Crown morphology, enamel distribution, and enamel structure in mouse molars

Abstract

Background: Biomolecular research and genetic manipulations have stressed the importance of thorough knowledge of normal organ morphology. Mouse molar teeth are convenient models for studying basic interactions in organ development and morphogenesis. The aim of the present study was to provide basic information on their morphology.Methods: Intact and sectioned/ground molars of mice of various ages were observed with SEM.Results: Enamel-free areas (EFA) were present on cusp tips at time of eruption. The dominating structural configuration in enamel was prism decussation in inner enamel and parallel prisms in outer enamel. Prism decussation tended to be absent at cusp ridges and in the bottom of grooves. In the former location, the distinction between prisms and interprism was often obscured in the middle enamel zone due to decreased difference in orientation of their crystals. A thin layer of enamel, often aprismatic, covered the distal aspect of cusps in maxillary molars and the mesial aspect of cusps in mandibular molars. The enamel abutting on EFA was often aprismatic. Aprismatic enamel exhibited incremental lines with a periodicity of about 1 m and was often traversed by cracks. The enamel surface was porous in the bottom of grooves. Parts of mouse molar enamel were incompletely mineralized at the time of eruption.Conclusions: SEM is a convenient method for combined studies of crown morphology and enamel structure. Based on morphological criteria, a modification of the cusp nomenclature is proposed. Enamel thickness and structure in mouse molars show regional variations. Fundamental similarities exist between mouse molar cusps and mouse incisors. Mouse molar enamel undergoes posteruptive maturation. Anat.

Effects of in vivo transfection with anti-miR-214 on gene expression in murine molar tooth germ

“…Transient arrest of amelogenin synthesis by injection of a specially designed ribozyme into developing murine mandibles yielded a tooth phenotype with normal morphology and with normal enamel structure, but with defects suggesting hypomineralization (25). This is in accordance with the present findings where both decreased expression of Amelx and diminished levels of amelogenin were associated with both normal morphology and normal enamel structure of the mature tooth; missing prism decussation in certain areas being a normal feature of mouse molar enamel (24). Evidence of enamel hypomineralization with porosities and organic material residues together with diminished surface roughness following acid etching was however apparent in treated molars (Fig.…”

A role for suppressed incisor cuspal morphogenesis in the evolution of mammalian heterodont dentition

“…The lack of enamel at the incisor grooves is reminiscent of the enamel-free zones located at the tip of the cusps of rodent molars that result from failure of complete ameloblast maturation (16)(17)(18). Before eruption of rodent molar teeth, the enamel-free zones are covered by ameloblasts, similar to those observed in the grooved incisors of Lrp4 hypo/hypo mice ( Fig.…”

Comparative studies between mice molars and incisors are required to draw an overview of enamel structural complexity

“…In the molar, four characteristics are noted: (1) decussation of rods observed in the inner third and absent in the upper ridges and in the bottom of grooves, (2) a feather-like rod organization also forms lamellar enamel in the inner third (Figure 2A), (3) all rods seen in the outer enamel are radial [right angle to the surface (Figures 2A,C)] and/or exhibit the same oblique orientation tangential to enamel surface (Figure 2C) (Koenigswald and Clemens, 1992), (4) incremental lines with a regular periodicity constitute the superficial aprismatic enamel (Lyngstadaas et al, 1998). Enamel organization is strongly dependent on the zone investigated (Risnes, 1979).…”

“…A strong link may be established between regional variations of enamel structure and the rod-interrod scaffold, which allows strain resistance (Figures 2– 4 ). The predominant structure consists in several waves of rod decussation in the inner enamel and in rods which are radial in outer enamel (Lyngstadaas et al, 1998) (Figure 2A). …”