Introduction toDental Local Anaesthesia

Hans EversGlenn Haegerstam

TrigeminalnerYeTtre trigeminal nerve is predominantly sensorymd the cell bodies of these sensory fibres formlhe semilunar ganglion (the Gasserian ganglion),which lies in Meckel's cavity in the bottom ofthe middle cranial fossa. Three large trunksoriginate from tlre ganglion: the maxillary nerve,the ophtlwlmic nerve, and the mandibular rurv e(Irferbr alveols neme)(Fie D.

Fig. 1.1. Tiigeminal nerve2. Tiigeminal (Gasserian) ganglion3. Ophthalmic nerve4. Nasociliary nerve5. Supraorbital nerve6. Lacrimal nerve7. Frontal nerve8. Supratrochlear nerve9. Infrarochlearnerve

10. Maxillary nervelL. Zygomatic nerye1 2. Middle superior alveolar nervel3. Posterior superior alveolar nerve14. Anterior superior alveolar nerve15. Infraorbital nerve16. MandibularnerveL7. Auriculotemporal nerve18. Mandibular nerve (Inferior alveolar nerve)19 . Lingual nerve20. Buccalnerve21. Mental nerve

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Maxillary nerve\\e nwcillary nerve, excfusively sensory passes

through the foramen rotundum to reach thepterygopalatine fossa, where it gives off anumber of branches. Two branches enter thesphenopalatine ganglion, and come to form thegreater palatine nerve , the rwsopalatine nerve, andposteri.or nasal rrcme nvigs. Just before it entersthe infraorbital canal, the maxillary nerve trunkgives off the zygomatic nerve which passes

anteriorly and laterally, and the descendingposterior $ryeri.or alveolnr branches (Fig. 1).

Infraorbital nerveAnterior superior alveolar nen'e trigs leave thetrunk just before the exit of the infraorbitalforamen, and outside the foramen r,wigs to theskin between the nostril and the eye (Fig. 1).

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Fig.2.

8

ContentsTrigeminal nervePhysiology of the peripheral

nen/eBlocking of nerve conductionPharmacodynamic aspectsTechniques of regional anaesttresia indentisfy

Clinical requirements for localanaesthesia

Solution properties of clinicalimportance

Anaesthesia of the upper jawGeneral considerations

Incisors and caninesOperative aspectsInjectionSpread of analgesia

Infraorbital blockSpread of analgesia

hemolarsOperative aspectsInjection

Supplementary injection in thepalate

Spread of analgesiaMolars

Operative aspectsBuccal infilnationTuberosity injectionSupplementary blocking of the

greater Palatine nerveSpread ofanalgesia

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31

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Anaesthesia of the lower jawGeneral considerations

Incisors and caninesOperative aspects

Supplementary blockingof the lingual nerveSpreadof analgasia

PrremolarsOperative aspects

Mental blockSupplementary blocking

of the lingual nerveMolars

Operative aspectslvlandibular blockBlocking of the lingual nerveBlocking of the buccal nerve

Failure to anaesthesiaComplications

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The superior dental plexusThe superior dental plexus is formed by thesuperbr posteior and anterior alveolar branches.The teeth and the buccal gingiva ofthe upperjaware innervated by this plexus. Sometimes aninegular branch - the middle superior alveolarbranch - is also present (Fig. 2).

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One of the posterior alveolar branches passesdownward on the surface of the maxillary bone tothe gingiva of the buccal side of the molarregion. The posterior part of the mucousmembrane of the cheek is also innervated by thisbranch (Fig. 3).

Fig.3.

Superior gingival branches from the superiordental plerus penefrate the bone and supply theinterdental papillae, the periodontal ligament andthebuccal gingiva.

Nasopalatine nerveThe nasopalatine nerve leaves thesphenopalatine ganglion through thesphenopalatine foramen. It passes forward anddownward on the nasal septum to reach theincisal canal, where it gives off its terminalbranches. The mucous membrane and gingiva inttre anterior part of the hard plate are innervatedby the nasopalatine nerve (Fig.4).

Greater palatine nerveThe gredter palatine nerve leaves thesphenopalatine ganglion and descends throughthe greater palatine canal to emerge from thegreater palatine foramen. The posterior part ofthe mucous membrane of the hard plate and thepalatal gingiva are innervated by this nerve (Fig.4).

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Fig.4.

10

.zyl,rnsilico \sto.\Zygomatic nerve -L ,,KMq\,* $*"t.'\The zygomatic nerve enters t}re orbital cavity viathe inferior orbital fissure. It runs along thelateral wall of the orbital cavity and divides intotwo branches. These branches penetrate the boneto reach the skin over the anterior temple and thelateral angle of the eye. The zygomatic nervecommunicates with the lacrimal nerve (Fig. 5).

Infraorbital nerveThe infraorbital nerve emerges fqom theinfraorbital foramen and ramifies. Th{inferiorpalpgbral branclus innervate the lower eyelid.TWexternal rwsal brancfups pass to fre skin onthe side of the nose. ThYlnterrul nasal branchesinnervate the mucous me,nbrane of thevestibulum of the nose. ThPs uperior labialbranclrcs pass to the skin and mucous membraneof the upper lip (Fig. 6).

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Fig. 5.

Fig. 5.

Ophthalmic nerveT}ne ophtlalmic nerve is purely sensory. It entersthe orbit via the superior orbital fissure and thenforms three branches, the lacrimd nerve, thernsociliary nerve, andthefrontal nerve (Fig. l).

Lacrimal nerveThe lacrimal nerye courses in ansuperoanterolateral direction to reach ttre lacrimalgland. It also innervates the conjunctiva and theskin ofthe lateral angle ofthe eye (Fig. 7).

Postganglionic secretory fibres from thesphenopalatine ganglion reach the lacrimal nervevia a communicating branch of the zygomaticnerve.

Nasociliary nerveThe nasociliary nerve crosses the orbital cavityin an anteromedial direction toward ttre medialorbital wall. The terminal brqnches innervale themucous membrane of the superoanterior part ofthe nasal cavity and the skin between the noseand the medial angle of the eye (Fig. 7).

Fig. 7.

Frontal nerveT)ne frontal nerve conttnues in the direction ofthe ophthalmic nerve trunk. lt divides in theorbital cavity. The largest branch (thesupraorbital nerve) the orbit to supply the skinof the upper eyelid, the forehead and ttre anteriorscalp region. The supratrochlear nerve leaves thefrontal nerve deep in the orbit and approaches theupper medial angle of the orbit and innervates theupper eyelid and the forehead (Fig. 7).

Fig. 7.1. Supraorbital nerve2. Frontal nerve3. Lacrimal nerve4. Nasociliary nerve5. Maxillary nerve6. Zygomatic nerve7. Infraorbital nerve8. Lateral branch of the frontal nerve9. Medial branch of the frontal nerve

10. Supratrochlearnerve1.L. Infratrochlear nerve12. Nasopalatine nerve

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Mandibular nerve\\e nwndibulu neme is a mixed nerve, thoughmainly sensory. It reaches the infratemporalfossa via the foramen ovale. Motor branches forthe muscles of mastication leave the trunk in thefossa. The nerve then gives off several sensorybranches (Fig. 8).

Fig. 8.

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Auriculotemporal nerveThe auriculotemporal nerve leaves the maintrunk medial to the neck of the mandibularcondyle, passes behind the condyle up to supplythe external auditory canal and the skin of theanterior aspect of the temple (Ftg. 10).

Buccal and deep temporalnervesThe buccal rurve and the deep temporal nervesleave the mandibular nerve together, and passupwards to innervate the anterior and posterioraspects of the temporalis muscle @g.10).

Masseter nerveThe masseter nerve passes in front of thetemporomandibular articulation and enters themasseier muscle (Frg. 10).

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Fig. 10.

Buccal nerveThe buccal rurie, which is a sensory branch,passes along the medial side of the mandibularramus anterior to the inferior alveolar nerve. Itthen crosses the anterior border of the mandibulmramus and ramifies. The branches innervate thebuccal glngrva between the second premolar andthe secondmolar.

Inferior alveolar nerveThe inferior alveolar nerve passes downwardalong the medial side of the mandibular ramus tottre mandibular foramen. In the mandibular canalthe nerve gives off branches which form theinferior dental plexus from which branches inner-vate the teeth and gingiva of the lower jaw.

Before the nerve enters the mandibular foramenit gives off the mylohyoid branch, whichcontinues along the mandibular ramus. Themylohyoid muscle and ttre anterior belly of thedigastric muscle receive motor fibres from thismixed nerve branch (FtS. 12).

Mental nerYeT\e irfeior alveolqr nerve gives off a branch inthe mandibular canal - the mentul nerve - whichpasses through the mental foramen !o innervatethe bucal gingiva between the midline and thesecond premolar, and the skin of the lower lipand chin (Fig. 11).

Fig.12.

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Fig. 11.

15

Lingual nerYeThe lingual nerve passes downwards togetherwith the inferior alveolar nerve, andcommunicates with the clorda tympani of the

facial rcrve just before reaching the mandibularforamen. This connection gives off secretoryfibres to the submandibular and sublingual glandvia the submandibular ganglion and specialsensory fibres to the taste buds on the tongue.

The trunk of ttre lingual nerve gives off smallbranches to the lingual gingiva in the molarregion. The lingual gingiva of the anterior aspectof the lower jaw, and the mucosa of the floor ofthe moutlr are supplied by the sublingtml nerve,a branch of the lingual nerve. The terminalbranches of the lingual nerve enter the tongueand innervate the corpus linguae (Fig. 13).

Fig. 13.

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Physiology ofthe peripheralnerveThe conduction process in the nerve fibre isessentially dependent upon changes in theelectrophysiological status of the nervemembrane. When a nerve is inactive there is anegative "resting" potential of -50 to -70 mVwithin the cell (by comparison with the exteriorsrface of the cell membrane). When excitationoocurs, a distinct tansmembrane action potentialcan be recorded by means of an intracellularelectrode (Frg. l4).

The sequence of events after excitation is asfollows: a relatively slow phase of depolarizationoccurs during which the electrical potentialwithin the nerve cell becomes progressively lessnegative. When the potential difference betweenthe interior and exterior surface of the cellmembrane reaches a critical level, the "threshold@Igntial" or "firing level", depolarizationreverses the potential so that the nerve interior ispositively charged by comparison with theexterior aspect of the cell membrane. At ttre peakof the action the intracellular positive potentialreaches about 40 mV. Thereafter, a process ofrcpolagzaliOn begins, continuing until theinnacellular resting potential of -50 to -70 mV isrestored.

Fig. 14.

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Fig. 15.

The interior of a resting peripheral nerve cell -the cytoplasm (Frg. 15) - is possessed of a highconcentration of potassium ions and a lowconcentration of sodium ions. This state is theopposite of that in the extracellular fluids. Atrest the isibout 30, and it is this gradient which accountsfor the negative intracellular resting po ntial. Atrest, the cell membrane (Fig. 17) is relativelyresistent to ion passage, but, on excitation, cellmembrane permeability increases and there is,initially, an influx of sodium ions into the cell.This accounts for the"depolarization phase of theaction potential @ig. 16).

When the cell ismaximally dopolarizgd, SOdiumion+assagp-s-afipssgG and-poEssnruo-ious pass

ou!_g[_tbe_sell. This effects aglar]zqqbn ofthe cell membrane (Fig. l8).

Fig. 16.

Fig. 17.

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Fig. 18.

This sodium and potassium movement duringexcitation is passive, since both ions movealong a concentration gradient, but afterrepolarization there is an inracellular imbalancein comparison with the resting state - too manysodium ions intracellularly and too manylntassium ions estracellularly. In this situationlb necessary movement of ions must be active,because the movement is against the ionicmcentration gradient. SqdiUAjs gltrudeAlly@5qdg!q_pump, and the necessary energy isderived from the o&dalivg_4qClabOliSnl of@. 1e).

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Fig. 19.

A metabolic pump may also effect therestoration of the resting intracellular potassiumion concentration, because the necessarymovement is also against the concentrationgradient. Alternatively @tmay be effected along the electostatic gradientbetween the resting cell and its milieu. Thiswo.uld not reouire energv exDenditue.

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This localized change in electrical potentialacross the nerve mernbrane initiates a chainreaction which produces a sequential series ofdepolarizations along the nerve fibre' It is thisseries of depolarization steps which isresponsible for the propagation of an impulsealong a nerve fibre. In myelinated fibres these

changes in potential occur at the nodes ofRanvier. The nerve impulJe travels in a salatoryfashion from one node of Ranvier to the next(Fig.20).

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Fig. 20.

Fig.21.

In unmyelinated fibres no nodes of Ranvier exist.In these nerve fibres the impulse moves from theinitial area of depolarization to the next contig-uous segment of nerve. Thus, one depolarizedsegment of nerve activates the adjacent poladredarea (Fig. 2l).

20

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Blocking ofnerve conduction

Reversible block by the proper application oflocal anaesthetic agents is an invaluable clinicalaid. These anaestetic agents belong to thechemical groups of amino-esters, or amino-amides.

Amino-esters

O ,CH2-CH3

",* fN 8-o-"n,-cH2-N/ttttt

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Fig.22.

All local anaesthetics in this group in clinicaluse are esters of para-aminobenzoic acid. Thefirst was, procaine (1905), which was the standarddrug for more than 40 years, and is still in use. Ithas no topical anaesthetic properties (Fig.22).

Amino-amides

/cH' o .cHz-cHrE\t/(Ol NH-c-cHz-N\Yl 'ctt'-cn'

CH:

Fig.23.

The first commercially available agent in theseries of amino-amides was lidocaineGignogeine), which became available in 1944.Because of its significant pharmacologicaladvantages over procaine, lidocaine soon becamethe standard drug. It is still the most widely usedlclcal anaesthetic in dentisry. Lidocaine possesses

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d!,u"-E-ef*-r,.'\\,// ICHz CHz

br,, -"(Fis.24.

Another agent in these series is r.nepivacaine,.which is similar to lidocaine in many respectsbutl@@ig.2q.

3 ,,HNH_C_CH_N

CHr

Fig. 25.

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The most recent of the agents in this series ispilocaine, a compound similar to lidocaine. ItsIow systemic toxicity is the main clinicaladvantage of this potent local anaesthetic agent(Fig.25).

Structure-actiYityrelationshipsAll local anaesthetics in clinical use have atypical chemical alrangement - an aromatic andamine constituent connected by a chain. Thearomatic part of the molecule is responsible forthe l-ipophilic properties; the amine end isassociated with hvdrophilicitv. Changes in any ofthese portions will alter the characteristics oflipid/water solubility and protein-binding. Theconsequences of such changes will be an alteredanaesthetic effect Such alterations arereflected inchanges in intrinsic anaestetic potency, onsettime, duration of action, toxicity ratio, and rateof degradation.

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Pharmacodynamic aspects

Fig. 26.

Mode of ActionThe excitation process in the nerve membranecan be inhibited in various ways. Local anaesthg-

zation phase bv reducing the influx of sodiumiglq The potasium efflux, on the o , is

ofc@. The sequenceofevents is as follows: the reduction in cell mem-branetheT

sodium

Intrinsic potencyThe minimum concentration of a local anaes-ttreti npotential by the half of its amplitude within 5minutes is taken as the measure of the intrinsicpotency of the agent. Procaine is the least potentof the agents used in dental practice. Mepiva-caine, prilocaine and lidocaine are respectively,2,3 and.4 times as potent as procaine.

action potential is .

conduction (Frg.26).

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Thus there is no

Fis.27 .

Onset of blockadeOnset of nerve block is much the same formepivacaine,' prilocaine and lidocaine, butprocaine takes longer. Physico-chemicalproperties of the agents are probably responsible.Agents with high lipid solubility and low pKaact faster. At the physiological pH in the nerve,the base form of the agents mentioned abovepredominates. This form peneEat€s the connec-tive tissue barrier to reach the nerve fibres, andthis capacity for peneftation is dependent on thelipid solubility of the agent (Fig. 27).

Site of actionThe axon membrane is the site of action of localanaesthetic agents. It is highly probable thatthese agents interact wittr specific receptor sitesin the membrane. These are probably situated inthe vicinity of the sodium channels on both tlteexternal and the internal surfaces of the nervemembrane. Clinical local anaesthetics seem !oaffect only the internal receptor sites.

Sodium flux may also be hindered by lessspecific mechanisms. The hiehly lipid soluble

the lioid content ofand membrane

sage is

24

uqp4rqg (Frg. 28).

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Fig. 28.

Form of actionThe clinically used local anaesthetic agents existin solution both as f:eg_basg-lB) and as posi-tively charged=gg1tion1@H*). The equilibrium ofItese two forms is determined mainly by the pHof the solution and the pKa of the anaestheticagent. The latter is a constrant, characterizing theequilibrium of a particular compound. When pHmd pKa have the same value, the two forms (Bild BH*) exist in solution in equal quantities.The relative proportion of free bases and charsdcations is thus critically dependent on the pH ofthe solution. The free base penenates biological

rhisftrm which penerates the conrgeblh9_AlA4!. Equilibrium between base andcatron is re-established at fiie e,and the cations bind to the receptcns, effecting agductionbtock.

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Duratlon of blockLocal anaestlptics used in dentistry usually havea short duration of acfion, especially afterinfiltration methods and unless a localizing(vasoconstrictive) agent is added. This durationdepnds qthe concenration of the crogld-th9-elg!$-and the concenEation depends,

in turn, on the diffusion capracity of the anaesthe-tic asent- and the rate of elimination of theagent-Elimina-tion is the consequence of passive

diffusion of'the agent along a concentrationgradient away from the nerve to theexftafascicular space, and of absoption into bloodvessels in and around the nerve (Ftg. 29).

26

Techniques of regional

Fig. 30.

anaesthesia in dentistryPreparation of the patientAn injection may be routine for the dentist, butit is often an unpleasant experience for thepatient. Re-assurance, psychological support, isessential, and will increase the patient's confi-dence in his dentist (Fig. 30).

No particular formula is universally applicable.Some patients will gain confidence if a forthrightq4roach, fully informative with nothing hidden,is used. Sometimes fears cannot be allayed, andthe dentist must accept avoidance behaviouriclosed eyes, clenched fists, and breath holding)while giving the injection. Often such patientswill admit that the procedure was not as bad as

freyhdfearcd.Judicious use of premedication may help in

pre.paring a restless or frightened patient for aniljection, and allow the dentist more scope toprrctise his psychology. The ultimate success oflhe treatment depends heavily on a calm andconfident patient - the anaesthetic must beeffective, and it may be that the premedicationshould include an antianxiety agent.

27

Fig.31.

Position of the patientWhen possible, treatment should be given withthe patient supine, which entails little risk ofvasovagal attacks - hypotension and syncope(Fig. 31). Some physical or emotional condi-tions make the position impractical or impos-sible to use. For example, it is not suitable inpregnant women, in patients with someorthopedic disabilities, nor in those who simplycannot be trained, or psychologically reassured,so that they will accept treatment in the supineposition.

Fig.32.

Comfort to the patientTight fitting garments may partially obstruct theflow ofblood in the head and neck area. A blouseor shirt collar sholud be loosened to avoid thistrig.32).

The operation light should give good visibilityfor the dentist, but not blind the patient Gig.33).

Fig. 33.

28

Pre-injection topicalanaesthesiaUsing modern disposible n@dles, the actual painof penetration is minimal if the dentist'srechnique is in order. Distraction analgesia alsoblps. If the tissue are gently pressed at somedisance from the intended puncture site, or if thepatient's lip is lightly compressed, the perceptionof punc$re pain will be further diminished (Fig.v).

29

DurationDuration of topical anaesthesia is short. Despiteexperimentally demonsEated differences benveendifferent preparations, only exceptionally willmucosal analgesia persist for more than 10minutes.

We find topical anaesthesia ointment, spread ona cotton pellet, to be best. The dentist places thepellet at the desired site, and the patient holds irin place for the desirable minimum of 2 minutes.Before injection, the area is wiped with a drycompress to remove excess ointment and preventunfue qpread.

SIow injectionDespite adequate mucosal anaesthesia, pain maybe experienced not during punctue, but duringthe fluid injection, especially if this is made roorryidly.

pH

Local anaesthetic solutions with a vasoconstric-tor additive have a pH of 4, or even lower if theyhave not been properly stored.

Experimental studies show that plain solutionswith near normal pH tend to cause less initialpain on injection. The temperature of the injectedsolution was found to be not critical. Warmingof the solution to body temperature was withouteffect on the perception ofpain.

Ointment and sprayThe mucosa at the puncture site can be anaesthe-tized in advance by a suiable topical ointment orspray. The most effective of these topicalpreparations contain the base form of the localanaesthetic agent. Those containing the watersoluble hydrochloride salt have less of ttre baseform, and are, in consequence, less active (Fig.35).

Despite the proximity of the terminal nervetwigs near the surface of the mucosa, some timeelapse - at least 2 minutes - must be allowed ifttrc Oopical agent is to effectively block the painof puncture. Clinical studies of shorter periodsindicate that ttre mucosal block is inadequate, andany claims that a topical agent has a shorteronset of action than 2 minutes should be regardedwith scepticism.

Iocal anaesthetic sprays tend to taste badly, andmay induce salivation, especially if the spraycontacts the tongue. It is also difficult to restrictthe spray o the desired area, and its spread in theqguth elici8 strong taste reactions, especially inchildren.

30

Fig. 35.

Clinical requirementsfor local anaesthesiaSterilityIn principle, the adminisration of a local anaes-ftetic should be made under sterile conditions, asfor all other surgical procedures. The fact that itis practically impossible to achieve sterility inthe oral cavity does not relieve the dentist of hisprinciple responsibility. Great care must betaken, and everything ttrat can be sterile, must besterile. In practice, injections made into healthyoral tissues virtually never give rise to infection.If the tissue at the injection site, or in thevicinity, is infected, there is a distinct risk ofWead.

In the particular patient, for example a patientwith rheumatic heart disease, everything possiblemust be done. Even though the oral cavitycannot be sterilized the number of bacterialcolonies can be reduced by disinfection. Thisshould be done in the special case, prophylacticantibiotics given to cover the procedure.

Up to this point, the situation is one ofnecessary compromise, but no compromise isallowable in respect of the instruments. Theneedle and cartridge and syringe must beabsolutely sterile. 0.00004 ml of infected serumis all that is necessary to communicate serumhepatitis! A new sterile disposible needle a freshcarfidge, and a sterile syringe, are obligatory foreach andeverypatient.

It should not be necessary to emphasize thisfinther, but the use of "non-aspirating" cartridgesyringes is no safeguard. Blood is, in fact,aspirated in more than 30Vo of such cartridges(Fig. 36)! Therefore a new cartridge for eachpatient!

Fig.36.

The carridge system is better than the multipledose vial, but even with a cartridge, exta caremust be taken. The rubber diaphragm should berinsed in 70Vo alcohol, two minut€s before use.

Aspiration and injectionThe patient's dentures must be removed! Beforeinjection, control aspiration must always bemade. Thereafter, the injection should be givenwith as little pressure as possible. In general, thefluid flow will be virtually free, but injectionsinto the papillae and hard palate require somepressure. The mucosa of fte hard palate is tightlyadapted to the periost€um - inject slowly usingno more force than is absolutely necessary, and,normally, not more than0.2 ml of the solution.

Preparing the syringePrior to injection the rubber plunger of thecartridge should be displaced by slight pressureon the piston, because the plunger sticks to theglass during storage. If this is not done, therewill be a jerk at the beginning of the injection,and the patient will experience pain, because ofinitially too rapid injection (Frg. 37).

The air bubble in the cartridge should beexpelled so far as possible, at the same time.

Gas bubblesWhen carridges are used the actual needle cannotbe filled with the solution because of theelasticity of the rubber plunger, but the volumeis so small that this is of no consequence.

Larger air bubbles in the system must beeliminated to avoid the potential hazard of airinjection into a vein.

Fig.37 .

INITIAL PRESSURE

INJECTION PRESSURE

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32

Solution properties ofclinical importanceOnset timeAfter infilration of the solution, diffusion fromthe depot at the buccal fold to the apex of thetooth is rapid, especially in the frontal, and upperpremolar areas @g. 38). Modern solutions wotrwithin two minutes, and the amide localanaesthetics are virtually identical in their effecr,though differences can be demonsnated by refinedmethods. One preparation may work perhaps 15

seconds quicker than another, but this is of noclinical importance.

The onset of mandibular block takes longer,irrespective of the solution - about 3 to 5minutes.

SpreadGood spreading capacity can be an advantage,especially in the frontal area. One injection maycover several adjacent teeth. An injection at tlteapex of the upper lateral incisor induces pulpanalgesia in the npo adjacent teeth in about 80 %of subjects (Fig. 39). Good spread also helpswhen needle placement cannot be, or is not,ideal, and it has been proposed that a spreadingagent, e.g. hyaluronidase, be added to somedental local anaesthetic solutions. In someinstances this might be of use, but the logicalcorollary ofbetter spnead is reduced concentratimof the agent overall - also in the area whereoptimal effect is desirable.

Frequency of effectiveanalgesiaSolutions with an efficacy of less than 90Vo at avolume dosage of l-2 ml are of no interest inmodern practice. Most available solutions meetthese requirements, but there are exceptions.Lidocaine 27o with noradrenaline is only justadequate. Plain solutions of high concentrationre somewhat unpredictable.

Duration of anaesthesia may be very short" andeffects vary widely between individuals. It isimportant to realize that "failures" with thesesolutions are just as likely to be attibutable toduration of anaesthesia, as to failure because offrulty technique.

In regional blocks, e.g. mandibular, successdepends rather more on technique than on theproperties of a particular agent.

Duration of pulp anaesthesiaIocal anaesthetic solutions differ most in respectof the duration of pulp anaesthesia. A specificsolution with vasoconstric0or additives differingboth in concentration and type has differentdurations of action. Clinical documentation ofthis is difficult, but differences are clear whenBjdrn's electrical stimulation experimentalmethod is applied.

Infilration of 2Vo hdcr,arne containing 10-12.5pg/ml adrenaline, gives good pulp analgesia forabout one hour, though variation betweenpatients can be great.

If solutions containing higher percentages oflocal anaesthetic ale used, frequency of analgesiamay be slightly increased, while the duration ofanalgesia is not much prolonged.

In general, a fine balance between the concen-fiations of the local anaesthetic and is vasocon-strictor additive determines the duration of theanalgesia, whereas frequency of effect ispnmarily a function of anaesthetic concenfiation@ig. a0).

Exftemely lipid soluble local anaesthetics, e.g.bupivacaine and etidocaine, have longer durationofeffect, from 6-8 hours, when used for regionalblocks. This is an advantage when procedurcs arelong - extraction of an impacted lower wisdomtooth, for example, but the patient is forced toaccept numbness of the lips often over a longpostoperative period of time.

It is in general surgery, below the umbilicus,where these agents are of primary use. Anepidural block, for example, will give substantialanalgesia long into ttre postoperative period.

Fig. 40.

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33

Duration of soft tissueanaesthesiaThe persistence of soft tissue anaestlesia longafter the cessation of pulp anaesthesia is anundesirable side effect of dental local anaesthesiaPractically, nothing can be done about this if amandibular block is made, but, when infiltrationanaestlesia is used, the duration of numbnessdepends rather more on the choice of local anaes-

thetic. Thus, the duration of soft tissue numb-ness can be reduced by about an hour if a plainsolution (with no vasoconstrictor additive) isused. But this is not without cost! - the durationof pulp anaesthesia is also reduced (Ftg. 41).

Tissueconc.

Fis.42.

Injection techniqueSome practitionen inject a few drops under themucosa as soon as the puncture is made, andthen proceed each advance of the needle towardsttre target area with drop injections. This is notnecessary. It does not help because the analgesiaeffect is always delayed, and may in fact, cause

extra discomfort because of the distension of the

tissues. Fan movements of the needle in thevicinity of the target areil are also unnecessary.

Modern agents are fust spreading.So, in summary, the needle should be inserted

gently and directly in one continuous movement[o the trrget area, where, after careful aspiration,the injection should be made, exerting as littlepressure on the plunger as possible. Take time!

lvlanual dexterity is very important, both duringintroduction, and fixation of the needle beforeinjection is made (Fig.aD.

Fig.41.

34

SOFT TISSLJE ANAT-GESIA LEVEL

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rt

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e

gp

*;ffisfu*-**

Fig.43.

The fingers must provide a constant and stablereference and rest for the syringe. Any patient,apecially a child, may suddenly move ttre head.Use the teeth and face as anchor poins for thefingers of the injecting, and supporting hand.The method shown in the diagram is to berecommended (Fig. 43). Always precede aninjection by aspiration. Inject slowly so that nocounter pressure is produced. The hard palate andpapillae constitute exceptions because themucosa is tightly adherent to the periosteum.Some pressure is tirerefore necessary to effect theinjection, but use no more pressure than isabsolutely necessary. Inject slowly, and keep theinjection volume under 0.2 ml. Intravascularinjections are not uncommon in the palate. Becareful! A sudden loss of tissue resistence duringinjection may betoken vessel puncture, and,retrospectively, bleeding from the puncture sitewhen the needle is withdrawn.

@: "-€

<Y

de@ buckhiij

Fig.44.

Do not scrape the periosteum with the needlepoint (Fig. 44).

35

*+

.: =:==.. ..:

r:'.rl'*

Fig. 45.

Post-injection precautionNevs leave the patbns alme after an injection.Allergic or o$er reactions may occur instanta-neously at any time. Dentist or nurse mustalways be present, and modern anaestheticsolutions wsk so quickly that there is, today, noexcuse to leave fte parient (Frg. 46).

Fig.45.

Never introduce the tip of the needle into aforamen. Risk of damage to vessels and nerves isconsiderable. Haematoma, paraesthesia, andprolonged anaesthesia may result (Frg.aD.

36

Anaesthesiaof theupper jaw

37

General considerationsThe outer bone lamina covering the maxilla iscomparatively thin and in many areas- porous'

Thiifaciliates diffusion from an injection depot

over the buccal fold to the target area at the

apices of the upper teeth. To obtain an effective

biockade of t[e palatal roots of the molars,additional infiltration must be made at the palate

to block the fibres from the greater palatine

nerve.In many patients, the structure of the lower

border of ttte zygomatic arch is such that the

distance between the buccal fold, where the

injection depot is layed, and the buccalapices ofni not and second molars, is increased. Despite

this, the diffusion capacity of modem solutions

is virnrally always adequate, and anaesthesia., at

least good enough for routine cavity preparanon'

is achieved.As in the frontal area in the lower jaw, it is

very important to make needle contact wittr the

bone before injection of the solution. If this isnot ensured, th6 fascia of the circumolar muscles

will hinder diffusion to the apex of the tooth.Regional blocks in the upper jaw can-be used

to advantage, e.g. infraorbital block and the so-

called tuberosity bloct, especially in connectionwith surgical interventions. These areas are

highly viscular, and, particularly with theinFaorbital block, which necessitates injectionnear to a bony canal, a sound knowledge of the

anatomy is obtgatory.

38

Incisors andcanines

Anatomy of the upper front areaThis region is innervated by ttre superior alveolarnerves which branch off from the infraorbitalnerve just before it emerges from ttre infraorbitalcanal below the orbit. These branches supply theincisors and canines, the buccal gingiva and theperiosteum (Fig. a8). These nerves anastomoseover the midline. The palatal gingiva, mucosaand periosteum are innervated by ttre nasopalatinenerve which emerges from the bone through theincisal foramen. The medial spread of the localanaesthetic may be hindered by the labialfrenulum in the midline.

The maxillary bone is covered by a thin andporous lamina easily penerated by a local anaes-thetic solution injected at the level of the apices.

39

/-,.-t-/:J '- ) -.

#ffi,'ffiF,oaffi,c"

1/,

l.,i

,)

t

lu

fl/,'tJt

N

O buckhdJ-

the labial muscles (Fig. a9). Diffusion willhindered, and anaesthesia reduced. A tooinjection in this arda, especially at the

A too superficial placement of the needle Ientail that the point lies between the fasciae

Fig.49.

spine, may unduly distend, even tear the tissThe resultant pain may be particularly seYere'

40

Operative aspects

Cavity preparations and pulpsurgeryA buccal fold injection suffices for restorativework, and when making cavity preparations, itwill often be found that diffusion from a singleinjection is sufficient to cover the adjacent teeth,so that adjacent cavities may be prepared withoutfurther local anaesthesia procedure. If a rubberdam is used, a supplementary palatal injectionmay be necessary to relieve pain caused byligatures or clamps.

Surgical proceduresFor exftactions the palatal gingiva must also beanaesthetized. This is effected by supplementaryinjection at the edge of the incisive papilla(nasopalatine block) or for a single extraction, as

infiltration anaesthesia of the palatal mucosa near

the affected tooth. For apical resections, or inother cases where a flap must be raised during an

operation, complete anaesttresia must be attainedbefore commencing the operation, as it may bedifficult to supplement anaesthesia after the bonesurface has been exposed. In periodontal surgery(e.g. gingivecbmy), anaesthesia is produced byinfiltration into the operation field with aninjection in the buccal fold. Sometimes it maybe advisable to complete the local ischaemicdect by injecting a few drops of solution intothe papillae. This injection should be given afteranaesthesia has been attained by infiltration inthe buccal fold.

Sometimes there is a supplementary inner-vation from twigs of the nasopalatine nerve.These often account for unsatisfactory, incom-plete, anaesthesia of the field, but can easily beblocked by a swab soaked in topical anaestheticcream and placed ino the nostril.

4l

Fig. 50.

The injectionThe incisors and canines'of the upper jaw areusually anaesthetized by injections in the buccalfold (infiltration anaesthesia). The injection isapplied just adjacent to or mesial to the tooth.The needle is introduced near the bone, andpassed axially towards the apex of the tooth.This ensures minimal distance between needlepoint and the apex target area (Figs. 50 and 51):

If the needle is inroduced obliquely, the anaes-thetic deposition may well come to lie too farfrom ttre target area. When contact is made withthe bone, a slow injection of I-2 ml solution(Fig. 52) will effect anaesthesia of the targettooth, and one, or both, of the adjacent teeth.Central incisors are best anaesthetized by some-what distal injections, because of the proximityof the nasal spine.

Fig. 51.

Fig. 52.

42

Spread of analgesiaThe injection of a standard volume of 1-2 ml ofthe solution will ensure adequate analgesia of thetooth pulp in this area (Fig. 53 and 55). The rootof the canine is longer than those of the incisors

Fig. 53

and the apical part of the root is often distallyoriented. This must be kept in mind during theinjection of the solution.

The area of soft tissue anaesthesia correspondsto the coloured zone in the figures 54 and 56.

Fie. 55.

3/\

l

7>Ia'

l l

i

Fig. 54. Fig. 56.

43

\

F>ffi

Fig. 57.

The infraorbital blockIn certain cases, especially in connection withoral surgery, the anterior teeth of ttre upper jawcan also be anaesthetized by conductionanaesthesia, i.e. infraorbital block @igs. 57 ands8).

The intraoral technique is the simplest fordental purposes and is applied as follows.

O buckhcjr-

Fig. 58.

Fig.59.

The cenEe of the inferior margin of the orbit ispalpated with the index finger. The finger is thengently passed to a point about I cm below theorbital margin. At this point in most cases onecan detect a bundle of vessels and nervesemerging from the infraorbital foramen. Theindex finger is held at this point while the upperlip is lifted with the thumb (Fig. 59).

Fig. 60.

The syringe is held in the other hand and theneedle is introduced into the buccal fold directlyover the canine. The needle is gently pushedforward near to the bone towards the tip of theindex finger (Fig. 60). When the needle hasreached this site, aspiration is performed to verifythat the tip of the needle is not placed in avessel. About 1 ml of solution is slowly injectedThe index finger tip is kept in place during theinjection to control the deposition of thesolution. The puncture can also be made in thebuccal fold just over the first premolar where theunderlying bone is flat.

45

Fig.61.

Spread of analgesiaThe injection of 1.0 ml at the infraorbitalforamen will anaesthetize the teeth and bonewithin the coloured area (Fig.61)

Gingival and soft tissue anaesthesia afterinfraorbital block @ig. 62).

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Fig. 63.

The area of anaesthesia resulting whensupplementary block is made of the palatinenerves at fte ircisive 1ryilla, and at the majorpalarine fumen {Eg- 63).

To enwre csnplerc mffibesia of ttre medialincistr in fu sme qu*ant it may be necessaryto block anastomosing fibres from the dentalnerve plexus from the opposite side of themidline. In such cases fte infraorbital block issupplementd qith dout 0.5 ml of the solutioninFcted in fre cmtmtaceral buccal fold.

Fis.62.

46

@ buckh<ir-

PremolarsAnatomy of the premolar areaThe region is innervated by the superior dentalplexus, which is formed by convergent branchesfrom the superior, posterior, and anterior alveolarnerves (Fig. 6a). The presence of the middlesuperior alveolar nerve is irregular. Whenpresent, it innervates the premolars, the buccalgingiva and the periosteum around these teeth,and often the mesiobuccal root of the first molar.The palate is innervated mainly by the greaterpalatine nerve, but anastomosing branches fromthe nasopalatine nerve may occur in the area ofthe first premolar.

{J

t-

Diffusion of the solution from the depot in thebuccal fold is especially good in ihis area, so thatthere are no problems with the anaesthetizing ofthe palatal roots of the premolars.

The diffusion barrier is thin; the apices of theteeth lie very near the surface of the bonylamina. Small volume injection suffices.

I,,f'

Fig. 64.

O buckhot

47

Operative asPects

Cavity preparations and PulPsurgeryIn tliese Lases sufficient anaesthesia is obtained

by infiltration in the buccal fold. If bothpiemolars are to be anaesthetized, the solutionian be deposited in the apical region benpeen the

teeth.

Surgical interventionsA supplementary injection must be appliedoalataliv to anaesthetize the palatal soft tissues'

ilather than blocks of both the greater palatine

and the nasopalatine nerves' which practice

requires two injections, it is better 10 9trect- the

aeiired anaesthesia by one injection in the palatal

mucosa adjacent to the Premolars.

InjectionThe premolars of tlre upper jaw are anaesthetizedby infiltration in the buccal fold next to theteeth. Affer puncture, the needle is advancedaxially (Figs. 65 and 66).

1.0-1.5 ml of solution is deposited in the apicalregion of the premolars (Fig. 67).

Fig. 67.

49

:!.::r.:'{:r.

Fig. 58.

Supplementary injection inthe palateFor extractions and gingivectomy, the palatalmucos:l and gingiva arc most easily anaesthetizedby puncture at dght angles to the mucosa at apoint roughly one half the rooth height (Figs. 68and 70). Inject about 0.1 ml there (Fig. 69).

This injection obviates the need to block boththe nasopalatine and gfeater palatine nerves

Fig. 69.

I

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50

Fig.70.

4N-u-\:{l =:-.1'l [\

llI

Fig. 71.

Spread of analgesiaTeeth and bone anaesthesia after buccal foldinjection of 1.0 ml solution (Figs. 7f and72).

Fig.73.

Soft tissue anaesthesia (Fig. 73).After additional blocking of the palatine by

injection at the lingual side of the premolars@ig.7q.

:-- )-r

J'i

Fig.74.

5l

MolarsAnatomy of the molar areaThe molar region of the upper jaw is innervatedby the superior posterior alveolar nerve, whichbranches from the infraorbital nerve before itreaches the orbital cavity. These branches passdown the maxillary tuberosity, which they enterto innervate the upper molals, the buccal gingivaand periosteum in this region. The palatalgingiva, mucosa, and periosteum are supplied bythe greater palatine nerve, which runs from thepterygopalatine fossa, down the pterygo-palatinecanal, and passes through the greater palatineforamen to reach the hard palate (Frg. 75).

Fig.75.

52

The distance between the buccal fold and theapices of the upper molars varies from patient topatient. Sometimes tle lower margin of thezygomatic arch lies so low that the distance istoo great for adequate quantities of anaestheticsolution to diffuse from the buccal depot to theapical target.

I

Operative aspectsCavity preparations and pulpsurgeryEffective anaesthesia is usually obtained byinfilradon in the buccal fold next to the toothinvolved. In some cases it may be necessary 0o

supplement blocking of the palatal root by aninjection on the palatal side.

Surgical proceduresA supplementary block of the greater palatinenerve will also anaesthetize the palatal grngrvaand mucosa. See also "Incisors and canines".

The teeth can be anaesthetized by infilration inthe buccal fold" This applies also the 2nd and 3rdmolars, which used to be anaesthetized byregional block (tuberosity anaesthesia). Thisblock is no longer to be recommended due to theprescence of the venous plexus, increasing therisk fG intravascular injection. Best is a modifi-

cation which gives results equivalent to thoseobtainedby brccal fold infiltration. The injectionis made at the apex of the actual tooth - not inthe pterygopalatine fossa

Sometimes, and particularly when a recess ofthe maxillary sinus extends down between thebuccal and palatal roots, local anaestheticdiffusion from a buccal depot is impaired. Inthese cases a palaal injection should also beglven.

The tuberosity anaesthesia block (mentionedabove) was used especially when the infra-zygomatic crest was well developed; because thiscrest was reckoned to make infiltration anaes-thesia difficult. The vicinity of the pterygoidvenous plexus, however, entails that the tuberos-ity anaesthesia block is potentially hazardous,and it is relatively conraindicated because of therisk of inravenous injection and/or haematomaformation. If unavoidable, aspiration conrol andneedle tip connol mustbe extremely rigorous.

53

Buccal infiltrationInfiltation anaesthesia of the upper molars is

canied out by injecting close to the tooth.-The

buccal fold ii punctured somewhat mesially to

the tooth.The tip of the needle is then advanced upr,vards

and baikwards towards the apex until bone

contact is felt. 1-2 ml of solution is then injected(Figs.76-78).

If an injection is to be made in the distal aspect

of tft" ,ipp". jaw, it is advisable not to open the

patient's ^morin

too widely. If the mouth is too

*ia.ty opened the coronoid process of the

*-ALf. is moved ventally, and may cover the

injection site.

3g.r::B:::. I

Fis.77.

54

Thberosity injectionIf this injection cannot be avoided, the followingprocedure should be used: palpate the infrazygo-matic crest, as shown, and make the puncturedorsal to the retracting finger at, or slightly distalto, the second molar. Then advance the needlekeeping close to the maxillary tuberosity,inwards, backwards, and upwards, about 2 cm.Inject 1-2 ml of the solution (Figs. 79-81).Avoid the pterygoid plexus, and confirm this byaspiration, which is an obligatory safeguardbefore injection.

Fig. 80.

Numbness of the soft tissues (lip), often asubjective confirmation for the patient that he isanaesthetized, is often only slight or absent wheninjections are made into the buccal molar area.Inform the patient of this before stafiing theprocedure to allay false fears ttrat the anaethetichasnt worked.

Fig.81.

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Fig. 79.

t- -^ t',

Fig. 82.

56

/i

\

Supplementary blocking of thegreater palatine nerve

To anaesthetize the palaal gingiva and mucosa inthe molar region, insert the needle 0.5-1 cmabove the gingival margin at the second molarand at right angles !o the mucosa (Figs. 82 and83).

When the needle reaches bone withdraw it 1 mm,aspirate and inject about 0.1 ml (Fig. 84). Thiswill block the greater palatine nerve at its exitfrom the greaterpalatine foramen.

Fig. 83.

Fig. 84.

Fig. 85.

Spread of analgesiaTeeth and bone anaesthesia after buccal iniectionat the first molar (Fig. 85).

Gingival and soft tissue anaesthesia. Observerelative absence of lip anaesthesia @g. g6).

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Fig. 87.

Teeth and bone anaesthesia after tuberosityinjection of 1.5 ml of solurion (Fig. S7).

Gingival and soft tissue anaes0resia after tuberos-ity injection of 1.5 ml. Lip anaesthesia is inmany cases minimal (Fig. 88).

-)l-r

l\

i

@ bucllhcir-

={-r/i

it/

l-s )\

/'i

Fig. 88.

O buckh<iJ-

57

Fig. 89.

Teeth and bone anaesthesia after supplementaryblock at the greater palatine nerve (Fig. 89).

Gingival and soft tissue anaesthesia after supple-mentary blocking of the greater palatine nerve(Fie.90).

Anaesthesiaof thelower jaw

59

@ buckhijt

General considerationsBy contrast with the upper jaw, the roots of theprernolars and molan in the mandible are coveredwith a thick compact bone lamina, whichdectively prevents diftrsion of a local anaesthe-tic bolus near tlre apices. A proximal target area,before the nerve enters the bone, is thereforenecessary (Frg. 92).

lvlandibular block is only successful when thedentist is master of the anatomy of the area, andwhen the full cooperation of the patient isobtained.

General principles of local anaesthesia areinsufficient guides in the mandibular region. Onemust particularize. Thus, to anaesthetize the firstpremolar, a mental block is necessary, and thissometimes effects anaesthesia also of the secondpremolar. The mandibular bone here is thick andimpervious to diffusion. In the frontal area, theapices of the canines and incisors can be reachedby infiltration anaesthesia, because the buccalbone lhmina is relatively thinner and porous, andallows diffusion.

Fig.92.

60

Incisors andcaninesAnatomy of the lowerfront areaThe incisive nerve, a distal branch of the inferiordental nerve, innervates the canine and incisorteeth. Its coluse lies within the bone but it maybe anaesthetized by diffusion because thecovering bone lamina is thin and porous (Fig.93). The tip of the needle must be in conract

with the bone in the lower front area, becausediffusion will otherwise be hindered by the fasciaof the circumoral muscles, and the pulp andperiodontal anaesthesia will be inadequate.

The canines in children and adolescents, may beanaesthetized by infilration at the apex, because,here again, the bone lamina is thin. In adults thebone may become impenetrable, and a mandibu-lar or mental block is to be preferred.The anterior aspect of the lower jaw can also beanaesthetized by regional block, but there areoften anastomoses over the midline. These mustalso be blocked by bilateral infiltration, or bybilateral mental block.

\

Fig. 93.

6l

Fig.94.

The buccal soft tissues are innerYated by themental nerve while the lingual gingiva andperiosteum are supplied by the sublingual nerve

Fig. g+). The later is blocked by injection underthalingual attached gingiva at the apex of thetooth, or by similar injection at the premolarlevel.

62

Operative aspects

Cavity preparations and pulpsurgeryThese procedures may be conducted underinfiltration or conduction block anaesthesia. Ifpulpal ischaemia is desired, infiltrationanaesthesia is the method of choice, becauseconduction block at the mandibular or mentalforamen has only minimal effects on pulpcirculation, even though the solution contains avasoconstrictor.

Surgical proceduresFor extractions, the lingual gingiva andperiosteum must also be anaesthetized. This isdected by infilnation of the floor of the mouthon the lingual aspect of the mandible near thetooth. Avoid damage o the blood vessels in thefloor of the mouth.

63

---,F

The injectionWith the patient in a supine position singleincisors in the lower jaw are easily anaesthetizedby injecting through the buccal fold near thetooth (Fig.95).

Fig.96.

In a pauent siidng upright the needle is g,uided

fuom a larrC appoach. lnjection of the solutionis made during sithdra'*'al of the needle (Fig.

e6).If resistence Lq ielt during injection it may

mean that the needle rip is situated in a

circumoral rnusle la,'cia, ar some distance fromthe ideal zupraperiosteal prosition.

&

Fis. 97.

{f,xi

Supplementaryblocking of thelingual nerveThe lingual nerve is blocked by infiltration justunder the atrrched grngrva (Fig. 98 and f00).

tttr

65

Spread of analgesiaThe injection of a standard volume of 1 ml of thesolution will ensure adequate analgesia of thetoottr pulp and the bone in this area (Figs. f01and 102).

Fig. 102.

6

Fig. 103.

Gingival and soft tissue anaesthesia after buccalinfiltration @g. 103 and 104).

I

bt

I

PremolarsAnatomy of thepremolar areaThe premolar region of the lower jaw is innervat-ed mainly by the inferior alveolar nerve @ig. 1).The buccal grngiva in the premoldr atea is inner-vated by the buccal nerve, while the lingualgngiva is supplied by the sublingual nerve. Themental foramen lies just below and usuallybetween the apices of the premolars @g. 105).

Fig. 105.

67

The thick, compact mandibular bone sunoundingthe premolars makes the use of infiltrationanaesthesia in this area impossible. A mandibu-lar injection or a mental block must be used(Fig. 106).

6{rriil,'.,: i,riliir,-, t'df$,ti,"'. fil$i'ri

, ,'l 1 r'li'

Fig. 107.

From the mental foramen the mental nervespreads out in the buccal grngiva and innervatesthe lower lip, the mucosa and the skin (Fig.107).

68

The position of the mandibular, lingual buccaland mental nerves in the premolar area (Figs.108 and 109).

69

Operative asPects

Cavity preparations and PulPsurgerye, manditular block ensures effective anaesttresla

but if only the first premolar is to be treated, a

mental biock will iuffice. Irrespective of the

naurre of the solution, a mandibular block has

only a weak ischaemic effect on the tooth pulp.

Surgical proceduresIn mandibular anaesthesia, the lingual nerve san

be blocked by injection at the mandibulartemporal crest. This will anaesthetize the lingualsinsiva and oeriosteum in this area. The buccal

iodti.tu", are anaesthetized by injecting at the

buccal nerve or by local infiltration. These

injections may also be necessary as supplements

of a mentalblock.

70

Mental blockThe anatomical direction of the bony canal wherethe mental nerve is situated is medial-venfial-caudal @g. 110).

A needle oriented in this direction and insertedinto the bony canal may lacerate the nerve andblood vessels (see p. 99).

Even though profound analgesia may result,this procedure is not to be recommended. Aslightly larger injection volume will ensureadequate penetration of the mental nerve whenthe needle is inserted at an angle to the dircctionof the canal. This is a much safer procedure.

When a mental block is to be carried out, themental foramen is palpated with the index finger.The needle is inserted at an angle to the bony.canal at the mental foramen. After aspiration 1-1.5 ml is injected (Figs. 111 and lt2).

Mental block sometimes produces only partialanalgesia of the premolar pulps. The prefenedmethod is a block of the inferior alveolar nerve(mandibular block).

Fig. 112.

I

7l

Fig.11l.

g. 110.

/l'-

Supplementaryblocking of thelingual nerveThe lingual nerve is blocked by introducing the

needle just below the surface of the mucosalingually to the premolar (Fig. ff3 and- 114).

lUout ti.S mt of the solution is injected (Ftg.

rl$. Care should be taken not to damage the

blood vessels in the area. Fig. 114-

Fig. 115.

Fig. 113.

Fig.116. Fig. 117.

Some of the peripheral fibres of the buccal nervewill also be blocked by the injection ar rhemental foramen, anaesthetizing a comparativelylarge area of the buccal soft tissues (Fig. 117).

Spread of analgesiaA menhl nerve block will cause analgesia in thefirst and, in some cases, in the second premolar.Penetration of the medial constituents of theinferior alveolar nerve is poor, and, therefore, thecanines are sometimes not anaesthetized (Frg.116).

MoIarsAnatomical asPectsThe apices of the molars of the lower jaw are

embedded in thick compact bone, and innervated

by the inferior alveolar nerve, which passes inttre mandibular canal (Fig. 1).

Like the prunolrs, ttre molars cannot be anaes-

thetized by infiltration because of the massive

mandibular bone (Fig. 118). Analgesia of the

molars is thus only achieved by block of the

newe, before it enters the mardibular canal.

Fig.118.

74

I

L

Innervation of themandibleThe mandibular nerve (inferior alveolar nerve)innervates the teettr and the mandibular bonefrom the molar area to the mandibular midline(Fig. u9).

Fig. 119.

The lingual gingiva in the molar area is innervat-ed by fte lingual nerve, some branches of whichspread out ovsr the lingual mandibular mucosa(Fig. 120).

Fig. 120.

75

The terminal branches of the buccal nervepenetrate the buccinator muscle and innervate thebuccal gingiva in the molar area (Fig. 12f).

O h4ldrdi Fig. L22.

The mandibulr nd fie lingud nerves may beblockdby oe ini:abn" while the buccal nerverequires a sepae inlectim $ig. l?2).

Fig.121.

Special considerationsThe soft tissues in the vicinity of the injectionsite form a space, the actual position of whichvaries, somewhat, from patient to patient. Itshould be indentified and filled with anaestheticsolution (Fig. 123).

Fig. 123.

A common position of this space, projected overthe mandibular bone. Here demonstrated byinjection of a radioopaque solution (Ftg. lZ).

77

Fig. 125.

Minimum dosage calculations suggest ttnt thefull content of a cartridge is necessary to achive areliable mandibular block (Fig. 125). Lesservolumes give inconsistent results (126).

Fig- 126.

Operative aspects

Cavity preparations and pulpsurgeryIn these cases a mandibular block is used and noblocking of the lingual nerve is necessary.Ischaemia in the pulp cannot be expected.

Surgical proceduresRegional anaesthesia of the inferior alveolarnerve slpuld be supplemented by a deposition ofsolution at the lingual nerve.

The buccal soft tissues surrounding the molarsare anaesthetized by blocking the buccal nerve.

79

The mandibular blockDirect methodThe patient's mouth should be widely opened toensure good visualization of the anatomicallandmarks @ig.l27).

Fis. r27.

80

i

Fig. 128.

The coronoid notch is palpated with the lefrindex finger (Fig. 128).

Fig. 130.

With the syringe directed rom the premolarregion of the opposite side, the needle is insertedat the level of the index finger @g. 130).

In adults, the injection point lies about 1

centimeter above the occlusal surfaces of themolars and just medially to the index finger butlaterally to the pterygomandibular plicae @g.r29).

8r

,{

l

l

l

Fig. 131.

r

The pterygoid muscle is snetched and t€nse if ihemouth is widely opened, and particularly thetense liateral aspects of the muscle may hinderproper placement of the needle (Fig. 131).

82

Fig. 132

After imertin d fu db, insruct the patientto reduce the dcgre of mouth openingsomewhal This rdftres me of the pterygoidrcnsim (Fig- 132).

The needle is now advanced dorsally I.5_2 cmalong-the mediat side of *,e ,amus"b*i"itilt,procedure the needle should always be in

"8nl.tlvrtfr the bone of the ramus and fi. ,ning" f,!fain the original horizontal ppsition,"fiti"i t"'tt "occlusal plane @gs. 133_i34).

I r:.

E

83

;e

Fig. 136.

Fig. 135.

When the needle.meets resistance from themiddle section of the ramus witMraw the syringeslightly (1-2 mm) (Figs. 135-136) Carefullyaspirate and inject very slowly 1.5 ml ofsolution (Fig. 137).

Fig. 137.

I

!E-

84

Fig. 140.Fig. 138.

Blocking of the lingualnerveThe lingual nerve is blocked by injecting 0.4-0.5ml of solution at the mandibular temporal crest(Figs. 138 and 141).

The injection is made in conjunction with amandibular block. When withdrawing ttre needlefrom the mandibular foramen the fingual nerve isUtryte-{ at g point 0.5 cm mesially and ventrallyto the lingula (Figs. 139 and 140).

@ buckhdj

85

Fig. 141.

\/

Blocking of the buccalnerveThe buccal nerve can be anaesthetized byinfiltration. The mucosa is punctured just abovethe buccal fold near the third molar (Fig. 142).

Fig.142.

Fig. 143.

The needle is tren guided horizontally under themucosa in adisal direction towards the mandibu-lar ramrn, while simultaneously injecting a totalof about 0.5 ml (Figs. 143 and 144).

Fig. r44.

I

86

Fig. 145.

Spread of analgesiaA successful injection at the mandibular foramenwill anaesthetize the molars, premolars, canineand incisors on the same side of the mandibleFig. lat.

The coloured area shows the spread ofanaesthesiain the teeth, buccal gingiva, and the soft tissuesafter supplementary block of the contralateralmental nerve (Fig. 146).

I

t,ii

'i

Fig. 146.

Failure of anaesthesia

Variation betweenpatientsThe duration of operative anaesthesia may beunexpectedly short. It is clearly important thatthe treatment must be begun as quickly aspossible after the injection. Too long delay is, infact, the most common reason for failure of theanaesthesia. Infiltration anaesthesia should beestabished wittrin 2 minutes, and regional block(mandibular), within 5 minutes.

In young children, srnall volume injections aregiven. Both diffusion and absorption of theanaesthetic may be expected to be more rapid,and, again, there is the factor of biologicalvariafion. Duratln of anasbesia may be short,and the hrency period is also likely to bephorterttnn in an adull The trearment must be begun as

s(x)n as possible (about 2 minutes after injec-tion), especially after infiltration (Fig. 1a8).

Fis. r47. Fig. 14E.

r'l!

il

ii

ii

Intravascular injectionIf part or all of the injection is made intra-vascularly, there will be little or no anaestheticeffect (sed also page 92).@g. la9).

Fig. 149.

Injection into musclesThe correct placement of the needle point forinfilration anaesthesia is very near the bone andthe tooth apex. If the point lies in muscle, thediffusion distance, and the diffusion barrier, areboth increased. Anaesthesia may well beinadequate.

Individual reactionsAlways bear in mind that a dose adequate in onepatient, may be inadequate in another, not alonebecause of biological variation, but also becauseof negative conditioning or experience, anxietyorfear. The dentist must be a good psychologist.Practise understanding and re-assurance, and, insome difficult instances, have recourse to pre-medication.

89

Some reasons forfailure of mandibularblockBone contact musl be established beforeinjection. If this is not assured, the needle pointmay lie in the tissue medial to ttre mandibularramus - that is, in the medial pterygoid muscle(Fig. 150). The block is likely to be ineffective,and there is danger of severe and persistentpostoperative complications: local irritation ofthe muscle and trismus.

If the needle is passed yet deeper in this sameincorrect plane, the parotid gland or the greatvessels of the head and neck may be penerated.The certain establishment of bone contactensures against these contingencies.

If the needle point touches the mandibularnerve, the patient experiences parasthesiae - anelecric shock spread over the area of ilre nervedisribution. The needle must be withdrawn 0.5-1.0 mm. The nerve may be damaged byintraneural injection, and the symptoms are oftenperistent

Fig. 150.

90

h-

9r

Fig.151.

Injections into infectedareasThese injections should be avoided because theinfection may be exacerbated or spread. pH in aninfected area tends to be low, and anaestheticsolutions are less potent at low pH.

The problem of lack of anaesthesia by concom-itant infection is most frequently encountered inpulpitis cases, and by acute apical processes.

Do not infiltrate the infected area, but makeregional blocks of the relevant nerves at somedistance from the inflamed area @ig. 151).

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Toxic complicationsThe pharmacology is considered elsewhere. Localanaesthetic overdosage, or very rarely ahypersensitivity reaction, may induce symptomssimilar to those appearing due to toxicity. Theremay be convulsions, loss of consciousness andreqpiratory depression, or cardiovascular phenom- .

ena may predominate, presenting as circulatorycollapse.

Despite the fact that dental local anaestheticsolutions are highly concenEated, and injectedinto extremely vascular areas, toxic reactions arevery rare. They may also be of such shortduration that they are not even observed.

To avoid a toxic reaction, the practitioner mustbe completely familiar with the local anatomy,aspiration must be made before injection, andinjection must be made slowly. Tbke it step bystep, observing the patient with some vigilance.Use a stop watch to conEol the injection rate,and be prepared to stop the injection, instan-taneously.

AllergyAmino-amide local anaesthetics (lidocaine,prilocaine, mepivacaine) have largely replaced theester types (e.g. procaine, tetracaine), and thishas eintailed that allergic reactions are rarely seentoday. About 2000,000 dental local anaestleticinjections are given every day using the amidegroup members, but reports of allergic reactionsare very few and isolated. Thus, complicationsoccurring in the dental surgery are very unlikelyto be caused by local anaesthetics.

A preservative (methylparaben) is oftenincluded in local anaesthetic solutions, and suchallergic reactions as do occur, are more likely tobe caused by this substance.

Reports of unusual reactions should not benonchalized. If the history could fit, then thepatient should be refened for allergic testing.This can be done at most hospitals. If thefindings are negative, the patient is, virtuallycertainly, not at risk.

Drug interactionDrug interaction is a relatively new problem inmedicine and dentistry. In many cases, unex-pected effects may be observed. [n sorne patientsthe adminisration of two drugs will counteracteach other, while in others potentiation willacur. Potentiation of the blood pressure respon-se to noradrenaline, even in small dosage, occursin patients who are under treatrnent with tricyclicantidepressants.

This interaction is clinically important. Espe-cially if ttre local anaesthetic solutidn, contain-ing noradrenaline, is administered inravascularly.Fatal reactions have been reported.

Solutions containing adrenaline will onlypotentiate the blood pressure response to a lesserdegree, which is of minor clinical importance.Felypressin (Octapressino) has been found not topotentiate tricyclics.

Other vasoconstrictors have not been investi-gated in this respect, so their safety in patientson tricyclic agents is yet unproven.

MAOI (Monoaminooxidaseinhibitors) arepotentiated by indirectly acting sympatico-mimetic amines, (e.g. tyramine) but not bycaFcholamines (adrenaline and noradrenaline).'Thus, dental local anaesthetics, in general use,can be given with safety.

Long lists of drugs which may possiblyinteract with dental local anaesttretics have beenpublished, often in connection with advertising.This author is sceptical!

Theatment of generalcomplicationsStaff in all dental surgeries should be trained to

handle emergencies. An absolute minimum,*uit"*"nt ii a mask attached to a balloon with

*n=ittt artificial respiration can be given' The

oatient can be ventilated intermittently and

harassed personnel have just time o-callteJp or

make the^emergency telephone call (Fig' 152)'

Primarily, the vital functions must be

tnAntaned. Keep a clear airway, ventilate the

puti"nt, and give-heart massage if necessary fig'1s3).--Ir,iedicaments

are best given by experienced

medical personnel - a ftightened dentist may do

more harm than good - but there is one excep-

til". f the patien-t's s[ate is one of anaphylactic

rtro.t, adrenaline (epinephrine) TuI te.life-sauing, and it must be given,quickly, ideally as

;; i.;: injection, or ai an injection into the

trongue.--ffii fotto*ing emergency procedures should be

practised.

Lowered head PositionAn unconscious patient must immediately be

olaced in the supine position with the head lower'ttlan tfre body.

-Blood will thus flow from the

lo*". "*tt"tnities

o the brain. In most cases this

overcomes cerebral hypoxia and consciousness

;hr"t;. If the legs are -eievated

above the level ofittr tr"utt, this-will increase the volume ofciicotating blood and tend to raise the blood

pressure.' If consciousness is not restore'd practically

immeOiatety by these procedures with the patient

in O" "ttuit,

he should immediately be p]aced on

the floor. The non-elastic floor is a far more

Jiectine place for resuscitation procedures than

the soft dental chair.

Free airwaYsAny loose objects in the mouth (depfures' cotlon

torit,iariua L;e"to., etc.) must be removed at

;;;;. if dre pitient vomits, the mouth must be

cleaned, to avoid regurgitation' a.very senous

complication. A high capacity suctionapparatus

i; ;;rt useful ai it wilt remove fluid and

particles without gening obstructed'

Fie. 152. Fig. 153.

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Artificial respirationA patient in respiratory arest must be ventilatedimmediately, by the mouth to mouth or moutfrto nose method, if necessary, but better withoxygen given through a standard bag and maskresusciator, which are marketed by several firms.This gives more freedom of action for communi-cation of the necessary mea$res, and it is moreeffective.

Cardiac arrestThe patient is rapidly placed on rhe floor. Ifrespiration stops, the pulse must be examinedwithout delay. The simplest way is to feel for thecarotid artery in the neck. If no pulse is felt, theheart should be started again by a determinedblow with the clenched fist on the sternum. Theshock-wave produced by this on the heart mayinitiate the cardiac nervous system and start theheart functioning.

If the pulse is still not felt and the pupils aredilated, external cardiac massage must becommenced at once and lung inflation must becontinued. The procedures, themselves, aresimple, and all personnel should be familiar withthem, and practised in their use.

Local complicationsContaminated needleInfection may be hansmitted, most importantserum hepatitis.

Too rapid injectionThe tissues may be orn. This causes postope-rative pain, and necrosis may also occur, particu-la,rly in the firmly adherent palatal tissues.

Too large injection volumeThis may also tear the tissues, aspecially of thepalate. Give no more than absolutely necessary.

Infected areaAll injections into an infected area should bcavoided. This can generally be done byinfiltrating mesially and distally to the tooth obe operated upon, or by making a regional blockinstead of an infilration, as is the rule for acci-dent cases in hospital dental surgery.

Ion-contamination ofsolutionsIf vials are used, a faulty syringe-filling tech-nique entails risk of copper ion contamination ofthe solution.

When carridge syringes are left lying for somehours after loading and before use, copper ionsare freed from *re needle canal. These cause localirritation at the injection site. Oedema developsbut may not become apparent until2-3 days afterthe treatment. This may persist for a week orlonger, and is experienced and can be reported bythe patient as persistence in soft tissue anaes-thesia.

Laceration of a nerveNerves may be lacerated when making regionalblocks. The needle penetrates the nerval sheathwhich may be damaged. tf parasthesiae areelicited the needle should always be withdrawn alittle. If injection is made without withdrawal therisk of damage is greater.

Injections into restricted spaces, bony canals(the menal and palaal foramina and canals) areespecially dangerous. The nerves are easily

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damaged as are the investing venous and arterialplexi. Imal irritation anil prolonged anaesthesiawill result.

Laceration of an artery or aYeinExcept in the hard palate, arteries are seldompenenated by the needle because of the rathertough character of the artery walls. The risk ismuch greater with veins. InEavasal injections aremost common in mandibular blocks and intuberosity injections, where the veins form aplexus near the nerves. lvlandibular blocks cannotbe avoided, but tuberosity injections should bereplaced by local infiltrations in the posteriormaxillary region.

If a vein has been punctured, there will be animmediatg swelling in the injection area due toblood leaking out into the tissues.Generally no risk are involved and within a weekthe haematoma will have disappeared. Aspirationis of couse necessary to avoid a rapid absorptionof the local anaesthetic solution into the circula-tion, but it will not help in preventing thehaematoma if the vein has already been lacerated.

Injection into an artery causes ischemia disalto the puncture. The effect may be due to con-traction of the vessel by vasoconstriction or toreflex vasospasm.

Laceration of the periosteumThe periosteum is richly vascularized and rich innerve supply. It is very sensitive o physical andchemical trauma. Therefore one should be verycareful !o avoid any rough manipulation wittr ttreneedle. A contact should of course always bekept with the bone for orientation during, forinstance, the start of a mandibular block injec-tion. The dentist must therefore have a delicatetouch when making these injections. Thesymptoms from a rough needle contact with theperiosteum will be initial pain on injectionand/or postoperative pain in the injected area.Some[imes a swelling will also be observed.

Tbismusmore or less pronounced trismus and pain maysometimes occur after a mandibular injecton. Thesymptoms usually appear one or tWo days post-operatively and may persist over a fairly long

96

perid. It may be due to intramuscular injectioninto the medial pterygoid muscle. A simulta-neous infection will accentuate the local sidedect.

Bleeding at the injectionpointWhen a solution with a low vasoconstrictorcontent is used, there may be stght bleeding atthe point of injection. The slight localischaemic effect of these solutions cannot inhibitbleeding to the same extent as solutions withhigher vasoconstrictor content. The bleedingstops spontaneously after a short time.

Facial paresisThis is caused by inroducing the needle toodeeply in a mandibular injection, and thesolution is injected at the posterior margin of theramus. The paresis is manifested by the patient'sinability to frown, and move the lips on theaffected side. Recovery is usually as quick as anormal recovery from a local anaesthetic, but,occasionally, the symptoms persist for a longerperiod.