Four patients were referred for the evaluation and treatment of a lower right second premolar (Figure 1A-1D), a lower left second premolar (Figure 2A-2D), a lower right canine and first premolar (Figure 3A-3E), and a lower left first molar (Figure 4A-4F), respectively. The preoperative radiographs of all cases (Figures 1A, 2A, and 4A) showed the presence of a periapical radiolucency, except for 1 (Figure 3A). It was re-treated in only 1 case (Figure 1A). In all clinical cases, after rubber dam isolation, the old restorations and root canal filling materials, if present, were removed (Figure 1B). The pulp chamber was opened using high-speed rotating diamond-coated burs and the root canal orifices were located using low-speed carbide burs and/or endodontic ultrasonic tips under magnification using a dental operating microscope (Figure 4B). After the scouting phase and establishing the working length (Figures 2B, 4C, and 4D), all root canals were shaped using Mtwo instruments (VDW, Munich, Germany) using the simultaneous technique, irrigated with 5% sodium hypochlorite (NaOCl) alternating with 17% ethylenediaminetetraacetic acid (EDTA) and finally obturated with warm preheated thermoplasticized gutta-percha (MicroFlow, Microseal system, Sybron Endo, Orange, CA, USA), and sealer corresponding to Rickert's formula (Pulp Canal Sealer, Sybron Endo) according to the hybrid Microseal/PacMac obturation technique refined by 1 of the authors of the presented cases [10]. The Microseal obturation technique involves the use of preheated gutta-percha inserted inside the root canal, applied on a conical ISO 25 0.04 PacMac (Sybron Endo) introduced up to 2–3 mm from the apex, and activated at 6,000–7,000 rpm (Figure 5A-5G). The first to describe this technique in 1993 was John T. McSpadden [11], who referred to it as the multiphase gutta-percha obturation technique. Since then, some modifications have been made to this technique, which was later named Microseal [1213], such as the use of a 0.2 tapered gutta-percha master cone brought to 1 mm from the working length to limit overfilling [10]. The quantity of sealer used in the Microseal technique is very minimal; the master cone of gutta-percha only gets dirty at the tip (Figure 5D), and the canal is filled by the preheated preplasticized gutta-percha applied to the PacMac instrument (Figure 5F-5G).

Overfilling occurred during obturation in all cases (Figures 1C, 2C, 3B, and 4E), but the radiographic follow-up at 10 years showed complete or almost complete resorption of the filling material beyond the apex and healing of the periapical lesions or maintenance of healthy periapical status (Figures 1D, 2D, 3E canine, and 4F). Radiographic follow-up (Figure 3E) showed healing of the lower canine restored with radiolucent composite resin, but also a periapical lesion on the first lower right premolar contiguous to the canine, part of the porcelain-fused-to-metal (PFM) bridge, where 5 years earlier slightly short canal filling was performed (Figure 3C and 3D).

A 50-year-old male patient was referred for evaluation and treatment of the lower left right first premolar tooth (Figure 6A-6E). The patient had no pain and the clinical examination revealed a moderate tenderness to percussion without a sinus tract. The diagnosis of chronic apical periodontitis was made for the tooth, which needed to be treated. For economic reasons, the old PFM bridge was preserved and the endodontic treatment was performed through the PFM crown covering the tooth. After rubber dam isolation, the root canal was negotiated (Figure 6A), shaped according to the manual technique using stainless-steel K and H files, irrigated with 5% NaOCl alternating with 17% EDTA, and finally obturated with preheated thermoplasticized gutta-percha (Sybron Endo) and sealer corresponding to Rickert's formula (Pulp Canal Sealer, Sybron Endo) according to the Microseal technique. During obturation, overfilling occurred (Figure 6B), but the radiographic follow-ups at 1, 10, and 20 years showed complete resorption of the filling material beyond the apex and the healing of the periapical lesion (Figure 6C-6E). Curiously, in the last follow-up radiograph, after insertion of a fiber post to retain a new single PFM crown, the obturation material seemed short of the radiographic apex, showing that the resorption of filling material may also continue inside the apical root canal space, as evidenced by a thin radiopaque border at the apex of the tooth, suggesting the formation of new hard tissue (Figure 6E).

A 26-year-old female patient was referred for evaluation and treatment of the upper right central and lateral incisor (Figure 7A-7G). The patient had pain and clinical signs of abscess, and both elements were unresponsive to thermal pulp sensibility tests. A preoperative radiograph showed the presence of a radiolucency between the middle and apical third of the root of the lateral incisor, with a direct communication between the endodontium and the periodontium (Figure 7A). The diagnosis of internal root resorption with apical chronic periodontitis was made for the lateral incisor, which needed to be treated with endodontic orthograde therapy combined with surgical therapy. Instead, the diagnosis of asymptomatic irreversible pulpitis was made for the central incisor. Both incisors had incongruous obturation, and under the filling of the lateral incisor there was a layer of cement-like material for capping the pulp. Under rubber dam isolation, both elements were instrumented with stainless-steel K and H files, irrigated with 5% NaOCl, and obturated with a large calibrated gutta-percha master cone (Sybron Endo) and sealer corresponding to Rickert's formula (Pulp Canal Sealer) following the cold lateral condensation technique. Overfilling occurred in both teeth (Figure 7B). In the same operative session, surgical therapy was performed to remove the apical fragment of the lateral incisor without performing retrograde preparation and obturation. Subsequently, both incisors were reconstructed with direct composite resin.

Radiographic follow-ups at 20 months, 10 and 25 years showed healing with complete disappearance of the periapical lesion (Figure 7C-7E); the 30-year radiographic follow-up revealed a still minimal presence of the overfilling material in the lateral incisor with a clearly distinguishable reduction in the diameter of the calibrated gutta-percha master cone at the apex. In the central incisor, complete resorption of the last millimeters of the gutta-percha filling material was observed (Figure 7, white arrow), with the formation of a radiopaque bridge closing the apex (Figure 7F). After another 5 years, at the 35-year follow-up, the patient did not report symptoms and there was no mobility, and on a radiographic evaluation, the apex of the central incisor appeared to be stable. On the contrary, in the area of the lateral incisor, it was possible that reabsorption of the gutta-percha and root was continuing (Figure 7G) and a new periapical lesion seemed to have appeared, probably due to loss of the apical seal.