The Oral Apparatus of Rodents
-
Upload
robertdruzinsky -
Category
Science
-
view
131 -
download
2
Transcript of The Oral Apparatus of Rodents
The Oral Apparatus of Rodents:Variations on the theme of a
Gnawing Machine
Robert E. Druzinsky
Dept. of Oral Biology, College of Dentistry, University of Illinois at Chicago
Mastication in Rodents
• Sciurids retain “primitive” tribosphenicmammalian pattern (Butler, 1984)
• Many rodents retain basic lateral-medial, anteriorly directed power stroke
• Propalinal chewing not primitive – has evolved many times independently
• “Bi-lateral” chewing uncommon, if it occurs at all
4 “types” of rodent masticatory muscles
• Historically, sub-orders of the Rodentia have been based on these “types” of masticatory muscles
• Do the “types” of rodent masticatory muscles represent biomechanical strategies for the production of jaw
closing forces during chewing?
The moment arm of the adductor muscles is relatively longer in sciuroidea than in the protrogomorph, Aplodontia.
The Rodent Masticatory Complex
• A functional complex for propalinal chewing movements?
• NO!
Rodents are all GNAWING MACHINES
Some primates have very little enamel on the lingual surface of the central
incisors
These teeth are tools that sharpen themselves through use –
Self-sharpening incisors
Many texts describe the incisors of rodents (and lagomorphs) as
“self-sharpening”
BUT THEY ARE NOT
• Glires actively sharpen upper and lower incisors
Rodents Gnaw
• A mechanical complex for gnawing with specializations of the
– Jaws
– Jaw joints
– Incisors
Diastema
Loss of lingual enamel
Glires
Rodentia
Lagomorpha
Continuously
erupting incisor
Synapomorphies of Glires
Diastema
Loss of lingual enamel
Glires
Rodentia
Lagomorpha
Loss of second upper incisor
Loss of articular
eminence
Continuously
erupting incisor
Synapomorphies of Rodents
Hypothesis:
Rodents and lagomorphs should be able to sharpen the upper
incisors equally well
But
Rodents should have
sharper lower incisors
than lagomorphs
0 1 2 3 4 5 6
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
0.20
0.22
R
R
R
L
LL
LLL
L
L
L
LL
L
L
LL
L
R R
R
R
RR
RR
R
R
R
R R
R
R
R
Upper Incisors
Sca
led
Ra
diu
s (
r/W
)
AP Width (mm)
t=-1.89515
p=0.0666
Sca
led
Ra
diu
s (
r/W
)
AP Width (mm)
0 1 2 3 4 5 6
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
RRRR
LLLL L
L
LL
L
L
LL
LLL
LLL
RR R
RRR
R
R
RR RR R
R
R R
Lower Incisors
t= -2.61424p= 0.01298
Three “types” of incisors compared in mice
• Wild type
• Sprouty transgenic (SPRY 2+/-,4-/-)
• Amelogenin knock out transgenic (AMELX -/-)
“Sprouty tooth” – lingual enamelAmelogeninKnock-out
No enamel
Labial surfaces
“Wild type tooth” – no lingual enamel
Incisors Loaded in Compression
• Approx. 4 micron voxels
• Image stacks imported into Avizo as binary files
• Incisors scanned unloaded and at 15 microns and 30 microns of compression
• Surface renderings created in Avizo comparing unloaded and 30 micron scans
Deformation in Axial Loading
Wild Type – no lingual enamel Amelogenin KO – no enamel
0 20 40 60 80 100
100
200
300
400
500
600
700
800
Ba
se
to
Tip
Difference in Microns
0 20 40 60 80 100
100
200
300
400
500
600
700
800
Ba
se
to
Tip
Difference in Microns
Deformation in Axial Loading
0 20 40 60 80 100
100
200
300
400
500
600
700
800
Ba
se
to
Tip
Difference in Microns
0 20 40 60 80 100
100
200
300
400
500
600
700
800
Ba
se
to
Tip
Difference in Microns
Spry – lingual enamel Spry – no lingual enamel
Loading to Catastrophic Failure
0
20
40
60
80
100
120
140
160
8196
7693
Co
mp
ress
ion
(in
mic
ron
s)
Sprouty
Normal
Incisors of Rodents are
• Sharp –
– Oral apparatus allows sharpening movements
– Tungsten-carbide chisel model
• Flexible - Mechanically tough?
– The sharp tips can be driven into an object and then they bend rather than break
Co-workers:Weizmann Institute of Science, Israel
• Gili Naveh• Steve Weiner• Vlad Brumfeld
Univ. of California, San Francisco• Cyril Charles (ENS de Lyon, France)• Ophir Klein
Univ. of Illinois, Chicago• Hannah Koeppl• Tom Diekwisch• Xianghong Luan• David Reed
Spry1 −/−;Spry2 −/− embryos do not form a glenoid fossa.
But the condyle and articular disc is essentially normal
.
Purcell, P., Jheon, A., Vivero, M. P., Rahimi, H., Joo, A., & Klein, O. D. (2012). Spry1 and spry2 are essential for development of the temporomandibular joint. Journal of Dental Research, 91(4), 387-393
Diastema
Loss of lingual enamel
Glires
Rodentia
Lagomorpha
Loss of second incisor
Loss of articular
eminence
Continuously
erupting incisor
Specializations of the Incisors
• Loss of lingual enamel• Ever-growing
• Rodents have a single central incisor