Zone Anesthetized

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

• The following areas are anesthetized by the inferior alveolar 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.

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 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 anesthetized 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 1:100 000 (L‐100) or 1:80 000 (L‐80) epinephrine is the 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 right‐side blocks and to the left in left‐side blocks).
  • Tongue at rest and low in the posterior part of the mouth (Keetley and Moles 2001).
• Dentist’s position and position of the non‐dominant hand (i.e. left hand in right‐handed clinicians), depending 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.
  • Left side:
    • 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 insertion 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 pterygotemporal 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 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 pterygotemporal depression.
  

  

  

  

  

  Some clinicians draw an imaginary line along the middle 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 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 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 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 missing.
  • One aid to finding the insertion height is, as noted earlier, 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 reabsorbed, the lingula is higher.
    • Patients with a wide gonial angle and wide ramus of the mandible, typical of class III Angle’s malocclusion 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).
  • Some clarifications are in order regarding modification 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 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 mandible and the sagittal or medial plane is 0–27° (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 minimize 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 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 anterior 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, ranging 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 in needle breakage as well as the fact that the depth is excessive to hit the landmarks for anesthesia of the inferior alveolar nerve.
    

    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

  • The insertion depth may vary (Angelman 1945) depending on:
    • The divergent angle between the ramus of the mandible 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 mm between sides (Angelman 1945).
  • If the needle is not successfully inserted because it fails to touch bone after 30 mm or because it touches bone too soon, in less than 15 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 removing the needle, a second aspiration is performed and the last ±0.3 ml in the cartridge is injected to anesthetize 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 cartridge 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 anesthesia is approximately 2 minutes after injection (Annex 27) and in nearly 90% of cases in less than 5 minutes (Annex 28).
    

    	Mandibular block	Supplementary buccal infiltration	Success rate (%)
    Reference	ml/LAS	ml/LAS	(absolute values)
    Haase et al. (2008)	1.8/A‐100	1.8/A‐100	96% (70/73)
    Kanaa et al. (2009)	2.0/L‐80	2.0/A‐100	92% (33/36)
    Gazal (2015)	1.8/M‐100	1.8/A‐100	100% (23/23)
    		Mean	96% ≈ 95%

    LAS, local anesthetic solution; A‐100, 4% articaine with 1:100 000 (10 μg/ml) epinephrine; L‐80, 2 lidocaine with 1:80 000 (12.5 μg/ml) epinephrine; M‐100, 2% mepivacaine with 1:100 000 (10 μg/ml) epinephrine.

  • In approximately 10% of cases the lower lip is not anesthetized in the first 5 minutes (Annex 28). Such cases are regarded as failures in practice and a second mandibular block is recommended (Cohen et al. 1993; Reisman et al. 1997; Nusstein et al. 1998; Fan et al. 2009).
  • Soft tissue anesthesia is denoted by the following.
    • In the lower lip ipsilateral to the injection site it is a sign of anesthesia of the inferior alveolar nerve, the primary aim of the procedure.
    • In the tongue ipsilateral to the injection site it is an indication of anesthesia of the lingual nerve. In 50% of cases, this precedes lip numbness (Angelman 1945; Ay et al. 2011).
    • In the auricular and temporal region ipsilateral to the injection site it is a sign of anesthesia of the auriculotemporal nerve. With this technique it occurs in only 20% of cases (Kim et al. 2003).

• Supplemental buccal infiltration.
  • After the first 5 minutes soft tissue anesthesia appears in the lower lip (an initial sign of mandibular block onset), verifying anesthesia of the inferior alveolar nerve, and supplementary buccal infiltration is recommended in posterior mandibular teeth requiring good pulpal anesthesia. This procedure raises the pulpal anesthesia rate from 60–70% (Table 16.1) to 95% (Table 16.5).
  • The infiltration is performed after 5 minutes to avoid the risk of masking or concealing mandibular block failure due to the overlapping of the effects of mandibular block and infiltration in the soft tissue.
  • The infiltration anesthetics recommended are:
    • In adults a potent solution such as a whole cartridge (1.8 ml) of 4% articaine with 1:100 000 epinephrine (A‐100) on the buccal aspect of the posterior teeth to be treated.
    • In teenagers and older children, a cartridge (1.8 ml) of the standard lidocaine solution (L‐100).
    • In children under 6–8 years, half a standard L‐100 cartridge (0.9 ml).
  • It takes an additional 5–10 minutes (10–15 minutes in all after starting mandibular block) for pulpal anesthesia to be fully effective.
• Duration of soft tissue anesthesia. This usually lasts 3–4 hours (200 minutes), a fact of which the patient should be notified after treatment.

Efficacy of this Technique

The efficacy of this technique, measured with an electric pulp tester in posterior teeth after injection of one or two cartridges of standard 2% lidocaine with 1:100 000 epinephrine (L‐100), is 60–70% after 10–15 minutes (Table 16.1) and 95% when reinforced by buccal infiltration with 1.8 ml of a potent solution such as 4% articaine with 1:100 000 epinephrine (A‐100) (Table 16.5).

When measured with less rigorous methods such as the system to determine grade A anesthesia used for routine procedures (normally extractions), the success rate for non‐reinforced mandibular block is 85% (Annex 30).

Complications Specific to this Technique

• Technical error. Inappropriate maneuvering leads to failed mandibular block and other complications, depending on the injection position (Figures 3.13 and 3.14, Chapter 3
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