Inside Dental Technology
The Canvas Cutback Technique for IPS e.max®Press and e.max® CAD
Find the right material to preserve the structural integrity of your restoration.
When discussing different cutback techniques for pressable or millable ceramics, the ingot or the block of choice plays an important role. In nature, the different incisal effects are created by the superimposition of different layers of enamels. When the enamels reach the incisal edge, the amount of dentin is reduced, which creates a transition of micro-characterizations and juxtapositions of different opacities. This re-creates an internal signature based in the variations of low and high values that represent the mamelon structures.
Based on these phenomena and the level of opacity inherent in the porcelain base (blocks and ingots), there is a need to use the cutback technique in some areas to block the dense opacity and allow light to pass through and be absorbed, reflected, or deflected.
The consideration of ingots or blocks of porcelain must be based more on stump shade or dentin color that tends to show through the porcelain. This causes some level of discoloration or variation in the case from the influence of the underlying color from the inside out. Normally, when the porcelain is more opaque, the level of cutback needs to be greater to provide the technician freedom to re-create all the different characterizations in the incisal edge. However, the greater the cutback, the more porcelain layering is required. Many technicians are afraid of losing the control in the final contouring.
On the other hand, lithium disilicate has been the real revolution of the dental industry. It has never existed before—a combination of strength, high esthetics, and friendly use of a porcelain. One of the biggest features of this material is the 360 MPa to 400 MPa flexural strength when fabricating full contour or keeping the monolithic structure. Based on this statement, it is smart to keep the full strength of the material in the functional areas and layer to try to re-create nature without compromising the strength.
In the case presented here, the dentist restored the entire upper arch. The material chosen for this case was IPS e.max® Press Low Translucency ingot B1 (Ivoclar Vivadent, www.ivoclarvivadent.com). The lower arch was stabilized with fixed orthotic to calm the occlusion for the upper arch fabricated in ceramics.
Figure 1 shows the preliminary condition of the patient before the full-mouth rehabilitation. The rehabilitation was completed in two stages—the first stage involved rehabilitation of the upper arch with the lower arch receiving fixed orthotic to stabilize the occlusion, and the second stage of the treatment plan to complete the rehabilitation of the lower arch with ceramics.
Before the treatment plan was executed, the patient was analyzed and diagnosed using the K7 Evaluation System (Myotronics, www.myotronics.com) and J5 Myomonitor TENS unit (Transcutaneous Electrical Nerve Stimulation) (Myotronics) to assess muscular activities, mandibular dynamics, and joint sounds. A preliminary position of the mandible was located.
After determining the ideal position for the mandible, a lower occlusal splint was fabricated to stabilize the new mandibular position (Figure 1). After a period of 6 months, the body developed muscle engraming, or muscle memory, and recognized this new position—even without the appliance, the patient was able to hold the mandible position (Figure 2).
Polyvinyl impressions were taken using Aquasil Rigid and XLV (DENTSPLY Caulk, www.caulk.com), and the bite was transferred using DENTSPLY Regisil® bite registration material (DENTSPLY Caulk) to fabricate diagnostic wax-ups, preparation guidances, and matrices to fabricate the temporaries in the mouth.
The patient was prepared following the diagnostic wax-ups provided by the laboratory, and then temporaries were fabricated with Integrity bleach shade (DENTSPLY Caulk) and placed in the patient’s mouth (Figure 3).
The Canvas Cutback Technique
This technique was designed to preserve the strength of the incisals, canines, and premolars in the lingual areas, maintaining the full occlusal anatomical table in a monolithic structure.
After feedback from the patient, some modifications to the temporaries were taken into consideration for the final ceramic work. The case was re-waxed and pressed using IPS e.max Press Low Translucency B1. The case was then divested and the interproximal contacts were adjusted on the solid model.
The canvas cutback technique started with an approximate 0.5-mm facial reduction from gingival to incisal. This allowed layering of the entire facial surface to create a natural blend from the gingival down. The second segment of the cutback technique involved creation of a concavity from distal to mesial forming a spoon-shaped depression that did not compromise the incisal length and preserved the lingual monolithic structure of the lithium disilicate (Figure 4 through Figure 6).
After the canvas was created, the space needed to layer porcelain was complete. By using a thin layer of IPS e.max Ceram glaze paste as a foundation, and mixing universal blue stains in the incisal edge, a dramatic change in the value was achieved to create the illusion of depth or translucency (Figure 7).
A mixture of 50% IPS e.max Ceram mamelon salmon combined with Dentin A1 and Glaze paste was then placed on top of the translucency layer to produce the consistency needed to place the mamelons that would contrast with the incisal blue (Figure 8).
To control the moisture, the ceramist proceeded by carefully sparkling IPS e.max Ceram Opal 1 on top of the layered surfaces (Figure 9). This was done to create a more static effect and to texturize the mamelons in a more irregular manner (Figure 10 through Figure 12).
It was important at this point to pay attention to the mamelons to ensure that they were not flat and that the canvas was maintaining the silhouette and holding the enamel layers (Figure 14). For the internal layering of the crowns, IPS e.max Ceram Opal 1 was applied in the mesial and distal areas of each crown because these areas needed to show more translucency (Figure 15).
A contrast was created on top of the mamelons by applying white and blue vertical stripes using IPS e.max Ceram Incisal 1 and Incisal 3 (Figure 16 and Figure 17). This mixture of values created a diffusion layer that would slightly block the mamelons’ effect. Layering was continued until reaching the premolar area. Figure 18 shows the layering effect before firing.
After creating this internal matrix, the final contour layer could be applied to complete the final canvas and enhance the natural effect of the full final contour (Figure 21). The final layer consisted of a mixture of 50% Opal 5 mixed with transparent neutral to create a warm translucent effect in the gingival area (Figure 22).
Now it was time to enhance the line angles with Opal 4 (Figure 23 and Figure 24). A blend from the gingival to the incisal was created using a combination of Opal 3 and Ti 1 in the middle section of the crown to complete the full contour (Figure 25 and Figure 26).
The crowns were fired a third time at 740° with a 30-second hold time (Figure 27). After firing, the case was seated on the solid model to control the contour and adjust the contacts (Figure 28). After adjusting the contacts on the solid model, an initial delimitation, or sketch, of the line angles was marked to create the areas of reflection and deflection of light (Figure 29).
Next, a drawing showing the depression areas and horizontal texture was marked (Figure 30 and Figure 31). After the drawings were completed, a low-speed handpiece was used to follow the pattern of the marked trace, first following all the depressions (Figure 32) and then the vertical and horizontal textures (Figure 33). After all of the teeth were texturized, the texture was controlled with some water (Figure 34) and final detailing was evaluated using Highlight gold powder (American Dental Supply, www.americandentalinc.com) (Figure 35 and Figure 36).
The restorations were final stained, glazed, and fired at 730° with a 40-second hold. Note the final internal effect of the incisal edges on the finished case (Figure 37 through Figure 40). Figure 41 and Figure 42 show the final restorations seated in the patient’s mouth.
About the Author
Javier Vasquez, DMD, MICCMO
Neuromuscular Technician and Master Ceramist
Doral Dental Lab