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Basic Injection Technique

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222

injections in the backside, in the mouth you use anesthesia.” This way, we separate the two parts of the body and the two concepts.

● The patient may ask to see the syringe and needle. In

this case, you say “No, because it’s clean and doesn’t have germs, so I can’t show it to you.” This explana‑ tion is generally sufficient. Some dentists tell children that they’ll show it to them at the end (only if the child remembers; if not, do nothing) and if they do, they do so with only the syringe (not the needle), or if they do show the needle it has the cap on.

7) Similarly, with adults, it is a good idea to explain what

you are about to do, how you are going to anesthetize them, and how comfortable they will feel. Something like this: “Just let me anesthetize you and you’ll see that it’s much less than you expect.” Or inject a dose of humor: “After I inject the anesthetic you’ll get addicted and be back every day for more.” Or “It’s not worth wor‑ rying about the anesthetic. You’ll see that it’s much easier than you think. Just let me show you.”

Remember, studies show that patients are anxious and have expectations of pain caused by the anesthetic and dental treatment that are more negative than necessary (Rousseau et al. 2002; Nanitsos et al. 2009). Giving the patient positive information allays and reduces the fear and anxiety (Van Wijk and Hoogstraten2006).

ApplicationofTopicalAnesthetic

Approximately 95% of dentists in the United States (Kohli et al. 2001) and UK (Meechan2008) administer topical anesthetic before intraoral injections to reduce pain and fear.

The time between applying the topical agent and the injection is very important. Many dentists wait less than 30 seconds (Gill and Orr1979), and a survey in the United States showed that 70% wait less than a minute (Kohli etal.2001). Holst and Evers estimated that the maximum time tolerated in clinical practice for topical anesthetic to take effect should not exceed 5 minutes (Holst and Evers1985). In addition, moisture in the mouth tends to inhibit adhesion of gels, ointments, pastes, creams, and solutions to the mucosal surface, thus hampering absorp‑ tion of the anesthetic, therefore maximum absorption is achieved during the first 30

seconds (Carr and Horton2001b). For all the above reasons, we need topical anesthetics that have a short onset of action, generally under 1–2 minutes, therefore the most commonly used agents in clinical practice are benzocaine 20% and lidocaine 5% in gels, ointments, and creams (Kohli et al. 2001; Meechan2008).

As seen in the chapter on topical anesthetic (Chapter12), aerosols and liquid solutions yield the worst results, there‑ fore the preferred form is gel, ointment, cream, or paste (Annex 19). In addition, topical anesthetic has little efficacy on the palate, which has a thicker and more keratinized mucous membrane, thus making it the least permeable part of the oral mucosa (Lesch etal.1989). Similarly, its efficacy is poor for reducing the discomfort/pain produced by man‑ dibular block, since the needle is inserted approximately 20–25

mm into the pterygomandibular space. As reported in clinical trials (Annex 19), topical anesthetic cannot reach this level (Meechan etal.1998). Remember that in truncal injections the most painful part is the advance of the needle into the soft tissue (Annex 23). In any case, the placebo effect of the topical anesthetic is observed.

MethodofApplication

1) Tell the patient that topical anesthetic is going to be

used to reduce the “discomfort” associated with admin‑ istration of local anesthetic. This measure has been shown to reduce anxiety and increase tolerance to pain (Martin etal.1994).

2) Clean and dry the puncture site with gauze or air pres‑

sure to remove saliva and soft debris (Figure13.2). If this is not sufficient, the amount of saliva in the mouth can be reduced by placing cotton roll in the vestibule, at the orifice of the Stenon duct, or under the tongue at the orifice of the Wharton duct.

3) Aspirate saliva to ensure that it does not dilute the topi‑

cal anesthetic which is about to be applied.

4) Apply the ointment or gel by rubbing a cotton swab

directly over the injection site (Figure 13.3). Apply a small amount; it is important to remember that the

Figure13.2 Using gauze to clean the area where the topical

anesthetic is to be applied.

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Figure13.3 Application of topical anesthesia with a

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cotton swab.

cotton bud will absorb part of the gel or ointment (Holst and Evers1985).

5) Cover the area with gauze or a cotton roll so that the

anesthetic remains in place and is not dispersed throughout the mouth or diluted in saliva (or at least as little as possible) (Roghani et al. 1999; Munshi etal. 2001). Here, again, some of the gel or ointment will be absorbed by the gauze or cotton roll (Lim and Julliard2004).

6) Wait sufficient time for the anesthetic to take effect,

generally 30 1–2

minutes for lidocaine. Remember that one of the

seconds to 1 minute for benzocaine and

reasons for failure of topical anesthetic is that not enough time is left for it to take effect (Gill and Orr1979).

7) Clean the area before injection to remove the topical

anesthetic and leave the area clean. Owing to continu‑ ous stimulation with saliva, the injection site is always being contaminated, therefore it is more important to keep it clean than disinfected (Mink and Spedding1966).

8) Prevent contact between the anesthetic and skin, since

many anesthetics are ester agents (benzocaine, tet‑ racaine, cocaine) and can lead to allergic sensitization (Roberts and Sowray1987).

Note: Owing to diffusion of the topical anesthetic, the mucosa of the tongue or pharynx often becomes anesthe‑ tized at some distance from where the topical anesthetic was applied. This is a common complaint (Nakamura etal. 2013).

ObservationsonAerosols

As we have seen, topical anesthetic in the form of aerosols is not recommended owing to the low efficacy resulting from dispersion in the mouth and dilution in saliva (Annex 19),

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although when they are used, it is important to take into account the following:

1) A cannula should be used to prevent– as much as pos‑

sible – the aerosol solution from extending and dispersing.

2) Advise the patient to hold his/her breath when the

agent is applied so that the drug is not inhaled. This would lead to anesthesia of the pharynx and an uncom‑ fortable sensation of anxiety (Roberts and Sowray1987).

3) Press the aerosol for 1 second, no more than 2 seconds,

especially if it contains tetracaine, since it is easy to administer a toxic dose (Bennett 1984; Roberts and Sowray1987).

Finally, aerosols are not recommended in children because they may lead to sudden uncooperative behavior owing to the noise they make and bad taste as the anes‑ thetic spreads through the mouth (Frasier1967; Evers and Haegerstam1981).

TransferoftheSyringe

1) The assistant finishes preparing the syringe (continua‑

tion of section “Preparation Phase”, point 4). Once the syringe is prepared with the cartridge, needle, and protective disk, the assistant separates the anterior cap to break the seal and replaces it using the protective disk. The risk of a needle

‑ stick injury is minimized

because of the protective disk (Figure11.10, Chapter11).

2) The dentist’s supporting hand, i.e. the hand not holding

the syringe (the left hand for right

‑ handed dentists) must carry out the following operations simultaneously (Figure13.4):

● Stabilize the patient’s head by holding it with the

hand and fingers. The objective is to prevent sudden movements by the patient during insertion of the needle (Marks etal.1984).

● Separate the soft tissue to ensure that the injection

site is clearly visible.

● Block the view of the syringe (especially in children)

with the fingers extended over the face or the wrist. There may also be cases where the upper lip can be raised.

3) Children. The dentist must look the child directly in the

eye throughout the transfer maneuver to ensure the following:

● The child is prevented from seeing the syringe, given

that he/she tends to follow all the dentist’s actions and movements. Look directly at the child through‑ out, especially if he/she is nervous.

● By looking directly at the child’s face, the dentist can

observe whether he/she is feeling pain or notices the

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224

prick of the needle by gestures such as frowning, rais‑ ing the eyebrows, blinking, or moving the nose. On the other hand, the patient may not modify his/her expression, thus indicating that the insertion has been asymptomatic or well‑ tolerated.

● The child should not close his/her eyes (almost no

children do it, on the contrary, they look at everything the dentist is doing) (Mink and Spedding1966), since the disappearance of one sense increases the sensitiv‑ ity of the others, with the result that sensations such as touch and pressure are more easily perceived as pain. Furthermore, with the eyes closed, the patient can imagine horrible threats that are not seen when the eyes are open (Mink and Spedding1966).

● The dentist can also ask the patient to place his/her

hands under his bottom, that is, away from the mouth and supported by his/her own body (Figure13.4). In addition, since children see the word “bottom” as a nice word, even a little naughty, they accept it very well.

4) The dentist extends and opens his/her right hand (right‑

handed dentist) to receive the syringe from the assistant without looking (he/she is looking at the child) and out‑ side the child’s field of vision (behind the head rest or under the chin and near the left ear).

5) The assistant places the syringe in the dentist’s hand:

● The syringe is presented with the needle cap and

protective disk pointing toward the assistant (Figure13.5).

● The assistant takes the syringe with his/her right

hand by the body of the syringe, or barrel (Figure13.5).

Figure13.4 Note the following: (1) the position and function

of the dentist’s supporting hand, and (2) the assistant’s arm extended across the child’s body. Source: Redrawn with modifications from Snawder (1987).

Figure13.5 The assistant holds the syringe before passing it

to the dentist with the right hand on the body or barrel of the syringe. Note the protective disk over the cap of the needle.

● The syringe is passed across out of the view of the

patient, that is, behind the headrest or under the patient’s chin.

● The syringe is placed correctly in the dentist’s hand

with a slight tap on the dentist’s open hand (so that the dentist is aware of receiving the syringe).

● The assistant removes the anterior sheath or cap of

the needle so that it is exposed. Remember that the seal of the cap has already been broken (section “Transfer of the Syringe”, point 1), therefore it is easy to remove the cap.

6) With the syringe in his/her hand, the dentist pushes the

plunger slightly to:

● Purge the syringe (one or two drops) to eliminate sili‑

cone and aluminum powder residue that have entered the lumen of the needle when it pierces the silicone diaphragm of the mouth of the cartridge with the posterior needle (Kelly and Cohen 1984; Piesold etal.1998). This residue is found in around 10% of cases and can measure as much as 0.3–0.5 mm and carries a risk of entering a vessel or muscle and caus‑ ing pain or trismus (Kelly and Cohen1984).

● Eliminate the initial sudden pushing and shaking

movement (Tzafalia and Sixou 2011) caused by the fact that the plunger is usually blocked or sticks to the glass of the cartridge. This will ensure that it moves smoothly down the barrel (Figure13.6). The plunger used to be lubricated with paraffin or glycer‑ ine wax that became hard over time and at low ambi‑ ent temperatures. Lubricants are currently made of silicone and are much better than the previous ones. However, even though the problem has been some‑ what resolved, it has not disappeared (Jastak et al. 1995; Malamed 2004). The problem is worse with plastic cartridges than with glass cartridges (Malamed2004).

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Initial pressure

Pressure of the injection

Figure13.6 Control the sudden shaky initial movement to

ensure that the solution is injected smoothly.

The way the hand moves and the use of cartridge‑ type metal syringes make these initial brusque move‑ ments difficult to control. This is one of the advantages of computerized injection techniques, which solve this problem almost perfectly (Tzafalia and Sixou2011).

7) With the syringe now purged in his/her right hand, the

dentist can direct it toward the patient’s mouth.

InsertionoftheNeedle

1) Children. The assistant extends his/her left arm over

the child’s body to hold the arms in place gently but firmly and remains alert to possible disruptive move‑ ments (Mink and Spedding1966; Ram and Peretz2002) (Figure13.4).

2) The dentist warns the patient when pain is unavoidable.

Our body does not react well to surprises and reactions are often uncontrollable. For example, injections into the palate or using the intrapulpal technique can be painful, therefore we must tell the patient that the pain will last only a second and show interest and concern for the fact. For the same reason, when we say “this won’t hurt,” we should be sure that this is in fact the case. If the injec‑ tion actually does hurt, then the patient may become counter‑ conditioned, with the result that every time we say something similar, the patient will expect to feel pain (Jackson 1974) and not relax. This defective approach to providing information is disliked by 75% of patients (Rankin and Harris1985).

3) The dentist always holds the syringe stable to maintain

control and prevent unexpected movements of the nee‑ dle (Ram and Peretz2002). This is done by supporting the body of the syringe on the patient’s teeth or lips or

with the dentist’s fingers placing the syringe on the patient’s mouth or face. Do not rest on the patient’s arms or shoulders, since he/ she can move them unexpectedly while keeping the mouth still.

4) The dentist should perform counter- irritant/counter-

stimulant measures immediately before inserting the needle.

Traction and stretching of the soft tissue can be applied with the fingers in the area near the injection site to leave the area tense. This enables the needle to penetrate the mucous membrane with minimum resist‑ ance and discomfort. If the soft tissue remains lax and soft, the needle will push against it before being inserted, therefore insertion will be more difficult and painful. Pressure or vibratory stimulus can also be applied by making rapid movements with the fingers or a cotton tip applicator. These maneuvers enable the following:

● The patient’s attention is diverted from the “prick,”

thus ensuring that the pain threshold does not decrease (anxiety reduces the pain threshold) and the stimulus of the penetration of the needle (which is at its limit) falls below the pain threshold (Woolgrove1983; Sokol etal.1985).

● Activation of the gate control system at the level of

the trigeminal caudate nucleus, which partially inhibits the passage of painful stimuli upwards, thus helping to maintain the stimulus below the pain threshold (Melzack and Wall1965; Dubner1978) (see Chapter11).

5) During the insertion of the needle, the dentist can dis‑

tract the patient further with a continuous monolog, for example, “I hope everything is OK.. .now open your mouth, a little more,... that’s it, a little more,... that’s it, perfect, just like that,...”

6) Depending on whether the injection is an infiltration or

mandibular block, we can make a few suggestions:

● Buccal infiltration. We recommend the minimum

intervention (minimum volume/minimum injection

time), which consists of injecting a single drop at the injection site in 1–2 seconds and waiting a minute; we then inject again at the same site (the appearance of a blood spot is common), one or two drops in 1–2 seconds and waiting half a minute. We inject at the same site again, although this time ±0.25 ml (an eighth of a 1.8‑ ml cartridge) in 7–10 seconds after aspirating; we now wait another half minute. Finally, we inject, slowly at the same site, the quantity we intended to administer (again, after aspirating). This method enables anes‑ thesia of the soft tissues and prevents the discomfort resulting from distension of the tissues by injecting most of the solution.

‑

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● Mandibular block. We recommend a light but firm tap

followed by quick insertion. This approach involves

giving a light but firm tap with the supporting hand (generally the left in right

‑ handed persons) at the same time as the hand holding the syringe (generally the right) inserts the needle quickly to reach the bone immediately. This is a very important maneuver, since the traumatic stimulus limits the pain threshold (in this case, the passage of the needle across the soft tissue), which lasts some time, so that the initial threshold can be overcome and pain appears (Fuller etal.1979). A slower advance reduces the threshold considerably, and, if some drops of anesthetic are injected as the needle advances, then the situation worsens (Appendix), in addition, the anesthetic does not act immediately (Nusstein etal.2006; McCarney etal.2007). It is important to remember that passage of the needle is the factor that produces most pain in truncal blocks (Annex 23).

7) Avoid injuring the periosteum. The periosteum is rich

in nerve endings and any injury to it causes pain at the time of the lesion and in the post

‑ operative period. In

order to avoid this injury, we recommend the following:

● Place the bevel of the needle facing toward the bone

(Figure13.7) since if it comes into contact with the peri‑ osteum, it will tend to slide across without damaging it. This classic concept is currently under discussion since evidence from clinical trials indicates that the direction of the bevel does not affect the onset of pain (Carr and Horton 2001b) or the efficacy of the anesthetic in achieving pulpal anesthesia (Steinkruger etal.2006).

● If the tip of the needle touches the bone, we withdraw

it 1–2

mm before injecting (we do not exert pressure by pressing it against the bone) for the following rea‑ sons: (i) so as not to leave anesthetic solution below the periosteum and (ii) so as not to blunt the needle, especially if the tip barbed outwards, since this can damage muscles, nerves, and vessels on withdrawal (Stacy etal.1994) (Figure22.2, Chapter22).

8) Never insert the needle up to the hub. This is the

weakest and most vulnerable part and the level at which needles always break (Orr 1983; Marks et al. 1984; Burgess 1988; McDonogh 1996; Zelster et al. 2002). Therefore, in the case of a breakage, the end part of the needle will remain outside the soft tissue and can be withdrawn before it disappears fully into the tissue. Long needles should be used in techniques where it is necessary to insert the needle deep into the soft tissue, for example mandibular block (Dentists’ Desk1983).

9) In children, voice control should be used if the patient

complains, cries, or tries to move when the needle is inserted.

In principle, the syringe should not be withdrawn, since this would reinforce the child’s disruptive behav‑ ior and hamper subsequent administration of local anesthesia (Mink and Spedding1966).

Voice control accompanied by strict facial expression (nonverbal communication) gives us an authoritarian air. We can then move close to the child’s ear and tell him/her in a soft voice that it is time to stop behaving badly. If the child’s behavior continues to be disruptive, we raise our voice suddenly and considerably, and use expressions such as “Open your mouth!”, “Don’t move!” Once we have the child’s attention, we change our tone of voice, thanking him/her for stopping behaving badly and gently explaining that “You’ll hardly feel a thing.”

Aspiration

In 1957, the Council on Dental Therapeutics of the American Dental Association highlighted the need for systematic aspi‑ ration before injecting dental local anesthetic (Council on Dental Therapeutics1957). Today, there are still many den‑ tists who do not routinely use aspiration in the belief that intravascular injection is very uncommon or that if it does occur, it has few adverse effects (Bartlett1972; Meechan and Rood1992). Some surveys show that more than 20% of den‑ tists do not routinely aspirate (Malamed2004).

The aim of aspiration before injection is to prevent intra‑ vascular injection and therefore systemic toxic effects resulting from the sudden passage of the solution into the bloodstream (Forrest 1959; Shira 1962; Bos et al. 1971), which can sometimes increase toxicity 200‑ fold (Meechan and Rood1992).

Figure13.7 Prevent the tip of the needle from damaging the

periosteum (1) by placing the bevel parallel to it (2).

FalsePositivesandNegatives

Matters may be further complicated by false positives and false negatives:

● False positives, when the cartridge fills with blood without

a vessel having been injected (Alling and Christopher1974;

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Figure13.8 False positives in aspirations due to residual

blood on crossing a vessel (1) or by aspirating blood extravasated from the tissue spaces (2). Source: Redrawn from Alling and Christopher (1974).

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Figure13.9 False negative caused by the bevel being on the

internal layer of the vessel (adventitia or endothelium). Source:Redrawn and modified from Watson and Colman (1976).

Watson and Colman 1976) as a result of the following (Figure13.8):

1) Aspiration of extravasated blood from tissue spaces

caused by the trauma resulting from passage of the needle.

2) Residual blood remaining in the lumen of the needle

as it crosses a vessel.

● False negatives, when the cartridge does not fill with

blood despite the fact that the tip of the needle is in a ves‑ sel as a result of:

1) Excess negative pressure when the plunger is pulled

backward to aspirate, thus leading to collapse of the ves‑ sels, especially vessels measuring less than 1.5 mm (Alling and Christopher1974; Watson and Colman1976).

2) If the angle of insertion of the needle has the misfor‑

tune to lie parallel to the inner layer (adventitia) of the vessel, then the endothelium (adventitia) occludes the lumen of the needle on aspiration, especially in small vessels (Figure13.9).

3) Formation of a punch cylinder of epithelial mucosal

cells in a little more than 1% of cases, leading to obstruction of the lumen (Piesold etal.1998).

HowtoInterpretaPositiveAspiration

While it is impossible to make an infallible interpretation, we suggest the following (Watson and Colman 1976; Cooley and Robinson1979):

● A cartridge colored lightly or more intensely but in a dif‑

fuse fashion usually indicates a false positive.

● An intensely colored cartridge with blood return enter‑

ing it is usually a true positive (Figure13.10). If the

Figure13.10 Genuinely positive aspiration, shown by the fact

that the cartridge is colored by an intense stream of blood.

return reaches halfway up the syringe, it usually indi‑ cates a small vein (<1.5 mm); if it is very intense and fills the cartridge, it usually indicates an artery or a large vein (>1.5 mm). it is therefore important to use 25G or 27G needles (25G is better) since these make it possible to evaluate the characteristics of the blood return that colors the cartridge. This is not possible with 30G needles because the return is always weak (see Chapter11).

AspirationTechnique

According to the criteria of Forrest, we can indicate the fol‑ lowing steps to ensure correct aspiration (Forrest1959):

1) Move the tip of the needle to the target area.

2) Inject a few drops to clear the lumen of punch cylinder

(thus avoiding false negatives) and any blood remaining in the interior after crossing tissues or a vessel (thus avoiding false positives).

3) Aspiration is performed by dragging the plunger

smoothly back by pulling the support ring of the syringe 1–2

mm with the thumb (without moving the tip of the needle) for 2–3 seconds to create a “soft” negative pres‑ sure. This prevents a false negative through collapse of the small veins owing to excessive traction.

4) If the result is negative (the cartridge does not fill with

blood), we turn the needle a few degrees and re‑ inject a few drops before softly aspirating again. We thus

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prevent a false negative that would have occurred if we had initially placed the bevel parallel to the adventitia. If the result had been a positive aspiration (the cartridge fills with blood), the needle is withdrawn 1–2

mm and we aspirate again, as indicated above. If the result is negative again, we proceed with the injection; however, if it is positive again, we recommend removing the car‑ tridge, changing it for a new one, and starting again, since it is difficult to evaluate a new aspiration with the syringe reddened by blood (Forrest1959; Allen1979).

5) If the result is finally negative, we proceed with the

injection, but we aspirate every 0.25–0.5

ml to slow the injection and prevent false negatives, given that in con‑ ventional aspiration syringes (where it is necessary to pull back), the tip of the needle can be moved a little during the maneuver, therefore some authors prefer self

‑ aspirating syringes (Lloyd1992).

Remarks

● In positive aspirations, it is impossible to know whether

we have reached an artery or a vein (Bartlett1972).

● For reasons that are not clear, there is considerable indi‑

vidual variability in the percentages of positive aspira‑ tions (Bos etal.1971; Persson etal.1974; Meechan and Blair1989; Lopez and Rosello1995).

● Even if the aspiration is negative, a new cartridge should

be used for each patient, since blood or tissue liquid is detected in 10–25% of cartridges (Trapp and Davies1980; Lipp et al. 1993), with the risk of transfer of organic materials and fluids and, therefore, infection.

● There is little correlation between adverse effects (vas‑

ovagal reactions, palpitations, pallor) and positive aspi‑ rations (Forrest1959; Goldman and Gray1963; Persson etal. 1974; Blair and Meechan1985; Lipp et al.1988), possibly owing to the following:

○ Other factors that can contribute to adverse effects,

such as anxiety and fear, pain, vascular irritation when the needle comes in contact with a vessel.

○ During aspiration, traction of the plunger with the

thumb in the ring leads the tip of the needle to move involuntarily for a second (Cowan1972; Williams and Simm1975; Lloyd1992) and in such a way that it is practically imperceptible (Kämmerer etal.2016). An invitro study performed in 2016 found that this move‑ ment of the needle was around 2.5 mm with syringes that took a conventional cartridge and some 2 mm with self‑ aspirating syringes (Kämmerer etal. 2016). Aspiration should therefore be repeated at each stage to ensure that it is successful (McClure 1968; Lloyd 1992), bearing in mind that there is general agreement that the risk of intravascular injection increases if the syringe is not aspirated first (Horowitz

Table13.2 Percentage ofpositive aspirations inanesthetic

techniques

Arch Technique Percentage(%)

Maxillary Periapical infiltration (buccal

infiltration) Periapical

infiltration– molars Posterior superior alveolar

nerve block High tuberosity technique Transpalatal technique 5 Infraorbital nerve technique Palate 1

Mandible Mandibular block:

– Standard technique 10 – Gow–Gates technique 5–10 – Laguardia–Akinosi technique 5

Periapical infiltration (buccal infiltration)

Infiltration mental area 5 Buccal nerve block 1 Lingual nerve block 1

Data from Goldman and Gray (1963).

Data from Karkut etal. (2010).

Source: data from Annex 22.

et al.2005). Partial intravascular injection has been reported in around 25% of cases despite previous nega‑ tive aspiration (Eickbohm etal.1991).

● After a second or third injection at the same site, the

probability of a positive aspiration increases as a result of aspiration of extravasated blood from injured vessels (Lopez and Rosello1995; Lustig and Zusman1999).

● Finally, Table13.2 shows the mean prevalence of posi‑

tive aspirations in the various dental intraoral anesthetic techniques. Truncal block is the technique that most frequently leads to positive aspirations.

Injection

1) Inject the solution slowly by pushing the plunger at a rate

of 1.8 ml in 40–60 seconds. This maneuver enables us to avoid the following:

● Pain during the injection caused by tissue expansion

with an excessively rapid entry of the solution and the resulting increase in pressure (Mamiya et al. 2001; Primosch and Brooks 2002; Kudo 2005; Kanaa et al. 2006; Whitworth et al. 2007; Aggarwal etal.2012). This pain is even greater than that caused

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by the prick of the needle during insertion (Carr and Horton2001a; Annex 19).

● Toxicity of the anesthetic solution, since there may be

rapid increases in plasma levels, especially with unnoticed intravascular injections (Adriani and Campbell1956; Campbell and Adriani1958; Adriani etal.1959; Scott 1986). Slow injections enable dilu‑ tion of the anesthetic solution in the systemic circula‑ tion (Adriani and Campbell 1956; Campbell and Adriani1958), thus enabling the lungs to retain the drug and attenuate the toxic effect (Tucker and Mather 1979; Scott 1986). Some authors consider slow injections to be the key to prevention of adverse reactions in dental anesthesia, even more so than aspiration (Malamed2004).

● Ineffectiveness of the anesthetic. Rapid injection

under pressure leads to turbulent diffusion of the solution to areas that are distant from the tip of the needle, thus reducing the amount of drug at the tar‑ get area, with the corresponding loss of effectiveness (McClure1968; Jorgensen and Hayden1970; Mamiya et al. 2001). Furthermore, clinical trials show that slow injections increase the percentage of success in

pulpal anesthesia (Kanaa etal.2006). Table13.3 shows the injection rates recommended by several authors, as well as real values from surveys. Most dentists inject a 1.8‑ ml cartridge in under 20–30

seconds. The conventional recommendation was

Table13.3 Rate ofinjection ofa 1.8- ml cartridge inseconds,

asrecommended by various authors andsurveys

Reference Seconds Remarks

Recommendations

Fischer (1912) 108 Classic 1 Nordenram (1971) 108 Bennett (1984) 108 National Heath

Foundation Australia (Oliver 1974)

Malamed (1986) 60

Roberts and Sowray (1987) 60

Linscott et al. (1978) 60 Kanaa etal. (2006) 60 Meechan (1998) 30

Survey

Malamed (1986) 20 80% of dentists Kohli etal. (2001) <30 56% of dentists

60 Currently, most

common criterion

30–60 33% of dentists

ml/min

to inject 1 ml per minute to avoid injection pain and prevent toxicity. Clinical trials have shown that injec‑ tions administered in more than 36

seconds are not painful in children (Maragakis and Musselman1996) and that there is no difference between administering injections in 60 or 100

seconds (de Souza Melo et al.2015). Furthermore, in the case of a child, the longer the injection takes, the more nervous the patient becomes and the more he/she associates the injection with pain (Jones et al. 1995). Therefore, modern convention suggests injecting a 1.8‑ ml cartridge in

seconds.

40–60

2) Aspirate every 0.25–0.5 ml of solution injected

(McClure1968; Lloyd1992) to confirm the safety of the injection, with multiple negative aspirations (remember the problem of movement of the tip of the needle), and to help slow the injection by blocking the natural ten‑ dency to inject quickly, as shown by surveys.

3) Keep the patient distracted with a monolog to ensure

that his/her attention is drawn away from the injection. Thus, “…hold your mouth open, that’s it, like that, …don’t move, keep it like that, perfect,... you can feel my fingers touching your lip,… raise your hand if it hurts,…”

FinalPhase

1) Remove the needle slowly and smoothly from the injec‑

tion site when the injection is complete. The direction of insertion and withdrawal should not be changed because of the risk of needle breakage (Orr1983; Marks et al. 1984; Zelster et al. 2002). If it is necessary to change the direction of the needle, then this should be done just below the mucous membrane, when the nee‑ dle is almost completely out. We do so by reinserting the needle in the new direction (Orr 1983; Marks etal.1984).

2) The assistant will place the cap on the needle. Remember

the importance of the protective disk on the cap to pre‑ vent needle‑ stick injury during the maneuver. The nee‑ dle should remain covered to prevent contamination and needle stick accidents (Dentists’ Desk1983). The assistant also takes the syringe from the dentist’s hands (once the cap has been replaced) out of the patient’s line of vision, generally under the chin.

3) The injection site should not be massaged or rubbed.

Massaging forces the anesthetic solution to spread throughout the more lax tissues along the least path of resistance and at some distance from the injection site, thus reducing its concentration and ability to cross the periosteum, cortical bone, and cancellous bone, and, paradoxically, increasing the area of superficially anesthetized soft tissue.

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Basic Injection Technique

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230

We may occasionally massage the area gently to reduce the burning sensation (beesting effect) caused by the acid pH of solutions containing sympathomi‑ metic vasoconstrictors, such as epinephrine.

4) If anesthetic solution enters the mouth, the patient usu‑

ally complains of a bitter taste resulting from sulfites in solutions with vasoconstrictors such as epinephrine (Klein1983). We can reassure adults that swallowing the solution is not toxic and we can use the aerosol of the syringe to force air and water into the mouth and use the aspirator to remove the bad taste. Moreover, in children, we can gain their confidence by telling them that the “medicine” (the anesthesia) tastes bad and that it would be a good idea if it tasted of chocolate, strawberry, or ice cream and asking them what they thought, if we should invent it, and what fla‑ vor would they prefer. Solution can enter the mouth for several reasons: (i) a few drops may be released when the needle is with‑ drawn from the tissue as a result of the remaining pres‑ sure in the plunger (the most frequent cause); (ii) if it occurs during the injection, it is caused by the fact that the needle pierced the diaphragm of the mouth of the cartridge off‑ center, thus forming an oval hole around the needle between the diaphragm and needle through which some of the solution escapes (Dentists’ Desk1983; Malamed1986; Jastak etal.1995), but this problem can be resolved by removing the needle and reinserting it appropriately into the mouth of the syringe; and (iii) breakage of the cartridge, although this is very rare (see Chapter22).

5) Children. The dentist continues to support the head

with his/her hand and looking directly at the child to monitor the situation. When the cap is placed on the syringe and the syringe is removed from the dentist’s hands, both the dentist and the assistant should keep the needle and syringe out of the child’s line of vision (Mink and Spedding1966; McClure1968). Very often, it is dur‑ ing this phase that we drop our guard and the child sees the needle and syringe, thus removing any benefit gained with the maneuvers made to reassure him/her (Mink and Spedding1966) (Figure13.1).

6) We must warn the patient that he/she will start to feel

the effect of the anesthesia on the lips and tongue. As the term “soft tissue anesthesia” is somewhat technical, the words “numbness,” “tingling,” “dullness,” “itching,” and feeling “pins and needles,” can be used; in children, we should use words like “tickling” or tell them that they’ll feel like they have a “fat lip” or a “fat tongue” (Table13.1).

7) The dentist, hygienist, or the assistant should remain

near the patient while the anesthesia takes effect

(Nordenram1971; Evers and Haegerstam1981; Council on Clinical Affairs2015; AAPD2020). Remember, most adverse reactions occur during the first 15–30

minutes (Nordenram1971; Kelly and Patterson1974). Clinical studies have found that around 50% of complications occur during the first 30 20–30% occur before 2–6

minutes and that a further

hours (Kaufman etal. 2000;

Batinac etal.2013).

8) Children who are more difficult to control. An available

option just after administering the anesthetic, and one which many pediatric dentists recommend, is to rinse the mouth to prevent the child from crying (if they are about to cry). This helps to take the child’s mind off the recent injection (Mink and Spedding1966).

EvaluationofAnesthesia

1) Subjective response. When the patient tells us that he/

she is experiencing soft tissue anesthesia (sensation described as numbness, tingling, dullness, tickling, or fat lip) (Table13.1), we know that the anesthetic is hav‑ ing an effect at least on the soft tissues. Phases of soft tissue anesthesia have been reported as follows (Lindsay 1929): first, sensation of heat followed by a sensation of numbness; when the numbness is more advanced, it is more marked and eventually very marked and accompanied by sensation of swelling.

2) Objective response in the soft tissue. We can check by

pinching the gingival papilla to the canine with a sickle probe and observing that it is in fact insensitive (Ellis et al.1990). However, this does not guarantee pulpal anesthesia (Vreeland et al. 1989; Cohen et al. 1993; Childers etal.1996; Certosimo and Archer1996).

3) Objective pulpal response. This occurs later (Figure5.3,

Chapter5) and can be evaluated in two ways:

● With an electric pulp tester. The electric stimulus is

very reliable in permanent teeth and only presents false negatives (the electric stimulus is negative, although there is still pain during the procedure) in 0–5% of cases (Dreven et al. 1987; Certosimo and Archer1996). Owing to the lack of complete innerva‑ tion in the odontoblast layer, the electric stimulus not very reliable in primary teeth (Fuss etal.1986). It is also important to bear in mind that in permanent teeth with acute pulpitis, false negatives occur in 20–40% of cases (Table13.4).

● With cold stimulus. Initially dichlorodifluorometh‑

ane (DDN) was used. This is at −50 °C when it leaves the container (Fuss et al.1986; Cohen etal. 1993; Hsiao‑ Wu etal.2007) and is reliable not only in per‑ manent teeth, but also in primary teeth (Fuss etal.1986), although this has now been replaced by

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Table13.4 Percentage offailure ofpulpectomy withpain after

anesthesia andlack ofresponse ofthe pulp tothe stimulus ofthe electric pulp meter inteeth (mainly molars) withacute irreversible pulpitis (hot tooth)

ml/LAS/time

Reference

After mandibular block

Dreven etal. (1987) 3.6/L Nusstein etal. (1998) 1.8/L Allegretti etal. (2016) 3.6/*/15′ 14 (6/43) Visconti etal. (2016) 3.6/L Ghoddusi etal. (2018) 3.6/L

After infiltration in the maxillary buccal space

Dreven etal. (1987) 3.6/L‑ 100/10′ 14 (2/14) Nusstein etal. (1998) 3.6/L

LAS, local anesthetic solution; ml, milliliters injected. Times are given in minutes: 5′=5 minutes. L‑ 100=lidocaine 2% with epinephrine 1 : 100 000.

* Solutions of L‑ 100, A‑ 100, and M‑ 100.

A‑ 100=articaine 4% with epinephrine 1:100 000. M‑ 100=mepivacaine 2% with epinephrine 1:100 000.

(min)

‑ 100/10′ 38 (6/16) ‑ 100/5′ 80 (8/10)

‑ 100/20′ 36 (5/14) ‑ 100/15′ 45 (13/29)

‑ 100/3′ 26 (6/23)

Percentage(%)with pain(proportion)

42.6

≈ 40

1,1,1,2‑ tetrafluoroethane (TFE) (Green Endo‑ Ice), which is more ozone and leaves the container at −26 etal.1998; Miller etal.2004; Hsiao is applied in 10–25

‑ friendly (Kennedy etal.2003)

°C (Nusstein

‑ Wu etal.2007). It

seconds, even in vital teeth with crowns (Miller etal.2004). This method can also pro‑ duce false negatives in teeth with acute pulpitis (Reader et al.2011; Chavarria

‑ Bolaños etal. 2017). The cold test has advantages over electric stimulus, in that it is easier and faster and does not require special equipment (Reader etal.2011).

In cases of acute pulpitis, these methods are always help‑ ful even if they fail, since in the case of a negative response we always run the risk of a false negative. However, if there is already pain when the electrical or cold stimulus is applied, then this indicates that the tooth has not been anesthetized and that anesthesia should be reinforced (Reader etal.2011; Chavarria‑ Bolaños etal.2017). Finally, it is important to note that in clinical practice, systems of objective evaluation are not common (except in acute pulpitis); we wait for standard periods after the patient reports a subjective response, except in spe‑ cial cases.

4) Wait for the standard periods to ensure pulpal

anesthesia.

● We wait 5 minutes in maxillary buccal infiltrations,

once the infiltration has finished, to guarantee pulpal anesthesia in most cases.

● In mandibular block, the criterion is to wait 5 minutes

for the onset of soft tissue anesthesia of the lower lip and from there, a further 5–10 pulpal anesthesia, which takes longer (10–15

minutes to guarantee

minutes

in total) (see Chapter16).

5) The definitive proof is treatment itself, therefore the

patient should be warned at the start of the procedure that he/she may feel a sensation of touch, pressure, or temperature (cold or heat), but not pain, since the anes‑ thetic solution is very effective at suppressing pain, but not other stimuli (de Jong 1977). We can also tell the patient that he/she can raise his/her hand in the case of discomfort and we will stop immediately (this gives the patient a sensation of control and thus reduces anxiety). We also insist on the need to avoid sudden move‑ ments since this could lead us to hurt the patient. We proceed cautiously with drilling instruments and the scalpel, monitoring constantly to see if the patient complains and/or raises a hand. We also follow a progressive system in children. We place the head of the drilling instrument over the tooth to observe the child’s response to the vibration. If this is appropriate, we place the drill over the enamel, and if the response is suitable, we continue with the procedure.

Post-treatmentPhase

1) Inform the patient how long the sensation of numbness

will last in the soft tissues when dental treatment has

utes (3–4 2% and epinephrine 1:100000 (10 (12.5

hours) with the standard solution of lidocaine

μg/ml) or 1:80000

μg/ml) and more than 5 hours in a little over 5% of

cases (Hersh etal. 2008). These times may vary with other solutions (see Chapter7). A degree of residual local anesthesia is desirable as it prevents the onset of pain. However, patients should be informed about the prolonged duration of soft tissue anesthesia, especially as it may impact their ability to speak, sing, drink, and eat, which may be a concern if the patient plans on going to a meeting or event follow‑ ing the appointment where they may be participating in aforementioned activities.

2) Warn against chewing while the soft tissues remain

anesthetized, since this can lead the patient to bite his/ her lips, tongue, and buccal mucosa (self‑ injury), which are numb, and cause injury and pain. Although many patients say that they can chew with “the other side,” it is wise to insist because it is difficult to control the

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