Core and advantages of the method
Unlike infiltration anesthesia, where a drug depot is created beneath the mucosa and diffuses into the bone, conduction anesthesia works on a larger scale. The local anesthetic is injected into the region of the nerve that conducts pain signals from the surgical site.
Methods of solution delivery:
- Perineural — used in the vast majority of cases. The drug is injected in close proximity to the nerve trunk, after which the solution gradually infiltrates the nerve fibers.
- Endoneural — administration is performed directly into the substance of the nerve trunk (used extremely rarely and only for specific indications).
The main advantage of the conduction technique is the ability to turn off sensation in a significant area of the maxilla while using a smaller amount of anesthetic than would be required for infiltration of the same zone.
Anatomical background and landmarks of the maxilla
The maxilla is distinguished by a thin compact plate of the alveolar process, which is penetrated by numerous small foramina. Because of this, indirect infiltration anesthesia works exceptionally well here (the anesthetic easily penetrates the cancellous bone tissue). However, for extensive surgical interventions, infiltration is often insufficient.
The topographical and anatomical principle of conduction anesthesia is that nerve trunks must be blocked at strategically important points:
- At the sites of their emergence from the bone tissue.
- Immediately before entering the bone.
In the maxilla, such key zones for needle insertion are the maxillary tuberosity and the region of the infraorbital foramen.
Rules for handling injection instruments
The safety and painlessness of the procedure largely depend on the correct choice of needles and the technique of holding the syringe.
Needle selection: Fine needles increase the risk of accidental vascular puncture and the anesthetic entering the bloodstream, and also do not allow for a reliable aspiration test. Furthermore, they are prone to bending. The mechanical match of needle length and diameter prevents tissue trauma.
Golden safety rule («The 1/3 Rule»): During any injection, at least 1/3 of the needle length must remain above the mucosal surface. It is strictly forbidden to insert the needle into tissues all the way to the hub. This creates a critical risk of bending and breaking the instrument, which would require a complex and traumatic surgical intervention to retrieve the fragment from deep within the tissues.
Hand position of the physician: The syringe is held with the right hand using three fingers (I, II, III) following the "pen grip" principle. The thumb (I) must freely control the distal end of the plunger, while the remaining fingers are positioned on the barrel as far as possible from the needle hub. The needle must be securely fixed to the syringe adapter (usually by screwing it on).
Patient and solution preparation
Any injection, especially conduction anesthesia, requires careful preparation:
- Temperature control: the anesthetic solution must be warmed to a temperature close to the patient's body temperature.
- Antisepsis: soft tissues (lips, cheeks) are gently retracted with a spatula. The future injection site is treated with a 1% iodine tincture or a pre-procedural mouth rinse with a disinfectant solution is performed.
- Minimization of pain: superficial (topical) anesthesia is indicated prior to injection. The needle should be advanced smoothly, continuously creating a leading depot of anesthetic ahead of it — this makes the needle path painless and pushes blood vessels away, preventing their trauma.
If infiltration anesthesia (including techniques such as subperiosteal or intraosseous anesthesia) proves ineffective due to anatomical features or the specifics of the pathological process, the clinician must switch to conduction anesthesia.
Briefly: answers to topical questions
Which nerve branches are blocked during tuberosity anesthesia?
During tuberosity anesthesia, the superior posterior alveolar branches are blocked. Additionally, the middle superior alveolar branch may be turned off depending on anatomical variations and the volume of the drug administered:
- Superior posterior alveolar branches (nn. alveolares superiores posteriores) — the main target of tuberosity anesthesia.
- Middle superior alveolar branch (r. alveolaris superior medius) — blocked when a large amount of anesthetic is administered (the solution penetrates into the infraorbital groove) or if it branches off from the trunk of the maxillary nerve together with the posterior branches.
What anesthesia zone is achieved with infraorbital anesthesia?
With infraorbital anesthesia, pain relief of the teeth, bone, and soft tissues of the anterior and lateral sections of the maxilla is achieved. The anesthesia zone includes:
- Teeth — incisors, canines, premolars, and partially the medial buccal root of the first molar.
- Bone tissue and mucosa — the alveolar process on the vestibular side in the region of the specified teeth.
- Maxillary sinus — the mucous membrane and bone tissue of the anterior, partially posterolateral, inferior, and superior walls.
- Soft tissues — the skin of the infraorbital region, lower eyelid, wing and nasal septum, as well as the skin and mucous membrane of the upper lip.
What anatomical landmarks are used for intraoral infraorbital anesthesia?
Landmarks on the oral mucosa and facial skin are used for intraoral infraorbital anesthesia. The main anatomical landmarks are:
- Projection of the infraorbital foramen (foramen infraorbitale) — determined by palpation on the skin to control the direction of the needle.
- Mucobuccal fold — the injection site is located 0.5 cm anterior to it above the maxillary incisors.
- Maxillary teeth — the injection is performed at the level of the space between the central and lateral incisors.
- Alternative landmarks — if standard access is not possible, the injection is performed at the level of the canine, first, or second premolar.
Which blood vessels are most frequently traumatized during tuberosity anesthesia?
During tuberosity anesthesia, blood vessels in the region of the pterygoid venous plexus are most frequently traumatized.
- Puncture of the veins of the pterygoid venous plexus can lead to the formation of an extensive hematoma.
- Damage to arteries and veins in this region is also possible.
Vascular trauma may occur when the tip of the needle slides along the surface of the maxillary tuberosity.
Which branches originate from the maxillary nerve (n. maxillaris)?
A number of sensory branches originate from the maxillary nerve (n. maxillaris), which are divided into two main groups.
Branches originating from the trunk in the pterygopalatine fossa:
- Zygomatic nerve (n. zygomaticus).
- Infraorbital nerve (n. infraorbitalis).
- Pterygopalatine nerves (nn. pterygopalatini).
- Superior alveolar nerves (nn. alveolares superiores) — include anterior, middle, and posterior branches.
Branches originating in the pterygopalatine ganglion:
- Greater palatine nerve (n. palatinus major).
- Lesser palatine nerves (nn. palatini minores).
- Nasopalatine nerve (n. nasopalatinus).
- Nasal branches (rr. nasales posteriores superiores).
Class and exam questions
What is the main difference between conduction and infiltration anesthesia?
Infiltration places the anesthetic directly into the surgical site, whereas conduction anesthesia is administered at a distance, blocking the entire nerve trunk on its approach to the jaw.
Is more drug required for conduction block?
No, quite the contrary. Conduction anesthesia allows desensitization of a large tissue area while using a smaller volume of a 1–2% solution than infiltration.
Why shouldn't the needle be inserted into tissues all the way to the syringe hub?
According to the "1/3 rule", a part of the needle must remain outside. Inserting the needle up to the hub significantly increases the risk of needle breakage, the removal of which requires emergency surgery.
What else to study on this topic
- Mechanisms of indirect infiltration anesthesia (dental plexus anesthesia).
- Specifics of anesthesia from the palatal aspect of the maxilla.
- Subperiosteal and intraosseous anesthesia: indications and technique.
- Periodontal methods: intraligamentary and intraseptal anesthesia.
- Complications caused by rapid anesthetic injection into tissues.
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