Effect of the Spatial Position of Transfer Fork Markers on the Accuracy of Digital Virtual Patient Registration

To investigate the impact of spatial positions of the transfer fork registration markers on the accuracy of generating a virtual dentofacial patient.

An in vitro study was conducted using a mannequin head with a standard maxillary dentition model. Radiopaque gauge markers were fixed on the face and dentition of the mannequin head. CBCT was performed and the distance and angle between the dentition and facial markers were measured in the CBCT as reference values. Intraoral scanners were used to obtain 3D morphological data of the maxilla. Two types of transfer fork were designed and fabricated. The registration markers on transfer fork A were positioned in the midline area, while those on transfer fork B were located at the corners of the mouth on both sides. The transfer forks were digitised and connected to the maxillary dentition within the mannequin head, and facial scanning was performed using a facial scanner five times in each group. A virtual dentofacial patient was built through matching and integration of digital dentition, face and transfer fork data using 3D reverse engineering software (Geomagic Wrap 2021, 3D Systems, Rock Hill, SC, USA). Measurement values including feature lengths and feature angles between six facial gauge markers and three dentition gauge markers were obtained in the virtual patients.

The mean trueness and precision of linear difference for virtual patients established using transfer fork A were -1.00 ± 0.11 mm and 0.27 ± 0.02 mm and the angle deviation was -1.88 ± 0.27 degrees, whereas for transfer fork B, the mean trueness and precision of linear difference were 2.66 ± 0.25 mm and 0.83 ± 0.06 mm, and the angle deviation was 3.74 ± 0.87 degrees. There is an overall significant difference in the trueness values of feature lengths (t = -13.963, P = 0.000) and angles (t = -5.985, P = 0.004) between transfer fork groups A and B, with group A showing better trueness and precision.

Linear and angular errors will be introduced in the process of building up a virtual dentofacial patient using a transfer fork. The trueness and precision of the transfer fork with the matching markers at the centre of the lips are more precise than the transfer fork, with matching markers on both sides of the mouth.