic injury tothe nerve. Such injuries are differentiated accordingto the Seddon classification: (i) neuropraxia; (ii) axo-notmesis; and (iii) neurotmesis. Neuropraxia iscaused by mild trauma without axonal damage and isusually considered to be transient in nature. Axonot-mesis is a more significant injury, where the nerveremains intact but some axons are interrupted. Dis-turbances may be permanent, but regeneration cantake place several months later. Neurotmesis involvesnerve disruption. Sensory recovery is not possiblewithout a timely action and microneurosurgical inter-vention (28, 40, 46, 47). When nerve injuries occur,not only must the clinician diagnose the neural prob-lem at an early stage, but also needs to differentiate,through careful and objective neurosensory testing,between patients undergoing spontaneous nerverecovery and those developing chronic dysestheticproblems. This neurosensory testing should beapplied for objective assessment and differential diag-nosis, with a strict follow-up regimen of up to 1 year(85).

In the event of acute nerve injury, timely nerve andimplant decompression are essential with supportiveanalgesic or anticonvulsant therapy. Indeed, earlyremoval of implants associated with mandibular nerveinjury (<36 h postinjury) may assist in minimizing, or

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even resolving, neuropathy (46). Removal of theimplants 2 days or more following nerve injury in ourcases did not show an improvement in sensation andmay place patients at higher risk of permanentaltered sensation. On this basis, a patient should becontacted after the local anesthetic has worn off (6 hpostoperatively) (46).

Apart from implant removal, direct nerve damagemay also require a primary anastomoses of the twoends, if possible even during the initial surgery (47).Early secondary repair within a widely accepted 3-month time frame is still possible, but success ratesare lower and risks for permanent problems arehigher (40). Nerve splits can be repaired by a timelymicroneurosurgical intervention, to re-establishproper alignment of nerve stumps and promote cor-rect regeneration in the event of neurotmesis withsome axonal interruptions (28). Furthermore, Kimet al. (47) propose a microsurgical end-to-end nerverepair without the need for grafting, by using a nervesliding technique, with direct closure of the nerve seg-ment without tension. Unfortunately, patients withpostsurgical nerve damage are often referred (too)late (87). In the event of unsatisfactory spontaneoussensory return, surgical exploration, microsurgicalrepair (with or without grafting), trigeminal infiltra-tion or neuroma resection should be considered, butthe success of such treatments decreases with lengthof time since the surgical damage. Once the patient ispresenting with a permanent neuropathic pain, topi-cal capsaicin treatment can help to reduce the symp-toms of this pain. For pain reduction, topicalcapsaicin (0.025%) seems effective in most patientswhen applied twice daily for a 4-week period, andwhen preceded by a topical anesthetic mouthwash(15% benzocaine/1.7% amethocaine) for 3 min toallow pain-free application of the capsaicin agent(110).

One should be aware that patients presenting witha postimplant neuropathic pain sometimes developparafunctional activity and myofascial head and neckpain, with the nerve injury being the suspected trigger(72, 90).

Concluding remarks

It is clear that oral implant placement, although a rel-atively common procedure, is not without risks.Although nerve disturbance after implant placementis rare, case reports show that – if it occurs – it canresult in life-disordering complications. Hemorrhagecan lead to a life-threatening complication of implant

placement, especially in the mandibular interforami-nal region. In this respect, anterior mandibular sur-gery should be reclassified, in view of the risks forneurovascular disturbance, rather than denoting it asan ‘easy’ and/or ‘safe’ surgical area. From the above-mentioned accumulated evidence, it can be statedthat in addition to careful clinical examination, metic-ulous presurgical imaging is a prerequisite to avoidsurgical complaints. The significant variability in neu-rovascularization of the human jaw and the occur-rence of unfavorable bone morphology, underline theimportance of three-dimensional imaging for virtualsurgery planning to provide a realistic depiction ofthe neurovascular structures. In this context, theintroduction of dentomaxillofacial cone beam com-puted tomography, offering three-dimensional digitalimaging at low radiation dose and relatively low costs,has increased the applicability and strengthened thejustification for cross-sectional presurgical imaging.

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