ABSTRACT
OBJECTIVES: To test the hypothesis that periodontal ligament (PDL) stress relationships that yield resistance numbers representing load proportions between different teeth depend on alignment load type. MATERIALS AND METHODS: Finite element models of all teeth, except the third molars, were produced. Four different types of loads were applied, and the third principal stresses of different teeth in standardized areas of most compression were calculated. Based on these results, resistance numbers, representing the load proportions for each tooth derived from PDL stress, were determined. RESULTS: The third principal stress values for typical alignment loads in the areas of most stress were very different for different load types for each tooth. Differences in resistance numbers between teeth also varied with different loads. CONCLUSION: Resistance numbers, that is, load proportion numbers between teeth to achieve similar stress at the compressive PDL zone, depend on the type of applied load.
Subject(s)
Periodontal Ligament/physiology , Tooth Movement Techniques/methods , Bicuspid/physiology , Biomechanical Phenomena , Computer Simulation , Cuspid/physiology , Finite Element Analysis , Humans , Incisor/physiology , Models, Biological , Molar/physiology , Orthodontic Wires , Stress, Mechanical , Tooth Movement Techniques/instrumentation , Tooth Root/physiologyABSTRACT
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
Dental studies evaluating microCT output often examine resolution as a parameter that affects the data, but many other factors can influence image quality. The objective of this paper is to present the issues involved with the optimization of microCT data acquisition and processing for two biomechanical animal models. The first model evaluates surface and volumetric changes in root structure after in vitro fatigue loading of dog incisors. The second evaluates the in vivo morphometric bone and tooth responses to application of orthodontic force in inbred and transgenic mice. This type of data required specific magnification and noise control microCT settings to segment and render objects with acceptable definition. The proposed procedures enabled high definition rendering of changes in tooth and bone morphology in orthodontic studies. They also allowed for the construction of solid models for finite element analyses.
