The decades old method of capturing a patient’s tooth morphology and related oral structures has involved taking a physical impression of some form and pouring that impression with some form of gypsum or resin product. Depending on the contraction rate of the impression material, one can determine what expansion rate the gypsum should roughly be to compensate for the shrinkage of the impression material. It is sort of a tug of war with the ultimate goal of producing a dental model as close to the dental structure in size and shape as possible.
Why does this matter? Well, imagine a gypsum material with an expansion that was too high. The model ends up too large (on a micron level, of course). This could potentially result in a restoration too large for the preparation interproximally as well as occlusally. This result leads to extensive adjustments chairside, costing time, money and lots of frustration for the dentist and assistant. Not the least of which to the patient, who already may be anxious about the entire process.
Conversely, if the expansion is too low, we could end up with a smaller than ideal restoration with light or open contacts and potentially out of occlusion. Getting the right size gypsum model can be tricky and can vary from doctor to doctor, depending on the contraction properties of their particular impression material.
Now with the advent of printed models as an option the game has changed. One has the option of scanning a traditional model or impression, or even scanning the mouth directly to manufacture a printed model. Once the design is processed, the model can be made solid or with removable dies or both. Multiple dies of prepared areas can even be printed for multi-use processes.
Should the ultimate printed model be off a bit in size, adjustments can be made in the design to get the correct fit for a restoration. With the files saved from the scan, the user may even want models printed out of different resins and colors. The scan will also serve as a template for not only the model but also restorations, partial frameworks, fixed restorations, night guards, surgical guides and custom trays. The digital approach can be a big time and material savings in some cases. Ultimately, every situation and facility is different and in some cases, there will be a mix of traditional and digital model fabrication.
Whichever way you choose to make models, pay attention to the manufacturer’s recommended instructions for use.