Results.
One hundred and fifty-four teeth in 101 patients were treated surgically. Eight teeth in eight patients were extracted during the procedure because of vertical root fracture or lateral perforation; they were eliminated from the study. Fourteen patients were eliminated because they did not attend regular follow-up appointments. Therefore, a group of 79 patients and 120 teeth were examined.
Of the 120 teeth evaluated at the end of the study (after 36 months), 94 teeth (78.3%) healed with complete bone  filling of the surgical cavity and adequate radiological periradicular architecture, 17 (14.1%) had an apical scar, only four teeth (3.3%) had uncertain healing and  five (4.1%)were classified as failures. The overall success rate was 92.4% (complete plus incomplete healing).A more detailed description of the data is presented in Table 2.
A cast post in the canals was seen in 46.6% of the teeth. For this reason, the frequency distribution of healed cases was analysed by dividing the teeth into two groups: post and no-post. As shown in Table 3, 56 teeth with cast posts included five failures. However, no statistically significant difference was noted (Mann- Whitney U-test P = 0.37) when comparing the two groups.
Further analysis was performed adding the first and the second categories (complete and incomplete healing) to the success case group and with the other two categories in the failure group. The results are reported in Table 4 and demonstrate only a marginally significant difference at the end of the observation period (chisquare, P = 0.051) (Fig. 5).
Most of the successful cases were considered healed within the first year of surgery (66.6%). The progression of cases classified as successful is presented in Fig.1. None of the cases that healed in the short term failed at a later date.

Figure 1. Nonresolving periapical lesion1 year after orthograde treatment.



Figure 2. Healed lesion 1 year after surgical treatment.



Figure 3. Distal root of first mandibular molar just after retrofilling.



Figure 4. Twelve months after surgery a small 'scar' is still present around the filling.



Table 3. Results divided into the two groups: post (teeth with cast post inside) and no post (teeth filled only by cement and/or gutta-percha).



Table 4. Outcome at 36 months of the two groups of teeth, with posts in root canals and without.



Figure 5. Graphical representation of the percentage of success cases in the teeth with and without posts. In Y-axis the percentage of success cases (complete or incomplete healing) whilst in X-axis the time in month related to the radiographical controls are given. The number of healing cases is similar in the two groups but a small difference was noticed in favour of the no-post group (chi-square at 36, P = 0.051)..

Discussion.
Studies on the outcome of periapical surgery have reported variable results, ranging from a 30-80% success rate (Rud et al.197 2a, b, Grung et al.1990, Lustmann et al.19 91, Frank et al.1 992, Hepworth & Friedman 1997). However, these studies differed in sample size, type of teeth, surgical technique, type of root end filling materials and radiographic evaluation criteria.
Recently, some longitudinal studies reported a higher success rate in periapical surgery of teeth not responding to orthograde endodontic treatment (Rud et al.19 96, Sumi et al.1996, Mehlha ff et al.19 97, Rubinstein & Kim 1999, Testori et al.1999, Zuolo et al.2000). In the present study, many of the more modern endodontic surgical techniques were adopted, and the cases were monitored over a significant time period of 36 months. In addition, inclusive criteria were not restrictive. The only one adopted was a root canal filling shorter than 3 mm from the radiographic apex and a compromised periodontal status. In the group of teeth scheduled for surgery, eight teeth with vertical fractures were excluded from the analysis as they were extracted during surgery procedures.
The overall success rate was 92.4% at 36 months; this is in agreement with other recent studies. Dorn & Gartner (1990) reported a 75% success rate for amalgam root end filling and over 90% for a zinc oxide-reinforced material. In contrast, some authors had a lower success rate using these materials (Friedman et al. 1991). Sumi et al.( 1996) reported a success rate of 92.4% using only micro headpieces for root end cavity preparation.

References.

Adamo HL, Buruiana R, Schertzer L, Boylan RJ (1999) A comparison   of MTA, Super-EBA, composite and amalgam as root-end filling materials using   a bacterial microleakage model. International Endodontic Journal 32, 197-203.
von Arx T, Gerber C, Hardt N (2001) Periradicular surgery of molars: a prospective   clinical study with a 1-year follow-up. International Endodontic Journal   34, 520-5.
von Arx T, Walker WA (2000) Third microsurgical instruments for root-end   cavity preparation following apicoectomy: a literature review. Endodontics   and Dental Traumatology 16,47-62.
August DS (1996) Long-term, postsurgical results on teeth with periapical   radiolucencies. Journal of Endodontics 22, 380-3.
Bader G, Lejeune S (1998) Prospective study of two retrograde endodontic   apical preparations with and without the use of CO2 laser. Endodontics and   Dental Traumatology 14, 75-8.
Bahcall JK, Di fiore PM, Poulakidas TK (1999) An endoscopic technique for   endodontic surgery. Journal of Endodontics 25, 132-5.
Briggs PF, Scott BJ (1997) Evidence-based dentistry: endodontic failure -   how should it be managed? British Dental Journal 183, 159-64.
Brunette DM (1996) Critical Thinking: Understanding and Evaluating Dental   Research. Chicago: Quintessence Publishing Co.
Carr GB (1992 a) Microscopes in endodontics. Journal of the California   Dental Association 20, 55-61.
Carr GB (1992 b) Use of ultrasonics in apical surgery. Journal of Endodontics   18, 416.
Carr GB (1997) Ultrasonic root end preparation. Dental Clinics of North   America 41,541-54.
Chong BS, Ford TR, Wilson RF (1997) Radiological assessment of the effects   of potential root-end filling materials on healing after endodontic surgery.   Endodontics and Dental Traumatology 13,176- 9.
DaninJ, Linder LE, Lundqvist G, Ohlsson L, Ramskold LO, StrombergT (1999) Outcomes   of periradicular surgery incases with apical pathosis and untreated canals.   Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics   87, 227-32.
Danin J, Stromberg T, Forsgren H, Linder LE, Ramskold LO (1996) Clinical   management of nonhealing periradicular pathosis. Surgery versus endodontic retreatment.   Oral Surgery, Oral Medicine, Oral Pathology, Oral Radiology and Endodontics   82, 213-7.
Delano EO, Tyndall D, Ludlow JB, Trope M, Lost C (1998) Quantitative radiographic   follow-up of apical surgery: a radiometric and histologic correlation. Journal   of Endodontics 24, 420-6.
Dorn SO, Gartner AH (1990) Retrograde filling materials: a retrospective   success-failure study of amalgam, EBA, and IRM. Journal of Endodontics 16,   391-3.
Forsberg J, Halse A (1997) Periapical radiolucencies as evaluated by bisecting-angle   and paralleling radiographic techniques. International Endodontic Journal   30,115-23.
Frank AL, Glick DH, Patterson SS, Weine FS (1992) Long-term evaluation of   surgically placed amalgam fillings. Journal of Endodontics 18, 391-8.
Friedman S, Lustmann J, Shaharabany V (1991) Treatment results of apical   surgery in premolar and molar teeth. Journal of Endodontics 17, 30-3.
Gray GJ, Hatton JF, Holtzmann DJ, Jenkins DB, Nielsen CJ (2000) Quality of   root-end preparations using ultrasonic and rotary instrumentation in cadavers.   Journal of Endodontics 26, 281-3.
Grung B, Molven O, Halse A (1990) Periapical surgery in a Norwegian county   hospital: follow-up findings of 477 teeth. Journal of Endodontics 16, 411-7.
Gutmann JL (1993) Parameters of achieving quality anesthesia and hemostasis   in surgical endodontics. Anesthesia and Pain Control in Dentistry 2, 223-6.
Gutmann JL, Harrison JW (1994) Surgical Endodontics. St . Louis, MO,   USA: Ishiyaku Euro America, Inc.
Harrison JW (1992) Surgical management of endodontically treated teeth. Current   Opinion in Dentistry 2, 115-21.
Hepworth MJ, Friedman S (1997) Treatment outcome of surgical and non-surgical   management of endodontic failures. Journal Canadian Dental Association (Journal   de 1 Association Dentaire Canadienne) 63,364-71.
Jesslen P, Zetterqvist L, Heimdahl A (1995) Long-term results of amalgam   versus glass ionomer cement as apical sealant after apicectomy. Oral Surgery,   Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 79,101-3.
Kim S (1997) Principles of endodontic microsurgery. Dental Clinics of   North America 41, 481-97.
Kim S, Rethnam S (1997) Hemostasis in endodontic microsurgery. Dental   Clinics of North America 41, 499-511.
Lin CP, Chou HG, Kuo JC, Lan WH (1998) The quality of ultrasonic root-end   preparation: aquantitative study. Journal of Endodontics 24, 666-70.
Lustmann J, Friedman S, Shaharabany V (1991) Relation of pre and intraoperative   factors to prognosis of posterior apical surgery. Journal of Endodontics   17, 239-41.
Mehlha DS ,Marshall JG, Baumgartner JC (1997) Comparison of ultrasonic and   high-speed bur root-end preparations using bilaterally matched teeth. Journal   of Endodontics 23, 448-52.
Min MM, Brown CE, Jr, Legan JJ, Kafrawy AH (1997) In vitro evaluation of   effects of ultrasonic root-end preparation on resected root surfaces. Journal   of Endodontics 23, 624-8.
Molven O, Halse A, Grung B (1987) Observer strategy and the radiographic   classification of healing after endodontic surgery. International Journal   of Oral Maxillofacial Surgery 16, 432-9.
Molven O, HalseA, Grung B (1996) Incomplete healing (scar tissue) after periapical   surgery - radiographic findings 8-12 years after treatment. Journal of Endodontics   22, 264-8.
Morgan LA, Marshall JG (1999) A scanning electron microscopic study of in   vivo ultrasonic root-end preparations. Journal of Endodontics 25, 567-70.
Patel N, Rushton VE, Macfarlane TV, Horner K (2000) The influence of viewing   conditions on radiological diagnosis of periapical inflammation. British   Dental Journal 189, 40-2.
Peters CI, Peters OA, Barbakow F (2001) An in vitro study comparing root-end   cavities prepared by diamond-coated and stainless steel ultrasonic retrotips.   International Endodontic Journal 34, 142-8.
Rubinstein R (1997) Endodontic microsurgery and the surgical operating microscope.   Compendium of Continuing Education in Dentistry (Jamesburg, NJ) 18, 659-64.
Rubinstein R, Kim S (1999) Short-term observation of the results of endodontic   surgery with the use of a operation microscope and Super-EBA as root-end filling   material. Journal of Endodontics 25, 43-8.
Rud J, Andreasen J, Moller JensenJ (1972 a) Radiographic criteria for the   assessment of healing after endodontic surgery. International Journal of   Oral Surgery 1, 195-214.
Rud J, Andreasen J, Moller Jensen J (1972b) A follow-up study of 1000 cases   treated by endodontic surgery. International Journal of Oral Surgery 1,   215-28.
Rud J, Rud V, Munksgaard EC (1996) Long-term evaluation of retrograde root   filling with dentin-bonded resin composite. Journal of Endodontics 22, 90-3.
Rud J, Rud V, Munksgaard EC (2001) Periapical healing of mandibular molars   after root-end sealing with dentine-bonded composite. International Endodontic   Journal 34, 285-92.
Sumi Y, Hattori H, Hayashi K, Ueda M (1996) Ultrasonic root-end preparation:   clinical and radiographic evaluation of results. Journal of Oral and Maxillofacial   Surgery 54, 590-3.
el-Swiah JM, Walker RT (1996) Reasons for apicectomies. A retrospective study.   Endodontics and Dental Traumatology 12, 185-91.
Testori T, Capelli M, Milani S, Weinstein RL (1999) Success and failure in   periradicular surgery: a longitudinal retrospective analysis. Oral Surgery,   Oral Medicine, Oral Pathology, Oral Radiology and Endodontics 87, 493-8.
Wada M, Takase T, Nakanuma K, Arisue K, Nagahama F, Yamazaki M (1998) Clinical   study of refractory apical periodontitis treated by apicectomy. Part 1. Root   canal morphology of resected apex. International Endodontic Journal 31,   53-6.
Zuolo ML, Ferreira MO, Gutmann JL (2000) Prognosis in periradicular surgery:   a clinical prospective study. International Endodontic Journal 33, 91-8.