Effects of Accelerated Eruption On the Enamel of the Rat Lower Incisor

Abstract

The effect of accelerated eruption of the rat lower incisor on enamel was studied in a series of segments obtained when the incisor was cut repeatedly out of occlusion over a five-week period. The segments were ground, cleaned, acid-etched, observed with SEM, and analyzed with EDX. Pigmentation was lost within 11 days. Pigmented superficial enamel was more acid-resistant than the rest of the enamel, but this quality decreased with decreasing iron content. Hypomineralized enamel first appeared in a restricted area at the mesio-labial angle of the tooth in the 6th-7th segment obtained after 11-14 days. Later, hypomineralization became more generalized. All enamel zones were retained throughout the experiment. The geometry of the prism pattern was affected. The angle between prism rows and the enamel-dentin junction increased from 44 degrees to 48 degrees, while the angle of decussation increased from 60 degrees to 70 degrees. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25 degrees to 29 degrees. However, the prisms retained their incisal direction. The connection between enamel and dentin was partly disrupted from about the 9th segment onward. The depth of the mesial concavity of the enamel-dentin junction decreased from about the 10th segment onward. Accelerated eruption affects all stages of enamel formation and is a suitable and predictable model for studying regulatory mechanisms in amelogenesis.

Cellular and Chemical Events During Enamel Maturation

“…The exact mechanism of secretion and the purpose for applying this material to the surface of mature enamel so that iron replaces some of the calcium in the crystal lattice (Halse and Selvig, 1974) is unknown, but it represents one of the very few examples of a secretory process in ameloblasts resembling "regulated" secretion-i.e., the ferritin material forming the basis of this pigment collects within secretory (pigment) granules of ameloblasts for a long period of time before it is released at a specific moment in time (Karim and Warshawsky, 1984;Ogura et al, 1984;Kubota et al, 1987;Mataki et al, 1989). Ameloblasts in teeth forming the pigment begin to accumulate ferritin particles in what appears as residual lysosomal dense bodies, starting about one-third of the way through the maturation stage of amelogenesis (Smith, 1979;Takano and Ozawa, 1981;Karim and Warshawsky, 1984;Risnes et al, 1996). The cells at this time are actively modulating in eight-hour cycles, and the enamel is just beginning to show signs of forthcoming massive protein degradation and loss (Figs.…”

A Novel Role of Periostin in Postnatal Tooth Formation and Mineralization

“…An alternative strategy of testing the potential role of periostin in postnatal tooth development is to determine whether there is a difference in mechanical responses between the periostin-null and the age-matched control mice in the absence of biting forces using a tooth trim method. It is known that there is a decrease in mineralization when incisor is repeatedly trimmed, which is thought to be lack of enough time for the enamel layer to mature (8,10). A representative backscattered SE image showed that normal enamel rods, which have the highest mineral content in the body, were sharply reduced in the mineral content and the size of the WT enamel in the absence of occlusion (Fig.…”

Comparative Temporospatial Expression Profiling of Murine Amelotin Protein during Amelogenesis

“…However, the structure of enamel is not homogeneous; the initial layer at the dentino-enamel junction (DEJ), and particularly the final, superficial layer at the enamel surface, is structurally distinct from inner (bulk) enamel. Inner enamel is characterized by the parallel arrangement of long apatite crystals within decussating prisms (layered in alternate directions), while outer enamel appears as a relatively thin region where enamel prisms display a honeycomb pattern in both rodents Risnes et al, 1996] and humans [Kodaka et al, 1991]. Subsequent to this, a very thin layer of prismless final enamel is deposited at the enamel surface within which the enamel crystals generally run perpendicular to the tooth surface.…”