White Zirconia, Pre-Shaded Colored Milling Discs, Which Is RIGHT For You

As the Operation Manager at Vsmiles, I've spoked with hundreds of different lab owners during last year. This vast amount of dialogue provides me with an awareness of the practices, questions, and concerns of the average dental lab.

Most often discussed are the advantages and disadvantage of the White Zirconia vs. Pre-Shaded milling discs. While some labs mill strictly white, others are strictly shaded, and some mill a combination of both. Although multi-layered (gradient shade) Zirconia is receiving growing attention, for the sake of this article, we are discussing strictly White Zirconia vs. pre-shaded discs.

Lab owners are seeking to satisfy three basic criteria when choosing a zirconia disc:

● Quality and Consistency of the final glazed product

● The efficiency of the manufacturing process

● Cost of the Zirconia Discs

So we decided to compare White zirconia discs to Pre-Shaded Zirconia discs in each of the three areas noted above, wish that can be help.

1. Quality and Consistency of the Final Glazed Product Winner is: "A Tie"

● Quality of the final glazed product goes to: "White Zirconia"

● Consistency of the final glazed product goes to: "Pre-Shaded"

Quality:

The White Zirconia zirconia disc offers the dental lab technician a pre-sintered "Blank Canvas" to create a life-like dental restoration. With incisal tone and inhibitor kits such as the AMS Incisal Tones product, the lab technician can build all the character traits they desire into every tooth they color. This process gives the technician the greatest ability to acquire the most natural transition from the gingival shade to the incisal shade. With every tooth having its own shape and height the technician can characterize the pre-sintered tooth to meet the appropriate requirements. The subtle downside to this process is that because each crown has a very different total mass of zirconia there can be some inconsistencies with the way the zirconia absorbs the colorant, leaving the post-sintered tooth too light or even worse, too dark.

Consistency:

The pre-shaded disc offers the technician the most consistency in terms of acquiring an accurate post-sintered base shade. That statement is assuming good manufacturing practices are followed by the zirconia disc manufacturer. But this consistency of the base shade comes at the cost of having no blend transition from gingival shade to incisal shade. This must be accomplished at the lab bench.

Summary:

We consider this category a tie. Although the White Zirconia has the best potential for the best final product, we also need to consider the benefit that pre-shaded offers for consistency.

2. Efficiency of the manufacturing process winner is: "White Zirconia"

In coming to our conclusion we considered the following factors:

● Group Nesting and Milling

● Post Processing Calculation Times

● Mill Swap-out/Set-up Times

● Post-Milling Labor Times

Group Nesting and Milling:

With White Zirconia, the lab technician only needs to sort and nest by tooth height. This allows the technician to group more teeth together in one disc for more efficient nesting times and more efficient milling times. Every time you start a new nesting project it costs you time to load the required disc and save a new file. Your mill also mills more efficiently due to fewer machine tool pick-ups while milling larger groups.

Alternatively, with pre-shaded discs, grouping by height and shade means more nesting loads and smaller machine runs. Both of these add to the inefficiency factor. When your machines are capable of milling at a rate of $300-$400 dollars, every 15 minutes of inefficiency costs your lab $75-$100.

Post Processing and Calculation Times:

At the end of every nesting sequence, the lab technician must run the post-processing calculation to create a file the mill can read. We have found that smaller groups of nested teeth add to the inefficiency factor. Here is an example of what we mean: Nest only one tooth and the post processor might take 2-5 minutes to calculate depending on your specific nesting software. Nesting 10 teeth DOES NOT add 10 times to the post-processing calculation times. The more teeth you nest, the less time 'per tooth' is required to run post processing. The more teeth you nest per time, the less time per tooth required. We also find that technicians tend to walk away during the post-processing. The computer may sit unattended for several minutes once the processing is complete. The more nesting solutions per day, the more the computer sits idle at the end of each run. Nesting larger groups of 6-10 teeth at a time is most efficient, and only possible with White Zirconia.

Mill Swap-out / Set-up Times:

Smaller groups of nested discs require more attention. We have found that mills tend to sit unattended once the mill has completed its milling cycle. Smaller groups mean more disc swap-outs/set-ups which take more man-hours and increase the chance for the mill to sit unattended waiting for the disc to be changed out. Larger runs make your mill more efficient and require less human attention. This is only possible with White Zirconia.

Post-Milling Labor Times:

This is the one area where pre-shaded has the advantage. Once the tooth has been separated from the disc, it only needs to be cleaned of all dust and it is ready for the oven. The White Zirconia, on the other hand, must be sorted by shade and then colored. In our milling center, sorting and coloring takes 75 seconds per tooth. Assuming 40 crowns per day, this only adds one hour of labor to the lab technician. We believe this one hour is easily offset through the efficiencies gained in nesting and milling.

Summary:

We believe that White Zirconia wins the overall efficiency evaluation even with the added labor of coloring by hand, which we also find saves time at the final stain and glaze procedure. The efficiency from file sorting, nesting, post-nesting processing, and milling machine disc changes makes White Zirconia the clear winner.

3. Cost of Zirconia Discs winner is: "White Zirconia"

● Per Disc

● Total Inventory Requirements

Per Disc Cost:

White Zirconia vs. Pre-Shaded cost per disc clearly goes to White Zirconia. The average cost difference of a 98mm x 12mm disc is about $10 per disc. This raises your cost for one pre-shaded tooth by about $1. By comparison, a White Zirconia tooth absorbs about (20 cents) worth of coloring liquid per tooth. At 40 teeth per day this will cost your lab over $8,000 per year or about $700 per month.

Total Inventory Requirement:

White only requires that you inventory the varies thicknesses of discs. To inventory Pre-Shaded, you must inventory the varies thicknesses and the various shades in combination. Although the Vita Classic shade guide has 16 shades, we find that the average lab keeps about 10X the amount of Pre-Shaded Zirconia stock than that of a lab using White Zirconia.

Summary:

It is considerably less expensive to mill in White Zirconia vs Pre-Shaded allowing you to reduce your total cost of production.

Article Summary:

Using pre-shaded discs provides you with the benefit of a consistent Chroma Color in the gingival 1/3 of the tooth along with the ability to go straight to sintering post-milling.

White offers you the best opportunity to achieve a more natural appearing restoration with a transition from Chroma Effect to Enamel Effect.

White is more efficient during the Nesting, Post Processing, and Mill Swap-out/Set-up processes.

White is less expensive per disc and requires less total inventory.