Porcelain Laminate Veneers: Minimal Tooth Preparation by Design

Porcelain laminate veneers have been one of the most used restorations for aesthetics. Aesthetics is a subject that is objective and necessitates excellent communication among the dentist, patient, and ceramist. The case must be carefully selected and treatment planned. The use of mock-ups, followed by a wax model, aesthetic pre-evaluative temporaries, and silicone index, provides the best aesthetic, phonetic, and functional outcome and allows for better communication with the patient and laboratory. The use of permanent diagnostic provisionals could have a further impact on this solid communication. Patients have the chance to evaluate the aesthetics, function, and phonetics not only by themselves but also with their immediate circle of family or friends.

A porcelain laminate veneer is one of the most conservative and aesthetic techniques that we can apply when restoring the human dentition. Since their development 25 years ago, interpreting the indications and applying the correct techniques has been key to providing their longevity . Long-term (15- and 20-year) retrospective studies indicated that the success rates of veneers are as high as 94% to 95% percent . Tooth preparation is one of the most important considerations in this technique. Bonding to enamel rather than dentin provides the best/strongest bond values when we want to bond porcelain to tooth structure . When a porcelain veneer restoration is bordered on all margins by enamel, microleakage or debonding of these restorations is not likely to occur. A main objective of any restorative case involving these restorations is to keep the preparation simple and be conservative in reduction of sound tooth structure.

Many other considerations come into play as the preparation becomes more aggressive and dentin is involved. A rigid veneer behaves differently when bonded to a rigid surface, such as porcelain, versus a less rigid surface, such as dentin, and the composite cement can only absorb so much of the stresses to which the restoration may be exposed. To minimize effects and possible problems, we should be precise and careful about case selection and tooth preparation . What if the teeth to be treated are not properly aligned? One of the major indications for using porcelain laminate veneer is space management. We are often asked to deal with spaced dentitions, crowded teeth, or a combination of both. The main challenges in these cases are visualizing the aesthetic outcome and providing the best tooth preparation to the ceramist to allow for the best aesthetic result.

Analyzing the smile

To have a solid understanding about the visualization of the final outcome, the existing smile should be analyzed carefully from a three-dimensional aspect.

Facial view

When the smile is analyzed from a facial view, we can only deal with the mesial-distal or vertical problems observed. In this particular case we see that the centrals are overlapping, which causes a vertical canting of the midline that is obvious even to the lay population. The existing teeth are short for this face proportion, and the gingival zeniths are asymmetrical ( Fig. 1 ).

Fig. 1
An unaesthetic smile. The maxillary anterior teeth exhibit relatively dark color, short crowns, uneven gingival zeniths, crowded incisors, an uneven incisal silhouette, and a deciduous canine in the upper left quadrant.

Viewing the teeth at a 45° angle (checking buccal-lingual dimension)

This view provides the opportunity to check the crowding more accurately. In this case we can see that the mesial-incisal tip of #8 is more buccally placed relative to tooth #9 ( Fig. 2 ). In this initial evaluation, it is difficult to decide which incisal edge position can be used as a reference point in a buccal-lingual dimension. Should we build up tooth #9 buccally or bring tooth #8 lingually?

Fig. 2
Analyzing the smile at a slight angle allows for easy visualization of overlapping central incisors.

Aesthetic occlusal plane

The third dimension to be checked in our aesthetic evaluation is the aesthetic occlusal plane. This evaluation can be accomplished by looking at right and left proximal views. In this case, a deciduous canine creates a problem related to aesthetic occlusal plane. This canine is too short in regards to the aesthetic occlusal plane ( Fig. 3 ). The angulation of the centrals is preferred to be perpendicular to the aesthetic occlusal plane.

Fig. 3
The upper left aesthetic occlusal plane exhibits a reverse curve to what we would like.

Functional evaluation

Functional evaluation of the teeth to bear the proposed restorations must be done carefully if we are to provide long-lasting restorations. One must be careful in checking the root of deciduous tooth #63 (European upper left deciduous canine) in the #11 position. If on the radiograph it is obvious that this deciduous tooth will most likely be able to withstand the lateral forces during occlusion, then a canine-guided occlusion can be planned. If there is some doubt, then splinting crowns using the deciduous canines in the #11 and #12 positions may be a good alternative.

Functional evaluation

Functional evaluation of the teeth to bear the proposed restorations must be done carefully if we are to provide long-lasting restorations. One must be careful in checking the root of deciduous tooth #63 (European upper left deciduous canine) in the #11 position. If on the radiograph it is obvious that this deciduous tooth will most likely be able to withstand the lateral forces during occlusion, then a canine-guided occlusion can be planned. If there is some doubt, then splinting crowns using the deciduous canines in the #11 and #12 positions may be a good alternative.

Treatment planning

It is almost impossible to visualize the final outcome of this case using only an intraoral examination. The practitioner may begin to visualize and realize the aesthetic final outcome and share this information with the patient with the help of a composite mock-up .

Mock-up

Simply stated, a freehand carved composite can help the patient and the doctor visualize what the final outcome may look like. At this time the composite mock-up need not be as precise as a laboratory wax model ( Fig. 4 ). It should give a general length of these teeth, the location of the facial bulkiness, and its effects on the lip structure, phonetics, and occlusion . This mock-up can be a great tool or guide if provided to the laboratory technician in a poured cast so that he or she may provide a wax model with a much more accurate idea of the possible outcome of the case .

Fig. 4
Our first step is to align the incisal edges with a composite mock-up. The incisal edge position is ideally fixed with this mock-up. Additional composite is applied over the soft tissues to determine where the soft tissue gingival zenith should be after the periodontal intervention. The length-to-width ratio of the teeth is carefully planned out.

More difficult cases may require a second intraoral composite mock-up. An example might be a case in which we need to alter the gingival levels, which changes the length of the restoration apically. It is often necessary for the dentist to make a second mock-up. After the periodontal surgery is performed and the tissue has healed, a new mock-up is produced ( Fig. 5 ) to show new proportions and the new smile design.

Fig. 5
After periodontal surgery (2–3 weeks of healing), a new mock-up is accomplished over the teeth to establish new proportions and relations to allow for an even better appearance of the patient.

This second postsurgical mock-up helps the dentist and ceramist to create precise teeth proportions relative to where the new gingival margins are positioned. In this case, a new impression is made out of the second mock-up and sent to the ceramist to provide guidance with the final wax model. A decision was made in this case to prepare the deciduous canine in position #11 and tooth #12 for crowns. They eventually will be splinted for better support and would provide group function design of the final wax model.

While the gingival tissue is healing from the periodontal surgery, it is possible to bleach certain areas with either an at-home or same-day bleaching method ( Fig. 6 ). It is easy to visualize that the incisal mesial corner of #8 must be positioned and restored lingually. The best choice of treatment would be orthodontically moving it lingually and continuing with minimally invasive techniques. Time limitation for this specific case did not allow for this treatment option, however. This information is communicated to the laboratory so that the technician knows to trim the corner of tooth #8 slightly inwards when creating the wax model.

Jun 15, 2016 | Posted by in Esthetic Dentristry | Comments Off on Porcelain Laminate Veneers: Minimal Tooth Preparation by Design
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