Selecting drill size for post space preparation based on final endodontic radiographs: An in vitro study.

BACKGROUND: For placement of intraradicular posts the intracanal filling material has to be removed. If drills are employed for this purpose, extra widening of the canal, incomplete cracks or root perforation are probable when inappropriate size of drill is used. OBJECTIVE: This in vitro study assessed the efficacy of radiographs taken after completion of root canal therapy in selecting the appropriate-sized Peeso reamer for post space preparation. METHODS: Canals of 53 extracted maxillary and mandibular teeth of different types were cleaned and shaped. Then with acrylic resin 3-dimensional model of the intracanal space of each tooth was fabricated. Next, all canals were filled with gutta-percha and teeth were radiographed buccolingually. Based on these radiographs two observers selected a Peeso reamer that best matched each canal's diameter. The diameter of the selected Peeso reamer was compared to the diameter of the corresponding resin model of each canal by two independent observers and the difference was measured. The data were analyzed by paired sample t-test using SPSS version 22. RESULTS: The diameter of the selected Peeso reamers ranged from 0.21 mm smaller to 0.12 mm larger than the diameter of intracanal spaces. The difference between reamer and resin model was less than 0.1 mm in 75% of the cases. CONCLUSION: The result of this study suggests that post-operation endodontic radiographs are reliable means for selecting a size of Peeso reamer that does not encroach on dentinal wall during removal of intracanal filling material and post space preparation.

Effect of Different Irrigants Applied After Post Space Preparation on Push-Out Bond Strength of a Self-Etch Resin Cement.

OBJECTIVES: The aim was to investigate the effect of intracanal irrigants and agents on the bond strength of intraradicular fiber posts to dentin. MATERIALS AND METHODS: Root canals of 72 decoronated single-rooted premolars were cleaned, shaped, and obturated with gutta-percha and AH26. The specimens were incubated at 37°C and 100% humidity for seven days. Next, the coronal 10 mm of the canals were prepared to receive size 2 D.T. Light fiber post, and the specimens were randomly allocated into six groups according to the irrigants used after post space preparation: normal saline (control group), 5.25% sodium hypochlorite (NaOCl)/15 seconds, 17% ethylenediaminetetraacetic acid (EDTA)/60 seconds, 2% chlorhexidine (CHX)/5 minutes, MTAD/5 minutes, and acid-etching/15 seconds. All canals were rinsed with normal saline and dried. Fiber posts were cemented using Panavia F2.0. After 24 hours, two mid-root slices of 1mm thickness were obtained from each specimen. Push-out bond strength test was performed in a universal testing machine at 0.5mm/minute. The maximum applied load was recorded, and the bond strength was calculated in megapascal (MPa). Data were analyzed by one-way analysis of variance (ANOVA) and Tukey's test. RESULTS: The mean shear bond strengths of etched (53.21±12.11 MPa), MTAD (52.47±14.75 MPa) and EDTA (49.08±10.19 MPa) groups were significantly higher than that of the control group (39.82±10.04 MPa). The difference was marginally significant for CHX group (49.8±13.57 MPa) and not significant for NaOCl group (47.15±17.64 MPa). CONCLUSIONS: Etching or irrigating the root canals with MTAD or EDTA after post space preparation increases the bond strength of Panavia F2.0 to dentin.

Effect of cement type and thickness on push-out bond strength of fiber posts.

Background. This study investigated the effect of the thickness of two resin cements on push-out bond strength of fiber posts to root dentin. Methods. Sixty decoronated single-rooted teeth were endodontically treated. The specimens were then randomly allocated to two groups (n=30); group 1: drill size 90 w, matching the size of fiber posts used; group 2: drill size 110, larger than the posts. The specimens in each group were divided into 2 subgroups (n=15); subgroup SE, in which the posts were cemented with self-etch Panavia F2.0 and subgroup SA, in which self-adhesive Panavia cement was used. After 72 hours, 2 slices with 1 mm of thickness were prepared from the mid-root of each specimen. Push-out bond strength test was performed in a universal testing machine at a crosshead speed of 1 mm/min. Data were analyzed with two-way ANOVA and t-test. Results. The mean bond strengths of the posts cemented in matched-size spaces for SE and SA groups were 4.02±1.6 and 4.12±2.3 MPa, respectively. For posts cemented in oversized spaces, the values were 4.9±2.3 and 2.8±1.3 MPa, respectively. In matched-size spaces, there was no significant difference between the two groups. Conclusion. The results of this study suggested that increasing the cement thickness would reduce the bond strength of fiber posts to root dentin when self-adhesive cements are used; however, self-etch adhesives were not affected.

The Effect of BC Sealer, AH-Plus and Dorifill on Push-out Bond Strength of Fiber Post.

INTRODUCTION: Dentinal canal walls are in direct contact with endodontic sealers prior to post space preparation and luting cements after post space preparation. This direct contact may affect the bond strength of intraradicular posts to root dentin. This study aimed to assess the effect of three different sealers on the bond strength of fiber posts to root dentin. METHODS AND MATERIALS: The canals of 56 extracted single-rooted human premolars after selection and decoronation were prepared. For obturation of the canals, specimens were randomly divided into four groups (n=14) according to the type of sealer used in conjunction with gutta-percha: group 1 (control) without any sealer; group 2 with AH-Plus sealer (resin based); group 3 with Dorifill sealer (ZOE-based); and group 4 with BC Sealer (calcium silicate-based). Nine mm-deep post space was prepared in the canal of each specimen. Intraradicular fiber posts were cemented using dual-cure resin cement (Panavia F2.0). Sections of 1 mm thickness were made at the coronal, middle and apical thirds of the post space of each specimen. The push-out bond strength of post to root dentin was measured in a universal testing machine. The data were analyzed using one-way ANOVA and post-hoc Tukey's test. RESULTS: The mean push-out bond strength in the coronal third was significantly lower in Dorifill group compared to AH-Plus (P=0.004). This value was significantly lower in BC Sealer group than AH-Plus (P=0.000) and control group (P=0.03). In middle and apical thirds, the mean push-out bond strength was not significantly different among the four groups (P=0.407, P=0.065, respectively). The mean push-out bond strength was significantly lower in apical than coronal third in AH-Plus group (P=0.001). CONCLUSION: Application of BC Sealer and Dorifill decreased the mean push-out bond strength of intracanal post to root dentin in the coronal third in comparison to AH-Plus.

Computer-Based Technologies in Dentistry: Types and Applications.

During dental education, dental students learn how to examine patients, make diagnosis, plan treatment and perform dental procedures perfectly and efficiently. However, progresses in computer-based technologies including virtual reality (VR) simulators, augmented reality (AR) and computer aided design/computer aided manufacturing (CAD/CAM) systems have resulted in new modalities for instruction and practice of dentistry. Virtual reality dental simulators enable repeated, objective and assessable practice in various controlled situations. Superimposition of three-dimensional (3D) virtual images on actual images in AR allows surgeons to simultaneously visualize the surgical site and superimpose informative 3D images of invisible regions on the surgical site to serve as a guide. The use of CAD/CAM systems for designing and manufacturing of dental appliances and prostheses has been well established. This article reviews computer-based technologies, their application in dentistry and their potentials and limitations in promoting dental education, training and practice. Practitioners will be able to choose from a broader spectrum of options in their field of practice by becoming familiar with new modalities of training and practice.

Single Tooth Replacement Using InCeram Resin Bonded Fixed Partial Denture: A Clinical Report.

This clinical report describes a treatment option for replacement of a missing mandibular anterior tooth using InCeram resin bonded fixed partial denture (RBFPD). The conventional approach for replacing mandibular incisors dictates the placement of either a conventional porcelain-fused-to-metal (PFM) bridge, Maryland bridge, or fiber-reinforced composite veneer bridge and several appearance-related disadvantages have been reported in the use of a prosthesis that incorporates a metal substructure. The InCeram bridge is a minimally invasive restoration and eliminates undesirable incisal graying frequently observed in metal RBFPDs. This method was successfully clinically applied to overcome shortcomings of other approaches that may require a minimal invasive technique to preserve lasting sound tooth structure.

Effect of eugenol-containing and resin endodontic sealers on retention of prefabricated metal posts cemented with zinc phosphate and resin cements.

PURPOSE: The aim of this study was to compare the effects of two endodontic sealers on the retention of posts cemented with zinc phosphate or resin cement. MATERIALS AND METHODS: Crowns of 72 mandibular premolars were removed at the cementoenamel junction. Root canals were prepared and specimens were randomly divided into two groups of 36. In each group, 12 specimens were obturated with gutta percha only; 12 specimens with gutta percha/ZOE sealer and 12 specimens with gutta percha/AH26. In the first group, 10mm Post spaces were prepared with Peeso reamers size 4 and, size 5 stainless steel Paraposts were cemented in with zinc phosphate. In the second group, 10mm Post spaces were prepared with Fiber Lux size 5.5 drills and size 5 Paraposts were cemented with Panavia F2.0. After mounting in resin blocks, posts were pulled out by universal testing machine at 1mm/min and results were analyzed by two-way ANOVA and Dunnett test. RESULTS: Mean forces (in Newtons) required to remove posts cemented with zinc phosphate in canals obturated without sealer, with ZOE, and with AH26 sealers were 270±83, 281±128 and 266±67, respectively; and for posts cemented with Panavia F2.0 were 520±290, 464±212 and 229±108, respectively. Statistical analysis showed that AH26 significantly reduced retention of posts cemented with Panavia F2.0 (p<0.05). CONCLUSION: Different sealers had no significant effect on retention of posts cemented with zinc phosphate. However posts cemented with Panavia F2.0 showed reduced retention in canals obturated with AH26.

The effect of multiple firings on microtensile bond strength of core-veneer zirconia-based all-ceramic restorations.

PURPOSE: Differences in core and veneer coefficients of thermal expansion, firing shrinkage, and speed of increasing and decreasing the temperature may generate stress in veneered all-ceramic restorations. Given the necessity of performing multiple firing cycles to achieve improved contour, color, and esthetics, the purpose of this study was to determine the effect of multiple firing cycles on the microtensile bond strength (MTBS) of zirconia core to the porcelain veneer in zirconia-based all-ceramic restorations. MATERIALS AND METHODS: Thirty blocks (12 × 12 × 4 mm(3)) of semi-sintered zirconia were machined and sintered according to manufacturer's instruction. Specimens were placed in three groups based on the number of firing cycles (4, 6, 8) for the veneering process. After veneering, the specimens were sectioned into microbars with 8 mm length and 1 mm cross-section. Twenty sound microbars in each group were stressed to failure in a microtensile tester machine at 1 mm/min. Fractured specimens were surveyed under a scanning electron microscope and classified as cohesive in core, cohesive in veneer, and mixed. MTBS data were analyzed using one-way ANOVA and Tukey test (p < 0.05). RESULTS: The mean MTBS (MPa) after 4, 6, and 8 firing cycles were 30.33 ± 2.13, 27.43 ± 1.79, and 25.06 ± 1.76, respectively. There was a statistically significant difference between the bond strengths of each of the three groups (p < 0.001). CONCLUSION: Increase in firing cycles decreased MTBS. Most of the failures (90-95%) in all three groups were cohesive in the veneering porcelain and did not change as the number of firing cycles increased.