PMC

The surface thickness of Dspp^–/– enamel is similar to Dspp^+/–, while the total enamel thickness is similar in both genotypes. Measurements of enamel thickness erupted portions of incisors in Dspp^+/– and Dspp^–/– one-month-old mice. A. SEM micrograph of the Dspp^–/– erupted incisor showing total enamel thickness in green, surface enamel thickness in red, bulk enamel thickness in blue and inner enamel thickness in yellow. The inset shows the line along which the measurements were carried out, connecting labial and lingual corners of the pulp cavity; B. SEM micrograph of the Dspp^+/– erupted incisor with the bulk enamel thickness shown in blue and the surface enamel thickness in yellow; C. The histograms show total enamel thickness, outer enamel thickness and outer to total enamel thickness ratio. One asterisk identifies p < 0.05, two asterisks identify p < 0.01. D—dentin, E—enamel. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)

Comparison of enamel block surface morphology after mechanical polishing and ultramicrotomy. (a) Reflected-light microscopy (differential interference contrast mode) of mechanically polished enamel showing polishing marks on the enamel surface with enamel (E) and resin (R). (b) Confocal laser scanning microscopy of mechanically polished enamel showing scratches and polishing marks. The microstructure of enamel (prisms and interprismatic substance) is not obvious with enamel (E) and resin (R). (c) AFM micrograph of mechanically polished enamel depicting scratches and polishing marks. (d) Reflected-light microscopy of the enamel block surface after ultramicrotomy, showing the microstructure of enamel (prisms and interprismatic substance) with enamel (E) and resin (R). (e) Confocal laser scanning microscopy of the enamel surface after ultramicrotome preparation, depicting numerous prisms and the interprismatic substance with enamel (E) and resin (R). (f) AFM micrograph of the enamel surface after ultramicrotome preparation showing numerous prisms (dark red area) and the interprismatic substance (yellow area). (g) Horizontal height profile of the mechanically polished enamel surface measured by AFM, showing the surface roughness at the microscale in detail. (h) Horizontal height profile of the same enamel sample after ultramicrotome preparation, measured by AFM.

Microcomputed tomography of incisors and molars with under- or overexpressed Ambn. Incisors of 7-week-old animals were analyzed in sagittal and transverse planes. (A) The sagittally sliced incisor displayed enamel formation from the beginning in the apical loop (AL) to the tooth eruption (Er). Ambn ^Δ5,6/Δ5,6 animals had ectopic minerals in the enamel organ (blue arrow) but no enamel. The timing of enamel formation was delayed in Ambn Tg⁺⁺⁺ and Ambn Tg ^+++/+++ relative to the transition from secretory to maturation stages (white arrow). Ambn Tg ⁺⁺ incisors harbored reduced mineral density at the dentino-enamel junction (DEJ) (green arrow). Ambn Tg ⁺⁺⁺ and Ambn Tg ^+++/+++ incisors displayed hypomineralized enamel lesions alternating with mineralized enamel (yellow arrows). (B) Transversely sliced incisors between the second molars marked the early maturation stage of enamel formation. In Ambn Tg ⁺⁺ incisors, the enamel was less mineralized, particularly along the DEJ (green arrow). In Ambn Tg ⁺⁺⁺ and Ambn Tg ^+++/+++ , the enamel was unevenly mineralized in buccal–lingual orientation and within the height of the enamel layer (yellow arrows). (C) Transversely sliced incisors close to the eruption site marked reduced enamel mineralization in Ambn Tg ⁺⁺⁺ and Ambn Tg ^+++/+++ , pronounced in the lingual half of the incisor (yellow arrow). In contrast, the Ambn Tg ⁺⁺ enamel appeared comparable to wild-type (WT) in the mineral content. (D, E) Molars of 7-week-old animals were analyzed in sagittal and transverse planes. (D) All three mandibular molars (M1, M2, and M3) were captured in the sagittal image. The severity of enamel hypomineralization on the outer surfaces increased, demonstrating larger lesion sizes and decreased enamel volumes, as Ambn Tg concentration increased to +++ and +++/+++ (yellow arrows). (E) Transversely sectioned second molars displayed hypomineralization on the slopes of buccal and lingual cusps (yellow arrow). Lesions were surrounded by the mineralized enamel. B, buccal; L, lingual.

Defective enamel mineralization in Gpr115-KO mice. A, micro-CT analyses of 8-week-old WT and Gpr115-KO mandibles. First column (a and b), 3D reconstructed image of mandible. Second column (c and d), 3D reconstructed image of molars and incisor enamel. c and d correspond to a and b, respectively. Blue, molar enamel; yellow, incisor enamel. Arrows indicate position used for measurement of enamel mineral density in C. B, total volumes of enamel in 8-week-old WT and Gpr115-KO molars and incisors (n = 4). Number above bar graph indicates ratio of volume (KO/WT). Mean values are shown as bars. Error bars represent S.D. **, p < 0.01; two-tailed t test. C, cross sections of micro-CT analysis images of WT and Gpr115-KO incisors. Position 1, late maturation of enamel; position 2, early maturation of enamel; position 3, transition stage of enamel. Dashed lines indicate enamel area. Arrowheads indicate differences in enamel density between cross sections of incisors from WT and Gpr115-KO mice. D, quantification of enamel and dentin mineral density. Cross sections in C indicate positions of measurement (n = 4). Mean values are shown as bars. Error bars represent S.D. *, p < 0.05; two-tailed t test.