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At least 829 records · Page 46Linked to original sources
PubMed2005

Shape retention in porcine and rabbit nasal septal cartilage using saline bath immersion and Nd:YAG laser irradiation.

BACKGROUND AND OBJECTIVES: The process of altering the shape of cartilage using heat has been referred to as thermoforming, and presents certain clinical benefits in reconstructive surgical procedures within the head and neck. Thermoforming allows cartilage in the upper airway and face to be reshaped without the use of classic surgical maneuvers such as carving, morselizing, or suturing. The goal of this study was to determine the dependence of cartilage shape change on both temperature and laser dosimetry using two thermoforming methods: saline bath immersion and laser irradiation. STUDY DESIGN/MATERIALS AND METHODS: Ex-vivo rabbit and porcine nasal septal cartilages were mechanically deformed and reshaped using the two thermoforming methods. With saline bath immersion using rabbit cartilage, each specimen was deformed by securing it to a small copper tube (outer diameter 8 mm) using dental bands. For porcine cartilage immersed in a saline bath, each sample was mechanically deformed between two pieces of wire mesh attached to a semicircular acrylic block. With both porcine and rabbit cartilage, the specimen and apparatus were then immersed in a hot saline bath for time intervals varying from 20 and 320 seconds and at constant temperatures between 62 and 74 degrees C. In laser reshaping, the cartilage specimens were mechanically deformed on a jig and consecutively irradiated with an Nd:YAG laser (lambda = 1.32 microm) in several spots for 6-16 seconds and irradiances of 10.2-40.7 W/cm2 per spot. After either saline bath heating or irradiation, cartilage specimens were immersed in room temperature saline for 15 minutes, then upon removal from the jig the length between the ends of each specimen was measured in order to calculate the resulting bend angle. RESULTS: The transition zone for cartilage reshaping was defined as where a significant increase in bend angle was observed between consecutive times of immersion/irradiation at the same temperature/irradiance. For the saline bath experiments, the transition zone was observed between 59-68 degrees C and 62-68 degrees C for porcine and rabbit cartilage, respectively. Similar transition zones occurred with laser irradiation below irradiances of 20.4 W/cm2 for both porcine and rabbit cartilage. In addition, the dosimetry pairs in the transition zones produce peak temperatures below the thresholds determined from the saline bath immersion studies. CONCLUSIONS: The critical transition temperature region was determined by the sharp increase in bend angle at consecutive times of immersion at the same temperature. This range was determined to be 59-68 degrees C and 62-68 degrees C for porcine and rabbit cartilage, respectively. Similar transition zones for dosimetry occurred below 20.4 W/cm2 during cartilage irradiation in both species.

Animals↗
PubMed2005

Film thickness and fluidity of various luting cements determined using a trial indentation meter.

OBJECTIVES: The purpose of this study was to evaluate a new trial apparatus which could measure film thickness (T(h)) under a low load, using an indenter. METHODS: Five commercial luting cements were measured using this apparatus. T(h) was determined using four kinds of indenter, which were 5.0, 10.0, 15.0 and 20.0mm in diameter. For each indenter, the load per contact area of the indenter with the platen equaled 150N per 200 mm2 described in ISO No. 9917. The effects of working time (30, 60, and 90 s) and load (2.86, 6.78, 10.7, and 14.7N) on the fluidity and T(h) were examined using the indenter with a diameter of 5.0mm. The duration of loading was 10 min. The fluidity was defined as the reciprocal of the apparent viscosity and was calculated using Stefan's equation. RESULTS: The T(h) obtained using this apparatus agreed with the film thickness obtained using the test described in ISO No. 9917. For Durelon (DU), T(h) increased 1.58 times and fluidity decreased 0.26 times as the working time increased from 30 to 90 s; T(h) decreased 0.56 times and fluidity increased 1.28 times as loading increased from 2.86 to 14.7N. For Ketac cement radiopaque (KE), Panavia fluoro cement (PA), Scotchbond resin cement (SC), and Vitremer luting cement (VI), although the fluidity and T(h) were not influenced much by duration (30-90 s), T(h) decreased 0.79, 0.74, 0.95, and 0.78 times for KE, PA, SC, and VI, respectively, and fluidity decreased 0.68, 0.51, 0.30, and 0.36 times, respectively, as loading increased from 2.86 to 14.7N. SIGNIFICANCE: This apparatus was proven effective in elucidating the flow properties of luting cement.

Composite Resins↗
PubMed1991

[The development of anesthesia in german-speaking regions in the 19th century].

Following the first public demonstration of ether anaesthesia by W.T.G. Morton on October 16, 1846, the pioneers to perform ether anaesthesia in German speaking countries were H. A. Demme, surgeon at the University Hospital Bern, Switzerland, on January 23, 1847, the German surgeon J. F. Heyfelder at Erlangen on January 24, and the Austrian surgeon F. Schuh in Vienna on January 27, 1847. The first books in German language referring to clinical experience with and experimental research on sulphuric ether were published in March/April 1847. After the introduction of chloroform the use of ether anaesthesia rapidly decreased. Chloroform administration was smoother and much more easier not requiring any special apparatus. Chloroform remained the preferred anaesthetic till the end of the century although there happened significantly more deaths due to this agent than to ether. Since 1863 nitrous oxide again was propagated for pain relief in dental practice. German investigators provided pioneering contributions to the development of local and regional anaesthesia. C. Koller, Vienna, was the first to operate on a patient in local anaesthesia with cocaine. The next steps were the introduction of infiltration anaesthesia by C. L. Schleich in 1892/1894 and of spinal anaesthesia by A. Bier in 1899. The ultimate success of local and regional anaesthesia was made possible by using adrenaline with the local anaesthetic (1901) and by the introduction of novocaine in 1905.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthesia↗
PubMed1996

Fracture strength of ceramic brackets during arch wire torsion.

This study evaluated the fracture strengths of eight new vintage ceramic brackets with application of torsional forces. Palatal root torque was applied at the distal side of right maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 x 0.027-inch rounded edge stainless steel arch wire. A specially designed apparatus that attached to an Instron machine was used to test the ceramic brackets. The amount of torque, degrees of torsion at failure, and fracture locations were measured. The monocrystalline bracket did not break when the torquing test was applied; the portion of the wire outside the slot of the bracket twisted on itself. The mean torquing forces at failure ranged from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three statistically different groups. The mean torsional rotation at fracture ranged from 32.7 degrees to 68.1 degrees for the polycrystalline brackets. The results suggested that all the brackets studied were sufficiently strong to withstand the commonly accepted magnitudes of arch wire torquing forces. The present investigation showed higher angulation values for all the brackets than those reported by Holt who used the same apparatus with older style brackets.

Analysis of Variance↗
PubMed1991

[Efficiency of various dental dust-aspiration-equipment regarding the treatment of cobalt-chromium alloys].

The comparative measuring of the dust-seizure-efficiency of aspirators is being carried out by a practice-related treatment of 5 cylindrical-shaped specimen made of a commercial cobalt-chromium-alloy with aluminum-oxide-grinding instruments and silicone-rubber-polishers. A small-filter-apparatus takes up the person related samplings of the occurring total-dust-amount, which is then being calculated by a gravimetric standard-measuring-procedure. The cobalt-chromium-dust-fraction in the total dust amount is determined through an x-ray-fluorescence-analysis. Workplace dust-aspiration-equipment of the firms KaVo, Freuding and Wassermann have been subjected to testing. The values of the efficiency of all aspirators turned out to be below the American Threshold Limit Value TLV-TWA (Threshold Limit Value-Time Weighted Average) of 0.5 mg/m3 for chromium. The strict TLV-TWA-value of 0.05 mg/m3 for cobalt it also--with the exception of the Freuding-aspirator A 84 with aspiration-tube--not exceeded.

Air Pollutants, Occupational↗
PubMed2000

[Recurrence: mechanisms and treatments].

An original analysis by computer has been imagined. Etiological diagnosis in recurrence's cases is based on asymmetry. Different levels were investigated: dental arch, ridge, basal bone and mandibular position. Dental shift, deformed bone, eccentric mandibular and occlusal distortion were found. Each molar is independently moving. Mandibular basal bone is stabilized in the transverse dimension. Mandibular deviation induces compression or stretching in temporo-mandibular articulation. Occlusal interferences involve distortion of cuspal plans. To reach stable objectives, molars require symmetrical position below one millimeter discrepancy, molar locking is to be had for the disto-vestibular cusp and ovoid arch. A special anchor apparatus allows to correct every wrong position of each individual molar, in each three-directional space. Mini-positioner or mini-splint perfect anterior misalignment. Sometimes, thermical memory archs are required. Ten fundamental rules that regulate occlusal and mandibular stability have been checked after treatment.

Alveolar Process↗
PubMed2003

Oral manifestations of triple A syndrome.

Triple A (four A; Allgrove syndrome) syndrome is a an autosomal recessive disorder characterized by alacrimia, achalasia, adrenocortical insufficiency, and various neurological abnormalities. We report a case of triple A syndrome in a 14-year-old female patient together with oral manifestations. The importance of this case report is to highlight the necessity of referring the young patients with xerostomia from dental to medical specialists.

Adolescent↗
PubMed1979

[Uses of the occlusal registration instrument (ORI)].

By means of the occlusal recording instrument (ORI), jaw models can be measured three-dimensionally and filed with respect to axes and skull. In clinical trials evaluated with the ORI, it was shown that the position of the maxilla in the skull can be transferred to the articulator with great accuracy. Suggestions are given for improvements to refine the method of measurement. If the third point of reference is also tattooed, the accuracy of the transference of the face-bow is considerably increased. Under these conditions the apparatus is suitable for checking the accuracy of the transference of the face-bow and for photographic documentation.

Dental Articulators↗
PubMed1979

[Determination and position of the masticatory surface complex and clinically necessary corrections (with special regard to Fehr's calotte articulation)].

The individual calotte articulation recommended by C. U. Fehr in 1947 has been used at the Free University of W. Berlin for clinical teaching since this time. The following studies were described and/or recalled and contrasted with other methods for determining position: 1. Studies of Grabert mandibular posture compared with the Ivo-Tray model. 2. Stoebe's studies of calottes with various radii, 3. Eichner's and Schmitthelm's roentgencinematographic studies, 4. Reese's study of biting force, 5. Husemann's comparison of different relational determinations, 6. Sauer's study of the success of reocclusion. Based on the clinical results and also the results of difficult comparative studies. we see no reason to depart from functional determination of relation using calotte-shaped, curved wax walls. Clinical example of the grinding surface complex, which is part of the method, guarantees construction of the complete denture within the range of tissue adaptation. No elaborate apparatuses are required. Even complicated tracing methods do not eliminate the possibility of additional work (e.g., removal of pressure areas, reocclusion).

Dental Impression Technique↗
PubMed2003

A preliminary study to investigate the potential of plasma screen technology in small group teaching for dental undergraduates.

AIM: This preliminary study was devised to ascertain whether students considered that they had an adequate view of demonstrated procedures, while observing these directly at the workbench, or indirectly on a remote plasma screen. In addition, this study sought to identify whether the students observing remotely believed that they had been disadvantaged by the inability to question the demonstrator during the demonstration. METHODS: Seventeen students divided into two groups observed a live demonstration of a laboratory technical procedure either at the workbench, or remotely at a plasma screen with the aid of video cameras. They subsequently observed a second demonstration with the roles reversed. Questionnaires were used to obtain the students' views of their ability to see and interact with the demonstrator. RESULTS: The responses of the students observing the demonstration at the plasma screen indicated that (they felt that) they were able to see the demonstration more clearly than those observing at the workbench. Those observing at the plasma screen first, in particular indicated this. The majority of students acknowledged their inability to ask questions while observing at the plasma screen. There was overwhelming support for the idea that the plasma screen should be used to complement the demonstration at the workbench. CONCLUSION: Plasma screen technology has considerable potential as a teaching tool for small groups of students, where it can afford significantly superior views of practical procedures. The students considered that the plasma screen would be best employed to provide close-up views to supplement a live demonstration. When used remotely, the apparatus may be used more satisfactorily if videoconferencing technology is also employed to facilitate interaction with the demonstrator.

Attitude↗
PubMed1997

Students' attitudes towards and use of computer-assisted learning in oral radiology over a 10-year period.

OBJECTIVE: To compare the attitudes towards CAL of today's dental students with those 10 years ago and to assess the use of CAL over a 10-year period. METHODS: A questionnaire was given to 40 current dental students containing 15 identical questions to those asked 10 years previously. Attitudes were ranked on a scale from 1 (worst) to 5 (best). Over the entire period, 420 students (mean = 42 students/year, range 33-56) used the programs. The material consisted of interactive computer-based teaching programs on: intraoral radiography, X-ray density and sharpness, basic radiation physics, radiation biology, X-ray apparatus and a multiple choice bank. A central computer served the PCs which the students could use as they required. Each program start was recorded at the server. Due to rebuilding and change of server, no data were sampled during 7 months of 1991. RESULTS: Overall, there was no statistically significant difference (P > 0.05) between students' attitudes in 1996 and 1985. Two questions were scored significantly higher in 1996. The programs were run 12,269 times in the 10-year period. Use of the programs increased steadily whereas number of dental students/year decreased. Program runs in each year, expressed as percentage (in brackets) of total runs over the 10-year period, were: 1986 (1), '87 (8), '88 (8), '89 (11), '90 (9), '91 (3), '92 (13), '93 (13), '94 (16), '95 (18). CONCLUSIONS: The favourable attitudes seen 10 years ago when CAL was initiated could not be ascribed to a Hawthorne effect as similarly or more favourable attitudes were recorded in 1996. Though not mandatory, CAL was frequently and increasingly used by dental students over the 10-year period.

Adult↗
PubMed1985

Chemical softening and wear of dental composites.

The purpose of this work was to determine the influence of chemical food-simulating liquids on the wear of various commercial dental composite restoratives. In many cases, pre-conditioning the restoratives in these liquids for one week produced swelling of the polymer matrix and considerable surface damage. The resulting degradation reduced the hardness and enhanced the wear as measured by a pin-and-disc apparatus. Four kinds of commercial composites were investigated: a conventional quartz-filled, a strontium-glass-filled, a visible-light-activated, and a microfilled composite. The liquids employed were heptane and several aqueous solutions of ethanol with solubility parameters, delta, ranging from delta = 1.5 to 4.8 X 10(4) J1/2m-3/2. With all restoratives, the decline in hardness during pre-conditioning maximized at about delta = 3 X 10(4), which corresponds to a 75% ethanol solution. The wear behavior was considerably more complicated and variable, as discussed in the text. For the most part, the increase in wear rate from pre-conditioning corresponded to the fall in hardness. A notable exception was for the strontium-glass-filled composite pre-conditioned in pure water. Here the wear was enhanced considerably, with no decrease in hardness. In this case, the degradation mode is assumed to be different from the others in that it is attributed to stress corrosion of the glass filler.

Acrylic Resins↗
PubMed1989

Electromyography of masticatory muscles in three jaw registration positions.

The purpose of this study was to investigate whether anteroposterior changes in mandibular position affect masticatory muscle activity. The electromyographic (EMG) activity of masticatory muscles during full and partial (10%) clenching in three mandibular bite registration positions--retruded contact position (RCP), intercuspal position (IP), and muscular position (MP)--was studied. Three groups of subjects with different ranges of anteroposterior positioning of the condyles were evaluated (normal occlusion, Class II, Division 2 malocclusion, and dual bite malocclusion). A posterior stabilizing splint for each registration position was made. EMG data were obtained from three bilateral muscles (masseter, anterior temporal, and posterior temporal). Clenching in the RCP elicited the lowest masseter muscle activity during full clenching, and the highest anterior temporal and posterior temporal muscle activity during partial clenching. If the relationships of the masticatory muscles are analyzed through a ratio that represents the interaction between biting and positioning muscles (masseter/posterior temporal muscle ratio), the RCP as compared with other positions had the lowest ratio. The RCP required more positioning muscle activity and permitted less biting muscle activity. There was no significant difference in the muscle activity between the IP and MP registrations. Small changes in jaw position (anterior to RCP) are not critical for the masticatory apparatus provided there is good intercuspation. The results of this investigation suggest that intercuspation in RCP is not the optimal position.

Adolescent↗
PubMed2001

Mechanism of the inhibitory effect of histamine on amygdaloid-kindled seizures in rats.

PURPOSE: The mechanism of the inhibitory effect of histamine on amygdaloid-kindled seizures was investigated in rats. METHODS: Under pentobarbital anesthesia, rats were fixed to a stereotaxic apparatus, and bipolar electrodes were implanted into the right amygdala. A guide cannula made of stainless steel tubing was implanted into the right lateral ventricle. Electrodes were connected to a miniature receptacle, which was embedded in the skull with dental cement. EEG was recorded with an electroencephalograph; stimulation of the amygdala was applied bipolarly every day by a constant-current stimulator and continued until a generalized convulsion was obtained. RESULTS: Intracerebroventricular (i.c.v.) injection of histamine at doses of 2-10 microg resulted in a dose-related inhibition of amygdaloid-kindled seizures. I.c.v. injection of calcium chloride at doses of 10-50 microg and A23187 at doses of 2-10 microg also caused dose-dependent inhibition of amygdaloid-kindled seizures. Calcium chloride at a dose of 10 microg, which showed no significant effect on amygdaloid-kindled seizures when used alone, significantly potentiated the effect of histamine. Similar findings were observed with A23187 at a dose of 2 microg. In addition, EGTA and EGTA/AM antagonized the inhibition of kindled seizures induced by histamine. Moreover, the inhibition of kindled seizures induced by histamine was antagonized by KN62. However, calphostin C did not antagonize the inhibitory effect of histamine. CONCLUSIONS: These results indicated that histamine-induced inhibition of amygdaloid-kindled seizures may be closely associated with a calcium calmodulin-dependent protein kinase II activation pathway.

Amygdala↗