The impact of surface dimensions on the accuracy of an intraoral scanner

Intra-oral scanners are being used to measure small changes to the surface form. This study aimed to identify the limits of detection of an intra-oral scanner (IOS) on depth and width of surface form.

We performed investigations on artificial teeth with increasing width and depth of discrete surface features captured by an intra-oral scanner at baseline and compared the data to a gold-standard white-light profilometer (WLP). 81 surface features with widths varying between 150 - 1300 µm and depths 5 - 360 µm were scanned five times using the WLP (n = 405) and IOS (n = 405) and analysed using a validated registration and subtraction algorithm. Both scan outputs used reference and an iterative closest point (ICP) registration to the Z-axis to analyse change and control variation of data. 2D maximum step height depth (µm) and 2D width (µm) of the surface features were calculated.

The depth measurement error of the IOS had a negative linear association to width (Pearson correlation = - 0.87 (95 % CI - 0.90, - 0.82 p < 0.001 and r² = 0.76). The error of depth measurement was 100 % at 250 µm, 20 % at 750 µm and 0 % at 1200 µm. Overall, the IOS overestimated surface feature width by 155.5 µm and underestimated surface feature depth by -20.2 µm.

The accuracy of the IOS to capture surface features improved above 750 µm in width and was close to 100 % accuracy at 1200 µm. Caution is needed if an IOS is used to measure surface features below 1200 µm in width.