third molars

Question 1

what age do third molars usually erupt

Answer 1

18-24

Question 2

what age does crown and root calcification of 3rd molars occur

Answer 2

crown - begins age 7/10 finishes age 18
root - complete by age 15-18

Question 3

what proportion of adults will be missing at least 1 3rd molar

Answer 3

1 in 4

Question 4

at what age, if no third molar on radiograph, are no 3rd molar likely to develop

Answer 4

14

Question 5

what is the most common reason 3rd molars fail to erupt

Answer 5

impacted by adjacent tooth , alveolar bone, surrounding mucosa or combination of these

Question 6

name 3 potential complications of 3rd molar impaction

Answer 6

caries
pericoronitis
cyst formation

Question 7

what 4 nerves are at risk during 3rd molar surgery

Answer 7

IAN
lingual
nerve to mylohyoid
long buccal

Question 8

what does the IAN supply

Answer 8

all mandibular teeth on that side, mucosa and skin of lower lip and chin on that side

Question 9

what does the lingual nerve supply

Answer 9

sensory innervation to anterior 2/3 of tongue (both dorsal and ventral)
branch that supplies lingual gingivae and floor of mouth on that side

Question 10

what location to the mandible is the lingual nerve

Answer 10

0-3.5mm medial to mandible

Question 11

name 3 therapeutic indications for extraction of 3rd molars

Answer 11

infection - caries, pericoronitis, perio disease
cysts
tumours
external resorption of 7 or 8

Question 12

pericoronitis

Answer 12

inflammation around the crown of a partially erupted tooth
Food and debris get trapped under operculum and cause inflammation and infection

Question 13

operculum

Answer 13

piece of gum tissue present over occlusal surface of tooth after eruption

Question 14

name 3 bacteria that may be implicated in pericoronitis

Answer 14

anaerobes:
prevotella intermedia
streptococci
actinomyces

Question 15

what age group are normally affected by pericoronitis

Answer 15

20-40

Question 16

what is the only general health condition that increases risk of pericoronitis

Answer 16

upper respiratory tract infection - unclear why

Question 17

signs and symptoms of pericoronitis

Answer 17

pain - often throbbing
swelling - intra or extra oral, usually intra oral over impacted tooth
bad taste/ pus discharge
occlusal trauma to operculum
ulceration of operculum
evidence of cheek biting
foetor oris (bad breath/ halitosis)
dsphagia (difficulty swallowing)
systemically unwell - pyrexia, malaise, regional lymphadenopathy

Question 18

trismus is a characteristic sign of what type of abscess

Answer 18

sub masseteric

Question 19

what is the usual treatment for pericoronitis

Answer 19

usually self limiting and transient (non permanent and self recovering)
irrigation with warm saline or chlorhexidine
incision of localised pericoronal abscess if required
frequent warm saline or chlorhexidine mouth rinses

Question 20

antibiotic of choice for pericoronitis

Answer 20

metronizadole four hundred mg 3x daily for 3 days

Question 20

antibiotic for pericoronitis if patient cant have metronizadole

Answer 20

amoxicillin 500mg tablets, 1 tablet, 3x daily for 3 days

Question 20

predisposing factors for pericoronitis

Answer 20

partially erupted and vertical or distoangular impaction
opposing maxillary molar causing mechanical trauma contributing to recurrent infection
upper respiratory tract infection as well as stress and fatigue
insufficient space between mandibular ramus and distal aspect of M2M
white race
full dentition present