In vitro study investigating the mass of tooth structure removed following endodontic and restorative procedures.

STATEMENT OF PROBLEM: There is limited scientific evidence which quantifies the amount of tissue removed during endodontic and restorative procedures. PURPOSE: The purpose of this study was to measure and compare the mass of tissue structure removed from incisor and canine teeth following successive preparations. MATERIAL AND METHODS: Twenty-two intact, disease- and restoration-free teeth (n=11/group) were collected from consenting patients undergoing dental extractions at Eastman Dental Hospital. The teeth were stored in 4% formaldehyde saline and successively prepared for an access opening (AC), endodontic instrumentation (EI), porcelain laminate veneer (PC), metal-ceramic (MC) crown, and post-and-core (PC) preparations. The baseline mass for each tooth was measured and recorded, in grams, at baseline and after each preparation, on a digital analytical balance. A standard protocol was applied to ensure accurate mass measurements. Repeated measures analysis of variance (ANOVA) was used to make comparisons between the incisor and canine groups (alpha =.05) for actual mass of tooth in milligrams, percentage of tooth mass remaining compared to baseline, and percentage decrease in mass compared to the preceding procedure. RESULTS: The estimated marginal percentage mass lost was significantly greater (P<.001) in the incisor group compared to the canine group, as an overall trend, with the incisors losing proportionally more mass for each procedure (P<.001). CONCLUSIONS: Mean percentage of removed tooth tissue increased successively from EI, AC, PC, and PV preparation, with greatest change from the previous procedure occurring for MC crown preparation.

Acetylcholinesterase enhances neurite growth and synapse development through alternative contributions of its hydrolytic capacity, core protein, and variable C termini.

Accumulated indirect evidence suggests nerve growth-promoting activities for acetylcholinesterase (AChE). To determine unequivocally whether such activities exist, whether they are related to the capacities of this enzyme to hydrolyze acetylcholine and enhance synapse development, and whether they are associated with alternative splicing variants of AChEmRNA, we used four recombinant human AChEDNA vectors. When Xenopus laevis embryos were injected with a vector expressing the synapse-characteristic human AChE-E6, which contains the exon 6-encoded C terminus, cultured spinal neurons expressing this enzyme grew threefold faster than co-cultured control neurons. Similar enhancement occurred in neurons expressing an insertion-inactivated human AChE-E6-IN protein, containing the same C terminus, and displaying indistinguishable immunochemical and electrophoretic migration properties from AChE-E6, but incapable of hydrolyzing acetylcholine. In contrast, the nonsynaptic secretory human AChE-I4, which contains the pseudointron 4-derived C terminus, did not affect neurite growth. Moreover, no growth promotion occurred in neurons expressing the catalytically active C-terminally truncated human AChE-E4, demonstrating a dominant role for the E6-derived C terminus in neurite extension. Also, AChE-E6 was the only active enzyme variant to be associated with Xenopus membranes. However, postsynaptic length measurements demonstrated that both AChE-E6 and AChE-E4 enhanced the development of neuromuscular junctions in vivo, unlike the catalytically inert AChE-E6-IN and the nonsynaptic AChE-I4. These findings demonstrate an evolutionarily conserved synaptogenic activity for AChE that depends on its hydrolytic capacity but not on its membrane association. Moreover, this synaptogenic effect differs from the growth-promoting activity of AChE, which is unrelated to its hydrolytic capacity yet depends on its exon 6-mediated membrane association.