ABSTRACT
Optimum stresses for a favorable response to orthodontics are still unknown. Here, we compared the effects of initial periodontal ligament (PDL) stresses over time in orthodontic external root resorption (OERR), necrosis, and the TRAP+ cell population. Forty-two rats (Fischer CDF) were treated with 10 cN of force for 5 different time periods. Finite element (FE) models of the first maxillary molars were constructed from µCT scans to calculate initial PDL stresses. The scans were also used for OERR measurements before histology. Time, stress, and their interaction were significant to result in an OERR increase only in the regions of medium and high stress. OERR was not significantly different between control and treated animals over time in the region of low stress. After 30 days, OERR was increased by 5- and 3-fold in the zone of high- and medium-stress regions, respectively. The TRAP+ cell population initially followed the stress gradient, but changed after bone and necrotic tissue resorption. In the 30-day modeling cycle, the correspondent 3rd principal stress range to promote direct bone resorption and insignificant OERR was between -9.92 and -7.75 KPa. These translate to approximate forces of 30 to 40 cN applied at the bracket level (tipping) of a human maxillary canine.
Subject(s)
Dental Stress Analysis , Periodontal Ligament/pathology , Root Resorption/pathology , Tooth Movement Techniques/adverse effects , Tooth Root/pathology , Acid Phosphatase/metabolism , Animals , Disease Models, Animal , Finite Element Analysis , Isoenzymes/metabolism , Maxilla , Molar , Orthodontics/methods , Periodontal Ligament/metabolism , Rats , Rats, Inbred F344 , Root Resorption/etiology , Root Resorption/metabolism , Stress, Mechanical , Tartrate-Resistant Acid Phosphatase , Time FactorsABSTRACT
We have constructed bacterial artificial chromosome (BAC) libraries from two grass species that reproduce by apospory, a form of gametophytic apomixis. The library of an apomictic polyhaploid genotype (line MS228-20, with a 2C genome size of approximately 4,500 Mbp) derived from a cross between the obligate apomict, Pennisetum squamulatum, and pearl millet ( P. glaucum) comprises 118,272 clones with an average insert size of 82 kb. The library of buffelgrass ( Cenchrus ciliaris, apomictic line B-12-9, with a 2C genome size of approximately 3,000 Mbp) contains 68,736 clones with an average insert size of 109 kb. Based on the genome sizes of these two lines and correcting for the number for false-positive and organellar clones, library coverages were found to be 3.7 and 4.8 haploid genome equivalents for MS 228-20 and B12-9, respectively. Both libraries were screened by hybridization with six SCARs (sequence-characterized amplified regions), whose tight linkage in a single apospory-specific genomic region had been previously demonstrated in both species. Analysis of these BAC clones indicated that some of the SCAR markers are actually amplifying duplicated regions linked in coupling in both genomes and that restriction enzyme mapping will be necessary to sort out the duplications.
