Porcelain Veneers can last 15 years or more. Some do not stand the test of time. This short article will detail and explain, in terms that most laymen will understand, some of the important factors involved with achieving a successful porcelain laminate restoration. For a veneer to be a success a number of steps need to be taken by a dentist, not all of which have to do with their appearance.
Steps required in order to allow laminates to last for a truly long time include: the proper hydrofluoric acid etching of the internal surface of the veneer, silanation of the etched surface, proper fitting and seating of the laminate in the mouth, freedom of saliva or blood contamination while bonding the laminate, gentle removal of the excess bonding material used to attach the laminate are just a few of the things steps involved with the successful insertion of porcelain veener restortions.
After the final insertion, care must be taken to adjust all occlusal excursion to limit lateral and vertical forces on the incisal edges of the restorations. All the margins also should be smoothed and polished so that they do not become plaque traps. Plaque, when left undisturbed on bonding can cause porosities to develop that will pick up stain.
In the discussion that follows, a brief explanation of of each of the previously mentioned steps will be included. This should help a reader will understand why each is important to success of a bonded porcelain.
Although the external surface of a bonded porcelain restoration should be highly glazed, the internal surface should not. Areas that are to bonded to composite cement must be made porous in order to help mechanically attach the bonding to the porcelain. This is best accomplished by etching the glazed porcelain surface with hydrofluoric acid. Hydrofluoric acid is a unique acid that will etch any glass that it is in contact with. Treating the porcelain with this acid allows hundreds of microscopic porosities to develop on the internal surface of a porcelain restoration which help greatly in improving the restorations retention.
After the veneers have been tried in and a proper fit has been insured they should be cleaned in alcohol to remove all organic debris and then silinated by the dentist. Silane is used to treat the etched internal surface because it helps create a chemical bond between composite cement and the porcelain.
Prior to bonding a veneer, the prepared tooth surface should be cleaned and all organic or other debris should be removed from tooth surfaces that will receive the porcelain restoration. Any debris that is left behind may weaken the bond strength of a veneer or may create voids that will pick up stains later. Often a dental assistants help is used to insure the tooth remains clean while a dentist is dealing with the laminate just prior to its insertion.
Bonding agents are placed on the tooth that will receive the laminate and composite cement is placed in the restoration prior to seating it in the mouth. After placement of the restoration, the dentist should remove most of the excess cement in order to make sure that the restoration is properly seated. Excess cement may make it difficult for a dentist to be sure that the restoration is properly seated.
Proper seating of the restoration is desirable for esthetic as well as functional reasons. Not only will a well seated restoration retain the position that the ceramicist intended , but will also ensure the proper cement thickness of the composite luting cement. This can be important since when the luting material is too
Thick, it may weaken the restoration and make it more prone to premature failure. A properly executed veneer has a thin an uniform thickness of luting cement.
After the veneers are inserted, but before the patient is dismissed it is important for a dentist to check the patients occlusal excursions to see if the “incisal guidance” needs adjusting. Incisal guidance refers to the path the lower jaw makes against the upper jaw when making excursive movements, both side to side and front to back. Often the incisal edges of the maxillary anterior teeth do make contact with the lower teeth when these movements take place. It is of utmost importance that the dentist checks these excursions as they affect the newly created edges of the veneered teeth. Often small adjustments of the palatal aspect of the veneer need to be made in order to minimize potentially harmful forces that may stress the cemented laminates. All jaw movements should be smooth against the anterior teeth so that there is no stressful ‘banging’ on the porcelain incisal edges. If the excursions hang up momentarily on an edge it can create a stress concentration that may over time cause a veneer to dislodge or break. All excursion should be smooth so that these stress concentrations tend not to occur.
Also it is equally important to make sure that all porcelain margins are smoothed and all excess cement removed. Rough overhanging margins can be a plaque trap and can cause gingival inflammation as well be more likely to pick up dark stains at a later time. For this reason it is important for the dentist to smooth all margins using diamond abrasives and polishing wheels, prior to dismissing the patient.
Lastly, when patients have had extensive restorations of their anterior teeth most dentists are in agreement that patients would do well to wear a night guard at night that will protect against any undue forces or excursions that take place while they are sleeping. Often during sleep patients brux or grind there teeth in ways that they do not during the day. These night habits can have a destructive effect on porcelain restorations when a night guard is not worn.
Certainly there are additional factors that can affect the long term prognosis of bonded porcelain veneers, but this article has covered and explained a number of important considerations. Often porcelain veneers for different patients are made by the same dental laboratory, but can have a different life expectancy in the mouth. This article might explain why this may be so and why veneers do better for some patients than others.