Indication, Preparation and Restorative Material for Supragingival Minimally Invasive Porcelain Veneers
The indications for porcelain veneers should be expanded. Porcelain veneers can be used for the traditional esthetic rehabilitation of a tooth or teeth (Figure 7.1a–c, 7.2a,b). Porcelain veneers are the ideal material for restoration when teeth are badly damaged by fractures, large caries or old restorations, and when teeth have undergone endodontic procedures. Fractured teeth are great candidates for porcelain veneers to replace the damaged or missing incisal edge. Some in-vitro studies suggest that teeth with an extensive incisal edge missing could be at a higher risk of fracture or failure with veneers [1,2]. This may lead to the assumption that large fracture cases should be treated with more aggressive procedures, such as full crowns. This approach is counterintuitive, as it suggests that the solution to a large fracture or damage on a tooth would be to cut further large amounts of tooth for a full crown (Figure 7.3a,b). Fortunately, extensive clinical experience and the literature reports the success and durability of this restoration, even when several millimeters of incisal length are replaced (Figures 7.4a–c, 7.5a,b, 7.6a–e) [3,4].
Veneers can also be used for an occlusal rehabilitation to regain lost anterior guidance, although many experts have suggested that veneers are contraindicated for restorations of teeth with severe wear and when occlusal problems are present [5,6] fearing a decrease in durability. In fact, these fears lead to the promotion of full-coverage crowns as the ideal treatment for worn-out teeth [7,8]. Nevertheless, porcelain veneers are the ideal restoration to repair occlusal trauma. They can help to regain lost tooth structure, and the necessary anterior guidance and posterior disclusion, without the need to grind away more of the already ground-down teeth (Figure 7.7a–e). Clinical experience and the literature also show that the durability of ceramo-metal crowns used in occlusally affected patients is equally compromised [9,10], with all the added disadvantages of a full crown. The success of porcelain veneers increases dramatically when the occlusion is managed, using good occlusal principles, such as the three golden rules of occlusion (Figure 7.8a–e). In other words, any time that a tooth requires an indirect restoration, a supragingival minimally invasive adhesively retained porcelain veneer should be the procedure of choice, because it will be as successful at restoring a damaged tooth as a full crown , with the benefit of less tooth preparation, decreased pulp irritation and supragingival margins, especially when margins are kept on the enamel.
Consequences of Unnecessary Tooth Removal
The aggressive tooth preparation required for full crowns of the anterior teeth has the disadvantage of further weakening badly damaged teeth [12,13]. The fact that anterior teeth are small and thin further amplifies the need to conserve as much of the remaining healthy structure as possible (Figure 7.9). Partial coverage bonded porcelain veneers in particular can be of great value to badly damaged teeth, as they allow the teeth to regain their optimal strength and rigidity. Full crown preparation weakens the tooth structure. Porcelain veneers should be considered as a complete substitute for full crowns. Porcelain veneers are an especially desirable option, even when the tooth has been treated with an endodontic procedure. As the literature shows, when the cingulum is preserved, the tooth maintains its rigidity better than when it is cut for a full crown and the cingulum is removed . Enamel gives the thin anterior teeth their necessary rigidity.
The original veneer preparation was minimally invasive , as described by Bertolotti, a pioneer in this technique (Figure 7.10). Over the years, more aggressive preparation has become more popular, for multiple reasons, including laboratory demands for more space, as thinner veneers are more difficult to do than thick veneers, and the choice of certain restorative materials which require more space [16,17]. The literature suggests that aggressive tooth preparation is detrimental when using bonded porcelain veneers; the more tooth is removed, the lower the survival rate and higher the rate of fracture . Conversely, the more tooth-conserving is the preparation, the more durable the results can be expected to be [19,20]. Durability studies show a decrease in longevity with veneers bonded largely to dentin . Removing the enamel layer and bonding to dentin increases unpredictability, can lead to an increased risk of postoperative sensitivity and pulp damage, and may decrease longevity of adhesion, as dentin is a less predictable bonding substrate. Nevertheless, with the impressive performance of modern self-etching bonding systems for dentin, the long-term success of veneers bonding to dentin may dramatically increase [22,23].
Improper or incomplete diagnosis also leads to unnecessary tooth removal. The space needed for the restorative material should always be visualized from the final external outline of the finished restoration, using the “blueprint” wax-ups, not the current position of the tooth. This approach can help to save a considerable amount of enamel and increase long-term durability (Figure 7.11). This approach is explained in more detail in Chapter 8.
When patients are confronted with a decision of what is more important: a visible metal margin in the esthetic zone and healthy gums, or an invisible subgingival margin, risking the health of the gums, 63% of patients would choose healthier gums . Additionally, Crispin found that gingival margins in the esthetic zone are not visible in approximately 50% of the population, making the need for subgingival margins additionally unnecessary . When the appropriate level of translucency is used, the optimum blending of the veneers at the cervical margin can be achieved, making subgingival margin placement unnecessary (Figure 7.12). Preparation with subgingival margins will always complicate successfully bonded cementation. Isolation is so difficult to achieve when the clinician must fight with inflamed gingiva and blood (Figure 7.13). Using a supragingival protocol, such as the five principles of supragingival dentistry, which include enamel margin preservation techniques, margin elevation and other techniques geared towards minimizing the need for subgingival margins for restorative reasons, will permit the goal of completing the restoration with supragingival margin placement, making the entire procedure more simple and the outcome more predictable.
Tooth Preparation for Supragingival Minimally Invasive Porcelain Veneers
While the goal of the facial preparation for porcelain veneers is always to remain supragingival and within the enamel, creating a window in preparation for porcelain veneers, some buildups and other special techniques must be used in cases of badly damaged teeth. The simple preparation is the basic preparation for a mostly intact tooth, to create the space required by the restorative material of choice, to outline requirements for esthetic needs and requirements to simplify fabrication by the laboratory technician. It is desirable to be as minimally invasive as possible, preserving the healthy enamel, and always keeping a supragingival margin placement (Figure 7.14a–d). Studies evaluating the current literature in regards to preparation design point to window preparation with a butt lingual–incisal margin as the least invasive, with the most durable results, as this technique allows for maximum enamel retention . Simple veneer preparation may need to be varied for esthetic needs, such as excessive proclination or misalignment, which may require a more aggressive tooth reduction, leading to heavy dentin exposure. In such cases, immediate dentin sealing is desirable (Figure 7.15a–c) .
The same preparation for a badly damaged vital tooth can be used for a single damaged tooth or as part of an esthetic rehabilitation. There are special considerations, which may include the repair of heavy interproximal caries, old failing restorations or large fractures, and will require extensive repairs and buildup. The literature shows that bonding porcelain veneers to teeth with composite restorations yields similar adhesion and marginal seal as bonding to natural tooth (Figure 7.16a–d). [28,29].
The preparation for an endodontically treated tooth can be used for a single damaged tooth as part of an esthetic rehabilitation. This use also requires special considerations, such as extensive buildups and in some situations a bonded post. Regardless of how damaged the tooth is, a supragingival minimally invasive adhesively retained porcelain veneer maintains the goal of restoring the damaged tooth back to its ideal esthetics and functional state. In the most minimally invasive way, preservation of the majority of the remaining healthy enamel and dentin, and avoiding the unnecessary invasion of the periodontium, is the goal.
Restorative Material for Supragingival Minimally Invasive Porcelain Veneers
Supragingival minimally invasive preparation, as the name suggests, means that the restorative margin will remain above the gum and the preparation will preserve as much healthy tooth structure as possible. This requires choosing a restorative material with the appropriate characteristics. The restoration should be able to be made very thin but still provide a natural polychromatic appearance and have maximum margin blending abilities to allow for a supragingival margin placement (Figures 7.17a,b, 7.18). The material of choice which fulfills these characteristics is layered feldspathic porcelain. A master technician can predictably fabricate a feldspathic layered porcelain veneer. In the cervical area, a higher chroma with more translucency can be used, with a slightly higher value in the middle third, and creating the incisal edge effects in the incisal third, all within the desired thickness (Figure 7.19a–c). The literature is replete with data showing the overwhelming success of restorations fabricated with feldspathic porcelain. With the above being said, the minimum space required for a feldspathic porcelain veneer is approximately 0.3–0.4 mm in the cervical margin, 0.6 mm in the middle third of the tooth and 1 mm for the incisal edge. Attention should be placed on the term “space required”; this does not necessarily mean “tooth reduction”. In many cases, the final outline of the restoration may be longer or fuller than the current tooth, so no actual tooth reduction may be necessary to the final outline (Figure 20a,b). The final outline is dictated by proper diagnosis and smile design.
While thin feldspathic porcelain will provide the most esthetic results, more recently the use of lithium disilicate has been strongly advocated by many for porcelain veneers. While the benefits are clear (increased strength and much simplicity of fabrication) lithium disilicate has the strong disadvantage of not having enough translucency naturally, at least in the currently available version. While thick lithium disilicate can be layered and can achieve great beauty, experience shows that the opacity of the restoration will lead to poor marginal blending and the need to place the margins subgingivally (Figure 7.21). The only way of using this material and still achieving acceptable supragingival margin blending is to use it extremely thinly, thus increasing its translucency . A maximum of 0.3–0.4 mm  in the cervical third and 0.5 mm in the facial third should be used, while the incisal edge can be 1 mm or more (Figure 7.22a–c). Very thin e-Max has the esthetic disadvantage of being gray, with low value. Experience shows that once lithium exceeds 0.5 mm, it becomes too opacious and this will increase the difficulty in achieving good margin blending. Even in cases when space is not an issue, a thin cervical third is desirable for translucency. Experience and the literature show that decreased thickness does not make veneers more fracture prone . Very thin lithium disilicate will then be monochromatic, but the thinness of the material will allow some of the undelaying color to show through. Lithium disilicate may be a good choice of material for occlusally driven rehabilitations with lesser esthetic needs.
The basic facial preparation for porcelain veneers is usually done in mostly intact teeth. Sometimes a small class III cavity or filling may be present, which may need to be repaired or replaced and will then be treated as an intact tooth.
Step by Step Simple Preparation
- Step 1: Supragingival veneer margins should be above the gums. In most cases, the preparations should be as close to the gingiva as possible without touching it (Figure 7.23a). This allows for optimal periodontal health at cementation, as well as for the life of the restoration and the tooth. Ideally, a silicone matrix should be used to assess how much of the tooth structure must be removed. The use of a silicon matrix is the best way of assessing the amount of space currently available, based on the desired final external outline, and thus being able to decide how much, if any, of the tooth needs to be prepared or removed (Figure 7.23b). The silicon matrix is made from the correctly designed “blueprint” waxup (Figure 7.23c), which will be made after proper smile design and occlusal analysis (discussed in Chapter 13). The matrix is then cut in an L-shape, allowing for an incisal and facial reduction assessment (Figure 7.23d). A second matrix is later used to fabricate the prototype provisionals.
- Step 2: The amount of space or tooth reduction needed for the incisal edge is 1–1.5 mm. If the space is already available due to wear or fracture, there is no need for additional reduction. Simply flatten the incisal edge to 100 degrees from the cervical plane. The 1–1.5 mm reduction can be accomplished using a diamond bur which is 1 mm in the middle of the cutting surface and 1.5 mm on the base of the cutting surface (Figure 7.23e). Sinking the diamond to its full thickness in multiple places along the incisal edge provides depth cuts. The incisal reduction should be at 90 degrees or greater from the gingival plane, to ensure a facial path or insertion, and end in an incisal–lingual butt, as this has been shown to be preferable than a wrap-in to lingual surface (Figure 7.23f) [33,34,35]. The facial–incisal transition should be gently rounded (Figure 7.23g), then all the depth cuts can be joined together, giving a nearly consistent 1 mm reduction.
- Step 3: The cervical margin reduction is the one that will be done in all cases, regardless of space. The purpose is to create sufficient room for the thin porcelain to be seated without creating “steps” between the porcelain and the tooth. It also serves to index the restoration for easier orientation while undertaking the bonded cementation. Ideally, the preparation should remain on the enamel, but the cervical area is thinnest at the enamel so sometimes dentin will be exposed. Creating a thin feldspathic porcelain margin requires much skill. It is virtually impossible to make a porcelain margin of less than 0.3 mm; realistically, the best we can hope for is about 0.4–0.5 mm. For this reason, a 0.4 mm cervical reduction and margin is the goal. The same chamfer diamond bur will be used to create 0.3–0.4 mm depth cuts (Figure 7.23h). The diamond should be aligned parallel to the cervical plane, and sunk approximately halfway into the tooth, or approximately 0.4 mm depth, as the diamond is 0.8 mm in thickness at the tip (Figure 7.23i). A trick to gain even reduction after the depth cuts is to mark the depth of the cut with a sharp pencil (Figure 7.23j). Then, change the angulation of the diamond and join the depth cuts together (Figure 7.23k). When the marks disappear, there should be a consistent 0.4 mm reduction.
- Step 4: The mid-tooth facial reduction should be about 0.6 mm of reduction or space and parallel to the facial plane of the tooth. Just as with the cervical area, complete several depth cuts, mark them with a pencil, then blend them together (Figure 7.23l). By the time the pencil marks are erased, the 0.6 mm reduction will be achieved.
- Step 5: Sink the margins halfway in the interproximal region. It is important to note that this type of preparation never breaks contact. The goal is to just bring the repair halfway to the contact (Figure 7.23m). The tooth must be looked at from both sides to ensure that the cavosurface margin is not exposed. The purpose of this is to not be able to detect the cavosurface margin when looking at the mesial or distal areas. If the color is ideal, the proximal margin can be in full contact and cavosurface margins more superficial (Figure 7.23n).
- Step 6: In some cases, the contact will be placed deeper interproximally and will require a step to break contact very slightly (Figure 7.23o), which can be done using a metal strip (Figure 7.23p). This perfects the interproximal surface. Remove any J margin and create a slight separation to allow the laboratory to see the margins and produce a restoration that is properly adapted. Unless dictated by already open contact, it would be a disadvantage to intentionally and unnecessarily fully break contact and have porcelain in lingual contact. As the bite changes over the life of the patient, the porcelain on the lingual side will break more easily when in contact with the opposing teeth. Figure 7.23q shows an example of a patient who keeps breaking the lingual side of his anterior restorations.
- Step 7: Place a triple “0” retraction cord and take a full arch final impression with a highly hydrophilic impression material, such as Panasil (Kettenbach).
- Step 8: Provisionalize using a silicon matrix of the wax up. Spot bonding will enhance retention.
A Badly Damaged Vital Tooth
Badly damaged teeth with fractures, caries, or failing old restoration will often require a procedure to preserve the enamel margin, elevation, or other type of buildup. After the tooth is repaired, the preparation can be finished as a simple preparation.
- Start by performing steps 1–7 of Simple Preparation (above) developing the ideal preparation outline (Figure 7.24).
- When a large class III cavity or old restoration is present, repair as a normal class III direct restoration and refinish that section of the tooth, treating the composite filling as if it were tooth (Figure 25a–e).
- When a class IV caries or failing restoration is present, repair the lingual portion of the damage. There is no need to rebuild the entire lingual surface or the incisal edge, as the veneer will replace whatever part of the tooth is missing. The purpose of repairing the lingual surface is to avoid unnecessary removal of the facial enamel, further weakening the tooth, and losing more support for the restoration.
- When fractures are present, the incisal border of the fracture will be treated as the new incisal edge, and the preparation will be finished at that point (see Figures 7.5a and 7.6a). When lingual damage is present, the fracture should be treated similarly to class IV. Repair to preserve as much of the facial tooth structure and enamel as possible.
- When caries approach the cervical margin and threaten to go subgingival, the supragingival protocol (five principles) should be activated. Preventing a subgingival margin is the ideal approach. When prevention is not possible because the caries and/or old restoration are subgingival to a depth greater than 1.5 mm, elevate the margin to simplify and make cementation more predictable (Figure 7.26a–e). See Chapter 3 for full details.
- All necessary buildups should be performed with one application of adhesive and in one procedure for efficiency, followed by taking an impression and temporization.
An Endodontically Treated Tooth
The literature suggests that endodontically treated anterior teeth with minimal loss of structure do not require a full coverage restoration. Here, a simple bonded composite repair of the endodontic access would be sufficient [36,37]. Traditionally, full crowns are used when endodontically treated teeth are badly damaged, requiring extensive buildups and post, followed by cutting a full crown, which often removes most of the remaining natural tooth structure, leaving the post and buildup to be the main support for the crown. This approach requires long ferrules to increase strength and decrease fractures , with the added disadvantage of forcing restorative margins to be placed subgingivally.
Porcelain veneers are the ideal means to restore endodontically treated teeth, to regain ideal esthetics and the best possible function, with the healthiest possible outcome. When past damage and endodontic procedures are responsible for a severe loss of tooth structure and rigidity of the anterior teeth , to successfully restore these teeth an effort must be made to regain rigidity. Porcelain veneers help to regain original crown rigidity and stiffness . When much of the coronal structure is missing or very weak, a correctly bonded fiber-reinforced post has been shown to have an important effect on fracture resistance . A post is also desirable when the neck of the tooth is narrow .
A minimally invasive porcelain veneer will preserve as much of the healthy coronal tooth structure as possible, and will increase the overall strength. It is assumed that a porcelain veneer on a non-vital tooth may have a shorter durability than porcelain veneers on a vital tooth . Logic and clinical experience suggest that full crowns placed on badly damaged endodontically treated teeth will also have considerable complications and shorter durability than crowns placed on more ideal vital teeth.
Some endodontically treated teeth may be considerably darker than the adjacent teeth. The traditional approach is to deal with this issue by placing an opacious full-coverage crown with subgingival margin placement to hide the color difference, with all the disadvantages previously discussed. Internal bleaching, or walking bleaching, is a desirable alternative to the more destructive crown option. Internal bleaching has been shown to be successful, durable and safe [44,45]. Rotstein and others have shown that sodium perborate has been found to be as effective as hydrogen peroxide, with a suggested decrease in the risk of oxidative irritation and root resorption (Box 7.1) [46,47]. Because endodontically treated teeth may have a tendency to darken over time, more tooth-preserving techniques such as porcelain veneers are not performed, to avoid this possibility. Tooth color changes can be minimized by correctly cleaning the pulp chamber of pulp remnants and endodontic filling materials . In cases where the teeth become darker over time, internal bleaching can also be performed, even years after porcelain veneer is placed.