Periodontal defects of the furcation are characterized by several inherent anatomic factors that can make successful periodontal therapy difficult and results unpredictable. The severity and rate of occurrence of periodontal disease are directly related to the location of the furcation relative to the cementa-enamel junction and anatomical form of the root by limiting the accessibility and effectiveness of the periodontal instrumentation. This study investigated the reliability and accuracy of panoramic radiograph diagnoses of the periodontal state of mandibular molars, particularly regarding the diagnosis of furcation area periodontal defects, treatment planning, and prognosis prediction. This study examined a total of 110 teeth belonging to 33 subjects (19 male, 14 female) presenting with incipient to moderate periodontitis 4-7mmpocket depth. The alveolar bone level, length and width of the root trunk, and root separation angle were measured using the panoramic radiograph and compared to the results taken directly by retracting a full-thickness flap. The results of the study are as follows: 1. Data regarding the alveolar bone level of the mandibular first molar showed that the directly taken surgical measurements resulted in $5.1{pm}0.9mm$ that was slightly deeper than the corresponding panoramic measurement resulted in $4.8{pm}0.8mm$, but these differences were statistically insignificant (p>0.05). 2. The data of the directly taken surgical measurement of the mandibular second molar $(5.1{pm}1.1mm)$ was slightly deeper than the corresponding panoramic measurement $(4.7{pm}1.2mm)$, but these differences were statistically insignificant (p>0.05). 3. The measured values of the length and width of the mandibular first molar root trunks were determined to be $4.1{pm}0.6mm$ and $7.3{pm}0.9mm$, respectively, while the values of the mandibular second molar root trunks were determined to be $4.6{pm}1.3mm$ and $7.6{pm}0.9mm$ respectively. The differences between these values were found to be statistically significant (p<0.01). 4. The measured values of the root separation angle showed that the mandibular first molars averaged $34.5{pm}4.4^{circ}$, while the mandibular second molars averaged $23.0{pm}10.0^{circ}$. The differences between these values were found to be statistically significant (p<0.01).