MIRANDA K-S- WONG, D.D .S.; PETER L- JACOBSEN, D .D .S., PH.D.
ain and the need to control pain is a constant factor in dentistry. Pain control w ith local anesthesia is required for m any dental procedures. Local anesthesia injected carefully and accurately not only perm its comfortable and painless treatm ents, b u t also increases the p atien t’s confidence in the dentist. D ental injection techniques are based on anatom ic norm s and statistical averages of bone structure and nerve pathw ays. They are designed for the average p atien t and a norm al healthy physiological and biochemical environm ent a t the injection site. Every case is not so ideal, however, and every dental practitioner has encountered patients who have unusual difficulty obtaining adequate profound local or regional anesthesia. This is particularly tru e for m andibular block anesthesia, or for an infected tooth. About 4,000,000 local anesthetic blocks and infiltrations are given by U.S. dental practitioners annually. Approximately h alf of the injections are inferior alveolar
ABSTRACT
U .S. d en ta l p r a c titio n er s a d m in iste r ab ou t 4,000,000 lo c a l a n e sth e tic b lock s an d in filtr a tio n s ann ually. T he fa ilu re ra te to a c h ie v e a d eq u a te a n e sth e sia for th e p roced u re is e stim a te d to b e 5 p e r ce n t to 15 p ercen t. T his a r tic le d escrib es fiv e d ifferen t c a te g o rie s o f fa ilu r es and su g g e sts w a y s to tr o u b lesh o o t them . injections. The percentage of failure to achieving profound inferior alveolar anesthesia is estim ated to be 5 percent to 15 percent' (about 100,000 to 300,000 injections). Regional anesthesias of the inferior alveolar nerve in patients who are extrem ely obese, edentulous or who have large and laterally flaring m andibles can be especially troublesome. Similarly, a highly anxious p atien t m ay perceive any kind of stim ulation as pain. This article addresses the
various reasons for failures in local anesthesia, and techniques and ideas to troubleshoot and solve these problems. INFILTRATION TECHNIQUE
Local infiltration is usually all th a t is needed to anesthetize the m axillary teeth and soft tis sues for general operative pro cedures. As long as the needle is placed correctly in the buccal fold n e a r the apex of the tooth to be anesthetized, th e volume of solution will diffuse from the injection site through the perio steum and compact bone to reach the nerve stru ctu res th a t innervate the pulp, periodonti um and jawbone. Because of bone density around the tee th in the m andible, these tee th cannot be predictably anesthetized by infiltration techniques. Therefore, nerve bundles branching to the m andibular teeth m ust be blocked. Some operators in filtrate individual teeth using a periodontal ligam ent space infiltration th a t requires a special needle and syringe to p enetrate the space. This technique, though useful for some operators, has an JADA, Vol. 123, January 1992
69
increased incidence of local side effects and is not discussed here. INFERIOR ALVEOLAR BLOCK TECHNIQUE
For m andibular anesthesia, the p a tie n t’s m outh should be opened widely. After the depth of the g reatest concavity on the anterior border of the ram us (the coronoid notch) is palpated w ith the left thum b, the index finger is placed behind the ram us below the ear (midway betw een th e head of the condyle and th e gonial angle of the greatest concavity). Ideally, the m andibular foram en lies m idway on a horizontal line draw n from these two points. W ith the syringe directed from the prem olar region of the opposite side, the needle is inserted a t thum b level. In adults, th is injection point lies about 1 centim eter above th e occlusal surfaces of the m andibular m olars. In children, th e m andibular foram en lies about 0.5 cm. lower th a n in ad u lts.2 The needle insertion point should be ju st lateral to th e pterygom andibular raphe— th e union line betw een fibers of th e superior constrictor and buccinator muscles. As the initial mucosal penetration is m ade lateral to the pterygom andibular raphe, th e practitioner should contact bone im m ediately a t a point ju s t posterior to the internal oblique ridge. After bone has been contacted, the needle can be w ithdraw n slightly and redirected medially. The needle is advanced dorsally along the m edial side of th e ram us and should always be in contact w ith the ram us. The syringe should be held in the original horizontal position. 70
JADA, Vol. 123, January 1992
Figure 1. Simple concept of the nerve supply of the mandibular teeth.
The average depth of the needle penetration in the adult is 2.5 cm. The anesthesia should be carefully aspirated and then slowly injected. After the needle is w ithdraw n from the m andibular foramen, the lingual nerve can be blocked 1 cm. mesially and ventrally to the lingula. The rem aining 0.3 m illiliter of solution of the rem aining capsule should be deposited. ANATOMIC VARIATIONS AS A CAUSE OF FAILURE
Anatomic variations can cause failed infiltrations, usually because of extra dense bone. They also often account for failed or incomplete inferior alveolar block. V ariations include: ™ a wide flaring mandible; ■* a wide ram us m andibularis in the anterior-posterior direction; ■■ a long ram us m andibularis in the superior-inferior direction;
**■ bulky m usculature or excess adipose tissue; ■■ edentulous patients or young patients; *■ any combination of the variations. Anatomic variation problems can be solved, no m atter how m any changes have obliterated visual anatom ic landm arks, because certain bony landm arks rem ain unchanged. By palpating all the described bony landm arks to orient the needle and syringe, and coordinating soft tissue landm arks visually, fairly accurate ideas of the anterior-posterior size of the ram us, the superior-inferior height of the ram us from condyle to gonion, the degree of ram us m andibularis flare and the superior-inferior orientation for the m andibular foram en location emerge. Thus, it will not be difficult to locate the m andibular foramen. Most often, the injection needs to go higher and deeper.
In situations w here bifid canals are recognized and the possibility of a second, more inferiorly placed foram en exists, alte rn a te sites for anesthetic solution placem ent should be considered if routine attem pts to achieve total anesthesia are not successful. In such cases, depositing the anesthetic solution below the norm al anatom ic landm arks m ay provide more complete anesthesia. If successful, this variation should be noted in the p atien t’s chart as a rem inder for future anesthetic blocks. TECHNICAL ERRORS OF INJECTION MYLOHYOID
MENTAL
Figure 2. Diagram of the intrabony mandibular plexus. The most consistent communications are marked.
The m andibular h ard and soft tissues are supplied by a plexus of nerves.3 This plexus, with its m any comm unications, may allow sensation even if the prim ary inferior alveolar nerve is blocked. A block of other nerves in this plexus m ay be required to render the m andibular tee th insensitive. The m ain nerve in this plexus is the inferior dental nerve, b ut lingual, buccal and mylohyoid nerves also occasionally innervated the teeth. To perform restorative tre a tm e n t on these teeth, it m ay be necessary to adm inister more th a n an inferior alveolar block. These patients may require inferior alveolar and lingual nerve block injections and a buccal injection to achieve complete anesthesia. Because of the norm al complex anatom y of the m andibular nerve supply, however, some localized areas of sensations m ay need to be
abolished w ith additional infiltration injections. Frequently, incomplete anesthesia, especially one close to the midline, after a single m andibular block suggests a branch of the cutaneous colli nerve of the cervical plexus is supplying sensory fibers to the m andibular incisal area.4 Simply infiltrating a few drops of local anesthesia adjacent to the tooth usually rem edies th e problem. Occasionally, a bifid m andibular nerve and the possible consequences of an inferiorly positioned second m andibular foram en can be seen on a panoram ic radiograph. This branch m ay not be anesthetized by traditional block or auxiliary injection techniques. A panoram ic radiographic survey4 of 3,612 patients found th a t 0.9 percent (33 people) in the study had a bifurcation of the m andibular canal.5
■* Too low. An injection too far below the level of the lingula m andibulae will produce lingual anesthesia with inadequate anesthesia of the teeth or bony structures. The inferior course of th e lingual nerve after it separates from the inferior alveolar nerve and continues on to innervate the tongue explains this phenom enon.1The m andibular teeth or alveolar ridges are reference points to aid orientation in this plane. M aintaining the barrel of the syringe parallel to this m andibular reference point will aid orientation throughout the entire needle penetration. ■■ Too deep (posteriorly). If a m andibular block injection is m ade too deeply, the solution may be deposited into the parotid gland, resulting in facial nerve anesthesia and paralysis w ithout m andibular nerve anesthesia. Fortunately, this paralysis is tem porary and disappears with absorption of the anesthetic solution.4 To avoid this error, m aintain the syringe on the contralateral canine region and stay on bone JADA, Vol. 123, January 1992
71
(medial aspect of the ram us). ■■ Too m esial. Introducing the needle into the tissues too far m edially of the ram us may cause anesthesia failure. The solution is deposited in the m edial pterygoid muscle which, a p a rt from unsatisfactory pain blocking, m ay also cause postoperative complications, such as muscle inflam m ation and trism us. Avoid this problem by advancing the needle slowly along the m edial surface of the ram us. Too superficial. If a m andibular block injection is m ade too superficially, the solution will deposit in the pterygom andibular space. Too d ista n t from the m andibular sulcus to reach the inferior dental nerve, this injection results in inadequate or no anesthesia.4Avoid this problem by injecting th e needle to sufficient depth and staying on bone. ■* Too high. If the injection is m ade too high, th e solution will be deposited into the sigmoid notch or against the neck of the condyle, resulting in no anesthesia. Visually bisecting the angle formed by the m axillary and m andibular teeth, or alveolar ridges in the edentulous patient, and using the needle and syringe as the bisector, aids in determ ining the height of mucosal penetration during the injection. “ In travascular injection. If all or p a rt of the solution h as been injected intravascularly, little or no anesthetic effect results. Positive aspirations during dental injections were most commonly reported in 2.6 percent to 30 percent of inferior alveolar injections.6A spirated blood m ay arise from a blood 72
JADA, Vol. 123, January 1992
vessel or from blood spillage caused by a traum atized, lacerated blood vessel.7 W ith the proxim ity of the inferior alveolar vessels to the inferior alveolar nerve, introducing a needle can easily enter or ru p tu re the vessel. If this vessel, particularly an artery, is penetrated or traum atized, blood m ay extravasate into the tissue with hem atom a formation. Hem atom a can also be associated w ith the posteriorsuperior alveolar and infraorbital nerve block, producing facial swelling.7 Inadequate inferior alveolar anesthesia was associated w ith possible hem atom a form ation shown by palpable swelling in the retrom olar area and the pterygom andibular space. The p atien t’s lip m ay feel num b, yet anesthesia is incomplete. U nder such circum stances, failed anesthesia m ight be caused by the dilution of the local anesthetic solution by the blood, which may, to some extent, inactivate the anesthetic.7 A spiration during injection can decrease hem atom a formation, especially during m andibular block where the inferior alveolar a rtery is so close to the inferior alveolar nerve. If hem atom a does occur, Traeger7 reported th a t satisfactory and complete anesthesia was obtained using the Gow-Gates high block technique w ith 4 percent prilocaine (Citanest). HIGHLY ANXIOUS PATIENTS
Highly anxious dental p atients norm ally pose the most treatm en t problems for the dental practitioner. Anxiety and fear may cause a p atien t to
complain of pain even when the anesthesia is complete. W einstein and his colleagues8 found a strong relationship betw een patients who have previous difficulties with local anesthesia and patients who have recent suboptim al anesthesia. M any of these patients actually expect th a t they are unable to become and rem ain numb. Early identification of highly anxious patients and patients with previous experiences of difficulty w ith anesthesia perm it proper charting to direct tre a tm e n t requiring a larger volume of anesthetic, greater field of coverage and careful technique. These patients should be approached with a stress reduction protocol. The operator should tell the p atien t th a t the goal is to achieve good anesthesia and interact calmly and confidently w ith the patient. The patient should be informed in advance of the type of procedure to be performed. Dover4 suggests the adjunctive use of some m eans of general analgesia superim posed on local anesthesia analgesia such as Dr. Wong is a preoperative resident, Advanced sedation, Education in General inhalation Dentistry, University of the Pacific, analgesia School of Dentistry, using N 2OSan Francisco. oxygen, hypnosis or audio analgesia—any of which helps to overcome the p a tie n t’s apprehension and preconception th a t the anesthesia will not work. Many patients who appear refractory
or resista n t to local anesthestic action need nothing more th an a little extra atten tio n and reassurance. INFLAMMATION AND INFECTION
Ineffective3 infiltration injections adm inistered into inflamed tissue are usually attributed to acidotic tissue fluid interfering w ith the dissociation of the anesthetic drug.9 Others think th a t inflamm ation modifies the Dr. Jacobsen is activity of peri director, Oral Diagnosis and pheral sensory Treatment Planning, nerves.3 University o f the Inflamm ation Pacific, School of Dentistry» produces an Department of area of prim ary Diagnostic Science, 2155 Webster St., hyperesthesia San Francisco, Calif. m ediated by 94115. Address requests fo r reprints chemicals th a t to Dr. Jacobsen. decrease the threshold of the sensory receptors. W hen inflamm ation induces hyperesthesia, a given stim ulus produces increased sensitivity. This increased nerve response is blocked less effec tively by a given am ount of anesthesia. This problem can be solved simply by increasing the concentration (not necessarily the volume) of anesthetic to lower the action potential of the nerves.
anesthestics. C artridges of solutions less frequently used m ay lose th eir potency on the shelf. Rem ember to store the anesthetic properly, avoid the use of brands where quality control is uncertain and do not use anesthetic p a st the expiration date on the package. If in any doubt, either dispose of the batch or re tu rn the unused portion for lab investigation. SUMMARY
F ailure to achieve profound regional anesthesia is sometim es caused by: ■* anatom ic variations; ■" technical errors of adm inistration; ■** highly anxious patients; «■» inflam m ation and infection; defective solutions. To achieve good local anesthesia: « Place the anesthetic solution as close as possible to the nerve. ■* Become oriented to the bony landm arks by palpation, and then coordinate visually w ith soft tissue landm arks before inserting the needle, as proper needle placem ent (anesthetic solution) is based on the anatom y of the region. ■* W hen placing the needle, asp irate carefully to prevent injecting inadvertently into blood vessels. ■** Use anesthetic solutions th a t have been stored properly and
check to be sure they are not p ast th eir expiration date. To tre a t highly anxious patients: ■«*Approach them calmly and confidently. ■■ Inform patients in advance of w hat you plan to do in each step. ■■ Consider adjunctive use of preoperative sedation, inhalation analgesia, hypnosis or audio analgesia to reduce the patien t’s stress and anxiety as m uch as possible. ■ 1. Milles M. The m issed inferior alveolar block: a new look a t an old problem. A nesth Prog 1984;31:8790. 2. Evers H, H aglund J. Local an aesth esia in d entistry. Illu strate d handbook on d en tal local anaesthesia. A stra Lakemedel: 1990. 3. Rood JP. Some anatom ical an d physiological causes of failure to achieve m an d ib u lar analgesia. B r J Oral S urg 1977-78;15:75-82. 4. Dover WR. The m andibular block injection - why it som etim es fails. O ral H ealth 1971;61:12-14. 5. G rover PS, Lorton L. Bifid m andibular nerve as a possible cause of inadequate an esth esia in the mandible. J O ral Maxillofac Surg 1983;41:177-9. 6. A iling CC, C hristopher C. A s ta tu s rep o rt on dental an esthetic needles an d syringes. JADA 1974;89(5):1171-6. 7. T raeger KA. H em atom a following inferior alveolar injection: a possible cause for anesthetic failure. A nesth Prog 1979;26:122-3. 8. F iset L, K aufm an E, Milgrom P, Ram say D, W einstein P. P atien t perceptions of failure to achieve optim al local anesthesia. Gen D ent 1985;33:218-20. 9. deJong RH, C ullen SC. B uffer-dem and and pH of local anesth etic solutions containing epinephrine. Anesthesiology 1963;24:801.
DEFECTIVE SOLUTIONS
If none of the aforem entioned reasons accounts for the recent failures of your local anesthesias, simply check to see if you have an im pure or im potent batch of local
JADA, Vol. 123, January 1992
73
ain and the need to control pain is a constant factor in dentistry. Pain control w ith local anesthesia is required for m any dental procedures. Local anesthesia injected carefully and accurately not only perm its comfortable and painless treatm ents, b u t also increases the p atien t’s confidence in the dentist. D ental injection techniques are based on anatom ic norm s and statistical averages of bone structure and nerve pathw ays. They are designed for the average p atien t and a norm al healthy physiological and biochemical environm ent a t the injection site. Every case is not so ideal, however, and every dental practitioner has encountered patients who have unusual difficulty obtaining adequate profound local or regional anesthesia. This is particularly tru e for m andibular block anesthesia, or for an infected tooth. About 4,000,000 local anesthetic blocks and infiltrations are given by U.S. dental practitioners annually. Approximately h alf of the injections are inferior alveolar
ABSTRACT
U .S. d en ta l p r a c titio n er s a d m in iste r ab ou t 4,000,000 lo c a l a n e sth e tic b lock s an d in filtr a tio n s ann ually. T he fa ilu re ra te to a c h ie v e a d eq u a te a n e sth e sia for th e p roced u re is e stim a te d to b e 5 p e r ce n t to 15 p ercen t. T his a r tic le d escrib es fiv e d ifferen t c a te g o rie s o f fa ilu r es and su g g e sts w a y s to tr o u b lesh o o t them . injections. The percentage of failure to achieving profound inferior alveolar anesthesia is estim ated to be 5 percent to 15 percent' (about 100,000 to 300,000 injections). Regional anesthesias of the inferior alveolar nerve in patients who are extrem ely obese, edentulous or who have large and laterally flaring m andibles can be especially troublesome. Similarly, a highly anxious p atien t m ay perceive any kind of stim ulation as pain. This article addresses the
various reasons for failures in local anesthesia, and techniques and ideas to troubleshoot and solve these problems. INFILTRATION TECHNIQUE
Local infiltration is usually all th a t is needed to anesthetize the m axillary teeth and soft tis sues for general operative pro cedures. As long as the needle is placed correctly in the buccal fold n e a r the apex of the tooth to be anesthetized, th e volume of solution will diffuse from the injection site through the perio steum and compact bone to reach the nerve stru ctu res th a t innervate the pulp, periodonti um and jawbone. Because of bone density around the tee th in the m andible, these tee th cannot be predictably anesthetized by infiltration techniques. Therefore, nerve bundles branching to the m andibular teeth m ust be blocked. Some operators in filtrate individual teeth using a periodontal ligam ent space infiltration th a t requires a special needle and syringe to p enetrate the space. This technique, though useful for some operators, has an JADA, Vol. 123, January 1992
69
increased incidence of local side effects and is not discussed here. INFERIOR ALVEOLAR BLOCK TECHNIQUE
For m andibular anesthesia, the p a tie n t’s m outh should be opened widely. After the depth of the g reatest concavity on the anterior border of the ram us (the coronoid notch) is palpated w ith the left thum b, the index finger is placed behind the ram us below the ear (midway betw een th e head of the condyle and th e gonial angle of the greatest concavity). Ideally, the m andibular foram en lies m idway on a horizontal line draw n from these two points. W ith the syringe directed from the prem olar region of the opposite side, the needle is inserted a t thum b level. In adults, th is injection point lies about 1 centim eter above th e occlusal surfaces of the m andibular m olars. In children, th e m andibular foram en lies about 0.5 cm. lower th a n in ad u lts.2 The needle insertion point should be ju st lateral to th e pterygom andibular raphe— th e union line betw een fibers of th e superior constrictor and buccinator muscles. As the initial mucosal penetration is m ade lateral to the pterygom andibular raphe, th e practitioner should contact bone im m ediately a t a point ju s t posterior to the internal oblique ridge. After bone has been contacted, the needle can be w ithdraw n slightly and redirected medially. The needle is advanced dorsally along the m edial side of th e ram us and should always be in contact w ith the ram us. The syringe should be held in the original horizontal position. 70
JADA, Vol. 123, January 1992
Figure 1. Simple concept of the nerve supply of the mandibular teeth.
The average depth of the needle penetration in the adult is 2.5 cm. The anesthesia should be carefully aspirated and then slowly injected. After the needle is w ithdraw n from the m andibular foramen, the lingual nerve can be blocked 1 cm. mesially and ventrally to the lingula. The rem aining 0.3 m illiliter of solution of the rem aining capsule should be deposited. ANATOMIC VARIATIONS AS A CAUSE OF FAILURE
Anatomic variations can cause failed infiltrations, usually because of extra dense bone. They also often account for failed or incomplete inferior alveolar block. V ariations include: ™ a wide flaring mandible; ■* a wide ram us m andibularis in the anterior-posterior direction; ■■ a long ram us m andibularis in the superior-inferior direction;
**■ bulky m usculature or excess adipose tissue; ■■ edentulous patients or young patients; *■ any combination of the variations. Anatomic variation problems can be solved, no m atter how m any changes have obliterated visual anatom ic landm arks, because certain bony landm arks rem ain unchanged. By palpating all the described bony landm arks to orient the needle and syringe, and coordinating soft tissue landm arks visually, fairly accurate ideas of the anterior-posterior size of the ram us, the superior-inferior height of the ram us from condyle to gonion, the degree of ram us m andibularis flare and the superior-inferior orientation for the m andibular foram en location emerge. Thus, it will not be difficult to locate the m andibular foramen. Most often, the injection needs to go higher and deeper.
In situations w here bifid canals are recognized and the possibility of a second, more inferiorly placed foram en exists, alte rn a te sites for anesthetic solution placem ent should be considered if routine attem pts to achieve total anesthesia are not successful. In such cases, depositing the anesthetic solution below the norm al anatom ic landm arks m ay provide more complete anesthesia. If successful, this variation should be noted in the p atien t’s chart as a rem inder for future anesthetic blocks. TECHNICAL ERRORS OF INJECTION MYLOHYOID
MENTAL
Figure 2. Diagram of the intrabony mandibular plexus. The most consistent communications are marked.
The m andibular h ard and soft tissues are supplied by a plexus of nerves.3 This plexus, with its m any comm unications, may allow sensation even if the prim ary inferior alveolar nerve is blocked. A block of other nerves in this plexus m ay be required to render the m andibular tee th insensitive. The m ain nerve in this plexus is the inferior dental nerve, b ut lingual, buccal and mylohyoid nerves also occasionally innervated the teeth. To perform restorative tre a tm e n t on these teeth, it m ay be necessary to adm inister more th a n an inferior alveolar block. These patients may require inferior alveolar and lingual nerve block injections and a buccal injection to achieve complete anesthesia. Because of the norm al complex anatom y of the m andibular nerve supply, however, some localized areas of sensations m ay need to be
abolished w ith additional infiltration injections. Frequently, incomplete anesthesia, especially one close to the midline, after a single m andibular block suggests a branch of the cutaneous colli nerve of the cervical plexus is supplying sensory fibers to the m andibular incisal area.4 Simply infiltrating a few drops of local anesthesia adjacent to the tooth usually rem edies th e problem. Occasionally, a bifid m andibular nerve and the possible consequences of an inferiorly positioned second m andibular foram en can be seen on a panoram ic radiograph. This branch m ay not be anesthetized by traditional block or auxiliary injection techniques. A panoram ic radiographic survey4 of 3,612 patients found th a t 0.9 percent (33 people) in the study had a bifurcation of the m andibular canal.5
■* Too low. An injection too far below the level of the lingula m andibulae will produce lingual anesthesia with inadequate anesthesia of the teeth or bony structures. The inferior course of th e lingual nerve after it separates from the inferior alveolar nerve and continues on to innervate the tongue explains this phenom enon.1The m andibular teeth or alveolar ridges are reference points to aid orientation in this plane. M aintaining the barrel of the syringe parallel to this m andibular reference point will aid orientation throughout the entire needle penetration. ■■ Too deep (posteriorly). If a m andibular block injection is m ade too deeply, the solution may be deposited into the parotid gland, resulting in facial nerve anesthesia and paralysis w ithout m andibular nerve anesthesia. Fortunately, this paralysis is tem porary and disappears with absorption of the anesthetic solution.4 To avoid this error, m aintain the syringe on the contralateral canine region and stay on bone JADA, Vol. 123, January 1992
71
(medial aspect of the ram us). ■■ Too m esial. Introducing the needle into the tissues too far m edially of the ram us may cause anesthesia failure. The solution is deposited in the m edial pterygoid muscle which, a p a rt from unsatisfactory pain blocking, m ay also cause postoperative complications, such as muscle inflam m ation and trism us. Avoid this problem by advancing the needle slowly along the m edial surface of the ram us. Too superficial. If a m andibular block injection is m ade too superficially, the solution will deposit in the pterygom andibular space. Too d ista n t from the m andibular sulcus to reach the inferior dental nerve, this injection results in inadequate or no anesthesia.4Avoid this problem by injecting th e needle to sufficient depth and staying on bone. ■* Too high. If the injection is m ade too high, th e solution will be deposited into the sigmoid notch or against the neck of the condyle, resulting in no anesthesia. Visually bisecting the angle formed by the m axillary and m andibular teeth, or alveolar ridges in the edentulous patient, and using the needle and syringe as the bisector, aids in determ ining the height of mucosal penetration during the injection. “ In travascular injection. If all or p a rt of the solution h as been injected intravascularly, little or no anesthetic effect results. Positive aspirations during dental injections were most commonly reported in 2.6 percent to 30 percent of inferior alveolar injections.6A spirated blood m ay arise from a blood 72
JADA, Vol. 123, January 1992
vessel or from blood spillage caused by a traum atized, lacerated blood vessel.7 W ith the proxim ity of the inferior alveolar vessels to the inferior alveolar nerve, introducing a needle can easily enter or ru p tu re the vessel. If this vessel, particularly an artery, is penetrated or traum atized, blood m ay extravasate into the tissue with hem atom a formation. Hem atom a can also be associated w ith the posteriorsuperior alveolar and infraorbital nerve block, producing facial swelling.7 Inadequate inferior alveolar anesthesia was associated w ith possible hem atom a form ation shown by palpable swelling in the retrom olar area and the pterygom andibular space. The p atien t’s lip m ay feel num b, yet anesthesia is incomplete. U nder such circum stances, failed anesthesia m ight be caused by the dilution of the local anesthetic solution by the blood, which may, to some extent, inactivate the anesthetic.7 A spiration during injection can decrease hem atom a formation, especially during m andibular block where the inferior alveolar a rtery is so close to the inferior alveolar nerve. If hem atom a does occur, Traeger7 reported th a t satisfactory and complete anesthesia was obtained using the Gow-Gates high block technique w ith 4 percent prilocaine (Citanest). HIGHLY ANXIOUS PATIENTS
Highly anxious dental p atients norm ally pose the most treatm en t problems for the dental practitioner. Anxiety and fear may cause a p atien t to
complain of pain even when the anesthesia is complete. W einstein and his colleagues8 found a strong relationship betw een patients who have previous difficulties with local anesthesia and patients who have recent suboptim al anesthesia. M any of these patients actually expect th a t they are unable to become and rem ain numb. Early identification of highly anxious patients and patients with previous experiences of difficulty w ith anesthesia perm it proper charting to direct tre a tm e n t requiring a larger volume of anesthetic, greater field of coverage and careful technique. These patients should be approached with a stress reduction protocol. The operator should tell the p atien t th a t the goal is to achieve good anesthesia and interact calmly and confidently w ith the patient. The patient should be informed in advance of the type of procedure to be performed. Dover4 suggests the adjunctive use of some m eans of general analgesia superim posed on local anesthesia analgesia such as Dr. Wong is a preoperative resident, Advanced sedation, Education in General inhalation Dentistry, University of the Pacific, analgesia School of Dentistry, using N 2OSan Francisco. oxygen, hypnosis or audio analgesia—any of which helps to overcome the p a tie n t’s apprehension and preconception th a t the anesthesia will not work. Many patients who appear refractory
or resista n t to local anesthestic action need nothing more th an a little extra atten tio n and reassurance. INFLAMMATION AND INFECTION
Ineffective3 infiltration injections adm inistered into inflamed tissue are usually attributed to acidotic tissue fluid interfering w ith the dissociation of the anesthetic drug.9 Others think th a t inflamm ation modifies the Dr. Jacobsen is activity of peri director, Oral Diagnosis and pheral sensory Treatment Planning, nerves.3 University o f the Inflamm ation Pacific, School of Dentistry» produces an Department of area of prim ary Diagnostic Science, 2155 Webster St., hyperesthesia San Francisco, Calif. m ediated by 94115. Address requests fo r reprints chemicals th a t to Dr. Jacobsen. decrease the threshold of the sensory receptors. W hen inflamm ation induces hyperesthesia, a given stim ulus produces increased sensitivity. This increased nerve response is blocked less effec tively by a given am ount of anesthesia. This problem can be solved simply by increasing the concentration (not necessarily the volume) of anesthetic to lower the action potential of the nerves.
anesthestics. C artridges of solutions less frequently used m ay lose th eir potency on the shelf. Rem ember to store the anesthetic properly, avoid the use of brands where quality control is uncertain and do not use anesthetic p a st the expiration date on the package. If in any doubt, either dispose of the batch or re tu rn the unused portion for lab investigation. SUMMARY
F ailure to achieve profound regional anesthesia is sometim es caused by: ■* anatom ic variations; ■" technical errors of adm inistration; ■** highly anxious patients; «■» inflam m ation and infection; defective solutions. To achieve good local anesthesia: « Place the anesthetic solution as close as possible to the nerve. ■* Become oriented to the bony landm arks by palpation, and then coordinate visually w ith soft tissue landm arks before inserting the needle, as proper needle placem ent (anesthetic solution) is based on the anatom y of the region. ■* W hen placing the needle, asp irate carefully to prevent injecting inadvertently into blood vessels. ■** Use anesthetic solutions th a t have been stored properly and
check to be sure they are not p ast th eir expiration date. To tre a t highly anxious patients: ■«*Approach them calmly and confidently. ■■ Inform patients in advance of w hat you plan to do in each step. ■■ Consider adjunctive use of preoperative sedation, inhalation analgesia, hypnosis or audio analgesia to reduce the patien t’s stress and anxiety as m uch as possible. ■ 1. Milles M. The m issed inferior alveolar block: a new look a t an old problem. A nesth Prog 1984;31:8790. 2. Evers H, H aglund J. Local an aesth esia in d entistry. Illu strate d handbook on d en tal local anaesthesia. A stra Lakemedel: 1990. 3. Rood JP. Some anatom ical an d physiological causes of failure to achieve m an d ib u lar analgesia. B r J Oral S urg 1977-78;15:75-82. 4. Dover WR. The m andibular block injection - why it som etim es fails. O ral H ealth 1971;61:12-14. 5. G rover PS, Lorton L. Bifid m andibular nerve as a possible cause of inadequate an esth esia in the mandible. J O ral Maxillofac Surg 1983;41:177-9. 6. A iling CC, C hristopher C. A s ta tu s rep o rt on dental an esthetic needles an d syringes. JADA 1974;89(5):1171-6. 7. T raeger KA. H em atom a following inferior alveolar injection: a possible cause for anesthetic failure. A nesth Prog 1979;26:122-3. 8. F iset L, K aufm an E, Milgrom P, Ram say D, W einstein P. P atien t perceptions of failure to achieve optim al local anesthesia. Gen D ent 1985;33:218-20. 9. deJong RH, C ullen SC. B uffer-dem and and pH of local anesth etic solutions containing epinephrine. Anesthesiology 1963;24:801.
DEFECTIVE SOLUTIONS
If none of the aforem entioned reasons accounts for the recent failures of your local anesthesias, simply check to see if you have an im pure or im potent batch of local
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