CROWN Flashcards
a. Function of post (2m)
The functions of post
the provision of retention for the core/coronal restoration
distribution of the functional loads to the supporting structures
b. 2 Post materials of (i) prefabricated (ii) custom made (4m)
- Prefabricated posts
- Steel posts (ParaPost system)
- Ceramic
- Custom made posts
- High-gold
- Fiber
c. Two advantages of fiber post compared with metal (2)
Less stiff
More favorable stress distribution
Improved aesthetics
d. Which canal of maxillary first molar will the post be put in? Explain. (2)
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.
e. Risk of placing a post (3)
Endodontic Failure
Root fracture
Post and Core Detachment
f. 2 commonly used all-ceramic crown material (2)
Feldspathic Ceramic Zirconia
g. Factor affecting your choice of crown material (4)
Esthetics
Relative cost to patient
Tooth substance left
Resistance to wear
Resistance to fracture
- How tooth preparation for crown will harm the originally intact 15
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.
a. How will you do a clinical assessment of a full metal crown? (5 marks)
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
b. What are the advantages and disadvantages of full metal crowns compared to ceramometal crowns? (3 marks)
Advantages: less tissue reduction, less damaging to opposing teeth,
Disadvantages: not aesthetic
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)
Study cast production
Custom tray
Silicone index for crown preparation
Wax up
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)
Under natural light, shade matching under daylight, moist teeth, create lip shadow by covering with finger, ask patient’s opinion
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?
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)
HPC, MH, DH, FSH
Hard food habit
Parafunctional habit
Any info related to crown fracture (when, how, where…)
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)
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
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)
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
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)
- 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
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)
- 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
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)
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
