Designing the inside of the crown

Aus Amann Girrbach
Version vom 5. Januar 2017, 10:47 Uhr von WikiSysop (Diskussion | Beiträge) (The cement gap)
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This step covers the design of the inside of the crown/inlay – the part that will be in contact with the preparation. This part of the construction, and the parameters involved, are crucial for proper fitting. In case you are not happy with the fitting of the produced part, it's here where you should look for possible parameter changes.

The cement gap

Kronenboden 2.png

The thickness of the cement gap can be set using the slider [1]. The default value corresponds to the setting in the Ceramill Mind record card. Changes made here only apply for the current design (in contrast to changes in the Ceramill Mind record card, which then apply as new standard values with the dentist selected). Move the slider [1] to alter the thickness of the cement gap – changes are adapted in real time, the effects of the action can therefore be seen immediately.

A click on the text “Add another area” [2] activates an additional slider, which can be used for marking a second cement gap area and defining its thickness.

Areas of the crown base can be individually defined using the brush function. To define an area click on the “Brush” button [3] and mark the required area on the crown base with a left click.

The slider “From the margin” [4] defines the start of the cement gap in relation to the preparation margin in millimetres. If, for example a value of 1 mm is selected, the surface [6] in an area of 1 mm around the preparation margin will not have a cement gap. In the same way the end of the cement gap can be specified “from the top” [4] using the slider to define a surface [8] without a cement gap in the occlusal area of the crown. The arrow [9] shows the path of insertion again. If this arrow is highlighted red, the die has undercuts in the area of the preparation margin using the selected path of insertion.

Tip With the second cement gap, e.g. very sharp edges on the die can be blocked out more extensively.

Additional spacing

By unfolding the „Additional spacing“ expander, you will get access to options [10] and [11] which allows you to add additional spacing.

  • This can be defined separately for axiale and radial direction by using the slider [10].
  • Additional spacing is also applied in the area where there is no cement gap
  • Additional spacing is applied in addition to the cement gap in area where there is a cement gap
TipThe higher the values here, the looser the fitting. You can also use negative values here, to create a tighter fitting.

Desiging the crown border

Kronenboden Rand.PNG

The second tab of the „Crown Bottoms“ dialog gives you access to parameters that define the shape of the crown border. The graphic [5] gives an illustration of meaning of the sliders [1-4].

[1] Defines the horizontal crown border width. Typically, material properties enforce certain limits here; e.g. for Zirconia a common minimum value is 0.2mm.

[2] Defines the length of the angled part of the border. This may commonly be set to zero.

[3] Defines the angle of the angled part.

[4] Defines an additional vertical border. Commonly this is also set to zero.

Dealing with undercuts

Kronenboden Unterschnitte.PNG

The third tab in the „Crown bottoms“ dialog gives you access to undercut-related options and milling parameters.

Undercuts in the preparation are blocked out by default, unless you specifically choose not to do so, by checking checkbox [1].

A certain (small) angle may be applied for blocking out undercuts, as defined by [2]. By default, a value of zero is used, meaning that undercuts are blocked out „straight down“. Slider [3] defines an „untouchable zone“ around the preparation margin, where the crown is never blocked out, even if it should be (due to undercuts being present above). We will further elucidate the effect of this option with an example. Consider the two images below (for this tooth, we have intentionally set an incorrect insertion axis to illustrate the problem).

Kronenrand 01.PNG Kronenrand 02.PNG

The graphic on the left shows the behavior with „Don't block out zone near prepline“ set to 1mm. Observe how the upper part is blocked out, but as soon as the untouchable zone is reached, the crown bottom will go back to the preparation (note that it is not possible to produce this kind of restoration with Ceramill Motion). The graphic on the right shows behavior with „Don't block out zone near prepline“ set to zero. As you can see, the crown will not be in contact with the preparation around the margin. In both cases, the result will be non-optimal and the restoration will need manual work (either by manual milling, or by adding ceramic) for a proper fit. It is up to the operator to decide which option may be better in the particular clinical case.

TipIf at this point in the construction, you find that the insertion axis is not optimal, you can still easily change it: Right-click on the tooth for which you'd like to change the insertion axis, and choose „Set insertion direction“. You can then change the insertion direction by orienting the view to the insertion direction and clicking „Set current view as insertion axis“.
Einschubrichtung Korrigieren.png

Any parameters you change in this screen will not be applied in real time, as these are computing-intensive operations. Click „Apply“ [5] to see the effect of your changes. To visualize undercuts which remain (e.g. due to usage of „Don't block out zone near prepline“), click the „Show undercuts“ button [4].

When done, click „Next“ to proceed to the next step.