## 4 Discussion  
This systematic review aims to assess the clinical and radiological parameter (PD reduction, CAL gain, recession coverage, bone fill), which changed from baseline after using guided tissue regenerative therapy (resorbable versus non-resorbable membranes) in the treatment of intrabony defects in chronic periodontitis patients solely relying on RCTs. This systematic review included eight randomized controlled trials, among which six studies were eligible for a meta-analysis. There was no statistically significant difference between the resorbable group and non-resorbable group with respect to CAL gain and pocket probing depth; however, a significant result was seen in gingival recession (at a 6-month interval) and intrabony defect depth (at all intervals and at a 6-month interval), favoring the resorbable membrane group. A subgroup analysis was carried out assessing the PPD at all intervals based on the study design. Astonishingly, it was found that the studies with split mouth design showed statistically significant effects, favoring the non-resorbable membrane. This could be due to the fact that split mouth RCTs are robust, and the effect could be exhibited in a similar oral environment without much bias in inter-patient variability and patient compliance. The main advantage of a resorbable barrier membrane is that it does not require second surgical exposure for the removal of the membrane. Moreover, the tendency for membrane exposure and bacterial contamination are the problems commonly associated with a non-biodegradable membrane which might affect the defect fill. Among the included articles, two studies showed favorable results in terms of assessing gingival recession at a six-month interval [27; 31]. The reason could be due to the need for removing the non-resorbable membrane, which will require a second surgical intervention. This could lead to progressive attachment loss and ultimately result in less recession coverage. Four included studies [27; 28; 29; 32] showed significant results favoring the resorbable membrane in terms of intra-bony defect depth at all intervals (6-12 months) and at 12-month intervals [29; 32]. Few studies have presented histological evidence of regeneration of bone through the use of lactic acid membrane and bovine bone matrix membrane respectively [33; 34]. Moreover, one study did use an advanced imaging technique (CBCT) to estimate the quality and quantity of the newly formed bone via bone density and Hounsfield units, and these values suggested that collagen membranes were effective [35]. On the contrary, few studies have suggested that there is no statistically significant difference between collagen-covered defects and uncovered defects in terms of bone regeneration [36; 37]. The results of this present study are in accordance with another study, which compared a non-resorbable GTR membrane with a conventional flap, in which there was no statistically significant difference in the test and control groups in terms of improvement of CAL and PPD [38]. When a resorbable polyglycolide membrane (RESOLUTXT) was used in aggressive periodontitis patients, an average \(\Delta\)CAL of 3.4 [2.3] mm and an \(\Delta\)PPD of 4.0 [2.1] mm at 12 months post-operatively were reported [39]. In contrast, a follow-up study carried out by [PERSON] et al. resulted in significant improvement in the CAL and PPD gain in sites treated with resorbable membranes and deproteinized bovine bone material [40]. CAL gains at 1 and 2.5 years were significantly  
Figure 11: Meta-analysis of intra-bony defect depth (IBDD) at 12 months. reduced from that at 6 months. A significant improvement in PD was also noted: mean reductions in PD at 6 months and 2.5 years were 4.0 \(\pm\) 0.8 and 3.2 \(\pm\) 0.8 mm, respectively. The defect fill in this systematic review is in correlation with the other studies by [PERSON] et al. [17] and [PERSON] et al. [41].