Statistical management of periodontal data

Association between bone loss in periodontal disease and polymorphism of N-acetyltransferase (NAT2)

BACKGROUND

The individual susceptibility to periodontal disease is probably the result of an interaction of multiple genetic and environmental influences. Polymorphism of the N-acetyltransferase (NAT 2) modifies the individual susceptibility to toxicity from certain therapeutic drugs or heterocyclic amines including substances from cigarette smoke. Subjects are to be classified as 'slow' or 'rapid' acetylators according to how fast their bodies metabolise such xenobiotics. Differences in their ability to detoxify these substances may contribute to an increased risk for periodontitis in subjects exposed to cigarette smoke or other xenobiotics.

OBJECTIVE

The purpose of this study was to assess whether the NAT2 genotype is a risk factor for periodontal disease in Caucasian patients suffering from adult periodontitis.

MATERIAL AND METHODS

154 Caucasian subjects were assigned to one of the 3 groups: no, moderate, and severe periodontal disease based on bone and attachment loss. In all subjects, genotyping for mutations on the N-acetyltransferase (NAT2) gene was performed by means of PCR and RFLP analysis.

RESULTS

Comparison of frequency distribution of NAT2 acetylation types between the most diseased group and not or moderately affected subjects showed a tendency to over-representation of slow acetylators with severe disease. When using bone loss as measure of periodontitis, this over-representation shows a significant association with the disease (odds ratio=2.13, p=0.025). In the logistic regression analysis, adjusted for age and smoking, NAT2 slow phenotype was significantly associated with the severity of bone loss, the odds ratio being 2.09 (95% C.I. 1.02-4.26, p=0.043). In a case-control analysis (controlled for smoking, gender and age) mean bone loss showed a significant difference between the 2 NAT2-type groups (Mann-Whitney test p=0.041).

CONCLUSION

The data suggest that the slow acetylator phenotype may be associated with a higher risk of periodontitis, especially in smokers. Possible explanations regarding the mechanism are discussed; however, such attempts are highly speculative at this time.

Important differences in clinical data from third, second, and first generation periodontal probes

This study compared relative attachment levels (RAL) and probable crevice depths (PCD) from 6 periodontal probes (1 third, 4 second, and 1 first generation). A single clinician recorded RAL and PCD in 6 patients with chronic adult periodontitis (mean age 48.2 years) during two visits (interval: 1 week) using a Latin square examination order. Replicate measurements were recorded at the 4 interproximal sites of the Ramford index teeth to examine intra-probe differences. Additional single measurements were recorded at similar sites of units 11, 26, 31 and 46 to investigate interprobe differences. Intra-probe RAL and PCD reproducibility was < or = 1 mm at > 94% of the sites. All intra-probe Pearson correlation coefficients were > 0.85 (P = 0.00). Inter-probe RAL and PCD agreement was < or = 1 mm at > 49% of the sites for RAL and > 61% of the sites for PCD. All inter-probe Pearson correlation coefficients were > 0.42 (P = 0.00) for RAL and > 0.49 (P = 0.00) for PCD. Analyses of variance showed significant differences in RAL and PCD between the first generation probe and the second generation probes (P < 0.005); in RAL between the third generation probe and the first and second generation probes (P = 0.0354); and in PCD between the third generation probe and the first and second generation probes (P = 0.0475). Inter-probe differences were clinically significant in the recorded percentages of pockets > or = 4 mm and > or = 6 mm. Significant inter-probe differences were found in RAL and PCD which have clinical importance in data interpretation and comparison.

Design principles and statistical considerations in periodontal clinical trials

Although clinical trials are a small subset of conducted biomedical research, they have become powerful investigational tools for the evaluation and approval of new treatments by clinician groups and regulatory agencies like the US Food and Drug Administration. To impact the delivery of care, trials in general must meet three criteria: clarity, comparability, and generalizability. Accordingly, trials can offer meaningful data if they have procedures which are well defined and subjects who represent a reasonably homogeneous population. The evaluation of periodontitis interventions presents several challenges due to the disease's heterogeneity and its irregular, episodic pattern; nevertheless, the intent of these novel interventions is to prevent, diagnose, inhibit, or reverse periodontal disease progression. Careful consideration of the trial's objectives should dictate clinical endpoints (primary and surrogate), comparison groups (placebo, standard therapy, test therapy), and equivalence versus superiority as the basis for conclusions. Several design elements such as control population specification, randomization, masking, sample size calculation, and standardization of procedures for patient care and assessment can decrease potential bias and variability. In both parallel and paired (split-mouth) design trials, multiplicities of endpoints, treatments, and subgroups require strategies which address the broader scope of chance findings without excessive loss of study power. Also, the longitudinal assessment of multiple periodontal sites within patients produces correlated data structures for which analytic methods need to account for the appropriate sampling unit. With these design and analytic elements, clinical trials can provide important evidence to investigators, patients, and governmental agencies for the introduction of novel interventions in periodontal practice.

Periodontal status among male industrial workers in southern Finland with or without access to subsidized dental care

The association between subsidized dental care and periodontal status was studied in male industrial workers in southern Finland in 1994. Clinical examinations and a multiple-choice questionnaire were completed for 325 workers (age, 38-65 years) with access to subsidized dental care and 174 controls without access. The CPITN scores based on full-mouth recordings were analyzed, using both the individual and sextant as units of analysis. Overall, 6% of the subsidized group and 2% of the control group had no periodontal treatment need (p < 0.05). Deep pockets > or = 6 mm were found in 5% of the subsidized workers and 11% of the controls (p < 0.05). In the logistic regression analyses the probability of calculus was negatively associated with access to subsidized dental care. Smoking was the strongest independent factor affecting periodontal status. Our findings show a positive relationship between access to subsidized dental care and periodontal status.

Risk factors for periodontal diseases in Ilala, Tanzania

The purpose of this study was to evaluate associations between periodontal diseases and the common risk factors in Ilala, Tanzania. To determine behavioural and socioeconomic background, a total of 1764 subjects (827 males and 937 females) aged 3-84 years were randomly selected and interviewed. The subjects were examined clinically for the presence of plaque, calculus, gingival inflammation, periodontal probing depths and gingival recessions. Logistic regression analyses showed that the risk factors for gingivitis were male sex, presence of plaque or calculus and use of local "mswaki", the risk factors for periodontal pockets were age of 35 years or more, presence of plaque, and rural residence. The risk factors for gingival recession were identified as age of 35 years or more, male sex, lower educational status, presence of plaque and gingival inflammation. The most significant risk factors to have periodontal diseases in this study population were age, sex, education, rural residence, plaque and calculus.