Objectives: Amelogenin trityrosyl motif peptide (ATMP) in amelogenin binds to GlcNAc/NeuAc to stabilize enamel. LRAP, a polypeptide devoid of ATMP, failed to bind to the sugars.  ATMP when provided exogenously during enamel formation in culture may compete with amelogenin to impair enamel growth; Methods: Mouse first mandibular molars were dissected from E16 mouse embryos were cultured (12 days) in the presence of different concentrations of ATMP, T-ATMP (proline replaced with threonine) and LRAP. Tooth-organs were sectioned and stained with Mallory; Results: The control (postnatal day 3) showed staining differences in Mallory as follows:  Dentin: Aniline Blue reactive (AB+); Predentin:  Hyalin, did not stain; Enamel:  Fuchsinophilic; Ameloblasts: AB(+) with fuchsin granules. The fuchsinophilic substance in enamel is embedded on AB(+) matrix.  After LRAP (34.5 nmol/dish), enamel growth is augmented, ameloblasts width is reduced (Table 1). After T-ATMP (34.5 nmol), the enamel matrix is AB(+) with intermittent fuchsinophilia; Conclusion: In the presence of ATMP, enamel has detached from dentin confirming that ATMP competes with amelogenin to bind to dentin. LRAP accelerated enamel growth and reduced the ameloblasts-size.  In enamel, the fuchinophilic material is embedded over AB(+) matrix, suggesting a heteromolecular interaction in enamel matrix. Supported by NIH-NIDCR RO1 DE 13204-05. rravindr@usc.edu 

Table 1. Morphometry of dentin, enamel and ameloblasts before (in vitro-control) and after treatment with ATMP, T-ATMP and LRAP (All measurements done at 200 m below the cusp)

Regions	Controls		ATMP (m)		T-ATMP (m)		LRAP (m)
	In vivo  (m)	In vitro (m)	A	B	A	B	A	B
Ameloblast	46-50	33-41	24-31	20-30	26-27	26-27	10-19	19-22
Enamel	10	21-23	23-36*	20-30	25-38		30-34	30-40
Dentin	12-19	8-9	21-28	10-15	22-28	10-15	17-23	15-20
Predentin	5-10	2-3	2-3	2-3	2-3	2-3	2-3	2-3

A: 34.5 nmol/dish (n=4); B: 8.6 nmol/dish (n=4).  * Spongy or puffy swelling and enamel detached