Survival rates of porcelain laminate restoration based on different incisal preparation designs: An analysis

When it comes to restoring the mouth with porcelain in order to improve the aesthetics, the porcelain laminate veneers (PLVs) are one of the most conservative and aesthetic techniques that we can apply. The longevity of the veneers are quite long and durable especially if the right indications are chosen and the correct techniques are applied.[1] The conservation of sound tooth structure helps preserve tooth vitality and reduce postoperative sensitivity. Innovative preparation designs, like those for PLVs, are much less invasive than conventional complete-coverage crown preparations.[2]

Edelhoff et al, found that ceramic veneers and resin-bonded prosthesis retainers were the least invasive preparation designs, removing approximately 3-30% of the coronal tooth structure by weight. Approximately 63-72% of the coronal tooth structure was removed when teeth were prepared for all-ceramic and metal-ceramic crowns. For a single crown restoration, the tooth structure removal required for a metal-ceramic crown was 4.3 times greater than for a PLV, facial surface only preparation and 2.4 times greater than for a more extensive PLV.[1]

The dentin-enamal junction (DEJ) is very important for the structural strength of the tooth. The explanation lies in the most fascinating feature inherent to the natural tooth-a complex fusion at the DEJ, which can be regarded as a fiber-reinforced bond.[3] Because when we limit our preparations on enamel, the tooth will not flex and it will stay as rigid as a tooth can be.[4] Even if our preparation line passes through the DEJ margin and enters into dentin, it would not create a major problem for minor invasions. However, if we end up finishing our preparation on large amounts of dentin, we very well may end up with other kind of problems. This will not only create complex bonding issues on dentin, but will also free the “flexing” factor on the tooth structure.[5] Over preparing the rotated or aggresive preparation of protrusively placed teeth will cause us to end up in the dentin structure which will lower our bonding values as well as causing the flexing of the tooth structure.. And when the tooth starts flexing, a different phenomena occurs in this situation. First of all, we have the tooth which is agressively prepared that wants to bend, to flex and on top of it we are bonding a veneer, a porcelain material, which is very rigid and in between those two structures we will be using the adhesive luting resin which will stay in between and will try to absorb all the stresses. If the tooth receives some different occlusal forces and keeps on flexing, the luting resin at the magrin will start peeling off slowly. So in these situations we will most probably end up with some micro-leakage or de-lamination.[5]

In order to minimize those effects and problems, we have to be very precise and careful about case selection and tooth preparation.[6] The ideal cases which we would want to place the veneers are when the teeth are aligned perfectly on the dental arch and maintaining their original facial volumes which means that the facial structures of the teeth is not worn as it happens by aging. That means, we exactly need to remove the tooth structure equivalent to the thickness of the veneer that we will be placing on the tooth itself.[7]