# Influence of the Angle of Periodontal Intrabony Defects on Blood Clots: A Confocal Microscopy Study
## 1 Introduction  
Periodontitis is a chronic immune-mediated inflammatory oral disease that progressively destroys the tooth-supporting apparatus (periodontium). Patients, once diagnosed with periodontitis, should be treated according to a pre-established stepwise approach to therapy. The goal of non-surgical treatment is reduce the bacterial load to a threshold where the host response can defeat it; however, the deeper the probing depth (PD), the more challenging it is to approach the most apical portions of the pocket and the efficacy of the non-surgical therapy might decrease [1; 2; 3]. [PERSON] 2022 [4] concluded that non-surgical periodontal therapy (NST) was able to reduce PD \(\geq\) 5 mm from 28% to 11.7%, so that NST was able to eliminate, at 12 months, 2/3 of the baseline pockets, achieving 90% of sites with PD \(\leq\) 4 mm. Furthermore, it was seen that non-surgical therapy left a mean number of 7.33 sites with PD \(\geq\) 6 mm--sites that must face further surgical therapy if the patient wants to reach periodontal stability. Therefore, according to the 2020 EFP Guidelines, it is recommended to treat teeth with residual deep pockets associated with infrabony defects with periodontal regenerative surgery, which aims to increase the periodontal attachment and bone level, which may result in pocket depth decrease and increased stability. [PERSON] [5] have shown how regeneration therapy is effective in the treatment of one-, two-, and three-wall intrabony defects; the morphology of the defect is important because it is one of the factors that determines the stability of the blood clot, which is fundamental for regeneration [6]. Even though it seemed that deeper intrabony defects could heal with more clinical attachment gain than shallower ones, [PERSON] showed that they had the same potential for regeneration, since the percentage of clinical attachment level (CAL) gain related to the baseline defect depth was similar [7]. Indeed, an acute angle has a greater potential for regeneration because it creates a narrower area for the creation and stability of the coagulum and wider defects have been associated with reduced amounts of clinical attachment level and bone gain at 1 year [8]. Therefore, a wider angle has less regenerative potential and this might be due to the reduced capacity to create a self-maintaining space for the coagulum, and to the possible collapse of the membrane [9]. The problem concerning this study was the low number of samples, and therefore, the reduced power to detect any possible statistical inconsistency for both angle and clot retraction. Different surgical techniques have been introduced and more preservation of interdental tissue can be achieved to maintain clot stability; a wide defect which is non-supporting can be compensated for by the use of biomaterials such as bone substitutes and membranes. Another aspect, about which little is still known, is the chemical treatment of the root surface. In the past, various chemical conditioning agents have been proposed as topical treatments of the exposed root surface as adjunctive therapy during periodontal treatment [10,11]. The most widely used are CA (citric acid), PA (phosphoric acid), and EDTA (ethylenediaminetetraacetic acid). Of these, EDTA, thanks to its neutral pH and its ability to remove the smear layer and widen the dentin tubule, has been commonly used in periodontal therapy in different concentrations from 12% to 24%, without damaging biological structures [10, 11, 12]. Until now, no precise standardization protocols has been proposed for the use of EDTA, and there is a need to understand the best way to promote proper fibrin clot formation to enhance healing capacity, which is a determining factor in early wound healing. The early phase of the healing is crucial in maintaining the interface between the coagulum and the radicular surface in order to achieve a successful regeneration [13]. Therefore, it is important to maintain space in the defect for the coagulum.