Application of principal component analysis to the elucidation of perioral soft tissue movements during mastication

Abstract

We considered that elucidation of the movements of perioral soft tissue during mastication would be useful in evaluating masticatory movements. However, the evaluation of these movements is difficult because multivariable analysis is needed. In this study, we considered whether principal component analysis (PCA), a form of the multivariate analysis, can reduce the number of degrees of freedom (d.f.) of perioral skin movements (i.e. the time-series data with 45 d.f.). The subjects were 15 healthy persons with complete natural dentition. The chosen experimental food for this study was sufficiently softened chewing gum. Over 95% of the perioral soft tissue movements of healthy subjects with complete natural dentition during mastication could be expressed by PCA using the first three principal components (PCs). Therefore, perioral soft tissue movements in these subjects during mastication were considered to be spatially smooth. Moreover, time analysis of these movements was made possible by the application of proportion diagrams. The results of this study showed that the spatiostructural and temporal analyses of the movements of perioral soft tissue during mastication made possible by the application of PCA.

Time‐series analyses of mandibular and perioral soft tissue movements during mastication

“…The system used in this study enabled measurement of three‐dimensional movements on the surface of the perioral skin and at a target point attached to a lower incisor to within 0·1 mm in accuracy without the need to attach complex measuring instruments to the subjects. The movements of target points were recorded by two charge‐coupled device (CCD) cameras, and the three‐dimensional coordinates were calculated by applying the triangle survey method to the parallax (Sakaguchi et al ., 2001a). Figure 1 shows a block diagram of this system.…”

“…The eigenvalue λ m ( λ 1 ≥ λ 2 ≥ λ 3 ≥ 0) was calculated from the covariance matrix, and then the eigenvector ( a m1 , a m2 , a m3 , ···, a m46 , a m47 , a m48 ) (m=1, 2, 3) was calculated from the eigenvalue λ m (m=1, 2, 3). The m th PC ( Z m ) could be expressed by the following linear joint equation (Sakaguchi et al ., 2001a):…”

Spaciostructural analyses of mandibular and perioral soft tissue movements during mastication

“…The target points on the skin of the lower face were marked by attaching black dots of 1 mm in diameter at 15 points, and at eight points in Camper’s plane on the skin (Fig. 3) (Sakaguchi et al ., 2001). The reference point (a black dot of 1 mm in diameter) attached to a lower incisor was set outside the oral cavity, about 20 mm in front of the lower incisor and on the occlusal plane by a bent clutch made of stainless steel, in order to allow for movement of the lower lip during mastication (Fig.…”

“…Forty‐eight degrees of freedom are needed to evaluate both the movements of 15 target points on the perioral skin (Sakaguchi et al ., 2001) and the movement of a lower incisor.…”

“…Analysis of the movements of perioral soft tissues has been carried out using X‐ray TV cinematography (Ohmori, 1979), the moire method (Kawai et al ., 1990; Chen & Iizaka, 1995), stereo photogrammetry (Leonard et al ., 1981; Motoyoshi et al , 1992), and stereo imaging (Nanda et al , 1996; Sakaguchi et al ., 2001). However, there have been no reports on quantitative evaluation of the relationship between the movements of the surface of perioral skin and the mandible by time‐series data and simultaneity.…”