|
|
||||||||
RESEARCH REPORT |
Department of Orthodontics and Craniofacial Developmental Biology, Hiroshima University Graduate School of Biomedical Sciences, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan; and
1 Department of Functional Anatomy, ACTA, Amsterdam, The Netherlands
* corresponding author, etanaka{at}hiroshima-u.ac.jp
| ABSTRACT |
|---|
|
|
|---|
KEY WORDS: temporomandibular joint condylar cartilage dynamic property
| INTRODUCTION |
|---|
|
|
|---|
To measure the resistance to compression, indentation is typically applied to a cartilage sample up to the yield point. This kind of characterization of material properties is limited to static loading conditions that are in contrast to the dynamic nature of biological stresses to which skeletal tissues are subjected (Mow et al., 1989; Athanasiou et al., 1995; Hu et al., 2001; Tanaka and van Eijden, 2003). The mechanical properties depend on the rate of applied strain. In general, stiffness of the articular cartilage increases with the loading rate (Silyn-Roberts and Broom, 1990; Oloyede et al., 1992). Thus far, however, relatively little information is available on the dynamic properties of the condylar cartilage under compression (Hu et al., 2001). To characterize these properties, we investigated them in the mandibular condylar cartilage from pigs over a wide range of loading frequencies.
| MATERIALS & METHODS |
|---|
|
|
|---|
The articular surface of the condyle was divided into 4 quadrants: anteromedial, anterolateral, posteromedial, and posterolateral (Fig. 1A
). After the articular disc had been carefully dissected, the condylar head was cut perpendicularly to the condylar axis, into medial and lateral halves, by the use of a surgical knife blade. Each half was separated into an anterior and posterior section by a vertical cut parallel to the condylar axis. From each of these quadrants, a whole-thickness sample was prepared (approx. 12 x 15 mm in anteroposterior and mediolateral lengths), consisting of subchondral bone covered with the articular layer. To be able to determine the amount of applied strain for each sample, we measured the thickness of the cartilage using a needle penetration method (Swann and Seedhom, 1989). The thickness was 1.1 ± 0.2 mm (mean ± SD), 1.0 ± 0.3 mm, 0.7 ± 0.2 mm, and 0.8 ± 0.3 mm in the anteromedial, anterolateral, posteromedial, and posterolateral regions, respectively.
|
During the test, a dynamic compression was applied to the specimen by a sinusoidal strain of
=
0 + 
sin(
t), with
0 = 1.0% and 2
= 0.4%. The stress behavior was described by
=
0 + 
sin(
t +
). In the present study, each region of each specimen was exposed to oscillation frequencies ranging from 0.01 to 10 Hz: 0.010.1 Hz with intervals of 0.01 Hz, 0.11.0 Hz with intervals of 0.1 Hz, and 1.010.0 Hz with intervals of 1.0 Hz.
Dynamic Viscoelastic Parameters
Due to the viscosity, the stress-strain response was generally out of phase, and the phase difference between the stress and strain was somewhere between 0 and 90 degrees (Fig. 1B
). This response can be described by the complex compressive modulus E*, which can be decomposed into a storage modulus E' and a loss modulus E''. The former is directly proportional to the energy storage in a cycle of deformation, and the latter is proportional to the average dissipation or loss of energy. The loss tangent, tan
, is the ratio of energy lost to energy stored during cyclic deformation.
For calculating the dynamic complex modulus |E*|, we assumed that |E*|
E, where the indentation modulus, E is determined by
![]() |
where v is the Poissons ratio, S the contact stiffness = 
/
, and A an area function related to the cross-sectional area of the indenter (Stolz et al., 2004). Although the Poissons ratio is probably dependent on region and frequency (Hu et al., 2001), it was assumed to be, on average, 0.34, which was measured in cartilage of other joints (Athanasiou et al., 1991; Mow and Hayes, 1991; Tomkoria et al., 2004). Using the phase angle
, we determined the storage and loss moduli, E' and E'', by E* = E' + iE'; E' = |E*| cos
; E' = |E*| sin
, where i =
1, and tan
= E''/E' is the loss tangent.
The moduli were determined after a steady-state response of more than 20 cycles. After a recovery time of 5 min, a second series of indentation tests was conducted at the same location and in reverse order. The results of the second series did not differ significantly from those of the first series, which implied that the testing order and the degree of recovery had no effect on the stress-strain relationship.
In each region, the mean and standard deviation of |E*|, E', E'', and tan
were calculated for each excitation frequency. One-way ANOVA was carried out to determine whether statistically significant differences of |E*|, E', E'', and tan
existed between strain frequencies in each region. We performed Tukey tests to check for regional differences in the |E*|, E', E'', and tan
at the frequency of 1.0 Hz. Probabilities of less than 0.05 were considered to be significant.
| RESULTS |
|---|
|
|
|---|
|
decreased from 0.68 to 0.17.
|
|
| DISCUSSION |
|---|
|
|
|---|
With respect to joint morphology, the porcine TMJ has a shape more or less similar to that in humans (Bermejo et al., 1993). Functionally, the porcine TMJ shows both translational and rotational movements during mastication, like that of humans (Langenbach and van Eijden, 2001; Sun et al., 2002), although the chewing frequency in the pig is typically 23 Hz (Druzinsky, 1993), which is larger than that in the human (approx. 1 Hz) (Gallo et al., 2000). The pig can perhaps be assumed to be the best animal model for the TMJ (Sun et al., 2002; Herring, 2003). In this study, we investigated the influence of frequency on the dynamic properties by examining a range of frequencies (from 0.01 to 10 Hz). This range can be considered sufficient to cover habitual loading in both pigs and humans (Druzinsky, 1993; Langenbach and van Eijden, 2001).
In our study, the dynamic complex and storage moduli increased as the frequency increased, regardless of the region. This implies that the stiffness of the condylar cartilage enlarges with frequency. The loss modulus E'' increased but slightly from 0.01 to 0.1 Hz, and was almost constant thereafter. E'' describes the viscous behavior of the cartilage and is proportional to the average dissipation of energy through heat by deformation (Tanaka and van Eijden, 2003). Two mechanisms are responsible for the viscoelastic behavior of cartilage (Stolz et al., 2004): (1) a flow-independent mechanism, intermolecular friction, exhibited in all polymeric materials; and 2) a flow-dependent mechanism that is present if loading conditions allow water to move through the structure. Our findings indicate that fluid flow within and out of the cartilage is slower during cyclic compression. Below a certain frequency (approx. 0.1 Hz), the fluid flow may match up to the applied frequency, resulting in a flow-dependent mechanism. Meanwhile, at higher frequencies (more than 0.1 Hz), the proteoglycans occupying the interfibrillar spaces interfere with smooth fluid flow, which leads to strain energy dissipation, resulting in a higher stiffness. This is probably due to a flow-independent mechanism.
Within the frequency range examined in the present study, values of 1.0 Hz reflect chewing conditions (Druzinsky, 1993; Gallo et al., 2000). These values are considered to be important in assessment of the clinical significance of the results. Therefore, in this study, the regional difference of the dynamic viscoelasticity was evaluated by use of the results at 1.0 Hz, although chewing frequency in pigs is typically 23 Hz. A similar significant difference can be expected at 23 Hz. The sinusoidal strain used in this study was 1%, because the tissue could maintain contact with the plate during the compression/tension cycles. The anterior regions exhibited significantly higher values than the posteromedial and posterolateral regions in complex modulus |E*| and storage modulus E'. Furthermore, the loss modulus E'' showed significant regional differences, i.e., the anteromedial region had a significantly higher value of E'' than did the other regions. Therefore, it can be concluded from the present study that the viscoelasticity of the condylar cartilage is a region-specific behavior. Hu et al.(2001), using fresh fibrocartilage samples of rabbit condyles, conducted nanoindentation with atomic force microscopy, and showed that regional differences of its ultrastructure and viscoelastic properties appear to be correlated. They also revealed that the gradient distribution of Youngs moduli from the highest anteromedial region (mean, 2.34 MPa) to the lowest posterolateral region (mean, 0.95 MPa) further differentiated between the stress-bearing capacities among different regions. Since they conducted nanoindentation tests at 14 Hz, the values of elastic moduli were greater than those in our study at 1 Hz. However, the regional difference, that the anteromedial region exhibited the highest moduli in the 4 regions, is consistent with our result. It is known that highly stressed regions of articular cartilage are stiffer in compression than regions that experience less-compressive stresses (Ahmed and Burke, 1983). These regional differences are statistically significant, indicating that different regions may have been constructed to withstand a gradient propagation of shear stress. Furthermore, according to Hu et al.(2001), the porcine condylar surface shows a decreasing gradient of surface roughness from the anteromedial to the posterolateral region, indicating a co-regulation of the ultrastructural properties of fibrocartilage with its viscoelastic properties. The regional difference of the surface roughness might result in regional differences of compressive moduli and subsequent stresses. However, histochemical studies have not detected obvious regional differences of proteoglycans, such as aggrecan, in the condylar cartilage, although versican, which is the large interstitial chondroitin sulfate/keratan sulfate-proteoglycan, was predominantly localized in the anterior area of the condylar cartilage (Shibata et al., 2001). These GAGs are considered to be a determinant for the capacity for resistance to compression. Consequently, the regional difference in the viscoelastic properties in the condylar cartilage, as observed in the present study, may reflect the distribution of GAG associated with compressive resistance of the condylar cartilage.
| ACKNOWLEDGMENTS |
|---|
Received July 12, 2005; Last revision January 19, 2006; Accepted February 16, 2006
| REFERENCES |
|---|
|
|
|---|
Athanasiou KA, Rosenwasser MP, Buckwalter JA, Malinin TI, Mow VC (1991). Interspecies comparisons of in situ intrinsic mechanical properties of distal femoral cartilage. J Orthop Res 9:330340.[ISI][Medline]
Athanasiou KA, Agarwal A, Muffoletto A, Dzida FJ, Constantinides G, Clem M (1995). Biomechanical properties of hip cartilage in experimental animal models. Clin Orthop Relat Res 316:254266.
Bermejo A, González O, González JM (1993). The pig as an animal model for experimentation on the temporomandibular articular complex. Oral Surg Oral Med Oral Pathol 75:1823.[ISI][Medline]
Del Santo M Jr, Marches F, Ng M, Hinton RJ (2000). Age-associated changes in decorin in rat mandibular condylar cartilage. Arch Oral Biol 45:485493.[ISI][Medline]
Druzinsky RE (1993). The time allometry of mammalian chewing movements: chewing frequency scales with body mass in mammals. J Theor Biol 160:427440.[ISI][Medline]
Gallo LM, Nickel JC, Iwasaki LR, Palla S (2000). Stress-field translation in the healthy human temporomandibular joint. J Dent Res 79:17401746.
Herring SW (2003). TMJ anatomy and animal models. J Musculoskelet Neuronal Interact 3:391394; discussion 406407.[Medline]
Hu K, Radhakrishnan P, Patel RV, Mao JJ (2001). Regional structural and viscoelastic properties of fibrocartilage upon dynamic nanoindentation of the articular condyle. J Struct Biol 136:4652.[ISI][Medline]
Kuboki T, Shinoda M, Orsini MG, Yamashita A (1997). Viscoelastic properties of the pig temporomandibular joint articular soft tissues of the condyle and disc. J Dent Res 76:17601769.
Langenbach GEJ, van Eijden TMGJ (2001). Mammalian feeding motor patterns. Am Integr Comp Biol 41:13381351.
Mao JJ, Rahemtulla F, Scott PG (1998). Proteoglycan expression in the rat temporomandibular joint in response to unilateral bite raise. J Dent Res 77:15201528.
Mow VC, Hayes WC (1991). Basic orthopaedic biomechanics. New York: Raven Press.
Mow VC, Gibbs MC, Lai WM, Zhu WB, Athanasiou KA (1989). Biphasic indentation of articular cartilagePart II. A numerical algorithm and an experimental study. J Biomech 22:853861.[ISI][Medline]
Mow VC, Ateshian GA, Spilker RL (1993). Biomechanics of diarthrodial joints: a review of twenty years of progress. J Biomech Eng 115:460467.[ISI][Medline]
Oloyede A, Flachsmann R, Broom ND (1992). The dramatic influence of loading velocity on the compressive response of articular cartilage. Connect Tissue Res 27:211224.[ISI][Medline]
Sharawy M, Ali AM, Choi WS (2003). Experimental induction of anterior disk displacement of the rabbit craniomandibular joint: an immuno-electron microscopic study of collagen and proteoglycan occurrence in the condylar cartilage. J Oral Pathol Med 32:176184.[ISI][Medline]
Shibata S, Fukada K, Suzuki S, Ogawa T, Yamashita Y (2001). Histochemical localisation of versican, aggrecan and hyaluronan in the developing condylar cartilage of the fetal rat mandible. J Anat 198(Pt 2):129135.[ISI][Medline]
Silyn-Roberts H, Broom ND (1990). Fracture behavior of cartilage-on-bone in response to repeated impact loading. Connect Tissue Res 24:143156.[ISI][Medline]
Soltz MA, Ateshian GA (1998). Experimental verification and theoretical prediction of cartilage interstitial fluid pressurization at an impermeable contact interface in confined compression. J Biomech 31:927934.[ISI][Medline]
Stegenga B, de Bont LG, Boering G, van Willigen JD (1991). Tissue responses to degenerative changes in the temporomandibular joint: a review. J Oral Maxillofac Surg 49:10791088.[ISI][Medline]
Stolz M, Raiteri R, Daniels AU, VanLandingham MR, Baschong W, Aebi U (2004). Dynamic elastic modulus of porcine articular cartilage determined at two different levels of tissue organization by indentation-type atomic force microscopy. Biophys J 86:32693283.
Sun Z, Liu ZJ, Herring SW (2002). Movement of temporomandibular joint tissues during mastication and passive manipulation in miniature pigs. Arch Oral Biol 47:293305.[ISI][Medline]
Swann AC, Seedhom BB (1989). Improved techniques for measuring the indentation and thickness of articular cartilage. Proc Inst Mech Eng [H] 203:143150.[Medline]
Tanaka E, van Eijden T (2003). Biomechanical behavior of the temporomandibular joint disc. Crit Rev Oral Biol Med 14:138150.
Tanaka E, Aoyama J, Tanaka M, van Eijden T, Sugiyama M, Hanaoka K, et al. (2003). The proteoglycan contents of the temporomandibular joint disc influence its dynamic viscoelastic properties. J Biomed Mater Res A 65:386392.[Medline]
Tomkoria S, Patel RV, Mao JJ (2004). Heterogeneous nanomechanical properties of superficial and zonal regions of articular cartilage of the rabbit proximal radius condyle by atomic force microscopy. Med Eng Phys 26:815822.[ISI][Medline]
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| IADR Journals | Advances in Dental Research ® |
| Journal of Dental Research ® | Critical Reviews (1990-2004) |