Comparative Evaluation of Push-Out Bond Strength of Three Bioactive Retrograde Filling Materials using Different Retro-Preparation Techniques (An in Vitro Study)

Background The aim of this study was to evaluate and compare the push-out bond strength around retrograde cavities prepared with ultrasonic technique and conventional method and filled by three types of retrograde bioceramic materials. Materials and methods 30 extracted single rooted human permanent maxillary teeth with mature apices were selected. The roots were prepared chemo-mechanically using protaper files (Dentsply Maillefer, Ballaigues, Switzerland) (SX to F5) with crown-down technique and then obturated with lateral condensation gutta-percha technique. The roots were sectioned transversally at two points 3 mm short of the apical foramen with straight fissure bur (which is the level of apicoectomy) and 4 mm coronally to this point to obtain an apical root section or slice of (4 mm) high. A total of 30 apical root slices were divided into three main groups according to the type of retrograde filling Group A (Biodentine group) (n=10) which were subdivided into A1 (n=5) in which a class I retro cavity were prepared using Piezoelectric ultrasonic device equipped with ultrasonic surgical retro tip (surgysonic I, ES03A) at (30-kHz) frequency and A2 (n=5) In which class I retro cavity were prepared with right-angled low speed Handpiece (W& H, Austria) equipped with carbide round bur #2 (Komet Dental, Austria). After that retrograde cavities were filled with Biodentine (Septodent, France) Group B (MTA group) (n=10) which were subdivided into B1 (n=5) in which a class I retro cavity were prepared using Piezoelectric ultrasonic device equipped with ultrasonic surgical retro tip (surgysonic I, ES03A) at (30-kHz) frequency and B2 (n=5) In which class I retro cavity were prepared with right-angled low speed Handpiece (W& H, Austria) equipped with carbide round bur #2 (Komet Dental, Austria). After that retrograde cavities were filled with MTA (ProRoot MTA, Dentsply). Group C (TheraCal LC group) (n=10) which were subdivided into C1 (n=5) in which a class I retro cavity were prepared using Piezoelectric ultrasonic device equipped with ultrasonic surgical retro tip (surgysonic I, ES03A) at (30-kHz) frequency and C2 (n=5) In which class I retro cavity were prepared with right-angled low speed Handpiece (W& H, Austria) equipped with carbide round bur #2 (Komet Dental, Austria). After that retrograde cavities were filled with TheraCal LC (Bisco, Inc. ). Then all the specimens were kept in wet gauze of normal saline for 2 day. The specimens were then fixed in an Instron universal testing machine (Instron Corp. , Canton, MA, USA). Maximum load applied to material at the time of dislodgement were recorded in Newtons and data were recorded using computer software, then bond strength was calculated from the recorded peak by special formula and the slices were then examined under a light microscope at 20 magnification to determine the nature of the bond failure. Results Statistical analysis showed a highly significant difference in push-out bond strength among the tested groups in which Biodentine has proved superiority in dislodgment resistance when compared to MTA and TheraCal. Also push-out bond strength was significantly higher with ultrasonic prepared cavities when compared with conventional method for Biodentin group and non significant difference for MTA and TheraCal groups between ultrasonic and conventional method. We observed mostly adhesive failures in MTA groups, while TheraCal showed predominance of mixed failures. Almost all Biodentine samples revealed a cohesive bond failure. Conclusion 1. The force needed for the dislodgement of Biodentine from root dentin was statistically highly significant when compared to MTA and TheraCal.2- Statistically significant differences were found comparing the results of ultrasonic retrotip preparation versus conventional bur preparation in which ultrasonics produced significantly better push-out bond strength for Biodentin group and non significant difference for MTA and TheraCal groups between ultrasonic and conventional method.