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Mechanobiology of Craniofacial Sutures

Departments of Orthodontics MC 841, Bioengineering, and Anatomy and Cell Biology, 801 South Paulina Street, University of Illinois at Chicago (UIC), Chicago, IL 60612-7211; jmao2{at}uic.edu

View larger version (32K): [in this window] [in a new window]   Figure 1. Representative waveforms and time courses of exogenous compressive forces (cf. Appendix Fig. 1: posteriorly directed horizontal arrow) at 5 Newtons applied to the maxillary incisors as measured by a load cell of a computerized servohydraulic system. In the left column, (A) static force, (B) sinusoidal cyclic force, and (C) square-wave cyclic force. Three plots in the center column (D,F,G) demonstrate the elicited waveforms of sutural strain of the pre-maxillomaxillary suture (PMS), whereas three plots in the right column (H,I,J) demonstrate representative waveforms of sutural strain of the nasofrontal suture (NFS). All strain traces were recorded with uni-axial strain gauges. The static force (A) and the resulting static sutural strains in the PMS (D) and NFS (G) lacked appreciable oscillation in force magnitude. Minor oscillation in G is attributable to rabbit breathing. Sinusoidal cyclic force (B) evoked corresponding sinusoidal sutural strains in the PMS (E) and NFS (H). Square-wave cyclic force (C) evoked corresponding square-wave cyclic sutural strains in the PMS (F) and NFS (1). Clearly, waveforms of PMS and NFS sutural strains are modulated by corresponding waveforms of exogenous forces.

View larger version (53K): [in this window] [in a new window]   Figure 2. Representative photomicrographs of the pre-maxillomaxillary sutures (PMS) and nasofrontal sutures (NFS) in response to compressive strain in the PMS, and tensile strain in the NFS (cf. Fig. 1). The PMS treated with cyclic strain (C) showed wide sutural separation, in comparison with sham control (A) and static strain (B). The same trend is true for the NFS: greater increase in sutural width by cyclic strain (F) than static strain (E) and natural growth (D). Blue lines were manually drawn to indicate the sutural edge between fibrous connective tissue of the suture and mineralized sutural bone. For quantitative analysis, H&E-stained histological sections were subjected to computerized image analysis with constructed circles and grids overlaid under low power (4x). A circle is constructed in the grid's center with the diameter of the circle equal to the sutural width at a given location. The diameters of all circles per sutural specimen were averaged to indicate the mean sutural widths and subjected to ANOVA with Bonferroni tests. H&E stain; scale bar = 100 µm. Reproduced from a manuscript in the J Bone Miner Res (in press) with permission of the American Society for Bone and Mineral Research.

View larger version (56K): [in this window] [in a new window]   Figure 3. Representative photomicrographs demonstrating fluorescence-labeled new bone formation with fluorescent calcein green (arrows) in the pre-maxillomaxillary sutures (PMS) and nasofrontal sutures (NFS) in response to compressive strain in the PMS, but tensile strain in the NFS (cf. Fig. 1). (A) Sham control of the PMS under normal growth; (B) static loading of the PMS; (C) cyclic loading of the PMS; (D) sham control of the NFS under normal growth; (E) static loading of the NFS; and (F) cyclic loading of the NFS. Areas of newly mineralized bone are indicated by green fluorescence. S, suture; NB, new bone. The PMS and NFS specimens treated with cyclic loading demonstrated greater amounts of calcein uptake and therefore a great amount of bone apposition in comparison with sutures treated with static loading and sham control. Undemineralized section; scale bar, 10 µm. Reproduced from a manuscript in the J Bone Miner Res (in press) with permission of the American Society for Bone and Mineral Research.

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