Eruptive and functional changes in periodontal ligament fibroblast orientation in CD44 wild-type vs. knockout mice.

BACKGROUND AND OBJECTIVE

Periodontal ligament (PDL) fibroblasts establish principal fibers of the ligament during tooth eruption, and maintain these fibers during occlusion. PDL development and occlusal adaptation includes changes in the orientation of PDL fibroblasts; however, the mechanism for these changes in orientation is unclear. The objective of this study was to compare PDL fibroblast orientation in different stages corresponding with first molar eruption and occlusion in CD44 wild-type (WT) and knockout (KO) mice.

MATERIAL AND METHODS

CD44 WT and KO mice were raised to six postnatal stages corresponding with first molar (M1 ) eruption (postnatal day 8, 11, 14 and 18) and occlusion (postnatal day 26 and 41). Coronal sections of the first mandibular molar (M1 ) were prepared and the orientation of fibroblasts in the cervical root region was measured. Angle measurements were compared across developmental stages and between strains using Watson-Williams F-test (oriana software) and ANCOVA.

RESULTS

PDL fibroblast orientation increased significantly in CD44 WT (9-87°) and KO mice (14-93°; p ≤ 0.05) between intraosseous eruption (day 11), mucosal penetration (day 14) and preocclusal eruption (day 18); however, the PDL fibroblast orientation did not change significantly with the onset of occlusion (day 26) or continued function (day 41). Within each strain, the variance in fibroblast orientation during preocclusal eruption (day 18) was significantly higher than the variance of all other time points (p < 0.0005). CD44 WT and KO mice showed a similar pattern of PDL development and eruption with a significant difference in CD44 WT vs. KO fibroblast orientations only during early function (day 26, 92° vs 116°; p = 0.05).

CONCLUSIONS

The development of PDL fibroblast orientation is highly similar between CD44 WT and KO mice. Between early (day 11) and late (day 18) eruptive stages PDL fibroblast orientation increases, corresponding with the upward movement of M1 . The PDL fibroblast orientation established in preocclusal eruption (day 18) is maintained during early (day 26) and late (day 41) stages of occlusal function, suggesting that PDL cells adapt to mechanical loads in the oral cavity before M1 occlusion.