The impact of 3D printer accuracy on the trimming quality for the in-house clear aligner production

Clear aligner in-house production has become popular for orthodontists in the last 5 years after treatment plan software, thermoform machine and trimming machine are available and affordable. In-house production reduces costs, lead-time and increase customer satisfaction, but the quality control is an issue for most orthodontists and technicians.

Clear aligner quality is affected by many factors like trimming machine structure, trimming process, foil, 3D printer and others. The impact of 3D printer accuracy is often underestimated. The printed models are not comparable to stone models because of the contraction and limitation of different additive manufacturing processes. Furthermore, dental model has complex surface and is very hard to measure, therefore users have no idea of actual accuracy of their printed models.

The article ‘Evaluation of current additive manufacturing systems for orthodontic 3-dimensional printing’ of American Journal of Orthodontics and Dentofacial Orthopedics, October 2021, evaluates and compares linear and surface accuracy of dental models fabricated using 3 different vat photopolymerization printing units.

The picture above shows the deviations could be up to 0.25mm and comparing the foil thickness 0.76 mm prior the thermoform, the deviation is big enough to influence the trimming quality. The printed models are bigger/smaller than the original STL file, but the trimming machine calculates toolpath based on the original STL file, the consequent is some areas of model are not cut through while some areas are cut deeply than normal. To overcome this deviation cut depth must be adjusted either in software or physically. Quark’s trimming machines KA-120/KA-200 are able to set the cut depth in software once the deviation is known.

In additional, to hold the model on the trimming machine fixtures or locators are designed on the model STL, they are mostly holes, slots or some geometries. Sometimes the deviation of printed fixtures will make even worse issues if the fixtures are not hold well and the model moves during trimming process. Quark’s trimming machines KA-120/KA-200 fixture uses 3 elastic pins to ensure the strong and reliable holding to achieve the best trimming quality.

Accuracy of 3D printer is one of the factors which impacts the quality of the trimming, understanding the fact will help orthodontics to manage the process of clear aligner in-house production better and effective.