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Review Practical Application of Anatomy for the DentalImplant SurgeonGary Greenstein,* John Cavallaro,* and Dennis Tarnow*

A procient knowledge of oral anatomy is needed to provideeffective implant dentistry. This article addresses basic ana-tomic structures relevant to the dental implantologist. Pertinentmuscles, blood supply, foramen, and nerve innervations thatmay be encountered during implant procedures are reviewed.Caution must be exercised when performing surgery in certainregions of the mouth. Furthermore, numerous suggestions areprovided regarding the practical application of anatomy tofacilitate successful implant therapy. J Periodontol 2008;79:1833-1846.

KEY WORDS

Anatomy; dental implants.

The study of anatomy familiarizes

the implant surgeon with normaland atypical oral structures.Knowledge of oral structures and ordi-nary anatomic variations, which usuallydiffer with respect to size and shape,enhance patient evaluations and facili-tate precise surgical procedures. A thor-ough understanding of anatomy providesthe implant surgeon with the condenceto resector augment tissues in anattemptto restore form, function, esthetics, andhealth. This article reviews the practical

application of basic anatomy to implanttherapy. It does not attempt to discussevery blood vessel, nerve, and musclefound within the oral cavity, but rather itfocuses on structures routinely encoun-tered, which are critically important toplanning and executing dental implantsurgery.

MANDIBULAR STRUCTURES

Mandibular Foramen The location of the mandibular foramenmay vary based on race and ethnicity,andthis can affectthe success of block in- jections. 1,2 Among adult cadaveric man-dibles, the foramen was found inferior tothe occlusal plane, at its level, or aboveit 75%, 22.5%, and 2.5% of the time, re-spectively. 1 In another study, 2 thegureswere 29.4%, 47.1%, and 23.5%, respec-tively. Therefore, according to these in-vestigations, 2.5% to 23.5% of blockinjections given at the level of occlusionwould be ineffective. Accordingly, it is

* Department of Periodontology and Implant Dentistry, New York University College of Dentistry, New York, NY.

Private practice, Freehold, NJ. Private practice, Brooklyn, NY. Private practice, New York, NY.

doi: 10.1902/jop.2008.080086

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advisable to inject patients 6 to 10 mm superior to theocclusal plane, 3 which usually accounts for anatomicvariations.Thedistancetothemandibularforamenas-sessed on cadavers revealed that it is within the reachof a short needle (needle length = 21 mm). 4 Therefore,short needles can be used to attain anesthesia in themandible. If there aresymptoms of a good block injec-tion, but the patient is still symptomatic, inltrate thelingual aspect of the molar teeth, because there maybe additional innervation from C 2 and C 3 (cutaneouscoli nerve of the cervical plexus). 5

Inferior Alveolar Canal The trigeminal nerve, the fth cranial nerve, has threemain branches: ophthalmic, maxillary, and mandibu-lar. 6 The mandibular nerve gives rise to the inferior al-veolar nerve (IAN). It enters the mandibular canal onthe medial surface of the ramus by the lingula. The ca-

nalis;

3.4 mmwide, and the nerveis;

2.2mmthick.7

Within the canal there is a nerve, an artery, a vein, andlymphatic vessels. The artery lies parallel to the nerveas it traversesanteriorly, but itsposition varies with re-spect to being superior or inferior to the nerve withinthemandibularcanal. 7 Therefore,itispossibletoinad-vertently penetrate into the mandibular canal andinduce neurologic damage without provoking hemor-rhaging and vice versa.

When developing an osteotomy over the mandibu-larcanal, corticalboneispenetratedrst,and theprep-aration terminates within softer cancellous bone. The

mandibular canal usually has cortical bone around it,which may provide some resistance to drilling. How-ever, clinicians should not rely on tactile feedback tosignal the canal is about to be penetrated, because atwist drill can enter the canal with little warning. Con-versely,when traversing from more to less mineralizedregions of the posterior mandible during osteotomydevelopment, a sudden decrease in resistance maygive an erroneous impression that the canal has beenbreached. Accordingly, there is no substitute for pre-cise radiometrics, safety devices (e.g., drill stops),and a plan for attaining specic implant lengths in thisregion of the mouth.

The IANmaypresent in different anatomic congu-rations. The nerve may lower gently as it proceeds an-teriorly,ortherecanbeasharpdeclineorthenervecandrape downward in catenary fashion (curled as hang-ingbetweentwopoints). 8 TheIANcrossesfromthelin-gualtothebuccalsideofthemandibleandoften,bytherstmolar,itislocatedmidwaybetweenthebuccalandlingual cortical plates of bone. 9 Usually, the IAN di-vides into thementalandincisive nerves in thepremo-larmolarregion. 10 Themental nerveemergesfromthemental canal, and anterior to the mental foramen themandibular canal is referred to as the incisive canal. 11

Implant placement buccal or lingual to the IAN is a

risky maneuver and should not be attempted withoutthe aid of computed tomography (CT).

The mandibular canal bifurcates in the inferiorsuperior or mediallateral plane in ; 1% of patients. 12

Abifurcatedcanalmaymanifestmorethanone mentalforamen and, the bifurcation may not be seen on pan-oramicor periapical lms. Theundetectedpresenceof a bifurcated mandibular canal can result in an incor-rect estimation of available bone superior to the man-dibular canal.

Denio et al. 13 evaluated cadavers to determine howclosetheIANwastotheapicesofmandibularposteriorteeth.Themeandistancetothesecondmolar,rstmo-lar, and premolars was 3.7, 6.9, and 4.7 mm, respec-tively. Similarly, Littner et al. 14 reported the upperborder of the mandibular canal was located 3.5 to5.4 mm below the root apices of rst and second mo-lars.Other investigators 15 found that the canal was of-

tenclosetotheinferiorborderofthemandible.Itisalsopossible for the mandibular canal to be adjacent to theapex of the mandibular molar (Fig. 1). Therefore, withregard to developing osteotomies over the inferior al-veolar nerve, it should be recognized that mean dis-tances between apices of teeth and the nerve canalreported in articles may notapply to anyparticular pa-tient. Hence, to avoid untoward sequelae in the poste-rior mandible, the location of the nerve needs to beveried before an osteotomy is created.

With regard to radiographs, Denio et al. 13 reportedthat in 28% of patients the mandibular canal could not

be clearly identied in the second premolar and rstmolar regions on periapical radiographs. Therefore,if the inferior alveolar canal cannot be seen on a peri-apical lm, it is recommended to obtain a panoramiclm and adjust distances for radiographic distortion.If it still cannot be detected, a CT scan is needed.Osteotomies should not be developed in the posterior

Figure 1.The mandibular canal is adjacent to the apex of the mandibular rst molar. Arrow points to mandibular canal abutting alveolus of

extracted tooth #30.

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mandibleuntilthepositionoftheinferioralveolarcanalis established.

Several additional facts about radiographs shouldbe considered. The angulation of the periapical lmcan affect the perceived location of the canal with re-spect to the bone crest. 16 For instance, if the x-raybeam is perpendicular to the canal, but not the lm,elongationoccurs, and the canal appears further fromthe crest than it really is. Conversely, when the x-raybeam is perpendicular to the lm, but is not parallelto the canal, foreshortening happens. Table 1 listsmean linear radiographic errors with respect to differ-entx-raytechniqueswhenlocatingthemandibularca-nal. 17 The numbers in the table represent mean errorsandcanbeincorrectbyevenlargeramounts.Thesein-accuraciesneedtobetakenintoaccountwhencreatingan osteotomyin sensitiveareas.To avoid misinterpre-tation of linear measurements on radiographs, clini-

cians can use markers of known dimension whentaking an x-ray (e.g., 5-mm-diameter ball bearing). 16

Mental Foramen and Nerve Commonly, three nerve branches of the mental nerveemerge from the mental foramen (each ; 1 mm in di-ameter). 11 They supply innervation to the skin of themental foraminal area, the lower lip, chin, mucousmembranes, and the gingiva until the second premo-lar. Occasionally, the mental nerve emerges from thebuccal plate of bone and reenters the alveolar bone toprovide innervation for the incisor teeth. 18

Thelocationofthementalforamendiffersinthehor-izontal and vertical planes, and these variations maybe related to race. 19-21 For example, horizontally theforamen is often found ankedby theapices of premo-lars in white individuals 19 and next to the apex of thesecond mandibular premolar among Chinese sub- jects. 20 Atypically, the foramen may be situated bythe canine or the rst molar. 20,21 In these situations,theincisivecanalstartswherethementalnerveemergesfrom the mandible.

Thepositionoftheforamenalsovariesintheverticalplane. 19 Pertinently,it wasreportedthat in therstpre-molar area of 936 patients, the foramen was situatedcoronal to the apex in 38.6% of cases, at the apex in15.4% of cases, and apical to the apex in 46.0% of cases.Theforamenslocation,inrelationtothesecondpremolar,was coronal to theapex in24.5%ofcases,atthe apex in 13.9% of cases, and apical to the apex in61.6%ofcases.Thus,cautionmustbeexercised,espe-cially when placing immediate implants in the premo-lararea,becausein25%to38%ofcasestheforamenislocated coronal to the bicuspids apex. 19

Theanterior loop of themental foramen refers to theIAN when it courses inferiorly and anteriorly to the fo-ramen and then loops back to emerge from the fora-men 22 (Fig. 2). Detecting and quantifying the size of

theanterior loop wasdone by using diverse diagnosticmethods:panoramiclmsofpatients,panoramiclmsofmarkers indriedskullsand cadavermandibles, peri-apical lms of cadaver jaws, CT scans of patients, andsurgicalcadaverdissections. 23 Conictingresultswithregard to the size and prevalence of the anterior loopmay be due to different criteria used to characterizetheanterior loopanddissimilardiagnostictechniques.

Surgical dissection furnished the best evidence forvalidating thepresenceof theanterior loop of themen-tal foramen. 23 Furthermore, comparing radiographicanddissectiondatafromthesameindividualssuppliedinsightas to thedependability of radiographs to detecttheanterior loop. 24-26 In this regard, Mardingeret al. 24

reported that anatomically identied loops often didnotshowonperiapicallms, andradiographs supplieda 40% false-positive nding when related to their cor-responding cadaver dissections. In another study, 25

loop dimensions varied from 0.0 to 7.5 mm on periap-ical radiographs and from 0 to 1.0 mm between

Table 1.

Distortion on Radiographs 17

Type of Radiograph Mean (mm; range) %

Periapical 1.9 (0 to 5) 14

Panoramic 3.0 (0.5 to 7.5) 23

CT scan 0.2 (0.0 to 0.5) 1.8

Figure 2. Anterior loop of the mental foramen (arrow). The inferior alveolar nervecourses beneath and mesial to the foramen and then loops back toemerge from the foramen.

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cadaver specimens; usually radiographs overesti-mated the extent of the anterior loop. 25 In a differentinvestigation, 26 the anterior loop was identied on 27%(six/22) of the panoramic lms and 35% (eight/22)of the cadavers. The dimensions of anterior loops inpanoramic radiographs varied from 0.5 to 3 mm,andcadaver specimensmanifestedanterior loopsthatrangedfrom 0.11 to 3.31 mm.However, the investiga-tors noted that 50% of the x-rays were interpreted in-correctly, and the presence of a loop was not veriedby surgical dissection. Furthermore, 62% of the surgi-cally detected loops were not found radiographically.In general, it can be concluded that many false-posi-tiveandfalse-negativendings occurwhen identifyingthe anterior loop with x-rays.

Thus, when there is concern with respect to the lo-cation of the mental nerve, it should be exposed toidentify its position before implant insertion. First, de-

termine ontheradiographwhere themental foramenislocated. If it is in the premolar region, create a verticalreleasing incision on the mesial aspect of the canineand reect the ap past the mucogingival junction.Then use wet gauze to elevate the ap apically andexpose the roof of the mental foramen. 23 The gauzeshields thenerve from being damaged, andthe perios-tealelevatorcanbeusedtopushthegauzeapically.Todetermine how much bone is available for implant in-sertion, measure the distance between the alveolarcrestandthe coronal aspectof theforamenwith a peri-odontal probe (Fig. 3). The chosen implant length

should provide a safety margin of 2 mm from thenerve. 23,27 This measurement minus 2 mm can alsobe used to safely insert an implant mesial, above, ordistal to the mental foramen up to the mesial half of the rst molar area. 27

When measurements are taken from thecrest of thebone to theroof of theforamen todeterminethe appro-priate implant length in the foraminal area, there issome additional safety room based upon three ana-tomic considerations: the foramen coincides with thebuccal plate and the osteotomy will be developed lin-gual to the foramen and its contents; the foramen iscone shaped, with the widest part of the funnel onthe buccal aspect; and the nerve emerges from a pathinferior to the foramen. 27 The mentalnerve comes outof the mental canal, which is angled upward at ; 50 (range, 11 to 70 ) from the mandibular canal (Fig.4). 28 Therefore, it should be noted that the inferioralve-olar nerve is lateral and apical to the mental foramen.

If it is desired to place an implant, which is largerthan the safety distance determined above, anteriortothementalforamen,aCTscanisnecessarytodeter-minewhether ananterior loop is present, or it is neces-sary to probe within the foramen to ascertain if there isan anterior loop. In this regard, a curved probe (e.g.,Nabers 2N probe) can be gently placed into the fora-

mentoassessifitsdistalaspectisopen.Ifitisnotopen,then the nerve entered on the mesial side, and this de-notes that an anterior loop is present (Fig. 5). The me-sial side of theforamen is consistentlypatent, becauseat this site the anterior loop emerges from the bone orthe incisal nerve proceeds anteriorly. Note that thepa-tency on the mesial aspect of the foramen leading tothe incisal region and an anterior loop feel similar, anditis notpossibletodistinguishbetween thesetwo struc-tures. 27 It must be emphasized that probing into themental foramen should be done very gently; other-wise, neurologic damage can be done to the nerve.Furthermore, even if the presence of an anterior loop

Figure 3.To determine how much bone is available for implant insertion over themental foramen, measure the distance from the alveolar crest to thecoronal aspect of the foramen (arrow) with a periodontal probe.

Figure 4.CT scan. The mental nerve emerges from the mental canal. The mentalcanal is angled upward at ; 50 (range, 11 to 70 ).


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is corroborated by probing, its length is still unknown.Therefore, as a general guideline, if there is an anteriorloop of the mental foramen and a CT scan is not avail-able to determine its dimensions, and it is desired toplace an implant deeper than thesafety measurementon the mesial aspect of the foramen, it is prudent toplace the distal aspect of the implant 6 mm anteriorto the mental foramen to avoid damaging the loopwhen drilling the osteotomy. 28

Mandibular Incisive Canal Numerous investigations 29-32 reported that there is atrue incisive canal mesial to the mental foramen,which is a continuation of the mandibular canal. It hasalso been noted that the incisive canal may appearas a maze of intertrabecular spaces, which includeneurovascular bundles. 33 The incisive nerve suppliesinnervation to teeth (rst bicuspid, canine, and lateraland central incisors).

The incisive canal is typically found in the middlethirdof the mandible (in 86% of cases). 30 It usuallynar-rows as it approaches the midlineand only reaches themidline18%ofthetime. 30 Thenerveusuallyterminatesapical to the lateral incisor and sometimes apical to thecentral incisor. 30 The incisive canals width is 1.8 0.5

mm, and it was found in 96% of as-sessedcadavers. 30 However, whenthe appearance of the incisive ca-nal on panoramic radiographswas evaluated, Jacobs et al. 34 re-ported that it was seen only on15% of the lms (n = 545). In con-trast, it was observed on 93% of CT scans.

In the interforaminal area, aslong as the mental foramen andthe anterior loop of the mental fo-ramen (if present) are avoided,implants can usually be insertedwithout too much thought given tothe presence of the incisive canal.However, if there is an unusuallylarge incisive nerve canal, a patient

can experience discomfort duringosteotomy development preclud-ing implant placement 35 or experi-ence postoperative pain requiringimplant removal. 36 Consequently,consideration should be given tothe size of the incisive canal beforeplacing implants deeply in theinterforaminal area.

Lingual Foramen and Lateral Canals Vascular canals are often presentin the midline and lateral to the

midline of the mandible. Gahleitner et al. 37 foundone to ve vascular canals per patient. The meandiameter of the midline canals was 0.7 mm (range,0.4 to 1.5 mm); the lateral canals in the premolararea were slightly smaller (mean, 0.6 mm). The lin-gual foramen was detected in 99% of the mandibleswhenevaluating skulldissections. 38 However, the fo-ramen was only found on 49% of the periapical lmsbecause the angulation of the x-ray beam affected itsimage.

The lingual foramen harbors an artery that corre-

sponds to an anastomosis of the right and left sublin-gual arteries. 39 Small canals with a diameter < 1 mmare unlikely to cause a problem if an osteotomy pene-trates into the foramen. 37 However, if there is a largercanal, excessivebleedingcouldbea complicating fac-tor; thus, consider avoiding implant insertion in themidline. 40 If excessive bleeding from an osteotomyin this area occurs, guide pins or the implant xture it-self can serve as effective methods of tamponade.

Submental and Sublingual Arteries The submental artery (2-mm average diameter) 41 isderived from thefacial artery, andthesublingual artery(2-mm average diameter) is a branch of the lingual

Figure 5. A) If placement of the probe into the mental foramen on the distal side reveals that the mentalcanal is patent, then the anterior loop is not present.B) If placement of a probe into the mentalforamen on the distal side reveals that the mental canal is not patent, then an anterior loop of the mental nerve exists. The nerve must have traversed inferiorly and looped back to the foramencreating an anterior loop. (Figure slightly modied from reference 23.)


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artery. 42 The sublingual artery is found above themylohyoid muscle and is the major nutrient vessel inthe oor of the mouth. 42 The submental artery fre-quently traverses inferiorly to the mylohyoid musclebutwasnoted to pierce through themylohyoidmusclein 41% of dissected cadavers. 43 Hofschneider et al. 41

also reported that the sublingual and submental arter-ies may course anteriorly in close proximity to the lin-gual plate, and branches of these blood vessels enteraccessory foramina along the lingual cortex (Fig. 6).Inadvertent penetration through the lingual corticalplate into the oor of the mouth while preparing an os-teotomycancausearterialtrauma,therebyresultingindevelopment of a sublingual or submandibular hema-toma.Itwasmentionedthatseveringanartery2mmindiameter with a probable blood ow of 0.2 ml per beat(70beatsperminute)canresultin420mlbloodlossin30 minutes. 44 This quantity of hemorrhage can cause

swelling, and the tongue may be pressed superiorlyand posteriorly, blocking the airway, and causing up-per airway distress. 45,46 The patient requires aggres-sive medical and possibly surgical management if anairway crisis develops.

It is also possible to induce hemorrhaging when el-evating a ap if a vessel entering an accessory canal issevered. On the lingual aspect, proper ap elevationand visualization where the osteotomy is being devel-oped helps to avoid accidental perforations. Bleedingfromtheoorofthemouthisrstmanagedbypressureand then ligation of severed blood vessels.

Submandibular and Sublingual Fossae Thesubmandibularfossaisadepressiononthemedialsurface of the mandible inferior to the mylohyoid line,anditcontainsthesubmandibulargland. 47 Thesublin-gualglandisfoundinthesublingualfossa. 48 Thisfossais a shallow depression on the medial surface of themandible on both sides of the mental spine, superiorto the mylohyoid line. The submandibular and sublin-gualfossaemustbepalpatedpriortoosteotomydevel-opment; if there is a large undercut, the lingual bonyplate can be perforated inadvertently, resulting inhemorrhaging. Lingual concavities with a depth of 6 mm were reported in 2.4% of assessed jaws (n = 212;CTscanswereused). 43 Ifthereisalargeundercut,anin-strumentcanbeplacedintoandparalleltotheundercutto visualize andmeasure theextent of thedepression. ACTscanwithradiopaquemarkers provides the most ac-curate information. Pertinently, the angulation thatthe

implant is placed needs to accommodate the undercutto remain in bone during osteotomy preparation.

The Lingual and Mylohyoid Nerves The mandibular branch of the trigeminal nerve givesrise to the lingual nerve. 49 Thisnerveprovides sensoryinnervation to the mucous membranes of the anteriortwo-thirds of the tongue and the lingual tissues. At thetime of implant surgery in the posterior mandible, thelingual nerve can be injured if the lingual ap is not re-ected cautiously. The lingual nerve is usually located3 mm apical to the osseous crest and 2 mm horizon-

tally from the lingual cortical plate in the ap.50

How-ever, in15%to20%ofcases, the nerve may besituatedator above the crest of bone, lingual to the mandibularthird molars. 51 In addition, 22% of the time the lingualnerve may contact the lingual cortical plate. 50 To cir-cumvent lingual nerve injury, the elevator should beused to protect the nerve in the ap, and the tissueshould be managed gently to preclude causing a tran-sient pressure-traction injury. It is recommended thatlingual, vertical releasing incisions be avoided. Fur-thermore, incisions distal to the second molar shouldbe made on the buccal aspect of the ridge to provideadditional room for safety, because the lingual nervemay be lying over the retromolar ridge. 51

The mylohyoid nerve is a branch of the inferior alve-olar nerve. 52 It arises just prior to where the IAN entersthe mandibular foramen. On the deep surface of thera-mus, it moves down in a groove to reach and innervatethe mylohyoid muscle and the anterior belly of the di-gastricmuscle. This nerve may alsocontribute to anin-ability to attain complete anesthesia due to accessorysensory innervation to the anterior and posterior man-dibularteeth. 52,53 Inpatientswhoexperiencediscomfortdespite signs of a good block injection, additional inl-tration on the lingual aspect in the posterior regionmay help to attain more profound anesthesia. 53

Figure 6.Blood vessels entering the lingual cortex of the mandibular anterior teeth. Arrows point to vascular channels in the lingual cortical plate

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The Long Buccal Nerve The buccal nerve is a branch of the mandibular nervethat is derived from the trigeminal nerve, and it beginshigh in the infratemporal fossa. 54 It transmits sensoryinnervation to the buccal gingiva and mucosa of thecheek from the retromolar area to the second premo-lar. It courses between thetwo headsof thelateralpter-ygoidmuscle,underneaththetendonofthetemporalismuscle, and then under the masseter muscle to con-nect with the buccal branches of the facial nerve onthesurfaceof thebuccinatormuscle.An anatomicvar-iation of the long buccal nerve, called Turners varia-tion, consists of the nerve emerging from a foramenin the retromolar fossa. When this variation exists,trauma in this region can cause paresthesia to the adjacent gingiva and mucosa. 55

Muscles Attached to the Mandible There are 26 muscles attached to the mandible. 56

There are two single muscles (orbicularis oris andplatysma) and 12 pairs of bilateral muscles, whicharelistedinalphabeticorder:anteriorbellyofdigastric,buccinator, depressor anguli oris, depressor labii infe-rioris, genioglossus, geniohyoid, masseter, mentalis,mylohyoid, lateral pterygoid, medial pterygoid, andtemporalis. Several of these muscles are of particularconcern to the implant surgeon.Mentalis Muscle Thementalismuscleisapairedsmallmusclethatorig-inates in the incisive fossa of the mandible and insertsinto the integument of the chin. 57 The muscle berspass in an inferior direction, and upon contraction,they elevate the lower lip. When a ap is raised in thisregion, the entire mentalis muscle should not be re-leased off from the mental protuberances, becausethe muscle may fail to reattach well. 58 This can resultin an appearance referred to as a witchs chin (doublechin). 58 Full-thickness replaced aps, which do notreachtheinferiorborder,usuallydonotaffectfacialap-pearance. However, vestibular incisions that sharplydissect this muscle require special suturing (i.e., themuscle layer and then the overlying soft tissues).

Mylohyoid Muscle Two at mylohyoid muscles form a sling inferior to thetongue, supporting the oor of the mouth. 59 Their or-igin is the mylohyoid line on the medial aspect of themandible, which extends from the symphysis to thelast molar. They insert on the body of the hyoid boneandoverliethedigastricmuscles.Thismuscleisanim-portantanatomicbarrierseparatingthesublingualandsubmandibular spaces. The submandibular fossa isbelow the mylohyoid muscle, and thesublingual fossais superior to the muscle.

Manipulation of the muscle should be performedonly to fulll clearly dened objectives. In this regard,sometimes there are situations, such as guided bone

regeneration procedures (GBR), when it is desirableto advance a ap a large distance to achieve primaryclosure. To achieve this, besides ap elevation onthebuccalaspect, it maybe necessary to partiallydis-lodge themylohyoidmusclefromits origin to facilitatelingual ap advancement. First, the lingual ap is ele-vated to the mylohyoid muscle, and wet gauze can bepressed apically with a periostealelevator or the oper-atorsnger to achieve blunt displacementof themus-cle. Subsequent to surgery, the partially displacedmuscle reattaches without untoward sequelae.

Genial Tubercles (genioglossus and geniohyoid muscles) Thegenialtuberclesaresmall,bonyelevationslocatedon the lingual surface of the mandible. They are foundon either side of the midlineclose to the inferior borderofthemandibleandserveasthepointofinsertionofthegeniohyoid and genioglossus muscles. 60 There aretwosuperiorandtwo inferior tubercles. Thegenioglos-sus originates from the superior genial tubercles, andthe geniohyoid originates from the inferior genial tu-bercles. The lingual foramen may be found in the mid-dleof the tubercles. Theaverage heightof thesuperiorgenial tubercleis 6.17mm, and its widthis 7.01mm. 61

If there is advanced bone resorption in the mandibularanterior region, theheightof thesuperior tubercle maycoincide with or behigher than the superior level of theridge(Fig.7).Whenelevating aps forsurgicalaccess,

Figure 7. A) Because of osseous resorption of the alveolar ridge, the genialtubercle area (arrow) is now superior to the alveolar ridge.B) Panoramic x-ray demonstrating genial tubercle area is superior to

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the genioglossus muscle should not be completely re-ected off from the tubercles because the tongue mayretract to the posterior part of the throat and obstructthe airway. 58

Depressor Anguli Oris and Depressor

Labii Inferiorus Two muscles that overlie the mental foramen need tobe displaced when exposing the roof of the foramen:depressoranguli oris (triangularis) anddepressor labiiinferioris (quadratus labii inferioris). 62 Once the ap iselevated past the mucogingival junction, these mus-cles can be released by using wet gauze to push backthe ap. The wet gauze is used to protect the mentalnerve. Reection of these muscles does not result inuntoward sequelae.

Buccinator and Orbicularis Oris Muscles The submucosa is strongly attached to the buccinatormuscle in the cheek region and the orbicularis oris inthe lip area. 63 When a surgical procedure is done adjacent to one of these muscles, such as GBR, a soft tis-sue ap often needs to be advanced to attain primaryclosure. In this regard, it may be necessary to createan incision that provides periosteal fenestration andpenetrates several millimeters into the submucosa,thereby incising one or both of these muscles to facil-itate coronal positioning of the ap.

Masseter Muscle The masseter muscle consists of two portions: super-cial and deep. 64 The supercial part arises from thezygomatic arch and zygomatic process of the max-illa. 64 It inserts into the angle and lower half of the lat-eral surface of the ramus of the mandible. The deepportion arises from thezygomatic arch andinserts intothe upper half of the ramus and into the lateral surfaceof the coronoid process. When the mandibular ramusareais usedas a donor sitefor bonegrafting (i.e., blockgraft), part of themassetermuscle is releasedfrom theramus when the periosteum is elevated in this region.

MAXILLARY STRUCTURES

Thickness of the Gingiva and Palatal Mucosa The thickness of the gingival and palatal epithelium is; 0.3 mm. 65 The gingiva is supported by a laminapropria (rm connective tissue), whereas palatal epi-thelium is sustained by a lamina propria and submu-cosa. Average gingival thickness ranges from 0.53to 2.62 mm (mean, 1.56 mm), 66 and palatal widthvaries from 2.0 to 3.7 mm, with a mean of 2.8 mm. 67

The best location for harvesting a connective tissuegraft is in the maxillary caninepremolar region. 68

Thin grafts may be garnered several millimeters awayfromthegingivalmargin,andthickergraftscanbehar-vestedfurtherawayfrom thegingival marginwherethesubmucosa is wider. 68 The thickest grafts can be ob-

tainedinthetuberosityregion(i.e.,5mm). 68 Thewidthof the palatal tissue can be estimated by sounding thebone with a periodontal probe or a needle that has anendodontic stopper. Graft height is limited by the po-sition of the greater palatine artery, whose location issubsequently discussed.

Nasopalatine Foramen The nasopalatine foramen is also referred to as the in-cisive foramen (Fig. 8). 69 Upon ap reection withinthe foramen, two lateral canals are noticeable, whicharecalled incisivecanalsor foraminaof Stenson. Theytransmit the anterior branches of the descendingpalatine vessels and the nasopalatine nerves. Occa-sionally, one to four canals may be present. 69 Thenasopalatine foramen is ; 4.6 mm wide and is located; 7.4 mm from the labial surface of an unresorbedridge. 69 The nasopalatine canal (mean length, 8.1mm) exits the incisive foramen. A large incisive canalmay beanobstacle to implant placementin thecentralincisor region. When a large canal was present, Artziet al. 70 displaced its contents (moved it over withoutelimination) and placed an implant. In contrast,Rosenquist and Nystrom 71 enucleated the canal, in-serted a bone graft, and subsequently placed an im-plant. It is also often possible to angle an implantand avoid the canal.

When performing surgery in the nasopalatine area,some clinicians create a crestal incision labiallyaround the incisive papilla to avoid transecting thecontents of the nasopalatine canal. 72 An incisionthrough the canal region does not usually have a det-rimental affect; however, it occasionally results insome numbness of the anterior palatal tissue.

Infraorbital Foramen The infraorbital nerve and blood vessels emerge fromthe infraorbital foramen. The foramen is usually lo-cated directly under the pupil of the eye on the inferiorportion of the infraorbital ridge, and it can be palpated

Figure 8.

Incisive foramen exposed (nasopalatine canal [arrow]).


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through the skin of the cheek. The infraorbital nerve isfound5mmbelowtheinferiorportionoftheinfraorbitalridge, 73 and it can be injured during surgery. It is a sig-nicant landmark, and intraoral ap elevation shouldcease several millimeters inferior to it. The averageheight of the maxillary sinus is 36 to 45 mm; 74 there-fore, a lateral window extending

;

15 mm from the al-veolar ridge crest usually avoids encroaching on theinfraorbital nerve. However, if advanced resorptionof the maxilla transpired, vigilance needs to be exer-cised when elevating a ap to avoid damaging the in-fraorbital nerve.

Greater Palatine Foramen Theposterior maxilla needs to be treated cautiously inthe region of thegreater palatine foramen. Thegreaterpalatine artery and nerve emerge from the foramenand traverse the palate anteriorly. The foramen wasfound opposite the third molar in 86% of cases, be-tween the second and third molar in 13% of cases,and opposite the second molar in 1%of cases. 75 Otherinvestigators 76 noted that the foramen was detectedby the third molar in55% of cases, between the secondand third molar in 19% of cases, opposite the secondmolar in 12% of cases, and distal to the third molar in14% of cases.

Theforamenis locatedhalfway betweentheosseouscrest and the median raphe. Wang et al. 77 reported amean distance of 16 mm from the center of the greaterpalatine foramen to the mid-sagittal plane of the hardpalate. Severing the palatal artery close to the foramencan present a problem, because it can retract into thebone, which precludes ligating it. The precise locationof theforamen can bedetermined prior toap elevationby sounding the bone with an anesthetic needle.

Blood Supply in the Maxilla The internal maxillary artery (maxillary artery) arisesfrom the external carotid artery behind the neck of themandible and provides branches to several regions of the face: mandibular, pterygoid, and pterygopala-tine. 78 Surgery in the maxilla can involve arteries inthe pterygopalatine region: descending palatine ar-tery, sphenopalatine artery terminal branch, infraor-bital artery, posterior superior alveolar artery, andthe artery of pterygoid canal.

GREATER PALATINE ARTERY

The descending palatine artery emerges from thegreater palatine foramen and traverses anteriorly in agroove on the medial side of the hard palate to the inci-sive canal. 79 The end branch of the artery enters theincisive canal to anastomose with the nasopalatinebranch of the sphenopalatine artery. Monnet-Cortiet al. 80 reported that the distance from the gingivalmargin to the greater palatine artery ranged from12.07 2.9 mm in the canine area to 14.7 2.9 mm

at the mid-palatal aspect of the second molar level.With regard to the greater palatine artery, it is prudentto assess the height of the palatal vault to establishthe extent to which a surgical procedure can be per-formed(e.g.,harvestinga connectivetissuegraft)with-out damaging the artery. It is advantageous to leave2 mmbetween the artery and the end of the surgical in-cision. 81 Based upon the shape of the palatal vault, it ispossible to estimate how far the palatine artery is fromthe cemento-enamel junction: low vault (at) = 7 mm,average palate = 12 mm, and high vault (U-shaped) =17 mm. 81 The mean palatal vault height for malesand females is 14.9 and 12.7 mm, respectively. 81

When performing a connective tissue graft, a split-thicknesspalatal ap, andso forth, thesurgeon shouldbe ready to manage accidental injury to the greaterpalatine artery. If the artery is deemed to be close tothe site of surgery, it may be advantageous to place

deep sutures to lasso and ligate the greater palatineartery distal to the surgical site prior to initiating ther-apy. If the artery is damaged, this step may precludehemorrhaging. To manage bleeding from a damagedblood vessel, apply pressure, and clamp the palatalap where the incision was made with a hemostat. If the bleeding vessel is visible, ligate it, or apply electriccautery. Additional deep sutures are needed if thebleeding vessel is not visible.

SPHENOPALATINE ARTERY

The sphenopalatine artery emerges from the spheno-

palatineforamenandenters thebackpartof thesuperiormeatus of the nose. 79,82 It gives rise to the posterior andmedial lateral nasal branches. The former spreads for-ward over the conchae and anastomoses with nasalbranches of the descending palatine and ethmoidal ar-teries.Theposteriormedialnasalbranchessupplybloodto the posteromedial and posterior wall of the maxillarysinus.Whendoinga sinus lift, cautionmustbeexercisedtoavoiddamagingthesevesselsiftheprocedureisbeingextended to the posterior wall of the sinus.

INFRAORBITAL AND POSTERIOR SUPERIOR

ALVEOLAR ARTERY

The infraorbital artery provides branches to the ante-rior part of the sinus. These vessels anastomose withvessels of the posterior superior alveolar artery withinthe buccal plate of bone (intraosseous artery) and inthe buccal tissues (extraosseous artery). The intraos-seous artery is < 16 mm from the crest of the ridge in20% of cases, and it may need to be managed duringlateralwindowpreparation. 83 Iftheintraosseousarteryis severed, apply pressure with an instrument to thehemorrhaging site, or it can be touched with a cauteryunit (e.g., Bovie). If a lateral window was created,elevate the membrane, and compress the bone witha mosquito hemostat, thereby collapsing the


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ostium is the opening from the sinus to the middle me-atus of the nose (Fig. 12). It is situated on the superioraspect of the medial wall of the maxillary sinus abovethe rst molar. The mean distance from the most infe-rior point of the antraloor to the ostium is 28.5 mm. 86

Thus,when performing a sinus lift, the sinus should notbe overlledwith graftmaterial beyond 15mmto avoidpotentially blocking the ostium and causing sinusitis.

The maxillary sinus is surrounded by six walls. 87 1)The anterior wall contains the infraorbital nerve andblood vessels to the anterior teeth. The infraorbital ar-tery gives off the anterior superior alveolar arteriesthat supply the sinus mucosa in the anterior sectionof the sinus. 2) The superior wall is very thin andmakes up the orbital oor. A bony ridge containsthe infraorbital canal with the nerve andblood vessels.3) The posterior wall corresponds to the pterygomax-illary region, which separates the antrum from the

pterygopalatine fossa. It contains the posterior supe-rior alveolar nerve and blood vessels, including thepterygoid plexus of veins and internal maxillary ar-tery. 4) The medial wall separates the sinus from thenasal fossa. The maxillary ostium (around rst molararea) drainsinto themiddlemeatus of thenasal cavity.5) The sinus oor may extend between the roots of the maxillary molars. The oor may be 10 mm be-low the oor of the nasal cavity. 6) The lateral wallforms the posterior maxillary and zygomatic process.This wall providesaccessfor thesinusgraft procedure.

The medial wall derives its arterial supply from na-

sal mucosal vasculature. This comes from branchesof the sphenopalatine artery: posterior lateral nasaland posterior septal branches. The frontal, lateral,and inferior walls derive their arterial supply fromthe osseous vasculature (infraorbital, facial, and pal-atine arteries). The medial sinus wall drains throughthe sphenopalatine vein. All other veins drain throughthe pterygomaxillary plexus. Innervation is providedby nasal mucosa nerves and the superior alveolarand infraorbital nerves.

Septa (Underwoods clefts) have been located in31.7% of the maxillary sinuses in the premolar area,and they usually do not compartmentalize the an-trum. 88 However, they frequently get larger as theyproceed medially. Therefore, during a sinus lift, mem-brane elevation over partial septa should proceed lat-erally to medially, because elevation attemptedanteriorly to posteriorly is more prone to create a per-foration.To accommodatelargeor multiple septadur-ing a sinus lift, more than one lateral window can becreated as part of the antral opening. 88 In addition,septa are a concern if an osteotome sinus oor eleva-tion procedure is planned because it is difcult to in-fracture the subantral oor under them.

There are several other issues of interest regardingthemanagement of themaxillarysinusarea. Ifdiagnos-

tic imaging indicates that the inferior wall (alveolarridge) or the lateral wallof the sinus has abonyfenestra-tion, a split-thickness ap needs to be developed overthese defects to avoid tearing the Schneiderian mem-branewhentheapiselevated(Fig.13).Subsequently,aspartofthemembranerelease,theresidualtissueoverthebonedefectsmustbepushedintothesinus,becausethe sinus membrane cannot be separated from the softtissue that was lodged in the osseous defects.

During a lateral window preparation, if a tear in theSchneiderian membrane occurs and it is a relativelysmall defect, the opening can be patched with a colla-gen barrier. 89 However, when a tear occurs along theperiphery of the window and it is difcult to reengagethe membrane, before the tear elongates, extend theosteotomy several millimeters in bone away from theoriginal site. Remove the bone over the membraneto attain better visibility and accessibility, and re-

engage the membrane where it is not torn (Fig. 14).The normal width of the Schneiderian membrane isgenerally 0.3 to 0.8 mm. 90 However, it can appear

Figure 14.Perforation of the membrane along the periphery of the lateralwindow. To reengage the membrane and avoid tearing of the

membrane, more bone is removed to expose more membrane (arrows).

Figure 13.CT scan. There is a fenestration (arrow) in the inferior wall of the sinus.When a sinus lift is done, after a split-thickness ap is elevated, thetissue in the fenestration is pushed into the sinus because themembrane and the tissue are fused.


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Correspondence: Dr. Gary Greenstein, 900 W. Main St.,Freehold, NJ 07728. Fax: 732/780-7798; e-mail: [email protected].

Submitted February 10, 2008; accepted for publicationMarch 21, 2008.


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