Abstract
Micro-movement of human jaws in the resting state might influence the accuracy of direct three-dimensional (3D) measurement. Providing a reference for sampling frequency settings of intraoral scanning systems to overcome this influence is important. In this study, we measured micro-movement, or change in distance (∆d), as the change in position of a single tracking point from one sampling time point to another in five human subjects. ∆d of tracking points on incisors at 7 sampling frequencies was judged against the clinical accuracy requirement to select proper sampling frequency settings. The curve equation was then fit quantitatively between ∆d median and the sampling frequency to predict the trend of ∆d with increasing f. The difference of ∆d among the subjects and the difference between upper and lower incisor feature points of the same subject were analyzed by a non-parametric test (α = 0.05). Significant differences of incisor feature points were noted among different subjects and between upper and lower jaws of the same subject (P < 0.01). Overall, ∆d decreased with increasing frequency. When the frequency was 60 Hz, ∆d nearly reached the clinical accuracy requirement. Frequencies higher than 60 Hz did not significantly decrease Δd further.
Highlights
Primary oral CAD/CAM data is generally composed of 3D point cloud dentition and soft tissue surface data
Indirect method, during traditional impression making, doctors stabilize the rigid tray using their fingers to ensure a tight contact between the impression material and the tissue surface, reducing the impact of micro-movement on impression accuracy
The most direct way to overcome the influence of micro-movement is by increasing the sampling frequency, or the acquisition rate for creation of a single 3D image
Summary
Five volunteers were included in this study, aged 27 to 30 years old, in good health, with no clear causes of involuntary systemic tremor symptoms, no alcohol habitat or physical habitual action, no severe respiratory symptoms, and normal temporomandibular joint after examination. Mark points on the stationary dental model were tracked as a group, and the resulting dataset was used as the control. The procedure was repeated three times at three different sampling frequencies (60, 150 and 300 Hz) using the optical tracking system, and 3,600. The same procedure was utilized for recording micro-movement tracks of the stationary dental model. Micro-movement tracking was re-sampled at 60 Hz at four intervals (11, 5, 3 and 2 track points) to obtain the track point trajectory at four sampling frequencies: 5, 10, 15 and 20 Hz. The 3D surface shape data of dentition and cylinder center points were obtained using the intraoral scanner. The range of Δ d of dentition on a jaw was obtained based on the Δ d of all feature points at the 60 Hz sampling frequency.
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