## 3 Results  
All consecutive histological sections in the histologic control groups stained with hematoxylin and eosin confirmed the presence of pulp tissue in the apical, middle, and coronal portions of the mesial and distal roots for both evaluated groups (Figure 2A,B). In addition, the Gram stain of the necrotic group showed the presence of bacteria in all portions of both roots as well as in the dental tubules near the canal walls (Figure 2C,D). Only three samples out of twenty treated teeth presented pulpal debris after the instrumentation and irrigation procedure--one from the _symptomatic irreversible pulpitis_ (SIP) group and two from the necrotic _symptomatic apical periodontitis_ (SAP) group (Tables 2 and 3). Vital and symptomatic irreversible pulpitis (SIP) group: In nine out of ten specimens, no pulp tissue or debris was detected in the apical, middle, or coronal portion of the mesial and distal roots. This included two specimens with fused roots. Figure 3 shows an example of (3A) main canal and apical lateral canals and (3B) main canals and isthmus which are free of pulp debris. Figure 3C,D show isthmuses and fins free of debris. In addition, Figure 3E,F show that there is no debris in the uninstrumented portions of the root canal. Figure 2: Photomicrographs of the histologic control groups. The hematoxylin and eosin technique was used to detect tissue and the Gram staining technique was used to detect the presence of bacteria. The photomicrographs show representative cross-sections of the vital controls (**A**, 4\(\times\) and **B**, 20\(\times\)) and the necrotic controls (**C**, 10\(\times\) and **D**, 20\(\times\)) in the apical region of mandibular molars. Pulp necrosis and symptomatic apical periodontitis (SAP) group: In eight out of ten specimens, no pulp debris was detected in the apical, middle, or coronal portion of the mesial and distal roots including the ramifications, isthmuses, or lateral canals. In two specimens, pulp debris was found in the apical portion of the mesial buccal root canal (Figure 4A,B). In ten out of ten specimens, no bacteria were detected in the main canals, isthmuses, or lateral canals of the mesial and distal roots. The apical portion of distal root shows complete pulpal debridement of the main and lateral canal (Figure 4C,D). Some bacteria were found deep in the dental tubules in all coronal sections of 10 specimens (Figure 4E,F). Table 1 shows the mean percentage of bacteria remaining deep within the dental tubules in the apical, middle, and coronal portions of the root canals. Figure 3: Photomicrographs of representative cross-sections from the vital mandibular molars group that have undergone H&E staining. The apical regions of the mesial canals of vital mandibular molars show main canals and the difficult to reach areas including the isthmus and apical deltas free of pulpal debris. (**A**, 10\(\times\)) and middle (**B**, 10\(\times\)). The middle portion of the mesial-buccal (MB) and mesial lingual root canal shows the lack of pulpal debris in the isthmus and fins. (ML) (**C**,**D**, 10\(\times\)). **E** and **F** show the apical portion of a mesial root. Note in (**E**, 10\(\times\)) the lack of pulp tissue or debris in the uninstrumented portion of the root canal and isthmus. (**F**, 10\(\times\)) shows the absence of pulp or tissue debris in completely uninstrumented canals as indicated by the irregularly shaped canal walls. Statistical analysis: Table 2 shows the analysis of deviance table for the generalized linear mixed effect model (GLMM) for the fixed effects of group (vital, necrotic), zone (coronal, mid, apical), and location (MB, ML, DB, DL root canal) on percent of teeth with pulp tissue remnants. The repeated measure effects of multiple cross-sections for each individual tooth were included as a random effect in the GLMM.