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PubMed1993

Mechanical properties of artificial teeth.

In selecting the teeth for fabrication of complete or partial dentures, each patient's anatomic and physiologic requirements and the properties of the artificial teeth themselves should be taken into consideration. The purpose of this study was to evaluate the mechanical properties of the artificial teeth by the static compression test and the impact test. Specimens were the lower first molar porcelain and resin teeth (Livdent FB-20 teeth by G. C. Co., Tokyo, Japan). All were of the same shape. In the static compression test, the fracture load and deformation of the artificial teeth were measured with an Instron-type universal testing machine at a cross-head speed of 1.0 mm/min. Elastic modulus, ultimate strength and absorbed energy were calculated. In the impact test, the acceleration of a falling impactor was measured with a drop impact apparatus. The load applied to the specimen was equivalent to 300N. Absorbed energy and deformation were calculated. The resin teeth showed a lower elastic modulus, higher fracture toughness and shock-absorbing ability than the porcelain teeth. Resin teeth should be selected when the first requisite is high shock-absorbing ability, and porcelain teeth should be selected when the first requisite is high masticating efficiency.

Dental Porcelain↗
PubMed1994

Effect of polyethylene fiber reinforcement on the strength of denture base resins polymerized by microwave energy.

This study investigated the effect of addition of polyethylene fibers on the transverse strength, deflection, and elastic modulus of two denture base acrylic resins polymerized by microwave irradiation. Specimens of each resin, Lucitone 199 and Acron MC, were fabricated with 0.0%, 0.5%, 1.5%, and 3.0% fiber loading. Specimens were tested with use of a three-point flexure apparatus with an Instron universal testing machine after storage in water for 10 days at 37 degrees C. The results showed that polyethylene fibers significantly decreased the transverse strength of Acron MC resin and slightly increased the transverse strength of Lucitone 199 resin at a loading of 0.5% by weight. Fiber loading did not significantly affect the deflection and the elastic modulus of either material.

Acrylic Resins↗
PubMed1990

Comparisons of different debonding techniques for ceramic brackets: an in vitro study. Part I. Background and methods.

Techniques for removing metal orthodontic attachments are, for the most part, not as effective with ceramic brackets because the properties of ceramic brackets differ greatly from those of the conventional metal orthodontic brackets. Currently available ceramic brackets are composed of aluminum oxide crystals in either a polycrystalline or monocrystalline form that has a low fracture toughness compared with that of stainless steel. Metal brackets will deform 20% under stress before fracturing, whereas ceramic brackets will deform less than 1% before failing. The purpose of this study was (1) to evaluate the debonding characteristics of three different types of ceramic brackets when removed by techniques recommended by the manufacturers; (2) to evaluate and compare the conventional, ultrasonic, and electrothermal bracket-removal techniques, and (3) to evaluate and compare the mean enamel loss from removal by high-speed bur, by slow-speed bur, and by the ultrasonic method. In the first phase of the investigation, 140 teeth (70 maxillary central incisors and 70 third molars) were bonded with one of three types of ceramic brackets. Three different debonding methods were tested--(1) the conventional method recommended by the manufacturer (either pliers or wrench), (2) an ultrasonic method that employed specially designed tips, and (3) an electrothermal method involving an apparatus that transmits heat to the bracket. In each of the test groups, five variables were evaluated during and after bracket removal: (1) the incidence of bracket failure, (2) the amount of adhesive remaining after bracket removal, (3) the site of bond failure, (4) the debonding time for each technique, and (5) enamel damage resulting from bracket removal.(ABSTRACT TRUNCATED AT 250 WORDS)

Aluminum↗
PubMed1983

An evaluation of the vibrating reed method for determining the mechanical properties of materials.

The vibrating reed method is a recognized technique for the mechanical analysis of materials and offers a number of advantages over other types of test. However, little detailed evaluation of the method has been reported, particularly those aspects which affect accuracy and reproducibility. In this investigation, a vibrating reed apparatus was constructed which incorporated automatic detection of the reed displacement. A number of clamp designs were assessed and a range of materials, including some of biomedical interest, was examined. It was found that significant experimental inaccuracies were present and that these led to errors of approximately 15% in the measured properties. The most important contribution to this error arose from the clamping mechanism.

Acrylic Resins↗
PubMed2003

Combined effect of vestibular and craniomandibular disorders on postural behaviour.

A correlation has been reported in the dental literature between temporomandibular disorders and musculoskeletal abnormalities, however, the question whether they modify body postural sway remains controversial. In the present investigation, the Craniomandibular Index was used to evaluate the clinical extension of temporomandibular joint dysfunction and related problems in 40 patients with normal vestibular function and in 42 patients with peripheral vestibular disorders. Balance function was assessed by static posturography and body sway area was measured in two conditions: i) eye open, and g) eye closed. Data were compared to those of 40 healthy subjects. Postural control showed a significantly different behaviour between groups with an increase in average body sway in patients with craniomandibular disorders as opposed to controls (p < 0.005). Although the involvement of the stomatognathic apparatus was not quantitatively different in the two groups of patients, those also presenting a peripheral vestibular disorder exhibited greater average body sway than patients with only craniomandibular disorders (p < 0.005). The latter showed a greater average body sway than controls only in the trial with eyes closed (p < 0.05). The results demonstrated that craniomandibular alterations could produce moderate postural instability in patients with a normal vestibular function. Conversely, their association with peripheral vestibular disorders becomes a real challenge to the upright quiet stance probably due to a negative effect of somatosensory origin on the vestibulo-spinal reflex impairment.

Adult↗
PubMed1978

[A method for management of midfacial fractures (author's transl)].

In the treatment of severe "dish-face" deformities which result from Le Fort II and III middle face fractures, reposition and fixation of the maxilla can be achieved by an extraoral cranial fixation apparatus. We describe a modification of the Georgiade head frame which achieves higher stability in fixing the maxilla and arch wires. The joints applied to the rigid wire connecting the arch bar to the head frame make an adaptation to the upper lip possible; traction of the maxilla to maintain its fixation can be applied extra-orally so that closure of the lips with correction of occlusion is possible, making easier the uptake of nourishment.

Dental Occlusion↗
PubMed1993

Facial pain: trigeminal neuralgia.

Atypical facial pain is a loose term used to encompass a wide range of facial pain syndromes including those of dental and ear, nose and throat (ENT) aetiology. Often, it is associated with psychiatric conditions like depression and psychosomatic illnesses. This facial pain typically does not follow anatomical boundaries or its explainable by present day neurophysiological understanding. The pain is often constant with no remission and is aggravated by stress. Treatment is difficult and often directed to the psychiatric cause. Surgical treatment is contraindicated. Trigeminal neuralgia on the other hand, can be effectively treated. Pain in the trigeminal distribution is paroxysmal, precipitated by trigger factors and there is no pain in between attacks. The aetiology of trigeminal neuralgia is still unknown though current thinking is that there is a peripheral disturbance or damage with cerebral brainstem disinhibition of the trigeminal apparatus. This results in a paroxysmal discharge and reverberation of pain impulses when a trigger point is elicited. Therefore, anti-epileptic drugs like tegretol can be effective in controlling trigeminal neuralgia in the majority of patients, at least in the initial stages. For unknown reasons however, medical treatment either is not effective at all from the very beginning or fails after a few years. Surgery then becomes the only available therapeutic option. If the peripheral disturbance is due to an organic cause like a tumour, surgical approaches should be directed towards its removal. Often the pain will also resolve. If the trigeminal neuralgia is of the idiopathic variety, then the surgeon has a choice of either peripheral percutaneous retrogasserian ganglionectomies or central approaches like microvascular decompression and trigeminal tractotomy.

Anesthetics, Local↗
PubMedDate not supplied

No relationship between subchronic fluoride intake and DNA damage in Wistar rats.

Fluoride has been widely used in dentistry because it is an effective caries prophylactic agent. However, excess fluoride may represent a hazard to human health, especially by causing injury on the genetic apparatus. Genotoxicity tests form an important part of cancer research and risk assessment of potential carcinogens. In the current study, the potential DNA damage associated with exposure to fluoride was assessed by the single cell gel (comet) assay in peripheral blood, oral mucosa and brain cells in vivo. Male Wistar rats were exposed to sodium fluoride (NaF) at a 0, 7 and 100 ppm dose for drinking water during 6 weeks. The results pointed out that NaF did not contribute to the DNA damage in all cellular types evaluated as depicted by the mean tail moment and tail intensity. These findings are clinically important since they represent an important contribution to the correct evaluation of the potential health risk associated with dental agents exposure.

Analysis of Variance↗
PubMed1989

[Materials technology research on the problem of friction between bracket and arch].

Orthodontic tooth movement along the arch wire is associated with a frictional force between bracket and wire. There is as yet little certainty as to how much force is lost as a result of friction. Therefore a measuring apparatus was used to measure torque in relation to bracket angulation. In all, five types of wire, each of different dimensions were measured in three brackets of differing widths. The results showed significant differences between the types of wire. As the wire dimensions are increased, so likewise are the frictional forces. Bracket with and frictional force bear an inverse relationship to each other. Frictional force increases the greater the surface roughness of the wire.

Dental Alloys↗
PubMed1995

The centered T-loop--a new way of preactivation.

The force system of a prefabricated and preactivated T-loop used for reciprocal space closure was determined by simultaneously measuring the horizontal and vertical forces, as well as the moments using a computer controlled measuring apparatus. Interbracket distances of 21, 24, 27, and 30 mm were used to mimic typical clinical situations. At a loop activation of 7 mm, the anterior and posterior segments first underwent controlled tipping, then translation, and finally, root uprighting as the moment-to-force ratio increased with deactivation. After the loop has been deactivated to 4 mm, however, it should be exchanged to avoid root abutment.

Analysis of Variance↗
PubMed2001

Preprosthetic clinical crown lengthening procedures in the anterior maxilla.

Clinical crown lengthening procedures (CCLP) are used to enhance aesthetics and/or provide adequate tooth structure for placement and retention of a restoration while respecting the attachment apparatus. When restoration margins extend beyond the biologic width, inflammation and anatomic changes can develop. Anterior CCLP are indicated to increase the labial exposure of the clinical crown and/or the sound tooth structure coronal to the bone crest. Preservation of the interproximal papillae is mandatory to obtain desirable final results in the aesthetic region. This article illustrates various methods of CCLP used to achieve successful oral rehabilitation in the anterior maxilla.

Crown Lengthening↗
PubMed1996

[Digital radiology using the DIGORA registration technic].

Improvements in computer technology have brought about great changes in the manner in which X-ray diagnostics can be carried out. Both the registering and analysis of X-ray images can now be facilitated by the use of computer apparatus. The registering of X-ray images can be carried out with an X-ray sensitive sensor (CCD-sensor), which is inserted in the mouth and is linked to the computer by a thin cable. Another technique is based upon the use of storage phosphor plates. These are made of a material that can hold the latent X-ray image for some time after radiation and can be read by stimulation with laser light. The advantages of this method are that there is much similarity with the way in which X-ray photographs are registered on X-ray film and that the sensor is not connected to a cable. This latter quality allows one more freedom of movement in relation to the computer apparatus in the place were the X-ray photos are taken. Storage phosphor plates are less suitable than CCD systems for very precise quantitative measurement of X-ray photos. For diagnostic purposes, however, their picture quality is in no way inferior to that of CCD systems and of film-based X-ray techniques.

Equipment Design↗
PubMed1992

A computer-based biomechanical analysis of the three-dimensional motion of cementless hip prostheses.

A computer-based mathematical technique was developed to measure and completely describe the migration and micromotion of a femoral hip prosthesis relative to the femur. This technique utilized the mechanics of rigid-body motion analysis and apparatus of seven linear displacement transducers to measure and describe the complete three-dimensional motion of the prosthesis during cyclic loading. Computer acquisition of the data and custom analysis software allowed one to calculate the magnitude and direction of the motion of any point of interest on the prostheses from information about the motion of two points on the device. The data were also used to replay the tests using a computer animation technique, which allowed a magnified view of the three-dimensional motion of the prosthesis. This paper describes the mathematical development of the rigid-body motion analysis, the experimental method and apparatus for data collection, the technique used to animate the motion, the sources of error and the effect of the assumptions (rigid bodies) on the results. Selected results of individual test runs of uncemented and cemented prostheses are presented to demonstrate the efficacy of the method. The combined effect of the vibration and electrical noise resulted in a resolution of the system of about 3-5 microns motion for each transducer. Deformation effects appear to contribute about 3-15 microns to the measurement error. This measurement and analysis technique is a very sensitive and powerful means of assessing the effects of different design parameters on the migration and micromotion of total joint prostheses and can be applied to any other case (knee, dental implant) where three-dimensional relative motion between two bodies is important.

Biomechanical Phenomena↗
PubMed2005

Stereolithographic models for simulation and transfer of vector in vertical distraction of the mandibular ramus: a technical note.

Mandibular distraction osteogenesis is, despite impressive results, compromised as a treatment modality by difficulties with vector control independent of whether intra- or extraoral devices are used. Resistance of the masticatory muscles and the remaining soft tissue envelope toward elongation and incorrect planning and transfer of the vector cause lack of vector control. To ensure predictability in correct placement of intraoral distraction devices and thereby treatment outcome, a combined planning, simulation, and transfer method was developed. The purpose of the simulation and transfer technique is to duplicate the planned and simulated position and orientation of the distraction device during surgery. The preoperative plan is based on frontal and lateral head films, and the planned position and orientation of the distraction apparatus was applied on the stereolithographic model. The model was cut according to the planned osteotomy, and the distraction was simulated on the stereolithographic model. Based on plaster models transferred to the stereolithographic model, an individual guiding splint was fabricated to reproduce the planned and simulated distraction treatment in the patient. The details of the simulation and transfer technique are presented and discussed in two cases.

Adolescent↗
PubMed2000

Epiglottic hypoplasia associated with lacrimo-auriculo-dental-digital syndrome.

We present a case of a young boy with clinical manifestations of lacrimo-auriculo-dental-digital syndrome (LADD) with the additional finding of a hypoplastic epiglottis that caused airway obstruction at birth. We also reviewed the 30 cases of LADD that have been reported since 1967. It is a rare syndrome that includes lacrimal system, aural, digital, and dental anomalies. Our patient has lacrimal duct obstruction, deficient tissue in the inferior portion of the ear pinnae, and a hypoplastic epiglottis with collapse of the supraglottic tissue. Many findings of LADD are recognizable at birth. The clinical spectrum has widened with more case reports. Our patient adds a life-threatening airway abnormality, a hypoplastic epiglottis, to the clinical spectrum of LADD.

Abnormalities, Multiple↗
PubMed2006

Lack of DNA damage induced by fluoride on mouse lymphoma and human fibroblast cells by single cell gel (comet) assay.

Fluoride has widely been used in Dentistry because it is a specific and effective caries prophylactic agent. However, excess fluoride may represent a hazard to human health, especially by causing injury on genetic apparatus. Genotoxicity tests constitute an important part of cancer research for risk assessment of potential carcinogens. In this study, the potential DNA damage associated with exposure to fluoride was assessed by the single cell gel (comet) assay in vitro. Mouse lymphoma and human fibroblast cells were exposed to sodium fluoride (NaF) at final concentration ranging from 7 to 100 microg/mL for 3 h at 37 degrees C. The results pointed out that NaF in all tested concentrations did not contribute to DNA damage as depicted by the mean tail moment and tail intensity for both cellular types assessed. These findings are clinically important because they represent a valuable contribution for evaluation of the potential health risk associated with exposure to agents usually used in dental practice.

Analysis of Variance↗
PubMed1998

Metal strength of direct bonding brackets.

Because the strength of direct bonding brackets is both important and difficult to measure, a related property, microhardness, has been investigated. Twelve popular U.S. brands of direct bonding brackets have been tested with a Vickers-Hanemann microhardness apparatus. The tests have shown a consistently wide difference in hardness between brands, the highest values being exhibited by those using the precipitation hardened steel known as PH 17-4, and the lowest by those using the austenitic 316L. As the first steel proved to be significantly less corrosion resistant than the last one, it seems that today there are too few attachments that are both strong and chemically resistant.

Analysis of Variance↗
PubMed1997

Comparative functional morphology of mandibular forward movement during mastication of two murid rodents, Apodemus speciosus (Murinae) and Clethrionomys rufocanus (Arvicolinae).

The anatomy of the masticatory apparatus, the direction in which masticatory muscles act during mastication, and jaw muscle forces as estimated by muscle dry weight are compared between two murid rodents, the Japanese field mouse (Apodemus speciosus, subfamily Murinae) and the gray red-backed vole (Clethrionomys rufocanus; subfamily Arvicolinae). The occlusal forces exerted by the deep masseter and the anterior temporalis are large in C. rufocanus. Furthermore, in this species, the angle between the sagittal plane and the occlusal plane of the cheek teeth is larger than in A. speciosus. Therefore, a relatively large occlusal force can be generated in C. rufocanus. The estimated line of action of the anterior temporalis differs markedly between these two species. The functional significance of this difference is discussed relative to the adaptive dental characteristics for food processing, the forces required to masticate different types of food, and the forces that control mandibular forward movement.

Animals↗