Study Design: Case Control Study
What it is basically?
• Principal study with retrospective design.
• People who have a given condition (cases) are compared to people
who do not have the condition.
• Permits derivation of the odds ratio, a numerical statement of
probability very similar to relative risk.
• Can demonstrate risk indicators for a disease because of its
Investigate radiographically the relationship between tobacco smoking and periapical
status of teeth by using retrospective case control study design.
Smoking is not associated with an increased risk of radiographically detectable
Records of 79 controls and 79 age and sex matched cases were examined.
Periapical status was assessed by panoramic radiographs using periapical index score
as a template.
• History of smoking and diabetes, number of teeth and root-filled teeth, and the
quality of root fillings was recorded.
• Statistical analysis conducted by using Cohen kappa test, Pearson’s Chi square test,
Student’s t test, and logistic regression analysis.
• Among the 79 cases, 75% of the pts. had history of smoking, whereas among the 79
pts. in the control group, only 13% had history of smoking.
• After adjusting for covariates including age, gender, diabetes, satisfactory and
unsatisfactory root filled teeth, a strong association was observed between presence
of at least one periapical lesion visible on radiographs along with history of smoking.
MATERIALS AND METHODS
• Protocol was approved by the Ethic Committee of the Dental Faculty of Barcelona, Spain.
• Informed consent was taken from each subject taking part in the study, the consent was taken
in signed form after explaining the nature of the study.
• The participants were enlisted among the pts. presenting at the routine dental care, not
emergency care, at the dental clinic of University of Barcelona, Spain.
• Voluntary participation was encouraged among pts. who met the inclusion / exclusion criteria.
• Inclusion criteria were: pts. should be greater than 18 years of age, have at least 8 remaining
teeth in oral cavity, and agreed to radiographic examination.
• Exclusion criteria: pts. who are younger than 18 years of age, have less than 8 remaining teeth
in oral cavity, and not agreeing to radiographic examination.
• Case was defined as patient who had at least 1 radiographically detectable periapical
lesion in the mouth
• Control was defined as patient who had no radiographically detectable periapical lesion
• 300 pts. were examined.
251 (83.6%) were eligible to take part in study based on inclusion exclusion criteria
79 pts., of whom 50 men and 29 women (age range: 23-83 years) were classified as
cases after radiographic analysis (average age: 52.0 years)
Among 172 pts. left, 79 pts. were age and sex-matched with the case pts. and
constituted the control group (average age: 51.8 years)
Anamnestic and Radiographic Examination:
• Interviewer administered questionnaires were circulated for smoking history. Patients
were classified as smokers or non-smokers on basis of their answer as “yes” or “no” to
the question “Have you ever smoked?”.
• Radiographic periapical status was concluded on the basis of digital panoramic
radiographs of the jaws. Two trained radiographic technicians were employed for
taking radiographs by an orthopantograph machine.
• An observer with 12 years of experience in endodontics was employed to observe the
radiographs. Observer participated in a calibration course for PAI system prior to the
study with 100 radiographic images of teeth, some root-filled and some not.
• Periapical status was assessed by using Periapical Index (PAI). The worst score
among all roots were taken to represent PAI score index for multi-rooted teeth.
• All teeth were recorded. Root filled teeth were categorized separately if radiopaque
material was visible in root canal(s). Quality of root fillings was assessed too.
• Root filling was considered satisfactory if adaptation of filling to root canals and
length of root was adequate.
• Raw data was entered in Microsoft Excel spreadsheets.
• Analysis was done in an SPSS environment (Statistical Package for the Social Sciences, first
comprehensive data analysis software available on PCs)
• Data reported as mean ± standard deviation.
• Chi squared analysis, student’s t test were used to analyze the distribution of study factors
between cases and controls.
• Logistic regression analysis was performed to measure strength of association of smoking
with presence of radiographic periapical lesions after adjusting for covariates.
• No significant difference between cases and controls with regards to age, gender, and number of
Age: mean age ± SD
Controls: 51.8 y ± 15.3;
Cases: 52.0 y ± 15.5
Controls: 50 males, 29 females;
Cases: 50 males, 29 females.
No. of teeth: mean ± SD
Controls: 23.4 ± 6.0;
Cases: 23.0 ± 5.7
• Root filled teeth were more common in the case group.
• Average root filled teeth per subject was 2.1 in cases and 1.4 in controls.
• One or more root filled teeth were found in 45 control subjects and 58 case subjects.
• Among case subjects, 29 patients had at least 1 inadequate root filling.
• Among control subjects, 11 patients had at least 1 inadequate root filling.
• Type 2 diabetes was present in 17.7% of controls and 27.8% of cases, but difference was not
significant (p value > .05). No patient had type 1 diabetes.
• Among cases, 59 patients had history of smoking. Among controls, only 10 patients had been
• A strong association was observed between smoking and presence of 1 radiographically
detectable periapical lesion in the cases.
• Aim was to investigate possible association of smoking with radiographic periapical status by
using case control study design.
• Null hypothesis: Smoking is not associated with an increased risk of radiographically detectable
• Results reveal statistically significant association between tobacco smoking and radiographically
diagnosed periapical lesions.
• Control and case subjects were age and sex matched, along with average number of teeth in their oral
cavities. As missing as well as number of teeth present indicate oral health status, the fact that the
average of teeth was relatively close shows that the oral health statuses between controls and cases were
• PAI system was first described for periapical radiographs, but now epidemiologic studies use it for
panoramic radiographs as well.
• In logistic regression analysis model, groups, cases, and controls were age and sex matched,
including various other independent variables:
number of teeth,
root filled teeth
unsatisfactory root filling
• Covariates were put against the dependent variable (radiographic signs of apical periodontitis)
to eliminate bias in the results by potential confounders mentioned above.
• Quality of root filling shown to be a major predictor of persistent apical periodontitis associated
with RFT. Therefore could act as a confounding factor.
• 37% of cases had at least 1 unsatisfactory root filling, but only 14% of controls has at least 1
inadequate root filling.
• Thus, no. of RFT and quality of root fillings could be major confounding factors biasing the
results as well.
• No differences b/w controls and cases with history of diabetes, thus diabetes is not a confounding
• Inclusion question “Have you ever smoked?” used to classify smokers and non-smokers.
• Self reporting smoking status among adult respondents to a population based survey is
• Duration and quantity of smoking should be considered as well.
• Increased number and size of periapical lesions would be expected in smokers.
• High percentage of cases (75%) had history of smoking. Only 13% of controls were smokers.
• After multivariate regression analysis, smoking and positive periapical radiolucency still remained
statistically significant (odds ratio 32.4%, CI 95%, p: .0000)
• Periapical lesions were assessed by radiographic methods; no clinical examination was carried out.
• Radiographic evaluation is not a perfect method of assessment because inflammation can be
present in the absence of radiographic signs.
• Several orthopedic studies show that bony healing in smokers is slower than in non-smokers,
suggesting delay in healing and over-representation of disease in the smoking group in the study.
• Smoking hardly can be graded as the primary cause of root canal infection & apical periodontitis;
caries, restorative procedures and dental trauma however can be identified as causes.
• Periodontal status, immune disorders, endocrine diseases, metabolic syndrome, bone diseases,
and socio-economic status: all these factors are not considered in the exclusion criteria
• Avg. no. of teeth almost equal in cases and controls does not justify the fact that identical risk
exposure for pulpal disease, root canal infection, and apical periodontitis were present for cases
• Tobacco exacerbates bone loss in oral cavity, impairs immune responses to infection.
• PMNs, macrophages, T-cell lymphocytes, antibodies, immunoglobulins A, G, and M suppressed in
smokers, induced chronic systemic inflammatory response by increased CRP levels in serum.
• Decreased oxygen delivery, damage to pulpal circulatory system, decreased blood’s oxygen
carrying capacity, increased levels of carboxyhemoglobin, vascular dysfunction, reduced blood
flow volume, restricted nutrient supply and impeded cellular repair.
• Early tissue death in pulp cavity, surrounding structures affected. Therefore higher frequency of
radiographic periapical lesions in smokers than non-smokers.
• Therefore, results show that after adjusting for age, gender, number of teeth, endodontic status,
quality of root fillings, and diabetic status as independent variables, tobacco smoking is strongly
associated to the presence of radiographically diagnosed periapical lesions, thus nullifying the