The flexible gingival mask: an aesthetic solution in periodontal practice.

Dramatic aesthetic results have been obtained with the flexible silicone gingival mask which can be used to correct deformities remaining after destructive periodontal inflammation has been controlled. The silicone mask may also be used as an interim measure to improve the appearance of anterior crowns after initial periodontal therapy to allow time for healing and the establishment of periodontal stability and prognosis. A simple two-stage impression technique is described, enabling a suitably trained dental technician to produce comfortable and accurately fitting masks, which are very stable during use. Virtually no problems have been encountered.

Locally delivered antimicrobials in periodontal therapy.

The rapid growth in our understanding of the pathogenesis of periodontal disease has led to a change in therapeutic emphasis, supplementing traditional, non-specific, mechanical plaque control with a more focused targeting of pathogenic organisms. New topical preparations provide high antimicrobial doses at diseased sites without the systemic antibiotic loading which is now, in itself, a cause of concern due to the increasing tendency of micro-organisms to become resistant to antimicrobial agents. This article reviews the current methods of delivering antimicrobial agents to the gingival crevice and evaluates their roles in practical periodontal therapy.

Emmetropia approach dynamics with diurnal dual-phase cycling.

Numerical experiments are performed on a first order exponential response function subjected to a diurnal square wave visual environment with variable duty cycle. The model is directly applicable to exponential drift of focal status. A two-state square wave is employed as the forcing function with high B for time H and low A for time L. Duty cycles of (1/3), (1/2) and (2/3) are calculated in detail. Results show the following standard linear system response: (1) Unless the system runs into the stops, the ready state equilibrium settling level is always between A and B. The level is linearly proportional to a time-weighted average of the high and low states. (2) The effective time constant t(eff) varies hyperbolically with duty cycle. For DC = (1/3) and t1 = 100 days, the effective time constant is lengthened to 300 days. An asymptote is encountered under certain circumstances where t(eff) approaches infinity. (3) Effective time constants and steady state equilibria are independent of square wave frequency f, animal time constant t1, magnitude and sign of A & B, and diurnal sequencing of the highs and lows. By presenting results on dimensionless coordinates, we can predict the drift rates of some animal experiments. Agreement between theory and experiments has a correlation coefficient r = 0.97 for 12 Macaca nemestrina eyes.

Non-surgical periodontal therapy: essential and adjunctive methods.

The presence of bacterial deposits on teeth has been observed since the birth of microbiology but it has taken over 300 years to understand which elements of the various hard and soft dental deposits must be removed in order to arrest the destructive processes caused by the periodontal diseases. This article reviews the current state of knowledge regarding non-surgical periodontal therapy, including adjuncts such as mouthrinses and antibacterials and considers when other treatment modalities would be beneficial for the patient.

Optical constants and dimensions for the myopic, hyperopic and normal rhesus eye.

Complete optical constants and physical dimensions are presented for eight ametropic rhesus eyes in the range from -11.00 diopters of myopia to +8.00 diopters of hyperopia and compared with the same measurements from 40 essentially emmetropic normal control eyes. The optical constants are calculated from a Gullstrand analysis modified for the rhesus eye, and include focal lengths, cardinal points, lens power and total optical power. The physical dimensions, from keratometry and ultrasound, include corneal radius, anterior chamber depth, lens thickness, vitreous depth and axial length. A regression analysis of the data shows that refraction is strongly correlated with both axial length and vitreous depth (at the rate of 3.7 and 4.2 diopters mm-1, respectively; correlation coefficients of -0.962 and -0.821) but is essentially independent of lens power, corneal power, and total optical power. These results allow us to infer that experimentally induced ametropia in the rhesus is caused by a distortion of the globe, and is not caused by the cornea or the lens.

Optimal geometry for oval sprint tracks.

Track aspect ratio is defined as the percentage of lap length devoted to turns on an oval running track. Equations based on experiments are developed to model a composite runner with a specified top speed, during an acceleration phase in the straightaways and a centripetal phase in the turns. We calculate velocity deficits for several common track sizes over the range of aspect ratios and predict that, under our assumptions, a perfect circle is the optimal track shape.

Dark-rearing interference with emmetropization in the rhesus monkey.

Dark rearing has been shown to protect against the development of lid-suture myopia in monkeys and tree shrews. Dark-reared monkeys and cats, with or without lid suture, are significantly hyperopic in comparison to light-reared controls. The time course of refractive change during dark rearing has only been systematically investigated in chicks, with hyperopia increasing from 14 to 42 days after hatching. Longitudinal refractions of dark-reared monkeys have not been reported previously. Five infant rhesus monkeys were dark reared with their mothers from the first day of life until 58 to 161 days of age. Cycloplegic retinoscopies were performed at 2-week intervals and were compared with cross-sectional data from 18 normal monkeys at ages 1 to 81 days. The normal monkeys typically had hyperopic refractions from +4 to +8 diopters at birth with an average refraction of +2.8 diopters between 30 and 81 days of age, compared with an average refraction of +5.3 diopters between 30 and 81 days of age for the monkeys raised in darkness (difference significant at P less than 0.05). Three of the dark-reared animals retained an average of 7.0 diopters of hyperopia. Darkness thus slowed or interrupted the normal loss of hyperopia in three of the five experimental subjects, and may be useful for creating model hyperopic animals on the order of +5 to +8 diopters.

Sprinting with banked turns.

Bank angle effects can attenuate peak running speed on the order of 10%. Experimental and theoretical results are presented here to quantify this phenomenon over a wide range of bank angles theta b and turn radii R. Experimentally, eleven subjects ran on a 34 m long plywood test track with variable radius and bank angle to sample the (R, theta b) space. From another study, ten subjects are borrowed to examine the theta b = 0 degrees case in greater detail. Various gait parameters were measured from high-speed film, and after parallax correction, compared with the theoretical predictions. The theory is a simple two-parameter constant force model requiring only the effective ankle pulley ratio beta and the runner's top speed vm. A closed-form dimensionless solution is presented for the speed ratio (v/vm) as a function of the radius number (Rg/v2) and the bank angle theta b. Agreement between theory and experiment is limited by experimental scatter. For twenty different subjects and twelve different combinations of R and theta b, the apparent ankle pulley ratio is beta = 0.27 +/- 0.22 based on 128 separate trials. Applications are discussed briefly for the design of indoor and outdoor running tracks. The theory allows a calculation of foot force, bone force, and tendon tension for the general case of arbitrary maximum speed, turn radius and bank angle.

Time course of rhesus lid-suture myopia.

Axial-length and refraction measurements are presented for the lid-sutured rhesus monkey at 6-month intervals during the first 1.5 years of life. The experimental data are fitted to an exponential growth theory allowing the calculation of time constants, apparent time origins, and correlation coefficients for 10 eyes from five animals. On average, axial length develops with a time constant of 0.40 year for lid-suture myopia, compared with 0.42 year for the normal eye. A practical application of this work is that one must allow 1.6 years of lid suture to achieve 95% of the total refractive or axial-length change.

Closed-form ametropic pressure-volume and ocular rigidity solutions.

Basic closed-form theoretical results are derived relating the stress-strain sigma = sigma(epsilon), pressure-volume p = p(V), and ocular rigidity-pressure K = K(p) functions for a spherically symmetric eye of contant thickness and material properties. The results can be used to predict the pressure-volume and ocular rigidity behavior of both hyperopic and myopic eyes, in addition to the emmetropic case. The theoretical results are compared with eight different experimental studies from the literature. Five experimentally obtained mechanical variables, the pre-exponential stress-strain constant A (Pascals), the dimensionless exponential stiffening constant alpha, the pressure-volume globe stiffness intercept a (mm Hg/mm3), the globe stiffness slope b (mm-3), and the ocular rigidity K(mm-3) are found on average to agree with the theoretical predictions within a factor of 3 or better. Possible clinical applications might include measuring the ocular rigidity function K = K(p, Vo) to infer the mechanical strength of the corneo-scleral shell. The results may also be useful to help understand glaucoma dynamics as a function of refraction, and also with respect to tonometer calibration.

Thermal torsion of F-actin.

The equipartition theorem is used to calculate the mode amplitudes for F-actin thermal torsion. The amplitudes phi n are found to scale as n-1, (EI)-1/2, and L1/2, where n is mode number, EI is actin bending stiffness, and L is filament length. Depending on conditions, the amplitude can be as large as 15 degrees; this is discussed briefly in terms of skeletal muscle mechanics.

Running on flat turns: experiments, theory, and applications.

Theoretical and experimental results are presented which demonstrate the mechanical effects of running along a circular turn. The theory is a simple one-parameter model, requiring only the top speed Vo of the runner as an input. The dimensionless parameter (Rg/v2o), a reciprocal Froude number or dimensionless parameter (Rg/v20), a reciprocal Froude number or dimensionless radius, appears as a natural result of the theory. This radial Froude number allows for the comparison of the theory and experiment for a large number of individuals on the same set of axes. The parameters of speed, foot contact time, ballistic air time, step length, stride length, and stride time are all predicted and measured for 23 different subjects. The agreement between theory and experiment is good. Exact solutions and approximate asymptotic results for the speed-radius relation are presented. Applications are made to the practical problem of the design of indoor and outdoor running tracks for athletic competition.