Fracture strength of preformed zirconia crown and CAD-CAM zirconia, ceramic, and hybrid composite crowns for the restoration of primary molars: An in vitro study.

BACKGROUND: Paediatric-preformed zirconia crowns have been associated with several issues, primarily their inability to be crimped and the need for extensive tooth preparation. Additionally, the capacity to adjust the size, shape, and fit of these crowns is very limited. AIM: To evaluate and compare the fracture strength of four different types of dental crowns intended for paediatric patients. DESIGN: The fracture resistance of four types of paediatric crowns was evaluated using the universal testing machine; freshly extracted primary molars received one of the following: preformed zirconia crowns, custom-made computer-aided design and computer-aided manufacturing (CAD-CAM) zirconia crowns, custom-made CAD-CAM ceramic crowns, and custom-made CAD-CAM hybrid composite crowns. Data were statistically compared using the Kruskal-Wallis test followed by the Bonferroni test, and the level of significance was set at 5%. RESULTS: Results showed that there was a statistically significant difference among the four groups (p < .001). The highest value of fracture force was observed for the milled zirconia crown and the lowest for the prefabricated zirconia. CONCLUSION: The implementation of the CAD-CAM digital crown fabrication technique has the potential to address issues associated with preformed crowns in paediatric patients, particularly in terms of fracture resistance.

Impact of Final Irrigation Protocol on the Push-Out Bond Strength of Two Types of Endodontic Sealers.

Aim: The aim of this study was to assess the impact of the final irrigation protocol on the push-out bond strength of calcium silicate-based sealers when compared to an epoxy resin-based sealer. Materials and Methods: Eighty-four single-rooted mandibular human premolars were shaped using the R25® instrument (Reciproc, VDW, Munich, Germany) and then divided into three subgroups of 28 roots each depending on the final irrigation protocol: EDTA (ethylene diamine tetra acetic acid) and NaOCl activation, Dual Rinse® HEDP (1-hydroxyethane 1,1-diphosphonate) activation or sodium hypochlorite (NaOCl) activation. Then, each subgroup was divided into two groups (14 each) according to the sealer used (AH Plus Jet® or Total Fill BC Sealer®) for single-cone obturation. Dislodgement resistance using a universal testing machine, samples' push-out bond strength and failure mode under magnification were determined. Results: EDTA/Total Fill BC Sealer® showed significantly greater values of push-out bond strength compared with HEDP/Total Fill BC Sealer® and NaOCl/AH Plus Jet®, with no statistical difference with EDTA/AH Plus Jet®, HEDP/AH Plus Jet® and NaOCl/Total Fill BC Sealer®, whereas HEDP/Total Fill BC Sealer® showed significantly lower values of push-out bond strength. The apical third demonstrated higher means of push-out bond strength compared with middle and apical thirds. The most common failure mode was cohesive but showed no statistical difference compared to other types. Conclusions: Irrigation solution and final irrigation protocol affect the adhesion of calcium silicate-based sealers.

Lack of Correlation Between the Penetration of Two Types of Sealers and Interfacial Adaptation to Root Dentine.

OBJECTIVE: This study aimed to determine the correlation between sealer penetration into dentinal tubules and interfacial adaptation to root canal walls using a hydraulic calcium silicate-based sealer, Endosequence Bioceramic Sealer (Brasseler USA, Savannah, GA, USA), and an epoxy resin-based sealer, AH Plus (Dentsply DeTrey, Konstanz, Germany). METHODS: Sixty-four maxillary central incisors were endodontically prepared with nickel-titanium rotary instruments and randomly assigned into two groups (n=32). Roots were filled with gutta-percha using a single-cone technique in conjunction with one of the two sealers, AHP or BCS. Sealers were mixed with Rhodamine B and analysed under a confocal laser scanning microscope. Transverse sections at 5 mm from root apex were obtained. The circumference of the root canal wall was first outlined and measured to determine the circumferential percentage of sealer penetration. The regions along the canal walls where the sealer had penetrated the dentinal tubules were delineated and measured. Then, the outlined distances were divided by the canal circumference. The width of each gap was measured and pooled for each specimen for comparison to determine the interfacial adaptation. The measurements were repeated twice to ensure reproducibility. Mann-Whitney tests were performed to compare continuous variables between AHP and BCS groups. The correlation between gap width and percentage of sealer penetration was investigated using the Spearman correlation coefficient. RESULTS: No significant difference was observed between groups regarding the percentage of sealer penetration (P>0.05) and the gap width (P>0.05). Also, there was no significant correlation between the two variables analysed for AHP (r=0.165; P>0.05) and BCS (r=-0.147; P>0.05) and in the overall sample (r=0.061; P>0.05). CONCLUSION: The present results show no correlation between interfacial adaptation and sealer penetration in dentinal tubules in the total sample and among sealer subgroups. The ability of root canal sealers to penetrate dentinal tubules cannot be considered a sign of better interfacial adaptation.

Effect of 2 Heat-treated Nickel-Titanium Files on Enlargement and Deformation of the Apical Foramen in Curved Canals: A Scanning Electronic Microscopic Study.

INTRODUCTION: The aim of this study was to evaluate under scanning electronic microscopy the enlargement and deformation of the apical foramen of curved mesiobuccal roots with both reciprocating and rotary single-file systems made of a newly heat-treated alloy through the use of Reciproc Blue (REC Blue; VDW, Munich, Germany) and XP-endo Shaper (XPS; FKG Dentaire, La Chaux-de-Fonds, Switzerland). METHODS: Forty mesiobuccal roots of mandibular and maxillary molars presenting a curvature ranging from 20°-40° were used in this study. The apical foramens were initially scanned with a scanning electronic microscope under 200× magnification. Roots were divided into 2 groups (n = 20): the REC Blue group instrumented with the REC Blue system and the XPS group instrumented with the XPS system. Both groups were instrumented at the foramen. The apical foramens were scanned after root canal preparation. The area, circularity, and ratio of the Feret diameters were calculated from each image. The Kolmogorov-Smirnov, Mann-Whitney, and Wilcoxon tests were used for statistical analysis (P ≤ .05). RESULTS: The area of the foramen increased significantly after canal shaping with REC Blue and XPS. The variation of the area was significantly greater with XPS. However, there were no significant differences in circularity and the ratio of the Feret diameters with both instruments. CONCLUSIONS: No transportation was found when using REC Blue and XPS. The newly heat-treated nickel-titanium alloy did not promote deformation of the apical foramen in curved canals.

Influence of the Maxillary Sinus on the Accuracy of the Root ZX Apex Locator: An Ex Vivo Study.

This study evaluated the accuracy of the Root ZX (J. Morita, Tokyo, Japan) electronic apex locator in determining the working length when palatal maxillary molar roots are in a relationship with the sinus. Seventeen human maxillary molars with vital pulp were scheduled for an extraction and implant placement as part of a periodontal treatment plan. The access cavity was prepared, and a #10 K file (Dentsply Maillefer, Ballaigues, Switzerland) was inserted into the palatal root using the Root ZX apex locator in order to determine the electronic working length (EWL); then, the teeth were extracted. To determine the real working length (RWL), a #10 K file was introduced into the root canal until its tip touched a glass plate. EWL and RWL were compared. Images reconstructed with CBCT (cone beam computerized tomography) revealed that eight palatal roots were related to the maxillary sinus, whereas nine were not. The results showed a significant difference between the EWL and the RWL of the palatal roots related to the sinus (p < 0.001). No significant difference was observed in measurements of roots not in contact with the sinus (p > 0.05). Within the study limitations, the reliability of Root ZX was influenced by the relationship of the roots with the maxillary sinus.

Dentinal tubule penetration of AH Plus, BC Sealer and a novel tricalcium silicate sealer: a confocal laser scanning microscopy study.

OBJECTIVES: The aim of this in vitro study was to assess the dentinal tubule penetration of three different sealers, AH Plus, BC Sealer and a novel tricalcium silicate sealer (NTS). MATERIALS AND METHODS: Ninety-six human maxillary central incisors were divided into three experimental groups (n = 32) and were filled with gutta-percha using a single-cone technique in conjunction with one of the three sealers: AH Plus, BC Sealer or NTS. The roots in each group were cross-sectioned at 1 and 5 mm from the root apex, and the surfaces were examined under confocal laser scanning microscopy (CLSM). The sealer penetration depths were measured at their maximum depths and at four circumferential depths (12, 3, 6 and 9 o'clock) and were evaluated using ImageJ software (ImageJ, NIH). RESULTS: The maximum and mean penetration depths were significantly higher at 5 mm compared to 1 mm from the apex in the AH Plus (p < 0.001), BC Sealer (p < 0.001) and NTS groups (p < 0.001). No significant difference was observed between the groups at 1 mm for both parameters. The maximum and mean penetration depths were significantly lower at 5 mm for AH Plus compared with the other two groups (p = 0.012). CONCLUSIONS: Within the study limitations, the BC Sealer and NTS demonstrated better tubule penetration results than the AH Plus sealer. CLINICAL RELEVANCE: Although no study has confirmed a relationship between the penetration depth of root canal sealers and the prevention of apical periodontitis, dentinal tubule sealer penetration may improve obturation quality.

Influence of the EndoActivator Irrigation System on Dentinal Tubule Penetration of a Novel Tricalcium Silicate-Based Sealer.

This study compared the effects of a conventional endodontic needle with an agitation system on a novel tricalcium silicate-based sealer (NTS) in terms of dentinal tubule penetration and interfacial adaptation to a root canal. Fifty single-rooted, recently-extracted human maxillary central incisors were randomly distributed into two homogeneous groups characterized by two different final cleansing systems: Conventional endodontic needle, or EndoActivator®. After instrumentation, all the teeth were filled with the gutta-percha single cone technique in conjunction with the novel tricalcium silicate-based sealer. Teeth were horizontally sectioned at 1 and 5 mm from the apex and were observed under a confocal laser scanning microscope (CLSM) at five magnifications. The maximum, mean, and the circumferential percentage of the sealer penetration inside the tubules were measured. Moreover, the gap width was evaluated using Image J software (National Institutes of Health, Bethesda, MD). EndoActivator® did not result in a significantly higher circumferential percentage of sealer penetration than conventional irrigation (p > 0.05). However, the gap width was significantly lower with EndoActivator®, compared to conventional needles at both 1 mm (p = 0.035) and 5 mm (p = 0.038). The EndoActivator® irrigation system did not significantly improve the NTS penetration, as compared to the conventional endodontic needle irrigation. Activation of the irrigation reduced the gap width significantly.