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Managing Pain

Many options are available when choosing the most appropriate injectable local anesthetic for dental patients.

Pain control is a critical element in successful dentistry. Many anesthetic agents are available to help clinicians provide comfortable patient care. Oral health professionals are charged with choosing the most appropriate anesthetic agent for patients, considering medical history concerns and treatment needs.

Several important pharmacological principles should be considered prior to selecting an anesthetic agent, including onset time, duration of anesthesia, contraindications, potential adverse effects, and maximum recommended dose (MRD). An important note regarding MRD: the United States Food and Drug Administration’s maximum doses are based on a 150-pound healthy patient. For patients who weigh less than 150 pounds, the MRD should be calculated per their individual weight. Additionally, when administering more than one local anesthetic agent, the lowest MRD should be used to establish the maximum dosing level. There are also MRDs for vasoconstrictors (0.2 mg epinephrine per appointment for a healthy patient; 0.04 mg epinephrine per appointment for patients with relative contraindications; and 1 mg levonordefrin per appointment for all patients).1 Calculations for the maximum number of cartridges need to account for both the anesthetic and the vasoconstrictor. The lower of the two numbers is the maximum number of cartridges.

Vasoconstrictors increase the depth and duration of anesthesia, and reduce the risk of toxicity.1 Vasoconstrictors have absolute and relative contraindications. An absolute contraindication is a situation in which vasoconstrictors should not be administered under any circumstances, such as a patient with uncontrolled hyperthyroidism.2 For patients with a relative contraindication, the risk vs benefit ratio should carefully be considered. For example, when using a vasoconstrictor with a patient taking tricyclic antidepressants, the vasoconstrictor should be limited to the lower dosage limit of 0.04 mg.2 Lidocaine 2% is available with 1:50,000 epinephrine. This concentration of epinephrine is indicated when strong hemostasis is needed. Administering infiltrations in the treatment area will control bleeding in the field. An epinephrine concentration of 1:100,000 will provide the same depth and duration of anesthesia, while administering half as much epinephrine. The epinephrine concentration of 1:100,000 should be the most concentrated amount administered for pain control in most dental procedures.1 Prilocaine and articaine are available in formulations with epinephrine 1:200,000. This concentration provides similar depth and duration of pain control as 1:100,000, using half as much epinephrine. These formulations can be appropriate options for patients with relative contraindications for vasoconstrictor use.

ASSOCIATED RISKS

Amides and esters are the main categories of anesthetics used in dentistry. All of the injectable drugs are amides, and many topical drugs are esters. While allergies to local anesthetics are rare, most are related to esters. When patients report a history of allergic response, all anesthetics should be avoided until appropriate allergy testing can be completed.

The use of prilocaine in pa­tients with a history of methemoglobinemia or other medical conditions characterized by re­duced oxygen-carrying capacity raises the risk of methemoglobinemia, therefore it is contraindicated.3 Large doses of benzocaine may also raise the risk of methemoglobinemia.3 

Research demonstrates that 4% anesthetic solutions (articaine and prilocaine) have an increased risk of post-operative paresthesia, primarily with mandibular nerve blocks.4–8 The risk of a post-operative paresthesia, however, is still very low.5,6 Research also shows that articaine provides more reliable anesthesia than other agents when administered via infiltration.3,4,9,10 However, articaine has not demonstrated significant advantages over lidocaine when administered via mandibular nerve block.8 

INJECTABLE ANESTHETICS

Injectable dental local anesthetic agents provide a range of anesthetic durations. Selection should be made with the individual patient’s procedure and medical history in mind. All injectable solutions are contraindicated in patients with known allergies to amide anesthetics or any component of the formulation.1

The solution of 2% lidocaine, 1:100,000 epinephrine has an onset of 3 minutes to 5 minutes. It provides pulpal anesthesia for 60 minutes and soft tissue for 180 minutes to 300 minutes.1 The MRD is 3.2 mg/pound, or a maximum of 11 cartridges, based on the MRD of epinephrine. Absolute maximum is 500 mg.

The onset of plain 3% mepivacaine is 3 minutes to 5 minutes and it provides pulpal anesthesia for 20 minutes via infiltration and 40 minutes via nerve block. It offers 120 minutes to 180 minutes of soft tissue anesthesia.1 Mepivacaine plain, however, is not indicated for procedures requiring lengthy or profound anesthesia.1 It has an MRB of 3.0 mg/lb, or a maximum of 7.4 cartridges per appointment. Absolute maximum is 400 mg.1

The solution of 2% mepivacaine, levonordefrin 1:20,000 offers a 3-minute to 5-minute onset and provides pulpal anesthesia for 60 minutes and soft tissue for 180 minutes to 300 minutes.1 The MRD is 3.0 mg/lb, or a maximum of 7.4 cartridges per appointment. Absolute maximum is 400 mg.

Plain 4% prilocaine has an onset of 3 minutes to 5 minutes and provides pulpal anesthesia for 10 minutes to 15 minutes via infiltration and 4 minutes to 60 minutes via nerve block. It offers soft tissue anesthesia for 90 minutes to 120 minutes via infiltration and 120 minutes to 240 minutes via nerve block. Prilocaine is contraindicated in patients at risk for methemoglobinemia.1 The MRB is 3.6 mg/lb, or a maximum of 8.3 cartridges per appointment. Absolute maximum is 600 mg.1

The solution of 4% prilocaine, epinephrine 1:200,000 may be appropriate for patients who need profound anesthesia but have cardiac health issues or other concerns that limit their dosing of vasoconstrictors. It has an onset of 3 minutes to 5 minutes and provides pulpal anesthesia for 60 minutes to 90 minutes and soft tissue for 180 minutes to 480 minutes.1 Prilocaine is contraindicated in patients at risk for methemoglobinemia. The MRD is 3.6 mg/lb, or a maximum of 8.3 cartridges per appointment. The absolute maximum is 600 mg.1 

Articaine 4%, epinephrine 1:100,000 offers an onset of 2 minutes to 3 minutes with 60 minutes to 75 minutes of pulpal anesthesia and 180 minutes to 360 minutes of soft tissue anesthesia.1 It is contraindicated in patients with sensitivities to sulfites. Safety and efficacy for children younger than 4 have not been established. The MRD is 3.2 mg/lb. The manufacturer does not list an absolute maximum dose, but for a 150-lb patient, the maximum dose is 480 mg (6.6 cartridges) per appointment. Articaine 4% is also available in a formulation with epinephrine 1:200,000. This may be a good choice for patients who need profound anesthesia but have cardiac health issues or other concerns that limit their dosing of vasoconstrictors. Pulpal duration for this formulation is 45 minutes to 60 minutes, and soft-tissue duration is 120 minutes to 300 minutes.1

The onset of 0.5% bupivacaine, epinephrine 1:200,000 is 6 minutes to 10 minutes,1 which is much slower than other injectable anesthetics. It offers 90 minutes to 180 minutes of pulpal anesthesia and 240 minutes to 540 minutes of soft tissue anesthesia. Bupivacaine is not recommended for use in children or other patients at risk for post-operative soft-tissue injury due to the lingering soft tissue anesthesia.1 The MRD is 0.9 mg/lb, or a maximum of 10 cartridges per appointment. Absolute maximum is 90 mg. Bupivacaine is primarily indicated for procedures in which prolonged pulpal anesthesia is required (longer than 90 minutes) or for post-operative pain control.1

BUFFERING OF LOCAL ANESTHETICS

Buffering is the addition of sodium bicarbonate to the anesthetic solution to raise the acidic pH to a more physiologic range (pH of 7.35 to 7.45).1 This process decreases the pain on injection due to the acidic nature of an unbuffered anesthetic and speeds time of onset by increasing the proportion of available ions to penetrate the nerve membrane.1,11 Research on the buffering of local anesthetics is mixed. Some studies concluded there were no statistically significant differences between the use of buffered and nonbuffered solutions regarding injection discomfort and onset time.12,13 Others show that buffering anesthetics effectively decreases the discomfort of the injection and speeds onset.11,14–16 Buffering systems include buffering solutions and mixing devices. With one system, the clinician uses a mixing pen to add sodium bicarbonate to a traditional dental cartridge. Another system uses large vials of lidocaine and sodium bicarbonate that are mixed in a cartridge contained inside a dispenser. The clinician uses a proprietary syringe to withdraw buffered anesthetic from the dispenser. There are no significant contraindications for using buffered anesthetics. Mixing systems provide a level of control that ensures precise buffering. If too much buffering solution is added, the anesthetic will lose effectiveness, and tissue damage can result if the pH of the solution is above 7.8. For this reason, a mixing system is recommended.

Oral health professionals who are well versed in the selection of local anesthetic materials will be best able to choose the optimum solution for individual patient needs. With the range of anesthetic agents and related products available, clinicians can ensure good patient experiences during dental care.

REFERENCES

  1. Malamed S. Handbook of Local Anesthesia. 6th ed. St. Louis, MO: Elsevier Mosby; 2013.
  2. Logothetis D. Local Anesthesia for the Dental Hygienist. St. Louis, MO: Elsevier Mosby; 2012.
  3. Ogle OE, Mahjoubi G. Local anesthesia: Agents, techniques, and complications. Dent Clin North Am. 2012;56:133–148.
  4. Becker DE, Reed KL. Local anesthetics: Review of pharmacological considerations. Anesth Prog. 2012;59:90101.
  5. Gaffen AS, Haas DA. Retrospective review of voluntary reports of nonsurgical paresthesia in dentistry. J Can Dent Assoc.2009;75:579.
  6. Garisto GA, Gaffen AS, Lawrence HP, Tenenbaum HC, Haas DA. Occurrence of paresthesia after dental local anesthetic administration in the united states. J Am Dent Assoc. 2010;141:836844.
  7. Piccinni C, Gissi DB, Gabusi A, Montebugnoli L, Poluzzi E. Paraesthesia after local anaesthetics: An analysis of reports to the FDA adverse event reporting system.  2015;117:52–56.
  8. Moore PA, Haas DA. Paresthesias in dentistry. Dent Clin North Am. 2010;54:715730.
  9. Leith R, Lynch K, O’Connell AC. Articaine use in children: A review. Eur Arch Paediatr Dent. 2012;13:293–296.
  10. Kanaa Whitworth JM, Corbett IP, Meechan JG. Articaine and lidocaine mandibular buccal infiltration anesthesia: A prospective randomized double- blind cross-over study. J Endod. 2006;32:296298.
  11. Malamed SF, Tavana S, Falkel M. Faster onset and more comfortable injection with alkalinized 2% lidocaine with epinephrine 1:100,000. Compend Contin Educ Dent. 2013;34:10–20.
  12. Bowles WH, Frysh H, Emmons R. Clinical evaluation of buffered local anesthetic. Gen Dent. 1995;43:182–184.
  13. Primosch RE, Robinson L. Pain elicited during intraoral infiltration with buffered lidocaine. Am J Dent. 1996;9:5–10.
  14. Whitcomb M, Drum M, Reader A, Nusstein J, Beck M. A prospective, randomized, double-blind study of the anesthetic efficacy of sodium bicarbonate buffered 2% lidocaine with 1:100,000 epinephrine in inferior alveolar nerve blocks. Anesth Prog. 2010;57:59–66.
  15. Kashyap VM, Desai R, Reddy PB, Menon S. Effect of alkalinisation of lignocaine for intraoral nerve block on pain during injection, and speed of onset of anaesthesia. Br J Oral Maxillofac Surg. 2011;49:e72–75.
  16. Davies RJ. Buffering the pain of local anaesthetics: A systematic review.  2003;15:81–88.

From Dimensions of Dental HygieneMarch 2017;15(3):24,26. 

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