Clinical Continued »
design is completed (Figure ı0). At the end of the appointment, an impression is taken. Then the mock-up impression can be used to make the provisional restora- tion (Figure ıı). A preparation based on this principle of tissue conservation ensures that only necessary enamel surfaces need to be adjusted for aesthetic and functional results.
Limitations of the technique In certain specific cases, when one or more teeth are malaligned from the desired archform, it will be necessary to prepare and reduce these teeth first. This prevents any risk of incorrect positioning of the thermoformed index or the impression when doing the mock- up. To ensure a perfect placement of the mock-up impression over the teeth, one should check first that the initial reduction is enough with the help of a silicone index. The labial surfaces are fully
ALL-CERAMIC RESTORATIONS
All ceramic crowns
Pressed veneers (leucite, lithium disilicate)
Feldspathic veneers
LABIAL 1.2 0.8
0.6
MINIMUM THICKNESS (IN MM) LINGUAL OCCLUSAL
1.2 Not
applicable Not
applicable
Table 1 : Minimum thickness recommended for different ceramic types on a non-discoloured substructure
REFERENCE (ISO)
868B 834
801 L 801 L
DIAMETER OF CHUCK
1.6 mm 1.6 mm
1 mm (top part) 1 mm (top part)
DIAMETER OF BUR (ISO)
2 mm (020) 2.1 mm (021) 2.3 mm (023)
2.9 mm (029)
CUTTING DEPTH
0.4 mm 0.5 mm
0.65 mm 0.95 mm
Table 2: ISO references, diameters and cutting depth of selected burs for veneer preparations
involved in this technique. However, when it comes to the palatal area, it is difficult to extend this technique for partial crowns. With the help of the silicone
indexes, it is possible to visually control the situation in static and dynamic occlusion and to ensure a proper thickness of material.
1.5 1.5
1.5
Conclusion Saving tooth structure should be the foremost concern because it ensures both a better longevity and, more importantly, makes future interventions more feasible. Each decision and clinical intervention should be made taking a therapeutic gradient into consideration. When it comes to tissue conservation, it is fundamental to recognise that bonding to enamel is far superior to that to dentine when indications call for adhesive bonding. In other words, all techniques
that make it possible to preserve enamel should be favoured when the thickness of the restoration allows this. The most successful development in this respect is based on the management of the final mock-ups, used as a template for the preparation, associated with drills of optimal shape for a controlled penetration.
® Full references for this article are available upon request.
64 Scottish Dental magazine
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