According to the research conducted by Silverstein et al., (2000), the pressure used to place the probe tip at the base of the periodontal sulcus is approximately 50 N/cm2 and at the base of the junction epithelium is 200 N/cm2. A tip diameter of 0.6 mm is needed to reach the base of the sulcus. Clinical inflammation does not reflect the severity of histological inflammation, and the recordings may not illustrate probing depth. Therefore, probing depth does not identify anatomical locations at the base of the sulcus. Probe tips must have a diameter of 0.6 mm and a 0.20 gram force (50 N/cm2) to gain a pressure which demonstrates estimated probing depth. This pressure is useful for the measurement of the reduction of clinical probing depth, which includes the formation of a long junctional epithelium as a result of treatment. but, different forces or diameter tips are essential for the measurement of healthy or inflamed histological periodontal probing depths.

A research was done to establish whether probing force had an influence on the amount of clinical attachment-gain assessed after treatment by scaling and root planing. A probing device was constructed which permitted concurrent monitoring of probing force and probe penetration and which standardized the insertion pathway for recurring measurements. In 10 periodontal patients, 2 deep pockets were selected then measured before and after periodontal treatment by scaling and root-planing. Depth-force plots were compared by superimposition. Depth values were determined at 5 different force levels (0.25, 0.50, 0.75, 1.00 and 1.25 N) on every plot and changes of clinical attachment levels were calculated. A major relationship was seen between probing force and attachment level.

The values obtained with 0.25 N. were extensively different from the values obtained with higher forces (p < 0.001). Minor, but non-significant differences were noted in the amount of attachment-gain obtained at the 5 force levels. At a probing force level of 0.25 N, there was 0.80mm mean attachment gain. With 0.50 N, there was a gain of 0.70mm; with 0.75 N. The gain amounted to 0.67 mm in mean. At 1.00 N. And at 1.25 N, a gain of 0.66 mm was recorded. (Fowler et al., 1982)

The present research to determine the threshold pressure value to be applied in provoking bleeding on probing in clinically healthy gingival units. Regression study revealed an almost linear association and a high connection coefficient between bleeding on probing and probing force. The result demonstrated that the bleeding on probing test using uncontrolled forces may result in a part of false positive readings and a strong possibility exists for the traumatizing of clinically healthy gingival tissues if a probing force exceeding 0.25N is applied (Lang et al., 1990)

Bleeding on probing and gingival index is clinically used to characterize the extent of gingival inflammation. However, it is not clear to what level these parameters correlate to each other and to probing pocket depth. This study was to evaluate the relationship between bleeding on probing and gastrointestinal bleeding (scores of 2 and 3), as well as the relationship of these variables to probing depth, in a group of patients presenting with naturally-occurring gingivitis. Based on screening examinations of 125 patients with at least 20 teeth, at most 4 sites with probing depth over 6mm a bleeding on probing frequency of 30% or more, and no systemic condition that would influence the inflammatory response, were selected. Two weeks after screening patients were examined at 6 sites per tooth for plaque index, gastrointestinal bleeding, probing depth and bleeding on probing.

A standardized pressure sensitive probe (Florida Probe) with 20g probing force was used for bleeding on probing and probing depth measurements. Means of 40.9% (S.E. = 1.36) bleeding on probing sites and 35.3% (S.E. = 1.81) gastrointestinal bleeding sites per patient were found. A total of 20,008 sites ranging in probing depth up to 5.9mm were evaluated, though, most sites (19,723, 98.6%) presented with < 4 mm probing depth. When sites were evaluated, bleeding on probing confirmed a positive correlation with probing depth, whereas gastrointestinal bleeding correlated with probing depth. For sites characterized by the absence of bleeding on probing and gastrointestinal bleeding (scores 0 and 1), the highest percentage of union between the 2 indices (77.7%) was found in shallow sites (0.1-2 mm) index (Chaves, 1993).

Another study showed that the bleeding on probing test using uncontrolled forces may result in an amount of false positive readings when used as a parameter for inflammation. A strong likelihood exists for the traumatizing of clinically healthy gingival tissues if a probing force exceeding 0.25 N. is applied. The aim was to evaluate the relationship between probing pressures...

10 patients enrolled in a periodontal maintenance program after treatment of moderate to advanced chronic inflammatory periodontal disease were used. They were chosen on the basis of a record of excellent oral hygiene practices for at least 2-6 years and nearly complete absence of clinical inflammation after successful periodontal therapy.
Probing force of 0.125, 0.25, 0.375 and 0.5 N. was applied in the 4 jaw quadrants at 2 different occasions with an interval of 10 days, then bleeding on probing was assessed. Oral hygiene and gingival conditions were determined using the criteria of the plaque and gingival index systems. All patients showed major increases in mean bleeding on probing percentage with increasing probing force applied (2.5%-7.9%). Regression analysis discovered an almost linear relationship and a major correlation coefficient between bleeding on probing and probing force. Almost identical slope inclinations were found when the 6 patients with the lowest mean bleeding on probing at 0.25 N. were compared with the regression analysis of the whole group (Karayiannis, 1992).

A research was done to assess the bleeding on probing tendency and periodontal probe penetration when various probing forces were applied at implant sites in patients with a high standard of oral hygiene with well-maintained peri-implant tissues. 17 healthy patients with superb oral hygiene in a maintenance program treatment for periodontitis were recruited. Their missing teeth had been replaced using oral implants. The bleeding on probing and probing depth was assessed at the mid-buccal, mid-oral, mesial and distal aspects of the buccal surfaces of every implant. Contra-lateral teeth were designated and assessed for bleeding on probing and probing depth in the same locations and at the same observation visits.

At every visit, implants and contra-lateral teeth were at random assigned to one of the standardized probing forces (0.15 or 0.25 N). The second probing force was applied at the repetition of the examination after 7 days. The results showed that increasing the probing pressure by 0.1 N. from 0.15 N. brings about an increase of bleeding on probing percentage by 13.7% for implants and 6.6% contra-lateral teeth. There was a significant difference of the mean bleeding on probing percentage at implant and tooth sites when a probing pressure of 0.25 N. was applied. A considerably deeper mean probing depth at implant sites compared with tooth sites was found regardless of the probing pressure applied. The results of the study showed that 0.15 N. might characterize the threshold pressure to be applied to avoid false positive bleeding on probing readings around oral implants. Therefore, probing around implants confirmed a higher sensitivity compared with probing around teeth. (Gerber et al., 2009).

1.7 Histopathological alteration in the periodontal tissues

A study about histopathological alteration in the periodontal tissues was designed and 22 patients were enrolled. Out of 22 patients, gingival tissue biopsies samples were obtained from active sites of 10 and 12 periodontal-healthy and periodontal disease, probing depths >5mm patients, respectively. The groups was again divided into 25 -- 50 and >50 years age subgroups.

The result showed a significant decrease in the appearance of Tumors Necrosis Factor Receptor-Associated Death Domain (TRADD). This was observed in 25 -- 50 years of periodontal disease group compared to the periodontal healthy group. BCL2-associated X protein expression in the periodontal disease group was considerably decreased in 25 -- 50 years age group but increased in the >50 years age group compared to periodontal healthy age groups. Periodontal disease patients of both 25 -- 50 years and >50 years age increased in the expression of Cytochrome C. And Caspase-3 compared to the respective periodontal healthy groups. The periodontal disease patients showed a stronger correlation with age in the expression of Tumors Necrosis Factor Receptor-Associated Death Domain and BCL2-associated X protein compared to the periodontal healthy groups. (Archives of Oral Biology)

Non-surgical periodontal therapy results in a great decrease of pocket probing depths and bleeding on probing, and attachment gain. When combined with periodontal maintenance a long-term stability of periodontal conditions, which shows a decreased incidence of extra attachment loss and reduction in bleeding on probing is possible and has been evidenced even in residual pockets with probing depths of greater than 7 mm. This data shows that significant changes in the immune/inflammatory response take place after treatment. Though, it is not clear, whether the clinical signs following periodontal therapy are related with an expression profile…