Original Article
Nonlinear stress-strain behavior of periodontal ligament under orthodontic loading*,**,*,**,*,**

https://doi.org/10.1067/mod.2002.124997Get rights and content

Abstract

Previous studies of the periodontal ligament (PDL) have applied high forces to the dental units to examine the stress-strain behavior of this soft tissue. In this study, cadaveric specimens of mandibular premolars from 2 young adult and 2 elderly adult donors were tested to determine the biomechanical behavior of the PDL over an orthodontic force range. Transverse specimens were prepared from 9 premolars and subjected to loading in intrusion and extrusion. Stress-strain curves for both loading directions had distinct toe and linear regions, demonstrating nonlinear behavior of the PDL. The average linear shear modulus was higher for intrusion than for extrusion. The toe extrusive modulus was higher for the young group, and extrusive toe size was larger for the elderly group. In extrusion, the average modulus was higher for the cervical margin and the apex regions than for the midroot regions. The size of the toe region was smaller for intrusion than extrusion. The results indicate age-dependent, location-dependent, and load-direction-dependent nonlinear properties of the human PDL and suggest that analytical computer simulations of orthodontic tooth movements might benefit from incorporating the nonlinear material properties of the PDL. (Am J Orthod Dentofacial Orthop 2002;122:174-9)

Section snippets

Material and methods

Tooth specimens were harvested from 4 frozen human cadavers obtained through the University of Alabama at Birmingham's Willed Body Program. All procedures were approved by the University's Institutional Review Board (E990513003). The young donors were white men, 24 and 27 years old, and the elderly donors were white men, 78 and 79 years old. The causes of death were gunshot wound, asphyxia, cardiac arrest, and emphysema, respectively.

After thawing, each mandible was isolated, and external soft

Results

Of the 56 specimens tested, data from the 22 young specimens and the 8 elderly specimens were included in the analyses presented. Data from the remaining specimens were excluded because of PDL failure during testing. The coefficients of determination, r2, illustrate goodness of fit of the linear regressions to the experimental data.

Distinct linear and toe regions were observed for all specimens in both loading directions (Figs 4, 5, and 6).

. Extrusive shear behavior for young premolars. Toe on

Discussion

The current study offers unique information about the nonlinear elasticity of the PDL in the range of orthodontic forces for intrusive and extrusive loading of young and elderly samples. Although limited in sample size, the data from cadaveric testing show complex elastic behavior of the PDL from which 4 generalizations can be made.

The linear modulus was higher in intrusion than extrusion, indicating that less force was required to achieve an orthodontic level of stress in intrusion than

Conclusions

In this study, cadaveric specimens of mandibular premolars from 2 young adult and 2 elderly donors were tested to determine stress-strain behavior of the PDL over an orthodontic force range. The following conclusions could be made:

  • 1.

    Stress-strain curves for both intrusion and extrusion had distinct toe and linear regions, demonstrating the nonlinear mechanical behavior of the PDL.

  • 2.

    The average linear shear modulus was higher for intrusion than extrusion, suggesting anisotropic material properties

Cited by (0)

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aDepartment of Biomedical Engineering.

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bDepartment of Orthodontics.

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cDepartment of Orthopedic Research.

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dDepartment of Biostatistics.

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This research was supported by NIDCR Grant K16DE00279.

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Reprint requests to: Alan W. Eberhardt, PhD, HOEHN Room 370, 1075 13th St South, Birmingham, AL 35294-4440; e-mail, [email protected].

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