• in 13% of mice all teeth are present but the lower incisors and third molars are hypoplastic

• in 35% of mice tooth defects differ between the right and left halves of the lower jaw

• at E13.5 the size of the mesenchymal cell condensations underlying the posterior part of the dental lamina is reduced, but the dental papilla of the first molar has formed

• in most cases the lower incisors are absent

• the lower first molars show significant attrition and formation of reparative and reactionary dentin

• the upper and lower third molars are unilaterally or bilaterally absent

• lower third molars and incisors may fail to erupt

• a mixture of reactionary and reparative dentin seen in molars

• in 35% of mice up to 3 teeth are absent (hypodontia) and in 52% of mice 4 or more teeth are absent (oligodontia); however the secondary palate is intact and digit duplication is not seen

• thymus morphology is normal and no signs of defective parathyroid or ultimobranchial body function (as shown by normal calcium and phosphate homeostasis) are seen (J:104121)

• underrepresented at weaning

• at E13.5 the size of the mesenchymal cell condensations underlying the posterior part of the dental lamina is reduced, but the dental papilla of the first molar has formed

• in the upper incisors ameloblasts are present at 2 months of age but absent by 5 months

• in the upper incisors ameloblasts fail to elongate and produce only a thin layer of pre-enamel

• at P0 all third molars are arrested prior to the bud stage and the lower second molars are arrested at the bud stage

• at P0 the lower first molars have reached the bell stage but lack polarization and alignment of the ameloblasts and odontoblasts

• at P0 the upper first and second molars are mostly growth retarded

• all mice lack lower incisors

• the lower first molars show significant attrition and formation of reparative dentin

• the upper third and lower second and third molars are unilaterally or bilaterally absent

• lower third molars and incisors fail to erupt and other teeth in the lower jaw may also fail to erupt

• irregular dentin formation is indicated by the presence of 'contour lines of Owen'

• the upper incisors lack enamel; however enamel formation in the molars is normal

• more severe tooth loss than in Pax9^tm1Hpt homozygotes with all mice lacking at least 4 teeth (oligodontia) and some lacking all lower teeth

• thymus morphology is normal and no signs of defective parathyroid or ultimobranchial body function (as shown by normal calcium and phosphate homeostasis) are seen (J:104121)