[First and second order generalized estimating equations and it's application in analyzing longitudinal microleakage data]

Longitudinal data are frequently obtained in medical studies. When the main aim of a study is marginal modeling of the mean and the correlation structure is considered as a nuisance parameter, the first- order generalized estimating equations [GEE1] is usually an appropriate option. However, when the modeling of correlation structure is considered the aim of a study, the second- order generalized estimating equations [GEE2] may be the first choice for analyzing the available data. The aim of the study was to evaluate application of first- and second-order generalized estimating equations to analyze longitudinal microleakage data. In this study, GEE1 and GEE2 methods were used to analyze data obtained from a study of microleakage in two root- end filling materials [CEM and MTA] in two different thicknesses and two diameters at three different times of measurement [one day, one week and one month after treatment]. The obtained results from these statistical approaches were compared in continuous and binary [presence of absence] microleakage data. The results from the GEE1 and GEE2 methods showed that time of measurement, material type, diameter and thickness of filling material had significant effects on [continuous] microleakage rate. In addition, in binary microleakage data, these methods revealed that only time and material type were the significant factors. The correlations between measurements were not significant in continuous data, while they were significant in binary response microleakage data. Since the correlations between pairs of measurements were not significant in continuous microleakage data and the obtained estimates were similar in both GEE1 and GEE2 methods, so the simpler GEE1 method seems to be adequate for these data. In contrast, in binary microleakage data, significant correlations were found between measurements. Therefore, in this case the GEE2 methodology may be used to estimate the correlation structure more efficiently

[Relationships between smoking and IL-1 beta concentrations in chronic periodontal patients]

Cigarette smoking is a significant risk factor in pathogenesis and progression of periodontal diseases. Smoking could interfere with pro-inflammatory cytokines in inflammatory process. IL-1 beta is a main inflammatory cytokine in gingival crevicular fluid [GCF] which contributes in periodontitis. In fact it is a key molecule in pathogenesis of periodontitis. This study aimed to investigate the correlation between cigarette smoking and concentration of cytokine interleukin [IL]-1 beta in GCF of patients with moderate-to-sever chronic periodontitis. Sixty subjects were entered into this analytical case-control study, divided equally into smokers and non smokers. Two groups were matched in clinical parameters, age and sex. GCF samples were collected in one diseased and one healthy site from each subject. The IL-1 beta concentration in all 120 samples was determined by ELISA kits, specific for IL-1 beta. The observed data were analysed with SPSS 13 software using T, Paired T, Chi-square and Mann-whitney tests. Mean concentration of GCF IL-1 beta in healthy sites of the smokers was significantly more than non smokers [p<0.01]. But in diseased sites no significant differences were shown between the two groups. The differences between concentration of IL-1 beta in smokers and nonsmokers were not significant. Although no significant differences were found in concentration of IL-1 beta between all smokers and all non smokers, there were significant differences between two groups in healthy sites, which require more investigations

[Validity of teeth width measurements on conventional versus 3D models]

For proper diagnosis of orthodontic problems of a patient, different measurements and analysis should be performed on dental cast. In recent years, due to introduction of paperless offices, 3D reconstruction methods and softwares are available in order to build virtual dental casts and measurements on them. The purpose of the present study was to compare the validity of teeth width measurements on conventional versus 3D models. In this diagnosis study, twenty set-ups of upper and lower casts using artificial teeth corresponding to various malocclusions were created. Impressions were taken of them providing 20 plaster models. The plaster models were scanned by laser surface scanner and the crown widths measured by its software. The gold standard was the teeth width measured by caliper before setting up the teeth. The mesiodistal crown width was also measured on casts as conventional method. The crown width was compared between the three methods by F test, ICC and Dahlberg formula. Coefficient of validity between measurements by 3D scanning and gold standard in overall teeth measurements [premolar to premolar] was 0.914. The mean difference between laser scanning method and gold standard was 1.7 mm and between conventional method and gold was 0.34 mm. In most of the measurements, the difference between mesiodistal crown width belonged to canines. The accuracy of laser surface scanning system was clinically acceptable and in the range of similar studies, but these is not enough for research purposes and it should be improved. In reference to advantages of computerized methods in near future, these methods will be the clinical standard for orthodontic diagnosis

[Fluoride retention in saliva following toothbrushing with two Iranian fluoride dentifrices, Nasim and Crend in comparison with sample dentifrices]

The presence of fluoride in oral fluids, is necessary for prevention of dental caries. The aim of this study was to determine the extent of fluoride retention in saliva after brushing with two Iranian fluoridated toothpastes, Nasim and Crend in comparison with MacLeans and Crest. Ten adults used a nonfluoride dentifrice for 10 days before the experiment and between different stages of the experiment. The dentifrices included Nasim and MacLeans [with sodium monofluorophosphate] and Crend and Crest [with sodium fluoride]. In each procedure, participants brushed their teeth with 1.5 gr of the dentifrices under trial for 1 minute. Saliva samples were collected at baseline, 1, 30, 60; 120 minutes after tooth brushing and fluoride ion were measured by potentiometry technique. The data were analyzed by Repeated Measurements, Paired t, One Way ANOVA and Tukey tests. All dentifrices under this trial, had the highest fluoride concentration in saliva 1 minute after brushing [P<0.005] and after that time fluoride concentration decreased gradually. Crest toothpaste in comparison with Crend had higher fluoride retention in the 60 and 120 minutes [60 minutes: [0.9824 +/- 0.0988, 0.5173 +/- 0.770] [P<0.005]; 120 minutes: [0.8103 +/- 0.0615, 0.3651 +/- 0.0580] [P<0.008]]. The Crest dentifrice showed the most fluoride retention in saliva, MacLeans and Nasim dentifrices had similar values of fluoride retention while the Crend dentifrice showed the least values of fluoride retention

Correlation between periodontal diseases and mouth breathing

Some studies have reported direct relationship between mouth breathing and increased susceptibility of patients to develop periodontal diseases. The present study was designed to evaluate the correlation between periodontal diseases and mouth breathing in Iranian population. This historical cohort study was conducted with 90 participants aged 20-35 years-old, who were referred to Isfahan Dental School and few other private dental clinics in the city of Isfahan in the year 2003. All participants had to be free of relevant systemic conditions. The cases were defined as patients with mouth breathing, having dome-shaped palate and open mouth [lips] when in rest position. Oral examination was conducted using 3 diagnostic criteria. Forty-five patients who were confirmed by all three criteria were included in the study as cases. The control group was composed of subjects who had normal breathing from their nose. The gingival index was determined for posterior and anterior regions of all participants. The statistical analysis was conducted and Mann- Whitney U tests was used in order to determine group differences. The gingival indices in the anterior region of cases were determined. The number of individual with scores 1, 2 and 3 were five [11.1%], 36 [80%] and four [8.9%] respectively. The scores in control group for five subjects [11.1%] was [0] or had no gingival condition, 32 [71.1%] subjects had score one and eight [17.8%] had score 2. The group differences were statistically significant [P < 0.001]. No significant difference was detected in posterior gingival indices [P > 0.05]. Mouth breathing can be a contributing factor in increasing the risk of periodontal diseases

Modified index of orthodontic treatment needs [IOTN] assessment by senior dental students

Rater's reliability is an important issue in index calculation. The purpose of this study was to evaluate the intra-examiner agreement in identification of orthodontic treatment needs using modified IOTN. In this analytical cross-section study, six senior dental students identified IOTN on 42 dental casts by means of a standard DHC ruler with a two-week time lag. The kappa and association models were used to analyze the data. The kappa statistics showed intra-rater agreements between 0.54 and 0.77 [ +/- 0.65], which can be considered as [good]. About 33% of the students had problems in distinguishing the first and second levels of the index, while there were fewer problems in distinguishing between the second and third levels. The category identification with most problems was the distinction between the first and second levels [0.48], and the one with the least problem was that of the second and third levels [0.99]. The distinction of the first and second levels in modified IOTN is hard for the examiners. Therefore, this issue should be considered in calibration training programs when using this index in screening, survey or epidemiological evaluations