CROWN

Question 1

a. Function of post (2m)

Answer 1

The functions of post
 the provision of retention for the core/coronal restoration
 distribution of the functional loads to the supporting structures

Question 2

b. 2 Post materials of (i) prefabricated (ii) custom made (4m)

Answer 2

• Prefabricated posts
  
  • Steel posts (ParaPost system)
  • Ceramic
• Custom made posts
  
  • High-gold
  • Fiber

Question 3

c. Two advantages of fiber post compared with metal (2)

Answer 3

 Less stiff
 More favorable stress distribution

 Improved aesthetics

Question 4

d. Which canal of maxillary first molar will the post be put in? Explain. (2)

Answer 4

 In those molars that do require a post, the post should be placed in the largest, straightest canal, which is the palatal canal in the maxillary molars and a distal canal in the mandibular molars

 Reason: Generally has the greatest root thickness, is relatively straight in the coronal third, has a high level of endodontic success and runs less risk of fracture should the post need to be removed

 Indications for post in molars are when the coronal part is extensively destroyed hence the root chamber cannot provide retention.

Question 5

e. Risk of placing a post (3)

Answer 5

 Endodontic Failure
 Root fracture
 Post and Core Detachment

Question 6

f. 2 commonly used all-ceramic crown material (2)

Answer 6

 Feldspathic Ceramic  Zirconia

Question 7

g. Factor affecting your choice of crown material (4)

Answer 7

 Esthetics

 Relative cost to patient

 Tooth substance left

 Resistance to wear

 Resistance to fracture

Question 8

2. How tooth preparation for crown will harm the originally intact 15

Answer 8

 Excessive tooth preparation poses risk on causing pulpal exposure of 15 which may jeopardize the vitality of the tooth

 If the tooth preparation involves an increase of heat to the tooth, pulpal necrosis can occur.

Question 9

a. How will you do a clinical assessment of a full metal crown? (5 marks)

Answer 9

 Use a probe to probe at the margins of the crown to see if the margins are still acceptable

 Check the aesthetics of the crown, see if there is any staining
 Check for allergy
 Check if there is any fracture of the crown
 Check if there are any secondary caries
 Check if there is any wear of crown and opposing dentition
 Check if there is any cracks in the crown

Question 10

b. What are the advantages and disadvantages of full metal crowns compared to ceramometal crowns? (3 marks)

Answer 10

 Advantages: less tissue reduction, less damaging to opposing teeth,

 Disadvantages: not aesthetic

Question 11

A middle aged man requesting treatment for his upper front teeth, with history of allergy to antibiotics Periapical radiograph: apical radiolucency at 11
Intra-oral photographs:

• 11MB fractured (Class IV), restored with pin retained composite resin, white spot lesion and caries on

11B

• 21B Class V composite discolored, with stained margin
  a. What do you have to prepare in the laboratory before anterior crowns are required by this patient? (2)

Answer 11

 Study cast production
 Custom tray
 Silicone index for crown preparation

 Wax up

Question 12

A middle aged man requesting treatment for his upper front teeth, with history of allergy to antibiotics Periapical radiograph: apical radiolucency at 11
Intra-oral photographs:

• 11MB fractured (Class IV), restored with pin retained composite resin, white spot lesion and caries on

11B

• 21B Class V composite discolored, with stained margin
  b. How do you ensure that the colour of the crown matches the colour of the adjacent teeth? (3)

Answer 12

 Under natural light, shade matching under daylight, moist teeth, create lip shadow by covering with finger, ask patient’s opinion

Question 13

50 year old man. Clinical photo (anterior teeth apart front view), PAN, Study Cast.
C/O: reduced height of anterior tooth.
HPC: Sharp pain on cold drink. Not spontaneous.
I/O Photographs: showing generalized attrition and erosion of upper and lower arch. (mainly anterior) PAN

a. How to bond ceramic to metal in a CMC?

Answer 13

Question 14

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

a. What questions will you ask the patient? (5)

Answer 14

 HPC, MH, DH, FSH
 Hard food habit
 Parafunctional habit
 Any info related to crown fracture (when, how, where…)

Question 15

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

Describe the clinical photo (2)

Why porcelain will fracture? (3)

Answer 15

 Presence of microcracks due to several factors listed below within porcelain or at the bonding interface will propagate towards surface when porcelain is under external stimulations like temp, occlusal force and frequency, which eventually fracture due to its poor tensile strength and brittleness

PLEASE READ PAGE 117, REALLY LONG ANSWER

Question 16

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

d. What will be consequence if the condition is left untreated (4)

Answer 16

 Recurrent caries
 Hypersensitivity due to thermal conduction
 Loss of vitality
 Galvanic shock
 Continuous breakage of crown
 Tooth fracture
 Loss of occlusal contact causing overeruption of opposing tooth

Question 17

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

e. 3 treatment options (3)

Answer 17

• Simple repair with composite restoration (sandblasting with silica-coated alumina, silane coupling agent)
  
  • Prevent unnecessary tooth tissue removal and weakening of remaining tooth structure, preserve
• vitality
• Replace the whole crown
• Extraction and replace with implant

Question 18

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

f. How to remove the crowns? List the instruments that you need (4)

Answer 18

• Cut groove vertically from gingival margin to occlusal surface, preferably on buccal side just through the cement
• Use heavy instrument like cumine scaler / chisel to spring open the crown to break the luting cement
• Sometimes need to expand the cut across the occlusal surface or even the lingual side
• Diamond bur for ceramic, beaver bur for metal
  
  • Beaver bur is special TC bur with very fine crosscuts, which cut metal without juddering of jamming and less risk of breakage than conventional TC bur
• Followed by crown remover, forceps, straight chisel, or assisted by ultrasonic scaler

Question 19

Patient complains of fracture of teeth
Clinical photo showing CMC crown on 2,16,17 (look like splinted together) Fracture of porcelain on 16 PO showing the metal base plate

g. Why would the vitality of the tooth be compromised during the process of making a CMC on that tooth? (4)

Answer 19

 Thermal damage during crown preparation by high speed burs

 Direct pulpal exposure due to over-preparation of tooth

 Impression taking

 Exothermic reactions and residual monomer released by acrylic as temporary crown material

 Acidic stimulation to pulp by zinc phosphate cement during cementation of crown

 Marginal leakage of crown allow thermal, acidic stimulation to pulp or bacterial invasion result in recurrent caries

 Improper or incomplete seating of crown cause occlusal trauma