Failure of Crowns and

Fixed Dental Prosthesis

Dr. Hesham I. Othman,

Prof. and Head of Crown and Bridge Dept. Al-Azhar Univ.

FACTORS CAUSING FAILURE OF CROWNS AND BRIDGES

COULD BE CLASSIFIED ACCORDING TO THE STAGE IN WHICH IT OCCURS AS FOLLOWS:

CEMENTATION

Failure of fixed

prosthesis

Biologic

Failure

Mechanical Failure

Esthetic Failure

Maintenance Failure

Classification according to mechanism of

failure

Patient complaint may be;

1- Immediate

2- Delayed

1.

2.

3.

4.

5.

6.

7.

Biological Failure

Excessive Pressure on soft

tissues

Retention of food on the occlusal

surface

Traumatic occlusion

Torque Cervical hypersensitivity of

the abutment

Improper pontic/

ridge relationship

Lack of auxiliary

escape grooves

Premature contact Lack of parallism

between abutments

Over displacement

of gingival tissue

during impression

taking

Foreign body

pressing on the

ridge

Improper buccal

and lingual

embrasures

---

Absence of

temporary

protection

Over extended

temporary

protection

Over extension

cervical margins of

retainers or crowns

---

---

---

Over extended

cervical margins of

restoration

Faulty proximal

contact

--- --- --- Short or open

cervical margins of

restoration

Improper labial or

lingual contour of

retainers or pontics

---

---

---

Cervical caries

Discomfort, Pain and Sensitivity

CARIES

1.

2.

3.

4.

5.

6.

PULP INJURY

due to;

1. Improper use of coolant.

2. Over reduction leaving insufficient dentin protective

barrier.

3. Minute pulp exposure.

4. Improper or absence of temporary protection.

5. Use of irritating luting agent.

6. Recurrent caries under the restoration

7. Low grade pulp irritation as a results of traumatic

occlusion

PERIODONTAL BREAKDOWN periodontal breakdown may lead to loss of abutment

Patient suffer from;

- Mobility of abutment

- Periodontal pocket formation

- Periodontal abscess

- Pain which prevent mastication at the side of restoration

- Bad odor and taste

Periodontal breakdown may be due to;

1. Inadequate abutment teeth in long span bridge.

2. Periodontally affected abutment teeth.

3. Patient with poor oral hygiene.

4. Poor marginal adaptation.

5. Over or under contour of axial walls

6. Extensively large connectors that restrict the cervical

embrasure.

7. Pontic with large contact area on edentulous ridge.

8. Improper or absence of proximal contact causing

food impaction and periodontal pocket formation.

9. Irregular or rough cervical margin of prosthesis.

OCCLUSAL PROBLEMS

Premature contact in centric and eccentric occlusion

excessive tooth mobility.

TOOTH PERFORATION

due to;

- Faulty preparation during pinhole preparation.

- Faulty during post space preparation.

TOOTH FRACTURE 1- Coronal tooth fracture

Due to;

1. Over reduction of abutment

2. Recurrent caries

3. Un-retained restoration

4. Presence of premature contact or heavy occlusal

force

5. Application of excessive force during seating of

improperly fitting restoration

6. Incorrect removal of cemented restoration

2- Root fracture

Due to;

1. Excessive widening of root canal during endodontic

treatment or during post space preparation

2. Forceful seating of post

3. Caries extended to root surface

4. Trauma

MECHANICAL FAILURE

1. Cementation failure; looseness and/or dislodgment of

restoration, it could be due to

a- Cement failure

b- Retention failure

c- Occlusal problems

d- Different degree of abutments mobility

2. Restoration failure ( retainer, pontic, or connector )

3. Occlusal wear or perforation

1- Cementation Failure

a- Cement failure This could be due to;

1- Cement selection

2- Expired cement

3- Clinician not follow manufacturer’s instructions

4- Incomplete removal of temporary cement

5- Inadequate isolation

6- Inclusion of cotton fibers

7- Incomplete isolation

8- Insufficient pressure seating

1- Cementation Failure b- Retention failure This could be due to;

1- Excessive taper

2- Short clinical crown

3- Misfit

4- Misalignment

1- Cementation Failure c- Occlusal problems

This could be due to;

1- occlusal interference

2- Occlusal perforation

3- Parafunctional activity

4- Loss of occlusal contacts

1- Cementation Failure d- Different degree of abutments mobility

This induce stresses on the cement which lead to

cementation failure

How to confirm cementation failure?

1- Pull the restoration margin and

see for movement of it.

2- Bubbles come out of the margin

or perforation (if present) when the

restoration pushed by occlusal

pressure

2- Restoration Failure

a- Retainer failure;

- Perforation

- Marginal discrepancy

- Veneering separation, fracture or wearing

b- Pontic failure;

- Pontic fracture (Porcelain) with unfavorable occlusal

load

- Limited occlusocervical height due to over eruption

c- Connector failure;

This could be due to;

1- Improper designing of connector size and position

2- Thin metal at the connector

3- Incorrect selection of solder

4- Porosity

Occlusal wear or perforation

Heavy chewing, clenching or Bruxism

wear of restoration

perforation of occlusal surface of

the metal restoration

Leakage, cement dissolution & caries

Esthetic Failure ► Improper shade matching ► Insufficient tooth reduction ► Disharmony between restoration and neighboring

teeth

► Improper masking of metal by esthetic material ► Use of improper shade of cement with all ceramic

restoration

► Unnecessary display of metal in case of partial veneer metal restoration

► Improper marginal adaptation, form, roughness, or extension which lead to gingival inflammation

causing unnatural soft tissue color

Maintenance Failure

Poor oral hygiene and improper maintenance of a well

done restoration may lead to failure of prosthesis.

The patient must be fully informed about his responsibility

in success or failure of restoration

The dentist must recall the patient for periodic clinical and

radiographic examination to detect early any harmful

changes that might occur.