## 4 Discussion  
Previous studies have shown that foreign bodies, such as GP (infected and non-infected), prevent wound healing and bone formation [19]. The aim of this pilot study was to test the hypothesis that biofilm and GP would induce bone destruction, whereas bone defects alone would not, using a rat calvarium model known in periodonontology for its ability to show bone formation [20; 21]. To the best of our knowledge, this is the first study testing this hypothesis using the methodology described above. Root canal treatment aims to eliminate infection from the root canal and prevent reinfection by filling the root [22]. Despite the highest standards of care, some cases still result in failure due to persistent or secondary intraradicular infection or extraradicular in  
Figure 5: Histologic micrograph of foreign material surrounded by a thin fibrous connective tissue capsule. The matrix contained mild inflammatory cell infiltrate composed primarily of lymphocytes and few scattered small blood vessels (arrows). H&E: hematoxylin & eosin stain, \(\times 200\). Figure 6: Magnified view showing mild inflammatory cell infiltrate composed primarily of lymphocytes and few scattered small blood vessels (arrows). H&E: hematoxylin & eosin stain, \(\times 200\). fection [10]. It has been claimed that failures in other cases are due to non-microbial factors, such as extruded root canal filling materials; this may cause a foreign body reaction [10; 23]. Contrary to our hypotheses, GP, per se, did not cause bone destruction at the calvaria, and surprisingly, biofilm-infected GP also did not cause bone destruction. Likewise, a mild inflammatory reaction was observed in the adjacent tissue in the non-infected group, and a newly woven bone matrix surrounded by osteoblasts was noted in some specimens. In the infected group, a mild foreign body reaction with a few inflammatory cells was observed adjacent to the capsule. A newly woven bone matrix surrounded by osteoblasts and mature bone was detected at 60 days. GP points consist of approximately 65% zinc oxide, 20% GP, 10% radiologists, and 5% plasticizers [24]. [PERSON] and [PERSON] (1975) studied the reaction of rat connective tissue to some formulations of GP in common use for up to 64 days and noticed that most of the specimens initially showed an acute response, followed by fibrous tissue encapsulation [25]. [PERSON] et al. (1995) claimed that the size of the GP particles determines how the tissues react to the material [26]. These investigators studied the tissue reaction to various GP sizes subcutaneously implanted in guinea pigs and found that large particles (1-2 mm in size) were well encapsulated while the surrounding tissue was free of inflammation [26]. However, fine particles (50-100 um in size) evoked an intense, localized tissue response characterized by the presence of macrophages and multinucleated giant cells [25]. [PERSON] (2008) claimed that GP particles in apical tissue might gradually fragment into fine particles that induce a foreign body reaction [8]. In this research, we used a rat calvarium model, which is known in periodontology for its ability to evaluate bone formation [20; 21]. In aim was to assess the ability of a foreign body, such as GP (infected and non-infected), in preventing wound healing and bone formation. GP, per se, did not cause bone destruction at the calvaria, but more surprisingly, infected GP with biofilm was also incapable of causing bone destruction. It seems this biofilm alone could not cause bone destruction unless there is a connection between the infected root and the periapical lesion. \"It is possible that other types of bacteria are capable of causing such isolated infection; the independent extraradicular infection probably does not occur often and is usually associated with apical actinomycosis\" [27]. Further research is warranted regarding GP fragmentation into fine particles in apical tissues and the response of apical tissues to fine particles.