## 4 Discussion
In the present study, we observed radiographic periapical healing in 91.2% of the patients and uncertain healing in 8.8%. This result was similar to those of other studies that reported a high periapical healing rate of 90-100% [4; 19; 30; 37; 38]. However, the stratification of the anterior and posterior teeth demonstrated significantly different outcomes with respect to root development. The change in RRA was greater than that in root length, consistent with previous reports [19; 36; 37]. Interestingly, the average change in RRA was 26.2% for the anterior teeth and 39.3% (\(p=0.037\)) for the posterior teeth. Similarly, the average relative increase in the root length was 6.14% in anterior teeth and 11.3% in posterior teeth (\(p=0.029\)). The aforementioned increase in molar root dimensions was in accordance with that reported by [PERSON] et al. [12]. There are insufficient reports on the outcomes of REP in molars. [PERSON] and [PERSON] [30] evaluated the effect of aetiology on the REP success rate in 445 samples consisting of 432 anterior teeth and premolars and only 13 molars. However, they did not specify if'success' denoted periapical healing, an increase in root dimensions, or both. The aetiology of necrosis in their sample included dental trauma (65%), broken dental cusps (29%), and dental caries (6%). There was no significant positive association between the aetiology of pulp necrosis and the REP success rate. Another meta-analysis examined the dimensional changes among anterior and posterior teeth according to the etiological factors such as caries, trauma, and dental anomalies. The majority of pronounced dimensional changes were observed in the dental anomalies group [19]. The above-mentioned studies are the only reports on the outcome of REP in molars; thus, it was difficult to draw any clear conclusions, and there is a need for further studies to determine the effect of aetiologic factors on REP outcomes. In this study, all posterior teeth presented with caries as the etiological factor, and RRA in the carious teeth was 13% greater than that in the anterior teeth, in which trauma was the etiological factor. Unlike the results of the present study, [PERSON] et al. [4] demonstrated that teeth with caries were associated with a significantly lower increase in the RRA than those with trauma. This discrepancy may be attributed to the difference in the sample size as follows: the present study included 14 posterior teeth, all with caries causing pulp necrosis, whereas the San Antonio study [4] included only five teeth with caries as the aetiology with two (out of five) failures. [PERSON] et al. [4] speculated that caries, as a predictor of failure, may be attributed to a long-standing biofilm structure and the inability of sufficient disinfection to eliminate it. The variations in the types of biofilms that characterised both studies may be a possible explanation for the differences in success rates between the studies. The patients referred to our clinic were young and were referred immediately following the diagnosis of pulp necrosis. The biofilm on their teeth was presumably young and susceptible to the disinfection protocol. [PERSON] et al. [33] reported that the root canal microflora of traumatised teeth is diverse and differs from that of root canal infections not caused by trauma. Our findings demonstrated no significant difference between the anterior and posterior teeth with regard to periapical healing; however, significant statistical differences regarding changes in the root dimension may contribute to the aetiological effect on the outcomes. Trauma exerts a detrimental effect on root development [39; 40]. [PERSON] et al. [39] reported that severe trauma has the potential to cause damage to the Hertwig's epithelial root sheath and/or apical papilla; thus, traumatised teeth may be less likely to achieve clinically meaningful continued root development than immature teeth with pulp necrosis caused by caries.