Aim: The following case report aims to demonstrate the vestibular bone healing after “bone window technique” and a resorbable collagen membrane in a small lesion of endodontic origin with four walls.

Introduction: Although microsurgical endodontics is a reliable treatment option for treating apical periodontitis with a success rate of more than 85 %, its success is questionable in apico-marginal defects Class 2 and Class 3 (1) Class E, F (2), therefor regenerative therapies are recommended. Nevertheless, using regenerative therapies in small lesions of endodontic origin with four walls are not fully investigated and results inconclusive.

Materials and Methods: 42 years old female was referred to the author’s office with symptomatic apical periodontitis. On PA x-ray it was evident a radiolucent image around the apex and extruded root canal obturation material with preserved vestibular bone on the CBCT (Fig. 1, 2). As NSRCT was performed twice for the last three years and the root canal obturation seemed homogenic but over-extruded, it was decided to be treated surgically. Nicely adjusted temporary crown was present without pathological probing depths and no bleeding on probing. No sinus tract was present (Fig. 3-5). Symptomatic apical periodontitis Class 1 ( (Von Arx&Cochrane 2001); Class B (Kim&Kratchman 2005) and previously performed root canal treatment was the final diagnosis. Submarginal full thickness flap with two releasing incisions was performed with a double rounded microblade No.69 (Swann-Morton); (Fig. 6, 7). The vestibular bone was intact, therefore bone window technique was used and performed (Fig. 6-8) with a piezo device (Woodpecker DTE AI Surgery) and tips “US1, UC”1 (Guilin Woodpecker Medical Instrument Co., LTD). The block was kept in saline during the intraoperative stages. Apical resection (Fig. 8) was performed using “UC1” (Guilin Woodpecker Medical Instrument Co., LTD) and the root was inspected for a VRF (Fig. 13) on a 3 mm round mirror “MM4” (Hu-Friedy Manufacturing Co LLC). The root end polishing (Fig. 11) was done using “UL4” (Guilin Woodpecker Medical Instrument Co., LTD). Curettage of the bony crypt was done by hand curretes, but also piezo tip “UL3” (Guilin Woodpecker Medical Instrument Co., LTD) was utilised to speed up the healing process by removing any additional epithelial lining in the bony crypt (Fig. 9, 10). Three mm retro preparation (Fig. 14-17) was accomplished by using the “JT2SA” tip (B&L Biotech). The retro preparation was inspected again for guttapercha remnants, rinsed and dried with paper points (Fig. 18-20), followed by a retro seal (Fig. 21-23) of “Neo Mta plus” (Avalon Biomed). The bony block was repositioned (Fig. 24) in its original position and resorbable collagen membrane “Jason membrane” (Botiss Biomaterials GmbH) was used to cover the block window (Fig. 25). For suturing of the soft tissues (Fig. 26), non-resorbable 6.0 monofilament sutures were used (SMI) and removed on the 5-th day (Fig. 27).

Results: On the 1-year follow up on CBCT and PA it was confirmed: complete healing according to Molven criteria (3) and RAC-B overall score 2 (2-2-2/ 2) at 1 year CBCT follow up (Fig. 30-32), (4, 5,). No recession on the soft tissue was evident on the 1 year follow up, just a slight colour difference between the surgical wound healing and the keratinized tissue, but is of no concern to the patient (Fig. 28).

Discussion: First micro surgical endodontics was recorded more than 50 years ago by Rud&Andreasen (6) and they found out that loss of vertical or palatal bone resulted in fibrous tissue healing. Experimental studies on animals demonstrated that healing of the vestibular bone comes last and it’s healing rate is 70 % at 6 months follow up, while Von Arx demonstrated only 54 % healing of the vestibular plate on the 1st year CBCT follow up (7). Its loss could require regenerative therapy with graft materials. F. Khoury and R. Hensher described the bone window technique for the first time in 1987 aiming not only at increasing visibility and space for the surgical procedure, but also to preserve the vestibular bone and replace graft materials with autologous ones(8). In this case, the block window technique together with a resorbable collagen membrane can fully restore the integrity of the vestibular bone and the bone crypt in a very short period of time as demonstrated in this case report and also in the literature (9). The procedure is easy and convenient which provides better visibility and space through the apical resection, retro preparation and retro fill. Some authors are suggesting bone fixation if the block is big while others did not find a difference in the healing rate and suggested placing a collagen material between the donor and the recipient site if the block is not stable (9). As mobility of the repositioned bone block may interfere with osteotomy healing, its important to warn the patients not to press the surgical site and decrease the chance of block necrosis and sequestration.

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2. Kim, Syngcuk, and Samuel Kratchman. “Modern endodontic surgery concepts and practice: a review.” Journal of endodontics vol. 32,7 (2006): 601-23. doi:10.1016/j.joen.2005.12.010

3. Molven, O et al. “Observer strategy and the radiographic classification of healing after endodontic surgery.” International journal of oral and maxillofacial surgery vol. 16,4 (1987): 432-9. doi:10.1016/s0901-5027(87)80080-2.

4. Chen, Ian et al. “Healing after root-end microsurgery by using mineral trioxide aggregate and a new calcium silicate-based bioceramic material as root-end filling materials in dogs.”
Journal of endodontics vol. 41,3 (2015): 389-99. doi:10.1016/j.joen.2014.11.005.

5. Von Arx, Thomas et al. “Evaluation of New Cone-beam Computed Tomographic Criteria for Radiographic Healing Evaluation after Apical Surgery: Assessment of Repeatability and Reproducibility.” Journal of endodontics vol. 42,2 (2016): 236-42. doi:10.1016/j.joen.2015.11.018.

6. Rud J, Andreasen JO, Moller Jensen JE. A multivariate analysis of the influence of various factors upon healing after endodontic surgery. Int J Oral Surg 1972;1:258–71.

7. von Arx T, Janner SF, Heanni S, Bornstein MM. Agreement between 2D and 3D radiographic outcome assessment one year after periapical surgery. Int Endod J 2016;49:915–25.

8. Khoury F, Hensher R. The bony lid approach for the apical root resection of lower molars. Int J Oral Maxillofac Surg 1987;16:166–70.

9. The Application of “Bone Window” Technique in Endodontic Microsurgery Su-Min Lee, DDS, MSD, DScD,* Ya-Hsin Yu, DDS, MS,* Yu Wang, DDS, MS,† Euiseong Kim, DDS, MSD, PhD,‡ and Syngcuk Kim, DDS, PhD, MD(Hon)*