A novel method for monitoring the maxillary tooth movement during orthodontics in 3D space.

AIM: The present study aimed to develop a method for measuring 3D maxillary tooth movement during orthodontic treatment and to verify the accuracy of the method. MATERIALS AND METHODS: A 3D model analysis method was established to measure tooth movement by combining the effects of CBCT and intraoral scans. Transformation matrices were used to abstract the motion features of the teeth and translate them into translations and rotations. To test the validity and reliability of the method for clinical application, the inclination of the central incisor was measured using a 3D model analysis method and cephalometric analysis. Measurement error, correlation, and agreement between the two methods were analyzed using the Dahlberg formula, intraclass correlation coefficient, and Bland-Altman analysis, respectively. The performance of the 3D model analysis method was evaluated by monitoring the canine movement of a patient who underwent a premolar extraction. RESULTS: The measurement error was 0.58 degrees for the 3D model analysis and 2.02 degrees for the cephalometric analysis. There was no significant difference in the central incisor inclination measurements between the cephalometric and the 3D model analyses methods. A high correlation (0.974) and narrow limits of agreement (-3.55 degrees, 4.16 degrees) were obtained between the two methods. Minute movements and additional details of orthodontic tooth movements could be observed using the 3D model analysis method. CONCLUSION: The 3D model analysis method was reliable and reproducible for clinical application in monitoring the 3D maxillary tooth movement during orthodontic treatment. The trueness should be further evaluated. (Int J Comput Dent 2023;26(1): 49-0; doi: 10.3290/j.ijcd.b3818301).

Frequency-related viscoelastic properties of the human incisor periodontal ligament under dynamic compressive loading.

Studies concerning the mechanical properties of the human periodontal ligament under dynamic compression are rare. This study aimed to determine the viscoelastic properties of the human periodontal ligament under dynamic compressive loading. Ten human incisor specimens containing 5 maxillary central incisors and 5 maxillary lateral incisors were used in a dynamic mechanical analysis. Frequency sweep tests were performed under the selected frequencies between 0.05 Hz and 5 Hz with a compression amplitude that was 2% of the PDL's initial width. The compressive strain varied over a range of 4%-8% of the PDL's initial width. The storage modulus, ranging from 28.61 MPa to 250.21 MPa, increased with the increase in frequency. The loss modulus (from 6.00 MPa to 49.28 MPa) also increased with frequency from 0.05 Hz- 0.5 Hz but remained constant when the frequency was higher than 0.5 Hz. The tanδ showed a negative logarithmic correlation with frequency. The dynamic moduli and the loss tangent of the central incisor were higher than those of the lateral incisor. This study concluded that the human PDL exhibits viscoelastic behavior under compressive loadings within the range of the used frequency, 0.05 Hz- 5 Hz. The tooth position and testing frequency may have effects on the viscoelastic properties of PDL.

Viscoelastic properties of human periodontal ligament: Effects of the loading frequency and location.

OBJECTIVES: To determine the viscoelastic properties of the human periodontal ligament (PDL) using dynamic mechanical analysis (DMA). MATERIALS AND METHODS: This study was carried out on three human maxillary jaw segments containing six upper central incisors and four lateral incisors. DMA was used to investigate the mechanical response of the human PDL. Dynamic sinusoidal loading was carried out with an amplitude of 3 N and frequencies between 0.5 Hz and 10 Hz. All samples were grouped by tooth positions and longitudinal locations. RESULTS: An increase of oscillation frequency resulted in marked changes in the storage and loss moduli of the PDL. The storage modulus ranged from 0.808 MPa to 7.274 MPa, and the loss modulus varied from 0.087 MPa to 0.891 MPa. The tanδ, representing the ratio between viscosity and elasticity, remained constant with frequency. The trends for storage and loss moduli were described by exponential fits. The dynamic moduli of the central incisor were higher than those of the lateral incisor. The PDL samples from the gingival third of the root showed lower storage and loss moduli than those from the middle third of the root. CONCLUSIONS: Human PDL is viscoelastic through the range of frequencies tested: 0.5-10 Hz. The viscoelastic relationship changed with respect to frequency, tooth position, and root level.

Tensile testing of the mechanical behavior of the human periodontal ligament.

BACKGROUND: The periodontal ligament (PDL) plays a key role in alveolar bone remodeling and resorption during tooth movements. The prediction of tooth mobility under functional dental loads requires a deep understanding of the mechanical behavior of the PDL, which is a critical issue in dental biomechanics. This study was aimed to examine the mechanical behavior of the PDL of the maxillary central and lateral incisors from human. The experimental results can contribute to developing an accurate constitutive model of the human PDL in orthodontics. METHODS: The samples of human incisors were cut into three slices. Uniaxial tensile tests were conducted under different loading rates. The transverse sections (cervical, middle and apex) normal to the longitudinal axis of the root of the tooth were used in the uniaxial tensile tests. Based on a bilinear simplification of the stress-strain relations, the elastic modulus of the PDL was calculated. The values of the elastic modulus in different regions were compared to explore the factors that influence the mechanical behavior of the periodontal ligament. RESULTS: The obtained stress-strain curves of the human PDL were characterized by a bilinear model with two moduli (E1 and E2) for quantifying the elastic behavior of the PDL from the central and lateral incisors. Statistically significant differences of the elastic modulus were observed in the cases of 1, 3, and 5 N loading levels for the different teeth (central and lateral incisors). The results showed that the mechanical property of the human incisors' PDLs is dependent on the location of PDL (ANOVA, P = 0.022, P < 0.05). The elastic moduli at the middle planes were greater than at the cervical and apical planes. However, at the cervical, middle, and apical planes, the elastic moduli of the mesial and distal site were not significantly different (ANOVA, P = 0.804, P > 0.05). CONCLUSIONS: The values of elastic modulus were determined in the range between 0.607 and 4.274 MPa under loads ranging from 1 to 5 N. The elastic behavior of the PDL is influenced by the loading rate, tooth type, root level, and individual variation.