7)Local Anaesthesia Flashcards
Definition of LA
- Loss of sensation in a circumscribed area of body causes by:
- A depression of excitation of nerve endings
- An inhibition of conduction process in peripheral nerves - without loss of consciousness
Types of LA - Esters
Amino-ESTERS
- Metabolised by pseudocholinesterase rapidly - short acting
- Clinical use - Esters of para-aminobenzoic acid
- PROCAINE - standard drug used for more than 40 years - no topical anaesthetic properties
- BENZOCAINE- Ester linked, water insoluble + poorly absorbed
- excreted in urine
Types of LA - Amides
Amino - AMIDES
- Metabolised mainly by liver microsomal P450 enzymes slowly - longer acting
- LIDOCAINE - 1st commercially available agent
- ARTICAINE - Both amide + ester
- PRILOCAINE + MEPIVACAINE - similar to lidocaine w/low systemic toxicity
- Lidocaine + articaine widely used LA in dentistry - good topical anaesthetics
- excreted in urine
- Hydrophobicity - increases potency + duration of action
Chemical Structure of LA
- Aromatic + Amine groups connected by a chain
- Aromatic part - responsible for lipophilic properties
- Amine end - associated w/hydrophilicity
- changes in these portions will alter lipid/water solubility + protein binding - altering anaesthetic effect
- changes occur in: intrinsic anaesthetic potency/onset time/duration of action/toxicity/ratio/rate of degradation
Mechanism of Action
- Excitation process in the nerve membrane can be inhibited
- LA agents interfere w/nerve conduction by decreasing rate of depolarisation phase of action potential (AP)
- The membrane resting potential is not influenced
- LA agents interfere w/depolarising phase by reducing influx of Na+ ions
- K+ efflux influenced very little - lack of change in resting potential
- Reduction in cell membrane Na permeability = reduction in degree of depolarisation phase
- Critical potential threshold not reached = no AP = No conduction
Maximal Doses of LA for Adults + Children
- 1 / 200,000 adrenaline dose - 5 ųm/ml
- cannot be used for children under 9 yrs - only plain anaesthetic
- Pregnant women also cant use adrenaline - causes contraction in 3rd trimester or complications in 1st trimester - 2nd is fine
- Only plain lidocaine suitable for pregnant women
To work out max dose:
Max Dose = mg x kg
Max cartilage = Max dose (mg x kg) / mg in 1 cartridge
Supraperiosteal Nerve Block
Indication: Intraseptal injection - for periodontal surgical techniques
Intraosseous injection - for a single tooth
Nerves anesthetised - Terminal branches of the dental plexus
Insertion point - height of the mucobuccal fold over the targey tooth
Target Point - Periapical area of tooth
Process:
- Lift the lip, pulling the tissue
- hold syringe parallel to the long axis of the tooth
- insert needle at the height of the mucobuccal fold over the target tooth
- advance the needle until its bevel is at/above periapical region of the tooth
- Aspirate - if negative deposit 0.6ml slowly over 20 seconds
Anaesthetic effect - ALL maxillary teeth due to thin cortical plates
Complications - Pain on needle insertion w/tip against the periosteum
Posterior Superior Alveolar Nerve Block
Indication - several molar teeth in one quadrant
Nerves Anaesthetised - PSA Nerve and all its branches
Insertion Point - Height of mucobuccal fold over 2nd molar
Target Point - PSA nerve as is enters the posterior/infratemporal surface of maxilla
Process:
- Insert needle at height of mucobuccal fold over 2nd molar
- Advance upward 45° to occlusal poplane
- Inwards medially at 45° to occlusal plane
- Backwards - 45° to long axis of 2nd molar
- Advance depth of 20mm to reach alveolar foramina, for smaller adults + children 15mm
Anaesthetic Effect - Pulps of all maxillary molars apart from mesiobiccal root of 1st molar
- Adjoining alveolar bone of these teeth, buccal periodontium + buccal mucoperiosteum
- Adjacent lining of maxillary sinus
Complications - Hematoma + Infection
Middle Superior Alveolar Nerve Block
Indication - For extraction premolars in one quadrant
Nerves Anaesthetised - MSA nerve
Insertion point - Height of mucobuccal fold over 2nd premolar
Target point - Alveolar process of maxilla
Process:
- Advance tip of needle reach well above the apex of 2nd premolar
- Needle should be parallel to the bone
Anaesthetic effect - Vestibular area of premolar + sometimes mesiobuccal root of 1st molar
complications - Haematoma
Infraorbital Nerve Block - Anatomy
2 Approaches - Bicuspid + Central incisor
Anatomy - Infraorbital nerve emerges from infraorbital foramen + ramifies
- Inferior palpebral branches innervate lower eyelid
- External nasal branches pass to skin on the side of the nose
-Internal nasal branches innervate mucous membrane of vestibulum of the nose
-Superior labial branches pass to skin + mucous membrane of upper lip
-Centre of the inferior margin of the orbit (zygoma-maxillary suture) can be palpated w/index finger and the infraorbital foramen is about 0.5-0.7 cm BELOW the orbital margin
Infraorbital Nerve Block - Indication, Insertion + Target Points
Indication - Oral + Periodontal surgical procedures in the soft + hard tissues involving 2 or more maxillary teeth
- Restorative + endodontic procedures involving more than 2 maxillary teeth
- Anterior teeth in 1 quadrant
Nerves anesthetised - ASA, MSA, infraorbital nerve w/terminal branches - Inferior palpebral, Lateral Nasal + Superior labial
Insertion points:
Bicuspid Approach - Mucobuccal fold over 1st premolar w/needle held parallel to long axis of tooth
Central Incisor Approach - Direction of needle bisects crown of ipsilateral central incisor for the mesioincisal angle to the distogingival angle. At height of mucobuccal fold
Target Point:
Bicuspid approach - Infraorbital nerve as it comes out of the infraorbital foramen
Central Incisor Approach - Infraorbital nerve as it comes out of the infraorbital foramen between levator labii superioris muscle above the levator anguli oris muscle
Infraorbital Nerve Block - Process
- Finger is gently passed - 0.5 - 0.7cm below the orbital margin
- Index finger is held here whilst thumb lifts upper lip
- Syringe held in other hand + needle inserted into buccal fold directly over the lateral incisor
- Needle gently pushed near the bone towards the tip of the index finger
- When needle has reach site, aspirate to ensure tip of needle is not placed in a vessel
- Around 1ml of solution is slowly injected - index finger tip is kept in position to control deposition of the solution
Anaesthetic effect - Pulps of Maxillary central + lateral incisors + canine + premolars + mesiobuccal root of 1st molar
- Supporting alveolar bone + labial or buccal periodontium of these teeth
- Overlying labial/buccal mucoperiosteum in region of incisors, canines + premolars
- Skin of lower eyelid + both surfaces of conjunctiva, skin of lateral aspect of nose + skin/mucosa of upper lip
Complications - Haematoma (rare)
-Paresis of face - occurs when injection is given superficially, when needle lies on the vicinity of muscles of facial expression/nerves innervating them. Effects disappear as LA wears off
Greater Palatine Nerve Block
Indication - For palatal soft + osseous tissue treatment, distal to canine in one quadrant
Nerves anaesthetised - Greater palatine Nerve
Insertion Point - 0.5cm anterior to greater palatine foramen
Target Point - Greater palatine foramen
Process:
- Locate Greater palatine foramen by placing cotton swab at junction of maxillary alveolar process + hard palate in the groove
- Press firmly posteriorly from 1st maxillary molar
- Swab will fall in the depression created by GPF located usually distal to 2nd maxillary molar
- patients mouth should be as widely open as possible
Anaesthetic effect - Posterior part of hard palate + overlying soft tissues
-Anteriorly as far as canine/1st premolar + medially upto midline/median palatine raphe
Complications - Ischemia + Necrosis due to concentrated vasoconstrictor solution used for hemostasis
Nasopalatine Nerve Block - Part 1
Note - Extremely painful
Anatomy - Nasopalatine nerve leaves sphenopalatine ganglion through sphenopalatine foramen
- It passes forward + downward on nasal septum to reach incisal canal, where it gives off terminal branches
- Mucous membrane + gingiva in anterior part of hard palate innervated by nasopalatine nerve
Indication - for palatal soft + osseous tissue treatment from canine to canine bilaterally
-Restorative therapy for 2 or more teeth
Nerves anaesthetised - Left + Right nasopalatine nerves
Insertion Point - Incisive papilla
Target Point - Incisive Foramen
Nasopalatine Nerve Block - Part 2
Process: Labial Approach :
- Prepatory - Insert needle into labial intraseptal tissue between maxillary central incisors
- Needle inserted at right angle to labial cortical plate + passed into tissues until resistance is felt
- 0.25ml of LA solution is deposited
Palatal Approach
- Prepatory - Tip of needle should be placed in depression surrounding incisive papilla + small amount of LA injected until papilla blanches/turns white
- inject slowly as soon as needle enters mucosa
- Needle withdrawn + reinserted slowly into crest of papilla
- needle is advanced slowly into incisive foramen about 0.5cm into canal
- 0.25 - 0.5ml of LA injected
Anaesthetic effect - Anterior [portion of hard palate from mesial of right canine/1st premolar to mesial of opposite teeth respectively
Complications - Necrosis of soft tissues is possible
Inferior Alveolar Nerve Block - Mandibular Block anatomy
Note - do not inject if bone is NOT contacted
Note - Onset for hard tissue anaesthesia is 3-4 mins + duration is 40mins - 4 hours
Anatomy - Inferior alveolar nerve passes downward along the medial side of the mandibular ramus to the mandibular foramen
- In the mandibular canal nerve gives off branches to form inferior dental plexus
- Before nerve enters mandibular foramen, it gives off mylohyoid branch which continues along mandibular ramus
- Mylohyoid muscle + anterior belly of digastric muscle recieve motor fibres from this mixed nerve branch
Inferior Alveolar Nerve Block
Indication - Procedures on multiple mandibular teeth in 1 quadrant
Nerves anaesthetised- Inferior alveolar nerve + incisive + mental branches, lingual + buccal nerve
Insertion point - ¾ distance from anterior border of ramus
Target point - foramen rotundum/ foramen ovale
Process:
- Patient mouth widely opened so all 3 nerve4s are closer together
- After detection of pterygomandibular plicae, syringe is directed from premolars region of opposite side
- needle inserted at level 0.5cm under occlusal surface of last upper molar
- if no teeth 1.5cm under alveolar crest mucosa
- needle advanced dorsally 1.5-2cm along medial side of ramus
- When tip of needle meets resistance from middle section of ramus, aspirate + inject slowly 1.5-2ml
- withdraw 1cm + inject 0.5ml for lingual nerve
Anaesthetic effect - Mandibular teeth
- Body +Ramus of mandible
- Buccal mucoperiosteal
- Anterior ⅔ of tongue - lingual nerve
Complications - trismus, transient facial palsy + haematoma
Inferior Alveolar Nerve Block
Indication - Procedures on multiple mandibular teeth in 1 quadrant
Nerves anaesthetised- Inferior alveolar nerve + incisive + mental branches, lingual + buccal nerve
Insertion point - ¾ distance from anterior border of ramus
Target point - foramen rotundum/ foramen ovale
Process:
- Patient mouth widely opened so all 3 nerve4s are closer together
- After detection of pterygomandibular plicae, syringe is directed from premolars region of opposite side
- needle inserted at level 0.5cm under occlusal surface of last upper molar
- if no teeth 1.5cm under alveolar crest mucosa
- needle advanced dorsally 1.5-2cm along medial side of ramus
- When tip of needle meets resistance from middle section of ramus, aspirate + inject slowly 1.5-2ml
- withdraw 1cm + inject 0.5ml for lingual nerve
Anaesthetic effect - Mandibular teeth
- Body +Ramus of mandible
- Buccal mucoperiosteal
- Anterior ⅔ of tongue - lingual nerve
Complications - trismus, transient facial palsy + haematoma
Gow’s Gates Technique
anatomy - Buccal nerve passes along medial side of mandibular ramus anterior to inferior alveolar nerve
- It crosses anterior border of ramus + ramifies
- Branches innervate buccal gingiva between 2nd premolar + 2nd molar
Indication - Procedures on multiple mandibular teeth in one quadrant + inferior alveolar nerve block fails
-When buccal soft tissue anaesthesia is required for dental procedures in mandibular molar region
Nerves anaesthetised - IAN, Lingual, Buccal, Mylohyoid, Auriculotemporal
Insertion Point - Insert needle high into the mucosa at level of 2nd maxillary molar just distal to mesiolingual cusp
- Use the intertragic notch to corner of the mouth as imaginary LINE
- Alignment of needle should be parallel to angulation of the ear
Target Point - Needle should be advanced until bone is reached, then withdraw 1mm
- Depth should not exceed 25-27mm
Gow’s Gates Technique - Part 2
- Site of penetration is oral mucosa along the medial border of ramus lateral to pterygomandibular depression, but medial to site of temporalis muscle tendon
- While patient’s mouth is wide open, insert needle along the line extending from corner of mouth opposite to the side of infection to the lower border of the tragus
- Alignment of needle should be parallel to angulation of the ear to the face of injection
- Needle should be advanced until bone/neck of condyle is contacted then withdraw 1mm
- Anaesthetic solution deposited after negative aspiration
Anaesthetic effect - Soft tissue + periosteum buccal to mandibular molars
- Mandibular teeth to midline
- Body + Ramus
- Buccal Mucoperiosteum
- Anterior ⅔ of tongue
Complications - Trismus, Temporary paralysis of III, IV + VI, Haematoma
