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Minor Oral Surgery > Failure of LA 1 > Flashcards

Failure of LA 1 Flashcards

1
Q

Outline the reasons why local anaesthetic injection may fail

A
  • poor operator technique
  • pharmaceutical reasons
  • treatment reasons
  • anatomical reasons
  • pathological reasons
  • psychological reasons
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2
Q

What are the methods by which local anaesthetic solutions may lose their efficacy?

A
  • use past expiry date
  • improper storage
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3
Q

What is the consequence storing LA cartridges in heaters or in direct sunlight?

A

they hasten the oxidation of epinephrine leading to a decrease in efficacy

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4
Q

How should LA cartridges be stored?

A

in the dark at no higher than room temperature

if they are stored in a refridgerator they should be allowed to return to room temperature before injection in order to reduce discomfort

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5
Q

What is the most difficult treatment to provide successful anaesthesia for?

A

endodontics

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6
Q

What treatment is more likely to be “pain-free” following LA?

A

extractions

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7
Q

The efficacy of anaesthesia varies between operative procedures. True or false

A

true

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8
Q

Outline some anatomical reasons that may contribute to the failure of LA delivery

A
  • barriers to LA diffusion
  • variations in position of foramina
  • position of tooth in jaw
  • accessory nerve supply
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9
Q

Identify instances where anatomy poses a barrier to LA diffusion

A
  • zygomatic buttress around the upper first molar
  • dense cortical plate in the mandible which may limit infiltration as it prevents entry of LA solution into cancellous space
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10
Q

How can you overcome potential LA failure due to the presence of the zygomatic buttress?

A

injecting mesial and distal to the zygomatic buttress

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11
Q

How can you overcome potential LA failure due to the presence of the dense cortical plate in the mandible ?

A

regional block techniques

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12
Q

Why might a posterior superior alveolar nerve block be insufficent in providing anaesthesia to the maxillary first molar?

A

the mesio-buccal root of the maxillary first molar may also be supplied by the middle superior alveolar nerve

thus a middle superior or infra-orbital nerve block may be required

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13
Q

How is anaesthesia achieved using intraligamentary injection?

A

LA solution enters the cancellous bone via perforations in the socket walls (the so-called cribriform plate)

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14
Q

Why does intraligamentary anaesthesia have a poor success rate with mandibular anterior teeth?

A

this is because the number of bony perforations in the cribriform plate (via the socket walls) are fewer in the lower incisor region and thus less LA solution reaches the cancellous bone

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15
Q

What can you use as an aid for needle positioning to demonstate the location of the mandibular foramen?

A

panoramic radiograph

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16
Q

Molar teeth show greater incidences of pulpal anaesthesia when compared to anterior teeth following IANBs. True or false

Suggest possible reasons for this

A

true

  • position of nerve supplying different teeth will vary within the IAN bundle; those in the centre of the bundle will be more difficult to anaesthetise
  • accessory supply in the anterior part of the mouth- lower incisors have bilateral supply to their pulps - anastomosis
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17
Q

Give examples of nerves that may provide accessory nerve supply to the dental pulps in the maxillary arch

A
  • greater palatine nerve
  • nasopalatine nerve
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18
Q

Give examples of nerves that could provide accesory nerve supply to the pulp of mandibular teeth

A
  • lingual nerve
  • long buccal nerve
  • mylohyoid nerve
  • auriculotemporal nerve
  • cervical nerves
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19
Q

What is the evidence that accessory supply is a factor in the failure of IANBs?

A
  • deposition of the solution in the optimum position (at the mandibular foramen) by the use of ultrasound guided needles not providing success
  • Gow- gates method which counters a number of nerves that contribute to accessory nerve supply has been reported to provide greater success than the standard technique
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20
Q

How can accessory nerve supply be countered in the maxilla?

A

palatal injections

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21
Q

How can accessory nerve supply be countered in the mandible?

A
  • combination of regional blocks
  • use of “high” blocks
  • use of intraligamentary or intra-osseous injections
  • use of intra-pulpal anaesthesia
  • use of infiltration injection
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22
Q

With regards to the Gows-gates method of LA injection, where is the needle positioned?

A

positioned at the mandibular condyle

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23
Q

How can lingual nerve anaesthesia be achieved?

A
  • as a consequence of the standard IANB
  • modification of the IANB technique
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24
Q

How can long buccal nerve anaesthesia be achieved?

A
  • infiltration
  • true long buccal nerve block
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25
Q

When is a true long buccal nerve block required?

A

if the pulpal supply from the nerve trunk (of the long buccal nerve) enters the bone in the retro-molar region

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26
Q

How is a long buccal nerve block achieved

A

injection at the coronoid notch of the mandible - this is the most concave part of the anterior ramus

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27
Q

How can mylohyoid nerve anaesthesia be achieved?

A
  • lingual infiltration
  • mylohyoid nerve block
28
Q

Briefly describe how a mylohyoid nerve block can be achieved

A

deposition of the solution beneath the mylohyoid muscle at the distal root of the first molar tooth

29
Q

Give examples of “high” blocks

A
  • Gow Gates
  • Akinosi Vazirani
30
Q

What nerves are anaesthetised following Gow-Gates method?

A
  • IAN
  • lingual
  • long buccal
  • mylohyoid
  • auriculotemporal
31
Q

What can you conclude from the fact that the Gow-gates methods does not obtain 100% success?

A

it may be an indication that cervical nerve may innervate the pulpal tissue in some individuals

32
Q

“High” blocks do not depend on locating the mandibular foramen. What is the implication of this?

A

individual variations in the position of this landmark are rendered unimportant

33
Q

When is the use of high blocks recommended ?

A

if soft tissue anaesthesia of the lip is not apparent after repeated standard approach of the IANB

34
Q

Why are intra-ligamentary and intra-osseous anaesthesia thought to increase efficacy of anaesthesia?

A

they nullify nerves that arrive from all directions- nullify accessory nerves

35
Q

What is the limitation of pulpal anaesthesia?

A

pulp must be exposed to allow access for the needle

36
Q

What is the success/efficacy of intrapulpal anaesthesia dependent on?

A
  • success is related to the pressure of the injection
  • it appears to be independent ot the solution being used; saline can be as effective as LA
37
Q

How is intrapulpal anaesthesia delivered in multi-rooted teeth?

A

needle must be advanced into each root canal as efficacy/success is dependent on pressure

38
Q

What is the method of choice for providing anaesthesia to children?

A

infiltration anaesthesia

39
Q

The use of buccal infiltration anaesthesia in the molar region has a poor success rate for anesthesia of the first permanent molar pulps. True or false

A

true

40
Q

Outline reasons why teeth with irreversible pulpitis are more difficult to anaesthetise using infiltration anaesthesia than non-inflammed teeth

A
  • alterations in tissue pH
  • increased vascularity leading to elimination of the anaesthetic
  • loss of anaesthetic solution via draining sinuses

these reasons do not explain the reduced efficacy of regional block anaesthesia in the presence of inflammation

they do not explain why lip anaesthesia is still achieved following IANB whilst pulpal anaesthesia remains ineffective

41
Q

Suggest reasons for the reduced efficacy of regional block anaesthesia in the presence of inflammation

A
  • nerve becomes hyperalgesic and thus they fire more readily
  • this is a result of sensitisation and activation of nociceptive fibres

heightened pain response

42
Q

Briefly describe how LAs work

A

they act as chemical roadblocks to sodium entry thus inhibiting transmission of impulses along the nerve

43
Q

Sodium channels on nociceptive fibres have been reported to be 4x less sensitive to the action of LA. How can this problem be overcome?

A
  • change the drug
  • increase LA concentration
  • inject more solution
44
Q

What form must LA particles be in in order to enter the cell ?

A

the uncharged form

45
Q

Local anaesthetic solutions exist as …

A

weak bases

BH+ = B + H+

46
Q

What form of LA binds receptors (sodium channels) once inside the nerve cell?

A

protonated form
BH+

47
Q

What is the effect of pKa on LA solution?

A

lower pKa means that more uncharged forms of LA are present thus there is better entry into the nerve cell

48
Q

What is the agent with the lowest pKa available in the UK?

A

Mepivacaine (pKa 7.6)

49
Q

What is the pKa of procaine?

A

9.1

50
Q

What is the pKa of lidocaine

A

7.9

51
Q

What are the problems associated with increasing LA concentration

A
  • local toxicity- nerve damage
  • systemic toxicity
52
Q

The viability of nerves in cell culture is compromised by exposure to LA solutions in concentrations above __%

A

2%

53
Q

The use of greater concentrations of LA is thought to be problematic, particularly in relation to what type of anaesthesia?

A

regional block anaesthesia

54
Q

What is the ceiling dose of 2% lidocaine in mg?

A

300 mg

55
Q

What is the ceiling dose of 2% mepivacaine in mg?

A

300 mg

56
Q

What is the ceiling dose of 3% mepivacaine in mg?

A

300 mg

57
Q

What is the ceiling dose of 3% prilocaine in mg?

A

400 mg

58
Q

What is the ceiling dose of 4% prilocaine in mg?

A

400 mg

59
Q

What is the ceiling dose of 4% articaine in mg?

A

500 mg

remember because of its low risk of systemic toxicity

60
Q

What has been postulated to be the most effective method of overcoming hyperalgesia?

A

injecting more solution

61
Q

The more nerve exposed to local anaesthetic the greater the efficacy. True or false

A

True

62
Q

What is the caveat of injecting more solution?

A

potential for overdose producing systemic toxicity

63
Q

What can you do if the maximum dose of the chosen anaesthesia does not anaesthetise the tooth?

A

another method of anaesthesia such as general anaesthesia should be chosen

a temporising approach can control the pain to allow another attempt at a later stage

64
Q

What are the benefits of intravenous conscious sedation?

A
  • reduce gagging
  • might make administration easier in some patients
  • can offer pharmacological protection against LA overdose
65
Q

What combination of LA and sedative can offer pharmacological protection against LA overdose?

A

lidocaine and midazolam

66
Q

Successful anaesthesia is difficult to achieve in anxious patients. True or false

A

True

Minor Oral Surgery (36 decks)

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