This is the first study reporting the prevalence and risk indicators of three periodontal diseases among adults in the northern part of Jordan. The prevalence of AgP was 2.2%, of CP was 5.5% and of gingivitis was 75.8%. The comparison of the current results with previous studies is hindered by the use of different nomenclature and diagnostic criteria across studies. The prevalence of CP was lower than expected, possibly because most participants were young and educated, or because of the strict exclusion criteria. The prevalence of AgP was within the range reported in the US for whites (0.6%) and African Americans (2.8%) . A study on Jordanian adolescents reported that deep pockets were found in only 0.29% of the study sample . A higher prevalence of AgP (6.0%) has been recorded in Iraq  and in Brazil (5.5%), but a lower prevalence (1.7%) was reported among Norwegian schoolchildren  than that obtained in the present study.
Most participants were 20-29 years old, probably reflecting the large proportion of young individuals in the Jordanian population or the possibility that most escorts were young. The lowest proportion of participants was ≥ 50 years of age, probably because many older individuals were patients (not escorts) and were not recruited. All AgP subjects were under 30 years, which is not surprising as it is universally accepted that AgP starts early in life in susceptible individuals. Many authors believe that age is not a risk determinant, but the life time disease accumulation . In the multivariate analysis, for each one year increase in age the odds of having periodontitis increased by 20% and most subjects with CP were above 40 years of age, in agreement with other studies [15, 17].
Our results demonstrated that most gingivitis patients were males, which may be attributed to poor attitude towards health and smoking. As mentioned above, AgP and CP were summed together into one "periodontitis group" when studying risk indicators (except age), because the number of AgP patients was low. The male to female ratio of periodontitis (1.6:1) is in agreement with other studies [18, 19].
With regard to AgP, studies on Caucasians and Hispanics have demonstrated a greater female preponderance, whereas studies involving Blacks demonstrated a greater prevalence in males. Albandar et al (2000)  reported a higher prevalence of AgP among females than males in Saudi Arabia with a ratio of 1.9:1. In a study in southern Brazil, AgP was distributed equally between males and females . The reasons for these gender differences may be genetic factors, attitude toward oral health and dental-visit behavior .
The prevalence of gingivitis and periodontitis was higher in the low income than in the high income category, probably due to difficulty in affording dental treatment and oral hygiene aids. Difference in the prevalence of periodontitis according to SES was observed in other studies . However, some studies have shown a weak association between SES and periodontitis after adjustment for oral hygiene and smoking [16, 24].
In the present study, a low level of education was significantly associated with increased prevalence of periodontitis and the odds of having periodontitis increased by 5.5 times in subjects with ≤ 12 years of education. A higher prevalence of periodontitis among subjects with low education has been reported in Thailand . In the USA, Borrell et al (2006)  reported that subjects with < high school education were 3 times more likely to have periodontitis than subjects with a higher level of education.
In the present study, subjects living in rural areas had a higher prevalence of gingivitis and periodontitis than subjects living in urban areas. Rural areas often have lower socioeconomic conditions and medical facilities than urban areas. Several studies have documented an association between area-based socioeconomic indicators and health outcomes . Borrell et al (2006), using data of the NHANES III, reported an association between periodontitis and neighborhood socioeconomic conditions.
A significantly higher prevalence of periodontitis was recorded among obese subjects than among normal weight subjects in the present study, which coincides with the results of the NHANES III in the USA . Gingivitis was most prevalent among overweight subjects, although it was high in all BMI categories, with no clear pattern of association. A dose-dependent association between BMI and periodontitis was reported in Japan  after adjusting for age, sex, smoking and frequency of toothbrushing. Other studies  reported no significant difference in the prevalence of periodontitis between obese, overweight and normal subjects in males. Imbalance in the host immunity due to increased blood lipid and glucose levels in obese subjects may play a role in this association .
A higher prevalence of gingivitis and periodontitis was noticed among subjects who reported emergency dental visits, compared to subjects reporting regular dental visits, which is in agreement with reports in Brazil . The lowest prevalence of gingivitis and periodontitis were observed among subjects reporting regular tooth brushing, whereas subjects reporting no tooth brushing had 25 times higher odds of having periodontitis. The effect of maintaining good oral hygiene on the periodontium is well documented [17, 31]. In Accordance with this, our study demonstrated that most individuals with low PI (< 1) were periodontally healthy, whereas most people with gingivitis, CP and AgP had a high PI.
In this study, gingivitis was observed mostly in current smokers, probably indicating the strong and rapid effect of smoking on gingival health. The prevalence of periodontitis was also higher among smokers, in agreement with other studies . Past smokers had a higher prevalence of periodontitis than current smokers; probably because the majority of past smokers were older in age and usually reported a long duration of smoking. Subjects who reported family history of periodontal disease had 5 times higher odds of having periodontitis than subjects with no family history. Positive family history of periodontal diseases has been reported previously [33, 34].
This study has demonstrated that when challenged with similar amounts of plaque, people with AgP suffer a greater amount of attachment loss, compared to subjects with CP, indicating a higher susceptibility of the AgP group to periodontal destruction.
The greatest attachment loss and probing depth were present among older subjects (≥ 50 years) and that the extent of periodontal destruction increased with increasing age, within all categories of disease severity (i.e. CAL categories), indicating cumulative periodontal destruction in susceptible individuals . When addressing the different severities of periodontal destruction an interesting finding was observed; as from CAL ≥ 5 mm the extent of disease decreased, indicating that more sites were affected by moderate periodontitis than by severe periodontitis; teeth affected by severe periodontitis may have been lost.
Limitations to the work
1. The main limitation of this study was unavailability of a portable x-ray unit to the researchers. Numerous commercially available units exist, but almost all of them suffer serious safety shortages such as back scatter of the x-rays. They were evaluated by a specialist radiologist and the only "safe" portable x-ray machine could not be obtained by the researchers, despite repetitive attempts. This dictated the choice of places where subjects could be recruited; i.e. clinics and centers where a dental x-ray unit was present. In future studies, a full portable examination unit should be obtained.
2. Many of the variables investigated depended on patients' reports such as oral hygiene habits, smoking and other. Subjects' reports may not be true or accurate sometimes.
Strength of the Study
The strength of the present study may be summarized in several points
1. The study sample was randomly selected from four centers in North Jordan; a large population in the Northern part of Jordan attend these centers.
2. Full clinical periodontal examination was performed for each subject.
3. Diagnosis of CP and AgP was based on, and strictly in accordance with, the criteria set by the AAP in 1999.
4. Diagnosis of periodontitis was confirmed radiographically using bitewing/periapical radiographs.