Practical steps for Porcelain Dental Veneers

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Published: Wednesday, 25 March 2015 13:34 Written by 

By Dr Wesam Alsadi BDS, orthodontic resident

First appointment:-
Shade Selection: -Clean teeth with pumice and water to remove any extrinsic stains, which exist. Select a tentative shade with your patient participating. Most patients want their teeth to be light. Many veneers are made with B1 porcelain since it is easier to darken the veneers when bonding than it is to lighten them. The B1 porcelains have the most scattering and can block out the darkest stains. It is much easier to establish the final shade in the porcelain rather than trying to modify the shade with the cement.

Diagnostic Wax Up:

- take a study model impression which will be poured and then mounted.

There is 2 ways of doing a diagnostic wax up:

1- Using a facial picture with the patient saying E in English à 6 feet from the patient. And using GPS a digital esthetic device over the patient picture to dispose and simulate the new shape, length, width of the new veneers.
2- Using smile guides to demonstrate different incisal characteristics.

For both system the patient’s preferences were documented and transferred to the mounted study models in wax (wax up)
- The wax-up then is duplicated instone to facilitate fabrication of clear stents and siliconmatrices which will be used to
* makeprovisionals that represent the wax-up.
*It can be used as an intraoral reduction guide for the dentist to ensure uniformity in the thickness of the preparation thus porcelain
* The dentist can fill it with composite (for the clear stent) or bis acrylic resin (for silicone matrix) to generate intraoral diagnostic mock-ups, so the patient will have an idea about how his teeth would look.


Teeth preparation:

-to prep or not to prep; not to prep is not recommended because of
- The facial surface of the of the veneer will be over contoured which will result in gingival irritation with accompanying hyperemia and bleeding
- The veneer will be more likely to be dislodged
# the only exception is in cases where the facial aspect of the tooth is significantly undercontoured because of sever abrasion or erosion

Prep is strongly recommended for
- To provide space for opaque, bonding or veneering materials for maximal esthetics without over contouring
- To remove the outer fluoride-rich layer of enamel that may be more resistant to acid etching
- To create rough surface for improved bonding
- To establish a definite finish line for accurate positioning and seating of an indirect veneer

Teeth preparation Step by Step
Various techniques for accurate tooth reduction have beenproposed, including silicone matrices, freehand preparation, depth limiting burs and using a clear matrix to “see through” and judge the amount of space available

These are the steps using depth limiting burs


1- The first step is to use a 0.5-millimeter depth reduction diamond to place horizontal depth cuts on the labial surface. It is recommended to place the depth cuts in the middle and incisal one thirds only. The cervical reduction, which will be about 0.3 millimeters, is done during marginal placement with a two grit reduction diamond
2-Next, a two-grit diamond is used to eliminate the areas of tooth structure between the grooves created by the depth-cutting bur
3-If 0.8 millimeters of tooth reduction is desired from the start, as for a pressed ceramic veneer, a 0.5-millimeter depth cutter is used and the grooves are eliminated. Then, a 0.3-millimeter depth cutter is used over the smoothed surface to uniformly remove another 0.3 millimeters of tooth structure
4- A two-grit cylindrical diamond is used to create a gentle chamfer margin at the gingival crest, or slightly above, unless defects, caries or dark discoloration extend subgingivally .
5- The gingival margin is carried interproximally to the facial side of the proximal contact. It is useful to lightly strip the interproximals with a diamond strip to facilitateremovable die fabrication for some laboratory techniques.If there is no proximal contact, the gingival margin should be extended to the lingual proximal line angle. If the adjacent tooth is close in proximity, a "needle diamond" can be used to develop interproximal reduction without scoring the adjacent enamel
6- A .5-millimeter depth cutting diamond is then used to create depth reduction grooves on the incisal edge
7- A two-grit cylindrical diamond is used to evenly reduce the incisal edge. When the reduction is complete, the incisal edge should form an acute angle with the facial surface to provide resistance to facial displacement (Resistance Form)
8- A small chamfer diamond is then used to refine the gingival margins. Once the preparation is complete,unmedicated retraction cord is placed in the sulcus. Even the unmedicated cord usually causes thetissues to recede slightly. Once the cord is placed the margins are refined apically to just above the levelof the cord. This will assure that the final margin is at or slightly below the free gingival margin. Oftenhemostatic agents are not required with these procedures. If it is required, it is best placed after all thecords are in place so that all the tissues experience the agent for the same period of time.
9-The interproximal finish line referred to as the "elbow" must be extended far enough interproximally at the gingival level to avoid visualization of the restoration margin after placement from the three quarter (oblique) view
10- If the incisal edge of the preparation is thick enough facial-lingually, a slight chamfer may be placed with this same diamond instrument at the lingual finish line
11- The entire preparation is then smoothed using a 30 micron rounded cylinder diamond.
12- A 3/4 inch fine garnet flexi disc is used on a latch mandrel to roundand smooth all transitional incisal and proximal angles. This will ensure precise fit with minimal stress concentration in the Class 4 areas of the completedrestoration.
13- Preparation guides made from the diagnostic wax-up were used to verify the facial and incisal reduction, as well as to ensure uniformity in the thickness of the porcelain.

The problem with this techniqueis that depth cuts are only useful if, once you remove a specified amount of toothstructure you replace or “restore” that 0.7 mm, as the 0.7-mm depth cut is your only reference.This does not take into account the final3-dimensional (3-D) form and positioning at which the tooth needs to end up.


Diagnostic Mock UP:-

A mock-up is the creation of a “trial smile” — allowing the patient exciting prospect of actually being part of his/her own smile, and it serves as a “template” or “blue print” for the final veneers.
And it helps the Dr and guides him during preparing the patients teeth

Diagnostic Mock up can be prepared in lab with one facial picture of the patient smiling taken at 6 feet from the patient. The Mock up is done on the picture and then once accepted by the patient, impression are taken to send to the lab. The lab will produce the wax up with prepping guide and silicone matrix. Dentist is ready to prep, take the impression and put the provisional duplicating the Mock up during the time veneers come back from lab.

Or it can be done following method that is time consuming for both patient and dentist

How to make a traditional mock up?
1- A smile design wax-up is completed based on the patient’s esthetic desires and functional needs
2- A matrix is made with lab putty and tried in the mouth to verify complete seating.
3- Many times in an esthetic design there are additive components to the design (ie, the teeth are being built up) but there are also subtractive parts of the design (eg, a line angle is being brought back lingually). If there was stone removed on the cast to reshape the teeth esthetically then similar amounts of tooth structure need to be removed by esthetic tooth recontouring to be able to seat the matrix, allowing for the subtractive design done on the preoperative casts
4- A notch is cut into the matrix in the frenum area to allow visualization of proper and complete seating
5- Bonded mock-ups can be done with either composite or bis-Acryl temporary material, in some cases we may leave the mock up in the patient’s mouth to try it before he decided to do veneers. For longer-term stabilization (more than 3 months) the bonded mockup should be done with composite. Using bis-Acryl is much simpler than conventional composite. It has the disadvantage of much higher wear potential than composite and should only be used short term
6- Generally, cotton roll isolation is adequate for these procedures as long-term bonding is not necessary or even desirable since in a short time the mock-up will be removed.

7- The teeth are then etched with 32% or 37% phosphoric acid. It is extremely important to only etch a specific area. The etching pattern should cover the facial only (for veneers that are facial incisal veneers) and etch to 1 mm to 2 mmshort of the anticipated final veneer margin.Do not etch the marginal area because:-
- During the preparation appointment,when preparing the marginal area (finish line), this area of bis-Acryl willeasily flake off, facilitating margin placement.
- if this area has been etched and bonded to with bis-Acryl there is the potential of leaving small amounts at the final margin preparation, possibly affecting long-term marginal seal.
8- After 20 to 30 seconds, the etching material is rinsed with copious amounts of water. The surface of the teeth is air-dried; since most of the time this procedure is done to enamel, over-drying is not a problem.
9- Use a primer and adhesive combination on the whole surface of the tooth, even the unetched areas . This will create a minimal seal on unetched areas to help prevent leakage and staining at the margins during the trial restoration phase
10- The primer/adhesive is air-thinned and then light-polymerized
11- Bis-Acryl is then loaded into the matrix. The tip of the syringe should be placed in contact with the incisal edge or deepest area of the matrix and slowly back-filled. This will minimize the chance of trapping air bubbles
12-An amount slightly more than is anticipated to be necessary in order to not have any voids should be placed in the matrix.
13- The matrix is then completely seated in the mouth. Once the matrix is seated the material is allowed to set until it reaches a rubbery or doughy stage. The excess material beyond the edge of the matrix is easily removed at this stage with an instrument
14- The material is allowed to set fully and the matrix is removed. If the matrix fits well there should only be a thin “flash” of material beyond the anticipated veneer margins
15- Any excess material is trimmed with composite trimming carbides. It is recommended to use carbides that have a round tip, as there is minimal chance to damage tooth structure
16- It is important to open up the gingival embrasure to ensure that the patient can floss in these regions as the mock-up is left splinted together
17- Occlusion is adjusted in centricand all excursive movements. It is not recommendedto have the patient wear anocclusal splint at this point, as one of thegoals of this phase of treatment is to seeif the patient will adapt functionally tothe proposed anatomical changes.
18- The mock-up can then be adjusted as necessary for esthetic requirements. If additional material is needed then a bonding agent is applied to the area and flowable composite is built up freehand to the desired shape and cured.
19-The patient wears this until esthetic and functional acceptance is obtained and has held up quite well for several weeks. This technique has proven to be a great patient motivator to accept proposed treatment.

 

Controlling Reduction using the mock up:-
Once the smile design has been establishedand a 3-D model has been mockedup and bonded in the patient’s mouth, itis fairly easy to control reduction. Becausethe final 3-D positions of the teeth areknown, depth cuts become useful andpractical.

1- To obtain a relatively uniform preparation of 0.6 mm to 0.7 mm, a depth cutter of slightly less depth is used. This is because once the preparation is finished with fine diamonds it ends up removing 0.1 mm to 0.2 mm more than the depth cutter.For the reduction mentioned, a 0.5-mm depth cutter is used across the facial surface
2- A simple technique is used is to draw pencil lines at the base of the depth cuts, for better visualization
3- A coarse diamond bur is used to a depth across the whole facial surface up to the depth of the pencil marks
4- The incisal reduction is done the same way in that a specific sized bur is used to create depth cuts .The same bur is then used to remove material in between the depth cuts to obtain adequate incisal reduction
5- At this point the preparation is evaluated for any remaining mock-up material. Many times the preparation is still in the mock-up material. If this is the case, then the remaining mock-up material needs to be removed.
6- With a diamond, lightly prepare down to the bis-Acryl interface. The material near the margin will just flake or fall away as it was not bonded to the tooth.
7- The last step in the process is to place the margin. For conservative veneers a fine chamfer diamond is used to place a 0.3-mm to 0.4-mm chamfer finish line, Once the preparation is complete, unmedicated retraction cord is placed in the sulcus. Even the unmedicated cord usually causes the tissues to recede slightly. Once the cord is placed the margins are refined apically to just above the level of the cord
8- Any sharp line angles, such as the facial incisal line angle, are rounded so as not to concentrate stress in the porcelain restoration

The benefit of this technique is conservation of tooth structure.in some cases once ideal reduction was obtained, the preparation could still be in the bonded mock-up material. Only a minimal amount of tooth structure was actually removed to establish the peripheral margin. With the normal technique of only using depth cuts with no beginning reference, unnecessary tooth structure would have been removed

After preparation of the teeth
1- we can fill the clear stent or the silicone matrix which is already prepared,- with composite or (Bis-acryl resin temporary resin material)
2- Put the clear stent or the silicone matrix back on the prepared teeth and wait for the material to set, to generate intraoral mock-ups.
3- At this time it is possible to add or subtract to the mock-ups according to patient preferences this is the patient’s chanceto express personal wishes with respect to shape and arrangement ofthe final restorations.The importance of careful seatingand contouring of the provisionals according to the patient’s expectations cannot be emphasized enough. If the patient is not happywith the form of the provisionals it will be very hard for the technicianto “guess” the desired shape andcontour that will please the patient
4- Once the patient has accepted the shape and contour of the mock up, an impression is taken and poured in stone. This study model of the mock up can now be mounted against the opposing teeth and a silicone putty index can be formed to the incisal edges as well as the labial contours. This index aids the technician in the planning and build-up of the final porcelain restorations

Impression:
1-The retraction cord should be left in place if possible during the impression. Usually thecord is apical to the gingival margins and leaving it in place guarantees hemostasis and allows foranother impression to be taken immediately if the first fails.
2-An impression is taken using a well-designed custom tray
3- It is best to use a polysiloxane or polyethermaterial for the impression since multiple pours are often needed for the laboratory procedures.
4-a single stage impression technique, with heavy body material placed in the tray and light bodiedmaterial syringed around the teeth
5-Placingsoft wax or putty in the lingual embrasures prior to taking the impression will minimize tearing of theimpression in these areas.


Temporary Veneers-*A great majority of patients do not require that temporaries be placed. If they are necessary or desired, they are hand sculptured using composite, kept supragingival, out of heavy occlusion, and attached by spot etching the enamel in the center of the tooth away from any margins.
*Other methods can be used which include acrylic type indirect methods.Because teeth prepared for veneers are designed to haveminimal to no mechanical retention, retaining temporaryveneers is a problem.
1-Many techniques advocate allowing thetemporary material to cure on the teeth and lock intoundercut/retentive areas such as the interproximal embrasuresand incisal overlaps.
2- The excess flash is then carefully trimmedaway with a scalpel. The temporary veneers are then broken off at the time of cementation
3- It is not possible to accuratelytrim, verify and refine the margin of the temporary veneerswhile they remain in place on the teeth. Failure to do this maylead to:
-Gingival inflammation, which could complicate andcompromise the final cementation.
- The fact thatthere is no layer of temporary cement may allow ingress ofbacteria, which may stain the underlying teeth or cause toothsensitivity
- Another potentialproblem with this technique is that any modification to theshape of the temporary veneers and final polishing must bemade intra-orally.

To overcome these problems we can modify the technique as following:-
1- Removing thetemporary veneers carefully after they have polymerised on theteeth. This is carried out using a scalpel to remove excessmaterial as described earlier. In addition, any material that hasengaged retentive/undercut areas around the teeth is alsoremoved.
2- Once all the retentive areas of the temporary materialhas been removed, the temporary no longer has mechanicalretention and can be gently removed
3- Where necessary, themargins are relined/refined with a methylmethacrylateacrylicresin, which is more versatile for marginal relining than bisacrylresin
4- The temporary veneers are then cemented in place with aclear temporary cement and the excesscement is cleaned away
5- then small amounts of the acrylicresin are applied to the palatal, interproximal and incisal aspects to once again lock the temporaries into placemechanically and augment the retention provided by thetemporary cement

Whichever method is used, it is a time consuming procedure which needs to be considered when deciding on a fee.

 

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