RELEVANCE OF MAXILLOFACIAL ANATOMy IN ENDoDoNTICS: A REvIEw

A thorough anatomical knowledge is very essential for any surgical procedure. The idea of location of various structures in the body prepares the clinician for a better approach to establishing diagnosis and various surgical procedures. Unfortunately, anatomical variations can lead to hazards in diagnosis and treatment. Referred pain and pain of unknown origin or temporomandibular joint pain sometimes may lead to confusion or misinterpretation in proper diagnosis. Abnormal course and distribution of nerves and vessels may sometimes become a major problem. There may be an overlapping of the nerves of the two sides supplying the teeth or some of the nerves may be duplicated in the whole or part of their course. Such conditions may lead to problems in anesthetizing teeth or unexpected pain sensations expressed by the patient during the endodontic treatments. Anatomical relation of maxillary air sinus to the upper teeth and the possible clinical complications during the treatment is also important. Relation of neurovascular bundle to the sinus may sometimes vary. Lack of knowledge of normal anatomy may lead to misinterpretation of tests leading to wrong diagnosis and management. Concept of anatomical variations is of utmost importance to prevent complications of anesthetic procedures.


Uvod
Detaljno poznavanje anatomskih struktura od vitalnog je značaja za oralne hirurge u toku različitih hirurških procedura.Lokalna aneste zija se najčešće postiže ubrizgavanjem rastvo ra lokalnog anestetika u tkivo oko nerva koji rounding the nerve innervating the area to be treated.In many cases, the failure in anesthesia is due to anatomical abnormalities or variations 1 .The clinician must be able to assess whether it is operator's error or anatomical anomaly which is responsible for inadequate pain management.Therefore, it is relevant for dentists to discuss the normal and abnormal anatomy of the man dibular and maxillary nerves in relation to other anatomical structures like temporomandibular joint and maxillary sinus.

Mandibular nerve
Inferior alveolar nerve (IAN) is a branch of posterior division of mandibular nerve which traverses the mandibular canal and innervates the teeth of lower jaw.The course of the IAN vary 2 .The variations of mandibular canal can be divided into four categories: 1. High man dibular canals (within 2mm of the apices of the molars), 2. Intermediate mandibular canals, 3. Low mandibular canals, and 4. Duplication or division of the canal, apparent partial or com plete absence of the canal or lack of symme try 3 .mostly, the mandibular canals are bilater ally symmetrical with only one major canal on each side.Communication patterns between the mandibular nerve branches are a possible cause of incomplete anesthesia during dental prac tice 4 .IAN sending fibers to the lingual nerve (LN) through a communicating branch has been considered clinically relevant for the sup plementary innervation of the lower molars 5 .
During administration of local anesthet ics, intravascular puncture of maxillary artery which is passing through a communicating loop from the auriculotemporal to the inferior alveolar nerve can cause a hematoma which may compress nerves in the infratemporal fos sa, producing sensory alterations 6 .Course of maxillary artery through the inferior alveolar nerve, splitting it into superficial and deep divi sions may lead to its entrapment and may cause numbness or headache, can even interfere with injection of local anesthetics 7 .maxillary artery is variably related to the mandibular foramen 8 .Therefore, the use of panoramic radiographs should be considered in locating the mandibu lar foramen rather than relying on bony land marks 9 .Branches of the mandibular division or of its inferior alveolar or buccal branch may inerviše ciljano područije.U najvećem bro ju slučajeva razlog neuspeha anestezije leži u anatomskim abnormalnostima i varijacijama 1. Kliničar mora biti sposoban da proceni da li se radi o grešci lekara ili anatomskoj anomali ji.Stoga je razmatranje normalne, kao i abnor malne anatomije mandibularnih i maksilarnih nerava u odnosu na druge anatomske struktu re, poput TmZ i makslarnoig sinusa, od velike važnosti za stomatologe.
IAN within the mandibular canal may lie close to the roots of the teeth or it may be much lower in the mandible near its lower border 3 .more commonly, the nerve lies near the buc cal side of the mandible 11 .It may be intimately related to the root of the third molar tooth and may groove it, in the case of which the nerve may be at risk during the biomechanical prepa ration of third molar leading to its permanent sensory dysfunction.IAN block failures occur in 44% to 81% of cases, which may be due to objective location of neurovascular bundle, or an anatomic variation.Studies have shown the anesthetic success rates of 75%-97% with pe ripheral nerve stimulator 12 .25% of accurate blocks using radio-opaque dyes result in anes thetic failure due to the migration of anesthetic solution along the path of least resistance deter mined by fascial planes and structures encoun tered in the pterygomandibular space 13 .
The inferior alveolar neurovascular bundle was shown to be in contact or close to the lin gual cortical plate between the mandibular and mental foramina.It often gives rise to several branches at each level 14 .Absence of the ipsi lateral inferior alveolar canal, nerve and mental foramen are of importance to clinicians who deal with surgery 15 .Panoramic radiography can provide reasonable diagnostic accuracy in the preoperative evaluation of the relationship between third molars and the canal 16 .IAN and the molar root apices are sometimes very close, allowing pathologic periapical conditions to affect the nerve.The IAN can be damaged by traumatic-compressive or toxic injuries re sulting in neurapraxia of this nerve.When the causative agent is removed, the damage of the Schwann cells and the impairment of the my elin sheath can heal completely, thus making the clinical recovery predictable.

Accessory innervation of teeth by mylohyoid nerve
mylohyoid nerve innervation to mandibu lar teeth is approximately 60% and thus is the cause of many cases of anesthetic failure 17 .It supplies the pre-molar, canine, incisor teeth and sometimes the first molar 8,18 .
Postoje izveštaji o ograncima milohioidnog nerva koji ulaze u mandibulu kroz retromental ne otvore povezane sa lingvalnom kortikalnom in the vicinity of the second premolar tooth.The mylohyoid nerve arises from the inferior alveo lar nerve about 5 to 23mm above the level of the mandibular foramen and enters the mandible at a point distant to the mandibular foramen 18 .In ferior alveolar nerve block in the vicinity of the mandibular foramen does not block the mylohy oid nerve most often, hence, mylohyoid nerve block in the vicinity of the retromental foramina is recommended.Sometimes, the branching of mylohy oid nerve occurs about 14.7mm from the mandibular foramen 19 .This distance could also be beyond the area of diffusion of the deposited anesthetic in a conventional mandibular block, thus allowing the accessory nervous supply to continue.The contiguity of a supplementary branch of mylohyoid nerve with either the inci sor teeth or the incisive nerve proper has been demonstrated 20 .Communicating branch of the mylohyoid nerve to the lingual nerve contrib ute to the sensory innervation of the tongue.Thus, mylohyoid nerve block can lead to partial tongue anesthesia or lingual nerve lesion does not result in complete anesthesia of the anterior part of the tongue 21 (Figure 1).

Figure 1. Figure illustrates the schematic representation of communication between the mylohyoid nerve (MHN) and lingual nerve (LN). IAN-Main trunk of inferior alveolar nerve, COM-Communication between mylohyoid and lingual nerves,
MHM-Mylohyoid muscle, TON-Tongue.

Slika 2. Šematski prikaz bifidnog donjeg alveolarnog nerva. IAN-glavno stablo nerva, BIAN-Bifidne grane donjeg alveolarnog nerva, DP-pleksus dentalnih nerava, MN-mentalni nerv.
the presence of an accessory mandibular fora men and lingu lae.In patients with bifid canal, no specific pattern of division or duplication is seen 3 .Because the bifurcation of the nerve oc curs before entering the mandibular foramen, a normal inferior alveolar nerve block injection may be insufficient to block both branches.A high inferior alveolar nerve block may be ef fective in anesthetizing accessory nerve at or above its branch point.Only 0.08% bifurcation of the IAN is reported 22 .Evaluation of routine panoramic radiographs of 6.000 patients re vealed 57 (0.95%) cases of bifid mandibular ca nals 23 .The use of cone beam volumetric com puted tomography has been shown to detect the incidence of bifid canals in 15.6% cases, a higher incidence than with use of panoramic radiographs 24 .As a second neurovascular bun dle may be contained within the bifid canals, complications like traumatic neuroma, paraes thesia and bleeding could arise because of fail ure to recognize the presence of this anomaly.A case of trifid mandibular canal in panoramic radiographic study has been reported 25 .It is im portant for dentists to identify the presence of bifid or trifid canals to modify anesthetic tech niques to avoid pain and discomfort to patients (Figure 2).

Retromolar foramen
Long buccal or early accessory branches of the inferior alveolar nerve provide accessory innervations to the mandibular molars through retromolar foramina.In almost 40% of human mandibles with retromolar foramina, the infe rior alveolar nerve was contiguous with molar teeth via retromolar foramina 26 .Accessory in nervations via retromolar entry can lead to dif ficulty in achieving local anesthesia of the man dibular molar area.To overcome this problem, a small amount of local anesthetic can be de posited directly into the tissue of the retromolar area 27 .A high pterygoid entry injection can also be done but it would affect the inferior alveolar nerve in the pterygoid space before it gives any branches.

Kontralateralna inervacija prednjih zuba
Incizalna grana donjeg alveolarnog nerva obimno grana se i anastomozira u sredini do nje vilice sa kontralateralnom stranom stvara over the midline to the contralateral side, creat ing a crossover effect in the innervations of an terior teeth.The failure to anesthetize the inci sors completely can be attributed to two things, 1. Crossover of the incisive branch 2. The pos sibility of accessory innervations from buccal, facial, mylohyoid nerves and cervical plexus. 28hen complete local anesthe sia of the anterior teeth is not achieved after an ipsilateral man dibular block, steps must be taken to block sen sation due to any potential crossover and/or accessory fibers and a contralateral incisive nerve block is opted.Achieving bilateral nerve blocks would rule out the possibility of failure caused by crossover.mental/in cisive nerve block or periodon tal ligament injections are alternatives to bilateral mandibular nerve blocks for the pro cedures on the anterior part of the mandible.Bi lateral mandibular nerve blocks create complete mandibular anesthesia leading to postoperative difficulties with speech, eating, drinking and salivary control.If the accessory innervation arises from the branches of the buccal, facial or cervical plexus, and these branches are travel ing in the soft tissue of the area previous to the entry into the mandibu lar foramen, infiltration blocks may prove successful in determining the secondary innervations 28 ( Figure 3).

Slika 3. Šematski prikaz kontralateralne inervacije (CON) donjih zuba (MT) od strane donjeg alveolarnog nerva (IAN). Prikaz mentalnog nerva (MEN) i milohioidnog nerva (MYN). [Reprodukcija Somayaji i sar. Bratislava Med J. Article in press]
nent loss of sensitivity of the lip, chin and oral mucosa that is often associated with a limited intraoral xerostomia.The local factors like iat rogenic sequelae of endodontic therapy or sur gical procedures and the occurrence of acute apical periodontitis or an acute exacerbation of a chronic apical periodontitis have been report ed to be associated with mental nerve paraes thesia.The possible risk of hypersensitive reac tions to potentially toxic or allergenic materials via the root canal has been reported 29 .After the removal of the restoration, the paraesthesia could be completely resolved.

Maxillary Nerve
The maxillary nerve block should be per formed with utmost care to protect the ptery goid venous plexus in the pterygopalatine fossa.

Variations of the maxillary nerve
Six major types of variations of the maxil lary nerve have been described.a. missing mid dle superior alveolar nerve, b.Branch parallel to the infraorbital nerve supplying the upper lip, c.Bifid maxillary nerve, d.Posterior superior alveolar nerve innervating areas normally cov ered by the long buccal nerve, e. Branches from the pterygopalatine ganglion communicating with the abducent, optic or ciliary nerves, f.Various exchanges of nerve fibers among zygo maticofacial, zygomaticotemporal, infraorbital and lacrimal nerves 30 .Variations in the ana tomic distribution of the maxillary nerve may explain the lack of uniformity in anesthesia by conduction or infiltration.
In the absence of middle superior alveo lar nerve, the premolar region is supplied by a branch of anterior dental nerve which is most ly the largest of the superior dental nerves.A dental plexus formed by these dental nerves in nervate the teeth in 48% of cases.One to three posterior superior alveolar branches from the maxillary nerve in the zygomatic region pass through canaliculi in the lateral wall of the max illary sinus or under the mucous membrane of the sinus to form maxillary sinus plexus.Bony wall of the sinus separates this plexus from the superior dental plexus, located in the thick al veolar process of the maxilla and innervate the upper teeth 31 .ja na usni, bradi ili oralnoj sluzokoži, što je često udruženo i sa ograničenom intraoralnom kserostomijom.Postoje primeri da lokalni uzro ci kao što je jatrogeni faktor u endodonskim ili hirurškim procedurama ili prisustvo akutnog apikalnog paradontita kao i akutne egzacerba cije hroničnog apikalnog parodontita mogu biti udruženi sa parestezijom mentalnog nerva.Ta kođe je zabeležen moguć rizik hipersenzitivne reakcije na moguće toksične i alergene mate rijale koje prodiru kroz kanal korena 29 .Posle uklanjanja ispuna parestezija može u potpuno sti nestati.

Maxillary sinus
The floor of the maxillary sinus can be very thin and in some individuals the roots of the posterior teeth project through it.In these cases, the root tips are covered only by the Sch neiderian membrane of respiratory epithelium which lines the maxillary sinus 32 .The distance between the root apices of the maxillary poste rior teeth and the sinus is sometimes less than 1mm 33 .Great care must be taken during end odontic treatment, not to accidentally introduce foreign bodies into the antrum.The most com monly found foreign bodies are the displaced fractured roots of teeth, dental burs, gutta per cha points and silver points 34 .During the root canal treatment, the possibility of communica tion of the canal system with surrounding tis sue should be determined both clinically and radiographically.The recent like cone beam volumetric computerized tomography is proven to be better aid in diagnosing maxillary sinusitis due to failed endodontic treatment 35 .Overzealous preparation of root canal may cause extrusion of debris into the sinus leading to inflammatory reaction and delayed healing 36 .Incidence of sodium hypochlorite accident into the sinus and then to the pharynx has been re ported 37 .Sodium hypochlorite elicits inflam matory reaction and is cytotoxic to all cells.This can be avoided by irrigating the solution carefully 37 .
Intracanal medicament placed between ap pointments may extrude into the sinus.The use of calcium hydroxide is irritant to sinus tissue and has immediate degenerative effects on cells; before the material is removed by macrophages and foreign body giant cells 38,39 .The calcium hydroxide causes inflammatory re sponse of sinus mucosa, which initially acts as irritant and later as foreign body 40 .Extrusion of sealers like N2 into the sinus leading to severe pain has been reported 41 .Occasionally, foreign intra-sinusal bodies were seen as a result of dif ferent endodontic treatments of posterior max illary teeth 42 .
Gutta percha evokes two distinct types of tissue responses that are determined by the size and surface character of the material: 1) In case of large piece of gutta percha, the surrounding tissue is free of inflammation and gutta per cha is well encapsulated.2) Fine particles of gutta percha evoke localized tissue response characterized by the presence of macrophages
Cases have been reported, where spread ing of dental infection through the sinus lead ing to periorbital cellulitis, blindness and also cavernous sinus thrombosis.Intracranial exten sion of infection can occur by two mechanisms: (a) directly, by erosion through the posterior wall of the frontal sinus; and (b) indirectly, by thrombophlebitis or septic emboli via emissary veins 53,54 .Aspergillosis is often associated with concretions in the maxillary sinus, which on the basis of radiological and clinical findings have been considered to correspond to dental restor ative material.Zinc in maxillary sinus promotes the growth of Aspergillus species.In endodon tics, zinc oxide eugenol-based sealers which are used may trigger the fungal infection 55,56 (Fig ure 4).

Considerations of sinus in endodontic surgery
Perforation of the sinus during surgery is fairly common with a reported incidence of about 10 to 50% of cases 57 .In 146 reported cases of sinus exposure during periradicular surgery, there was no difference in their heal ing when compared with similar surgical pro cedures without sinus exposure 36 .The sinus membrane usually regenerates and a thin layer of new bone often forms over the root end, al though osseous regeneration is less predict able 58 .About 0.8-7mm thick bone separates toga što u svim slučajevima nije prisutno svih 5 navedenih odlika.

Uloga sinusa u endodontskoj hirurgiji
Otvaranje sinusa prilikom hirurške in tervencije je prilično često sa prijavljenom učestalošću od 10 do 50 % sučajeva 57 .U 146 prijavljenih slučajeva otvaranja sinusa u toku periradikularne hirurgije nije bilo razlike u za rastanju u poređenju sa sličnim hirurškim pro cedurama u kojima nije došlo do otvaranja si nusa 36 .Sinusna membrana se obično regeneriše i tanak sloj nove kosti se često formira na kraju vrha korena, mada je regeneracija kosti predvi diva 58 .Oko 0.8 do 7 mm tanke kosti odvaja vrh korena zuba od sinusa u bočnim segmentima  the teeth apices in the lateral segments of the maxilla from the sinus 59 .Adequate infiltration anesthesia in the region of the vestibule of the mouth and the palate at the level of the root apex suffices even when the sinus is locally af fected 58 .When the maxillary canine tooth and premolars are resected, additional nerve block ing in the region of the infraorbital foramen can be carried out 58 .A vertical releasing incision should be made at least one tooth mesial and distal to the surgical site, especially in cases when sinus perforation is possible, because the exposure site should be completely covered with mucoperiosteal flap to provide primary closure 60 .Displacement of root tip into the si nus can be avoided by cutting through the bone and approaching the root from front and below but never from above 61 .The root tip is then burred off to the desired level..Another meth od of preventing displacement of root into sinus is drilling a small hole at root apex and securing it with a suture before apicoectomy 62 .The pala tal roots of maxillary molars present a special challenge for surgical access.Palatal roots are 50% closer to the sinus than are to the palate 60 .They show apical communication with the si nus in 20% of the cases and are less than 0.5mm from the sinus in 40% of cases.The transantral approach is reflecting the buccal flap, resecting the buccal root, then enlarging the osteomy ac cess into the sinus to approximately 1 to 1.5cm.Then palatal root tip is dissected, ultrasonically prepared and filled 63 .The position of the ante rior palatine artery must be carefully consid ered when the incision is made and the flap is reflected 60 .The vertical releasing incision may be placed distal to the second molar, but should not approach the junction of the alveolar pro cess and roof of the palate.When the anterior palatine artery is severed, local clamping and pressure may not stop the hemorrhage.In such cases, the ligation of the external carotid artery may be necessary 60 .

Temporomandibularni zglob (TMZ)
Pulpitične tegobe mogu imitirati temporo mandibularne smetnje poput bola.Bol koji se pojačava na hladne stimulanse na zahvaćenom zubu potvrđuju da se radi o bolu izazvanom oboljenjem pulpe 64 .Pulpitični bol je uglavnom lokalizovan u predelu bolnog zuba, ali se paci jenti nekad mogu žaliti i na bol koji se širi pre more broadly to the jaw and mimics the loca tion and quality of TmD pain.TmD pain is usu ally an ache, pressure, dullness or all of these may include a background burning sensation, generally located in the masseter muscle or preauricular and / or anterior temporalis muscle regions.There may be episodes of sharp pain which may become throbbing.Palpation of the location of pain reproduces or intensifies the pain.TmD pain aggravates to stress, clenching and eating, whereas it is relieved by relaxing, applying heat to the painful area, taking over the counter analgesics or all of these.Referred pulpal pain is difficult to localize to a specific tooth, often also causes pain in the masseter muscle or the preauricular and or anterior tem poralis muscle regions; and can cause tightness in the masticatory muscles 65 .The two primary mechanisms for referred pain are central con vergence and central sensitization.more nerve fibers carry information into the central nervous system than the number of neurons that trans fer this information to the higher center.This needs the information carried by the multiple nerve fibers to be consolidated to fewer neurons carrying this information to the higher centers.This results in the higher centers to perceive the information from two or more regions 66 .Cen tral sensitization occurs from a continuous bar rage of painful input activating receptors that increase the sensitization of second order neu rons, altering normal processing to the higher centers, expanding the receptive field area and causing nonpainful information to be relayed as painful 67 .Central convergence and cen tral sensitization may occur in both the sensory trigeminal nuclei and thalamus (Figure 5).It has been demonstrated that when an inflam ma vilicama i imitira lokaciju i osobine bola u TmZ.TmZ smetnje najčešće uključuju senza ciju bola, pritiska, tupoće ili svega navedenog, kao i osećaj žarenja, uglavnom lokalizovan na maseteričnom mišiću ili u predelu preauriku larnog/prednjeg temporalnog mišića.mogu se pojaviti i napadi oštrog bola koji može posta ti pulsirajući.Palpacija bolnog mesta ponovo izaziva ili pojačava bol.TmZ bol se pojačava stresom, stiskanjem zuba i žvakanjem, a uman juje se aplikovanjem toplote na bolno područje i upotrebom standardnog analgetika.Iradirajući pulparni bol je teško lokalizovati i često izaziva bol u masteričnom mišiću ili predelu preauri kularnog/prednjeg temporalnog mišica i može uzrokovati zatezanje mastikatorne muskula ture 65 .Dva glavna mehanizma iradirajućeg bola su centralno spajanje i centralna senzaci ja.Većina nervnih vlakana nosi informaciju do centralnog nervnog sistema a onda brojni neu roni prebacuju ovu informaciju u više centre.Ovo podrazumeva da se informacija koju nose višebrojna nervna vlakna svede na manji broj neurona koji je dalje nose do viših centara.Kao rezultat, viši centri informaciju vezuju za dve ili vise rezličitih regija.Dva su primarna mehani zma odgovorna za nastajanje iradirajućeg bola: centralna konvergencija i centralna senzitiza cija.Više nervnih vlakana prenosi informaciju u centralni nervni sistem od broja neurona koji prenose ovu informaciju u više centre.Trebalo bi da informacija koju nosi veći broj nervnih vlakana bude konsolidovana na nekoliko neu rona koji je prenose u više centre.Ovo rezultira time da viši centri dobijaju informaciju iz dva ili više regiona 66 .Centralna senzitizacija nasta je kontinuiranom baražom bolnih aktivatinskih receptora koji povećavaju senzitizaciju drugog reda neurona, prosleđujući normalnu obradu informacije višim centrima, na taj način šireći matory irritant is placed on dental pulps, elec tromyograhic activity of masticatory muscles increases 64 .This finding may explain pain due to pulpalgia, which after ligamentary injection, will not cause tightness in masticatory muscles and have a greater range of joint motion.Cen tral sensitization can also be produced by glial cells that are activated by inflammatory irritants placed on dental pulps 68 .

Role of salivary glands
Saliva controls the plaque pH and regulates the oral flora.Dental carries is a common clini cal finding associated with xerostomia due to salivary hypofunction.Absence of salivary glands will lead to decrease in salivation, which eventually results in rapid spread of caries with pulpal involvement 69 .

Conclusion
Basic anatomical knowledge is vital for many successful dental procedures.Awareness of maxillary sinus involvement and complica tions due to endodontic treatments of upper teeth makes dentists to be very cautious.It also prepares the clinician for the differential diag nosis of symptoms of teeth and other orofacial regions.Concept of anatomical variations is of utmost importance to prevent complications of anesthetic procedures.Such a review of avail able literature regarding the anatomical anoma lies of structures encountered by the dentists during their clinical practice will be useful for better patient care.receptorno područije i dovodeći do toga da se informacije koje nisu bolne ispoljavaju kao bolne 67 .Centralna konvergencija i centralna senzitizacija mogu se odvijati i u senzitivnom trigeminalnom jedru i u talamusu (Slika 5.).Dokazano je da kada se inflamatorni iritans po stavi na zubnu pulpu, elektromiografska akti vnost mastikatornih mišića raste 64 .Ova otkrića mogu objasniti bol u toku pulpalgije, koji posle ligamentarne injekcije neće izazvati zatezanje mastikatornih mišića i postojaće veća moguć nost pokreta u zglobu.Centralna senzitizacija takođe može biti proizvedena glijalnim ćelija ma koje se aktiviraju postavljanjem inflamator nog iritansa na zubnu pulpu 68 .

Figure 2 .
Figure 2. Figure illustrates the schematic representation of the bifid inferior alveolar nerve.IAN-Main trunk of inferior alveolar nerve, BIAN-Bifid branches of inferior alveolar nerve, DP-Dental plexus of nerves, MN-Mental nerve.

Figure 3
Figure 3. Figure illustrates the schematic representation of the contra-lateral innervation (CON) of the mandibular teeth (MT) by the inferior alveolar nerve (IAN).Also shown are mental nerve (MEN) and mylohyoid nerve (MYN).[Reproduced from Somayaji et al.Bratislava Med J. Article in press]

Figure 4 .
Figure 4. Picture of the maxilla showing the obturating material (OM) extending into the maxillary air sinus (MS).