Partial least squares path modelling for relations between baseline factors and treatment outcomes in periodontal regeneration.

BACKGROUND: Some clinical outcome variables in periodontal research are mathematically coupled, and it is not feasible to include all the mathematically coupled variables in an ordinary least squares (OLS) regression analysis. The simplest solution to this problem is to drop at least one of the mathematically coupled variables. However, this solution is not satisfactory when the mathematically coupled variables have distinctive clinical implications. MATERIAL AND METHODS: Partial least squares (PLS) methods were used to analyse data from a study on guided tissue regeneration. Relationships between characteristics of baseline lesions and treatment outcomes after 1 year were analysed using PLS, and the results were compared with those from OLS regression. RESULTS: PLS analysis suggested that there were multiple dimensions in the characteristics of baseline lesion: vertical dimension was positively associated with probing pocket depth (PPD) reduction and clinical attachment level (CAL) gain, whilst horizontal dimension was negatively associated with the outcome. Baseline gingival recession had a negative association with PPD reduction but a small positive one with CAL gain. CONCLUSION: PLS analysis provides new insights into the relationships between baseline characteristics of infrabony defects and periodontal treatment outcomes. The hypothesis of multiple dimensions in baseline lesions needs to be validated by further analysis of different datasets.

Is there a temporal trend in the reported treatment efficacy of periodontal regeneration? A meta-analysis of randomized-controlled trials.

BACKGROUND/AIM: The aim of study was to conduct a meta-analysis to investigate whether or not there was a temporal trend in the treatment efficacy reported in the randomized-controlled trials (RCTs) on guided tissue regeneration (GTR) or enamel matrix protein derivatives (EMD) in the treatment of infrabony defects. MATERIAL AND METHODS: The treatment outcomes were changes in probing pocket depth (PPD) and clinical attachment level (CAL). Weighted multilevel and ordinary regression analyses were performed to test the temporal relationship between treatment effect difference or treatment effectiveness and publication years. RESULTS: For PPD reduction, non-significant positive relationships were found in the treatment effect difference or treatment effect of both GTR and flap operation. For CAL gain, a small positive relationship was found in the treatment effect difference, but a significant positive trend in the treatment effect of flap operation was found. No significant temporal trend was found in the treatment effect difference for EMD. CONCLUSIONS: There was no evidence to support or refute a temporal trend in the treatment effect of regenerative procedures, but a positive trend was observed in the control group. These results suggest that only RCTs should be included in the meta-analysis, as the treatment effect of the control group may not be constant.

Comparison of interdental cleaning methods: a randomized controlled trial.

BACKGROUND: Although interdental cleaning is an integral component of home plaque control for periodontally involved patients, limited data exist on the periodontal benefits of commonly used interdental cleaning methods before definitive root surface debridement is undertaken. Therefore, the aim of this study was to compare the effects of a customized interdental brushing technique and a customized flossing technique on clinical periodontal outcomes prior to root surface debridement in chronic periodontitis cases. METHODS: This was a single-blind, randomized controlled clinical trial. Seventy-seven patients with chronic periodontitis were measured for plaque, relative interdental papillae level, Eastman interdental bleeding index, probing depths, and bleeding on probing at interdental sites and underwent a 10-minute hand scaling to remove easily accessible calculus deposits. Before group allocation, patients were advised on toothbrushing and instructed in two customized methods of interdental cleaning involving dental floss and precurved interdental brushes. Materials were supplied after random allocation. Participants were recalled at 6 and 12 weeks for clinical measurements, reinforcement of instructions, and fresh materials. RESULTS: There were significant reductions from baseline for all indices in both groups (P <0.01). At 6 weeks, the interdental brush group improved more than the floss group in every parameter (P <0.05). By 12 weeks, the changes in plaque, papillae level, and probing depths were significantly greater in the interdental brush group than the floss group (P <0.01). CONCLUSION: This trial demonstrated that patients were able to improve clinical periodontal outcomes by interdental cleaning, particularly with interdental brushes, even before thorough root surface debridement was undertaken.

Evaluating the quality of active-control trials in periodontal research.

AIM: The increasing popularity of randomized-controlled trials (RCTs) has raised the issue of their quality. Frequently overlooked are the differences between superiority and equivalence trials. The purpose of this study was to apply specific methodological criteria to evaluate the quality of active-control trials using studies that compared guided tissue regeneration (GTR) with enamel matrix derivatives (EMD). MATERIALS AND METHODS: Seven RCTs were identified in the literature. Standard methodological criteria and seven additional criteria for trials using active-control groups were used to evaluate the quality of the seven RCTs. RESULTS: Two trials were considered as superiority trials. The remaining five provided no clear statement of their research aim. However, two claimed that EMD and GTR were equally effective, because their results failed to show a significant difference between EMD and GTR. Most trials did not meet the majority of the design criteria. CONCLUSIONS: The general lack of compliance with quality criteria might place doubt on the value of these trials and may render any conclusions questionable. It is therefore important to distinguish clearly between superiority trials and equivalence trials, and to incorporate appropriate additional criteria in the design of future RCTs with active-control groups.

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.

Ratio variables in regression analysis can give rise to spurious results: illustration from two studies in periodontology.

OBJECTIVES: For over a century, statisticians have highlighted concerns about the inappropriate use of ratio variables in correlation and regression analysis. However, little attention has been paid to these concerns in medical and dental research. The use of ratio variables in correlation and regression analysis can give rise to spurious results due to inappropriate model specification and mathematical coupling, leading to serious misinterpretation of data and consequently to incorrect study conclusions. METHODS: Data were reanalysed from two recently published articles: one on the efficacy of guided tissue regeneration on root coverage; the other a randomised controlled trial comparing three surgical approaches in the treatment of periodontal infrabony defects. The reanalysis was performed to examine whether the assumptions behind the correlation/regression analyses have been seriously violated in these two studies, and to see if the interpretation of results is tenable. RESULTS: Use of ratio variables seriously violated the assumptions underpinning the statistical methods utilised in these two studies, and consequently the conclusions were substantially misleading. Recommendations made in these studies were not tenable. CONCLUSIONS: The reanalyses illustrate how the inappropriate use of ratio variables remains prevalent in dental research, leading to incorrect interpretation of the evidence. This emphasises the need for collaboration between clinicians and statisticians to avoid the risk of yielding erroneous conclusions from flawed statistical analyses.