Simple and safe posterior superior alveolar nerve block.

BACKGROUND: The posterior superior alveolar nerve (PSAN) block is a dental nerve block used for profound anesthesia of the maxillary molars. Although it is being written in texts as a commonly used technique, but in dentistry it is rarely followed due to its nonreliable landmarks, variation in depth of insertion and frequent complications. The aim and objective are to find a technically simple method of the PSAN block without any complications. STUDY AND
DESIGN: This study was based on the experience gained from 200 patients of 125 males and 75 female in age group of 20 to 65 years in University of Vinayaka and department of oral and maxillofacial surgery of VMS Dental College and hospital, Salem, Tamil Nadu.
RESULTS: In 200 patients' positive anesthesia obtained within a period of 5 to 10 min. No visual complications reported in this study. There was no pain during and after extraction.
CONCLUSION: This study shows this PSA nerve block using curved needle would avoid all complications reported in the literature. Therefore, the technique described in this study is an ideal option to anesthetize PSA nerve.

INTRODUCTION

The posterior superior alveolar nerve (PSAN) block is a technique for achieving anesthesia for the maxillary molars. The PSAN is a major sensory branch of the maxillary division of the trigeminal nerve. A PSAN block injection is a procedure employed for effective pain control for the posterior maxillary teeth and surrounding structures supplied by this nerve.[1]

Regardless of the care used in administration of Posterior superior anesthetic technique, unusual reactions can occur. Complications arising from the PSAN block include hematoma formation, transient diplopia, blurred vision, and temporary blindness.[2] A case is presented in which posterior superior alveolar administration of two percent Lignocaine 1/100 000 epinephrine resulted in medial rotation of the orbit.[3] Reported complications and case reports of patient's experiences of ophthalmological visual or motor problems from PSAN injections denotes the technical difficulties in mastering this technique and current drawbacks of the present PSAN block. Many dentist prefer supra periosteal infiltration superior to molars to anesthetize maxillary molars rather than the PSAN block. Due to its complications and complex technique, the PSAN block is rarely practiced by dentists. These literature findings denote technically simple and safe PSAN block is an essential and needy one. Therefore, this study was aimed to find a simple and safe PSA nerve block.

AIMS AND OBJECTIVES

The aim of this study was to find a technically simple method of the PSAN block without any complications.

MATERIALS AND METHODS

After approval by the Hospital Ethics Committee and with the consent of patients, the PSA nerve block was performed in 200 adult patients, ASA I-II, aged between 20 and 65 years during the period from Jan 2011 to September 2011. Out of 200 patients, 125 were males and 75 were females. The PSA nerve block was administered to remove upper second and third molars. The efficacy of anesthesia was tested by identification of the subjective and objective symptoms after a latency period of 5 to 10 min. A probe was used to find the efficacy of the anesthetic technique. Buccal tissues in front of the upper second molar root and above the distal buccal root of the first molar were pricked with probe to test the anesthesia. No reaction of pain from the patient was taken as complete anesthesia of the PSA nerve.

The materials used were 2% lignocaine with 1:80000 adrenaline anesthetic solutions. A 24 g, 25 mm length needle was used to give injection. The needle was curved to the desired design.

Technique: Simple and safe PSA nerve block

The patient is made to lie down in semisupine position below operators elbow level. As shown in Figure 1.

Figure 1

Semisupine position below operators elbow level

Patient is asked to open the mouth partially and advised to bring the lower jaw toward side of injection.

With the help of mouth mirror retract the cheek to visualize the vestibule superior and distal to upper third molar as shown in Figure 2.

Figure 2

Retraction of cheek to visualize the vestibule superior and distal to upper third molar

A 24 mm length needle is curved as shown in Figure 3.

Figure 3

Needle curved

The initial site of needle insertion is in the depth of vestibule distal and superior to the third molar region (junction of the posterio lateral surface of maxilla and posterior surface of maxilla) as shown in Figure 4. Here few drops of the anesthetic solution are deposited to anesthetize the path of insertion.

Figure 4

Initial site of needle insertion

The curved needle is inserted further superiorly along posterior wall of maxilla to a distance of 5 mm and 1 mL of solution is injected.

The needle is advanced further superiorly to a distance of another 5 mm (totally 10 to 12 mm from the initial puncture point). Now the needle tip is in the middle third of posterior surface of maxilla, where the PSA nerve descends downward to reach its foramen; here 1 mL of solution is injected [Figure 5]. This is the final position of needle in this technique that is shown on skull Figure 6.

Figure 5

Final position of the needle

Figure 6

Final position of the needle shown in maxilla

This favors deposition of solution prior to the PSA nerve entry into its foramen. This helps to anesthetize the tissues supplied by PSAN. The anatomy of PSA nerve is shown in Figure 7.

Figure 7

PSA nerve anatomy

The efficacy of anesthesia was tested by identification of the subjective and objective symptoms after a latency period of 5 to 10 min. A probe was used to find the efficacy of the anesthetic technique. Buccal tissues in front of the upper second molar root were pricked with probe to test the anesthesia. No reaction from the patient was taken as complete anesthesia of PSA nerve [Figure 8].

Figure 8

Objective test of anesthesia

RESULTS

In all the 200 patients’ positive anesthesia obtained within a period of 5 to 10 min. Anesthesia duration was 60 to 90 min. No positive aspiration and no extra oral hematoma occurred in patients. No visual complications occurred in this study. There was no pain during and after extraction.

The VAS scoring method was explained to the patient prior to injection. Patients were asked to measure their pain in the 100 mm scale while probing the tissues superior to distal buccal root of first maxillary molar and after completion of extraction. All the patients measured their pain within 1 mm of 100 mm scale after injection and within 3 mm after extraction which denotes complete success of this alternate PSA nerve block.

DISCUSSION

Adequate use of local anesthetics is an important phase of modern dentistry. Regardless of the care used in administration of local anesthetics, unusual reactions can occur.[3] From the review of the literature following complications were found.

Maxillary local anesthetic injections, particularly those deposited near the pterygo maxillary fissure are known to cause diplopia of the ipsilateral eye and are estimated to occur in about 35.6% of cases. This often results from the local anesthesia diffusing superiorly and medially to anesthetize the orbital nerves. There are no known reports in the literature of permanent diplopia.[4]

The hypothesis for ophthalmological manifestation of an inferior alveolar nerve block has been proposed as local anesthetic solution reaches the orbit through vascular, neurological, and lymphatic network.[5]

They proceed to describe that oculomotor disturbance after injection of dental local anesthetics is that of inadvertent deposition of some of the drug into the inferior alveolar artery, mandibular canal or PSA artery. By reverse flow, the anesthetic agent then reaches the internal maxillary and middle meningeal arteries, the orbital branch of the latter anastomosing with the lacrimal branch of the opthalmic artery.[6]

A short needle is usually recommended for a PSAN block injection as a long needle will harm the pterygoid plexus. A cadaver study proved that the improper size and placement of needle could damage the pterygoid plexus.[7]

A patient whose abducent nerve is involved may complain of double vision and may exhibit limitation of abduction of the ipsilateral eye as well as paresthesia of the lateral side of the upper and lower eyelids in limited cases.[8]

The PSA nerve block technique described in the Monheim's text is given below.

The operator stands on the right side of patient. The patient is positioned so that the maxillary occlusal plane is at 45° angle to floor. The operator moves the left forefinger over the mucobuccal fold in a posterior direction from the bicuspid area until the zygomatic process of maxilla is reached. At its posterior surface, the fingertip will rest in a concavity in the mucobuccal fold.

At this point the left forefinger is rotated so that the finger nail is adjacent to mucosa and its bulbous portion is still in contact with the posterior surface of the zygomatic process.

Now the hand is lowered with the finger keeping the bulbous portion in contact with the zygomatic process so that the finger is in a plane at right angles to the occlusal surface of maxillary teeth and at the 45° angle to the patient's saggital plane.

The index finger should be pointing in the exact direction the needle is to follow.

A previously loaded syringe with 1 5/8 in 25 gauge needle is held in pen grasp and inserted into the tissues in a line parallel with index finger and bisecting the fingernail. The insertion is made to a distance of about ½ or ¾ in, going upward, inward, and backward. This should place the needle in the vicinity of foramen through which the nerves enter the maxilla.

Due to the complications that may arise after the administration of the above technique, many dentists do not follow this technique. The direction of needle insertion is difficult to follow practically. The depth of penetration is not constant for all individuals, so over penetration may produce immediate extra oral hematoma due to the needle entry into the pterygoid plexus. When the needle is directed superiorly, solution may be deposited near inferior orbital fissure that may result in visual complications.

One study stated that infiltration above molars is preferred to anesthetize the molars than this PSA nerve block due to its complex injection technique.

In this study, 24 mm needle is curved at its distance of 10 to 12 mm and injected directly nearer to nerve at the posterior surface of maxilla. Over penetration of needle is not possible because only 10 to 12 mm is the possible depth of needle insertion due to the curvature of needle from the initial site of insertion.

CONCLUSION

This study shows that this PSA nerve block using curved needle would avoid all complications reported in the literature. Therefore, the technique described in this study is a better option to anesthetize PSA nerve.