crown Flashcards
1
Q
Discomfort may be caused by:
A
- Malocclusion or premature contact. (one of the main causes because the patient will feel pain on chewing)
- An over-size or poorly positioned masticating area,with retention of food by pontics or retainers.
- Torque produced from the seating of the bridge or from occlusion. (part of the bridge comes in premature contact with the opposing and part is out of occlusion)
- Excessive pressure on the tissue. (closure of the embrasure)
- Plus or minus contact area. (plus contact exerts pressure on the neighboring tooth, and minus contact causes food impaction)
- Over protected or under protected gingival & ridge tissue.
- Sensitive cervical area.
- Thermal shock. (due to preparation without cooling for few seconds and intake of very hot drinks after preparation)
- Certain intangible sources, usually relatively unimportant & easily rectified if diagnosed.
2
Q
A bridge become loose because of:
A
- Deformation of the metal casting on the abutment.(long span bridge especially with weak metal)
- Torque.
- Technique of cementation.
- Solubility of cement.
- Caries.
- Mobility of one or more abutment.
- Lack of full occlusal coverage.
- Insufficient retention in the abutment preparation.
- Poor initial fit of the casting.
3
Q
Sensitivity of cervical margin causes
A
- Overextended margin of temporary bridge.
- During tissue retraction, if gingiva is too much retracted, giving rise to gingival recession and sensitivity.
- The use of caustic materials during tissue retraction
4
Q
Causes of recurrence of caries:
A
- Overextension of margins. (because if the crown is overextended under the finish line and gingival it will form an undercut and causes retention of food and recurrent caries)
- Short casting.(open margin with exposed dentine which is more liable to caries than enamel.
- Open margins.
- Wear. (due to malfunction, bruxism or griding teeth with no function, also usage of soft material in crown is a factor)
- A retainer becoming loose.
- Pontic form that fills the embrasure.(it turns from a self-cleansing area to area of food impaction)
- Poor oral hygiene.
- Use of wrong type of retainer which will promote caries susceptibility.
- Because temporary protection of the abutment uncovered the neck of the tooth by a prolonged or permanent displacement of the gingiva.
5
Q
- Open and underextended margins in restoration should be
A
remake.
6
Q
- Poor pontic form occurs in 3 cases
A
pontic encroach on the gingiva, pontic closes the embrasure or over-contoured pontic.
7
Q
Causes of pontic failure:
A
- Faulty occlusion, in lateral excursions, which was not corrected when the bridge was placed.
- An acrylic facing will wear and discolor quite rapidly.
- Improper pontic ridge relation: if the pontic is of saddle type (convex, concave ridge relationship), food accumulation and inflammation of the gingiva as well as gingival recession occur.
- Improper pontic contour: pontic pressing on the ridge if a cement particle entrapped between it and the ridge.
- This may lead to bone resorption. So, instruct the patient to use dental floss.
8
Q
Loss of the supporting alveolar process may result from overloading due to:
A
- Length of the span. (increasing the span length will cause more overload on the abutment teeth)
- Size of the occlusal table. (with increasing the occlusal table, more trauma to abutment teeth will occur)
- Embrasure form.
- Contour of the retainers.
- Too few abutment teeth.
- Ab overextension of the cervical margin of the preparation which interferes with or traumatizes the peripheral attachment of the periodontal membrane.
- In district band impression technique can also stimulate recession of the alveolar process.
- Too much pressure exerted in taking the impression forcing the band beyond the attachment of the periodontal ligament & either cutting or tearing it.
- The same things will happen if the band is not contoured to the proximal curvature of the gingival line.
9
Q
Causes of pulp degeneration:
A
- Too rapid preparation of the Improper cooling during preparation.
- Uncovered teeth exposed to saliva & irritation between visits.
- Undiscovered Caries under a retainer even by a radiograph. (Marginal examination with a mirror & explorer is essential).
10
Q
Causes of bridge framework fracture:
A
- Faulty solder joint or weak connectors.
- Incorrect casting technique.
- Overload on the metal due to the length of the span.
11
Q
Causes of veneer fracture:
A
- If a shelf of porcelain left exposed to opposing surface or cusps & subjected to either leverage or spot contact.
- Over rapid heating or cooling during glazing.
12
Q
Causes of loss of veneer:
A
- Too little retention.
- Badly designed metal protection.
- Deformation of the protecting metal.
- Malocclusion
- Improper curing or fusing technique.
13
Q
Lack of metal protection of deformation of metal requires:
A
- Equilibration.
- Reduction of the forces from occlusion.
- Change in the form of the occluding area.
- Increased number of pin holes providing retention
14
Q
Failure to Seat
A
- The abutment preparation may not be parallel.
2. Incorrect soldering or the relationship of the retainers may be altered during soldering.
15
Q
Loss of Function
A
- Loss of a tooth in the opposing arch without replacement
