Ultrasound-guided Inferior Alveolar Nerve Block Study
Condition: Ultrasound; Local Anesthetic
Study type: Interventional

Summary: 
      The primary objective is to compare the success of the inferior alveolar nerve block using
      ultrasound versus a traditional landmarking technique (which historically has an approximate
      failure rate as high as 33.8%). The secondary objective is to demonstrate that delivering a
      block under ultrasound guidance does not cause any additional pain to patients, as well as to
      reconfirm data shown in a previous study that the intra-oral transducer is well-tolerated
      among patients.
    

Detailed description: 
      Inferior alveolar nerve blocks are necessary to perform dental procedures in the mandible.
      The standard mandibular block (also known as the Halsted Technique, or the Inferior Alveolar
      Nerve Block) is based on intraoral landmarks but due to anatomical variation between
      patients, the failure rate, and therefore incomplete anaesthesia of the mandibular teeth, is
      high. Success rates have been reported anywhere from 66.2%-96.5% (Montagnese, 1984).
      Different approaches have been described to improve the success of blocking the inferior
      alveolar nerve but all have had varying rates of success (Blanton, 2002; Todorovic, 1986).
      Regardless, none are able to consistently and reliably block the inferior alveolar nerve
      one-hundred percent of the time.

      Ultrasound is a valuable clinical tool to improve the accuracy of nerve blocks, and is also
      an important teaching tool. Ultrasound imaging is capable of identifying the relevant anatomy
      in the region of interest and has become common place during placement of spinal nerve blocks
      and many commonly recognized peripheral nerve blocks (Denny et Harrop-Griffiths, 2005). In
      studies of peripheral nerve blockade of the spine, the use of ultrasound should be able to
      reduce the number of needle passes required to achieve anaesthesia of a peripheral nerve and
      has been shown to reduce procedural times (Griffin et Nicholls, 2010). In addition, onset of
      sensory blockade is faster because of more intimate proximity of the needle tip to the nerve.
      Finally, the ability to visualize, and thereby ensure, the spread of local anaesthetic around
      the nerve also aids in the speed of onset of the block (Griffin et Nicholls, 2010). However,
      ultrasound has yet to be used successfully in intraoral trigeminal nerve blocks.

      While Hannan et al. (1999) did compare ultrasonography to traditional landmarking for the
      inferior alveolar nerve block, there was no increase in success of the block. It should be
      noted that Hannan et al. was unable to visualize the nerve and instead used the inferior
      alveolar artery as a surrogate landmark to approximate proximity to the inferior alveolar
      nerve. Since the study by Hannan et al., there have been marked improvements to ultrasound
      hardware, i.e. transducers, and software, i.e. processors, to improve resolution and increase
      the ability to differentiate objects in soft tissue, specifically the neural structures from
      the vascular structures.

      The inferior alveolar nerve itself can now be visualized by ultrasound in unembalmed human
      cadavers and can be accurately targeted with a needle by placing dye around the inferior
      alveolar nerve and confirmed by dissection performed by a blinded anatomist (Chanpong, 2013).
      The same study had a clinician consistently identify the inferior alveolar nerve bilaterally
      in 20 living individuals by ultrasound. In addition, according to the satisfaction survey
      performed, the intraoral ultrasound probe was just as comfortable as a bite block placed on
      the contralateral side. Based on a 10 point Likert scale (1 being very uncomfortable and 10
      being very comfortable), the ultrasound probe scored a mean of 7.3 and the bite block a 7.5,
      and all 20 volunteers were able to complete bilateral scans. Given that the inferior alveolar
      nerve block can be easily visualized by ultrasound, the accuracy of needle placement may be
      significantly improved.

      Adjacent to the inferior alveolar nerve are the inferior alveolar artery and the inferior
      alveolar vein. The risk of inadvertent vascular puncture of these vessels while performing an
      Inferior Alveolar Nerve Block has been reported to be anywhere from 2.6% to 30% (Malamed,
      2013). By being able to guide the needle using ultrasound, the incidence of their puncture,
      and incidence of nerve puncture, may also be reduced.

      Finally, it has been noted that when patients experience a painful "electric shock"-like
      symptom during mandibular block anaesthesia, these events may be a result from direct contact
      to the lingual nerve (Harn et Durham, 1990). This sensation is said to occur approximately
      seven percent of the time during mandibular blocks and can be associated with persistent
      reduced sensation to the trigeminal nerve. Avoiding direct insult to any of the surrounding
      nerves would reduce intra-operative pain to the patient during inferior alveolar nerve
      blockade.

      In summary, ultrasound-guided inferior alveolar nerve block is a novel technique that may
      improve the success of the nerve block and reduce inadvertent puncture of surrounding
      structures. Currently, there is no published description of the use of ultrasound to guide
      precise needle placement to adjacent proximity of the inferior alveolar nerve to accomplish
      blockade of the respective nerve in living patients.
    

Intervention name(s): Ultrasound
Intervention type(s): Device
Intervention description(s): Will deposit local anaesthetic intra-orally with the aid of ultrasound to guide the location of the final deposition.
Allocation: Randomized
Intervention model: Single Group Assignment
Intervention model description: Split mouth study
Masking: Single (Participant)
Primary purpose: Device Feasibility