Ceramic veneers are popular for their ability to enhance the aesthetic appearance of anterior teeth. As partial extracoronal restorations, they primarily cover the labial-proximal surfaces and sometimes the incisal border of the teeth. These veneers correct color inconsistencies, improve tooth shape and texture, and restore function and alignment in the dental arch. However, the preparation for ceramic veneers varies and is determined by factors such as the condition of the tooth structure, existing restorations, clinical crown length, and any prior endodontic treatments.

Key Aspects of Tooth Preparation for Veneers

Preparing for veneers is a precise process that requires skill. The ideal reduction for laminate veneers falls between 0.3 and 0.5 mm, demanding a trained hand, as mistakes cannot be corrected once the procedure is finished. Each reduction must consider the amount of enamel versus dentin being altered, as bonding to enamel generally yields stronger results than bonding to dentin.

1. Enamel vs. Dentin: Enamel offers a superior bond with ceramic veneers compared to dentin. Enamel has an elastic modulus of approximately 70 GPa, while dentin is only about 18 GPa. Given that ceramic materials range from 65 to 95 GPa, enamel’s closer modulus alignment with ceramics results in a stronger, more durable bond. As a result, tooth preparation strategies often prioritize preserving enamel to maximize bonding strength.

2. Enamel Reduction: For successful bonding, reducing the enamel's top aprismatic layer is essential to improve resin composite retention. Careful enamel reduction also helps control tooth rigidity. However, excessive enamel removal can lead to tooth flexing, potentially compromising the restoration's longevity.

3. Shape and Design: The veneer preparation design affects both the appearance and longevity of the final restoration. Insufficient preparation can impact translucency and affect how the restoration interacts with natural light. Removing proximal enamel is also essential for achieving a smooth, labially placed finish line, which enhances aesthetics and minimizes plaque buildup.

When Is Tooth Reduction Necessary?

Reduction is essential in several scenarios:

1. Remove convexities and provide a path for insertion in those situations where either the incisal or the interproximal areas are to be included in the veneer.
2. Provide space for adequate opaquing or heavier coloring like in cases of a dark substrate. 
3. Provide a definite seat to help to position the veneer during placement.
4. Prepare a receptive enamel surface for etching and bonding the veneer.
5. Allow for a smoother transition from the veneer to the tooth surface, enabling the patient to more easily keep it plaque‐free.

Contraindications and Guidelines for Reduction

While reduction is usually beneficial, there are exceptions:

• Pulp Size: Younger patients or those with larger pulp cavities might risk sensitivity or irreversible damage. In such cases, alternative methods may be advisable.
• Patient Comfort: If patients feel uneasy about enamel reduction, the dentist may recommend no-reduction veneers initially, allowing for future adjustments if desired.

How Much to Reduce?

In general, enamel should only be reduced to the extent required for the veneer placement. For a successful result, mock-ups, wax models, and pre-evaluative temporaries allow clinicians to visualize the effect of reduction on aesthetics, speech, and function before finalizing the procedure.

In conclusion, ceramic veneer preparation requires careful planning to balance aesthetic enhancement with the preservation of natural tooth structure. By following these guidelines, dental professionals can achieve long-lasting, visually appealing results that meet the patient’s functional and aesthetic needs.

Stay tuned for more in-depth insights into advanced veneer preparation techniques in our upcoming posts.

Veneer Preparations: Techniques and Considerations

Overview of Preparation Techniques

The preparation for ceramic veneers has evolved significantly, influenced by various clinical factors including tooth shape, location in the dental arch, and the mechanical forces involved. The design of the preparation must consider:

• The amount and quality of the remaining tooth structure
• Anticipated final dimensions of the restoration
• The shade of the substrate to achieve optimal esthetics

Goals of Preparation

The primary objectives when preparing for veneers are:

• Create Sufficient Space: Ensuring adequate space for the ceramic material is crucial for both aesthetics and functionality.
• Preserve Enamel: Retaining as much enamel as possible is vital for achieving a strong bond.
• Definitive Finish Line: Establishing a clear finish line aids the technician in crafting the restoration.
• Smooth Preparation: Avoiding sharp line angles minimizes stress concentrations and improves the overall fit of the veneer.

No-Prep Veneers

The no-prep approach has gained popularity due to its appeal to patients, who may prefer to avoid tooth reduction. However, this technique has limitations:

• Aesthetic Concerns: Issues like overhangs can compromise the visual outcome.
• Laboratory Challenges: Creating ultra-thin veneers can be technically demanding and increase the risk of fracture during the bonding process.

This concept is particularly beneficial in cases where orthodontic movement has created the necessary space (approximately 0.5 mm) for veneer placement without unnecessary tooth reduction. However, it requires careful case selection and a thorough understanding of the desired aesthetic outcome.

Advantages of No-Prep Veneers:

• Preservation of healthy tooth structure.
• Reduced time needed for impression taking.
• Elimination of the provisional restoration step.
• Bonding occurs exclusively to enamel.

Disadvantages:

• Complex laboratory fabrication due to thinness.
• Increased risk of veneer fracture during various stages (laboratory, try-in, and cementation).
• Maintenance of aesthetic results can be more challenging.

Extensive Preparation

Extensive preparations may be necessary in some clinical scenarios, but they carry risks such as:

• Biological Irritation: Potential irritation to the dental pulp.
• Impaired Adhesion: Increased risk of adhesion failures.

In these cases, preparations may extend to the proximal surfaces and incorporate a "palatal overlap." This approach can enhance bonding by increasing the enamel surface area but may lead to complications:

• Frequent Debonding: Functional overload during occlusion can compromise retention.
• Dentin Exposure: Excessive preparation can expose dentin, heightening sensitivity and risk of decay.

For optimal outcomes, the palatal finish line should ideally avoid high-stress areas, such as the concavity of the cingulum, to reduce the risk of functional failure. Care must also be taken to ensure that the remaining incisal portion has sufficient thickness to prevent fracture, particularly when teeth are inherently thin.

Recommendations for Preparation

1. Consideration of Tooth Structure: When preparing teeth, especially those with a thickness of less than 1.5 mm, careful planning is required to prevent over-reduction. This often means removing only enough enamel to accommodate the veneer without compromising tooth integrity.

2. Cementation Pathways: While establishing an insertion path may simplify the cementation process, it can also lead to increased wear in proximal areas. Therefore, more conservative termination designs, such as straight incisal terminations, are recommended when reductions are necessary, as they promote a passive fit and greater preservation of tooth structure.

In summary, the preparation of veneers is a nuanced process that balances aesthetic demands with the biological needs of the tooth. Continuous advancements in techniques and materials aim to enhance outcomes while minimizing invasiveness. Further discussions will delve into the intricacies of veneer preparations, including specific case studies and advanced techniques. Stay tuned for more insights!

Conventional Veneer Preparation Process

Three main stages to get the final veneer preparation: 

1.cutting

2.refinement

3. Finishing & polishing

Four main areas: 

1. Incisal edge

2. Cervical margin 

3. Labial/buccal surface

4. Proximal surfaces.

Each tooth surface (incasal, cervical, labial/buccal, mesial or distal) will pass by these stages of preparation. So, let's get started..

Cutting 

An essential question for the dental practitioner; how to control your hand during teeth preparation for ceramic veneer?, or in other words, what is the penetration depth of the bur through the tooth surface? and The keypoint here is the Depth Cutters.

As we all know, the first step for the actual teeth preparation is to obtain a sufficient depth with the help of depth cutters. However, the depth cutters always reduce the same amount of tooth that their grid depth indicates. In other words, no matter what the position of the tooth is, or whether they are lingually or buccally inclined, the depth cutter will always remove the same amount of tooth structure that will not necessarily dictate the true depth of the restoration. For the inexperienced dentist, who religiously follows systematic preparation techniques for ceramic, the improper application of these depth cutters can be extremely destructive.

Four essential rules:

• No cervical groove 
• Incisal groove 2 mm from the free edge 
• 0.5 mm in the buccal (at the coronal two thirds) 
• 1.5- 2 mm at the free edge

Vertical Vs Horizontal depth cuts

Preparation of vestibular grooves in the vertical direction with rounded-ended conical diamond burs, respecting the axial inclinations (cervical, middle and incisal) to preserve the convergence of the buccal surface. The depth of each groove is defined according to each case and based on the diagnostic wax-up. In this way, one can check the amount of wear with a millimeter probe by comparing the prepared side with the intact. At this point, it is essential to have knowledge about the thickness of the labial enamel of a natural tooth, so that the completion of the preparation is performed, having also the preservation of enamel as a guide whenever possible. Then, joining the labial grooves with a conical diamond bur, the larger diameter to prevent deepening of the guide grooves and forming an uneven surface.

Horizontal “ depth cuts “  giving us more controlled cutting. A special three-tier diamond depth cutter comes in different thicknesses 0.3, 0.5, or 0.8 is used to cut across the labial surface then mark the depth cuts with a pencil or a marker then the cutting is completed respecting the triple angulation of the labial surface to the base of the depth cuts until reaching the markings. 

The depth cutter can only penetrate until the non-cutting shaft is flush with the tooth surface. The shape on the right represents the surface after the depth cutter is used at only one angle. Note that the only true depth is gained in the area of B (middle third, black dots), to reach the necessary depth in points A (gingival third, green dots) and C (incisal third, red dots), the bur should be used in three different angulation.

Homogenization of the grooves is done respecting the buccal convexity. Whatever the preparations to be performed, it is essential that the margins are properly defined (cervical and proximal) so they can be easily identified by the technician. This will allow a good fit of the veneers, better stability, and higher adhesion values.

Even if there is no need for thickness it is essential to use airborne-particle abrasion on the enamel surface in order to optimize bonding and remove the aprismatic enamel layer.

The preparation design consists of the preparation of different tooth surfaces:

1. Incisal edge preparation.
2. Cervial margin preparation
3. Labial/buccal surface "Triple angulation"
4. Creation of a proximal slide.

1. Incisal edge preparation:

There are two basic techniques for the placement of the incisal finish line:

1. The first terminates the prepared facial surface at the incisal edge. There is no incisal reduction or prep of the lingual surface and it can be in the form of a window or intra-enamel preparation or the feathered incisal preparation.
2. In the second technique, the incisal edge is slightly reduced and the porcelain overlaps the incisal edge "Butt-joint"

The two techniques were used equally and both provided clinically acceptable results.

Butt-joint margin

Instead of a chamfer margin that may weaken the final restoration (see Extensive preparation), a flat shoulder should be used at the incisal edge. However, if the tooth exhibits the length desired for the ceramic veneers, a reduction will be required which will establish a thickness of 2.0 mm in the buccal palatal direction of the incisal margin. Subsequently, a flat incisal surface that emerges perpendicular to the angle of the final emergence profile in the veneers should create the delicate incisal edge configuration where the incisal edge grooves are connected.

* Another interesting diamond point that I would like to use for incisal preparation is the wheel-shaped, but you have to be careful while using to protect the neighbouring sound teeth.

Another important aspect to be aware of is the condition of the palatal surface of the tooth that is about to be prepared. The finish line on the lingual aspect of the restoration should not end on a wear facet and it is also preferable not to place the finish line on the central contact points. In the case of a worn incisal edge, a 2 mm reduction from the desired length of the finished veneer is required. If the already existing tooth length is 1.5 mm shorter than the expected final outcome then in order to achieve a 2.0 mm incisal reduction, only 0.5 mm of preparation will be sufficient.

** The fracture potential of the final restoration can be avoided by the rounding of the incisal line angles that reduce the internal stress.

The butt joint preparation is simpler and consumes less time than the tooth preparation with palatal chamfer, and the master cast can be used for a precise palatal finish line. The path of insertion is from the facial. Therefore, only butt joint incisal preparations will allow such a buccal-palatal path of insertion.

Advantages:

• the porcelain is stronger and produces a positive seat during the cementation process.
• The proper seating of the veneer is made possible by the vertical stop that the incisal overlap provides.
• The esthetic characteristics of the porcelain veneer are more easily handled and controlled by the dental technician to improve the translucency of the veneer.
• it reduces stress concentration within the veneer by distributing the occlusal load over a wider surface.

The incisal involvement offers many advantages above all by the possibility of incorporating incisal characterizations such as translucency, evidence of the spindles, and of the opacity of the halo to the restorations, mimicking its naturality.

Window Design

A window design prepared entirely into the enamel was resistant to axial stress.

Advantage

It is considered the most conservative preparation design or window preparation is the treatment of choice when strength is the first priority.

Disadvantage

It may result in an aesthetic problem due to the fact that the preparation finishes in the most translucent area of the tooth. This is indicated in cases of substrates with the desired value without chromatic alteration in the incisal region.

2. Gingival margin preparation:

Peripheral delimitations of the preparation with spherical diamond burs surrounding the entire labial surface of the tooth without disruption of the proximal contact and without subgingival extension. A spherical diamond point, used at a 45-degree angle to the surface, so that only half the diameter of the point promotes the reduction. 

NB. Preparation of the subgingival cervical margin and initial finishing of the preparation in indicated situations with rounded-ended diamond burs. It is worth to emphasize the importance of gingival tissue protection during preparation, in order to prevent post-traumatic gingival re-cession, especially in thin marginal tissue.

The fabrication of the ceramic veneers is directly affected by the placement of the finishing line. Smooth margins that are fully exposed and readily cleansable generally provide the best results. The dentist has to determine where to place the finishing line where the margins of the restoration can be kept clean by the patient and properly finished. In addition, finish lines must be placed so that they can be duplicated by the impression, without tearing or deforming the impression when it is removed past them.

With no cement line or margin visible, the porcelain blends in with the underlying composite resin in a harmonious finish. Whenever possible, the finish lines should be placed in the enamel following the contour of the soft tissue from mesioproximal to distoproximal.

 

Supragingival Margin:

Placement of the gingival margin supragingivally or coronally frees the gingival margin. This has many advantages such as:

1. Eliminating the chances of injury to the gingival tissue
2. Decreasing the risks of undue exposure of the dentin in the cervical region
3. Obtaining crisp clear margins
4. offering easier access to the finishing and polishing stages with easily accessible margins. 
5. Impressions are easier to make.
6. During the try-in and bonding stages, proper isolation of the operative field is easier, so moisture control and the chances of contamination during adhesive procedures are reduced.
7. Postoperatively it eliminates the possibility of impingement on biological widths by an inadvertent overextension of the preparation
8. Making it possible for the patient to perform meticulous hygiene in this critical region.
9. Allowing the dentist to evaluate marginal integrity during the follow-up and maintenance visits.
10. Increasing the likelihood that the restoration will end on enamel and this increased area of enamel is extremely important for stronger adhesion and less microleakage in the future.

Restrictions to enamel is a necessity for marginal tooth preparations and bonded restorations as exposure of the dentin margins may reduce bond strengths and increase the chance of microleakage. When the preparation margins are completely located in the enamel, microleakage is minimal or none at the tooth-luting agent interface and negligible in the resin/porcelain interface. It is always better to finish the cervical margin on enamel since more microleakage has been found at the luting composite/tooth interface when the cervical preparation margin was located in the dentin.

Subgingival Margin:

The reaction of the gingival tissues largely depends on the cervical extension of the restoration in regard to the location of the gingival margin. Generally speaking, the major etiological factor in periodontitis is the subgingival placement of a restoration.

In a majority of the cases, it is best to place the subgingival extension of the intrasuclar margins at about half the width of the crevice depth;

• to create a buffer zone between the epithelial attachment and the bur, to prevent encroaching of the epithelial attachment of the biologic width if the preparation was extended deeper than the desired depth.
• to leave enough space for the gingival cord placement. 

The deeper the restoration margin resides in the gingival sulcus, the greater the chance of inflammatory response and that such tissues can bleed upon probing.

 

Disadvantage:

The difficulty of visually following the cervical margins so that even the experienced restorative dentist can miss marginal defects.

Advantage:

It allows the technician to preserve the existing height of the papilla as well as to make certain that all interproximal spaces and/or diastemas will be closed while permitting control over the emergence profiles.

* non or minor tooth color changes (such as one or two shades lighter), there is no need to prep the tooth subgingivally. In other words, once the teeth are free from discoloration or presenting "discreet color alteration", the gingival margin must not be placed in the gingival sulcus.

* It is not only the color but the nature of the lip-line as well that determines whether the ceramic veneers marginal placement will be supragingival, equigingival or subgingival. If there is gingival exposure while smiling, subgingival placement may be necessary in order to achieve desirable esthetic results, but to a certain extent, it depends on the esthetic expectations of the patient.

It is still recommended that the placement be supragingival whenever possible.

Chamfer Preparation

It is almost impossible to finish accurately fitting ceramic veneers without being overcontoured over a knife-edge preparation at the cervical area. Therefore, irrespective of its placement (sub or supragingivally), a chamfer is preferred for all the gingival margins.

• In comparison with the 90-degree shoulder, the chamfer finish preserves more natural tooth structure.
• Owing to the gradual color transition between restoration and tooth substrate, thereby avoiding the sudden delineation between tooth and crown, it is also a better option esthetically.
• Very distinct and visible finish line by removing of the serrated overhanging enamel prisms.

To avoid periodontal inflammatory responses and future gingival recession, improving the gingival architecture, survey lines and points of concavity with a chamfered margin while carefully controlling the anatomical contours in the cervical third, is of the utmost importance. The rounded tip of the fissure diamond bur will enable the cervical margin to be initiated slightly above the gingival level.

3. Triple angulation:

To provide a natural healthy look for the incisor that mimics its true convex nature, a uniform removal of the substrate is essential and can be achieved through the use of the bur, keeping it at three different angles.

One of the main characteristics of the veneers is biological preservation. This is possible when the buccal contour is preserved during preparation, by following the three inclinations of the natural tooth; the cervical third, middle third and incisal third. So, the veneer can be inserted in a rotational movement allowing preservation of the enamel and access to cervical and proximal undercuts areas.

It is important to note that:

* in the vertical dimension by using three angles of the bur

* in the horizontal dimension by following the tooth morphology.

Otherwise, one plane facial reduction may come too close to the pulp. When the diamond is swept in the mesiodistal direction, a gentle convex surface in the gingival and incisal 1/3rds is obtained.

Tooth preparation without respecting the facial convexity. Such straight preparation can result in irreversible pulp damage.

If the incisal or the cervical third is not prepared deeply enough, the final restoration may be overcontoured in this area.

A common error is to place the incisal third too far labially in the final restoration. This is frequently due to insufficient tooth reduction. The preparation must reproduce the natural convexity of a maxillary central incisor and provide for a minimum reduction thickness of 0.7 at the junction of the middle and incisal thirds of the tooth. Insufficient tooth reduction, in terms of leaving a sharp line angle and not rounding off the incisal labial area, is the leading cause of an over tapered preparation or produces opaque show through, or overcontouring of the incisal third of the restoration. 

This will not only influence the external facial form of the tooth but the light reflection as well. Light reflects off the tooth and travels through it at the incisal. If the edge has a rounded surface at the incisal-labial, that reflected light is being diffused and yields an ideal transition of the shade from the incisal color to body color.

4. Creation of a proximal slide:

This stage is characterized as one of the most conflicting points during preparations for a fixed prosthesis, performing reduction to enable insertion axis and elimination of retentions. It is essential to understand the fact that the majority of cases of ceramic veneers with or without preparation, presents a passive fit in the labial-palatal direction, and the supposed interproximal retentions are overlooked when veneers “fit in” without resistance. In this way, it is possible to carry out more conservative interproximal preparations, restricted mainly to the cervical region even if retentions exist when viewed pragmatically in an inciso-cervical sense.

The creation of a proximal slide allows placement of veneers when the proximal anatomy is challenging, as well as creation of proper emergence profile.

The preparation for the proximal surfaces must be thoroughly planned. The aim must be to place the margins beyond the visible area and to preserve the contact area. Esthetics should be carefully considered when placing the proximal "stop-line", providing that the teeth are free of proximal restorations. It is very important to go beyond the visible area that can be viewed from the front or side, especially when tooth color is very different from that of the laminate veneers.

Destroying the contact areas in order to create the margins is unnecessary, but, in some cases, the preparation margin may be extended further in a lingual direction. The margin can be drawn back even more in the lingual direction if the natural contact area has already been lost due to:

• a diastema
• restoring a broken angle
• to encompass a proximal composite.

A tapered diamond point of smaller diameter is used to extend the margins from both the mesial and distal aspects until they are out of the visible area. Performing the proximal preparation with a diamond bur of smaller diameter. The protection of the adjacent teeth with a metal matrix is imperative.

The proximal extension of the preparation is directly associated with the static and dynamic area of visibility and preexisting restorations. The observation of the preparation in a static way, merely by labial, gives a false impression that all visible areas of the substrate were included in the preparation. Thus, the dynamic view of the preparation laterally enables an actual verification on whether or not to proximally extend the preparation.

In order to be accurate and to achieve the best results esthetically and functionally, the dentist should always be able to visualize the three-dimensional form. For the biologic integration of laminate veneers into the area, one should have a better understanding of the placement and design of the proximal finishing line.

The dynamic visibility area is the entire region of the non-prepared tooth and which remains visible regardless of the angle of observation. See that, when observing the tooth from an oblique view areas of unprepared enamel can be seen. The preparation of this area is essential to the success of the esthetics restorations, especially in darkened teeth. Even non-discolored teeth, however, also require this care, to ensure long-lasting veneers. In the preparation of these regions, the same fine and extra-fine grit diamond points are employed. The aim is to extend the preparation until the margins are fully hidden, whatever the position of observation is. Note that within the subcontact proximal areas it is necessary to displace the preparation margins to a considerable extent towards the palatal. To minimize the chances of inadvertently reaching the proximal surface of the adjacent tooth, strips of a metallic matrix are recommended for protection. It is also interesting at this stage to work with diamond points slightly angled with respect to the long axis of the tooth so that only a small part of the active tip is in contact with the tooth structure.

After this initial preparation, it is not possible to view the proximal margin of the preparation, confirming that the dynamic visibility area was adequately hidden.

To facilitate the placement of interproximal extensions, the margin of the porcelain veneer should be hidden within the embrasure area. The proper interproximal extension will provide additional stability and retention, due to the wraparound effect.

** Yet, it should be considered that placing the finish line in the proximal contact area creates a higher risk of interdental decay, especially with patients with compromised dental hygiene. Another factor to consider in the placement of the interproximal margins is the size of the interdental space. If there is an unsightly gap that needs to be closed, the exact placement of the interproximal margin will vary depending upon the size of the space.

The larger the space, the further mesiolingually or distolingually the margin will need to be extended. Otherwise, the resultant contact areas will be bulky and potential food traps.

It is useful to divide this surface into two regions:

1. The gingivoproximal area, which extends gingivally from the interdental contact area
2. The interproximal contact area, which is located in the incisal two thirds of the proximal surface.

Gingivoproximal Preparation

To break the contact or not?

The esthetic and functional demands of the specific tooth involved will determine the design of the preparation of the proximal walls.

To keep the contact

Under normal circumstances, this preparation should stop just short of breaking the contact. The proximal margin on teeth that are free from color alteration or with slight discoloration should be hidden by the preparation made far enough into the contact area so that the proximal wall will end 0.25 mm facial to the actual contact area.

Throughout the placement of the proximal margin, the dentist must continually check for any portion of darkened tooth structure beyond the preparation that will still be visible after the restoration is complete, by frequently checking from different viewpoints.

Preferably, the interproximal margin should stay short of the contact area. Whenever possible, it is best to preserve the contact area, as it is an anatomical feature that is difficult to reproduce.

** In some instances, the dentist may only be preparing a single tooth or two teeth and must therefore pay extra attention not to scratch the tooth next to it, which will stay intact. One of the ways of protecting the proximal surface of the adjacent tooth is to place a metal matrix band in between. However, sometimes, poor placement of this metal band may injure the papilla.

** When the actual treatment is in progress and the teeth are not periodontally stable, then it becomes a challenge to keep them intact and to prevent displacement of the teeth between the preparation and placement sessions. Consequently, the try-in procedures are simplified and save clinical adjustments of the contact areas where the fine ceramics are intricately placed.

To open the contact

Certain clinical circumstances, such as:

• closing a diastema or changing the shape or position of a group of teeth, may require some specific preparation of the interproximal areas in order to allow the technician greater freedom in alteration of the form or position.
• the existence of caries, defects or preexisting composite fillings. In such cases, it is important that after a thorough elimination of carious dentin, the weakened residual enamel thickness be evaluated. 

At times it may be necessary to full-slice through the contact from the facial to palatal to open a diastema and to give freedom to the dental technician.

If for some reason the preparation must finish on the proximal contact area, instead of extending the preparation more palatally, which will cause the loss of intact enamel in the contact area, it can be stripped to achieve a clear interproximal margin.

A diamond stip should be used to create a definite clear marginal edge.

At the restoration dentin interface, the connection of resin cement to dentin may be the weakest link. Bonding ceramic veneers onto a composite filling considerably increases the risk of failure. When the preparation margin is located within an existing filling, numerous failures have been reported. The authors believe in the incorporation of all the existing composite fillings and caries cavities into the preparation as much as possible.

Finally, The depth of the interproximal preparation can be classified as short, medium and long wrapping (Magne).

Refinement

During preparation, gingival displacement is achieved by delicately inserting the braided retraction cords into the sulcus so as to avoid any bleeding. Supragingival preparations do not need special attention. However, if the preparation is subgingival, it necessitates the displacement of the gingiva, to avoid injury.

It may also be beneficial to use non-medicated deflection cords instead of the medicated ones as they may be the cause of a secondary gingival recession. While doing this, the coronal preparation limit of the gingival contour of the tooth can be recorded, before the gingival displacement.

NB. If the dentist wants to be certain of the exact placement of the cervical margin in order not to make a deeper preparation than that is necessary, he/she should draw a line at the present location of the gingival cavo-surface margin with a sharpened pencil or a water-insoluble pen before placing the tissue displacement cords into the sulcus.

At this time, we start to refine all the preparation surfaces using diamond points similar to those mentioned above already employed except with fine and extra-fine grits.

Before and after refinement

Finishing and polishing

A facial reduction of 0.5 mm with chamfered margins and 1.5-2 mm of incisal reduction are preferable considering the conservative nature of porcelain laminate veneers preparation. It is not difficult to ensure adequate uniform thickness that is necessary for structural integrity when under stress when there is an emphasis on conservative tooth reduction in this preparation phase. Higher stress at the surface and interface of the restoration may occur when the restoration is too thin or has a poor internal fit.

Using abrasive silicone rubbers and discs with decreasing granulation. Every angle and corner should be uniform, with rounded lines, to improve the adaptation of the resin cement and laboratory build-up.

One of the most important tasks is the manual instrumentation of the cervical margins. Often even after finishing and polishing, the region has small irregularities and sharp angles, related to the angle of enamel rods and the form of diamond points used for preparation. To eliminate these irregularities, the best alternative is using a manual cutting instrument. 

Guided Preparation

A major change in the reduction principle appeared in the early 2000s. There was a step back from an invasive preparation to a more conservative reduction in order to obtain surely enameled preparations. The return to an enamel finish minimized the risk of failure.

This modification of the reduction principle follows the biomimetic concepts advocated by Magne: “The use of a mock-up as part of esthetic planning, where preparation is guided by the future and not by the present, supported this approach and validated this new approach.”

One of the very crucial issues in the production of ceramic veneers is to keep the maximum existing enamel of the tooth structure. In order to preserve the maximum amount of tooth enamel, the final tooth reduction should be designed according to the expected final outcome "guided prep". If not, the reduction of dental structures will not be the same within the space requirements for ceramic veneers.

The preparation design for ceramic veneers should allow for an optimal marginal adaptation of the definitive restorations and maximally resembling the ideal tooth morphology. Therefore, a diagnostic wax-up should be utilized as a reference for tooth reduction. The spatial orientation and architectural dimensions of the wax-up will be used to pre-design and validate the intended preparations for the teeth involved. This illustrates the importance of using correct wax-up techniques in creating the exact tooth shape desired. In such a treatment the most important element in the process is the wax-up. In order to transfer these data to the clinic, the dentist should be supplied with transparent templates and silicon indexes fabricated upon the wax-up by the laboratory technician, although these indexes can be easily made at the clinic by the dentist/assitant.

Control of reduction can be achieved by using (preparation guides). Silicone guides, fabricated over the wax-up, provide simple and indispensable tools for the control and reduction of enamel. Two guides should be fabricated: a vertical guide (sectioned in the buccolingual direction) for reduction control in cervico-incisal direction; and a horizontal guide for the mesiodistal reduction control. Using the vertical and horizontal silicone guides, it is possible to check the uniformity of the labial reduction.

Guided preparation means that the same considerations of the conventional preparation are going to be implemented but through the mock-up. The amount of tooth reduction should never be made according to the existing tooth surface but rather to the final volume of the restoration.

Thanks to the technique of Galip Gürel, proposed almost 20 years ago. It is a simple technique, which has great value for controlling the depth of the preparation in such special cases, and can be easily used. This technique using composite resin/bis-acrylic can simply be added to the facial surfaces of lingually positioned teeth (additive cases) with spot etching and bonding up to where the tooth needs to be buccally reoriented or filled by volume. 

It mimics the final outcome that we aim to restore with the ceramic veneers. When the mockup is still on the tooth, it is logical to use the depth cutter bur over that composite/bis-acrylic build-up, so that the true depth will be reached when the depth cutter is used and thus preserve the maximum enamel on the tooth surface. By doing this, we limit our depth cutter to go only as deep as our smile design dictates, resulting in an even more conservative tooth reduction. 

For example, let us assume that the tooth is tilted 0.2 mm lingually. If we do not use the technique explained above, then when we use the depth cutter of 0.3 mm we will end up with a 0.5 mm space that the ceramic veneers must fill. However, if we add the mock-up, and use the depth cutter over that volume, we will end up with the necessary reduction of only 0.1 mm, which will still provide the 0.3 mm of thickness for the final PLV. This way the enamel is being preserved. 

Aesthetic Pre-evaluative Temporary (APT) / Mock-up

The patient must validate the esthetic project. In order to fill the esthetically missing volume, materials such as composite or bis-acrylic mock-ups can be added to the facial surfaces of these lingually positioned teeth. This will help to create the correct esthetic placement of the tooth surface on the dental arch. This is a very simple way of visualizing their positions in the new smile design. This is done not only to perceive how the new smile will look but also to evaluate its occlusal compatibility. 

The position and alignment of teeth in the arch can significantly affect the appearance and balance of a smile. Rotated lingually or facially positioned or aligned tooth or teeth will disrupt the total harmony and balance. Poorly positioned or rotated teeth not only distort the shape of the arch but also interfere with their apparent relative proportion. Thus, if a dentist has difficulties in trying to perceive where and how the teeth should be aligned from the start, the mock-up overcomes this problem by using a simple silicon index that is prepared from the diagnostic wax-up.

When the position of the tooth is corrected with the mock-up, before the actual material preparation;

• excessive healthy tooth reduction can be avoided 
• a thicker layer of porcelain built up over the unnecessarily overprepared tooth (which can compromise the natural value and chroma) that will result in restoration with an artificial appearance is prevented.

By placing this customized index over the teeth, the dentist can visualize the teeth or a portion of a tooth that creates disharmony, either by a facial protrusion or unnatural axial inclination. The dentist can now trim down the protruding incisal edges, marginal ridges or axial inclinations until they can easily fit into the silicon index. By doing so,  overextended teeth towards the facial, or those that tend to stay out of the expected arch line, will be brought into their esthetically pleasing positions both vertically and horizontally. In this way, the facial limits of the ceramic veneers will be well defined even before beginning the actual preparation stage.

**  However, this can not be easily implemented especially in cases that have a protrusion (subtractive cases) or some interferences that prevent the insertion of the mock-up. In such cases, we have to take the decision with the patient about some initial reduction (aesthetic pre-recontouring) that we have to implement to allow the mock-up insertion. The patient signs a consent and then we can start the treatment.

The ability of the dentist to reshape the tooth to conform or to enhance nature's given contours is truly an art form that is essential to esthetics. One of the most important avenues that require this artistic procedure is the aesthetic pre-recontouring (APR). In order to dictate the final outcome of a pleasant smile and to obtain an adequately equal tooth reduction for the technician for laminate veneers build-up, an APR should be considered before the actual material preparation.

Aesthetic Pre-recontouring (APR)

Teeth that are to be treated with ceramic veneers may exhibit positions on the dental arch different from what is considered to be pleasing. The final esthetic and functional form determines the actual tooth preparation and the entire restoration buildup we seek to achieve. In the restoration process, factors like occlusion, function, interproximal position of the adjacent teeth and their contact zone, the size of the pulp and the hard and soft tissues, along with the age of the patient, are all very important. 

Tooth preparation that has been done without prior evaluation and planning is doomed negatively to affect the final result. Teeth are single objects that are part of a whole - the dental arch. In the actual material preparation (AMP) the required amount of enamel, and sometimes dentin, must be removed to provide enough space for veneers build-up. However, before doing so, any minor or major problems must be evaluated and misalignments corrected. In other words, an APR has to be made in order to put these things into order and to obtain a pleasing symmetry and balance in the arch. This will depend on how many teeth are to be restored for the new smile design and should definitely be decided before the actual material preparation starts.

When the individual tooth position or its alignment needs to be altered, the basic principle of APR is to put the partially protruding axially misaligned or rotated teeth into proper alignment on the arch, having the imaginary finished ceramic veneers designs in the dentist's mind before starting the actual material preparation.

Protruding teeth or facially slanted teeth, even without color alterations, must be reduced more to allow adequate space, so that the finished restorations will not be overbulked. Occasionally with the tooth in the lingual version, very little preparation is necessary. Most of the time, preparation of the lingually tilted tooth may be limited to creating a finish line on the proximal and the gingival regions and/or the removal of surface luster on the facial enamel. This strategy is especially indicated to improve the appearance of cone-shaped lateral incisors.

Mock-up for exact facial reduction

The major advantage of using the mock-up (mock-up) is to ensure the final outcome is accepted by both the dentist and the patient. The exact facial thickness can be double-checked with the help of a silicone index. As the mock-up (APT) now mimics the final outcome, the teeth can be prepared very precisely through it being that they represent the final contours of the actual restorations. 

The mock-up's facial thickness and the use of depth cutters through it will dictate the necessary facial reduction. In doing so, the dentist will avoid the unnecessary loss of enamel associated with excessive tooth preparation and be able to supply the ideal preparation depth and volume for the ceramic veneers production. 

The rotated tooth may need both APR and APT in advance. When discussing such a condition, it is possible that the mesial portion of the tooth may be buccally rotated whereas the distal portion is lingually positioned. If a combination of the rules mentioned earlier is applied, it will be very easy to visualize the tilt that will transform the tooth into its normal position as it should be in a pleasant smile. 

** An interesting clinical trick that always facilitate this step is to use a transparent preparation guide (vacuum-formed tray) with light-body impression inside it. All the interferences will be easily shown through the colored material, then these areas can be trimmed down, after that the silicone index loaded by the bisacrylic material can be pasvely inserted.

It is obviously necessary to make a thorough, deeper preparation of the protruding prominent area so that the restoration can be made with the proper physiologic contour. This can be accomplished by first contouring any of the surfaces that extend buccally. The buccally positioned mesial part must be ground down enabling the dentist to visualize whether the necessary preliminary reduction has been achieved or not. 

The facially protruded central is trimmed down with a fissure diamond bur. So, the silicone index can passively sit on the unprepared teeth.

If the preparation is limited to one or two teeth, then the lingualy positioned teeth can be buccaly contoured with composite mock-up. (b) when multiple teeth are involved, a flowable composite can be placed on the teeth with the help of a transparent template, thus creating the APT.

Once the silicone index is properly seated over the facially reduced teeth, it confirms that the mock-up is successfully finished. Once this is established, the transparent template, which has actually been prepared to build up our provisionals, can easily be seated into its original position without touching the reduced facial surface of the tooth, which was protruding before. 

When this is achieved, the teeth are spot etched and an adhesive is applied to the surface area and light-cured. Then the template/silicone index is loaded with a small portion of the flowable composite or acrylic resin and seated over the teeth, and light-cured. This way the mock-up is firmly seated on the teeth that are about to be prepared. This now resembles the finished surface and volume of the final restorations. 

The two advantages of this application are that;

1. The patient will immediately see the final outcome even before we start treating the case.
2. Because the preparation will be executed through the partially bonded temporaries it will be a very conservative preparation with no removal of unnecessary enamel with the depth cutter. 

APR of Gingiva

The APR in some cases is not limited to the hard teeth tissue. It can also be applied to minor gingival alterations. Biologic parameters permitting gingival contouring to achieve proper height can be accomplished with a diode laser. While doing that, the zenith points can also be changed, especially in the diastema cases. When minor gingival tissue remodeling is done with the diode laser surgery, no post-op apical migration of the tissue is witnessed.

** Whenever possible the geometric principles of tooth preparation for porcelain veneers are followed to maximize their strength. However, in some certain cases, the tooth or teeth may be lingually positioned in the arch;

• For those teeth that are extremely lingually inclined, orthodontic intervention is a must.
• For the patients who do not want to receive orthodontic treatment with teeth that are only slightly inclined to the lingual, an aesthetic treatment is possible. The lingual inclination of the tooth can be more than the depth of our depth cutter. Therefore, the amount of composite/bis-acrylic mock-up added to that surface properly to align its position over the dental arch might be thicker than our intended reduction (e.g. more than 0.5 mm). In such cases, after we prep the tooth with our predecided depth cutter, we will still see some composite over the tooth.
  In this situation, the area that was prepped with the depth cutter relative to where the facial surface of the ceramic veneers will be is actually in a position deeper than the grid depth of the bur. This is why we should still see the mock-up material from underneath the prepped area of the depth cutter. If this is the case, and the dentist wants the finished ceramic veneers to have maximum contact with the enamel surface, he/she should go ahead and remove the remaining mock-up material from the surface and slightly roughen the enamel surface to remove the surface luster (aprismatic layer) for improved bonding, even though the result will be a veneer displaying greater thickness. This should be discussed with the lab, informing them that the thickness of the veneer will be thicker in that area. On such occasions, the most important issue is to be able to visualize the final outcome.

Mock-up for incisal Preparation

The use of a mock-up (APT) is not limited to preserving and exacting the final facial volume but is also used to determine the exact incisal length and the necessary amount of reduction of the incisal edge. Reduction during the preparation should also be done through the mock-up to exact the prepared incisal edge position. 

In the restoration process, it is important that the functional incisal edge has been properly contoured. When restoring the lingually inclined tooth, an overly thick incisal edge must be avoided. In order to reduce the faciolingual dimension of the incisal part of the tooth, the enamel must be prepared to the lingual edge of the incisal surface, if permitted by the occlusion. If the lingual areas take part in the functional contacts while engaging in protrusive movements, then no alteration can be introduced. However, if slight reductions of the incisal edge on the lingual surface of the tooth will not affect the anterior guidance, then this portion can be slightly modified within the limits of the enamel to prevent the excessive thickness of the final incisal outcome.

The previously explained APR and APT (mock-up) techniques enable these treatments to be accomplished with very little effort and the utmost precision. However, utilizing them sounds like a long and time-consuming procedure, it is not, and it is extremely beneficial to the final outcome as nothing is left to chance. Everything is controlled and the dentist very accurately dictates the result.

Preparation sequence 

1. Preparation depth of the bur through the mock-up
   
   Four essential rules:
   No cervical groove
   Incisal groove 2 mm from the free edge 
   0.5 mm in the buccal (at the coronal two thirds)
   1.5- 2 mm at the free edge
   
   
2.  Homogenization of the grooves is done respecting the buccal convexity. 
   
   
3. Creation of the butt-joint at the incisal edge through the mock-up.
   
   At this point the remaining mock-up is removed to complete the procedure. After removing the mock-up, there are two options;
   
   * Marks are visible on the teeth (mock-up thickness less than 0.5 mm)
   * No marks are visible on the teeth (mock-up thickness greater than 0.5 mm).
   
   
4. Positioning of the margins "cervical and proximal":
   Peripheral delimitations of the preparation with spherical diamond burs surrounding the entire labial surface of the tooth without disruption of the proximal contact and without subgingival extension. 
   * Supragingival cervical (0.5 mm) and proximal (mid-thickness of the contact point) margins are recommended in normal circumstances. 
   
   
5. Triple angulation of the buccal convexity.
   
   
6. Creation of a proximal slide.
   
   
7. Retraction of gingival tissues.
   
   
8. Refinement:
   repeat on all the prepared surfaces and margins using diamond points similar to those mentioned above already employed except with fine and extra-fine grits.
   
   
9. Finishing & polishing:
   Using abrasive silicone rubbers and discs with decreasing granulation. Every angle and corner should be uniform, with rounded lines, to improve the adaptation of the resin cement and laboratory build-up.

 Special Cases

Mandibular anterior teeth

From an esthetic standpoint, the mandibular veneer can provide an excellent result in most situations. However, its life expectancy can be drastically compromised unless the patient’s occlusion is favorable.

The usual problem with preparations for lower veneers is leaving enough tooth structure remaining after the horizontal and vertical reduction. A potentially weak point is at the inciso-labial junction, which must always be sufficiently reduced and rounded to allow the veneer to be thick enough in that area to have the strength to resist fracturing when placed under an occlusal load. Also, the incisal edge of the mandibular anterior teeth is usually the most visible part of the veneer so consider this fact when preparing the tooth. Sufficient incisal reduction is needed to ensure a normal incisal edge appearance for that patient.

One advantage of the mandibular veneer is that it is seldom necessary to go subgingivally, as with the maxillary veneer, because most people do not show the gingival margin of mandibular anterior teeth.

To reduce or not?

The most practical approach is to evaluate each patient, and indeed each tooth to be veneered, on the basis of:

1. the thickness of the veneer needed for covering or reshaping,
2. the degree of anticipated retention of the veneer, considering the receptivity of the tooth to the bonding agent and placement of the veneer, and
3. recognition of how the increased thickness of the veneered tooth will change its appearance, structure, alignment, and function.

Dark abutments

Tooth darkening represents a major challenge for the restoration of optical characteristics with the naturalness of adjacent teeth as a reference. The amount of tooth reduction is determined by the color of the substrate.

In this case, the alternatives for establishing a good result are;

• performing a more invasive preparation,
• using opacifiers before the impression taking,
• selection of less translucent ceramic, with sufficient masking capability
• use of more opaque and/or higher value resin cement,
• also the combined use of the aforementioned alternatives.

Conceptually, the rehabilitation of darker teeth requires greater preparation depth; however, the challenge of conservatism is to remove a minimal amount of tooth structure and at the same time avoid the risk of inadequate tooth reduction for the proposed ceramic restoration. Until recently, severely discolored teeth represented a situation of contraindication for veneers. However, the improvement of ceramic systems and the association of new ingots with higher control of light transmission have enabled performing more conservative techniques as well as build-ups on discolored substrates with an increasingly more natural result.

Darkly stained teeth often require more reduction for opaquing purposes. This will allow for a thicker, more opaque veneer. For veneers on tetracycline‐stained teeth, for example, the underlying tooth color will modify its shade dramatically. This is because, in most cases, the veneer is only 0.5 mm thick and rather translucent. As a result, the actual shade of the porcelain has only a nominal influence on the final color of the bonded veneer.

With teeth darkened by endodontic treatments in which the labial surface is intact and the rehabilitation of which will maintain the natural morphology, the silicone guide may be fabricated directly within the mouth and prior to preparation.

The darker the abutment, the more reduction we have to do ..

Generally speaking, a depth of 0.2 mm is needed to change the hue of the tooth by one shade.

By reducing the tooth, usually it will be possible to neutralize the underlying color and create the illusion of a normal tooth color by having the opaque incorporated into the veneer itself. Also, by making room for the application of opaquing layers under the veneer, additional opaquing can be obtained at the cementation appointment by using resin opaquers.

Wherever possible, the use of ceramic veneers on discolored substrates needs to provide a balance between its capacity to mask the substrate and the final aesthetic result. Increased thickness of the restoration and the use of a lower translucency ceramic collaborate with the masking. However, increased thickness necessarily means more invasive tooth preparation, which reduces the amount of enamel available for bonding procedures, thus decreasing the clinical success expected for the porcelain veneer.

Currently, the dental market makes available a range of ceramic systems with different degrees of translucency, suitable for the manufacture of ceramic veneers. Excessively opaque ceramics such as IPS e.max, MO (medium opacity), and HO (high opacity) (Ivoclar Vivadent, Liechtenstein) are incapable of simulating the optical behavior of tooth enamel, which is characterized by its translucency, lending to restorations an artificial, unsightly appearance. Although MO ingots are still offering good results.

Hilgert studied the ability of ceramic veneers to mask discolored backgrounds in an aesthetically acceptable manner with decreased biological cost, concluded as follows:

1. For non-discolored substrates, such as A1 (Vita Classical® shade guide, Vita, Germany), high translucency ceramic systems with a thin thickness may be reliably utilized (0.4 mm) - Empress Aesthetic® HT (Ivoclar Vivadent, Liechtenstein) and IPS e.max HT (Ivoclar Viva-dent, Liechtenstein).
2. Slightly discolored substrates (A3.5 VitaClassical® shade guide, Vita, Germany) were masked acceptably with a conservative preparation (0.4 mm reduction) if associated with low translucency ceramics (EmpressCAD® LT, Ivoclar Vivadent, Liechtenstein).
3. Severely discolored substrates (C4, VitaClassical® shade guide, Vita, Germany) were restored acceptably by merely executing an invasive preparation (1.0 mm) and low translucency ceramics (EmpressCAD® LT, Ivoclar Vivadent, Liechtenstein).

Aged teeth

This has been an aspect of veneer preparation often ignored or overlooked until now, but it becomes an important issue when this application is performed over facially eroded or aged teeth. These teeth, owing to the thinning of the existing enamel surface, have already lost their original facial volume and have become weakened. If this is not taken into account, the ignorant application of the depth cutter will be extremely destructive, resulting in the total loss of the existing thin enamel surface.

It is vitally important to respect the thickness of the enamel that remains during teeth preparation as well as the biomimetic recovery of the crown and the original enamel thickness. When these principles are followed, the healthy tooth structure is preserved because if the teeth are overprepared, nothing can replace the unnecessarily lost healthy tooth structure resulting in the loss of the enamel which is the source of the strength of the teeth. This has always created a problem during the preparation of aged teeth for ceramic veneers. The final forms and contours of the teeth can also be accomplished during the provisionalization phase.

During the natural aging process, the enamel thickness of the aged teeth gets thinner and thinner, gradually losing its original volume.

The thinner the enamel, the more flexible the tooth becomes ..

 

Therefore the dentist must try his/her hardest to preserve as much of the existing enamel as possible. This is one of the most important situations where the APT must definitely be utilized. If the APT is not used, at least a silicon index (prep. guide) prepared over the wax-up should be utilized. It will dictate the final volume and hence inform the dentist about the depth already lost to facial erosion. In this way, the maximum conservation of the enamel will be achieved. On the other hand, if a solid reference such as a silicone index is not used, the extreme preservation of enamel thickness during tooth preparation often leads to overcontouring of the final restorations.

Crowded teeth

Preparation of crowded teeth also needs a preplanned, delicate approach, especially if the mandibular incisors are of concern. Since some special cases need more aggressive preparation depths, such as in the case of the discolored or facially misaligned teeth, reduction of the facial surface on the teeth that suffer from severe discoloration must not be limited to the enamel. The preparation will have to be deeper, even if it exposes the dentin. Whenever it is feasible, increasing the depth of reduction to 0.5 mm in the cervical region and 0.7 mm in the middle third and incisal areas is recommended.

Dentin Exposure on the Margin

In the majority of cases, the placement of the gingival margins for the ceramic veneers is open to subjective criteria. However, there will be some situations where subgingival margins are unavoidable, such as in the case of caries or old fillings that extend under the gingiva.

Patches of dentin exposure are no longer a problem during the preparation as long as the margins are kept on the enamel. However, in most of the abnormal situations, such as extensive caries lesions in the gingival areas, placement of the subgingival margin can go as deep as to be placed on the dentin. Therefore, in order to stop, or minimize the possible marginal leakage, the dentist should very carefully identify the condition of the existing dentin. Thus, obtaining a successful bond to dentin with a perfect marginal seal that will not exhibit discoloration has become a much larger problem that has occupied many researchers over the past four decades.

Clinical considerations in Veneers Preparations

The primary concern is for healthy tooth structure. In the interest of maximizing bond strength, all the buccal enamel should be retained. Where some minimal preparation is necessary, however, the preparation must be left in the enamel layer if at all possible.

A, All the buccal enamel has been retained. B, Preparation for the veneer kept within enamel.

Almost any preparation penetrates to the dentin at some point, usually toward the gingival portion of the tooth where the enamel thickness flares down to a knife-edge at the cemento-enamel junction. 

Although the preparation in part A is entirely within enamel, most clinical preparations may enter the dentin as seen in part B.

The initial signs of subveneer staining were followed by percolation, then fracture of the gingival segment of the laminate. Even with the best of the newer dentin adhesive agents, the porcelain bond to enamel is still significantly greater than the adhesion to dentin, so it is advisable to minimize dentin exposure during the preparation.

Initial subveneer staining followed by percolation, fracture and repair of the veneer.

The margins of the porcelain veneer should be placed where the patient can readily access them for routine home maintenance. In particular, the gingival margin should be located supragingivally. The microenvironment of the veneer margin consists of a knife-edge silanated porcelain bonded onto enamel by a composite resin cement. 

The supragingival margin (A) causes no gingival irritation and is maintainable (B)

Home maintenance of the supragingival margin.

The enamel and porcelain are both biocompatible with the gingiva and well-tolerated. The composite, however, tends to cause irritation if it comes into intimate contact with the gingiva. When the margin is placed subgingivally, this luting material is in direct contact with the free gingival margin, eventually causing irritation and recession. With a supragingival margin, the composite is reasonably away from periodontal structures and is unlikely to cause tissue irritation.

The porcelain subgingival margin (A) and the luting cement irritates the gingival margin and is not readily maintainable (B)

Limited home maintenance of the subgingival margin.

All visually accessible areas of the tooth should be covered by porcelain. 

Crown and visible root (left) Veneer is slightly larger than facial surface of tooth (right).

The area most often overlooked in this respect is the gingival portion of the proximo-facial line angle. With the gingival recession, these areas of slight concavity are uncovered. The dark underlying tooth structure is visibly unesthetic when the patient is viewed from the side.

Proximofacial line angle not covered by porcelain.

A slight reduction of the proximo-facial line angle is usually all that is needed to permit an acceptable path of insertion for the proximally extended porcelain laminate.

A to C, The veneer allows show-through of darker dentin at proximogingival area D, Dentin is slightly reduced at the proximogingival area with a diamond bur E, The slight reduction of the proximofacial line angle eliminates dark show-through.