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Using computational simulation to aid in the prediction of socket fit: a preliminary study.

This study illustrates the use of computational analysis to predict prosthetic socket fit. A simple indentation test is performed by applying force to the residual limb of a trans-tibial amputee through an indenter until the subject perceives the onset of pain. Computational finite element (FE) analysis is then applied to evaluate the magnitude of pressure underlying the indenter that initiates pain (pain threshold pressure), and the pressure at the prosthetic socket-residual limb interface. The assessment of socket fit is examined by studying whether or not the socket-limb interface pressure exceeds the pain threshold pressure of the limb. Based on the computer-aided assessment, a new prosthetic socket is then fabricated and fitted to the amputee subject. Successful socket fit is achieved at the end of this process. The approach of using computational analysis to aid in assessing socket fit allows a more efficient evaluation and re-design of the socket even before the actual fabrication and fitting of the prosthetic socket. However, more thorough investigations are required before this approach can be widely used. A subsequent part of this paper discusses the limitations and suggests future research directions in this area.

Amputation, Surgical↗

Fitting hearing aids with the Articulation Index: impact on hearing aid effectiveness.

Although most clinical tests focus on how much a particular hearing aid improves speech audibility under controlled conditions, it is unclear how these measures relate to hearing aid effectiveness, or the benefit perceived by the patient under everyday conditions. In this study, the relationship between audibility and hearing aid effectiveness was examined in a cohort of patients who obtained hearing aids through the Veteran's Administration. The measure of audibility was the Articulation Index, a common index of speech audibility. Measures of effectiveness included two hearing-specific surveys and self-reported ratings of global satisfaction and hearing aid use adherence. Results indicated that there were no systematic relationships between measurements of improved audibility and patient ratings of communication ability. Additionally, improved audibility was not related to overall satisfaction with the amplification characteristics of the hearing aid (fitting). However, improved audibility is related to hearing aid use adherence, with patients who achieve better audibility reporting that they use their hearing aids more frequently.

Adult↗

Evaluation of a new method to achieve optimal passivity of implant-supported superstructures.

UNLABELLED: Statement of problem. Passive fit of implant-supported superstructures has been suggested as a prerequisite for maintenance of osseo-integration and for successful prosthetic reconstruction. PURPOSE: This study evaluated the degree of fit of superstructures cemented onto titanium abutments, compared to structures cast onto gold cylinders. MATERIAL AND METHODS: An impression was taken and a master cast made of five implants mounted in a stainless steel model. Six similar porcelain fused to metal superstructures with standardised dimensions were then fabricated. One group featured castings onto gold UCLA abutments, while in the other group the structures were cemented onto tapering titanium abutments. Vertical discrepancies between implants and both types of superstructures were measured on at six locations around each implant using a reflex microscope. Measurements were taken after securing the structures to the model with a single screw (torqued to 32 Ncm) placed in various locations and also after tightening all the retaining screws simultaneously to 10 Ncm. RESULTS: With the new single-screw procedure, no significant difference in mean gap size was noted between the two groups. The discrepancies were significantly larger for certain screw locations (1 and 5), indicating that the one-screw test might be an inaccurate way of assessing fit. After tightening all the retaining screws simultaneously to 10 Ncm, the mean gaps were 11.9 microns for the cemented group and 17.8 microns for the cast group. CONCLUSION: Although not statistically significant, cementing of superstructures onto titanium abutments improved the fit up to 50% compared to casting the structures onto gold UCLA-abutments. Tightening one terminal abutment screw and evaluating the discrepancies at the other abutments (one-screw test) distorted the results when evaluating the fit of long-span, implant-supported ceramo-metal superstructures. CLINICAL IMPLICATIONS: The results of this study indicate that cementing superstructures onto titanium abutments will lead to an improved degree of fit, compared to casting superstructures onto gold cylinders. In addition, the one-screw test may not be an accurate method of determining the level of passivity of long-span, ceramo-metal, implant-supported superstructures.

Analysis of Variance↗

Preliminary evidence of asymmetry in uncomfortable loudness levels after unilateral hearing aid experience: evidence of functional plasticity in the adult auditory system.

The aim of the study was to compare uncomfortable loudness levels (ULLs) in a group of adults before and after unilateral hearing aid experience. Twelve participants presented with a symmetrical hearing loss consistent with natural ageing. Pure tones were presented to each ear separately, commencing at 60 dB HL and increased in 5-dB step sizes until ULL was reached. The post-fitting ULLs were typically measured three years after fitting. Hearing thresholds were symmetrical and remained unchanged after fitting. Mean ULL values were symmetrical before fitting. The mean ULL values increased (i.e. greater tolerance) in both ears after fitting; however, the increase was greatest in the fitted ear: 14.5 and 7 dB at 2000-4000 Hz in the fitted and not-fitted ear, respectively. A separate two-factor repeated ANOVA (ear and frequency) was performed on the pre and post-fitting ULL data. There was no statistically significant difference for ear (p > 0.05) when comparing the pre-fitting ULLs. However, there was a statistically significant difference for ear (p < 0.01) when comparing post-fitting ULLs. The underlying mechanism for the asymmetry is unknown but it is consistent with learning induced reorganization within the auditory system.

Acoustic Stimulation↗

Comparison of linear gain and wide dynamic range compression hearing aid circuits: aided speech perception measures.

OBJECTIVES: The goal of this study was to test the theoretical advantages of a single-channel wide dynamic range compression (WDRC) circuit for speech intelligibility and loudness comfort for five speech spectra. DESIGN: Twelve adolescents and young adults with moderate to severe hearing loss were fitted with the Siemens Viva 2 Pro behind-the-ear instrument set to DSL 4.0 targets for both linear gain and WDRC processing. Speech intelligibility was measured in the unaided, linear gain and WDRC conditions using two tasks in quiet: nonsense words and sentences. The items were digitally filtered to represent five speech spectra: average speech at 4 m, average speech at 1 m, own voice at ear level, classroom at 1 m, and shouted speech at 1 m. The subjects also rated the loudness of each hearing aid/speech spectrum combination using a categorical rating scale. RESULTS: Both the linear gain and WDRC settings provided improved speech recognition relative to the unaided condition, and the two circuits resulted in equivalent performance for average speech input levels. On average, the WDRC aid resulted in high and uniform speech recognition scores across the five spectra. In contrast, the linear gain aid resulted in a lower recognition score for soft speech and shouted speech relative to that obtained with an average speech level. Analysis of individual speech recognition benefit scores revealed that 11 out of 12 subjects had equal or greater performance with the WDRC processing than the linear processing. Subjective loudness ratings in the linear gain condition were compatible with decreased sensation level for soft speech and loudness discomfort for shouted speech. CONCLUSIONS: WDRC processing has potential applications in hearing aid fittings for listeners with moderate to severe hearing loss because it provides a consistently audible and comfortable signal across a wide range of listening conditions in quiet without the need for volume control adjustments.

Adolescent↗

Comparison of flat and steep rigid contact lens fitting methods in keratoconus.

PURPOSE: The purpose of this article is to compare the safety and efficacy of flat- and steep-fitting rigid contact lenses in keratoconus. METHODS: The Collaborative Longitudinal Evaluation of Keratoconus (CLEK) Study is a 16-center observational study. Cross-sectional results at baseline were generated for 1091 subjects with longitudinal results from the 871 subjects who completed 8 years of follow up. RESULTS: Of the 761 rigid contact lens-wearing patients at baseline, 41% had a scar at baseline compared with 24% of the nonrigid contact lens wearers (odds ratio [OR], 2.15; 95% confidence interval [CI], 1.35-3.43; p = 0.001). Eighty-seven percent were fitted with flat-fitting lenses, whereas 13% were fitted with steep-fitting lenses. Rigid lens fitting method was also associated with incident corneal scarring. A greater proportion of the corneas wearing flat-fitting contact lenses were scarred (43% compared with 26% for the steep-fitted eyes; OR,= 2.19; 95% CI, 1.37-3.51; p = 0.001). After controlling for corneal curvature, the association of rigid contact lens fit and corneal scarring at baseline did not persist (adjusted OR, 1.20; 95% CI, 0.70-2.06; p = 0.52). Thirty-two percent of unscarred eyes at baseline fitted flat had developed an incident corneal scar by the eighth year follow-up visit compared with 14% of eyes fitted steep (OR, 2.93; 95% CI, 1.34-6.42; p = 0.007). CONCLUSIONS: The data reported here indicate that, after controlling for disease severity in the form of corneal curvature, keratoconic eyes fitted with a rigid contact lens resulting in an apical touch fluorescein pattern did not have an increased risk of being scarred centrally at baseline. This "natural history" sample cannot determine causal proof that one method of fitting lenses is safer than another. To achieve this, a randomized clinical trial is needed.

Contact Lenses↗

Bone-conduction amplification with completely-in-the-canal hearing aids.

Recent advances in miniaturization have provided clinicians with hearing aids that can be comfortably inserted as far as the bony portion of the ear canal. It is possible to take advantage of these deeply inserted hearing aids in new ways. For example, the physical vibrations of microphone and receiver components may be used to improve hearing aid gain through bone conduction. Three cases are presented that will introduce this phenomenon for two transcranial CROS fittings and for one unilateral otosclerosis fitting. In each case, functional gain measurements under headphones were obtained with the hearing aid receivers acoustically plugged. Considerable gain was still present. Potential benefits, ramifications, and side effects are discussed.

Adult↗

Fitting hearing aids on infants and children: a primer for otolaryngologists.

Fitting hearing aids on young infants presents a unique set of problems, and to some extent, requires a unique set of skills. First, a complete, frequency-specific evoked potential assessment is needed to define the loss and establish hearing aid fitting targets. The selected hearing aids must be flexible and must be adjusted to account for the acoustic characteristics of a small ear canal. Automatic volume control, wide dynamic range compression, directional microphones, and direct audio input are among the optional features to consider. In general, advanced technology, such as digital, programmable hearing aids offer the greatest flexibility in meeting the instrument-related challenges of the infant hearing-aid fitting. Finally, hearing aids are only one component of the management sequence. An early interventionist must be involved from the start to coordinate rehabilitation and ensure that the needs of the entire family are being met in the process.

Child↗

Comparison of the transfer precision of three different impression materials in combination with transfer caps for the Frialit-2 system.

Transfer of the precise position of implants to a master cast is a prerequisite for accurate and passive fit of the superstructure. Implants lack the mobility of natural teeth and, therefore, inaccurate frameworks result in stress within the mechanical parts and the implant-bone interface. Various impression methods have been described to achieve accurate reproduction of the intra-oral relation of the implants. The aim of this experimental study was to compare three different impression materials (polyether, polyvinyl siloxane, hydrocolloid) with the Frialit(R)-2 system and with the indirect technique. In addition, the use of transfer caps (TCs) to improve transfer precision was tested with all three materials. All measurements were performed using a three-dimensional (3D) co-ordinate measuring machine that is capable of locating points in space and calculating the relative distortions as angles of tilt (rot-XY, rot-XZ, rot-YZ) and 3D displacement. The results suggest that addition-silicone (a-silicone) and polyether are the materials of choice for implant transfer procedures. The use of TCs resulted in a significantly reduced rotation in the XY-plane but did not improve the absolute 3D displacement. A-silicone with the use of TCs proved to be most precise. Comparison between polyether and polyvinyl siloxane showed significant differences in the XY-rotation and the 3D displacement in favour of the silicone. Because the mean distortions between the original model and the master casts were about 100 microm, absolutely precise fit may be unattainable owing to the physical properties of the materials. Further studies will have to evaluate the amount of tolerable stress at the implant-bone interface.

Alginates↗

[Management of a deaf-blind patient with a 12-channel cochlear implant].

A case study of a deaf-blind patient implanted with the COMBI40+ cochlear implant is presented. The patient is a 70-year-old woman who has been blind since the age of 40. Since 1977 the hearing loss continuously increased. Before surgery she had a very small residual hearing (with hearing aid: 40% speech intelligibility by four syllable numbers) and she used Braille and finger-spelling on her hand to communicate with other people. The patient has a high intelligence and so she did not have any problems when the speechprocessor was fitted and during the hearing therapy. After one month she had an open-set-speech recognition. The quality of her life is much better than before surgery. The communication by finger-spelling on her hand is not necessary any longer.

Aged↗

Contact lens wear after photorefractive keratectomy: comparison between rigid gas permeable and soft contact lenses.

PURPOSE: To determine if rigid gas permeable (RGP) or soft contact lenses can be successfully worn after photorefractive keratectomy (PRK) to correct residual refractive errors. METHODS: Patients with residual stable ametropia after PRK were fit with RGP or soft lenses. Manifest refraction, corneal topography, and keratometry were performed, and post-PRK corneal haze was graded during the study visits. Contact lens fit characteristics and comfort were assessed. Lens centration, visual quality, and ocular surface status were graded, and visual acuity with contact lenses was charted. RESULTS: Eighteen patients were recruited for RGP lens fitting. The mean refractive error post-PRK was +0.80 D +/- 2.03 (range: -3.50 to+3.00 D). The mean contact lens power was -3.90 D +/- 2.03 (range: 0 to -7.00 D), and the mean contact lens base curve was 7.88 mm +/-0.16. A significant positive tear film at the site of the central ablation was noted, contributing to excessive minus lens power in all cases. Despite mild to moderate lens instability and de-centration, 14 patients reported excellent visual quality with the lenses, and pre-PRK best-corrected acuity was achieved in all patients. Twenty-five percent (4 of 16) of the patients were able to wear the lenses all day. Eleven patients were recruited for soft contact lens fitting-five from the RGP trial. The mean refractive error post-PRK was -0.64 D +/- 2.01 (range: -3.50 to +1.75D). The mean contact lens power was -0.60 D +/- 2.07 (range: -3.75 to +2.5 D), and the mean contact lens base curve was 8.33 mm +/- 0.42. Eight patients were corrected with lenses to their pre-PRK best-corrected acuity, and nine patients reported excellent visual quality with the lenses. All the patients had excellent lens centration. Thirty-six percent (four of 11) of patients were wearing the lenses all day. CONCLUSIONS: Fitting RGP lenses after PRK results in good visual acuity but may be associated with mild to moderate lens instability and decentration. Soft contact lens fitting also results in good visual acuity. Soft lenses were better tolerated by the subjects in our study because of improved lens centration and stability.

Adult↗

Optimization of contact lens fitting in keratectasia patients after laser in situ keratomileusis.

PURPOSE: To evaluate the clinical outcomes of contact lens fitting in eyes with keratectasia after laser in situ keratomileusis (LASIK) to optimize the performance of the contact lenses. SETTING: Contact Lens Clinic, Seoul National University Hospital, Seoul, Korea. METHODS: Six eyes of 4 patients with keratectasia were examined. Keratectasia was diagnosed based on abnormal topographic findings, progressive myopic changes, and uncorrected visual acuity with glasses. A multicurve lens or reverse-geometry lens (RGL) was selected based on the anterior elevation map. The base curve radius and peripheral parameters were determined based on the axial map and the evaluation of the fluorescein pattern of the lens. The contact lens fitting characteristics and visual acuity were evaluated. Patients were interviewed about their level of comfort, daily contact lens wear time, and glare. RESULTS: Multicurve lenses and RGLs were fitted in 4 eyes and 2 eyes, respectively. The base curve radius of the multicurve lenses ranged from 7.2 to 7.5 mm; the alignment curve radius of RGLs was 7.6 mm in both cases. The radii of peripheral curves were customized to enhance tear interchange. Visual acuity improved to 20/30 or better in all eyes. All patients were completely satisfied with the comfort of the fitting. The mean daily wearing time was 12.7 hours. One patient reported tolerable glare in the eye after being fitted with an RGL. CONCLUSION: Proper contact lens fitting based on topographic data and slitlamp evaluation allowed good visual rehabilitation and comfortable extended daily wear in patients with keratectasia after LASIK.

Adult↗

Rigid gas permeable contact lens changes in the aphakic infant.

PURPOSE: The purpose of this study was to describe and evaluate the frequent parameter changes required in aphakic infants fit with rigid gas permeable (RGP) contact lenses. METHODS: Twenty-five eyes from 18 patients with congenital cataracts were fit postoperatively with RGP lenses and followed for an average of 19 months. The original lens specifications were determined by keratometer readings, corneal diameter, and axial length or retinoscopy obtained under sedation just prior to or after cataract extraction surgery. The frequency of changes in contact lens power, base curve, and diameter was recorded and analyzed. RESULTS: Due to rapid growth and/or difficulty in achieving accurate measurements, repeated contact lens adjustments were needed to ensure proper power and fit. CONCLUSIONS: The data contained in this study indicates a relatively stable period--from 6 to 12 months postoperatively--where the likelihood that contact lenses will need to be modified falls below 50%.

Acrylic Resins↗

Electrical discharge machining.

This article describes a laboratory technique of achieving the highest degree of passive fit of an implant-retained restoration using electric discharge machining (EDM). This process can save time by eliminating the need for conventional soldering procedures, increase the longevity of the restoration, and when used along with the clinical technique of fabricating a verification index, eliminate the clinical try-in phase.

Dental Casting Technique↗

Managing hearing loss in a patient with Alzheimer disease.

This case study reports the management of hearing loss in a patient with Alzheimer disease (AD) living at home with a spouse care giver. The report highlights the interaction between symptoms associated with AD and hearing loss and the lack of data regarding remediation of hearing loss in this population. Specifically, the case illustrates the modifications in evaluation and verification of the hearing aid fitting that may be advisable when working with patients with AD. The data for this patient illustrate some novel measurement techniques that may assist the professional in documenting the impact of treatment in this population.

Aged↗

Complexity of contact lens fitting after refractive surgery.

PURPOSE: To quantify and describe the complexity of contact lens correction on corneas altered by refractive surgery. DESIGN: A case-control study involving postrefractive surgery patients and controls from one multidisciplinary contact lens practice. METHODS: The contact lens care of one randomly selected eye of 30 postrefractive surgery patients (15 postincisional and 15 postlamellar refractive surgery cases) was retrospectively analyzed and compared with that of 30 age-and-gender matched nonrefractive surgery controls. We quantified the complexity by the number of diagnostic lenses used to establish the initial lens order, the number of ordered lenses required to complete the fit, and the number of office visits during the first 4 months of lens care. Final contact lens optical powers, corrected visual acuities, complications, and lens success/failure were also studied. The nonparametric Mann-Whitney U test was used for statistical analysis. RESULTS: Postrefractive surgery eyes utilized statistically more diagnostic lenses (P =.048), ordered lenses (P =.008), and office visits (P <.0001). There were no statistical differences in the number of office visits, number of diagnostic contact lenses used, and number of ordered contact lenses between the postincisional and postlamellar refractive surgery patients. Although final contact lens optical powers were not significantly different (P =.06) between the two groups, contact lens corrected LogMAR acuities were statistically worse (P =.013) in the postrefractive surgery eyes than in the control group. Contact lens failures occurred in four postrefractive surgery eyes, while no eyes in the control group failed to tolerate contact lenses. CONCLUSIONS: Corneas altered by either incisional or lamellar refractive surgery techniques are more challenging to fit with contact lenses than nonsurgically altered eyes, requiring more lenses and chair time, while resulting in slightly poorer contact lens corrected visions and more failures.

Adult↗

In vivo stress behavior in cemented and screw-retained five-unit implant FPDs.

PURPOSE: When fixing implant-supported fixed partial dentures (FPDs), it is important to achieve passive fit. The objective of the in vivo study presented was to quantify the strain development during the fixation of screw- and cement-retained FPDs. MATERIALS AND METHODS: After informed patient consent had been obtained (Ethics commission Approval No. 2315; FAU Erlangen-Nuremberg, Germany), four groups of five-unit FPDs (five samples per group) were fabricated and investigated in vivo. Group 1: Cementable, repositioning technique impression, burn out plastic coping; Group 2: Screwable, pickup technique impression, burn out plastic coping; Group 3: Screwable, pickup technique impression, cast to gold cylinder; Group 4: Screwable, pickup technique impression, bonded to gold cylinder. Two strain gauges (SG) were attached to the pontics of each bridge (SG-M and SG-D) to measure the strains that occurred during either the cementing or screw-in process. The final values were recorded for analysis. RESULTS: The mean strain values (microm/m) for each SG were: Group 1: SG-M 32 microm/m, SG-D: 89 microm/m; Group 2: SG-M 302 microm/m, SG-D: 197 microm/m; Group 3: SG-M 458 microm/m, SG-D: 268 microm/m; Group 4: SG-M 269 microm/m, SG-D: 52 microm/m. CONCLUSIONS: Although the bridges were clinically acceptable, none of them revealed a truly passive fit with zero microstrain. In contrast to conventional screw-retained bridges, cement retention seems to result in lower strain levels. Bonding bridge pontics to prefabricated implant components seems to allow both the retrievability of a screw-retained bridge and produce moderate strain values.

Aged↗

Bilateral amplification for the elderly: are two aids better than one?

This paper reviews the advantages and disadvantages of bilateral amplification as opposed to unilateral hearing use for older persons with bilateral symmetric hearing loss. Binaural advantages, such as improved localization and speech recognition in noise, are presented as they pertain to the older population. In addition, contraindications, such as binaural interference, increased costs, cosmetic concerns, decreased manipulation skills, and additional hearing aid management issues, are discussed. A case study is provided in which unilateral hearing aid fitting was more beneficial to a patient than two hearing aids. It is concluded that bilateral amplification should be attempted for all elderly patients with symmetric hearing loss, unless a contraindication is suspected.

Aged↗