CAUSES FOR FAILURE IN FPD

Porcelain crown restorations can fail for a variety of reasons. Product failure however is seldom the cause … it is rare that the integrity of high grade porcelain or the fabrication process (in the dental lab) becomes suspect. Dental science and engineering have all but eliminated those types of failures.

How, when and in what fashion a crown fails is actually a function of two key elements. One consideration usually focuses on the preparations made for placing the crown. Under-preparation or over-preparation of the tooth structure can be suspect. Bonding issues related to cementation characterstics and possible contamination of the bonding surface can cause crowns to go bad.

A second consideration focuses on where the restoration was used in the patient’s treatment. Different locations involves different preparation and different bonding procedures for anterior teeth as compared to posterior teeth. In many instances… even the cementation requirements can differ.

Loose Fitting Crowns
Bite and occlusal issues are common causes… as well as generalized trauma to the affected tooth. Bite problems, if they are immediate, may suggest inaccurate treatment. If the bite problems occur over an extended period of time… it may be due to issues involving other tooth structures and the overall occlusal relationship.

Inadequate existing tooth structure or poor preparation of the existing tooth structure may be the culprit. In some instances, with Dr. Briglia’s patients, a build up and post may be implemented to create the needed structure for a crown to adhere to.

If certain physical properties aren’t monitored closely, even a brand new build up can fail, due to the inadequate relationships of physical forces (biting) and retention qualities of surface areas.

The bonding process and bonding materials can often lead to crowns becoming loose in a very short time. Issues of over-preparation or under-preparation can be the cause. Matching the ideal cement product with the type of bonding surfaces can be critical. Contamination of the bonding surfaces is a frequent cause, arising from air borne bacteria, saliva and even a patient’s breath can compromise a bonding procedure.

Older crowns often become loose due to decay occuring under the crown. Decay can become manifested either through leakage between the bonding surfaces that allow bacteria ot accumulate. In other instances the preparation process did not remove 100% of the existing decay.

This decay-causing-looseness event occurs frequently in certain types of bridgework applications. Anchor teeth restorations, due to the biting forces operating on the bridge, may cause bonding surfaces to flex and eventually leak.

Discolorations
Many of the older crowns produced during earlier generations of dentistry science become discolored because underlying metal characteristics. Errors in creating and assuring secure margins of the crown can also cause the “dark line effect” on a crown. The use of all porcelain crowns or porcelain fused to gold crowns, as used in our office, overcomes this age old problem.

Sensitivity – Pain
Tooth sensitivity (reactions to hot and cold temperatures) that occurs immediately after placement of a new crown can be caused by indequate bonding procedures. Internal structures of the original tooth structure are indequately sealed due either inaccurate preparation or contamination of bonding compounds.

Pain associated with biting pressure may indicate a crown treatment that may have too much height or poor match of occlusal surfaces of an adjacent tooth. In some severe instances, stories of new crowns being ground down to the point of exposing underlying metal structures are not unheard of. Precision use of Articulators enables dentists to overcome this issue. Unfortunately, articulators are not used as often as they should be.

Doctors who readily accept and/or seek out the development of complex multifaceted treatment plans tend to have the technical know-how of overcoming what should be common error issues in dentistry. Because of the vast experience acquired in successfully treating chronic dental problems, routine and common place errors in judgement and/or application of treatment rarely occur.