Third Molars

Question 1

give 2 causes of lack of space in dental arch - causing impaction.

Answer 1

evolutionary changes & lack of an abrasive diet

Question 2

what are the top 5 most commonly impacted teeth?

Answer 2

1. lower 8s
2. upper 3s
3. lower 3s, 4s and 5s
4. upper 1s and 2s
5. upper 8s

Question 3

why are lower 8s the most commonly impacted?

Answer 3

they erupt the latest

Question 4

what causes malpositioning of ectopic and displaced teeth?

Answer 4

ectopic - congenital factors
displaced - nearby pathology

Question 5

what happens to teeth at the level of a jaw fracture?

Answer 5

they are rendered non vital

Question 6

when is it not necessary to XLA impacted lower 8s?

Answer 6

asymptomatic, pt has no complaints, XLA risks nerve damage

Question 7

what is pericorinitis?

Answer 7

inflammation of tissues around crown of partially erupted or impacted tooth

Question 8

symptoms of pericorinitis & when to refer

Answer 8

pain, swelling, dysphagia, bad taste, malaise, may lead to cellulitis - if 2 or more cases then refer

Question 9

is operculotomy recomended?

Answer 9

no as will just re-grow

Question 10

list local measures for pericoronitis

Answer 10

irrigate w/ saline, OH measures, remove trauma

Question 11

what can be done if indentations/trauma seen on operculum?

Answer 11

XLA or grind down cusps of opposing 8

Question 12

when should pt be given antibiotics for pericorinitis? (3) what antibiotic & dose?

Answer 12

is systemically unwell
immunocompromised
if cannot drain locally - trismus, pt uncompliant
metranidazole 400mg 3x daily for 3 days

Question 13

what microbes are involves in pericoronitis?
what 2 bacteria are involved in increased pocket depths between 2nd & 3rd molars?

Answer 13

anaerobic
prevotella intermedia & campylobacter rectus associated w/ inc pocket depths of 2nd and 3rd molars

Question 14

list tx options for impacted lower 8s

Answer 14

do nothing, XLA, coronectomy

Question 15

what radiograph is used to assess lower 8s?

Answer 15

half/whole DPT - PA is 2nd choice

Question 16

what indicates close proximity of 8 to ID canal?

Answer 16

darkening, deflection or loss of lamina dura of ID canal as roots pass
roots of teeth get darker or deflect as they pass ID canal
juxta apical area - radiolucent area lateral to tooth

Question 17

what is the most common type of impaction?

Answer 17

mesial 1st
vertical 2nd

Question 18

when may CBCT be used to assess impacted 8?

Answer 18

when DPT suggests 8 close to IDC/high risk for XLA

Question 19

what is neuropraxia and when is it caused?

Answer 19

apex of tooth rubbing against IDC - mildest form of nerve damage

Question 20

how common is change in sensation to lower lip and tongue post XLA?
when should pt be informed of a risk?

Answer 20

lower lip - 5% short term, <1% long term
tongue - 10% short term, <1% long term
pt should be informed when risk >5%

review pt after 3 months to assess if long term damage has occured

Question 21

what procedure is indicated when high risk/tooth too close to IDN for XLA? what are risks of this procedure

Answer 21

coronectomy - leave roots behind
root migration and infection

Question 22

what flap should be done for lower impacted 8s?
explain design of this flap

Answer 22

triangular (3 sided)

distal relieving incision - up ascending ramus
round crown of 8 and half of 7 - include papilla between 7 and 8
mesial relieving incision - from centre of 2nd molar down depth of sulcus

Question 23

when is a 2 sided flap used? what incisions are made?

Answer 23

used if pericoronal pathology or cyst
distal relieving incision - up ascending ramus
round crown of 8 and all of 7 - ends just distal to 6

Question 24

what is used to remove bone? why and where is bone removal carried out?

Answer 24

round bur in surgical hand piece (chisels no longer used)
create a point of elevator application
create a narrow gutter mesiobuccally

Question 25

when are crown/roots sectioned/divided? (3)

Answer 25

horizontally impacted
distoangular crown
pincer roots w/ diff paths of removal

Question 26

what flap should be used for horizontally impacted 8? what must be done after flap raised? (3)

Answer 26

triangular
bone removal, section crown at ACJ, section roots at furcation

Question 27

intrinsic & extrinsic obstacles for XLA

Answer 27

intrinsic - root morphology
extrinsic - bone, adj teeth, ID canal

Question 28

what should you never do when elevating?

Answer 28

use adj tooth as fulcrum

Question 29

what is the most important suture of the flap?

Answer 29

suture placed from buccal to lingual tissues immediately distal to 7

Question 30

what material is used for suturing? when are sutures removed?

Answer 30

3/0 vicryl rapide
dissolve after 1 week

Question 31

maxillary 8s - thickness of bone, root shape/number, angle/impaction, positioning

Answer 31

thin cortical bone
short single conical fused root
mesioangled or vertically impacted - often very buccally placed

Question 32

what should be done to manage impacted upper 8? how many sutures to reposition flap?

Answer 32

buccal flap
remove thin friable bone w/ couplands
use elevator to move tooth down, back and buccally
use one suture to reposition flap

Question 33

what is the order of tx planning?

Answer 33

1. path of withdrawal
2. obstacles
3. point of application
4. bone removal
5. flap design

backwards to how it is carried out
POPBF