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Purpose: To evaluate the fracture strength of endodontically treated molars filled with different composite resins with vs without fiber reinforcement. Materials and Methods: A total of 60 intact mandibular molars were selected and endodontically treated. A standardized mesio-occlusal-distal cavity was prepared with cervical margins 1 mm above the cementoenamel junction and oral and buccal walls with 1.5-mm thickness. Universal adhesive was used in all specimens in etch-and-rinse mode. Specimens were divided into four groups (n = 15 each) according to restoration technique: group CSM = adhesive overlay with hybrid ceramic; group EXP = direct restoration with short fiber-reinforced composite; group ESU = direct restoration with nanohybrid composite; and group EST = direct restoration with nanohybrid composite reinforced with horizontal bidirectional glass fibers placed over the pulpal chamber floor. After 7 days of storage in water, samples were loaded until fracture using a universal testing machine. The maximum breaking loads were recorded in Newtons, and statistical analysis was then conducted with two-way ANOVA and post hoc Tukey test. Fragments were analyzed using scanning electron microscopy. Results: Mean fracture resistance values were: CSM = 1,428.91 ± 316.90 N; EXP = 1,874.57 ± 299.47 N; ESU = 1,557.44 ± 355.65 N; and EST = 1,870.27 ± 145.11 N. The CSM and EXP groups showed the highest strength values when compared to the other groups. The variable fiber insertion did not significantly alter the fracture resistance. The origin of the fracture was always located on the occlusal surface, mainly in the major contact loading area. Conclusion: The use of fiber-reinforced composite showed great improvement in fracture resistance, similar to a cuspal coverage restoration. However, only short fiber-reinforced composites showed a favorable fracture pattern. [ABSTRACT FROM AUTHOR]

Background: Endodontic ledge (EL) formation is the most common complication of endodontic treatment. Although various etiological factors have been identified, canal curvature is the most significant variable correlated with EL formation. The aim of this micro-computed tomographic (micro-CT) study was to evaluate EL position in the mesial canals of the lower molars in relation to the degree of canal curvature. Methods: Forty intact mandibular first molars with independent mesial canals with 20°–40° primary mesio-distal curvature, 10°–30° buccal-lingual canal curvature and 4 < r ≤ 8 mm main curvature radius were selected. Working length was measured with a K-File #10 and a high resolution pre-operative micro-CT analysis was performed. Ledges were created at the point of maximum canal curvature using stainless steel K-Files #30–35, alternating irrigation with 5% NaOCl and 10% EDTA. A post-operative high-resolution micro-CT analysis was then completed. Pre- and post-operative images were analyzed. The angle (α) formed between the vector passing through the geometric center of the EL and the center of the original canal lumen and the line joining the centers of the mesio-buccal and mesio-lingual canal orifices was calculated, and a descriptive statistical analysis was achieved. The α angle values were analyzed in relation to canal curvature using Kruskal-Wallis and post hoc Dunn's tests. The level of significance was set at P < 0.05. Results: The α angles appeared inversely proportional to canal curvatures in the buccal-lingual and mesio-distal projections. The mean α angle was 36.4° (standard deviation 10.64; 95% confidence interval 34.1–40.9). Conclusion: Within the limitations of this study, endodontic ledges develop in the opposite direction to the three-dimensional canal curvature and their position is influenced by the degree of curvature. Clinically, the α angle values may be related to the recommended direction to manage endodontic ledges. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the shaping ability of a modified ProTaper Next technique (PTNm) with that of TruNatomy (TN) in lower molars mesial curved canals using micro-computed tomography (Micro-CT). Sixty mesial canals of first mandibular molars were randomly assigned between two groups (n = 30). After canal scouting with K-File #10, glide path and shaping were carried out with TN or PTNm systems. The PTNm sequence consists of ProGlider, followed by ProTaper Next X1 and apical finishing with NiTiFlex #25 up to working length (WL) to ensure adequate apical cleaning. Samples were scanned using micro-CT and pre- and post-shaping volumes were matched to analyse geometric parameters: the volume of removed dentin; the difference of canal surface; centroid shift, minimum and maximum root canal diameters; cross-sectional areas; the ratio of diameter ratios (RDR) and the ratio of cross-sectional areas (RA). Measurements were assessed 2 mm from the apex and in relation to the middle and coronal root canal thirds. Data were analysed using ANOVA (p < 0.05). No statistically significant differences were found between the groups for any parameter at each level of analysis, except for RA at the coronal level (p = 0.037). The PTNm system showed the tendency to enlarge more in the coronal portion with a lower centroid shift at apical level compared with TN sequence (p > 0.05). Both PTNm and TN sequences demonstrated similar maintenance of original anatomy during the shaping of lower molar mesial curved canals. [ABSTRACT FROM AUTHOR]

The shaping outcomes after instrumentation with rotary and reciprocating glide path and shaping systems were evaluated through micro-computed tomography (Micro-CT). Thirty extracted maxillary first molars were selected. Mesio-buccal canals were randomized into two groups (n = 15): rotary system ProGlider and ProTaper Next X1, X2 (PG-PTN) and reciprocating system WaveOne Gold Glider and WaveOne Gold Primary (WOGG-WOG). Specimens were micro-CT scanned before, after glide path and after shaping. Increase in canal volume and surface area, percentage of removed dentin from the inner curvature, centroid shift and canal geometry variation through ratio of diameter ratios (RDR) and ratio of cross-sectional areas (RA) were measured in the apical and coronal levels and at the point of maximum curvature. The number of pecking motions needed to reach the working length (WL) was recorded. One-way ANOVA and post hoc Turkey–Kramer tests were used (p < 0.05). Post-glide path analysis revealed that in the coronal third, RDR was more favorable to PG and centroid shift was lower for WOGG in the apical third. Post-shaping analysis showed a reduced removal of dentin and a more favorable RA for PTN at point of maximum curvature. The number of pecking motions up to WL resulted in different between groups both for glide path and shaping phases. Despite a higher dentin removal for reciprocating instruments at the point of maximum curvature, both systems seemed to produce well-centered glide path and shaping outcomes. Rotary and reciprocating systems seemed able to respect the original canal anatomy. [ABSTRACT FROM AUTHOR]

To measure the thickness homogeneity of Invisalign (Align Technology Inc, San José, Calif) aligners with micro-computed tomography (micro-CT) scans. Starting from micro-CT scanning of 20 different aligners, multiplanar reconstructions were obtained. An orthodontist blinded about the study measured aligner thickness in different regions (molar, canine, incisor) and in different sites (gingival–buccal, buccal, occlusal, lingual, and gingival–lingual). To assess various thicknesses in different aligner sites and regions, the sample was stratified into subgroups and linear regression analysis was performed. Descriptive analysis showed that mean thickness of aligners in the incisor region ranged from 0.582 mm to 0.639 mm, in the canine region from 0.569 mm to 0.644 mm, and in the molar region from 0.566 mm to 0.634 mm. Student's t-tests showed no significant differences in the aligner thickness of different regions when data were stratified by different sites. Student's t-tests showed significant differences in thickness homogeneity for the molar region when the data were stratified by tooth (mean difference = 0.068 mm; 95% confidence interval, 0.009–0.126 mm; P =.024). Invisalign aligner thickness is characterized by small differences. The only significant difference was revealed in the molar region where thickness of the gingival–lingual edge is significantly thinner than that measured at the occlusal aspect. From a clinical perspective, the results of the present study could be considered to explain the reduced predictability of several orthodontic tooth movements in the molar region. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate 3D interfacial behavior, occlusal wear, and fracture resistance of endodontically treated molars restored with a full-crown restoration made with 2 different CAD/CAM materials after chewing simulation. Materials and Methods: 24 sound molars were selected and endodontically treated, shaped with PathFile and ProTaper Next (Dentsply Sirona) and filled using a warm condensation technique. Then a standardized MOD cavity was prepared and a fiber post (Panavia Post, Kuraray) supported build-up was performed. A standardized preparation for a complete crown with chamfer margin was done. Samples were then divided into two groups, according to restorative material: G1: zirconia-reinforced lithium silicate (Celtra DUO, Dentsply); G2: cubic zirconia (Katana, Kuraray). Preparations were scanned with Cerec Omnicam and restorations were milled with Cerec MXCL. The restorations were then luted (Panavia V5, Kuraray) following the manufacturer's instructions. After 7 days, the following tests were performed: micro-CT scan (Skyscan, Bruker); optical scan (Sinergiascan, Nobimetal). Fatigue and fracture resistance testing was performed with a chewing simulator (CS4.4, SD-Mechatronik). Thereafter, static fracture was tested using a universal testing machine (Instron) with a 6-mm-diameter steel sphere crosshead welded to a tapered shaft and applied to the specimens at a constant speed of 0.5 mm/min and an angle of 30 degrees to the long axis of the tooth. The load was applied perpendicular to the triangular crest of the palatal cusp. Samples were loaded until fracture; the maximum breaking loads were recorded in Newton (N). Each sample was scanned, radiographically and optically, before and after chewing. Data were imported into Mimics after smoothing and region growing; only external gaps were considered in the analysis. The STL optimal quality masks obtained were imported into Geomagic software for noise removal and volume calculation. Interfacial gap progression and occlusal wear data, expressed in mm3, and fracture resistance, expressed in N, were collected and statistically analyzed with two-way ANOVA (α < 0.05). Results: G1 showed a mean gap size of 0.43 mm3, while G2 had 0.39 mm3. Two-way ANOVA showed that interfacial gaps were not influenced by the material employed (p = 0.0674). Concerning the wear rate, lithium silicate showed a much larger volume reduction in mm3 than cubic zirconia (p = 0.00001). Fracture resistance (G1 = 1351,52; G2 = 1136,43) was significantly influenced by the material employed (p = 0.0001). Conclusion: The obtained results showed that cubic zirconia seems to better perform in the restoration of endodontically treated molars. Further studies are necessary to confirm present data. [ABSTRACT FROM AUTHOR]

Introduction Contracted endodontic cavities (CECs) have developed from the concept of minimally invasive dentistry and provide an alternative to traditional endodontic cavities (TECs). They have been designed in an effort to preserve the mechanical stability of teeth. The contracted cavity design preserves more of the dentin but may influence the geometric shaping parameters. The aim of this micro–computed tomographic study was to evaluate the influence of contracted endodontic cavities on the preservation of the original root canal anatomy after shaping with nickel-titanium rotary instruments. Methods Thirty extracted human mandibular molars with fully formed apices and independent mesial canals were randomly assigned to group 1 (TEC) and group 2 (CEC). Each group was shaped using ProGlider (Dentsply Maillefer, Ballaigues, Switzerland) and WaveOne Gold (Dentsply Maillefer). Irrigation was performed with 10% EDTA and 5% sodium hypochlorite. Samples were scanned before and after canal shaping to match canal volumes (SkyScan; Bruker microCT, Kontich, Belgium [100 kV, 100 μA, and 15-μm resolution]), and images were analyzed to evaluate canal volumes, surface areas, and centroid shift on cross sections at −1 mm and −3 mm from the apex. Results TECs showed a greater preservation of the original root canal anatomy with less apical transportation than CECs, possibly because of the absence of coronal interferences and, therefore, fewer pecking motions required to complete instrumentation. Conclusions Within the limitations of this study, TECs may lead to a better preservation of the original canal anatomy during shaping compared with CECs, particularly at the apical level. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate 3D interfacial behavior, occlusal wear, and fracture resistance of endodontically treated molars restored with an adhesive overlay with 2 different CAD/CAM materials after chewing simulation. Materials and Methods: 24 molars were selected and endodontically treated. Subsequently, a standardized MOD cavity was prepared, and a buildup was performed (Clearfil Majesty ES-2, Kuraray) after adhesive application (Clearfil SE Bond 2, Kuraray). A standardized overlay preparation was made. Samples were then divided in two groups, according to restorative materials: G1: Zirconia-reinforced lithium silicate (Celtra DUO, Dentsply); G2: Cubic zirconia (Katana, Kuraray). Preparations were scanned with Cerec Omnicam and restorations were milled with Cerec MXCL (Sirona). Restorations were then luted (Panavia V5, Kuraray) following the manufacturer instructions. After 7 days, the following tests were performed: 1. micro-CT scan (Skyscan, Bruker); 2. optical scan (Sinergiascan, Nobimetal); 3. fatigue and fracture resistance were performed with a chewing simulator (CS4.4, SD-Mechatronik). Afterwards, the restorations were subjected to static loading until fracture using a universal testing machine (Instron) with a 6-mm-diameter steel sphere crosshead welded to a tapered shaft and applied to the specimens at a constant speed of 0.5 mm/min at an angle of 30 degrees to the long axis of the tooth. The load was applied perpendicular to the triangular crest of the palatal cusp. Samples were loaded until fracture, and the maximum breaking loads were recorded in Newton (N). Each sample was scanned, radiographically and optically, before and after chewing. Data were imported into Mimics after smoothing and region growing; only external gaps were considered in the analysis. The STL optimal quality masks obtained were imported into Geomagic software for noise removal and volume calculation. Interfacial gap progression and occlusal wear data, expressed in mm3, as well as fracture resistance, expressed in N, were collected and statistically analyzed with two-way ANOVA (α = 0.05). Results: Two-way ANOVA showed that interfacial gap formation was not influenced by the material employed (p = 0.0657). Concerning the wear rate, lithium silicate showed a much larger volume reduction than cubic zirconia. Considering fracture resistance of overlays, there was no difference between the two materials (p = 0.0578). Conclusion: The obtained results showed that the restoration of endodontically treated molars with bonded overlays could be performed equally well with either lithium silicate or cubic zirconia. Further studies are necessary to confirm the present results. [ABSTRACT FROM AUTHOR]

Introduction The aim of this micro–computed tomography study was to describe the shaping properties of ProGlider/ProTaper Next (PG/PTN) and ScoutRace/BioRace (SR/BR) nickel-titanium rotary systems. Methods Thirty maxillary first permanent molars were selected. Mesiobuccal canals were randomly assigned ( n = 15) to PG/PTN or SR/BR groups. Irrigation was performed with 5% NaOCl and 10% EDTA. Specimens were scanned (voxel size, 9.1 μm) for matching volumes and surface areas and post-treatment analyses. Root canal centering ability, canal geometry enlargement, and thickness of dentinal wall at inner curvature were assessed at apical level and point of maximum curvature. Results were analyzed with 4 one-way analyses of variance. Results Canal centering ability was superior in PG/PTN ( P = .006 at apical level, P = .025 at point of maximum curvature). PG/PTN demonstrated a more conservative increase of canal areas ( P = .027 at apical level, P = .038 at point of maximum curvature). Centrifugal increase in canal diameters did not significantly differ between groups ( P = .65 at apical level, P = .61 at point of maximum curvature). Inner dentinal wall thickness was less reduced with PG/PTN compared with SR/BR, with no statistical differences ( P = .23 at point of maximum curvature, P = .89 at apical level). PG/PTN shaping taper ranged between 6% and 7%. Conclusions Neither system produced significant shaping errors in curved canals. PG/PTN system showed better preservation of canal anatomy. PTN offset section did not influence final preparation taper. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: X-ray computed micro-tomography scanning allows high-resolution 3-dimensional imaging of small objects. In this study, micro-CT scanning was used to compare the ability of manual and mechanical glide path to maintain the original root canal anatomy. Methods: Eight extracted upper first permanent molars were scanned at the TOMOLAB station at ELETTRA Synchrotron Light Laboratory in Trieste, Italy, with a microfocus cone-beam geometry system. A total of 2,400 projections on 360° have been acquired at 100 kV and 80 μA, with a focal spot size of 8 μm. Buccal root canals of each specimen (n = 16) were randomly assigned to PathFile (P) or stainless-steel K-file (K) to perform glide path at the full working length. Specimens were then microscanned at the apical level (A) and at the point of the maximum curvature level (C) for post-treatment analyses. Curvatures of root canals were classified as moderate (≤35°) or severe (≥40°). The ratio of diameter ratios (RDRs) and the ratio of cross-sectional areas (RAs) were assessed. For each level of analysis (A and C), 2 balanced 2-way factorial analyses of variance (P < .05) were performed to evaluate the significance of the instrument factor and of canal curvature factor as well as the interactions of the factors both with RDRs and RAs. Results: Specimens in the K group had a mean curvature of 35.4° ± 11.5°; those in the P group had a curvature of 38° ± 9.9°. The instrument factor (P and K) was extremely significant (P < .001) for both the RDR and RA parameters, regardless of the point of analysis. Conclusions: Micro-CT scanning confirmed that NiTi rotary PathFile instruments preserve the original canal anatomy and cause less canal aberrations. [Copyright &y& Elsevier]

To evaluate shear stress (SS) and normal pressure (NP) at the tooth-restoration interface of highly-filled flowable resin composite applied to deep margin elevation technique through FEM analysis generated by a microCT scan. A reference maxillary molar with two class II cavities was prepared according to deep margin elevation protocol. A geometrical model was segmented from a micro-CT scan generating separate volumes of enamel, dentin and restorative materials. The 3D Finite Element (FE) model was subsequently built-up and an axial chewing load was simulated. Data concerning the tooth-restoration interface were analyzed in terms of SS and NP. Different materials and techniques were tested in order to evaluate the effects of the restorative material, the usage of a highly-filled flowable composite as liner and the substrate of the cervical area. Both SS and NP presented similar distribution, but showed significant differences between tested materials. Composites showed more homogeneous behavior in stress distribution compared to ceramic. The use of a highly-filled flowable composite as liner on the cervical margin significantly reduced SS and NP on the cavity floor and the cervical margin area. Lastly, stress distribution in the cavity floor area varied according to the cervical margin substrate: enamel showed a protective role in stress distribution. Highly-filled flowable resin composites showed encouraging results when applied to deep margin elevation from an interfacial mechanical point of view. Further studies are needed to validate these data and to better define the role of cervical enamel in stress distribution. • Micro-CT can be used to create a realistic finite element model of the tooth-restoration complex. • Highly-filled flowable resin reduced shear and normal pressure stresses on the cavity floor. • Shear and normal pressure stresses presented similar distributions, being influenced by the different materials. • Resin-based materials showed a more homogeneous behavior in stress distribution compared to ceramic. [ABSTRACT FROM AUTHOR]

Abstract: Objectives: The aim of this study was to investigate the influence of post placement on fracture resistance of endodontically treated mandibular molars restored with adhesive overlay restorations. Methods: Endodontically treated human molars with two- and one-wall cavities either underwent or did not undergo fibre post insertion within composite build-up before cementation of indirect composite onlay restorations. The specimens were thermocycled, exposed to cyclic loading, and submitted to the static fracture resistance test. Fracture loads and mode of failure were evaluated. Results: Statistical analysis revealed that specimens with fibre posts demonstrated similar failure loads (p =0.065) but more favourable fracture patterns compared with specimens without fibre posts. No difference was found between two- and one-wall cavities. Conclusions: Within the limitations of this study, the insertion of fibre posts did not improve support under indirect composite overlays. Clinical significance: When restoring heavily broken down endodontically treated mandibular molars with an indirect overlay composite restoration, the fibre post inserted within the composite build-up do not provide any increase in fracture resistance. [Copyright &y& Elsevier]