According to the PSI evaluation, 17 subjects (15.2%) were diagnosed as having "no periodontitis" while 95 subjects (84.8%) were found to have "periodontitis". The high percentage of subjects with "periodontitis" seems to be due to the strict diagnosis. In terms of initial diagnostics, a strict attribution of "no periodontitis" for the PSR®/PSI scores 0, 1 and 2 and "periodontitis" for PSR®/PSI scores of 3 and 4 seems reasonable. However, in relation to the extent of treatment, there is a considerable difference depending on whether one or more sites of a tooth are assigned a score of 3 or 4.
In 70 (62.5%) of the 112 subjects, the radiographic diagnosis established "no periodontitis", and 42 subjects (37.5%) were diagnosed as having "periodontitis". Just as in daily practice, in the present study, the radiographic findings of the DPTs were made by measuring the distance between the cemento-enamel junction (CEJ) and the alveolar crest (AC). As the assessment of DPTs by different examiners could result in significant deviations, this evaluation was performed by two dentists using identical criteria for assessment, in order to achieve a high degree of objectivity .
The results demonstrate that both methods differ significantly from one another. In 59 subjects (52.7%), congruence was found in relation to the diagnoses "no periodontitis" and "periodontitis", while in 53 subjects (47.3%) this was not the case. Accordingly, three groups were obtained: congruence "no periodontitis", congruence "periodontitis", and "no congruence". In contrast to Walsh et al.  , who performed a similar study, the combination clinical diagnosis: "no periodontitis" and radiographic diagnosis: "periodontitis" was not found in the present study. Walsh et al.  examined the correlation between bone loss on the DPT and the clinical finding using CPITN. The results revealed that bone loss on the DPT was closely related to the CPITN scores . However, the calculated loss of bone structure was higher on the DPT than with the corresponding CPITN score. The authors therefore recommended the use of DPT for periodontal diagnosis . The results of Walsh et al.  were confirmed by our study only in relation to the group congruence "no periodontitis". In this group, the highest PSR®/PSI score was 2. In the study of Walsh et al.  only posterior sextants were examined and diagnosed, respectively. Moreover, the assessment of the distance between the cemento-enamel junction (CEJ) and the alveolar crest (AC) was evaluated with special reference splints. Afterwards, the distance CEJ-CA was statistically allocated in correlation to the root length and the magnification factor of the DPT . The results showed that the bone loss on the DPT was closely related to the CPITN scores . However, the calculated loss of bone structure was higher on the DPT than the respective CPITN score. This led to the conclusion that referring to the CPITN scores 0, 1, and 2, no difference in the distance CEJ-CA exists and thus no bone loss can be detected in the x-ray. The authors therefore recommend the DPT for periodontal diagnosis . However, accommodating daily routine in our study the radiographic finding was performed only by evaluating the distance between the cemento-enamel junction and the alveolar crest without any aids. This subjective assessment might be considered a weak point in diagnosis based on the radiographic finding. Moreover, it must be considered that x-rays only provide information on osseous structures/bone loss while the PSI reflects the current clinical situation [11, 25]. According to Lange,  x-rays are only of limited value in the detection of early periodontal bone loss. In DPTs, an initial loss of proximal bone is often either not detected or is underestimated, and even moderate lesions in the facial and/or oral direction are often not identified [11, 13, 14, 26]. However, in patients with advanced bone loss, the DPT yields reliable results [11, 16, 17].
All 42 subjects with the radiographic diagnosis "periodontitis" were identified as having periodontal disease using the PSR®/PSI, as well (congruence "periodontitis"). In this group, the majority of subjects had PSR®/PSI scores of 3 or 4, mainly in the posterior sextants. This result supports the findings of studies indicating that progressive bone loss can be reliably diagnosed using DPT [11, 16, 17]. In the "no congruence" group, all subjects were clinically diagnosed as having "periodontitis" whereas the radiographic evaluation revealed "no periodontitis". Walsh et al.  reported similar findings. In this group, a PSR®/PSI score of 3, occasionally a score of 4, was found exclusively in the posterior sextants. In the anterior region of the lower jaw, initial signs of inflammation, i.e. gingival bleeding on probing, calculus and gingival swelling with pseudo-pockets, were mostly found. These symptoms are signs of poor oral hygiene: the group "no congruence" had a significantly lower level of oral hygiene compared to the group congruence "no periodontitis". The discrepancies between the two methods of examination derive from different approaches. The PSR®/PSI differentiates between gingival inflammation and periodontal destruction. Therefore, the PSR®/PSI indicates even early symptoms of periodontal disease. According to the PSR®/PSI only a few participants were diagnosed having "no periodontitis". Since gingival inflammation is often accompanied with gingival swelling, i.e. pseudo-pockets; these findings PSR®/PSI (score 3 and 4) may only pretend "periodontitis". In this case gingivitis therapy, i.e prophylaxsis appointments (professional tooth cleaning) simply can reduce the PSR®/PSI scores.
According to Goodson et al.,  the PSR®/PSI shows the clinical process of initial periodontal disease that will sometime later result in bone loss which can be detected radiographically. Our results are in accordance with Khocht et al.;  they also compared the periodontal situation with radiographs (DPT) and PSR®/PSI and found no correlation between the two methods. This indicates that radiographs (DPT) taken in daily dental practice are not highly reflective of the real periodontal situation . In contrast to this, the PSR®/PSI seem to be a useful screening tool that will enhance identification of patients even with initial periodontal disease . For a specified diagnosis, the characterization, the treatment and the control of advanced periodontitis, x-rays in combination with detailed clinical records are essential.
Limitation of the study: It has to be considered that x-rays cannot diagnose "periodontitis" or periodontal disease. All a radiograph can do is demonstrating the consequences of periodontitis, i.e. bone loss, and will not provide information about disease activity. This point should be taken into consideration regarding our definition of the radiographic diagnoses: "no periodontitis" and "periodontitis", respectively.
The possible gap between radiography and clinical examination (at most 12 month) may be a weakness of the study, this concerned overall only three participants. However, it is rather unlikely that radiographic features may have changed in the mean time. A change could only be related to the clinical periodontal situation.