Interventions All treatment procedures will be performed by a single, duly trained operator. Group I (control) - conventional endodontic treatment
1. Prophylaxis with pumice stone and water and antisepsis of region with 0.12% solution of chlorhexidine using moistened gauze
2. Anesthesia
3. Absolute isolation, if possible; in cases of considerable loss of remaining tooth, relative isolation using cotton rolls
4. Opening of crown with spherical diamond tip burs (bur size compatible with tooth) (KG Sorensen - Indústria e Comércio, SP, Brazil) and high speed Z endodontic drill under water and air refrigeration
5. Millimeter measurement of root canal to 1 mm short of radiographic apex
6. Insertion of three sterile paper cones with diameter compatible with canal for 30 seconds for initial collection of bacterial sample and immediate placement into brain heart infusion broth
7. Surgical chemical preparation with series of Kerr files appropriate for each case, using initial file and an additional two files of larger size, with irrigation and aspiration with 1% sodium hypochlorite (Milton's solution) and endo PTC (Fórmula \& Ação) with each change of file
8. Insertion of three sterile paper cones for 30 seconds for second collection of bacterial sample and immediate placement into brain heart infusion broth
9. Filling of root canals with calcium hydroxide (Ultra-cal, Ultradent, Brazil); base of thin gutta-percha and filling with glass ionomer cement; restorative treatment performed in subsequent session
Group II - Conventional endodontic treatment + PDT
1. Prophylaxis with pumice stone and water and antisepsis of region with 0.12% solution of chlorhexidine using moistened gauze
2. Anesthesia
3. Absolute isolation, if possible; in cases of considerable loss of remaining tooth, relative isolation using cotton rolls
4. Opening of crown with spherical diamond tip burs (bur size compatible with tooth) (KG Sorensen - Indústria e Comércio, SP, Brazil) and high speed Z endodontic drill under water and air refrigeration
5. Millimeter measurement of root canal to 1 mm short of radiographic apex
6. Insertion of three sterile paper cones with diameter compatible with canal for 30 seconds for initial collection of bacterial sample and immediate placement into brain heart infusion broth
7. Insertion of sterile paper cone immersed in Chimiolux® methylene blue for three minutes; administration of wireless Therapy XT EC laser device (DMC - São Carlos, Brazil) after removal of cone; energy density: 4 J/cm², power: 100 mw; wavelength: 660 nm; exposure time: 40 seconds
8. Root canal irrigated with sterile saline solution and insertion of three sterile paper cones for 30 seconds for second collection of bacterial sample and immediate placement in brain heart infusion broth
9. Filling of root canals with calcium hydroxide (Ultra-cal, Ultradent, Brazil); base of thin gutta-percha and filling with glass ionomer cement; restorative treatment performed in subsequent session
