CHAPTER 9
MINIMALLY INVASIVE VENEERS OR NO-PREP VENEERS?
MARCO NICASTRO
Minimal tooth preparation and fabrication of thin veneers is a technique that not only preserves the tooth structure, but is also predictable when following proper procedures …
Minimally invasive veneers or no-prep veneers?
The veneer choice cannot be dictated by what is trendy. Certainly, in recent years the preservation of the enamel and the tooth structure has become an increasingly important issue, but no-prep restorations only give the illusion of being easier to perform than minimally invasive veneers.
PREPARATION TECHNIQUES
In recent years, restorative dentistry has seen a change in the approach to the preparation of the tooth structure toward more conservative methods, including when performing direct and indirect restorations. There has been a gradual reduction of tooth preparation, up to the complete absence of any interference in the tooth structure when creating additive restorations. This became possible thanks to the development of new restorative materials that exhibit greater durability than the materials used earlier. Let’s look at the possibilities of restoring teeth in the anterior segment.
Current preparation techniques covering the entire tooth surface at a depth of 0.6–0.7 mm of enamel thickness are no longer preferable. Instead, less invasive methods preserving the enamel are recommended, even up to the creation of additive restorations with no preparation, ie, no-prep veneers.1
TIP
No-prep veneers are not a recent discovery. They appeared in the 1980s as an ultraconservative technique, easy to implement, minimally invasive for the patient and economical.
PREPARATION TECHNIQUES MAY BE CLASSIFIED INTO THE FOLLOWING GROUPS:
A. Full-depth traditional preparation
B. Full-depth preparation with additive diagnostic wax-up
C. Minimally invasive preparation
D. No-prep veneers
First of all, it should be emphasized that the dentist must know all the types of preparation techniques because each of them still has its own specific indications. The last two techniques belong to the group, which we now call minimally invasive restorations.
A. FULL-DEPTH TRADITIONAL PREPARATION
Traditional preparation (full-depth) causes a significant reduction of the hard dental tissues.2,3 It was performed in the 1980s and it assumed the removal of superficial tissues to the thickness of the future restoration. At that time, only feldspathic porcelain was available, and this technique required enamel reduction to a depth of 0.5–0.7 mm.
This technique is perceived as too invasive, during which a large amount of dentin is very often exposed. For these reasons, Magne4 and Gürel5,6 proposed a technique with reduced preparation depth due to the wax-up and veneer preparation through the applied mock-up, which avoids dentin exposure. However, the traditional technique may still be necessary if we are restoring a single tooth in the dental arch or as interleaved elements (when we are working in a group of teeth and we need to prepare only some of them, leaving the others without veneer restoration), or when we are performing veneers on only one side of the maxillary arch, as happens after injures. In these situations, due to the esthetics and shape of the restoration, an additive diagnostic wax-up is not possible, as the contours of future restorations would extend beyond the contours of the adjacent teeth, resulting in poor esthetic result in this area. Therefore, we are forced to use a technique that causes the loss of the hard dental tissues to obtain compatibility with the patient’s remaining teeth.
Considering the veneer material choice, feldspathic ceramics made on a refractory die or platinum foil are undoubtedly the most appropriate in these cases. They allow the create a restoration with the appropriate color and individual characterization, which integrates well with the natural tissues of the adjacent teeth in the dental arch (Figs 9-1 to 9-4).
Case 1
Fig 9-1a
Example of a traditional preparation. Tooth preparation is at a depth of 0.5–0.7 mm to create a space for the restorative material (in this case, feldspathic ceramics was fired on a refractory die).
Fig 9-1b
Final result – visible good shape with the restoration color matching the adjacent teeth.
Fig 9-1c
Working cast with the platinum foil ready for firing the feldspathic ceramics.
Fig 9-1d
Final result after firing the layers of ceramics and removing the platinum foil. The veneer is ready for cementation.
Fig 9-1e
Patient’s smile after cementing the porcelain veneer.
Fig 9-2a
The right central incisor has an old composite restoration of incorrect size and shape.
Fig 9-2b
Full-depth preparation, with a remaining thin layer of enamel.
Fig 9-2c
By replacing the natural enamel with feldspathic ceramics, the proper contour and shape of the tooth can be created.
Fig 9-2d
Intraoral photograph after veneer cementation – palatal view.
PRACTITIONER’S ADVICE
Traditional preparation from the level of tooth structure, without mock-up, will be performed when we are absolutely sure that we want to make one veneer. It should be noted that any asymmetric prosthetic work is a difficult challenge for the dental technician!
Figs 9-3a and 9-3b
(a) A patient presented to the dental office with a fractured tooth 21. (b) An intraoral photograph shows the size of the tooth defect.
Fig 9-3c
Preparation was performed in the enamel, visible orientation grooves and applied silicone index as a “guidance” of the veneer preparation.
Fig 9-3d
It is clear how the presented veneer preparation technique allows you to obtain space for ceramic restoration that will not differ in shape from the adjacent teeth.
Fig 9-3e
Feldspathic ceramic fired on the refractory die. This is the first choice of material if a single veneer is made.
Fig 9-3f
Isolation with a rubber dam will allow adhesive cementation of the porcelain veneer.
Figs 9-3g and 9-3h
The final esthetic result after veneer cementation. The patient accepted the compromise of performing only one asymmetric restoration (laboratory work was done individually in the patient’s presence).
Another clinical case illustrating a difficult esthetic restoration. The patient is very young, with healthy teeth which are an ideal model on the side unaffected by the trauma, and delicate periodontal tissues. In this kind of situation, it is very important to plan what type of ceramic material will be used before starting the tooth preparation, as the preparation must be performed according to the type of selected restorative material.
The treatment plan included the use of feldspathic ceramics made on a refractory die. A consequence of this choice is the necessity of performing a preparation that will be as deep as the future thickness of the restoration, in order to follow the contour of the adjacent teeth and to obtain a satisfying esthetic result.7
Feldspathic ceramic represents the best solution for restorations in the anterior segment, where we encounter different color saturation, variable brightness, and individual tooth characterization. The canine has very high color saturation, and the central incisor has very high brightness but low color saturation. The lateral incisor has characteristics between these two, so you need a material that can be layered and handled in various ways. An additional difficulty in this case is large tissue loss caused by the Class IV cavity. Therefore, it is very important to mask the surface of the lost dentin with more opaque material, which will not reflect light and will guarantee a natural final outcome.
Feldspathic ceramics are fragile, so for safety reasons, it must have an adequate thickness of 0.5–0.7 mm. Consequently, the tooth preparation has to be done at that depth to create a veneer, which does not extend beyond the contours of adjacent teeth.
Figs 9-4a and 9-4b
A patient presented to the dental office due to a traffic accident, during which teeth 21, 22, and 23 were damaged.
Figs 9-4c and 9-4d
(c) Differences in color saturation, brightness, tooth characteristics, and (d) extensive Class IV tissue loss involve more than half of the tooth.
Fig 9-4e
When working on only half of the anterior dentition, we are forced to maintain the previous contour of asymmetrically located teeth. For this reason, a more invasive preparation is necessary, and this has to be compatible with the thickness of the future restoration.
Fig 9-4f
From an esthetic point of view, the first choice of material in difficult cases is feldspathic ceramics made on a refractory die. Only this material enables direct layering when fabricating a reconstruction.
Figs 9-4g to 9-4i
Fabricating porcelain veneers 21, 22, and 23 in the dental laboratory.
Figs 9-4j and 9-4k
Clinical situation after cementing veneers on teeth 21, 22, and 23 (j) from the right and (k) from the left semi-profile view.
Figs 9-4l and 9-4m
Patient’s smile after cementing veneers 21, 22, and 23 (l) from the right and (m) from the left semi-profile views.
Figs 9-4n and 9-4o
Clinical situation (n) before and (o) after cementing veneers 21, 22, and 23.
B. FULL-DEPTH PREPARATION WITH ADDITIVE DIAGNOSTIC WAX-UP
Full-depth preparation with the use of a silicone index taken from the cast with additive diagnostic wax-up is certainly the most common today. It was introduced to the literature by Dr. Galip Gürel and Dr. Pascal Magne in 2003 and 2004. It allows excellent esthetic results to be obtained, while maintaining a large amount of enamel after tooth preparation.
This preparation technique is most often recommended when changing the esthetics of a larger group of teeth in the anterior segment when there is a possibility to modify the contour of the teeth in an additive way. It is described in detail in Chapter 6.
C. MINIMALLY INVASIVE PREPARATION
Minimally invasive preparation is a consequence of the development of the previous technique,8 as well as a result of the availability of new ceramic materials on the market, which can be pressed to a very small thickness of 0.3 mm, for example, the Opal system (IPS e.max).
Such restorations are always additive to the tooth surface; they are rarely used for a single tooth reconstruction.9 However, they can easily be used in a comprehensive anterior segment treatment. This technique is indicated when we do not want to change the shape and color of the tooth significantly or when these changes are minor, as well as when closing the diastema and gaps between the anterior teeth. Principles of material selection and of the dental technician’s work are very similar to no-prep veneers. These restorations are characterized by minimal enamel preparation, involving tenths of a millimeter.
The author of this chapter prefers minimally invasive veneers over additive no-prep veneers because the advantage of minimal tooth preparation is a clearly marked preparation margin, which facilities the veneer positioning while cementing, which is not possible with no-prep veneers.
TIP
Covering the incisal edge with the veneer allows a more individual restoration to be created, reflecting all the characteristic features, which ensures an optimal esthetic restoration.
PREPARATION
The preparation technique begins with an additive diagnostic wax-up, then a silicone index is prepared on its basis, which helps control the preparation depth. Of course, the wax-up must be created to the full thickness of the future restoration. In this technique, if we start the preparation from the mock-up level, we should be very careful to keep the labial surface untouched or minimally affected by the bur and concentrate to clearly mark the outline of the restoration.
With such minimal preparation, it is necessary to use magnification, ie, dental loupes with four or fivefold magnification or, preferably, a microscope.
TIP
Although this approach is minimally invasive, certain rules from traditional preparations still apply.
These include:
- Reduction of the incisal edge to a depth of 1.5–2 mm in order to obtain sufficient space for the restoration
- Marked outline of the preparation margin with a minimal depth
- Minimal reduction of the labial surface
CEMENTATION
A well-marked border on the tooth circumference makes it possible to identify the preparation margin and easily apply rubber dam isolation, which is difficult to use in the no-prep technique where the preparation margin is not clearly marked.
Usually, dentists prefer to use a properly heated micro-hybrid composite when cementing veneers. However, in the case of very thin porcelain veneers, with a thickness of 0.2–0.3 mm, using a standard composite is difficult and may lead to cracking of the veneer during cementation.
For adhesive cementation of extremely delicate veneers, the author prefers to use a flowable composite cement. Due to its fluidity, this can be used as a thin layer and becomes the material of choice. When cementing thicker ceramic restorations, the color of the luting cement is not relevant, while for very thin restorations, the choice of the right color is extremely important.
Luting cement kits often include trial pastes based on water-soluble glycerin gel, and these correspond with the color of the composite cement (see Chapter 7).
Veneers can be fabricated with various types of ceramics, in particular:
Feldspathic ceramics made on a refractory die or platinum foil (75–90 MPa)
Leucite-reinforced ceramics (hot-pressed or fabricated in CAD/CAM technology) (120 MPa)
Lithium disilicate ceramics (hot-pressed or fabricated in CAD/CAM technology) (400 MPa)
In everyday practice, the author prefers feldspathic or pressed ceramics due to the greatest experience in this range, instead of restorations fabricated using CAD/CAM technology.
Especially for ultrathin veneers, lithium disilicate pressed ceramics are preferred, as this can be fabricated to a thickness of only 0.3 mm while maintaining very high strength.
Fabricating such thin restorations by a dental technician, even though it may seem simple, is extremely complex and demands very high precision. Working with the veneers during the try-in and cementation stage is difficult because they are very fragile and therefore very susceptible to any damage.
Feldspathic ceramics provide very good precision and esthetics, but have a low elastic modulus of 75–90 MPa, making the material very fragile. Attention also should be paid to an interesting publication by Magne et al concerning the effects of luting composite shrinkage while cementing porcelain veneers and thermal loads on the stress distribution during variable thermal conditions.10 The authors show through the finite element method the existence of a negative correlation between the thickness of the luting cement and porcelain veneer, and the distribution of stresses on the inner and outer surfaces.
Ceramic restorations underwent thermal shock testing, which showed a relationship between the thickness of the luting composite and the ceramics, and cracks in the porcelain veneers.
Thermal loads, in combination with stresses resulting from shrinkage of the composite material, are particularly dangerous for the veneers. Such loads lead to low compressive stresses, but they increase tensile stresses, which is very dangerous for porcelain veneers because this type of stress increases the risk of ceramic fracture.
The conclusions of this study are that the stress distribution is not related to the veneer’s incisal edge length, but rather to the thickness of the ceramics on the labial surface, and the thickness of the luting cement layer.
Too thin veneers combined with their poor fit to the core surface (thick layer of the luting cement) have resulted in the appearance of higher stresses, as well as on the porcelain surface and between the junction of the tooth and the veneer.
In conclusion, the relationship between the thickness of the luting cement and the ceramics may have a significant impact on the stress distribution in the porcelain veneer. The labial and cervical areas are the most critical parts of the restoration if they are fabricated of a thin ceramic layer, due to insufficient space for the restoration.
TIP
Suppose the porcelain layer has to be very thin to maintain the natural contour of the tooth. In that case, only a perfect fit of the veneer in the tooth, with a gap in the range of up to 100 µm, can prevent a decrease of the CER/CPR ratio (the thickness of the ceramic layer in relation to the thickness of the luting cement layer) below the optimal value, which should always be greater than three.
Stay updated, free dental videos. Join our Telegram channel
VIDEdental - Online dental courses
