Inferior dental blocks versus infiltration dentistry: is it time for change?

How can we improve our local anaesthetic practice?

There are five questions that we should first address in critiquing existing LA practice and assess if there is need for improvement.

Proposed tailored smart LA practice:

What is the role of LA in managing analgesia for dental patients?

Patients want two main outcomes when they visit a dental practice, first, pain free injections and second painless procedures.¹ However, needles and tablets are but a small part of the holistic pain management of dental patients.² The definition of pain is that it is ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’.³ The brain overlays the pain sensation on the part of the body that is getting hurt to protect it from harm. There are four types of pain:⁴ two healthy and two pathological. Healthy protective pain includes firstly; nociceptive pain, which is the conversion of tissue injury and release of algogenic factors (intracellular components released due to cell damage) which act as ‘foreign bodies’ exciting pain receptors on nociceptive nerve fibres (C, A delta and A beta fibres). These cause transduction from chemical inflammation into an action potential and the progression of an action potential advancing up to the tertiary order neurones to the somatosensory cortex; once reached, the ‘ouch’ results in reflex withdrawal of the ‘digit’ from danger. Inflammatory pain follows nociceptive pain, if tissue damage occurs promoting tissue healing. This process should usually resolve in days or weeks, depending on the degree of damage and persistence of infection.

Local anaesthesia blocks nociceptive pain very successfully but, due to the multiple components of pain there is increasing evidence supporting the education of patients in expected pain levels (managing their expectations), being caring, empathetic, providing appropriate anxiolysis and distraction. Some patients may be stoic types (‘rugby player’) able to cope with the anticipated and actual surgical discomfort, whereas others may be more susceptible to lack of coping and catastrophizing (‘football player patients’) needing a lot more attention. Holistic patient management is all important in pain management, with alternative techniques (hypnosis and acupuncture).

Patients' expectations are paramount and it is known that all patients expect pain when visiting their dentist.⁵ It is important for clinicians to point out to patients that they are not magicians but surgeons and it is impossible to do complex surgery on patients without causing some minor discomfort intra-operatively and, occasionally, moderate pain post-operatively. Perioperative dental pain is not managed well in dentistry and is the most common adverse event reported by dentists^6,7 and by patients.⁸ Regarding the dental experience involving pain, 60% of a representative sample of the general population aged 15 years or more has reported pain at least once during a dental visit.⁹

Local anaesthetic injection plus analgesic tablets are NOT enough! Local anaesthesia is only a small part of operative pain management.² Pain and its management is complex as the individual's pain experience is unique and based upon his/her gender, beliefs, religion, ethnicity, prior pain experience, psychological factors, nocebo and placebo effects etc.⁵ There are many psychological factors driving the response to acute pain related to surgery and in relation to the development of chronic post-surgical pain.

The key aspects for operative pain management include:

How do we minimize systemic complications of dental LA?

Over one billion dental local anaesthetic injections are given annually worldwide (personal communication: Malamed S, FDI lecture 2017). The reported adverse reaction rate is 1:1,000,000 and the mortality (death) rate from dental local anaesthetic injections has been stated at 0.000002%. Allergies are very rare and can often be psychosomatic.¹⁰

The definition of the term ‘adverse reaction’ covers noxious and unintended effects resulting not only from the authorized use of a medicinal product at normal doses, but also from medication errors and uses outside the terms of the marketing authorization, including the misuse and abuse of the medicinal product. The range of pharmaceuticals used in dental practice is relatively small, consisting primarily of sedatives, local anaesthetics, analgesics and antibiotics. Adverse drug reactions are categorized as type A or type B.

The most common adverse reactions to LA include:

Adverse events happen in relation to the concentration and dose of LA, the size and health of your patient and intravascular injections. This is more likely with block, intraosseous and periodontal injections. Minimizing risk of overdose includes avoiding:

Young and elderly patients must be suitably assessed for their weight. A child of 5 years weighs 18–20 kg therefore maximum dose 88 mg (2 x 2.2 ml lidocaine cartridges). Due to their size, children are at high risk of toxicity. Goodson and Moore have documented catastrophic consequences of this drug interaction in paediatric patients receiving procedural sedation, along with excessive dosages of local anesthetics.^14,15

Aspiration during dental LA is a legal requirement in the UK. Avoiding intravascular LA is possible by using aspiration and avoiding intraosseous injections and being aware of the increased vascularity of inflamed tissue whilst always observing clinical reactions by:

A recent survey of 2731 patients undergoing LA for dental treatment reported that 45.6% patients had medical risk factors (mostly cardiovascular). The overall LA complication rate was 4.5% complications (5.7% in risk patients/3.5% non-risk patients), which were, most commonly, dizziness, tachycardia, agitation and bronchospasm. Severe complications, including seizures and bronchospasm, occurred rarely (0.07%). Overall, there were fewer complications with articaine 4% I:100K epinephrine compared with articaine 4% I:200K epinephrine.¹⁶ Articaine is less toxic than lidocaine at the same concentration as it has high binding plasma rate thereby reducing crossing the placenta or blood brain barrier. Metabolism of articaine occurs in tissue and plasma (rather than in the liver for lidocaine or bupivacaine) and lidocaine only 50% is degraded after 1.5–3 hours, which is much slower than articaine of which 50% is eliminated after 20 minutes (Table 3).

All suspected adverse events to local anaesthesia should be reported and this can be done online via the MHRA Yellow Card website (at www.mhra.gov.uk/yellowcard) or by calling the National Yellow Card Information Service on 0808 100 3352 (10am to 2pm Monday–Friday). In addition, dental practices should sign up to receive MHRA alerts. Subscribe using the following link: https://www.gov.uk/drug-device-alerts/email-signup

What are the medical modifiers for dental LA?

There are few absolute medical contra-indications to local anaesthetic and these are listed in Table 4. There are some relative but not absolute contra-indications for adrenaline use including:

However, prudent avoidance of blocks, or aspirating when using blocks and slow injection, low dosage and staged treatments allows the use of adrenaline in patients with these conditions. Use of low dose adrenaline LA agents may be used in these cases (Table 5).¹⁶

Many complications or adverse events arise during dental local anaesthetics due to the patient being overly anxious or not well informed. Thus, the LA technique used must address several aspects including:

A key factor in patient satisfaction is a sense that the care-giver is doing his/her best and is genuinely concerned that therapy is adequate.¹⁸

How do we minimize regional complications of LA?/Avoiding failed LA

There are many myths regarding failed LA in dentistry.¹⁹ Local anaesthesia failure is often assumed to be the fault of the clinician due to the general overestimation of the effectivity of block anaesthesia providing pulpal anaesthesia in the mandible. The onset of lip numbness usually occurs within 5–9 minutes of injection and pulpal anaesthesia follows 15–16 minutes later.^20,21-22 Slow onset of pulpal anesthesia (after 15 minutes) occurs approximately 19–27% in mandibular teeth and approximately 8% of patients have onset after 30 minutes.²³ Lip numbness does not guarantee pulpal anaesthesia and failure to achieve lip numbness occurs about 5% of the time with experienced clinicians.^24,25

Inferior dental blocks are remarkably inefficient at providing pulpal anaesthesia for dental procedures.^26,27-28 Malamed stated that the rate of inadequate anaesthesia ranged from 31% to 81%. When expressed as success rates, this indicates a range of 19% to 69%. These numbers are so wide ranging as to make selection of a standard for rate of success for IDB seemingly impossible.¹⁰ There are many other possible components contributing to LA failure including:

How do we manage failed IDB?

There is no evidence supporting using direct or indirect Halstead IDB technique or the improved efficacy of using Gow Gates or Akinosi techniques. The main issues appear to be the overestimation of the efficacy of IDBs in general, impatience and lack of awareness that one must wait over 15 minutes for maximum efficacy of a lidocaine block, in addition to the lack of use of alternative techniques that provide improved pulpal anaesthetic rates for anterior teeth.

How do we minimize regional complications of LA?

Most of these complications can be avoided by careful technique and avoidance of intravascular injections, but even when clinicians use the utmost care, by aspirating before the injection and noting anatomical landmarks, intra-arterial injections can occur during inferior alveolar nerve blocks.⁵⁴ Fortunately, permanent damage to nerves, facial and oral tissues, and eyes is rare. Possible regional complications related to IDBs include:

The incidence of persistent neuropathy related to dental IDBs is rare, estimated to be between 1 in 14K temporary and 1 in 52K permanent (25% permanent),⁵⁹ 1:26,762 and 1:160,571,⁶³ respectively, 1 in 27.415 cases,⁷⁴ 1 in 785,000 injections, to 1 in 13,800.⁶⁶ The majority of nerve injuries are painful in patients seeking care, consistent with other surgical sensory neuropathies, leading to a condition known as chronic post-surgical pain. Unfortunately for these patients, the unforeseen complication of routine dental care leads to life-changing orofacial pain with subsequent significant functional and psychological sequelae.

What is wrong with our current practice and how can we do better?

Proposed tailored smart LA practice asks the questions:

The limitations of IDB in providing swift mandibular pulpal anaesthesia is recognized and recent evidence supports the use of infiltration mandibular dentistry. Interestingly, for decades dentists have routinely undertaken maxillary dentistry with infiltrations, accepting that nerves within bone are accessible to submucosal local anaesthetic techniques. With respect to maxillary infiltration anaesthesia, some studies have found 4% articaine to be more effective than 2% lidocaine for lateral incisors but not molars,⁷⁴ while others reported no clinical superiority for this injection.^75,76 A recent randomized controlled trial found a statistically significant difference supporting the use of 4% articaine in place of 2% lidocaine for buccal infiltration in patients experiencing irreversible pulpitis in maxillary posterior teeth.⁷⁷

As mentioned previously, nerve blocks are related to nerve injury and there are no indications for the use of palatal, incisal or infra-orbital nerve blocks for dentistry, except in very rare exceptions. An example of this is spreading infection from canines or premolars, when the use of block anaesthesia will prevent the need for GA drainage and extractions. Several studies report the lack of indications for palatal block injections.^78,79 There is increasing evidence that additional injections (buccal infiltration, intraseptal, intraligamental, intra osseous) can enhance and even replace IDBs.^32,35,47,77 Lidocaine infiltration is likely to be as effective as articaine for maxillary dentistry.⁸² A recent systematic review highlighted that there is no benefit in using articaine infiltration for maxillary dentistry but articaine is 3.6 more times effective than lidocaine for mandibular infiltration dentistry.⁸³

Can articaine 4% infiltration replace lidocaine 2% IDBs for routine dentistry?

Using infiltration and not IDBs improves patient comfort as patients prefer having full lingual sensation and shorter duration LA anaesthesia after dental treatment.³² Not only are buccal infiltration techniques proving to be more effective than IDBs, but intraligamental injections can also be used effectively for exodontia as they are effectively intravascular with more likely systemic effects but, in addition, there are reported higher post-restorative pain levels.^84,85

Benefit of computerized systems for infiltration techniques

There is limited evidence to support that computerized infiltration systems are more effective, but those regularly using these systems empirically report better patient acceptance and comfort during injections.⁹⁴

What is the best agent?

Articaine (4-methyl-3-[2-(propylamino)-propionamido]-2-thiophene-carboxylic acid, methyl ester hydrochloride) is a unique amide LA in that it contains a thiophene, instead of a benzene, ring. The thiophene ring allows greater lipid solubility and potency as a greater portion of an administered dose can enter neurons. It is the only amide anaesthetic containing an ester group, allowing hydrolysation in unspecific blood esterases. About 90% of articaine metabolizes quickly via hydrolysis in the blood into its inactive metabolite articainic acid, which is excreted by the kidney in the form articainic acid glucuronide. Its metabolism is age dependent, where clearance and volume of distribution decreases with increasing age. The elimination serum half-life of articaine is 20 minutes and of articainic acid is 64 minutes.^95,96-97 Articaine at three different comparative lidocaine concentrations provides more effective mandibular pulpal anaesthesia.⁹⁸ However, articaine is 3.6 times more effective for mandibular infiltration dentistry⁹⁹ and a recent study demonstrated that 2% articaine is as effective as 4% articaine using IDB for mandibular dental extraction in adults.^100,101 In summary, more research is needed before recommending replacing 4% with 2% articaine for all dental procedures.

The concentration of epinephrine may be reduced from 1 in 100 to 1in 200 and is equally effective for third molar extraction.¹⁰² An epinephrine concentration of 1 in 400 may only be required for paediatric extractions using 4% articaine.¹⁰³

So, is the future agent for dental anaesthesia 2% articaine with 1: 200–400K epinephrine for all LA techniques and dental procedures in adults? Could we use epinephrine-free LA for paedodontic dentistry? Further research is needed

What LA volumes should we be using?

The most common LA cartridge volume used worldwide is 1.8 ml.¹⁰⁴ Dentists in France and Japan use only 1 ml cartridges and the Commonwealth 2.2 ml cartridges. Dictation of LA volume should be related to diameter of nerve and accuracy of technique. For buccal Infiltration, average LA volume of 0.59 ml with 97.5% provided effective pain control.¹⁰⁵

Infiltration techniques require significantly less LA volume compared with block techniques: Gow Gates only block anaesthesia technique recommends full cartridge 1.8–2.2 ml; and infra-orbital LA block requires 1.8–2.2 ml¹⁰⁶ (Tables 7 and 8).

Thus the continued use of 2.2 ml cartridges should be questioned and changed to 1.8 ml cartridges, which would improve patient safety and likely impact minimally on repeated injections.

The future interest is the possibility of development of newer improved agents (sensory blocking agents only) and devices and techniques for achieving profound sensory anaesthesia. A nasal spray (http://clinicaltrials.gov/ct2/show/NCT01302483) which has been shown to anaesthetize maxillary anterior six teeth is set to be tested in an FDA Phase 3 trial, which will assess the spray's effectiveness compared to the current ‘gold standard’ treatment – painful anaesthesia injections. Buffering of acidic local anaesthetics to more neutral physiological pH allows for speedier LA onset and is already in use in the US. Another development is a syringe micro vibrator (SMV),¹⁰⁷ a new device being introduced in dentistry to alleviate pain and anxiety of intra-oral injections.

Summary

A radical change in LA practice is required with regard to many aspects of patient safety based upon current evidence, whilst acknowledging further research would be ideal. With the current research legislation, undertaking simple efficacy studies of existing commonly used LA agents is prohibitively expensive and unlikely to be funded by pharmaceutical companies, limiting the provision of future robust supportive research. Infiltration LA for implantology is a good example where common sense and application of optimal technique has occurred without a robust evidence base providing safer more effective patient care. The following are guidelines for the possible way forward: