Molecular characterisation of odontoblast during primary, secondary ...

3.3 MSX2 proteins and dentinogenesis.
3.3.1 Histology observations:
Results
No differences were observed for the first upper molar morphology of wild type and
heterozygous transgenic mice. In contrast, tooth morphology was strongly disrupted in
null mutant animals with crown morphology and root formation demonstrating clear
alterations. Changes were also observed in the dentine thickness (Figure 27).
3.3.1.1 At 7 days post-natally
Dentine thickness was slightly increased in null mutant animals, and on the side of the
cusp, a convex dome was observed instead of the concave shape seen in Wild Type (WT)
teeth.
In Msx2 -/- mouse teeth, a slight mineralization defect was noticeable on the top of the
first molar cusp. The mantle dentine thickness was also noticed to be greater than in
wild type animals.
On Msx2 null mutant animals, the course of the coronal dentine tubules was more
sinusoidal than those of Wild type (WT) animals; many lateral branches were clearly
visible and in higher number than in WT, although it was difficult to see any true
communication between them. The density of the lateral branching was greatest in
between cuspal areas rather than on the cusps themselves (Figure 28).
Root formation had already started in WT animals whereas it had not begun in -/-
animals.
The alterations in dentine morphology and tubular orientations confirm the disturbances
in dentinogenesis in the absence of the MSX2 protein. In the odontoblast palisade layer,
nuclear polarization was inverted in many cells. Such inversion of polarity was rarely
observed in WT or +/- samples (Figure 29).
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