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Mandibular Anesthesia I: Pulpal Anesthesia

281

Mandibular block is the technique of choice for pulpal anesthesia of the mandibular molars and premolars. Infiltration is much less effective when applied to the mandible, owing to the higher density of the cortical bone in the mandible as compared to the maxilla (Table3.2, Chapter3), especially along the external oblique ridge. Mandibular block accounts for nearly 30% of all anesthetic injections performed in dentistry (Annex 1). Although it also known as inferior alveolar nerve block, the term mandibular block is more semantically precise because the block often involves not only the inferior alveolar but also the lingual and buccal nerves, and the nerve to the mylohyoid muscle.

Mental nerve block has been excluded from this chapter

because of its two disadvantages:

1) The mental foramen is difficult to locate. In clinical

practice, it takes a full minute or longer to find when sought with a needle between the apexes of the two premolars in over 40% of cases (Joyce and Donnelly1993).

2) The risk of introducing the needle to the mental fora-

men and injuring the vascular nervous package is high. Clinical studies have shown that there is a 23% risk of hitting (Lustig and Zusman 1999) and a 12% risk of damaging the mental nerve (Joyce and Donnelly1993). Buccal infiltration with potent a local anesthetic such as 4% articaine with 1:100 000 epinephrine (A- 100) is a technique more readily mastered that yields good results and entails lower risk.

Indirect mandibular block or the 1- 2- 3 technique, developed by Heinrich Braun (Lindsay1929a) and furthered by Guido Fischer since 1910 (Fischer1910), has likewise been excluded. Known by that name because it consists of a three- phase attempt to reach the groove of the mandibular neck (sulcus colli) indirectly by varying the direction of the needle in the soft tissue (Figure16.1), the technique calls for very thick, stiff caliber 20G needles (no longer in use)

that neither break nor bend. It is characterized by major disadvantages, including needle breakage, increased technique sensitivity, and higher probability of injuring the periosteum or the medial (internal) pterygoid muscle (Lindsay1929b). Although there are more modern variations (Clarke and Holmes 1959; Sittitavornwong et al. 2017), the 1- 2- 3 technique is of primarily historic interest and is seldom used today.

All the techniques listed below and described in this chapter are intraoral because extraoral approaches are mostly confined to hospital scenarios.

● Mandibular block for pulpal anesthesia of molars and

premolars via the:

○ conventional or direct approach ○ Gow- Gates approach ○ Laguardia–Akinosi approach

● Double infiltration for pulpal anesthesia of the anterior

mandibular teeth.

Mandibular Block: General Remarks

The first known mandibular block was performed by William Stewart Halsted on a medical student in 1884, who was administered 0.4 (Hall1884). There is no record of whether the technique was intra-

or extraoral, although the three techniques most

commonly used today are intraoral.

The primary but not the sole aim of all these techniques is to introduce enough solution to anesthetize the inferior alveolar nerve before it enters the mandibular foramen (Berns and Sadove 1962; Galbreath and Eklund 1970). Given that the inferior alveolar nerve fibers are myelinated, at least three nodes of Ranvier (Blair and Erlanger1939) or a total of 6 mm must be anesthetized since the nodes in this nerve are spaced at 0.5–1.8 mm (Rood1978a,b).

ml of a 4% solution of cocaine

Local Anesthesia in Dentistry: A Locoregional Approach, First Edition. Jesús Calatayud and Mana Saraghi. © 2024 John Wiley & Sons Ltd. Published 2024 by John Wiley & Sons Ltd. Companion website: www.wiley.com/go/Calatayud/local

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Figure16.1 Mandibular block, 1- 2- 3 technique. Source: Redrawn from Andlaw and Rock (1994).

Zone Anesthetized

The various mandibular block techniques anesthetize the following nerve trunks, although to varying degrees.

● The following areas are anesthetized by the inferior alve-

olar nerve (all in same side, ipsilateral):

○ Teeth, pulp, and periodontal ligament in the entire

hemiarch on the respective side; molars and second premolar (via the inferior alveolar nerve itself) and first premolar, canine, and incisors via the incisive nerve, a branch of the inferior alveolar nerve.

○ Interdental papillae, including fibromucosa, bone,

and periosteum to the midline.

○ Vestibule, via the mental nerve; fibromucosa (alveolar

mucosa and attached gingiva), bone, and periosteum in the area between the premolars and the central incisor, including the molar zone in the 10% of cases where the buccal nerve is scantly developed (Hendy and Robinson1994); the skin over the ipsilateral half of the chin and in particular half of the lower lip, from the corner of the mouth to the midline, denoting successful anesthetization of the alveolar nerve.

● The lingual nerve affects the lingual side fibromucosa

(alveolar mucosa and gum), bone, and periosteum of the teeth, along with half of the floor of the mouth and the front two- thirds of the tongue on the side involved.

● The buccal nerve inneravates the following structures (all

ipsilaterally): the buccal fibromucosa (alveolar mucosa and attached gingiva), bone, and periosteum of the retromolar triangle; side of the lower molars (reaching the second premolar in 5%) (Hendy and Robinson1994).

● Other nerves proximal to the inferior alveolar nerve may

also be anesthetized:

○ The auriculotemporal nerve, innervating the skin in the

temporal region, in some cases as far as the border of the parietal, masseteric, frontal, and supraorbital regions. This nerve is only anesthetized in 20% of cases due to migration of the anesthetic, the odds of which are increased if the patient is in a reclined position (Kim etal.2003).

○ The mylohyoid nerve, primarily a motor nerve and

branch of the mandibular division of the trigeminal nerve, is located on the floor of the mouth. It also innervates the anterior belly of the digastric muscle; when anesthetized, the patient may feel discomfort during swallowing. The nerve to mylohyoid may provide supplemental innervation to the pulp of the posterior and anterior teeth on the side in question and even the contralateral incisors (Chapter3), as well as sensory innervation to the skin on the chin (Roberts and Harris 1973).This nerve trunk is frequently anesthetized in mandibular blocks.

Factors toConsider forthe Mandibular Block

The factors that affect the scope and limitation of the mandibular block are discussed in this section.

Efficacy is Correlated tothe Location ofTooth inthe Mandible

Mandibular block delivers acceptable results in molars and premolars (Table16.1). Pulpal anesthesia is successful in 60–70% of cases involving the posterior teeth within

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Mandibular Block: General Remarks 283

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Table16.1 Degree (%) ofpulpal anesthesia inlower teeth 10 and15 minutes after injecting one (1.8 ml) or two (3.6 ml)

cartridgesofa standard Leffect electric pulp tester data (see Annex 25).

Tooth

Posterior (M and PM) 60% 65% 80%/40 min 65% 70% 80%/40 min Lateral incisor 30% 35% 55%/40 Central incisor 10% 15% 25%/30

M, molar; PM, premolar.

10–15 minutes after injection of 1.8 or 3.6 ml of standard solution (2% lidocaine with 1:100 In contrast, as the results are poor in the anterior teeth

100 solution forconventional mandibular block, aswell asmaximum success rate (%) andtime ofpeak

1.8 ml 3.6 ml

Time after injection

000 epinephrine, L- 100).

Maximum success

min 30% 40% 55%/40 min min 15% 25% 35%/40 min

waiting 40 same applies to the soft tissue anesthesia peaking in the

Time after injection

Maximum success10 min 15 min 10 min 15 min

minutes is not normally practical today. The

lower lip after 40 minutes (Hersh etal.1995).

(Table16.1), mandibular block can be said to be effective in posterior mandibular teeth only.

High Failure Rate

As mandibular block is characterized by a high failure rate even in posterior teeth, it must be reinforced, as discussed later.

Unreliability ofLower Lip Anesthesia

An anesthetized lower lip is indicative of anesthesia of the mental nerve which innervates it but not of mandibular dental pulp (Annex 25). A numb lower lip is specific but not sensitive: its absence definitely indicates that the pulps are not anesthetized, but its presence is not a reliable indicator that the pulps are anesthetized (Chavarria- Bolaños etal.2017). In other words, a numbed lower lip is a necessary but not a sufficient indication of pulpal anesthesia.

Sequential Nature

The lower lip and teeth are anesthetized sequentially. The lower lip is anesthetized first, followed by pulpal anesthesia of the molars, premolars, and anterior teeth in that order (Table16.2). The conclusion is that anesthetic onset is longer than previously thought. Clinicians should wait at least 10–15 minutes after administering the anesthetic, which is when pulpal anesthetic onset is most rapid. After that time, anesthetic onset continues but much more slowly (Annex 25).

The Longer theTime, theMore Intense theAnesthesia

In 80% of cases, maximum pulpal anesthesia in posterior teeth is attained after 40 minutes (Table 16.1), although

Minor Effect ofthe Type ofAnesthetic

In mandibular block, the different local anesthetics available have little impact on success and all are effective (Annex

24). A mandibular block is effective if the anesthetic is injected close to the inferior alveolar nerve, spanning the lingula and a few aponeurotic membranes, to position the solution in a place from which it can spread passively toward the nerve essentially unobstructed. That is not the case in buccal infiltrations, in which the potency of the anesthetic is instrumental to efficacy because the solution must cross barriers (periosteum, cortical, and spongy bone) to reach the dental apex and anesthetize the pulp. In mandibular blocks, other factors such as accessory pulpal innervation (mylohyoid nerve, buccal nerve), anatomical variations (high lingula, double alveolar ducts), and the greater complexity of the technique affect the outcome, inducing failed pulp anesthesia even when the inferior alveolar nerve is successfully blocked (deeply numbed lower lip).

The anesthetic of choice for mandibular blocks is 2% lidocaine solution with 1:100 000 or 1:80 000 (L- 100 or L- 80) for the following reasons:

● It is just as effective as even the most potent solutions (with

high anesthetic or vasoconstrictor concentrations) such as

4% articaine with 1:100 000 epinephrine (A- 100) or 2%

lidocaine with 1:50 000 epinephrine (L- 50) (Annex 24).

● Lidocaine is less concentrated, which means that more

volume can be administered before reaching the maxi-

mum recommended dose (MRD). In more concentrated

local anesthetics, such as 3% mepivacaine or 4% artic-

aine, the MRD is achieved at a lower volume. For patients

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Table16.2 Reported and mean electric pulp tester- measured times (minutes) of lower lip and pulpal anesthesia in first molar

(first M), first premolar (first PM) and lateral incisor (LI).

Lower lip

Reference Sample size

Vreeland etal. (1989) 30 8.8 6.2 8.4 — 13.2 Chaney etal. (1991) 30 4.7 7.7 8.2 10.2 13.0 Hinkley etal. (1991) 30 6.1 10.6 8.8 10.6 12.3 McLean etal. (1993) 30 5.0 10.7 10.8 11.8 17.8 Kanaa etal. (2006) 38 — Steinkruger etal. (2006) 51 — Steinkruger etal. (2006) 51 — Goldberg etal. (2008) 40 — Kanaa etal. (2009) 36 —

Mean 6.2 8.8 8.3 9.9 13.6

weighing at least 70 kg, up to 8.5 cartridges (1.8 ml) of 2% lidocaine can be administered as the maximum dose (Annex 10), whereas with other solutions only 5.5 to seven cartridges can be injected. This is especially important when treating small children, as local anesthetic overdose and toxicity is more of a concern.

● It has been listed by the US FDA as pregnancy risk

B (safe).

● There is less risk for neurotoxic injury to the inferior

alveolar nerves when applied as a block. This is not a property that is inherent to lidocaine, but rather due to the lower lidocaine concentration (2%), as compared to 4% solutions of articaine and/or prilocaine, which has been implicated in such side effects (see Chapter22).

— 5.4 8.9 13.3 — 8.8 10.8 13.0 — 9.2 10.8 13.0 — 8.0 7.0 12.0 — 6.8 8.9 10.9

anesthesia is necessary. This procedure was initially believed to entail the risk of serious consequences, such as soft tissue (tongue and lip) injury due to inadvertent biting or discomfort for patients (i.e. dysgeusia, dysphagia as the tongue is anesthetized.) Nonetheless, the only problem reported to date is minor discomfort when swallowing or drinking (Adatia and Gehring 1972). Even in children, bilateral mandibular block has been found (antito lead to less selftwo reasons: (i) as bilateral blocks entail more extensive, lengthier treatment, the child’s soft tissues are anesthetized for less time after leaving the dentist’s office and (ii) as the soft tissue anesthesia is felt symmetrically, children are less inclined to explore and bite the tongue and cheeks, as they

First M First PM LISubjective Objective

intuitively)

injury than its unilateral counterpart for

do not feel a contrast in sensation between the two sides

Impact ofthe Volume Injected

(College etal.2000).

As Table16.1 shows, injecting two cartridges of the standard solution (3.6 ml of L- 100) improves pulpal anesthesia after 10–15 minutes in 5% of posterior teeth (Annex 25).

Long, Caliber 25G Needles

Mandibular block should be performed using caliber 25G needles (a slightly less optimal alternative is caliber 27G, in

Minor Effect ofthe Specific Mandibular Block Technique

The Gow- Gates technique was initially believed to deliver better results than the conventional or direct technique, but as discussed throughout this chapter that has not been proven. Overall, the conventional or direct technique affords the best clinical results of the three mandibular block approaches (Table16.3) and is the easiest to master.

as much as 25G needles are not readily available today) for the following reasons (see Chapter11):

● They deviate less across the linear insertion.

● They ensure good aspiration.

● They do not cause more pain (pain myth, Chapters 11

and13).

● They are less likely to break.

The 25G needle must be of sufficient length to traverse

Bilateral Mandibular Blocks

Bilateral mandibular blocks (on the right and left sides simultaneously) can be utilized when bilateral mandibular

20–30 mm of soft tissue before reaching the target and should never be inserted into the soft tissue up to the hub because they are more liable to break.

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Table16.3 Comparison ofconventional, Gow- Gates, andLaguardia–Akinosi mandibular block techniques:

clinical variables.

Mandibular block technique

Laguardia–

Variable

% Positive aspirations 10% 5–10% 5% Annex 22 % Lower lip failure

min

After 5 After 10

min % Lingual nerve anesthesia 95% 80% 85% Annex 29 % Buccal nerve anesthesia 60% 70% 70% Annex 29 Grade A anesthetic efficacy 85% 80% 80% Annex 30



10%



30%

Akinosi

 30% 20%

ReferenceConventional Gow- Gates

 Annex 28

Slow Injection

As noted in Chapter13, the injection speed presently recommended is 40–60

● Reduce pain because tissues are not distended abruptly.

● Reduce toxicity in the event of intravascular injection.

seconds for a 1.8- ml cartridge to:

ure for preventing adverse reactions, more even than aspiration (Malamed2004).

● Enhance clinical efficacy. Higher pulpal anesthesia suc-

cess rates according to clinical trials (Kanaa etal.2006).

Mandibular Block: Conventional orDirect Technique

The conventional or direct technique, also denominated the classic or standard (or inferior alveolar nerve block), is much more commonly used than others worldwide because of its greater efficacy and relative simplicity. It consists of inserting the needle, directed from the lower premolars on the opposite side, into the pterygotemporal depression and subsequently into the pterygomandibular space (Figure3.14, Chapter3) and from there to the sulcus colli in the ramus of the mandible above the lingula (Figure 16.2), where the anesthetic solution is deposited and where the inferior alveolar nerve lies in a wide open mouth. It is called “direct” because the needle is inserted directly to the target, with no need for prior maneuvering.

This technique was initially introduced by Parisian clinician Pageix in 1906, although he directed the needle from a point on the midline too high (15–20 plane (Lindsay1929a). Boris Levitt (NewYork) developed the technique as it is known today (Levitt 1924), while Ashley Lindsay (Toronto) was instrumental in its popularization (Lindsay 1929a,b). Nonetheless, a host of minor

mm) over the occlusal

Figure16.2 Sulcus colli above and behind the lingula, where

the anesthetic solution is deposited in conventional

mandibular block.

variations on the technique are in place and each dentist could almost be said to have their own.

Distribution ofthe Anesthetic Solution

The anesthetic solution normally spreads rapidly across the pterygomandibular space and it remains there for several minutes (Petersen 1971). It is confined between the anterior and posterior edges of the ramus of the mandible, although the course taken cannot be predicted because the path of least resistance is determined by the fascial planes

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and the structures inside the pterygomandibular space (Berns and Sadove1962; Galbreath and Eklund1970). That said, it tends to travel upward and backward (sigmoid distribution) (Berns and Sadove 1962; Galbreath and Eklund1970; Petersen1971), therefore the success rate is lower if the anesthetic is positioned too high and too far back of the inferior alveolar nerve (Galbreath and Eklund1970; Petersen1971). In such situations, while the solution tends to spread to the parapharyngeal space, it does so more slowly (Petersen1971).

The greatest factor in achieving a successful direct mandibular block is the position of the needle, which must be as close as possible to the beginning of the mandibular foramen and behind and close to the lingula (<5 mm), but this does not guarantee a perfect success rate (Berns and Sadove 1962; Galbreath and Eklund 1970). In contrast, placing the tip of the needle more than 5

mm away from and behind the mandibular foramen is associated with a large number of failures (Berns and Sadove1962; Galbreath and Eklund1970; Petersen1971).

Zone Anesthetized

The zone anesthetized is as described in the general remarks, although the degree to which each element is numbed varies from one technique to another. All techniques must anesthetize the inferior alveolar nerve, often indicated by soft tissue (the lower lip ipsilateral to the injection site). In 95% of cases, the lingual nerve is also anes- thetized with this technique and the buccal nerve in 60% (Table16.3 and Annex 29).

Technique

● Use a long (35–42 mm) needle, given the depth of the

insertion. Caliber 25G is ideal because it affords good aspiration and as it is thick and stiff, it deviates very little. If caliber 25G is not available, 27G can be used, although this is less effective because deflection is somewhat greater.

● Solution. In most cases standard 2% lidocaine with

000 (L- 100) or 1:80 000 (L- 80) epinephrine is the

1:100 option of choice (Annex 24).

● Patient positioning ○ Supine or semisupine in dentist’s chair. ○ Mouth opened maximally throughout the injection to

facilitate direct visualization of intraoral landmarks and ensure that the inferior alveolar nerve lies against the sulcus colli on the inner side of the ramus of the mandible (target area).

○ Head turned slightly to the same side as the side being

injected (i.e. right in rightleft-

side blocks).

○ Tongue at rest and low in the posterior part of the

side blocks and to the left in

mouth (Keetley and Moles2001).

● Dentist’s position and position of the non- dominant

hand (i.e. left hand in right-

handed clinicians), depend-

ing on the side to be anesthetized

○ Right side:

○ Dentist at 8:00 o’clock. ○ Index finger in the patient’s mouth (Figure16.3). ○ All other fingers stretching across the patient’s face

to block their vision and control the position of the mouth.

Figure16.3 Index figure of non- injection hand inside patient’s mouth for approach from right side, with other fingers stretched

across patient’s face.

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○ Left side:

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○ Dentist at 9:00–10:00 o’clock. ○ Thumb of the non- dominant hand in the patient’s

mouth, requiring the right-

handed dentist to pass

their left arm over the patient’s forehead (Figure16.4).

○ Dentist’s non- injection palm and wrist blocking

patient’s vision.

● Intraoral finger or thumb. The finger in the patient’s

mouth should rest on the anterior edge of the ramus of the mandible, in the concavity known as the coronoid notch

(Figure16.5). It should also be parallel to the occlusal plane of the mandibular molars to:

○ Bring the pterygotemporal depression into view. ○ Help visualize the zone and locate the needle inser-

tion site.

○ Tighten and stretch the soft tissue to make needle

insertion less traumatic. In 10% of cases the coronoid notch cannot be readily reached because it is underdeveloped or the adjacent soft tissue is very thick (anterior edge of the temporal muscle or adipose tissue and mucosa) (Angelman 1945). In such cases, clinicians should gently exert greater pressure to palpate the area and identify the anatomic landmarks.

● Insertion zone. The insertion zone lies in the ptery-

gotemporal depression, which consists of a fold or cleft in the oral mucosa that is elliptical and elongated in shape and runs parallel and outside to the pterygomandibular raphe or ligament (medial limit) (Figure 16.6) (Khoury etal.2011). Its lateral limit is the deep tendon

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ronoid

notch

Figure16.5 Intraoral index finger or thumb resting on

the anterior edge of the mandible in the hollow of the coronoid notch. Source: Redrawn from Evers and

Haegerstam (1981).

Tempora crest

Figure16.4 Thumb of non- injection hand inside patient’s mouth for approach from left side, with dentist’s palm and wrist blocking

patient’s vision.

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distinguish (Lindsay1929b). In such cases, the tip of the intraoral finger should stretch the proximal buccal mucosa and insert the needle outside the pterygomandibular ligament (always present), in the area where the vertex of the pterygotemporal depression is assumed to

Pterygotemporal

depression

Area of coronoid

notch

lie (Lindsay1929b).

● Injection height. ○ A site around 10 mm above the occlusal plane of the

mandibular molars is recommended because in 95–100% of cases this ensures by-

passing the lingula

(Table3.7, Chapter 3), leaving the path to the sulcus

erygomandibular

ligament

colli clear.

○ The exception is the occlusal plane of the third molar

(wisdom tooth), unless it is aligned with the other two molars (Bremer1952). The occlusal plane of the premolars can also be used as a reference if the molars are

Figure16.6 Pterygotemporal depression outward of the

pterygomandibular ligament or raphe.

missing.

○ One aid to finding the insertion height is, as noted ear-

lier, to draw an imaginary line backwards down the middle of the finger on the non- injection hand (that rests on the coronoid notch) toward the pterygotemporal depression (Figure16.7) (Angelman1945).

● Modification of the injection height. ○ It should be higher (>10 mm) in:

■ Toothless patients, for as the alveolar ridge is reab-

erygomandibular

ligament

sorbed, the lingula is higher.

■ Patients with a wide gonial angle and wide ramus of

the mandible, typical of class III Angle’s malocclusion

Pterygotemporal

depression

with mandibular hyperplasia (Hetson etal.1988).

○ It should be lower (<10 mm) in:

■ Children under 10 years and especially children

under 6

years (Benham1976) (Table3.8, Chapter3)

(Figure16.8).

■ Patients with a narrow gonial angle and ramus of

the mandible, typical of class II Angle’s malocclusion with mandibular hypoplasia (Hetson etal.1988).

Figure16.7 Needle insertion site in conventional technique

outside the pterygomandibular ligament, in the pterygotemporal depression, around 10 mm over the occlusal plane of the mandibular molars, with imaginary line projected distally from mid- finger to help find the insertion site.

○ Some clarifications are in order regarding modifica-

tion in height.

■ In patients with a wide gonial angle and narrow

ramus of the mandible or vice versa, the needle insertion height should be 10 mm.

■ Between its posterior and anterior the ramus of the

that attaches the temporal muscle to the temporal crest, exactly where the finger is rested on the coronoid notch (Figure3.14, Chapter 3) and thus highlights the ptery- gotemporal depression.

Some clinicians draw an imaginary line along the mid-

dle of the intraoral finger, parallel to the occlusal plane, and project it distally to pinpoint the insertion site (Figure16.7).

In children under the age of 7 years (Via1953) and in

35% of adults (Angelman 1945) this depression and its vertex lie under a mucosal pad and are difficult to

mandible is 30 mm wide on average, ranging from 20 to 40 mm (Table3.6, Chapter3).

■ The gonial angle is 120° on average, but may range

from 93° to 143°.

● Syringe direction. ○ In around 90% of cases the syringe is positioned over the

mandibular premolar zone on the opposite side, with the needle traveling toward the pterygotemporal depression and touching bone at the sulcus colli.

○ The divergent angle between the ramus of the mandi-

ble and the sagittal or medial plane is 0–27°

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(a)

(c)

0° angle (parallel)

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27° angle

(b)

Figure16.8 Height of lingula relative to occlusal plane in

year- old child, (b) 8- year- old child, and (c) adult.

(a) 4-

(Figure3.11, Chapter3). In the nearly 10% of cases where it is greater than 18° (Simon and Kömives1938), the syringe must be positioned further back to reach the sulcus colli, alongside the mandibular molars, for with such a wide angle, if it lies above the premolars the needle would run behind the ramus of the mandible without touching bone (Figure16.9).

● Needle insertion. The following is recommended to min-

imize discomfort associated with injection:

○ The intraoral finger should stretch and tighten the

mucosa overlying the pterygotemporal depression.

○ A light but firm tap followed by quick insertion is

regarded as the optimal technique. The site is lightly but firmly tapped with the non- dominant hand while at the same time quickly inserting the needle to hit

Figure16.9 Syringe positioned at contralateral mandibular

molars (rather than premolars) when the divergent angle of the ramus of the mandible is >18° (conventional approach). Source: Redrawn from Roberts and Sowray (1987).

bone. This maneuver is crucial because if the pain threshold’s peak traumatic stimulus (the needle advancing through the soft tissues) lasts too long it will exceed the initial threshold, giving rise to pain (Fuller etal.1979). Slower insertion triggers the initial threshold and if a few drops of anesthetic are injected as the needle advances the pain rises (Nusstein et al. 2006; McCartney et al. 2007; Chapter13 Appendix); moreover, the anesthetic does not take immediate effect. The factor that causes most pain in truncal blocks is needle movement (Annex 23).

● Insertion depth. ○ The insertion depth is the distance between the ante-

rior edge (pterygotemporal depression) and the sulcus colli, where the inferior alveolar nerve lies in a wide-

open mouth. That distance is around 20–25 mm, rang- ing from 15 to 30 mm (Table 16.4), and in children under 6–8 years old it is 15–20 mm.

○ Inserting the needle into the hub is a technical error

for two reasons: this is the weakest area and may result

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Mandibular Anesthesia I: Pulpal Anesthesia

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290

Table16.4 Needle insertion depth insoft tissue inconventional mandibular block.

Reference Sample size Factor assessed Mean (mm) Range (mm)

Angelman (1945) 300 Patient — 18–33 Bremer (1952) 100 Dry mandible 24

± 3.1 16–32 Waikakul and Punwutikorn (1991) 68 Patient 20–25 — Kronman etal. (1994) 39 Corpse 22 ± 1.8 15–28 Delgado-

Molina etal. (1999) 246 Patient 21 10–34 Hannan etal. (1999) 40 Patient 19 18–20 Tofoli etal. (2003) 20 Patient 20–25 — Simon etal. (2010) 38 Patient 19 ± 3.2 —

Mean 21.7 15.4–29.4

Rounded mean 20–25 15–30

in needle breakage as well as the fact that the depth is excessive to hit the landmarks for anesthesia of the inferior alveolar nerve.

○ The insertion depth may vary (Angelman 1945)

depending on:

■ The divergent angle between the ramus of the man-

dible and the sagittal or medial plane; the greater the divergent angle, the deeper the insertion.

■ The width of the ramus of the mandible; the wider,

the deeper.

■ The thickness of the mucosa and adipose tissue that

comprise the wall of the pterygotemporal depression; the thicker, the deeper.

○ Interestingly, the dimensions in a given individual

may vary by 1–4

○ If the needle is not successfully inserted because it fails to

touch bone after 30 soon, in less than 15

mm between sides (Angelman1945).

mm or because it touches bone too

mm, the recommendation is to

aspirate and slowly remove the needle, injecting 0.25 to

0.5 of a cartridge (0.5–0.9 ml) to anesthetize the pterygomandibular space and facilitate a second, less painful maneuver in a second attempt after a 1- minute wait.

● Pre- injection aspiration.

○ Once bone has been reached with the tip of the needle the

clinician should avoid exerting undue pressure to prevent injury to the periosteum (causing post- injection pain) and barb formation on the tip of the needle. If a barb forms outwardly, when the needle is withdrawn from the pterygomandibular space, the following structures may become injured: nerves (leaving persistent paresthesia in the lingual or inferior alveolar nerves), muscles (trismus due to injury to the medial pterygoid or temporal muscles), and the inferior alveolar artery and vein (hematoma) (Stacy and Hajjar1994).

○ After touching bone the needle is drawn back 1–2 mm

to aspirate. Aspiration is positive in 10% of cases (Annex 22), one of the highest rates in dental local anesthesia.

● Injection of the anesthetic solution and lingual nerve

anesthesia.

○ A 1.8- ml cartridge should be slowly injected, in 40–60

seconds. To anesthetize the lingual nerve the needle is slowly withdrawn along the same path as it was inserted through; at mid-

distance and prior to remov-

ing the needle, a second aspiration is performed and

the last ±0.3

ml in the cartridge is injected to anesthe-

tize the lingual nerve.

○ In the absence of this maneuver, the lingual nerve is

often anesthetized by diffusion across the pterygomandibular space. However, this maneuver ensures anesthesia of the lingual nerve.

○ Many clinicians aspirate every 0.25–0.50 ml, seeking to

further guarantee the safety of the injection with a series of negative aspirations (McClure 1968; Lloyd 1992); this also helps retard the injection by curbing the natural tendency to move faster.

● Amount to be injected ○ In adults, teenagers, and older children, a 1.8- ml car-

tridge is used (1.5 ml during deposition and ±0.3 ml while removing the needle to anesthetize the lingual nerve).

○ In children <6–8 years old, only ½ of a cartridge is needed.

● Subjective symptoms of anesthesia. ○ Soft tissue anesthesia appears in the lower lip on the

anesthetized side. Soft tissue anesthesia may be described as tingling, numbing, itching, dullness, feeling “pins and needles,” and feeling a “fat lip” sensation (Table13.1, Chapter13). The onset of soft tissue

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