Diederik Hentenaar

131 Influence of the cervical crown contour Crown contour assessment A new measurement protocol using image processing software (Rasband, W.S., Image J, U. S. National Institutes of Health, Bethesda, Maryland, USA, https://imagej.nih.gov/ ij/, 1997-2018) was developed. The protocol was as follows: first, calibration of the peri-apical radiograph in Image J was performed using the known implants lengths. After this, the apical-coronal direction of the implant position on the radiograph was assessed. For this purpose a vertical line was drawn through the middle of the implant axis, after which the angulation was computed. Parallel to the implant axis, on the first, second and third mm of the crown length, angles were assessed by calculating α (see Figure 1). A tangent function [tan(α) =’opposite side’/’adjacent side’] was used with the known lengths of the ‘adjacent side’ (1 mm, 2 mm, 3 mm respectively) and the measured lengths, using image J, of the ‘opposite side’. Negative ‘opposite side’ values (crown contour on the inside of the ‘adjacent side’) were considered as ‘0’ degree angle, since we assumed no additional influence from under-contoured crown areas compared to 0 degree angles. An online calculating tool (https://www.rapidtables.com/calc/math/ Arctan_Calculator.html) was used for inverse tangent (tan -1 ) calculation. Accordingly, angle α could be calculated. Chapter 6 Figure 1. Example of cervical crown emergence angle measurement on a peri-apical radiograph using tangent geometry. Figure 1. Example of cervical crown emergence angle measurement on a peri-apical radiograph using tangent geometry. 6