Veneers & Debonding Problems

The most embracing problem facing dentist in cosmetic dental treatment is a veneers debonding. There are many factors that help other porcelain restorations to be retained even though dentist or dental lab make some mistakes.(we will write about that with other newsletters) in versus there are many factors that help veneers to be debonded if dentist take them with tolerance. The challenge is that veneers restorations are the most porcelain restoration type that faces the highest shear stress than any other porcelain restorations. Therefore, there is no mistake tolerance with all procedures especially resin cementation steps. On other hand some mistake in these steps cannot be fixable. That means dentist will have to repeat veneers work completely from starting. Veneers bonding are more difficult than preparation and impression steps and more sensitive to any procedure mistake.

The debonding problem may happen within few or many days, months or even years but most likely happen in few months after resin cementation ( from 4-12 months). That might be related to different reasons. We try to divide it into following categories.

1. Resin problems
2. Bond problems
3. Etching problems.
4. Application problems.
5. Lab manufacturing problem.
6. Zirconium veneers
7. Occlusion problem.
8. Veneers thickness and size.
9. Periodontal problems and patient dental care.

In many veneers cases the debonding problem can be led by combined factors together. We will explain each one in details.

1- Bond problem: It is the most common reason of veneers debonding, the bond is always the king in any veneers cementation process because, all veneers mass loaded directly by resin’s bond. The problems may happen to bond that may lead to debonding :

• Bond storage problem: bond is very sensitive to temperatures, high temperature may damage bond too much specially when imported from country to other it is difficult to control cooled imported shipping.
• Thickness of bond layer: less thickness in bonding layer more resistance against shear stress. Transferring shear stress from resin layer to tooth done through bond layer. The thin bond layer makes this operation faster and less in time stress to finish this operation.
• Moisture: the bond is very sensitive to moisture. Sometime dentist dose not observe moisture coming from gingival groove especially if veneers made after gingival or periodontal treatment. The gingival groove area may still release some liquid that mingles with and weakens bond.
• Curing bond before insert the veneers with resin. This is not considered as a problem or practical mistake. Some cement producers instruct to light-curing cement as final stage after inserting veneers with resin and cure all in one stage. The positive of this procedure is to decrease the thickness of bond after press

Porcelain Veneers on fit margins. The negative is to make the shrinkage of resin after curing more than multi-curing step.

2- Resin problem: As known for all dentists there are three types of resin cement: self-cured, light-cured and dual-cured, for veneers cases using light-cured cement resin in a must. The benefit of light-cured resin is giving dentist time to place and press veneers on precisely fit margins. And removing excessive resin is much easier than self-cured resin.

Nowadays resin cement is used from many dentists to cement everything. PFM crown, porcelain filling. metal free restorations post and core, etc.…. But application of light-cured resin cement is a best choice to cement veneers on the tooth.

Why self-cured resin sometimes lead to debonding:

• Self-cured resin is more sensitive to moisture that leads to weakness in veneers toughness and strength.
• Self-cured resin has short time in work: some time dentist has limited time to fit veneers on margins precisely and that if happen even in few microns will produce difference in thickness of resin layer which will lead after sometime to breaking resin layer.
• Short working time make excessive cleaning is difficult therefore the remaining resin will increase marginal leakage and eventually will loosen bond under resin.
• The self-cure cement creating bubbles more than light cure cement.

3- Etching problem: Etching step in very important and easy step for veneers bonding. The problems may happen in this step are:

• Over –shorter etching time: the ideal dentin etching time is 15 seconds and for enamel 10 seconds. Over etching time will collapse enamel rods and make etched dentin area deeper to be penetrated by bond that may lead to post pain and weaken bond on enamel too much. Shorter etching time will make the depth of etched area on dentin and enamel less than required for veneers retention.
• Porcelain etching problem: some veneers resin producers instruct to etch internal face of veneers with phosphoric acid 30-40% concentration around 60 seconds. That may be enough for small size veneers which are not need too much retention to avoid debonding problem. But big veneers size needs to be etched with fluoride acid around 60 seconds it is more effective than phosphoric acid. Some dental labs make sanding to internal face of porcelain veneers that is very effective to increase veneers surface retention. And now some research about etching veneers by laser. We will talk about in later newsletters. 4- Application problems: this step is divided into three sections
• Preparation and impression steps: it will be specific newsletters about preparation and best practices. But the important in this section to provide precision in procedures that create minimal space between whole veneers area and teeth. Any problem with fitting either from dentist or dental lab will create variety with resin thickness in cementation area that will weaken resin layer in short time.
• Cementation procedures problem: always veneers need to be inserted by sliding veneer horizontally and vertically press it onto the tooth to have exact fit place. Any incorrect movement will displace veneer and weaken retention. This mistake is not fixable and dentists need to repeat veneer.
• Bubbles: it is a common problem and not remarkable from dentist and cannot be fixable If it happens. Bubbles are formed in two ways and places:

1. Inside resin mass: these bubbles formed when dentist inject resin on the veneer without moving resin to remove bubbles before inserting onto tooth.
2. Between the resin layer and tooth: these type of bubbles worse than first especially if they are big. As we said before this problem occurs when veneer is no well-pressed vertically onto tooth.

The type one of bubbles sometime do not make problem if there are in few number and small. The second type for sure make problem because they are most likely big and located on margin area.

All problems might be led by bubbles, in short term:

• Post veneers pain.
• Increase marginal leakage. ( by marginal bubbles)
• Discoloring resin layer.

In long term:

• Veneer debonding
• Porcelain break
• Caries and RCT

5- Lab manufacturing problems

The manufacturing problems are long discussion, but in brief any problem with margins will make effect retention and resin cementation. Some main problems may happen in veneers:

• Open margin to over-pass Under-Cut. This is not the problem of lab but problem from preparation. But open margin will increase the thickness layer resin. Difference in thickness with veneers layer will increase stress on some point more than other. Sooner or later will loosen resin layer.
• Over margin: this problem always happen with no preparation veneers type such as LUMINEERS® and Glam Smile® this type of veneers leave edge because no margin prepared. This area is difficult to be cleaned by patient. The companies now compete to be produce thinner veneers without weaken porcelain resistance.
• Sanding problem: some dental lab sanding the internal face of veneers to increase surface of retention. This has to be well-cleaned to avoid any contamination. Contamination (smear layer) may create bacterial colony and destroy bond layer.
• Casting problem: this problem happen with ingots porcelain. Some dental uses wax not specified for the same ingots porcelain company that can affect the dimension of restoration by shrinking or margin opening.
• Many times porcelain sintering: sometime some difficult veneers cases need modifications many times. Sintering porcelain many times will effect and make damage to margins and dimensions.

6- Occlusion Problems

This is very important factor causes veneers debonding and need experience to be diagnosed. The most observed debonding related to occlusion:

• Severe contact: it should be no contact palatally or slight contact this problem common for falling veneers.
• Posterior teeth: premolars receive high vertical stress especially on mandible.
• Uni-lateral mastication: veneers on mastication side receive high stress than other side.
• Edge-to-edge occlusion: this case is contradiction for veneers treatment.

7- Zirconium Veneers

There is an argument about manufacturing veneers from zirconium. What related to veneers debonding there is a disadvantage for that: Zirconium veneers sintered under 1500c in furnace. Therefore it cannot be etched or by any acid or sanded.

8- Veneers Thickness & Size:

Sometime dental technician need to increase thickness for esthetic purposes (to organize alignment of anterior teeth). In this cases bond will load and retain heavy porcelain mass that may be debonded specialty if mastication stress of patient is very high. On other hand Some patients have a gingival recession and dentist prepare cementum with enamel to cover all recessional area with veneers. In this case Veneers become very big and susceptible to fall down. (Some of these cases are contradiction for veneers treatment).

9- Periodontal problems

As we mentioned earlier, in some patient gingival release liquid continuously specially thick gingival tissue. Dentist sometime cannot dry this liquid special when prepared margin sub-gingival line. This liquid contaminate the bond create a weakness in retention. The coming newsletters of veneers best practice