Dental Retreatment (part 2): Crowns and Bridge

In the part 1 we saw retreatment for root canal treated teeth. In the part 2, the retreatment of the crows/caps and bridge will be covered briefly.
The crown and bridge treatment has been practiced for a very long time. The materials used have been metallic alloys, metal veneered with ceramic (metal ceramic) and full ceramic. The primary purpose of a crown is to reinforce tooth structure that has been weakened due to larger restorations, root canal treatment (endodontic treatment), trauma, or help in replacement of missing tooth/teeth.

Over a period of time, a root canal treated tooth undergoes multiple changes, weakening of structural integrity is one of the important change that needs to be considered. Usually the dentist advices for a cap/crown to be placed on the tooth. Now, some people may think that the dentist is trying to make money by prescribing crowning of the tooth. But the fact is, the clinician is aware of the various problems after root canal treatment thus a crown is necessary.

In case of replacing a missing tooth by a bridge, the adjacent teeth (abutment teeth) need to be prepared and the bridge is placed over them. Some times the teeth that need to be prepared may not be in proper alignment, these situations require the misaligned tooth to be reduced more on one side making it vulnerable to pulp exposure. In this situation the clinician advices to get root canal treatment done for that particular tooth and proceed with the treatment.

The reason why the root canal treatment is mentioned because the failures in crown/ bridge may also be associated with the former treatment. In situations where the crown/bridge treatment has been carried out without any problem and has been serving satisfactorily, there are instances where the root canal treatment has failed and caused infection. The diagnosis of this situation can be confirmed by a radiograph (x-ray). For this, root canal retreatment of the tooth/teeth is necessary. During this procedure, either the prosthesis is removed or the clinician creates an access to the root canal by drilling through the prosthesis.  

Factors Associated with Crown/Bridge Failure

Now once you have got a crown/bridge placed on tooth/teeth, the dentist may predict the longevity up 5 years, some may say 10 years some claim life time. But the fact is that the longivity of a crown depends on multiple factors which involves the clinician, patient and the dental laboratory technician skills to fabricate a crown.

The clinician associated factors depends on the ability to perform tooth reduction with precision and recording the prepared tooth with accuracy. In addition to this, when providing a bridge, the clinician should understand the various forces acting in the region where the bridge is placed. Clinician should have a sound understanding of the number of abutment teeth to replace a single tooth and also for multiple teeth. The clinician should be well aware of the material handling (impression material) as well as to  interpret the quality of an impression (acceptable or not). The biomechanical understanding of reduced tooth and the morphology that will help in retention of the prosthesis is of great importance. When the crown is delivered to the clinician from the dental laboratory, the protocol followed to cement the crown should be followed strictly. Apart from this, when the prosthesis is commissioned to perform during chewing, the opposing tooth comes in contact. The clinician should be able to identify if the crown is contacting the tooth in the opposite side before rest of the teeth (high point). The clinician should have a sound understanding of the shade matching in case of metal ceramic/full ceramic prosthesis. If the clinician is not confident, the dental laboratory technician should be called to reverify. Later the clinician should keep a 6monthly followup appointment after delivery of prosthesis.

The patient associated factors are purely dependent on how seriously the patient takes oral hygiene maintenance. As the prosthesis is a foreign body irrespective of the material used (metal, metal ceramic or full ceramic) it is susceptible to plaque formation on the surface as well as the tooth-prosthesis junction. Flossing is equally important to maintain health between the teeth. For a bridge, an ultra floss or super floss is available that helps in cleaning the part under the bridge.  One of the most ignored factor associated with patient is lack of communication regarding followup appointment and allergy to materials. Nickel allergy is most common and the use of nickel containing alloys have been discontinued many countries. Patients co-operation with the clinician is also an important aspect of the treatment.

The dental laboratory associated factors are equally important because, after the impression procedure made by the clinician the further steps are all laboratory dependent. The clinician and laboratory technician communication has to be clear so all the information regarding the prosthesis should be understood. Later steps depends on the skill level of the dental laboratory technician to provide an accurate prosthesis and follow the instructions provided by the clinician. The technician should be able reproduce the shade as provided by the clinician.

Failures of Crown/Bridge 

For patient understand, the failures will be enlisted and described at a basic level. Complications associated with crown/bridge treatment are minimum and can be managed without any trouble.

1. Dislodgement of Crown/Bridge.
2. Allergy to alloy.
3. Secondary caries.
4. Fracture of prosthesis.
5. Fracture of ceramic (in case of metal ceramic/full ceramic prosthesis).
6. Fracture of bridge.
7. Gingival inflammation.
8. Periodontal disease.
9. Tooth fracture.
10. Incomplete seating of prosthesis.
11. Pain in the opposing tooth (uncorrected high point)
12. Food impaction.
13. Pain in the gums.
14. Discoloration of prosthesis.
15. Miss-match of tooth-prosthesis shade (metal ceramic or all ceramic). 
16. Loss of crown/bridge from the implant.

The above mentioned failures have been summarized in a concise manner. Apart from the above mentioned information, if there are any doubts or need more information please feel free to ask.

Crown/Bridge Removal
When a prosthesis is diagnosed as fail, the clinician will advice removal. The prosthesis may be removed by cutting through with the drill, may use a puller, mechanical crown remover, pneumatic crown remover, bucco-lingual dimple technique . There are other techniques too but the mentioned systems are commonly used. Depending on the technique used, a word of caution, the experience may not be pleasant. During crown/bridge removal procedure there are chances of tooth fracture, make sure you ask your clinician regarding the unexpected consequences of the procedure.

Tooth preparation for crown

Gum disease associated with faulty prosthesis

Ceramic chipping of metal ceramic prosthesis

Failure in shade selection

 

Fracture of tooth