In Vivo Assessment of Natural Tooth Color After Orthognathic Surgery. A Pilot Controlled Clinical Trial

Overview

In six consecutive patients planned to receive combined orthodontic-orthognathic surgery natural tooth color on 8 incisors was measured before initiation of the combined treatment (Time Point 1- baseline) and after its completion (Time Point 2- after intervention). The statistical interpretation of the results showed that tooth color change in the surgical group was higher in comparison to control groups. Control group I included non treatment subjects, while control group II included standard orthodontic treatment subjects. The results indicated that orthognathic surgery may affect natural tooth color but to small degree, as the color differences were just bellow the threshold value of 3.7 ΔΕ units. Under this value a color change cannot be easily detected by a human eye.

The method of natural tooth color assessment included the use of the spectrophotometer Spectroshade Micro (MHT Zurich, Switzerland), which is a reflectance spectrophotometer with a LED technology light source with an output of 410-680 nm that is transformed into monochromatic light (λ = 400-720 nm) by means of grating. On this type of spectrophotometers, light is split so that teeth can be illuminated simultaneously from two sides at a 45° angle with the use of an intra-oral camera. The reflected light is directed at 0° on two detector areas (each detector area surface is of 18 x 13 mm2). One detector area is a color CCD chip responsible for the generation of the colored video image. A black-and-white CCD detector area records the spectrophotometric data. During a measuring process, light originating from the monochromator of the device is emitted in 10-nm intervals. Resulting images consist of 300,000 pixels. Initially, CIE tristimulus values are calculated and then converted to CIE-Lab values with the use of the accompanying software. Prior to every measuring cycle, the spectrophotometer had to be calibrated to a white and a green ceramic tile that are incorporated on the base of the device by the manufacturer. Assessments were performed with closed lips in order to exclude disturbance by daylight. In order to avoid methodical errors in the assessment of luminance teeth of the upper and lower dental arches were not in contact, thereby obtaining a uniform black background by the oral cavity without an overlapping of anterior teeth. Tooth color was measured in the study and in the control groups at Time point 1 and Time Point 2. To enhance reliability of the method two sequential pictures of each tooth (Left + Right) were obtained with the use of the spectrophotometer and imported to the dedicated MHT Spectroshade software v3.01 Build 1007a (MHT Zurich, Switzerland), licensed to Aristotle University (Station ID: 952317337-Serial NR LUA164-164-164). Using the synchronization tool followed by the synchronous measurement tool, the cursor was accurately positioned on the center of the clinical crown on both pictures simultaneously, and the software reported color measurements for both pictures. The cursor shape was a circle, while the size was set at 100 pixels. Due to the synchronization of the pictures, the cursor area was exactly the same for both. To consider the method reliable, the maximal allowed color difference between the two consecutive pictures, was set at ΔΕ≤1.