CHAPTER 6

PREPARATION – IMPRESSION – PROVISIONAL VENEERS

MACIEJ ŻAROW

Preparation should be closely related to the esthetic treatment planning … Conservative preparation means preserving the enamel, better adhesion, and durability of the veneers. Provisional veneers? They can be relatively simple for a dentist and remain in place until the next appointment if they are made according to the presented procedures …

Preparation – Impression – Provisional Veneers

Porcelain veneers went through tremendous evolution due to reduced tooth preparation. This is possible due to the proper planning and tooth preparation through the mock-up, utilizing magnification and new developments in ceramic materials. This chapter describes the steps to a successful preparation, accurate impression, and provisional veneers.

STARTING THE PREPARATION

If the patient accepts the drive-test of the smile (mock-up) and decides to follow the dentist’s treatment plan (including the cost estimate), you can start the tooth preparation for the veneers (Fig 6-1). Before the patient’s visit, the dental assistant arranges the study casts, the casts with diagnostic wax-up, the silicone index, which is made from the laboratory silicone (for control of the preparation), and the index made from a traditional silicone (for provisional veneers fabrication).

Fig 6-1a
A 41-year-old female patient presented to the dental clinic seeking a better esthetic outcome for the maxillary central incisors.

Figs 6-1b and 6-1c
Tooth 11 with extensive composite restoration, tooth 21 after root canal treatment (in the past internally bleached), with slight discoloration. The patient expected a change in teeth esthetics, preferably by making porcelain veneers.

Fig 6-1d
Palatal view showing the outline of the restorations.

Fig 6-1e
Radiograph of teeth 11 and 21.

Figs 6-1f and 6-1g
Clinical situation (f) before and (g) after the mock-up.

Fig 6-1h
The silicone index is taken from the diagnostic wax-up and cut along the gingival margin.

Fig 6-1i
The mock-up obtained from the silicone index based on the diagnostic wax-up.

THE VENEERS DRIVE-TEST (MOCK-UP) BEFORE PREPARATION

Veneer preparation needs to be performed through the mock-up (test-drive veneers). Why should we prepare on the test-drive veneers? Suppose we start the preparation on the natural teeth. In that case, there is a very high risk of dentin exposure. The thickness of the enamel is often different from what we find in an anatomy book and different from the dentist’s expectations.^1–7

The patient may have enamel wear due to the use of hard-bristle toothbrushes or abrasive toothpaste, or may have erosions or enamel defects. The mock-up preparation considers the definitive contour desired for the veneers. In most cases, exposure of the dentin can be avoided.

Silicone index as a template for preparation control

The silicone index is based on the diagnostic wax-up from the hard silicone and should be cut into two parts (Fig 6-2a). The palatal one will be used to control the space necessary for the incisal edge of the veneer (Fig 6-2b), and the labial one to control the volume for the veneer from the labial side (Fig 6-2c).

Fig 6-2a
The silicone index should be cut into two parts for veneer preparation control using a scalpel no. 13.

Fig 6-2b
The palatal part of the silicone index is used to control the reduction on the incisal edge.

Fig 6-2c
Labial part of the silicone index is used to control space for the veneer from the labial side.

When cutting the silicone index, a scalpel no. 13 should be utilized, and the procedure should be obtained in a glass pad. Cutting the index without the solid base may result in injury to the dentist’s fingers. The outline of the cutting line should be performed along the incisal edge – a bit more toward the buccal side (Fig 6-2a), so that way the incisal edge remains in the palatal part of the index. The cutting outline should include at least the teeth intended for preparation. Then, from the incisal cut, make a transverse cut toward the palatal part, dividing the index into two separate parts: palatal (part A) and labial (part B).

Then the incisal part of part B should be shortened, not to interfere with the visibility during the preparation control. Now part A can be used to control the reduction of the incisal edge and part B to control the reduction of the labial tooth structure.

TEN STEPS FOR A SUCCESSFUL PREPARATION

Step 1: The horizontal grooves (preparation through the mock-up)

The horizontal grooves are created on the labial surfaces and the incisal edge of the tooth (Fig 6-3a).⁸ On the labial surface, the grooves must have a depth of approximately 0.4 mm (bur no. 868B018), while on the incisal edge, we use a bur placed perpendicularly to the tooth axis to obtain 1.5 mm grooves (bur no. 68016). To better estimate the real tissue reduction, we mark the bottom of the grooves with a pencil (Fig 6-3b). Then we remove the test-drive veneers (mock-up; Fig 6-3c).

Fig 6-3a
The horizontal depth grooves on the labial surface and the incisal grooves (always through the mock-up).

Fig 6-3b
Marking the horizontal grooves with a pencil helps identify where sufficient tooth structure has been removed.

Fig 6-3c
After removing the test-drive veneers, we can see how minimal the amount of the actual tooth structure has been removed.

Step 2: The outline of the preparation

With the preparation outline with a round ball diamond bur (bur no. 801012), the preparation outline all around the labial surface is obtained (Fig 6-3d). Preparation is carried out very gently, not too deep toward the tooth tissues and not too close to the gingiva (remember that this is the initial outline only!) If we prepare too deeply, we can achieve “a gutter” – like chamfer. Remember to make only a slight outline margin! Accordingly, the preparation will be shallow, and it could be deepened in any step of the further preparation if necessary. The tapered bur no. 6844014 can be utilized as well to create the outline of the preparation.

Fig 6-3d
The preparation outline on the labial surface was created with a round ball diamond bur.

Step 3: The incisal reduction

The incisal edge is reduced by 1.5 to 2 mm in relation to the planned final length of the veneer.^9–11 The bur should be placed perpendicularly toward the axis of the tooth while cutting the incisal edge. Do not prepare a chamfer finishing line on the palatal surface. The preparation on the incisal edge should be finished with a butt joint – this type of preparation remains preferable by the authors (to see more, check page 128).

Step 4: The definitive reduction of the labial surface

In the next step, the labial surface reduction is obtained by the preparation of the structure situated between the horizontal grooves (Fig 6-3e). The leveling of the surface must be performed in three different inclinations, depending on which part of the tooth is prepared: the cervical, the middle, or the incisal (Fig 6-3f).^12–14

Fig 6-3e
The clinical situation after reducing the incisal edge and preparation after removing the horizontal grooves.

Fig 6-3f
During the veneer preparation, the inclination of the bur should differ, depending on which part of the surface we are working on: the cervical, the middle, or the incisal (bur no. 6844014).

When preparing the labial surface, the bur must always be positioned to obtain three separate surfaces with different angles: the cervical, the middle, and the incisal.

Step 5: The 45-degrees preparation (“elbow” preparation)

When the proximal surface consists of a healthy tooth structure, usually there is no need to pass with the bur toward the palatal surface; however, it is important to prepare the embrasure space situated under the contact area to hide the veneer margin. To achieve this, the bur needs to be placed at an angle of 45 degrees, and a gentle outline needs to be prepared under the proximal contact (Fig 6-3g). The operator should always control the tooth preparation by viewing the prepared teeth from different angles: from the front, left, and right profiles (Fig 6-3h).

Fig 6-3g
Preparation of the tooth structure under the proximal contact with a bur at an angle of 45 degrees.

Fig 6-3h
To confirm the 45 degrees preparation, you should view the prepared tooth from the patient’s semi-profile. In this position, the preparation margin usually becomes visible, which may create an esthetic problem after veneer cementation.

Step 6: Stripping of the proximal surfaces

If the proximal contact is loose, 45-degree preparation is usually sufficient. In the case of strong contact points, slightly loosening the proximal surfaces with an abrasive metal strip should be performed (Fig 6-3i). The purpose of loosening the proximal surfaces is to create a space for the impression material to freely enter the proximal contact and show the margin of the preparation. The loosening of the proximal surfaces should not be confused with the releasing of the proximal surfaces, which is a separate technique described in the next step.^15–17

Fig 6-3i
Gentle stripping between the central incisors allows the dental technician to better visualize the preparation margin.

Step 6 modified: Preparation of the proximal surfaces with an extension on the palatal surfaces

In some clinical situations, it is necessary to cover the entire proximal contact with a veneer.^18–22

We will implement such a procedure when:

• There is an existing restoration on the proximal surfaces (Fig 6-3j)

  

  Fig 6-3j
  Preparation of the proximal surface due to the extensive restoration of tooth 11.

  Video: The 45 degrees preparation https://books.dentist.com.pl/veneers/video/6

• We plan to shift the line between the two adjacent teeth
• We plan to close the diastema
• It is necessary to correct the width of the individual teeth
• For this purpose, the proximal surfaces should be prepared so that the contact tooth veneer is relocated to the palatal surface (Fig 6-3k).

  

  Fig 6-3k
  Clinical situation after preparing the proximal surface of tooth 11.

Step 7: Placing the first retraction cord

Suppose no retraction cord has been placed yet (for example, cord #000, Ultradent, not soaked in hemostatic agent). In that case, it is the right time to place it into the gingival sulcus for a minimal gingival retraction (Fig 6-3l).

Fig 6-3l
The retraction cord #000 is placed in the gingival sulcus before the definitive modification of the preparation margin or at an earlier stage for the veneer.

Step 8: Shifting the preparation margin toward the gingival outline

The preparation margin should be brought closer to the gingiva, and the outline should be clearly marked for the dental technician (bur no. 6844014).

Step 9: Control of preparation with the silicone index and correction with a fine diamond bur

The silicone index should be positioned, and the preparation should be checked at the different levels of the labial surface (Fig 6-3m) and from the incisal edge (Fig 6-3n).^23,24 Places that need more preparation should be corrected with a bur no. 8868016 (Fig 6-3o) and checked again with the silicone index.

Fig 6-3m
Control of the labial surface preparation with a silicone index.

Fig 6-3n
Control of the incisal edge reduction.

Fig 6-3o
Correction of the preparation with a bur.

Step 10: Definitive smoothing of the surfaces

Finally, the surface is smoothed with a silicone polisher no. 9608 (Brownie Point, used in the past for amalgam polishing, 5000 rpm). Smoothing is carried out until the entire surface clearly reflects the light (Fig 6-3p). After polishing, all imperfections (such as sharp edges and unrounded angles) are clearly visible. If necessary, a correction can be made with a super fine diamond bur and polished with a polisher.

Fig 6-3p
The clinical situation after polishing the preparation surface. The gingival margin of tooth 21 was slightly corrected with electrosurgery. Tooth 11 was not prepared too close to the gingival margin to maintain the symmetry between the planned veneers.

SUMMARY OF PREPARATION

Fig 6-4a
The horizontal orientation depth grooves are prepared on the labial surfaces and the incisal edge (bur no. 868B018).

Fig 6-4b
Creating a gentle outline of the labial preparation with a round ball diamond bur (no. 801012).

Fig 6-4c
If the round ball diamond bur appears too aggressive, we can use a chamfered diamond bur to outline the preparation.

Fig 6-4d
A decision has to be taken whether the veneer will cover the proximal surface or if the proximal contact point will be maintained within the tooth structures.

Fig 6-4e
When the contact point remains in a healthy tooth structure, preparation at the angle of 45 degrees must be carried out …

Fig 6-4f
… in such a way that the preparation covers all the visible surfaces from the outside, including when looking from the semi-profile view.

Fig 6-4g
In the event of an extended restoration on the proximal surface, the proximal reduction needs to be obtained with a narrow needle diamond, avoiding damage to the adjacent teeth.

Fig 6-4h
Ensure that the preparation margin is clearly visible (especially on the proximal surfaces) and that the preparation surface is properly polished.

Second gingival retraction cord

The first retraction cord, placed during step 7 of the preparation (Fig 6-3l), remains in the gingival sulcus. Its purpose is to seal the gingival sulcus and reduce the secretion of gingival fluid while taking the impression.

Next, the second retraction cord is placed (Fig 6-5a), soaked with a hemostatic agent (usually cord #0, Ultradent). The cord is cut to the appropriate length (Fig 6-5b) so that it can be placed in one piece on the entire labial side of the teeth prepared for veneers. The cord should be gently placed in the gingival groove. It should not be placed too deep, as its goal is to retract the gingiva outwards rather than inwards.

Fig 6-5a
The second gingival retraction cord should be a thicker one, so it will retract the soft tissues and allow the impression material to flow into the gingival sulcus (for example, cord #0).

Fig 6-5b
The second retraction cord is usually cut in an unconventional way so that it is long enough to run along the gingival groove of all the prepared adjacent teeth for veneers.

Positioning the cord in the gingival groove is usually achieved with a probe, and it should be left there for 5 to 10 minutes. While placing the retraction cord in the gingival sulcus (Fig 6-5c), moderate and gentle pressure should be applied on the cord with the instrument.

Fig 6-5c
The second retraction cord should not be placed deeply in the gingival groove. The purpose of placing this cord is to move the gingival tissue outwards, thus creating space for the impression material to flow into the gingival groove immediately after removing the cord.

Holding the cord for a while in the gingival sulcus with an instrument allows the soft tissues to accept the cord inside the groove.

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