The effects of sympathetic trunk stimulation on the position and mobility of the canine tooth of the cat

The effects of cervical sympathetic trunk stimulation on the position of the maxillary canine tooth and its movements in response to mechanical loading were studied using an ultrasonic transit time technique. Stimulation of the ipsilateral sympathetic trunk for 10–60s and frequencies between 1 and 20 Hz caused both longitudinal and transverse movements of the tooth. Bilateral carotid occlusion caused negligible movements in either direction. When a controlled force was applied in the palatal direction, sympathetic stimulation caused a labial shift of the tip of the tooth and usually an increase in the load-induced palatal displacement; i.e. the mobility of the tooth was increased and appeared to be dependent on the amount of labial shift of the tooth. It is concluded that interference with the vascular component has little, if any, direct effect on the tooth mobility.     

Analyses of layer-thickness effects in bilayered dental ceramics subjected to thermal stresses and ring-on-ring tests.

OBJECTIVES: The purpose of this study was to analyze the stress distribution through the thickness of bilayered dental ceramics subjected to both thermal stresses and ring-on-ring tests and to systematically examine how the individual layer thickness influences this stress distribution and the failure origin. METHODS: Ring-on-ring tests were performed on In-Ceram Alumina/Vitadur Alpha porcelain bilayered disks with porcelain in the tensile side, and In-Ceram Alumina to porcelain layer thickness ratios of 1:2, 1:1, and 2:1 were used to characterize whether failure originated at the surface or the interface. Based on (1) the thermomechanical properties and thickness of each layer, (2) the difference between the test temperature and the glass transition temperature, and (3) the ring-on-ring loading configuration, the stress distribution through the thickness of the bilayer was calculated using closed-form solutions. Finite element analyses were also performed to verify the analytical results. RESULTS: The calculated stress distributions showed that the location of maximum tension during testing shifted from the porcelain surface to the In-Ceram Alumina/porcelain interface when the relative layer thickness ratio changed from 1:2 to 1:1 and to 2:1. This trend is in agreement with the experimental observations of the failure origins. SIGNIFICANCE: For bilayered dental ceramics subjected to ring-on-ring tests, the location of maximum tension can shift from the surface to the interface depending upon the layer thickness ratio. The closed-form solutions for bilayers subjected to both thermal stresses and ring-on-ring tests allow the biaxial strength of the bilayer to be evaluated.     

Analysis of the degradation of a model dental composite

Dental composites undergo material property changes during exposure to the oral environment and may release compounds of potential toxicity, such as bisphenol A. Degradation of dental composites was studied in a simplified overlayer model in which bisphenol A diglycidyl methacrylate (BisGMA) was covalently bound to a porous silicon oxide surface. It was hypothesized that the chemical structure of this overlayer would allow release of bisphenol A, BisGMA, and the decomposition products thereof, upon exposure to water for an extended period. Liquid chromatography mass spectrometry found leaching of intact BisGMA and several degradation products that contained the bisphenol A moiety from the overlayer into distilled water after 2 wks of aging. The absence of bisphenol A release from the overlayer reduces concerns regarding its potential health risk in dental composites. Nevertheless, health concerns might arise with respect to BisGMA and the leached degradation products, since they all contain the bisphenol A moiety. Abbreviations: BisGMA, bisphenol A diglycidyl methacrylate; HPLC, high-performance liquid chromatography; LCMS, liquid chromatography mass spectrometry; MA, methacrylic acid; MPS, 3-(trimethoxysilyl) propyl methacrylate; m/z, mass-to-charge ratio; and TIC, total ion chromatogram.     

The influence of zero-value subtraction on the performance of two laser fluorescence devices for detecting occlusal caries in vitro

BACKGROUND: The aim of this study was to evaluate the influence of zero-value subtraction on the performance of two laser fluorescence (LF) devices developed to detect occlusal caries. METHODS: The authors selected 119 permanent molars. Two examiners assessed three areas (cuspal, middle and cervical) of both mesial and distal portions of the buccal surface and one occlusal site using an LF device and an LF pen. For each tooth, the authors subtracted the value measured in the cuspal, middle and cervical areas in the buccal surface from the value measured in the respective occlusal site. RESULTS: The authors observed differences among the readings for both devices in the cuspal, middle and cervical areas in the buccal surface as well as differences for both devices with and without the zero-value subtraction in the occlusal surface. When the authors did not perform the zero-value subtraction, they found statistically significant differences for sensitivity and accuracy for the LF device. When this was done with the LF pen, specificity increased and sensitivity decreased significantly. CONCLUSIONS: For the LF device, the zero-value subtraction decreased the sensitivity. For this reason, the authors concluded that clinicians can obtain measures with the LF device effectively without using zero-value subtraction. For the LF pen, however, the absence of the zero-value subtraction changed both the sensitivity and specificity, and so the authors concluded that clinicians should not eliminate this step from the procedure. CLINICAL IMPLICATIONS: When using the LF device, clinicians might not need to perform the zero-value subtraction; however, for the LF pen, clinicians should do so.     

A cost-efficiency analysis of a mobile dental clinic in the public services.

During 1997, the Gauteng Oral Health Services implemented a Mobile Oral Health Care System (MOHCS) in the province. For the first year (1997/98) one mobile dental clinic was utilised in the West Rand region of the province and services were provided by dentists, dental therapists and oral hygienists. The purpose of the MOHCS is to provide an accessible and affordable comprehensive oral health care service of high quality and standard. The aim of this study was to determine the cost-efficiency of the mobile dental clinic utilised in the West Rand region over the first year of implementation. After consultation with all stakeholders, an operational plan was finalised. The plan included a traveling schedule, clinicians available for service delivery, and a management information system (MIS). Statistics on dental materials, consumables, treatment provided, etc. were collected and analysed. During the study period 2072 patients received dental treatment at 38 different sites in the region. At an average cost of R56.50 (+/- US$11) per patient, services to the value of R92.45 (+/- US$18) per patient were delivered during 104 working days. Of the 1477 patients treated by a dentist or dental therapist, 53% were treated by extracting 1026 teeth, and 27% by restoring 570 teeth. For oral hygiene patients, 67% received an oral hygiene procedure and 13% received fissure sealants. With a net margin ratio of 0,39 and a breakeven point of 1173,46 patients and 58,90 days, an accessible and cost-efficient service was provided to health districts in the West Rand region.     

The effect of high fiber fraction on some mechanical properties of unidirectional glass fiber-reinforced composite

Objectives

This study was designed to evaluate the effect of an increase of fiber-density on some mechanical properties of higher volume fiber-reinforced composite (FRC).

Methods

Five groups of FRC with increased fiber-density were fabricated and two additional groups were prepared by adding silanated barium-silicate glass fillers (0.7 μm) to the FRC. The unidirectional E-glass fiber rovings were impregnated with light-polymerizable bisGMA-TEGDMA (50-50%) resin. The fibers were pulled through a cylindrical mold with an opening diameter of 4.2 mm, light cured for 40 s and post-cured at elevated temperature. The cylindrical specimens (n = 12) were conditioned at room temperature for 2 days before testing with the three-point bending test (Lloyd Instruments Ltd.) adapted to ISO 10477. Fiber-density was analyzed by combustion and gravimetric analyzes.

Results

ANOVA analysis revealed that by increasing the vol.% fraction of E-glass fibers from 51.7% to 61.7% there was a change of 27% (p < 0.05) in the modulus of elasticity, 34% (p < 0.05) in the toughness, and 15% (p < 0.05) in the load bearing capacity, while there was only 8% (p < 0.05) increase in the flexural strength although it was statistically insignificant. The addition of particulate fillers did not improve the mechanical properties.

Significance

This study showed that the properties of FRC could be improved by increasing fibervolume fraction. Modulus of elasticity, toughness, and load bearing capacity seem to follow the law of ratio of quantity of fibers and volume of the polymer matrix more precisely than flexural strength when high fiber-density is used.     

Orthodontics in general practice. 4. Eruption guidance appliances in orthodontics

Eruption guidance appliances are recommended for early orthodontic treatment or prevention of malocclusions. The treatment effect of eruption guidance appliances and functional appliances is similar. In addition to dentoalveolar and skeletal effects, eruption guidance appliances would also have myofunctional effects for treating open mouth behaviour and swallowing problems. However, there is no solid evidence for the myofunctional effect claimed. The position of erution guidance appliances in the orthodontic treatment arsenal is limited: early treatment of Angle Class II malocclusion in 2 phases has no advantage over a 2 phase treatment. When eruption guidance is needed, preference is given to an individually produced appliance.