Effect of material types on the fracture resistance of maxillary central incisors restored with CAD/CAM post and cores.

AIM: To evaluate the fracture resistance and failure pattern of endodontically treated teeth with post and cores made of different CAD/CAM materials in comparison with cast post and cores. MATERIALS AND METHODS: A total of 40 maxillary central incisors were divided into four groups. Post and cores were fabricated using the following materials: fiber-reinforced composite, high-density polymer, polymer-infiltrated ceramic network, and nonprecious metal alloy as a control group. Specimens were covered with lithium disilicate crowns and subjected to thermomechanical cyclic loading followed by fracture resistance testing until failure. One-way ANOVA followed by Bonferroni multiple comparison tests were used to determine significant differences between the four groups. The significance level was set at 0.05. 3D finite element analysis was then performed, and results were analyzed based on the von Mises stress distribution criteria and the maximum principal stress for the possible failure areas. RESULTS: No statistically significant differences were found in the fracture resistance between the four groups. In terms of unrestorable failures, no significant differences were found among the tested groups. CONCLUSION: The tested post and cores have comparable fracture resistance to that of metallic cast post and cores in the anterior region. CLINICAL SIGNIFICANCE: Post and cores made of CAD/CAM materials offer an acceptable alternative for the restoration of anterior teeth.

Marginal and Internal Adaptation of Lithium Disilicate Endocrowns Fabricated By Heat-Pressable and Subtractive Techniques.

PURPOSE: To evaluate and to compare the marginal and the internal fit of milled (MLE) and heat-pressed lithium disilicate endocrowns (PLE). MATERIALS AND METHODS: Thirty mandibular molars were prepared following the circumferential butt margin endocrown preparations; the cervical margin is parallel to the occlusal surface without ferrule design. A digital scan of molars was made using an intraoral digital scanner. The samples were separated into two groups (n = 15 per group); MLE: endocrowns were milled using LDS blocks and a 5-axis milling machine, PLE: endocrowns were heat-pressed using lost wax technique and LDS ingots. Marginal and internal adaptation were assessed using a replica technique and a stereomicroscope, selecting 32 measurements on each endocrown. Data were analyzed with one-way repeated measures ANOVA, two-way repeated measures ANOVA, student's t-test and paired student t-test (α = 0.05). RESULTS: Statistically significant interactions were recorded between fabrication technique and region (p < 0.05), F (1.97, 27.69) = 5.462. Group MLE displayed significantly smaller gaps than PLE in all regions (p < 0.001). The largest gap was observed at the pulpal floor in both groups. The internal gap was significantly larger than the marginal gap in MLE group (p < 0.001), while no statistically significant difference was observed in PLE group (p = 0.082). CONCLUSION: Heat-pressed and milled lithium disilicate endocrowns are clinically suitable, but the milled technique displayed a better fit than heat-pressed technique when marginal and internal adaptation were examined.

Alveolar Ridge Preservation in the Esthetic Maxillary Zone: Tuberosity Punch Technique of Gingiva and Bone: A Pilot Study.

AIM: This paper aims to present an alveolar ridge preservation technique, using an autologous punch formed of hard and soft tissues harvested from the tuberosity area. MATERIALS AND METHODS: Ten residual sockets in the anterior maxilla were filled with a punch of hard and soft tissues harvested from the tuberosity area. Clinical and radiographical data were collected at the surgical extraction time 0 (T0) and 5 months during implant placement (T1), from clinical and radiological measurements using cone-beam computed tomography scans and periapical radiographs. Core biopsy was harvested during implant placement for histological and histomorphometrical analysis. RESULTS: Clinically, the alveolar ridge presented a mean width of 10.3 mm before extraction which decreased to 8.85 mm at T1, where the mean horizontal loss is 1.45 mm (standard deviation [SD] 1.03 mm). The initial ridge mean height was 11.25 mm and increased to 12.85 mm after 5 months, where the mean vertical gain is 1.6 mm (SD 0.65 mm). The radiological evaluation shows a reduction in the horizontal dimension with a mean of 1 mm; however, the sockets show stability in the vertical dimensions. Histology showed a new lamellar bone formation with some areas of woven bone. Histomorphometric analysis showed that the percentage of new bone formed was 42.44 ± 5.54% and 48.62 ± 8.66% of the connective tissue and 8.94 ± 5.28% of the residual autogenous bone. CONCLUSION: At T1, the extraction sockets showed significantly lower vertical and horizontal bone changes, compared to T0. The described preservation punch technique resulted in greater stability in the horizontal and vertical dimensions after 5 months. CLINICAL SIGNIFICANCE: Clinical and radiological results show that the punch of hard and soft tissue graft reduces hard and soft tissue dimensional alteration after tooth extraction. In addition, using autogenous bone showed histological new bone formation.

Orthodontic Treatment Effect on Inclination of Maxillary Incisors and Growth Axes in Adult Patients with Various Mandibular Divergent Patterns.

AIM: To evaluate, in an adult population, the effect of orthodontic treatment on the inclination of maxillary incisors, facial, and growth axes in different mandibular divergence pattern. In addition, we aimed to determine if there is an association between the inclination of the maxillary incisors and facial and growth axes and if this association will change after orthodontic treatment. MATERIALS AND METHODS: Two-hundred and thirty-eight consecutive lateral cephalograms (119 at T1 and 119 at T2) of adult patients with an average age of 26.45 ± 9.11 years at T1 and 29.58 ± 9.36 at T2 were selected and digitized. Cephalometric maxillary incisors (I) inclination was measured to cranial base (SN), palatal plane (PP), nasion-A point (NA), nasion-basion (NBa), and true horizontal (H). Facial (FA) and growth (GA) axes' inclinations were measured relative to NBa and H. The sample was stratified in three subgroups based on cephalometric mandibular divergence to anterior SN (MP/SN). A-Hypodivergent = MP/SN ≤27° (n = 28); B-Normodivergent = 27 < MP/SN < 37° (n = 49); C-Hyperdivergent = MP/SN ≥37° (n = 42). Associations were tested using Chi-square tests for categorical data. Paired sample t-tests and Pearson's correlation were computed for continuous data. RESULTS: At T1, there was a tendency to have more proclined I in group A (I/SN = 105.59 ± 10.8°) and more retroclined in group C (I/SN = 99.06 ± 12.04°) with no statistical significance. However, at T2, maxillary incisors were statistically significant different between groups A and C (p = 0.002). Pre-treatment FA and GA were statistically significantly different among the three divergence groups (p <0.0001) with more increased angles in the group A (FA/Nba = 92.77 ± 5.07°) vs group C (FA/Nba = 86.28 ± 5.08°). This angle increases around 2° on average at posttreatment assessment (group A-p = 0.033; group B-p = 0.002). Correlations between I and facial/growth axes were not statistically significant at T1, whereas at T2 those correlations were higher and statistically significant between I/PP to FA/NBa (r = 0.408; p ≤0.0001). CONCLUSION: Correlations between the maxillary incisors' inclination and the facial/growth axes were not statistically significant initially whereas after orthodontic treatment, those correlations were higher and statistically significant. Differences in FA existed between pre- and postorthodontic groups in all divergence groups. CLINICAL SIGNIFICANCE: Orthodontists should assess the inclination of the maxillary incisors, not only to the maxilla and anterior SN but also to FA and take it into consideration in their treatment objectives.

Fracture Resistance of Three-unit Fixed Dental Prostheses Fabricated with Milled and 3D Printed Composite-based Materials.

AIM: To evaluate the fracture resistance of three-unit fixed dental prosthesis (FDP) made of composite, high-density polymers (HDP), fiber-reinforced composite (FRC), and metal-ceramic (MC) using different fabrication methods. MATERIALS AND METHODS: A typodont model was prepared to receive a three-unit FDP replacing a missing second maxillary premolar. The prepared model was digitally scanned using an intraoral scanner (Trios3, 3Shape, Denmark). In total, 60 FDPs were fabricated and divided into four groups (n = 15) according to the materials and fabrication method: the subtractive method was used for the FRC (Trilor, Bioloren, Italy) and the HDP (Ambarino, Creamed, Germany) groups; the HDP group was monolithic, whereas the FRC group was layered with a nanocomposite (G-aenial Sculpt, GC). The additive method was used for the 3D printed (3DP) nanocomposite (Irix Max, DWS, Italy) and the Cr-Co (Starbond CoS powder 30) infrastructure of the MC groups. The FDPs were adhesively seated on stereolithography (SLA) fabricated dies. All samples were subjected to thermomechanical loading and fracture testing. The data for maximum load (N) to fracture was statistically analyzed with one-way analysis of variance (ANOVA) followed by Games-Howell post hoc test (α = 0.05). RESULTS: The MC group reported the highest fracture resistance with a statistically significant difference (2390.87 ± 166.28 N) compared to other groups. No significance was noted between 3DP and HDP groups (1360.20 ± 148.15 N and 1312.27 ± 64.40 N, respectively), while the FRC group displayed the lowest value (839.07 ± 54.30 N). The higher frequency of nonrepairable failures was observed in the MC and FRC groups, while HDP and 3DP groups reported a high frequency of repairable failures. CONCLUSION: Significant differences were found in fracture resistance between the tested groups. The load-bearing capacity of the composite-based FPDs exceeded the range of maximum chewing forces. CLINICAL SIGNIFICANCE: 3D printed and milled composite-based materials might offer a suitable solution for the fabrication of FPDs.

Effect of different CAD-CAM materials on the marginal and internal adaptation of endocrown restorations: An in vitro study.

STATEMENT OF PROBLEM: Recent resin-based and ceramic-based computer-aided design and computer-aided manufacturing (CAD-CAM) materials have been used to restore endodontically treated teeth. Adaptation of the restoration is important for clinical success, but studies evaluating the effect of these materials on the adaptation of endocrowns are lacking. PURPOSE: The purpose of this in vitro study was to evaluate the effect of resin-based and ceramic-based materials on the marginal and internal adaptation of endocrowns. MATERIAL AND METHODS: Forty mandibular molars were divided into 4 groups (n=10); each group was restored with a different CAD-CAM material: group C: hybrid nanoceramic (Cerasmart; GC Corp), group T: fiber-composite material (Trilor; Bioloren Srl), group E: lithium disilicate glass-ceramic (IPS e.max CAD; Ivoclar Vivadent AG), and group V: zirconia-reinforced lithium silicate glass-ceramic (Vita Suprinity; VITA Zahnfabrik GmbH). A digital scan was made with an intraoral digital scanner (TRIOS 3; 3Shape A/S), and endocrowns were milled with a 5-axis milling machine (Coritec 250i; imes-icore GmbH). The replica technique and a stereomicroscope (×70) were used to measure the marginal and internal adaptation of the endocrowns at 32 points. All data were statistically analyzed using 1-way ANOVA and the Tukey honestly significant difference test (α=.05). RESULTS: Statistical tests showed significant differences among the tested groups (P<.001). The resin-based groups displayed larger discrepancies than the ceramic-based groups. The resin-based groups showed a mean marginal gap larger than the mean internal gap C (P=.009), T (P<.001), whereas the ceramic-based groups showed similar gaps, V (P=.396), E (P=.936). The largest gap was observed at the pulpal floor (P<.001). CONCLUSIONS: All materials had clinically acceptable internal and marginal gaps (≤150 µm), except for the marginal gap of the Trilor group.

Effect of material thickness on the fracture resistance and failure pattern of 3D-printed composite crowns.

AIM: To evaluate the fracture resistance and failure pattern of 3D-printed and milled composite resin crowns as a function of different material thicknesses. MATERIALS AND METHODS: Three typodont tooth models were prepared to receive a full coverage composite resin crown with different thicknesses (0.5, 1.0, and 1.5 mm). The prepared master casts were digitally scanned using an intraoral scanner, and the STL files were used to fabricate 60 nanocomposite crowns divided into two groups according to the material thickness (n = 10) and fabrication method: a 3D-printed group (3D) using an SLA printer with nanocomposite, and a milled group (M) using a milling machine and composite blocks. All crowns were adhesively seated on stereolithography (SLA)-fabricated dies. All samples were subjected to thermomechanical loading and fracture testing. The load to fracture [N] was recorded and the failure pattern evaluated. Data were statistically analyzed using a two-way ANOVA followed by a Bonferroni post hoc test. The level of significance was set at α = 0.05. RESULTS: The 3D group showed the highest values for fracture resistance compared with the milled group within the three tested thicknesses (P < 0.001). The 3D and M groups presented significantly higher load to fracture for the 1.5-mm thickness (2383.5 ± 188.58 N and 1284.7 ± 77.62 N, respectively) compared with the 1.0-mm thickness (1945.9 ± 65.32 N and 932.1 ± 41.29 N, respectively) and the 0.5-mm thickness, which showed the lowest values in both groups (1345.0 ± 101.15 N and 519.3 ± 32.96 N, respectively). A higher incidence of irreparable fractures was observed for the 1.5-mm thickness. CONCLUSION: 3D-printed composite resin crowns showed high fracture resistance at different material thicknesses and can be suggested as a viable solution in conservative dentistry.

Adaptation of Complete Denture Base Fabricated by Conventional, Milling, and 3-D Printing Techniques: An In Vitro Study.

AIM: The aim of this study was to compare the adaptation of complete denture base (CDB) manufactured by three different techniques: conventional, milling, and three-dimensional (3-D) printing. MATERIALS AND METHODS: A master cast was duplicated to create 60 gypsum casts. Twenty casts (n = 20) were attributed to each group. In the computer-aided design and computer-aided manufacturing (CAD/CAM) groups (milling and 3-D printing), the 40 gypsum casts reserved for these two groups were scanned. An STL file was obtained and a master CDB was designed and then fabricated according to each technique. In the conventional group, a polyvinyl siloxane putty mold was obtained from the milled CDB, and this mold was used to fabricate 20 conventional denture bases by compression molding using the silicon-gypsum technique in a bronze flask. The inner surfaces of the obtained 60 CDB were scanned and superimposed over their corresponding master cast. Deviation analyses were calculated using digital subtraction technique. Five functional areas (posterior palatal seal, anterior border seal, crest of the ridge, maxillary tuberosities, and palate) were selected to evaluate the variations in CBD adaptation. RESULTS: Based on the results and color maps of all selected regions, milling technique offers the best adaptation. The crest of ridge in the conventional technique showed the least adaptation and the posterior palatal seal in the 3-D printing technique showed the best adaptation. CONCLUSION: Within the limitations of this study, the CAD/CAM fabrication techniques seem to offer better adaptation of CDB compared to the conventional fabrication technique. Milled CDBs presented the most homogeneous distribution of adaptation, yet the 3-D printing process seems a promising techniques that needs to be addressed and perfected. CLINICAL SIGNIFICANCE: The CAD/CAM technologies can help overcome many limitations related to conventional impressions and therefore should be well investigated to improve the edentulous patient's quality of life.

Evaluation of the Adaptation of Complete Dentures Fabricated Using Intraoral Scanning and Conventional Techniques.

AIM AND OBJECTIVE: This study aimed to digitally analyze the 3-dimensional variations existing between conventional impressions and intraoral scans made in edentulous maxillae. MATERIALS AND METHODS: Ten (n = 10) edentulous maxillae of patients seeking a maxillary complete denture were scanned using an intraoral scanner. The same participants were subject to the conventional impression procedure for the fabrication of maxillary complete dentures. The dentures' intaglio surfaces were scanned and superimposed over their corresponding IOS files with a 2-base best-fit alignment. Deviation analyses were calculated using the digital subtraction technique. Four anatomical regions were preselected to evaluate the deviations at these sites (posterior palatal seal, anterior border seal, the crest of the ridge and palate). RESULTS: Based on the results and color maps of all selected regions, the overall difference between the two scans [IOS and denture intaglio surface scanning (DISS)] was not significant. The IOS technique allowed for predictable outcomes of treatment compared to those observed with conventional impression. The palatal area seems to be the region with the least deviation, while the highest incidence of discrepancy was reported in the anterior border seal. CONCLUSION: Within the limitations of this study, the IOS technique allowed the capturing of intraoral tissues and their immediate interpretation and transfer to a designing software making the impression procedure faster and easier. CLINICAL SIGNIFICANCE: The computer-aided design (CAD)/computer-aided manufacturing (CAM) technologies can help overcome many limitations related to conventional impressions and therefore should be well investigated to improve the edentulous patient's quality of life.

Fracture resistance and failure modes of endocrowns manufactured with different CAD/CAM materials under axial and lateral loading.

OBJECTIVES: The purpose of this in vitro study was to evaluate the fracture resistance and failure modes of endocrowns made of three computer-aided design/computer-aided manufacturing (CAD/CAM) materials subjected to thermo-mechanical cycling loading. MATERIALS AND METHODS: Eighty mandibular molars were divided into four groups (n = 20): one (C E) was restored with lithium disilicate glass-ceramic conventional crowns, three were restored with endocrowns made of three different CAD/CAM materials; (E E) lithium disilicate glass-ceramic, (E V) zirconia-reinforced lithium silicate glass-ceramic, and (E C) resin nano-ceramic. After cycling loading, half of the samples from each group were loaded axially and the other half was loaded laterally. Fracture resistance was recorded in Newton (N) and failure modes were classified. Two-way ANOVA, Bonferroni post hoc (α = .05), Chi-square, and multiple logistic regression tests were used to analyze data. RESULTS: Statistically significant interaction were recorded between fracture resistance (N) and loading (P < .001), and groups (conventuional crown and endocrowns; P < .001). Endocrowns presented higher fracture strength than conventional crowns. Fracture resistance was significantly larger under axial loading. The numbers of irreparable failures were extremely important in the endocrowns groups (Groups E E, E V, E C), and only conventional crowns (Group C E) showed almost no irreparable failures under axial loading. CONCLUSION: Lithium disilicate glass-ceramic recorded the highest fracture resistance under axial and lateral loading. CLINICAL SIGNIFICANCE: The number of irreparable failures with all endocrown materials tested do not suggest yet the use of this type of restorations in posterior teeth.

Marginal and internal fit of CAD/CAM fiber post and cores.

AIM: To evaluate the marginal adaptation and internal fit of milled fiber post and cores using different scanning methods. MATERIALS AND METHODS: Thirty typodont tooth models (Nissin) with pulp cavity were endodontically treated and prepared to receive 30 fabricated fiber post and cores. Three different methods of scanning were used (n = 10): an intraoral scanner (IOS) (Trios 3; 3Shape) to directly digitalize the post space (Group T) and a laboratory scanner to indirectly digitalize the resin pattern (Group RP) and the silicone impression (Group S) of the post space. All the specimens were examined using an optical microscope for the measurement of the vertical marginal discrepancy (VMD), and five in each group were scanned using microcomputed tomography (µCT) for the assessment of the VMD, the internal fit at the corner (IFC), post apex (PA), and at four horizontal cross-sections (CS1-4) inside the canal. All data were analyzed using mixed-design ANOVA, followed by pairwise testing to identify the differences (α = 0.05). RESULTS: Statistical analysis revealed that Group T was associated with the smallest cement space compared with Group RP (P = 0.001) and Group S (P < 0.001) for VMD using µCT or direct microscopy (OM) (P < 0.001). Similarly, the cement space for Group T was smaller than that of Group S (P = 0.039) when measured at the IFC (µCT), and smaller than Group RP (P = 0.025) when measured at CS1-4 (µCT), with CS1 larger than CS3 (P = 0.015). There was no significant difference at PA (P = 0.271). CONCLUSION: Better adaptation was achieved with a complete digital workflow. Scanning the resin pattern or the silicone impression introduced more variables in the digital process or milling of a one-piece fiber post and core.

Effect of Fabrication Technique and Thermal Cycling on the Bond Strength of CAD/CAM Milled Custom Fit Anatomical Post and Cores: An In Vitro Study.

PURPOSE: This study is to investigate the effect of milling custom fit anatomical post and cores from fiber reinforced composite and high-density polymer blocks using CAD/CAM technology on the bond strength to root canal dentin compared with prefabricated fiber posts, and to evaluate the influence of thermal cycling on the push out bond strength of the tested materials. MATERIALS AND METHODS: Eighty extracted single-rooted premolars, endodontically treated and prepared to receive the posts, were randomly divided into four groups (n = 20): BLC: Custom-milled fiber-reinforced composite posts and cores (Trilor, Bioloren), AMC: Custom-milled high-density polymer posts and cores (Ambarino, Creamed), BLP: Prefabricated fiber-reinforced composite posts and composite core buildups (Bioloren; Filtek Bulk Fill Posterior, 3M). The posts used have the same matrix and fiber composition as BLC, RXP: Prefabricated posts and composite core buildups (RelyX fiber post, 3M; Filtek Bulk Fill Posterior); used as a control group. All of the posts were cemented using a self-adhesive resin cement (RelyX U200, 3M). Half of the sample was randomly assigned to thermal cycling in distilled water for 6,000 cycles to simulate aging, while the other half was tested for bond strength without thermal cycling. A push-out test was conducted using a universal testing machine until failure. Bond strength values were calculated in megapascals (MPa). The mode of failure was observed using a stereo microscope. Results were analyzed by two-way ANOVA followed by a Bonferroni post hoc test for comparison. The level of significance was set at p < 0.05. RESULTS: Push-out bond strength was significantly higher (p <0.001) in the CAD/CAM post groups than in the groups with prefabricated posts regardless of the post material, while aging of the teeth did not significantly affect the push-out strength (p = 0.536). Failures were adhesive between cement and dentin for all groups except for AMC, where adhesive failure between the cement and the post was also observed. CONCLUSION: The CAD/CAM manufacturing technique was proved to ameliorate the retention of the post and cores in the root canal. Thermal cycling did not affect the bond strength of the tested groups.

Evaluation of the Adaptation and Fracture Resistance of Three CAD-CAM Resin Ceramics: An In vitro Study.

AIM: The internal fit and resistance to fracture of resin ceramics are to be evaluated compared to that of lithium disilicate as the control group. MATERIALS AND METHODS: Four groups of 20 crowns each (GC Cerasmart, Vita Enamic, Coltène Brilliant Crios, and e.max CAD) were cemented on identical metal dies. Marginal gaps were measured before cementation and load to fracture was applied after cementation, half of each group was thermodynamically aged (3,000 cycles of 5° to 55° immersion followed by 200,000 cycles of 100 N load), finally the crowns were loaded until fracture in a universal testing machine. Statistical package for social sciences (SPSS) package 23 was used for statistical work. RESULTS: Marginal gaps ranged between 68.5 ± 23.8 µm and 87 ± 29.1 µm while occlusal gaps ranged from 220.7 ± 33.3 µm to 275.5 ± 46.5 µm and were not significantly different between groups. Fracture loads ranged from 633.8 ± 127.3 N to 1596.4 ± 497.7 N with lithium disilicate glass ceramics (LDGCs) and Enamic having higher values than resin nano-ceramics (RNCs). The fracture resistance was more related to material than aging and gap value. CONCLUSION: The margin adaptation of resin ceramics was comparable to lithium disilicate with no significant difference. Lithium disilicate showed a higher resistance than resin ceramics and there was a higher resistance to fracture for polymer-infiltrated ceramic-network (PICN) than RNCs. CLINICAL SIGNIFICANCE: Resin ceramics can have marginal adaptation and fracture resistance within clinical acceptance; therefore, they can be a good chair-side solution achieved in a single appointment session.

Influence of Adaptation and Adhesion on the Retention of Computer-aided Design/Computer-aided Manufacturing Glass Fiber Posts to Root Canal.

AIM: The study aimed to assess the effect of friction and adhesion on the pushout bond strength of CAD/CAM fiber-reinforced composite (FRC) post and cores in comparison to prefabricated fiber posts. MATERIALS AND METHODS: Thirty extracted single-rooted premolars were divided into three groups (N = 10): CP: CAD/CAM FRC posts (Trilor, Bioloren) cemented with self-adhesive resin cement (Rely X U200, 3M) as control group. CPL: CAD/CAM FRC composite posts cemented with the same self-adhesive resin cement after lubricating the root canal with petroleum jelly (Vaseline, Unilever) to prevent adhesion. RXP: prefabricated posts cemented with self-adhesive resin cement. Specimens were subjected to thermal cycling and then to pushout tests. The mode of failure was observed using a stereomicroscope. Results were analyzed by two-way ANOVA followed by a Tukey's post hoc test for comparison, p = 0.05. RESULTS: Push-out bond strength was significantly lower in the RXP group (8.54 ± 3.35 MPa) in comparison to CP (12.10 ± 1.38 MPa), while no significant differences were concluded between the other groups. Failure was mostly adhesive for CPL and RXP and adhesive and mixed for CP. CONCLUSION: Custom made CAD/CAM posts have a positive effect on the retention of FRC posts to root canal walls while adhesion between self-adhesive cement and root dentin did not influence significantly the pushout bond strength of CAD/CAM posts to root canal. CLINICAL SIGNIFICANCE: The friction of well-adapted CAD/CAM fiber post and cores plays a predominant role in the success of post restorations of endodontically treated teeth.

Fracture Resistance and Failure Pattern of Endodontically Treated Teeth Restored with Computer-aided Design/ Computer-aided Manufacturing Post and Cores: A Pilot Study.

AIM: To evaluate the fracture resistance and failure pattern of custom made computer-aided design & computer-aided manufacturing (CAD/CAM) post and cores using a fiber reinforced composite material (FRC) and a high-density-polymer. MATERIALS AND METHODS: Thirty extracted mandibular second premolars were selected, endodontically treated and prepared to receive the posts. The specimens were randomly divided into three groups (n = 10) according to each material: group 1 (RXP) : fiber posts (Rely X, 3M-ESPE) with composite core build-up (Filtek Bulk Fill Posterior, 3M-ESPE) as a control group; group 2 (BLC): one-piece milled post and core from fiber reinforced composite blocks (Trilor, Bioloren); and group 3 (AMC): one-piece milled post and core from hybrid ceramic disks (Ambarino, Creamed). All the posts were cemented using a self-adhesive resin cement (Rely X U200, 3M ESPE). Fracture resistance was tested using a universal testing machine, failure patterns were then observed visually and radiographically then evaluated under SEM. Data was analyzed using One-way analysis of variance (ANOVA) followed by Tamhane post-hoc test in order to determine significant differences among groups (α = 0.05). RESULTS: The mean fracture resistance values were: 426.08 ± 128.26 N for group 1 (R X P), 367.06 ± 72.34N for group 2 (BLC), and 620.02 ± 54.29N for group 3 (AMC). Statistical analysis revealed that group 3 (AMC) had the highest mean load to fracture in comparison to the other groups (p = 0.000). failures were cohesive in group 2 and 3 and mixed in group 1 with no catastrophic failures reported in all groups. CONCLUSION: All systems evaluated presented sufficient mean load-to-failure values for endodontically treated teeth restorations. CAD/CAM post and cores made from high-density-polymer showed a better performance than prefabricated fiber posts.

Marginal and internal fit of pre-sintered Co-Cr and zirconia 3-unit fixed dental prostheses as measured using microcomputed tomography.

STATEMENT OF PROBLEM: Limited information is available on the precision of new metal processing technologies. PURPOSE: The purpose of this in vitro study was to evaluate the marginal and internal fit of pre-sintered cobalt-chromium (Co-Cr) and zirconia 3-unit fixed dental prostheses using x-ray microcomputed tomography. MATERIAL AND METHODS: Three-unit fixed dental prostheses were prepared on metal dies (N=12) using a typodont model from the maxillary first premolar to the first molar. A standardized preparation with a 1.2-mm chamfer (360 degrees) and a 2-mm occlusal reduction was prepared on abutment teeth. The dies were scanned and divided into 2 groups to receive the fixed dental prostheses (n=6) made of pre-sintered Co-Cr and pre-sintered zirconia. Each framework was seated on its cast, and marginal and internal discrepancies were measured at 9 points, starting from the most distal point from the pontic for the maxillary first premolar and the first molar (points 1-4, mesial; point 5, occlusal; points 6-9, distal) of each abutment tooth using microcomputed tomography. The data were analyzed using the Levene test, t test, and ANOVA (α=.05). RESULTS: When overall mean discrepancy values were compared, no significant difference was observed between pre-sintered Co-Cr and pre-sintered zirconia (P=.085). Discrepancy values for points 1, 2, and 3 were significantly different for pre-sintered Co-Cr and pre-sintered zirconia, with the lowest mean values for point 1 and the highest for point 5. On the abutment tooth basis, for the maxillary first premolar and the first molar, a significant difference was found only in points 6 (P<.001) and 8 (P<.003) for both materials. When the discrepancies for the maxillary first premolar were considered for pre-sintered Co-Cr and pre-sintered zirconia, the mean values were significantly different only at points 1 (P<.001), 2 (P=.007), and 3 (P=.003) and were smaller for pre-sintered zirconia. For the tooth the first molar, a significant difference was observed at point 2 (P=.002) and point 3 (P=.008) for both materials, where the mean values were higher for pre-sintered Co-Cr than for pre-sintered zirconia. The pairwise comparison between points showed a significant difference between measurement points within each material (P<.05). The increase in values between points 1 and 5 was evident for both pre-sintered Co-Cr and pre-sintered zirconia materials. CONCLUSIONS: Three-unit fixed dental prostheses made of pre-sintered Co-Cr or zirconia showed similar marginal and internal discrepancy values, with the highest discrepancy values at the occlusal region in both the first premolar and first molar.

P-Hacking: A Wake-Up Call for the Scientific Community.

P-hacking or data dredging involves manipulation of the research data in order to obtain a statistically significant result. The reasons behind P-hacking and the consequences of the same are discussed in the present manuscript.

Structural and Morphological Evaluation of Presintered Zirconia following Different Surface Treatments.

AIM: The aim of this study was to evaluate the effect of different surface treatments on roughness, grain size, and phase transformation of presintered zirconia. MATERIALS AND METHODS: Surface treatments included airborne particle abrasion (APA) before and after sintering with different particles shape, size, and pressure (50 µm Al2O3, 50 µm glass beads, and ceramic powder). Thirty-five square-shaped presin-tered yttrium-stabilized tetragonal zirconia polycrystal (Y-TZP) ceramic slabs (Zenostar ZR bridge, Wieland) were prepared (4 mm height × 10 mm width × 10 mm length) and polished with silicon carbide grit papers #800, 1000, 1200, 1500, and 2000 to ensure identical initial roughness. Specimens were divided into five groups according to surface treatment: group I (control): no surface treatment; group II: APA 50 µm Al2O3 after sintering; group III: APA 50 µm Al2O3 particles before sintering; group IV: APA 50 µm glass bead particles before sintering; and group V: APA ceramic powder before sintering. Specimens were analyzed using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD) analyses, and tested for shear bond strength (SBS). Data were statistically analyzed using one-way analysis of variance (ANOVA) followed by post hoc tests for multiple comparisons Tukey's test (a > 0.05). RESULTS: Air abrasion before sintering significantly increased the surface roughness when compared with groups I and III. The highest tetragonal to monoclinic (t-m) phase transformation (0.07%) was observed in group III, and a reverse transformation was observed in presintered groups (0.01%). Regarding bond strength, there was a significant difference between APA procedures pre- and postsintering. CONCLUSION: Air abrasion before sintering is a valuable method for increasing surface roughness and SBS. The abrasive particles' size and type used before sintering had a little effect on phase transformation. CLINICAL SIGNIFICANCE: Air abrasion before sintering could be supposed to be an alternative surface treatment method to air abrasion after sintering.

Effect of Cyclic Dislodging on the Retention of Two Attachment Systems for Implant-supported Overdentures: An In Vitro Study.

PURPOSE: The aim of this study was to compare and evaluate the retention of two new attachment systems used for implant-supported overdentures subjected to insertion-removal cycles. MATERIALS AND METHODS: Twenty custom-manufactured polyvinyl chloride models mimicking implant-retained over-dentureresin blocks were fabricated and divided into two groups (n = 10): group 1 ('Kerator' attachment) and group 2 ('EMI' attachment). Each model received two parallel implants (JD evolution®) 20 mm apart and was subjected to cyclic retention forces of 10, 100, 1000, 5000, 10000 and 14600 cycles using a universal testing machine in a 0.9% sodium chloride water solution at 22° C. Data were analyzed using one-way analysis of variance; the level of significance was set at a < 0.05. RESULTS: The 'Kerator' and 'EMI' attachment systems reported a significant decrease in retention (64 and 56.6% respectively) after 14600 insertion-removal cycles (p < 0.001). The 'EMI' attachment showed significant higher loss of retention than the 'Kerator' attachment all along the 14600 cycles (p < 0.05) except for cycles 100 and 5000 (p > 0.05). CONCLUSION: Within the limitations of this in vitro study, both attachments reported satisfactory retentive values during the 14600 cycles, the 'Kerator' attachment showed better retention than the new 'EMI' attachment. The initial retentive force of both attachments has gradually decreased. CLINICAL SIGNIFICANCE: Both attachment systems evaluated in this study can be used in clinical practice for implant-supported overdentures.

Comparison of Adhesion of a Novel Pre-sintered Cobalt-Chromium to Pre-sintered Zirconia and Cast Nickel-Chromium.

AIM: This study compared the bond strength of pre-sintered Ceramill Sintron to pre-sintered zirconia and cast nickel-chromium (NiCr). MATERIALS AND METHODS: Specimens (n = 60) (diameter: 15 mm; thickness: 2 mm) were prepared (n = 20/group) (Ceramill Sintron, Ceramill Zi, and Wirobond 99). Disks were layered with vita VM ceramic (4 mm). Specimens were randomly divided into two subgroups. Only one subgroup was thermocycled. Specimens were tested under shear strength. Energy-dispersive X-ray (EDX) mapping was done on one disk of each material before and after ceramic layering. RESULTS: Failure types were mostly mixed failures. Significant difference was found between the three materials for Y and Z failure types (p-values: 0.032 and 0.010 respectively). Thermocycling had no major effect on the results reported. Considering Fmax (force-inducing bonding failure) registered, significant difference was found between the control group and milled alloys groups. No significant difference was found between Ceramill Sintron and Zi. The EDX mapping showed a net increase in the control group oxide layer, whereas only slight increase and decrease were reported for Zi and Sintron respectively. CONCLUSION: When compared with cast NiCr, novel Ceramill Sintron has higher bond strength, comparable to Ceramill Zi. Thermocycling had no major effects on the results. CLINICAL SIGNIFICANCE: Ceramic-alloy bonding is a primary factor in the prosthesis' longevity.