Biomedical subjects

Sean S Kohles

Publications and source records attributed to Sean S Kohles.

10 recordsLinked to original sources

PubMed2004

Time-dependent surgical outcomes following cauda equina syndrome diagnosis: comments on a meta-analysis.

STUDY DESIGN: In this Journal Club review, we critically examine the methodology and results of a recently published meta-analysis describing the time dependency of surgical outcomes associated with cauda equina syndrome (CES) diagnosis. OBJECTIVES: Our objectives are to clarify the strengths, weaknesses, and appropriate use of statistics regarding the findings of the previous publication. SUMMARY OF BACKGROUND DATA: Surgical outcomes from published reports are related to both preoperative conditions and the time between surgery and diagnosis of CES. METHODS: We reexamined many of the papers that were used to create the surgical outcomes data set, including the publications that supplied quantitative information for logistic regression. Of special focus were studies that contributed to the "less than 24 hours from diagnosis" data. The use of statistical parameters such as probabilities and odds ratios to infer possible future outcomes is also addressed to clarify the papers' interpretations. To support the overall limitations of their generalized findings, we conducted a power analysis, which highlights the lack of statistical strength in the resulting conclusions. RESULTS: The results of the initial work state that an advantage exists in treating patients within 48 hours in comparison to treating them during a period greater than 48 hours after the onset of CES symptoms. However, the authors also state that no difference exists between the effects of an early surgery (less than 24 hours) compared with a subsequent period between 24 and 48 hours after CES onset. Key elements of logistic regression and meta-analysis are used to refute specific aspects of their methodology as well as their clinical interpretation regarding acute intervention. CONCLUSIONS: We conclude that a flawed methodology and misinterpretation of results are reported, understating the value of early surgical intervention.

Humans↗

PubMed2004

Analysis of bending behavior of native and engineered auricular and costal cartilage.

A large-deflection elasticity model was used to describe the mechanical behavior of cartilaginous tissues during three-point bending tests. Force-deflection curves were measured for 20-mm long x 4-mm wide x approximately 1-mm thick strips of porcine auricular and costal cartilage. Using a least-squares method with elastic modulus in bending as the only adjustable parameter, data were fit to a model based on the von Karman theory for large deflection of plates. This model described the data well, with an average RMS error of 14.8% and an average R(2) value of 0.98. Using this method, the bending modulus of auricular cartilage (4.6 MPa) was found to be statistically lower (p < 0.05) than that of costal cartilage (7.1 MPa). Material features of the cartilage samples influenced the mechanical behavior, including the orientation of the perichondrium in auricular cartilage. These methods also were used to determine the elastic moduli of engineered cartilage samples produced by seeding chondrocytes into fibrin glue. The modulus of tissue-engineered constructs increased statistically with time (p < 0.05), but still were statistically lower than the moduli of the native tissue samples (p > 0.05), reaching only about a third of the values of native samples.

Animals↗

PubMed2004

Prediction of growth factor effects on engineered cartilage composition using deterministic and stochastic modeling.

In the design of engineered tissues, guided balance of biomaterial degeneration with tissue synthesis offers refined control of construct development. The objective of this study was to develop a mathematical model that describes the steady state metabolism of extracellular matrix molecules (ECM: glycosaminoglycan and collagen) in an engineered cartilage construct taking into account localized environmental changes that may arise because of the application of growth factors. The variable effects of growth factors were incorporated in the form of random noise rather than the difference in rates of synthesis and catabolism. Thus, the frequency of ECM accumulation for each matrix molecule in the steady state under the random influence of growth factor was produced relative to the matrix carrying capacity. Published synthesis-rate time constants and steady state ECM conditions from chondrocyte-polymer scaffold composites provided both input and validation for the model. Although the presence of growth factors in the presented system dynamics were considered randomized, the results described a positive feedback or promotional ECM synthesis at low levels of growth factors. While a negative feedback or inhibition of ECM synthesis was characterized at higher levels of growth factors. This transition phenomenon is based on a comparison with the results of a steady state condition in the form of a deterministic model and supports previous reports of guided accumulation in musculoskeletal, connective, and neuronal tissues.

Animals↗

PubMed2004

Five-year survival distributions of short-length (10 mm or less) machined-surfaced and Osseotite implants.

BACKGROUND: In cases of reduced alveolar bone height, implants of short length (10 mm or less) may be employed although there is a perceived risk that because of their small stature they will be unable to tolerate occlusal loads and will fail to osseointegrate. PURPOSE: This report describes an analysis of prospective multicenter clinical studies evaluating the risk for failure of short-length implants, comparing dual acid-etched (DAE) Osseotite implants (Implant Innovations, Inc., Palm Beach Gardens, FL, USA) to machined-surfaced implants. MATERIALS AND METHODS: Admission criteria were the same for both data sets. Baseline variables of demographics including age, gender and smoking status, bone quality, location, implant dimensions, and types of prostheses were compared to ensure balance among groups. Cumulative survival rates (CSRs) were calculated with the Kaplan-Meier estimator. RESULTS: The implant data included 2294 implants for the DAE series and 2597 implants for the machined-surfaced series. Patient demographics showed similar percentages of occurrence for all variables. The distributions of implants between short- and standard-length data sets for baseline variables including width, location, and restorative type were similar, qualifying these data sets for comparison of the independent variable of length. Overall, there was a 2.2% difference in 5-year CSRs between the machined-surfaced short- and the standard-length implants. For these implants a 7.1% difference was observed in the posterior maxilla and an 8.5% difference in the anterior maxilla. For DAE implants the overall difference between "standards" and "shorts" was 0.7%, which is not statistically significant. CONCLUSION: In this analysis the difference in CSRs between short- and standard-length implants was greater for machined-surfaced implants than for DAE implants.

Adult↗

PubMed2003

A meta-analysis examining the clinical survivability of machined-surfaced and osseotite implants in poor-quality bone.

PURPOSE: A frequently cited cause of dental implant failure is the inadequate quality of bone found at the implant site during osteotomy preparation. Although bone quality clearly can affect integration rates, additional variables, such as the implant surface conditioning, can also influence long-term implant performance success. The following report examines outcomes of clinical studies that monitored the performance of machined-surfaced implants and dual acid-etched Osseotite (Implant Innovations, Inc., Palm Beach Gardens, FL) implants isolating the effect of bone quality and implant surface conditioning. MATERIALS AND METHODS: Implant data are derived from eight prospective multicenter clinical studies representing 2614 machined-surfaced implants and 2288 Osseotite implants. All implant placement surgeries followed a two-stage surgical approach with an unloaded healing period of 4 to 6 months. Bone quality was assessed by operator perception of resistance during drilling and ranked as dense, normal, or soft. At the time of this analysis, implant follow-up from placement ranged up to 66 months for the Osseotite and 84 months for the machined-surfaced implants. To isolate the effect of bone quality, other baseline variables were compared to ensure equal distribution between groups. Baseline variables included patient demographics, locations, dimensions of implants, and types of restorative cases. Implant performance was analyzed using nonparametric survival analysis (Kaplan-Meier estimator). Cumulative success rates (CSR) were calculated and differences between implant-bone quality combinations were assessed using the log-rank method. RESULTS: For the machined-surfaced implants, the 4-year CSR in all bone sites is 92.7%. For the implants placed in good (dense and normal) bone, the 4-year CSR is 93.6% compared with the 4-year CSR in poor (soft) bone of 88.2% (P < 0.05). For Osseotite implants in all sites, their overall 4-year CSR was 98.4%, 98.4% in good bone, and 98.1% in poor bone. CONCLUSIONS: Bone quality therefore seems to have a definitive impact on machined-surfaced implants, but this effect was not observed in the Osseotite implant series.

Acid Etching, Dental↗

PubMed2002

Modeling the dynamic composition of engineered cartilage.

Mathematical models to describe extracellular matrix (ECM) deposition and scaffold degradation in cell-polymer constructs for the design of engineered cartilage were developed and validated. The ECM deposition model characterized a product-inhibition mechanism in the concentration of cartilage molecules, collagen and glycosaminoglycans (GAG). The scaffold degradation model used first-order kinetics to describe hydrolysis (not limited by diffusion) of biodegradable polyesters, polyglycolic acid and polylactic acid. Each model was fit to published accumulation and degradation data. As experimental validation, cell-polymer constructs (n=24) and unseeded scaffolds (n=24) were cultured in vitro. Biochemical assays for ECM content and measurements of scaffold mass were performed at 1, 2, 4, 6, 8, or 10 weeks (n=8 per time point). The models demonstrated a strong fit with published data and experimental results (R(2)=0.75 to 0.99) and predicted the temporal total construct mass with reasonable accuracy (30% RMS error). This approach can elucidate mechanisms governing accumulation/degradation and may be coupled with structure-function relationships to describe time-dependent changes in construct elastic properties.

Animals↗

PubMed2002

Linear poroelastic cancellous bone anisotropy: trabecular solid elastic and fluid transport properties.

The mechanical performance of cancellous bone is characterized using experiments which apply linear poroelasticity theory. It is hypothesized that the anisotropic organization of the solid and pore volumes of cancellous bone can be physically characterized separately (no deformable boundary interactive effects) within the same bone sample. Due to its spongy construction, the in vivo mechanical function of cancellous or trabecular bone is dependent upon fluid and solid materials which may interact in a hydraulic, convective fashion during functional loading. This project provides insight into the organization of the tissue, ie., the trabecular connectivity, by defining the separate nature of this biphasic performance. Previous fluid flow experiments [Kohles et al., 2001, Journal of Biomechanics, 34(11), pp. 1197-1202] describe the pore space via orthotropic permeability. Ultrasonic wave propagation through the trabecular network is used to describe the solid component via orthotropic elastic moduli and material stiffness coefficients. The linear poroelastic nature of the tissue is further described by relating transport (fluid flow) and elasticity (trabecular load transmission) during regression analysis. In addition, an empirical relationship between permeability and porosity is applied to the collected data. Mean parameters in the superior-inferior (SI) orientation of cubic samples (n=20) harvested from a single bovine distal femur were the largest (p<0.05) in comparison to medial-lateral (ML) and anterior-posterior (AP) orientations: Apparent elastic modulus (2,139 MPa), permeability (4.65x10(-10) m2), and material stiffness coefficient (13.6 GPa). A negative correlation between permeability as a predictor of structural elastic modulus supported a parametric relationship in the ML (R2=0.4793), AP (R2=0.3018), and SI (R2=0.6445) directions (p<0.05).

Animals↗

PubMed2002

Dual-etched implants loaded after 1- and 2-month healing periods: a histologic comparison in baboons.

The purpose of this study was to evaluate the effect of early loading of Osseotite dual acid-etched commercially pure titanium dental implants in an established baboon model. Implant sites were prepared by removal of premolars and first molars at maxillary and mandibular sites in 10 adult female baboons (Papio anubis). The resultant edentulous ridges were allowed to heal for 6 weeks. Following the placement of 80 implants, 2-mm healing abutments were placed on each implant and protruded through the mucosa after flap closure. Each implant was functionally loaded with a single crown after either 1 month (n = 40) or 2 months (n = 40) of implant healing. All implants were removed in block section after 3 months of functional loading and prepared for histologic evaluation. Photographs of histologic slides were digitized for data collection. The amount of osseous tissue contact along the implant surface in the buccolingual plane was determined using image analysis. The fraction of direct bone-tissue contact along a standardized region of each implant perimeter was calculated and compared using analysis of variance. Implants loaded after 1 month of healing had a mean of 76.6% + 14.4% bone contact, and implants loaded after 2 months of healing had a mean of 77.2% +/- 12.2% bone contact. Statistically, the 1- and 2-month groups were similar (P = .81). No implant failures were observed in either treatment group. Reducing the surgical healing time from 2 months to 1 month did not statistically affect the amount of bone observed at the tissue-implant interface in baboons under functionally loaded conditions.

Acid Etching, Dental↗

PubMed2002

A meta-analysis evaluating the risk for implant failure in patients who smoke.

Failure of dental implants to achieve osseointegration is often attributed to patient baseline variables, such as smoking. This meta-analysis examines outcomes of clinical studies that monitored the performance of machined-surfaced and Osseotite, implants; the analysis also isolates the effect of smoking. The implant data for the machined-surfaced implants are derived from three prospective multicenter studies (n = 2,614) and from six prospective studies (n = 2,274) for the Osseotite implants. All implant placement surgeries followed a two-stage surgical approach with an unloaded healing period of 4 to 6 months. An evaluation of the data sets (i.e., smokers vs nonsmokers) was first performed to determine the existence of imbalance in baseline variables, including patient demographics, bone quality, location, dimensions, and types of prostheses. Analysis of the distributions of these baseline variables showed similar proportionalities and therefore qualified the data sets for comparison of the cumulative success rates (CSR) of the implants on the basis of smoking. For the 2,117 nonsmoking, machined-surfaced implants, the 3-year CSR is 92.8%; for the 492 implants in the smoking group, the CSR is 93.5%. The 3-year CSR for 1,877 nonsmoking Osseotite implants is 98.4%; for the 397 smoking implants it is 98.7%. No difference is observed between the smoking groups and the nonsmoking groups in these patient populations. There is, however, a clinically relevant difference observed between the two implant types.

Clinical Trials as Topic↗

PubMedDate not supplied

Direct assessment of profilometric roughness variability from typical implant surface types.

PURPOSE: Protocols for quantifying the surface roughness of implants are varied and dependent upon the roughness parameter produced by the particular measurement device. The objective of this study was to examine the accuracy and precision of typical roughness characterization instruments used in the dental implant industry. MATERIALS AND METHODS: The average roughness (Ra) was measured using 2 common surface characterization instruments: an interferometer and a stylus profilometer. Titanium disks were prepared to represent 4 typical dental implant surfaces: machined, acid-etched, hydroxyapatite-coated, and titanium plasma-sprayed. Repeated measurements from multiple sites on each surface were undertaken to establish statistical inferences. Qualitative images of the surfaces were also acquired using a laser scanning confocal microscope. After surface measurements were conducted, the disks were diametrically cut and cross-sectional profiles were examined using a scanning electron microscope (SEM) as a comparative measure of surface topography. An analysis of variance was applied to isolate the effects of the measurement site, measurement sequence, surface treatment, and instrument type on Ra values. RESULTS: The results indicated that surface treatment (P = .0001) and instrument (P = .0001) strongly influenced Ra data. By design, measurement site (diametrical: P = .9859; area: P = .9824) and measurement sequence (P = .9990) did not influence roughness. In the assessment of individual instrument accuracy, the interferometer was the most accurate in predicting SEM-based roughness (P = .6688) compared with the stylus (P = .0839). As a measure of aggregate precision over all measurements, the most repeatable instrument was the stylus (coefficient of variation [CV] = 0.108), followed by the interferometer (CV = 0.125) and SEM (CV = 0.273). DISCUSSION: These results indicate dependencies in accuracy and precision related to the surface characterization technique. CONCLUSION: Instrument variability may obscure functional correlations between implant surface topography and osseointegration.

Acid Etching, Dental↗