Consumer Durable Spending

macroeconomics, consumer, durable spending

The roles of wedging and friction in the mechanics of dental occlusal contacts

Objective: The primary aim of this project is to elucidate the basic mechanical engineering principles that govern and explain unexpected and counter-intuitive occlusal contact force measurements. Methods: Forces were measured on matched pairs of first molar denture, ceramic and stainless steel crowns during occlusion and disclusion, with human saliva and dry (control). The weighted maxillary assembly, guided by a precision slide, was lowered onto, and raised from, the mandibular crown. The forces experienced by the mandibular tooth were continuously measured by the load cell that supported it. Statistical analyses included LOESS smoothing splines and generalized additive models. Principles of basic statics and classic friction were applied to explain and validate the results. Results: It was determined that within the span of a single chomp, the in-occlusal plane force component (Flateral) on the tooth is highly variable in direction and/or magnitude. The most salient observations were that Flateral was higher in disclusion than in occlusion, and the largest Flateral did not necessarily occur when the bite force was maximum. Furthermore, saliva significantly affected the results. Conclusions: The results demonstrated that contacting teeth experience complex transient mechanical environments that can be readily explained with elementary engineering principles involving wedging and friction at the occlusal contacts

The effects of salivas on occlusal forces

Contacting surfaces of opposing teeth produce friction that, when altered, changes the contact force direction and/or magnitude. As friction can be influenced by several factors, including lubrication and the contacting materials, the aim of this study was to measure the occlusal load alterations experienced by teeth with the introduction of different salivas and dental restorative materials. Pairs of molar teeth were set into occlusion with a weighted maxillary tooth mounted onto a vertical sliding assembly and the mandibular tooth supported by a load cell. The load components on the mandibular tooth were measured with three opposing pairs of dental restorative materials (plastic denture, all-ceramic and stainless steel), four (human and three artificial) salivas and 16 occlusal configurations. All lateral force component measurements were significantly different (P < 0·0001) from the dry (control) surface regardless of the crown material or occlusal configuration, while the effects of the artificial salivas compared to each other and to human saliva depended on the crown material

A proposed mechanism for non-carious cervical lesions, root resorption and abutment screw loosening

Objectives The purpose of this paper is to present a mechanism for the shared etiologies of non-carious cervical lesions (NCCLs), orthodontics-associated root resorption and implant abutment screw loosening. These are persistent clinical problems with equivocal etiologies. Methods A matched pair of 1st molar denture teeth was set into occlusion within a testing apparatus. The weighted maxillary assembly, guided by slides, was cyclically lowered onto, and raised from, the mandibular tooth. The forces and moments on the mandibular tooth were continuously recorded by a load cell. The maxillary crown was rigidly fixed (ankylosed or implant supported). The mandibular tooth was rigidly fixed or supported by a PDL analogue. For statistics, 21 occlusal relationships were tested. Results The measurements confirmed earlier non- and counter-intuitive results. The directly relevant data were that the measured loads on the tooth, during the span of an individual chomp, are characterized by a wide range of magnitudes and directions. Moreover, these load profiles change with rigid vs. PDL support (p = 0.001), occlusal relationship (p < 0.001) and occlusion vs. disclusion (p = 0.002). Conclusion The demonstrated transient loads within the span of a single chomp produce complex mechanical environments. Thus, it is proposed that NCCLs, orthodontic root resorption and abutment screw loosening result from load component combinations, not from solitary occlusion forces as typically applied in experimental and numerical investigations. In principle, the loading combination concept applies to all phenomena that involve occlusal contacts, including occlusal trauma, implant loading, jaw fracture repairs, etc

The significance of loading profile on the occlusion mechanics of a viscoelastic periodontal ligament analogue-supported tooth

Background: Benchtop studies of occlusal contact forces have used teeth that were rigidly attached or supported by readily available viscoelastic (VE) materials that served as periodontal ligament (PDL) substitutes. More recent specimens have incorporated a precisely dimensioned VE PDL-behavior matched analogue. Objectives: The objectives of this study were to evaluate a modified loading protocol (step function) that is more appropriate to VE support than the previously used ramp function. The occlusion manifestations of the time-dependent behaviors (creep and recovery) of the PDL analogue were examined using the revised protocol. Methods: A mandibular 1st molar denture tooth was set into a precision-machined root/socket assembly. The PDL substitute was then cured to tight dimensional tolerances. The matching rigidly fixed maxillary denture tooth was aligned into a Class I centric molar relationship in a testing apparatus. The weighted maxillary assembly was then cycled onto and off of the load cell-supported mandibular assembly. For statistical purposes, three loading schedules were tested in 21 0.05 mm shifted occlusal relationships. Rigid attachment served as control. Results: Statistical analyses were performed on the peak values of Flateral, the net in-occlusal plane force component of the occlusal contact forces. It was found that there were statistically significant differences between: chomp-to-chomp (p < .038), PDL vs. rigid (p < .001) and loading schedules (p < .044 for PDL only). Conclusion: The loading protocol affects outcomes, and the step functions maintained consistent timing with prescribable creep and recovery periods

Baseline Biomechanical Properties of Epithelia prior to Tissue Expansion in Dogs

Background: Soft-tissue deficiencies pose a challenge in a variety of disease processes when the end result is exposure of underlying tissue. Although multiple surgical techniques exist, the transposition of tissue from one location to another can cause donor-site morbidity, long incisions prone to dehiscence, and poor patient outcomes as a result. Use of tissue expansion prior to grafting procedures has been shown to have success in increasing available soft tissue to aid in repairing wounds. However, the current tissue expanders have biomechanical limits to the extent and rate of expansion that usually exceeds the tissue capacity, leading to incisional dehiscence or expander extrusion. Understanding the baseline biomechanical properties of the tissue to be expanded would provide useful information regarding surgical protocol employed for a given anatomical location. Therefore, the aim of this study was to test and compare the baseline (preexpansion) biomechanical properties of different common expansion sites in dogs. Methods: Four samples measuring approximately 20 × 15 × 1 mm were harvested from 8 dogs. The samples were collected from the hard palate, alveolar mucosa, scalp, and chest of the animal and analyzed for stress, strain, maximum tangential stiffness, maximum tangential modulus, and tensile strength using a Texture Technologies TA.XT texture analyzer with corresponding biomechanical measurement software. Samples were compared as to their baseline biomechanical properties prior to any soft-tissue expansion. Histological sections of the samples were analyzed using hematoxylin eosin in an attempt to correlate the histological description to the biomechanical properties seen during testing. Summary statistics (mean, standard deviation, standard error, range) are reported for stress, strain, maximum tangential stiffness, maximum tangential modulus, and tensile strength and for the histological parameters by intraoral site. Analysis of variance was used to compare the biomechanical and histological parameters among the 4 locations while accounting for multiple measurements from each dog. Results: The scalp had significantly higher maximum stress (σmax) than chest, mucosa, and palate (P 0.63). Scalp site also had significantly higher maximum tangential modulus (ε) than chest, mucosa, and palate (P 0.17). The locations did not have significantly different maximum tangential stiffness (k; P = 0.72). Histologically, 2 separate patterns of collagen disruption were evident. Conclusion: Although different results were obtained than theorized, this study showed that the scalp had the greatest resiliency to expand prior to tearing, and the highest tangential modulus, with all sites having statistically similar modulus of elasticity. Based on this study, the scalp could be expanded more aggressively compared with the other sites

Multiple mechanistically distinct modes of endocannabinoid mobilization at central amygdala glutamatergic synapses.

The central amygdala (CeA) is a key structure at the limbic-motor interface regulating stress responses and emotional learning. Endocannabinoid (eCB) signaling is heavily implicated in the regulation of stress-response physiology and emotional learning processes; however, the role of eCBs in the modulation of synaptic efficacy in the CeA is not well understood. Here we describe the subcellular localization of CB1 cannabinoid receptors and eCB synthetic machinery at glutamatergic synapses in the CeA and find that CeA neurons exhibit multiple mechanistically and temporally distinct modes of postsynaptic eCB mobilization. These data identify a prominent role for eCBs in the modulation of excitatory drive to CeA neurons and provide insight into the mechanisms by which eCB signaling and exogenous cannabinoids could regulate stress responses and emotional learning