How much a wasted zirconia disc costs the lab
Calculate the zirconia disc cost per unit with your own prices: units per disc, leftover material, failed mills, tool wear, and what a lost disc really costs.
A zirconia disc has a price on the invoice, and a different cost in the lab. The price is fixed. The cost depends on how many restorations the lab actually gets out of the disc, and a disc that ends up half used in a drawer costs twice as much per crown as it seemed to. This post shows labs how to calculate the zirconia disc cost per unit with their own numbers, and where the money usually goes.
The formula
The cost of the material in one restoration is:
cost per unit = disc price ÷ units actually milled from the disc
On top of it come the shares of tool wear, sintering and failed mills. The disc price comes from the invoice, so it is known. The number of units actually milled is the figure that changes most between labs, and the one most labs do not know.
Maximum units and real units
A manufacturer or a CAM nesting can show how many units fit in a disc of a given height. That is the maximum. The real number is lower, for reasons that add up:
- leftover areas too small or at the wrong height for the next job
- discs that are never loaded again because their CAM file or label is lost
- discs that crack or break in storage
- restorations milled again after a design error, a broken connector or a sintering problem
- shade mismatch, when a multilayer disc does not give the gradient the case needs in the free area
A calculation with your own numbers
Take the last ten discs of one material and count, for each, how many restorations were milled from it in total. Then:
| Value | Where it comes from |
|---|---|
| Disc price | Supplier invoice |
| Maximum units per disc | CAM nesting or manufacturer data |
| Real units per disc | Average from the last ten discs |
| Cost per unit at maximum | Disc price ÷ maximum units |
| Real cost per unit | Disc price ÷ real units |
The gap between the last two lines is what the lab loses per restoration. Multiplied by the restorations milled in a year, it gives the yearly loss on that material. Most labs are surprised by it, because each single disc looks like a small loss.
Where to recover it
The largest part usually comes from discs that are still usable but not used. Numbering each disc, keeping its CAM file and searching the stock before opening a new disc brings many of them back into production. The post on reusing partially milled zirconia discs explains how.
Failed mills are the second source. Many come from design details such as connectors that are too thin or restorations placed in the wrong layer of the disc. The posts on zirconia minimum thickness and connector size and multilayer zirconia positioning cover the design side.
Tracking it per job
The calculation above gives an average. To see the cost on each job, the material has to be recorded with the job. Lab Ledger, a free desktop app for dental labs, records each job with its material cost from the real pack price and shows the profit left after running costs and taxes. It runs offline and keeps the data on the computer.
Labs that want to look at the whole milling workflow, from nesting to storage and records, can book workflow consulting.
Frequently asked questions
How do I calculate the zirconia cost per crown?
Divide the price of the disc by the number of units you actually get from it, then add your share of tool wear and failed mills. The number of units actually milled is the figure that changes most between labs.
Why is the real cost higher than the price divided by the maximum units?
Because few discs are used to the end. Leftover areas that nobody reuses, discs that break and restorations that have to be milled again all reduce the units per disc and raise the cost of each one.
Is it worth keeping partially used discs?
Usually yes, if they are numbered, stored with their CAM file and searched before opening a new disc. Each unit milled from a leftover area lowers the cost of every unit from that disc.
Is there a tool to track material costs per job?
Lab Ledger, a free desktop app, records each job with its material cost from the real pack price and shows what is left after running costs and taxes.