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PubMed2006

Linear and nonlinear hearing aid fittings--2. Patterns of candidature.

We studied candidature for linear, slow-acting AVC hearing aids, and fast-acting WDRC hearing aids in a within-subject within-device crossover design of 50 listeners with SNHL. Candidature dimensions include HTLs, ULLs, spectro-temporal and masking abnormalities, cognitive capacity, and self-reports and acoustic measures of auditory ecology. Better performance with linear fittings is associated with flatter audiograms, wider dynamic range, and smaller differences in dynamic range between low and high frequencies, and also with more restricted auditory lifestyles. Better performance with all nonlinear fittings is associated with more sloping audiograms, more restricted dynamic ranges, greater differences in dynamic range between low and high frequencies, and more varied auditory lifestyles. Differential performance between WDRC and AVC fittings is associated with patterns of variation in auditory ecology (rapid versus slow changes) and cognitive (high versus low) capacity. Differential performance between WDRC in two channels, and a hybrid with WDRC in a low-frequency and AVC in a high-frequency channel is associated with psychoacoustic tests of cochlear function (high susceptibility to spectral and temporal smearing, and high susceptibility to upward spread of masking respectively). Patterns of candidature include measures beyond auditory function in the domains of cognitive capacity and auditory ecology.

Aged↗
PubMed2004

Cement fixation and screw retention: parameters of passive fit. An in vitro study of three-unit implant-supported fixed partial dentures.

It is generally assumed that passively fitting superstructures are a prerequisite for long-lasting implant success. In the study presented, the strain development of three-unit implant fixed partial dentures (FPDs) was evaluated at the bone surrounding the implant and on the superstructure using a strain gauge technique. Six groups of three-unit FPDs representing the commonly used techniques of bridge fabrication were investigated with 10 samples each, in order to quantify the influence of impression technique, mode of fabrication and retention mechanism on superstructure fit. Two ITI implants (Straumann, Waldenburg, Switzerland) were anchored in a measurement model according to a real-life patient situation and strain gauges were fixed mesially and distally adjacent to the implants and on the bridge pontics. The developing strains were recorded during cement setting and screw fixation. For statistical analysis, multivariate two sample tests were performed setting the level of significance at P=0.1. None of the investigated bridges revealed a truly passive fit without strains occurring. About 50% of the measured strains were found to be due to impression taking and model fabrication, whereas the remaining 50% were related to laboratory inaccuracies. The two impression techniques used did not reveal any significant differences in terms of precision. Both modes of fixation--i.e. cement and screw retention--provoked equally high stress levels. In the fabrication of screw-retained FPDs, similar results were obtained from the use of burn-out plastic copings and the technique of casting wax moulds to premachined components. Bonding bridge frames onto gold cylinders directly on the implants significantly reduces strain development.

Aged↗
PubMedDate not supplied

Design of hearing aid shells by three dimensional laser scanning and mesh reconstruction.

Hearing aid shells (or earmolds) must couple the hearing aid with the user's ear. Earmolds have to fit the subject's outer ear canal properly to ensure a good performance of the aid. Because of the great variability in the anatomical pattern of the ear, earmolds are custom made. At present, an impression of the subject's ear canal is taken and used to fabricate the silicon-made mold. The postimpression activities that typically are performed during the fabrication process modify the physical dimensions of the resulting earmold and thus affect the fit of the product. A novel system for 3-D laser scanning and mesh reconstruction of the surface of ear canal impressions is presented. The reconstructed impression can be digitally stored and passed directly to dedicated CAD 3-D printing machines to model the silicon earmold and thus achieve the best possible fit. The proposed system is based on a couple of cameras and a commercial laser for the surface digitization and on a straightforward algorithm, based on the deformation of a geometric model, for the reconstruction of the acquired surface. Measurements on objects of well-known geometric features and dimensions are performed to assess the accuracy and repeatability levels of this 3-D acquisition system. Robustness to noise of the proposed reconstruction algorithm is determined by simulations with a synthetic test surface. Finally, the first measurements (acquisition+reconstruction) of closed surfaces from ear canal impressions are reported.

Algorithms↗
PubMed2004

The impact of hydrogel lens settling on the thickness of the tears and contact lens.

PURPOSE: To investigate the effect of contact lens insertion on the thickness on the prelens tear film (PLTF), the contact lens, and the postlens tear film (PoLTF). METHODS: Twelve contact lens wearers (mean age, 32.7 years; four males) inserted etafilcon A hydrogel lenses (power: -2.00 D, base curve: 8.3 mm) in both eyes immediately before testing. Previously described interference techniques, based on oscillations in reflectance spectra, were used to measure the thickness of the PLTF, contact lens, and PoLTF. The thickness of the layers is derived from the frequency of the oscillations. Spectra were captured 1 minute after lens insertion and every minute thereafter for 30 minutes. Least squares regression fits were used to determine the relation between thickness of each layer and time. RESULTS: The combined data from all subjects for PLTF thickness were fit with an exponential decay plus a constant thickness; the initial thickness was 4.5 micrometers, the time constant was 7.1 minutes (P < 0.001), and final thickness was 2.5 micrometers. The apparent thickness of the contact lens declined linearly at an average rate of 0.051 micrometers/minute (P < 0.001). The PoLTF thickness remained constant at 2.5 micrometers (P = 0.46). CONCLUSIONS: For most subjects, the PLTF thinned significantly over the course of the first 30 minutes of lens wear. The apparent thinning of the contact lens may be caused by a real thinning of the lens, but also may have a contribution from improved centration over the 30-minute period. The PoLTF remained relatively stable during this period.

Adult↗
PubMed2000

Preferred listening levels of children who use hearing aids: comparison to prescriptive targets.

The preferred listening levels (PLLs) of children with sensorineural hearing loss were elicited using conversation-level speech, heard through the children's own hearing aids. All hearing aids were fitted using the desired sensation level (DSL) method. Comparisons were made between the PLL and targets from the following prescriptive formulae: DSL version 4.1 and two versions of the National Acoustic Laboratories (NAL) procedure, including NAL revised for severe-profound losses (NAL)-RP and NAL nonlinear NAL/NL1. Results for this sample of children indicated that the PLL was similar to the DSL targets, and that, on average, NAL-RP/NL1 targets recommended less gain than that preferred by the majority of children in this study. The implications of factors such as acclimatization, test levels, and clinical procedures on these results are discussed.

Adolescent↗
PubMed1996

A quantitative method for comparing and evaluating manual prosthetic socket modifications.

Manually designed prosthetic sockets are difficult to evaluate since the hand-sculpting modification process does not retain the initial shape for comparison. A quantitative method for defining and comparing manual socket modifications was developed and integrated into the CADVIEW software package. The numerical comparison procedure consisted of a) digitizing premodification and post-modification models of a prosthetic socket, b) aligning these two shapes to a common axis (calculate cross section centroids, determine line of best fit through the centroids, rotate and move the line of best fit to a common axis), and c) displaying the differences in shape both numerically and using a color-coded three dimensional image. Alignment technique testing showed a between-radial-point average error of 2.5 mm using automatic alignment and 1.4 mm after further manual alignment adjustment. The between socket difference values were used to outline individual modifications and save these outlines to disk. Modification outlines from a series of patients were averaged to determine a prosthetist's general modification style. Averaged results from two prosthetists qualitatively supported the effectiveness of this procedure. This alignment and comparison system should help transfer hand-sculpting skills to prosthetic CAD/CAM systems, clinical research, and education for new clinicians.

Amputation Stumps↗
PubMed1998

Procera: a new way to achieve an all-ceramic crown.

The Procera System embraces the concept of computer-assisted design and computer-assisted machining to fabricate an all-ceramic crown composed of a densely sintered, high-purity aluminum oxide coping combined with a compatible veneering porcelain. Strength, precision of fit, color stability, cementation, and wear characteristics are among the many factors that concern clinicians when fabricating all-ceramic restorations with this new crown system. This article presents, in summary form, the data from the many studies on Procera AllCeram crowns that have been conducted at clinical and laboratory centers around the world. The evidence reported in these studies clearly demonstrates that the Procera AllCeram crown represents a combination of computer technology and creativity for which a positive prognosis can be made. Today its application is restricted to single crowns; however, with continued development, multiple unit all-ceramic anterior and posterior fixed partial dentures are clearly in the future.

Cementation↗
PubMedDate not supplied

Prosthetic radial head components and proximal radial morphology: a mismatch.

A morphometric study of the proximal radius was performed with magnetic resonance imaging scans to measure the anatomic dimensions of the radial head and neck. These dimensions were then compared with the manufacturer's size specifications of commercially available titanium prosthetic radial head components to determine whether these designs adequately match the morphologic characteristics of the proximal radius. A cadaveric correlation was performed to validate the accuracy and reliability of measurements obtained from the magnetic resonance scans. The narrow intramedullary dimensions of the radial neck negated fitting of even the smallest available metallic prosthetic component stem in 18 (39%) of 46 scans reviewed (confidence interval 26% to 53%). Of the 31 male patients who underwent scanning, 4 (13%) would not be able to be fitted with a prosthetic component according to the manufacturer's technique guide (confidence interval 0% to 29%). Of the 15 female patients who underwent scanning, 14 (93%) would not able to be fitted with a prosthetic stem (confidence interval 70% to 99%). In those patients in whom the radial neck could accommodate a prosthetic stem (n = 26), there was ineffective restoration of proximal radial head length in all cases (100%, confidence interval 87% to 100%). The average shortening was 4 mm of proximal radial length (range 1 to 7 mm). Our findings reveal that the commercially available metallic radial head design may overestimate the dimensions of the radial neck. Inadequate sizing of radial head prostheses may lead to an inadvertent change in proximal radial length, with potentially adverse effects on elbow, forearm, and wrist mechanics. Newer designs taking into account these anatomic dimensions may lead to an improvement in function after reconstruction.

Adolescent↗
PubMed2006

Clinical field testing of polyurethane feet for trans-tibial amputees in tropical low-income countries.

In a prospective controlled study, 172 polyurethane feet of different designs were fitted to 155 amputees with trans-tibial prostheses. These were followed in respect of their durability. The amputee compliance was in general good, and 87% were satisfied with their device. After 18 months the failure rate of 20% with the CIREC spring-blade foot was significantly better than the others, but poorer craftsmanship, higher complaint rate and lower compliance rate cast some doubt on the results. The results with the conventional SACH foot constructions with polyurethane as filling and covering materials were so poor after 18 months that their use cannot be recommended in tropical areas of the developing world.

Adolescent↗
PubMed2001

Extraoral maxillofacial prosthetic rehabilitation at the M. D. Anderson Cancer Center: a survey of patient attitudes and opinions.

STATEMENT OF PROBLEM: Measures of satisfaction after extraoral maxillofacial prosthetic rehabilitation have been sparsely reported. PURPOSE: This article reviews the care-related opinions of patients who were provided extraoral prostheses at the M. D. Anderson Cancer Center over the course of 10 years. MATERIAL AND METHODS: A questionnaire was delivered to 263 extraoral prosthetic patients to elucidate their degree of satisfaction with several parameters, including prosthetic use, care, quality, durability, longevity, and cost. In addition, issues relating to self-image, socialization frequency, and income-earning ability before and after rehabilitation were surveyed. RESULTS: The views of 76 respondents demonstrated a general satisfaction with their prostheses. A majority believed that their prostheses fit comfortably, and most were satisfied with cosmesis. In addition, a preponderance of respondents reported no substantial alteration in social activity after rehabilitation. Although the number of respondents relying on their own employment fell by more than 50% after rehabilitation, nearly all reported a relatively static income before and after rehabilitation. CONCLUSION: The survey revealed a high degree of patient satisfaction with extraoral maxillofacial prostheses. Nevertheless, areas of potential improvement were not lost on the survey's population. The patients desired prostheses that last longer and have improved color stability. An interest in improved retentive mechanisms was mentioned by several patients, and only about half of the respondents perceived prosthetic cost to be completely reasonable.

Adult↗
PubMed2003

Comparing goblet cell densities in patients wearing disposable hydrogel contact lenses versus silicone hydrogel contact lenses in an extended-wear modality.

PURPOSE: The current study evaluates the response of the ocular surface to extended contact lens wear by comparing a new silicone hydrogel lens to an ACUVUE 2 lens. METHODS: Twenty subjects with an average age of 28 years were randomly assigned to a fitting with ACUVUE 2 or PureVision lenses. Ocular surface assessment by impression cytology was performed at baseline and for the 6 months after initiation of lens wear. RESULTS: Although goblet cell density significantly increased with wear time, no statistically significant difference was observed between the contact lens groups. The average baseline goblet cell percentages were as follows: ACUVUE 2 group, 1.44; PureVision group, 1.11. The 6-month averages were as follows: ACUVUE 2 group, 3.16; PureVision group, 2.22. CONCLUSIONS: It appears that silicone hydrogel lenses may be slightly less irritating to the ocular surface than lenses not containing silicone. This could be a promising indicator for successful 30-day continuous wear.

Adult↗
PubMed1995

Comparison of strains transferred to a bone simulant among implant overdenture bars with various levels of misfit.

PURPOSE: To measure and compare strains transferred to a bone simulant by screw-fastening implant overdenture bars with various levels of fit or misfit. MATERIALS AND METHODS: Photoelastic resin was cast directly to two 3.75 X 13-mm Branemark fixtures (Nobelpharma USA Inc, Chicago, IL) situated 20 mm apart in a silicone mold of an edentulous mandible. Two strain-gauge rosettes were also incorporated in the resin to allow precise determination of principal stresses at two locations. Four groups of three overdenture bars with 0-, 180-, 360-, and 500-micrometer vertical gaps were fabricated. These bars were sequentially secured to the abutments with gold slot screws tightened to 10 N-cm. Strain indicator readings were recorded at a standardized time following the initial fastening of each bar. The test was repeated three times for each overdenture bar. RESULTS: Mean principal stresses and strains at the location of the rosettes were determined. The magnitude of these stresses and strains increased significantly with each increase in gap size. Strains were several times larger mesial to the fixture than they were distal. CONCLUSIONS: Strains are transferred to the bone when misfitting prostheses were secured. Some of the strains mesial to the fixture appeared to be unfavorable for regions of lower bone density when the groups with designed gaps were secured. These data will be compared with those in ongoing animal studies regarding the cellular response to prosthesis misfit.

Alveolar Process↗
PubMed2004

Corneal refractive therapy, uncorrected visual acuity, and "E" values: personal experiences.

PURPOSE: The author describes selected aspects of his clinical experience in fitting and prescribing orthokeratology lenses to temporarily reduce or eliminate myopia. The precision of videokeratography (VK) data in determining corneal sagittal depth is examined. Treatment outcomes are analyzed after overnight wear of two proprietary corneal remodeling systems. Two case reports describing off-label treatments are presented. METHODS: A retrospective analysis was performed of the baseline VK data of 25 consecutive candidates (50 eyes) for corneal remodeling, captured with a Keratron topographer. Sixteen consecutive patients fitted with Paragon corneal refractive therapy (CRT) lenses were compared against an age- and sex-matched group of patients fitted with the Mountford BE lens for 1-day, 1-week, and 1-month uncorrected visual acuity. RESULTS: The mean +/- SD of the apical radius ("Ro") and corneal eccentricity ("E") values was 0.03 +/- 0.01 mm and 0.03 +/- 0.01 degrees , respectively, indicating a spread of 24 microm in the sagittal elevation data. Mean target myopia and 1-day uncorrected visual acuity were -1.71 +/- 0.71 diopters and 20/20 +/- 20/0.86, respectively, for the Paragon CRT lenses and -2.30 +/- 0.89 diopters and 20/31 +/- 20/20.6, respectively, for the Mountford BE lenses. CONCLUSIONS: The Paragon CRT and the Mountford BE lenses delivered impressive reductions in uncorrected visual acuity after the first night of overnight wear. The Paragon CRT lens had the advantage of not requiring a previous overnight lens trial before commencing the treatment program.

Adolescent↗
PubMed1999

Simultaneous Analog Stimulation (SAS)--Continuous Interleaved Sampler (CIS) pilot comparison study in Europe.

The recent availability of the enhanced bipolar electrode array in the CLARION Multi-Strategy Cochlear Implant has permitted clinicians to fit patients successfully with the Simultaneous Analog Stimulation (SAS) strategy by means of bipolar coupling. Out of 22 consecutively implanted subjects, 20 subjects could be fitted with both Continuous Interleaved Sampler (CIS) and SAS strategies. Their performance was evaluated up to 3 months postoperatively. Speech perception results, as well as the patient's preference for either CIS or SAS, were examined. It was found that half of the subjects selected SAS as their preferred strategy and that the use of a preferred strategy resulted in higher overall patient performance. Further analyses showed that those subjects preferring SAS had higher electrode impedance values and lower threshold and most comfortable loudness levels than subjects preferring CIS. We presume that these psychophysical findings are, in part, related to the position of the intracochlear electrode array. Specifically, SAS users may have a more modiolus-hugging electrode array position.

Cochlear Implantation↗
PubMedDate not supplied

Consistency and accuracy of measurement of lower-limb amputee anthropometrics.

Lower-limb amputees often exhibit large fluctuation in residual-limb shape, necessitating careful observation and anthropometric measurement for prosthetists to ensure socket fit. Anthropometric measurement may become more important as an outcome measure indicating success in rehabilitation. This study investigated the accuracy and reliability of seven prosthetic anthropometric measurement devices as used by a group of eight prosthetic-orthotic practitioners and a group of five prosthetic-orthotic students to measure six common anthropometric dimensions on three foam positive models of transtibial amputee residual limbs. Two of the models were identical, enabling assessment of individual repeatability. Some clinically significant errors were noted in the results; however, the general variability in measurements was not clinically significant. Students were slightly more consistent than practitioners; students were more consistent with linear measurements, while practitioners were more consistent with circumferential measures. The results further demonstrated that the VAPC measurement device used in the study was both inaccurate and unreliable.

Adult↗
PubMed2004

Clinical performance and fitting characteristics with a multicurve lens for keratoconus.

PURPOSE: To evaluate the clinical outcome and fitting characteristics with a multicurve lens for keratoconus in a Korean population. METHODS: Sixty eyes with keratoconus were fit with a multicurve lens based on topographic index and fluorescein pattern on slitlamp biomicroscopy. Three-point touch was applied in 59 eyes, and apical clearance was adopted in an eye with a persistent epithelial defect. The mean follow-up was 11.4 months. Visual acuity, comfort, glare, daily contact lens-wearing time, and the changes in topographic indices after fitting were evaluated. The relationship between base curve radius (BCR) and topographic indices were analyzed along with the relationship between BCR and peripheral curve radius. RESULTS: A total of 71.6% of the eyes achieved a visual acuity of 20/30 or better. Flatter BCR was related to better visual acuity. Ninety-four percent of the patients tolerated the fitting, and 85% of them reported complete comfort. The mean daily wearing time was 11.9 hours. Four eyes reported glare. The change of Sim K during follow-up was not statistically significant. Prefitting Sim Kmax and average Sim K were significantly related to the BCR. Mean differences between the BCR and first peripheral curve radius were 1.06 +/- 0.21 mm with a BCR less than 6.00 mm and 0.81 +/- 0.2 mm with a BCR greater than 6.00 mm. These differences were statistically significant. CONCLUSIONS: Customization with the multicurve lens enabled patients with keratoconus to wear the contact lens comfortably and seemed not to aggravate the progression of keratoconus. Sim Kmax and the relationship between BCR and first peripheral curve radius seem to be useful information to optimize performance of the multicurve lens.

Contact Lenses↗
PubMed2006

CAD/CAM evaluation of the fit of trans-tibial sockets for trans-tibial amputation stumps.

The purpose of this study was to objectively evaluate the fit of sockets for trans-tibial stumps in order to establish a guideline for use in the automated production of prosthetic sockets. Subjects were 24 trans-tibial amputees. Using a CAD/CAM system, 11 parameters regarding the 3D shape of the stumps and the sockets were objectively evaluated. A correlation was found between the activity level and the upper and lower volumes of the socket, and between the cause of amputation and the upper volume of the socket. It was considered desirable to make the lower part of the socket looser for patients with lower activity levels, to make the upper part tighter for patients with higher activity levels, and to make the upper part looser for amputation patients with peripheral circulatory diseases.

Adult↗
PubMed2004

[Change of offset after implantation of hip alloarthroplasties].

The purpose of the present study was to evaluate the change of the offset after implantation of hip alloarthroplasties. In an experimental study the X-ray templates of 90 different implants (594 different sizes) were digitized (cup and stem) and virtually implanted in the hip joint of 50 consecutive patients who were on the waiting list for hip replacement. Implantation was performed on AP X-rays paying heed to the fit of the shaft and adequate leg length. In total 4500 implantations were performed. After virtual implantation the change of the offset was calculated. There was a wide variance in the ability to fit the implants to the individual patient. For some patients it seems to be extremely difficult to adapt the implant without changing the offset. Some implant designs were only suitable for 2 patients while other designs were suitable for 40 patients (mean: 17). The average change of the offset was 0.27 cm. Considering only the cases in which a change occurs this value increases up to 0.56 cm.For the individual patient the average number of implants that were suitable was 30 (range: 1-67) of a total of 90 designs. Here the average change of the offset was 0.4 cm (-1.04 -- +1.54 cm). Considering only the cases in which a change occurs this value increases up to 0.64 cm. In the majority of the cases the presently available implants do not allow anatomic reconstruction of the individual offset.

Bone Malalignment↗