What Ingot do I use for this crown? This is a daily call received at Williams Dental Lab. We are happy to support our doctors that have “in office” milling systems at any level we can. These calls are what prompted us to gather all of our resources, and put out some relevant information that can be understood easily.
There is a simple breakdown, and explanation, for the concept of choosing an ingot or a milling block for your CAD/CAM milling unit. If this is understood, it will be a simple process to pick a block or ingot for your crown.
There is a large variety of shades and opacity levels available in the Ivoclar E.max System. Starting with opal and value ingots and blocks; there are HO, MO, HT, LT, MT, Value 1, 2, 3, and Opal 1 and 2. Right now, you might be asking yourself, “Why so many?” A systematic approach should be considered which takes into account three variables that, uses the following criteria:
- Desired shade
- The underlying shade of the tooth prep
- Thickness of the restoration.
The next most important concepts are:
- Are we attempting to give the patient back their original shade using the color of the natural dentin as a background, or do we need to mask an undesirable background color and establish the hue and chroma within the restoration?
- Regardless of color background, and based on the tooth reduction, are we attempting to replace only enamel or both dentin and enamel? If only enamel, there is specific ingots made just to replace enamel.
In cases where we have complimentary color preps, our choices are simple. We will choose either Low Translucency (LT) ingots- milling blocks or High Translucency (HT). The answer to which of these are more appropriate is found by answering question #2. If we are replacing only enamel, one of the HT or Impulse Opal ingots-milling blocks will be appropriate.
If we must also replace dentin, the choice is either MT, Impulse (Value) or LT. In cases where an undesirable background color is present, such as dark, discolored dentin and if there is Tetracycline staining, metal posts, or implant structures, etc., the milling block-ingot of choice will typically be Medium Opacity (MO), High Opacity (HO), or a much higher value (brighter LT block).
The ability to achieve masking in these cases relies on an adequate tooth reduction to give sufficient thickness in the framework (coping) material without compromising the space needed to build both dentin and multiple enamels for esthetics. It should also be pointed out that a CAD/CAM custom implant abutment (whether, eMax, Zirconium or anodized Titanium metal) should be designed to accommodate 2mm of facial porcelain thickness for proper value control on implant restorations.
Ivoclar E.max is much stronger than its predecessor Empress. In the past, doctors have been willing to put up with the “perceptual” less than stellar aesthetics of eMax in exchange for strength in a restoration.
Why is that necessary?
At Williams Dental Lab, we feel strongly that eMax got a bad reputation for being grey (low value) due to incorrect ingot and block selection when E.max was initially introduced. Two years before Ivoclar released E.max, Williams lab was given the privilege to work with this material, and provide R &D feedback, as well as, our professional opinions about the product. Williams Dental Lab found out, quickly, that there needed to be a proper ingot and milling block selection chosen. It was always grey and low in value. If we didn’t choose an entire shade HIGHER in value, the result was lacking vitality (lifeless and too grey in appearance). It became clear, in the infancy of E.max, that the simplest way of making the restorations as aesthetic as Empress, was to use a higher value more opacified ingot-block, cutback, and layer it with a veneering ceramic. We use either E.max Ceram or GC LiSi veneering ceramic.
We must remember that most shade guides and shade tables are designed with a single thickness which correlates to the primary indication for the given ingot translucency. What this means is that for the HT blocks-ingots, and Opal blocks-ingots, which were designed to be used for enamel replacement only, the shade guides are designed to be 0.8 – 1.0 mm of thickness. If the restoration is thicker than 1.0 mm, even if you choose the correct ingot, the result is lower value and too much translucency. The choice is either: select a higher value HT ingot/block or select an LT ingot or block, and cut back and layer it. For the LT ingot/blocks, which were designed for dentin and enamel replacement, 1.2 – 1.5 mm, and for the MO and HO ingots, the shade guides are based on the minimum frame thickness of 0.6 mm with subsequent dentin and enamel layering.
The last deciding factor in the equation is the actual thickness of the restoration. As thickness varies, the optical translucency of the restoration will also change, and the influence of the underlying color will vary. If the restoration is thick, the underlying color will have less to no effect. If the restoration is thin, the underlying color can heavily influence the final outcome. Essentially, the thinner the wax-up (digital design), the greater the influence from the underlying structure (tooth, core build-up or metal object).
There is one final point to consider: With all the complex variables, the technician-dentist-assistant has to consider, sometimes, the ingot or block selection can come down to a choice between several potentially usable shades or translucencies. When in doubt, we always try to error on the side of slightly higher value and lower chroma. Our Williams Dental Lab technicians would always suggest choosing a brighter shade and warming it down to the correct shade. It is a relatively fast and simple color correction exercise to add chroma (color) or to lower value and decrease brightness. Eliminating unwanted chroma, or attempting to raise value, is far more complex (almost impossible without remaking) and frequently produces undesirable results. Ingot Shade Conversion Table