Biomedical subjects

Mark S Gilthorpe

Publications and source records attributed to Mark S Gilthorpe.

25 records · Page 2Linked to original sources

PubMed2004

Collinearity in linear regression is a serious problem in oral health research.

The aim of this article is to encourage good practice in the statistical analysis of dental research data. Our objective is to highlight the statistical problems of collinearity and multicollinearity. These are among the most common statistical pitfalls in oral health research when exploring the relationship between clinical variables using multiple regression analysis. We hope that this article will show why these problems arise and how they can be avoided and overcome. Examples from the periodontal literature will be used to illustrate how collinearity and multicollinearity can seriously distort the model development process as a result of the phenomenon of mathematical coupling. Knowledge of these problems can help to eliminate misleading results and improve any subsequent interpretations. Regression analyses are useful tools in oral health research when their limitations are recognized. However, care is required in planning and it is worthwhile seeking statistical advice when formulating the study's research questions.

Algorithms↗

PubMed2004

The application of multilevel modeling in the analysis of longitudinal periodontal data--part I: absolute levels of disease.

BACKGROUND: Statistical analyses of periodontal data that average site measurements to subject mean values are unable to explore the site-specific nature of periodontal diseases. Multilevel modeling (MLM) overcomes this, taking hierarchical structure into account. MLM was used to investigate longitudinal relationships between the outcomes of lifetime cumulative attachment loss (LCAL) and probing depth (PD) in relation to potential risk factors for periodontal disease progression. METHODS: One hundred males (mean age 17 years) received a comprehensive periodontal examination at baseline and at 12 and 30 months. The resulting data were analyzed in two stages. In stage one (reported here), the absolute levels of disease were analyzed in relation to potential risk factors; in stage two (reported in a second paper), changes in disease patterns over time were analyzed in relation to the same risk factors. Each approach yielded substantially different insights. RESULTS: For absolute levels of disease, subject-level risk factors (covariates) had limited prediction for LCAL/PD throughout the 30-month observation period. Tooth position demonstrated a near linear relationship for both outcomes, with disease increasing from anterior to posterior teeth. Sites with subgingival calculus and bleeding on probing demonstrated more LCAL and PD, and supragingival calculus had an apparently protective effect. Covariates had more "explanatory power" for the variation in PD than for the variation in LCAL, suggesting that LCAL and PD might be generally associated with a different profile of covariates. CONCLUSION: This study provides, for a relatively young cohort, considerable insights into the factors associated with early-life periodontal disease and its progression at all levels of the natural hierarchy of sites within teeth within subjects.

Adolescent↗

PubMed2004

The application of multilevel modeling in the analysis of longitudinal periodontal data--part II: changes in disease levels over time.

BACKGROUND: The aim of this study was to investigate the longitudinal relationships between the outcome measurements of changes in lifetime cumulative attachment loss (cLCAL) and changes in probing depth (cPD) in relation to potential risk factors or other risk markers for periodontal disease progression from a cohort of 100 young males. In order to account for the hierarchical data structure, and to explore explicitly the site, tooth, and subject levels simultaneously, multilevel modeling was undertaken. METHODS: The analyses were undertaken in two parts. Within a previous article, the absolute levels of disease were analyzed in relation to potential risk factors; within this article, changes in disease are analyzed in relation to these factors. Each analytical approach yielded substantively different insights. RESULTS: Subject-level risk factors had limited predictive value for cLCAL/cPD throughout the 30-month observation period. Tooth position demonstrated a near linear relationship for both outcomes, with disease increasing from anterior to posterior teeth. Supragingival plaque had no significant effect on cLCAL/cPD, while subgingival calculus and bleeding on probing were negatively associated with cLCAL/cPD. In contrast to the outcomes LCAL/PD, supragingival calculus had no significant protective effect on cLCAL/cPD. There was no significant influence of smoking in this cohort. CONCLUSIONS: This study provides, for a relatively young cohort, considerable insights into the factors associated with longitudinal patterns of early-life periodontal disease at all levels of the natural hierarchy of sites within teeth within subjects. Furthermore, it is demonstrated how multilevel modeling can provide considerable insight into some of the inconsistencies and controversies found in the previous periodontal literature.

Adolescent↗

PubMed2003

Rural/urban differences in the association between deprivation and healthcare utilisation.

Whilst associations between inequalities in healthcare utilisation and socio-economic deprivation are well established in the UK it is argued that deprivation indices, such as the Townsend index, remain insensitive to rural/urban differences. This study examines how Townsend and its components differ in their association with healthcare utilisation across the rural/urban spectrum of a large health region. Our research was carried out in the West Midlands National Health Service region (population 5.3 million), comprising of a similar geographical population diversity to that of the United Kingdom (UK) using Hospital Episode Statistics (1994/5-1998/9) and 1991 census socio-demographic data. Retrospective multilevel multivariate models compare three ward-level healthcare utilisation measures (standardised episode-, admission-, and bed-rates) in relation to the Townsend index of material deprivation, its components, and four rural/urban characteristics (population density, population potential, electoral ward area and perimeter size). The associations between outcomes and Townsend were generally not attenuated by the rural/urban characteristics. The constituent component of car-ownership was similarly unperturbed, whereas population potential significantly perturbed the home-ownership model and overcrowding was significantly perturbed by all four rural/urban characteristics considered. A deprivation index may encapsulate different meanings to that of its components when used to assess variations in healthcare utilisation. Constituent components may yield considerable perturbation in relation to healthcare utilisation across the rural/urban spectrum, whilst the composite measure does not. In particular, and contrary to anecdotal opinion, car-ownership and unemployment (as recorded in the 1991 UK census) exhibited a stable relationship across different rural/urban areas with respect to healthcare utilisation.

Automobiles↗

PubMed2002

Disparities in self reported oral health problems among a young Syrian adult population.

OBJECTIVE: To describe the prevalence of dental pain and other oral health problems among a young Syrian adult population and to identify socio-demographic factors associated with these experiences. SUBJECTS: An industrial sample of 400 men and women aged 18-34 years from Damascus, Syria. METHODS: Study participants were interviewed about their experience of oral health problems in the previous year (1998). Socio-demographic information was collected. RESULTS: 93% (369) of the interviews were completed. The prevalence of oral health problems was high, with 96% (353) of respondents claiming that they experienced one or more problems in the previous year. Two thirds of participants (65%, 239) claimed they had dental pain in the previous year. Analysis revealed that dental pain experience was significantly associated with age and gender. Analysis considering all factors revealed that the odds of experiencing dental pain were higher amongst the younger age group (18-24 compared to 25-34 year-olds). CONCLUSION: The prevalence of oral health problems was high among the population studied. Socio-demographic variations in experience of dental pain were apparent, with young men of lower education having the greatest odds of dental pain experience in the previous year.

Adolescent↗

PubMed2002

Multilevel survival analysis of amalgam restorations amongst RAF personnel.

OBJECTIVE: To introduce the concepts of multilevel survival analysis through an investigation into the longevity of amalgam restorations. BASIC RESEARCH DESIGN: The multilevel Cox proportional hazard model is illustrated using amalgam restoration data comprising three levels: repeated restorations at level-1, teeth at level-2, and subjects at level-3. The outcome was duration of amalgam restoration survival. Single-level and multilevel Cox methods are contrasted. PARTICIPANTS: The data were from a survey of amalgam restorations (reported elsewhere), involving 200 RAF personnel aged between 16 and 37 years at enlistment between 1947 and 1979, having served continuously for a minimum of 16 years prior to 1994. RESULTS: Differences existed between single-level and multilevel methods; the latter being the method of choice. Initial caries experience was a good predictor of longevity. Molar teeth fared worse than pre-molars and MOD & B, MOD & L, and MOD & BL restorations experienced considerably greater risk of failure than did MOD, MO, DO and MO/DO ext types, which in turn fared worse than occlusal restorations. Root-treated and pinned teeth also experienced an elevated risk of premature failure. There was a moderate but significant increase in restoration failure amongst subjects who were seen by more dentists throughout their service. CONCLUSIONS: The application of multilevel modelling to survival analysis provides an appropriate and powerful solution to the problem of lack of independence amongst dental restorations. It is beneficial that studies undertake a multilevel analysis in preference to ignoring hierarchy or omitting swathes of information in order to perform a single-level analysis.

Adolescent↗

PubMedDate not supplied

Changes in passive tactile sensibility associated with dental implants following their placement.

PURPOSE: This study investigated the changes that might occur in passive tactile sensibility during a period of 3 months following Implant placement in a group of edentulous subjects treated with dental implants. The effect of changing the velocity of force application on passive tactile sensibility was also investigated. MATERIALS AND METHODS: Five edentulous subjects who had been treated (as a part of an immediate loading study) with 2 or more Nobel Biocare dental implants in the anterior mandible were studied. Pushing forces were applied directly and perpendicular to the long axes of the abutments until the subjects felt the first sensation of pressure, using a computer-controlled, custom-made device. The force was measured with an integral transducer. The applied force had a ramped staircase pattern, which was used at 2 different tip velocities. The measurements were taken on 4 occasions: 1, 2, 4, and 12 weeks after fitting the abutments. RESULTS: Statistical analysis, using multilevel modeling, demonstrated that there was a significant decrease In the tactile threshold over successive weeks following implant placement. It also demonstrated that high velocity exhibited a higher threshold than low velocity. DISCUSSION AND CONCLUSION: It could be concluded that there was a significant increase In passive tactile sensibility during the healing phase following implant placement.

Aged↗