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At least 37 records · Page 2Linked to original sources
PubMed1999

New telescopic crown design for removable partial dentures.

STATEMENT OF PROBLEM: Special technical skills and experiences are required to fabricate a telescopic crown to provide adequate retention with precise frictional retention ("conus friction force") between coping and telescope. It is also difficult to control clinically alterations of retentive forces after prolonged usage. PURPOSE: This study examined an innovative telescopic crown system for removable partial dentures that can be fabricated without special technical skill or experience and readily adjusted retentive forces. The retention of telescopic crowns was investigated after repeated insertion/separation tests. MATERIAL AND METHODS: Ten telescopic crowns were constructed to evaluate retentive forces. Each telescopic crown was adjusted to provide a retentive force of approximately 9.8 N. Each telescopic crown was then subjected to 10,000 insertion/separation cycles, and retentive force of each telescopic crown was recorded initially and after every 1,000 cycles. The retentive force of each telescopic crown was re-adjusted after these measurements to provide a retentive force of approximately 9.8 N. The retentive force was recorded a second time after each 1,000 insertion/separation cycles up to 10,000 cycles. RESULTS: Retention of the telescopic crowns gradually diminished, depending on the number of insertion/separation cycles. The mean retentive force after 10,000 insertion/separation cycles was over 2 N. All 10 telescopic crowns were re-adjusted to exert a retentive force of 9.8 N after the initial 10,000 cycles, and the retentive force also diminished on the second 10,000 cycles. CONCLUSIONS: Reduction of retention was dependent on insertion/separation cycles. This new telescopic crown with reduced retention could be easily readjusted. Readjusted retentive forces were at least equivalent to the initial retention.

Analysis of Variance↗
PubMed2000

The calibration of a 2.5x Galilean focusable telescope as an optometer for refraction.

A 2.5x Selsi achromatic Galilean focusable telescope was calibrated for refraction at 6 m. In its calibration, minus power trial lens was placed at the objective of the telescope to simulate vergence of a target at a finite distance, before the back vertex power (BVP) of the telescope at each setting (telescope length) was measured by a focimeter. By using a graphical presentation of the results, the BVP of the telescope at each setting could be determined at different selected target distances. For a target vergence of -0.167 D or a distance of 6 m, the common testing distance in clinical practice, this calibrated telescope had a BVP or refraction measuring range of -7.27(-)+7.52 D. When this telescope was used to measure simulated manifest refractive errors at 6 m, it yielded a mean error of +0.13 D with a 95% confidence limit of agreement of -0.38(-)+0.64 D. These results indicated that the accuracy and precision of telescopic refraction were comparable to that of retinoscopy. Therefore, the calibrated telescope could be considered as a reliable and inexpensive instrument for determining spherical refractive errors. Telescopic refraction is applicable in refracting economically disadvantaged population in underserved areas where modern equipment and electricity are not available. In addition, it provides an alternative subjective refraction method for low vision population because the magnification of this calibrated telescope has the advantage of allowing low vision patients to be refracted at the common 6 m testing distance in clinical practice.

Adult↗
PubMed1989

Adaptation to telescopic spectacles: vestibulo-ocular reflex plasticity.

The vestibulo-ocular reflex (VOR) is a mechanism for the production of rapid compensatory eye movements during head movements. To investigate the adaptation of this reflex to spectacle magnifiers, the effect on the VOR of a brief period of wearing telescopic spectacles during head rotation was studied in normal subjects. VOR gain, as measured in darkness, was defined to be the ratio of compensatory slow phase eye velocity to head velocity. Initial VOR gain as measured for vertical axis sinusoidal head rotation at 0.1 Hz, amplitude 60 degrees/sec, was about 0.7. After 15 min adaptation by sinusoidal rotation during the viewing of a remote video display through X2, X4, or X6 binocular telescopic spectacles, 47-70% of subjects exhibited significant VOR gain increases of 7-46%. These increases were measured with occlusion of the unmagnified visual field peripheral to the telescopes during adaptation. There was considerable interindividual variability in adaptation to telescopic spectacles. Telescopic spectacle power had little or no effect on the amount of VOR change after adaptation, although all telescope powers produced a greater VOR gain change than did adaptation without telescopes. Testing of VOR gain at multiple frequencies indicated that adaptation to telescopic spectacles by rotation at a single sinusoidal frequency induces VOR gain changes across a broad spectrum of frequencies of head rotation. When the unmagnified peripheral visual field was unobstructed during adaptation, VOR gain increases were significantly less than when the unmagnified peripheral visual field was occluded, and were similar to those observed during adaptation without the wearing of telescopic spectacles at all. VOR gain adaptation was associated with amerlioration of symptoms of oscillopsia and motion discomfort initially experienced by about 20% of subjects wearing telescopic spectacles.

Adaptation, Physiological↗