Altered functional loading causes differential effects in the subchondral bone and condylar cartilage in the temporomandibular joint from young mice.
OBJECTIVE
Altered loading is an important etiological factor for temporomandibular joint (TMJ) disorders. Studies examining altered loading of the TMJ have been done in rats but the response of the TMJ to altered loading in mice is largely unknown. Therefore, due to the potential usefulness of genetically engineered mice, the goal of this study was to develop a mouse TMJ altered functional loading model.


METHODS
One hundred and thirty four, 21-day-old CD-1 female mice were divided into two groups: (1) normal loading (hard pellet diet) for 2-6 weeks and (2) altered functional loading (incisor trimming every other day and soft dough diet) for 2-6 weeks. The mandibular condylar cartilage was evaluated by histology, the subchondral bone was evaluated by microcomputed tomography (micro-CT) analysis and gene expression was evaluated by real time polymerase chain reaction (PCR) analysis.


RESULTS
Altered functional loading for 2-6 weeks caused significant reduction in the thickness of the condylar cartilage whereas, only at 4 weeks was there a significant decrease in the bone volume fraction and trabecular thickness of the subchondral bone. Gene expression analysis showed that altered functional loading for 4 weeks caused a significant reduction in the expression of SRY-box containing gene 9 (Sox9), Collagen type X (Col X), Indian hedgehog (Ihh), Collagen type II (Col II) and Vascular endothelial growth factor (Vegf) and altered loading for 6 weeks caused a significant decrease in the expression of Sox9, Col II, Vegf and Receptor activator of NF-kappaB ligand (Rankl) compared to the normal loading group.


CONCLUSIONS
Altered functional TMJ loading in mice for 2-6 weeks leads to a loss of the condylar cartilage and a transient loss in the density of the mandibular condylar subchondral bone.
Chen
J
J
University of Connecticut Health Center, School of Dental Medicine, Department of Craniofacial Sciences, Division of Orthodontics, Farmington, CT 06030, United States.
Sorensen
K P
KP
Gupta
T
T
Kilts
T
T
Young
M
M
Wadhwa
S
S
D000818:Animals; D001835:Body Weight; D015519:Bone Density / Q000502:physiology; D024043:Collagen Type II / Q000378:metabolism; D024121:Collagen Type X / Q000378:metabolism; D004032:Diet; D004195:Disease Models, Animal; D005260:Female; D051445:Fibrocartilage / Q000378:metabolism* / Q000473:pathology; D015870:Gene Expression; D006801:Humans; D007180:Incisor; D008335:Mandibular Condyle / Q000473:pathology*; D008409:Mastication; D051379:Mice; D008852:Microradiography; D016133:Polymerase Chain Reaction; D053245:RANK Ligand / Q000378:metabolism; D055758:SOX9 Transcription Factor / Q000378:metabolism; D013314:Stress, Mechanical; D013704:Temporomandibular Joint; D013997:Time Factors; D014057:Tomography, X-Ray Computed; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
D024043:Collagen Type II; D024121:Collagen Type X; D053245:RANK Ligand; D055758:SOX9 Transcription Factor; C527933:Sox9 protein, mouse; D042461:Vascular Endothelial Growth Factor A
Arch Oral Biol. 1996 Jan;41(1):127-31
8833602
J Am Dent Assoc. 2003 Jun;134(6):705-14
12839406
J Dent Res. 2003 Aug;82(8):627-31
12885848
Bone. 2006 Nov;39(5):1043-1047
16860618
Arch Oral Biol. 1998 Jan;43(1):83-92
9569994
Trends Mol Med. 2006 Jan;12(1):17-25
16356770
Am J Anat. 1988 Jul;182(3):197-214
3213819
J Clin Invest. 2005 Jul;115(7):1734-42
15951842
Histochem J. 1996 Feb;28(2):99-107
8737291
Odontology. 2005 Sep;93(1):7-15
16170470
Microsc Res Tech. 2005 Aug 15;67(6):325-35
16173089
Acta Odontol Scand. 1994 Jun;52(3):129-34
8091958
J Orofac Pain. 1999 Fall;13(4):295-306
10823044
J Dent Res. 1994 Jun;73(6):1150-6
8046103
Acta Anat (Basel). 1986;125(3):145-51
3962576
Ann N Y Acad Sci. 2006 Apr;1068:1-13
16831900
Eur J Orthod. 2004 Feb;26(1):1-5
14994876
Arch Oral Biol. 1983;28(10):939-45
6580850
Acta Anat (Basel). 1988;131(2):136-9
3369280
Arch Oral Biol. 1995 Jul;40(7):677-80
7575241
Crit Rev Oral Biol Med. 1997;8(3):291-305
9260045
Dev Dyn. 2007 Feb;236(2):426-34
17191253
Osteoarthritis Cartilage. 2006 Aug;14(8):807-13
16563813