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

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° to 48°, while the angle of decussation increased from 60° to 70°. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25° to 29°. 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.