11. Clinical Cases of Tooth Morphology

Question 1

You are going to extract a single, lone standing upper molar. No radiograph. How would you know which it is?

Answer 1

• upper 1st is a rhomboid, largest mesio-palatal cusp, smallest disto-palatal cusp, Carabelli’s tubercle on MP cusp
• irregular H-shaped fissure pattern (separated H by transverse oblique ridge)
• 3 roots - long large and circular
• upper 2nd smaller than 1st
• can be 4 cusped with smaller disto-palatal or 3 cusped with no disto-palatal cusp T-shaped fissure
• or compression type (unlikely) but fusion of mesio-palatal and disto-buccal cusp, oval crown with 3 straight line cusps (no transverse oblique ridge) 3 roots
• upper 3rd molar - most variable, resemble upper 2nd molar type 2 vibes but reduced to rounded triangular shape
• irregular fissure pattern, number of roots can be increased and fused or reduced

Question 2

Extraction technique depends on root’s cross-sectional shape. If one root and circular, forceps can be used rotationally to loosen tooth. However, bucco-lingual technique used to expand socket if multiple. What teeth could be rotated for extraction from the above?

Answer 2

• upper central and lateral incisors
• upper canines
• lower premolars

Question 3

You’ve placed a large amalgam filling in the lower second molar - must carve amalgam before it sets. In a normal class 1 occlusion, how do you locate where the cusp tips should be?

Answer 3

• in lower molars, buccal cusps are functional cusps and occlude with central fossa of upper molars
• not palatal like in upper
• all slightly to the right of the normal position

Question 4

How can you make minor adjustments to a ceramic crown to make it more natural?

Answer 4

• round off the distal corner of the incisal edge
• use a finishing diamond bur

Question 5

A 6 year old child presents with a history of ‘missing teeth’ and parents are concerned if he is also missing teeth. Using an intraoral exam, could you answer confidently?
What could you further do?
Which teeth are commonly missing in hypodontia?

Answer 5

• no as only primary teeth and maybe 6s are present in mouth at this age. Congenital lack of teeth often affects permanent teeth not always the primary
• take a radiograph - to observe developmental stage of perm teeth. should be able to see all at 6 except perhaps 8s. may come around 8-9 - could give 100% confident answer around this age
• lower 5s and upper lateral incisors - unsure for reason but likely that they develop last in their respective tooth class. same with 8s but not used for hypodontia classification

Question 6

A 5 year old child has had a playground accident and knocked out a primary upper central incisor and badly displaced the other.
What concerns other than the affected primarys would you have?
What would you warn parents about?

Answer 6

• permanent cental incisors normally emerge around 7-8 and can be accelerated at loss of primary teeth. May not be enough room in the maxilla and could cause tooth crowding and overlapping. Also, damage to developing tooth, forming it’s root at this time. Crown may be complete but damage to root/HERS could result in stunted/dilacerated roots
• check perm upper incisors regularly after eruption, if tooth is darker in colour etc for pulp health

Question 7

A 9 year old has fractured the crown of an upper central incisor. Damage involves pulp and this would normally lead to endodontic treatment.
What is the state of the root?
At what age would you be able to complete treatment?

Answer 7

• root may not be complete at this age - wait for apical closure before commencing - root filling will just run from open root
• check and confirm on radiograph when root closes - usually 9.3 in girls and 9.6 in boys
• can apply a protective cap until root is complete and treatment begins

Question 8

A 19 year old patient has a retained upper primary canine.
What could be the reason for this?
How would you treat this patient?

Answer 8

• unlikely to be hypodontia as canines rarely affected. Permanent could have been impacted and missing gubernacular canal guiding eruption pathway (remnants of dental lamina and connective tissue). could just have a long eruption pathway and if misaligned erupt bucally or in palate
• would take a radiograph to determine position or permanent canine and relationship with other teeth. if not badly misaligned, extract primary canine and move impacted canine into position with surgical exposure and orthodontic alignment.

Question 9

A 21 year old has both lower second primary molars retained. What is the preliminary diagnosis? How to confirm?

Answer 9

• most likely hypodontia
• would be replaced by second premolars/5s
• take a radiograph to confirm absence of 5s and see if roots of lower second premolars are splayed and not resorbed

Question 10

A 5 year old has sparse hair, unusual fingernails, distinctive facial appearance and high body temp. Suspect a genetic condition but no info on medical records. Diagnosed with ‘hypohidrotic ectodermal dysplasia’ - associated with missing teeth.
What would you predict is the state of his teeth?
Apart of necessary dental treatment, what can you do?
At what age could patient start making long term plans?

Answer 10

• in hypodontia/oligodontia, primary teeth not affected but in this genetic condition, could be possible. In severe forms, may be missing/malformed primary teeth but in most cases perm dentition severely affected with most teeth missing or abnormally shaped conical teeth
• refer family for genetic counselling, can suggest genetic testing to identify gene mutation and associated subtype to inform treatment and identify risk of another child
• around 12-13, all permanent teeth should have erupted (except 8s)