Mean Fracture Load Research Articles

Influence of thermo-mechanical aging on fracture resistance and wear of digitally standardized chairside computer-aided-designed/computer-assisted-manufactured restorations

ObjectivesTo investigate the influence of thermal cycling and mechanical loading (TCML) aging on fracture resistance and wear behavior of various chairside computer-aided-designed/computer-assisted-manufactured (CAD/CAM) premolar crowns cemented on standardized tooth abutments. MethodsEighty chairside CAD/CAM crowns were prepared using lithium disilicate (IPS e.max CAD; EM), zirconia-infiltrated lithium silicate (Celtra Duo; CD), polymer-infiltrated ceramic network (Vita Enamic; VE), and resin nanoceramics (Cerasmart; CS) (n = 20). The specimens were divided into two groups (n = 10). In one group, they were subjected to TCML: thermocycling (6000 cycles in distilled water at 5–55 °C) and mechanical loading (50 N for 1.2 × 106 cycles), while in control group they were stored in distilled water (37 °C for 24 h). The fracture load, height loss, and volume wear of the crowns were measured after TCML. Fractography was performed on fractured specimens. Data were analyzed using analysis of variance and multiple comparison tests (α=0.05). ResultsThe mean fracture loads of EM and CD were significantly higher than those of EC and CS (p<0.05). There was no significant change in the fracture load of any CAD/CAM crowns after TCML (p>0.05). CS exhibited a significantly higher volume wear than the other materials investigated. The wear tracts of all TCML crowns acted as failure origins during the fracture test. ConclusionsThe fracture resistance of glass-ceramic CAD/CAM crowns was significantly higher than that of resin composite crowns. A 5-year TCML aging did not affect the fracture resistance of CAD/CAM crowns investigated. However, TCML treatment produces a larger wear track in CS than in other materials. Clinical SignificanceAppropriate chairside CAD/CAM restorative material should be selected for successful clinical practice after considering the fracture and wear resistance of the crowns.

Effect of immediate dentin sealing on the fracture strength of indirect overlay restorations using different types of luting agents (A comparative in vitro study).

This study evaluates the effects of immediate dentin sealing (IDS) on the fracture resistance of lithium disilicate overlays using three different types of resin-luting agents (preheated composite, dual-cure adhesive resin, and flowable composite). Forty-eight maxillary first premolars of equal size were prepared using a butt joint preparation design. The teeth were separated into two primary groups, each with 24 teeth: Group DDS - delay dentin sealing (DDS) (non-IDS) teeth were not treated. Group IDS - dentin sealing was applied immediately after teeth preparations. Each group was subsequently separated into three separate subgroups of eight teeth. Subgroups DDS+Phc and IDS+Phc - cemented with preheated composite (Enamel plus HRi, Micerium, Italy), subgroups DDS+Dcrs and IDS+Dcrs - cemented with dual-cured resin cement (RelyX Ultimate, 3M ESPE, Germany), and subgroups DDS+Fc and IDS+Fc - cemented with flowable composite (Filtek Supreme Flowable, 3M ESPE, USA). The fracture resistance of each sample was evaluated using a test of a single load till failure, which was automatically recorded in Newton by a computer-controlled universal testing system. The fracture resistance of the subgroup IDS+Phc was the highest mean value, in which the overlay was cemented with preheated composite (1954 N), and the lowest mean was noted in the subgroup DDS+Fc, by which the overlay cemented with flowable composite without IDS (887 N). All IDS subgroups had a high mean fracture load. Both the Bonferroni test and the one-way ANOVA test identified a significant difference between all groups of 0.05. In general, teeth with IDS were stronger than teeth without IDS. When the preheated composite is used as a luting agent improves overall fracture resistance, followed by resin cement and flowable composite, respectively. However, the result showed that the ceramic overlays with and without IDS are strong enough to withstand the normal mastication force. Overlays was failed in a more catastrophic, irreparable mode of fracture than the clinical situation.

Influence of monolithic restorative materials on the implant-abutment interface of hybrid abutment crowns: An in vitro investigation.

Purpose This in vitro study aimed to investigate the long-term performance, stability, and fracture mode of monolithic hybrid abutment crowns, and the effect of different materials on the implant-abutment interface (IAI).Methods Eighty monolithic hybrid abutment crowns luted on titanium bases were manufactured from 3Y-TZP zirconia (ZY3), "Gradient Technology" zirconia (ZY35), 5Y-TZP zirconia (ZY5), lithium disilicate ceramic (LDS), zirconia-reinforced lithium silicate ceramic (ZLS), polymer-infiltrated ceramic network (MHY), polymethylmethacrylate (PMA), and 3D-printed hybrid composite (PHC) (n = 10 for each material). Eighty implants (Camlog Progressive-Line, diameter: 3.8 mm) were embedded in accordance with ISO standard 14801, and crowns were mounted. After artificial aging (1.2 × 106 cycles, 50 N, thermocycling), intact specimens were loaded 30° off-axis in a universal testing machine until failure.Results Seven specimens in the PHC group failed during artificial aging, and all the others survived. There were two subgroups based on the one-way analysis of variance and Dunnett's test (P < 0.05) of the mean fracture load values. The first comprised Z3Y, ZY35, Z5Y, and LDS, with mean fracture loads between 499.4 and 529.7 N, while the second included ZLS, MHY, and PMA, with values in the 346.2-416.0 N range. ZY3, ZY35, ZY5, and LDS exhibited irreversible, visible deformations of the implant shoulders with varying dimensions after load-to-fracture tests.Conclusions Crowns made of LDS, ZLS, MHY, and PMA may act as potential stress breakers, and prevent possible deformation at IAIs. Further clinical studies need to assess if these materials also withstand relevant loads in-vivo.

An investigation on fatigue, fracture resistance, and color properties of aesthetic CAD/CAM monolithic ceramics

ObjectivesTo evaluate and compare fracture resistance, translucency, and color reproducibility, as well as the effect of aging on the fracture load and color stability of novel monolithic CAD/CAM ceramics.Materials and methodsOne hundred crowns of uniform thickness were milled from five ceramic blocks (n = 20): partially crystallized lithium disilicate (PLD) and fully crystallized lithium disilicate (FLD), lithium metasilicate (LMS), 4Y-TZP (SMZ), and 5Y-TZP (UMZ) monolithic zirconia. PLD crowns were glazed, LMS was fired, and FLD was polished. SMZ and UMZ crowns were sintered and polished. Crowns were adhesively cemented to epoxy dies. Half of the crowns (n = 10) were subjected to 1.200.000 load cycles with thermal cycling. Color space values L, a, b defined by the Commission Internationale de l´Eclairage (CIELAB) were measured before and after aging, and (∆E) was calculated. Both aged and non-aged specimens were loaded until fracture in a universal testing machine and the fracture load was recorded. X-ray diffraction (XRD) and scanning electron microscope (SEM) fractographic analysis were carried out on fractured fragments of representative samples. For translucency and color reproducibility, 50 rectangular-shaped specimens were fabricated and processed as described previously. Color values were measured over black and white backgrounds, and the translucency parameter (TP) was computed. Using the shade verification mode, (∆E) to shade A3 was calculated. Data were statistically analyzed using one-way and two-way ANOVA, and t-test.ResultsAging did not affect fracture resistance significantly (p > 0.05). The highest mean fracture load was obtained for the SMZ and UMZ. A significant color change was observed after aging in all groups. The highest TP was noted for FLD. SMZ and UMZ had the best shade match.ConclusionsZirconia showed higher fracture resistance and color stability than lithium silicate ceramics. Lithium silicate ceramics were more translucent. The experimental FLD demonstrated high translucency.Clinical relevanceTested ceramics showed sufficient stability to withstand masticatory forces. Characterization of final restorations might be mandatory for better color match.

Different Cavity Designs with Additional Wings Increase the Fracture Resistance of Inlay-Retained Monolithic Zirconia Fixed Dental Prostheses.

To evaluate the effect of different cavity designs and cement types on the fracture resistance of monolithic zirconia inlay-retained fixed dental prostheses (IRFDPs). Four study models consisting of a second premolar, a missing first molar, and a second molar were used for the different cavity designs. Four different inlay cavity designs were prepared: DO-MO (disto-occlusal-mesio-occlusal cavity), MOD-MOD (mesio-occlusodistal-mesio-occlusodistal cavity), WDO-WMO (DO-MO with additional wings), and WMOD-WMOD (MOD-MOD with additional wings). A total of 64 epoxy resin models were produced and scanned individually. IRFDPs were then fabricated from monolithic zirconia using CAD/ CAM software. The bonding surface of the IRFDPs was airborne particle abraded (50-μm alumina/2 MPa), then cemented onto the epoxy resin models using two cementation protocols (n = 8 per group): (1) P = cemented with Panavia SA Cement Plus Automix; and (2) Z/C = cemented with MDP-containing primer (Z-Prime Plus) combined with Calibra Universal resin cement. All IRFDPs were fatigued through thermal aging (6,000 cycles/5°C to 55°C) and chewing simulations (600,000 cycles × 50-N load, 2.1 Hz). All IRFDPs were then subjected to a fracture resistance test using a universal testing machine with a crosshead speed of 0.2 mm/minute. Data were statistically analyzed using one- and two-way ANOVA and Bonferroni multiple comparisons test (P = .001). The mean fracture load (N) of the designs were as follows: WMODWMOD = 1,111.1; WDO-WMO = 1,057.4; MOD-MOD = 725.6; DO-MO = 682.7. According to two-way ANOVA, the differences among the cavity designs were statistically significant (P < .05). The cavity design of IRFDPs affected the fracture resistance. However, the fracture resistance of monolithic zirconia IRFDPs with any cavity design was enough to withstand expected posterior chewing forces.

Impact of Polymerization Technique and ZrO2 Nanoparticle Addition on the Fracture Load of Interim Implant-Supported Fixed Cantilevered Prostheses in Comparison to CAD/CAM Material.

ZrO2 nanoparticles (ZNPs) have excellent physical properties. This study investigated the fracture load of implant-supported, fixed cantilevered prosthesis materials, reinforced with ZNPs and various polymerization techniques, compared with conventional and CAD/CAM materials. Sixty specimens were made from two CAD/CAM; milled (MIL) (Ceramill TEMP); and 3D-printed (NextDent Denture 3D+). Conventional heat-polymerized acrylic resin was used to fabricate the other specimens, which were grouped according to their polymerization technique: conventionally (HP) and autoclave-polymerized (AP); conventionally cured and reinforced with 5 wt% ZNPs (HPZNP); and autoclave reinforced with 5 wt% ZNPs (APZNP). The specimens were thermocycled (5000 cycles/30 s dwell time). Each specimen was subjected to static vertical loading (1 mm/min) using a universal Instron testing machine until fracture. Scanning electron microscopy was used for fracture surface analyses. The ANOVA showed significant fracture load differences between all the tested groups (p = 0.001). The Tukey post hoc tests indicated a significant difference in fracture load between all tested groups (p ˂ 0.001) except HP vs. HPZNP and AP vs. MIL. APZNP had the lowest mean fracture load value (380.7 ± 52.8 N), while MIL had the highest (926.6 ± 82.8 N). The CAD/CAM materials exhibited the highest fracture load values, indicating that they could be used in long-term interim prostheses. Autoclave polymerization improved fracture load performance, whereas ZrO2 nanoparticles decreased the fracture load performance of cantilevered prostheses.

Stability of Cantilever Fixed Dental Prostheses on Zirconia Implants.

Background: The objective was to determine the optimal connector size and position within zirconia disks for implant-supported cantilever fixed dental prostheses (ICFDP). Methods: Two-unit ICFDPs (n = 60) were designed for the premolar region with connector sizes of either 9 or 12 mm2 and positioned in the enamel or dentin layer of two different types of zirconia disks. The restorations were milled and cemented onto zirconia implants. After simulated chewing for 1.2 Mio cycles, the fracture load was measured and fractures were analyzed. Results: No fractures of ICFDPs or along the implants were detected after simulated aging. The mean fracture load values were significantly higher for a connector size of 9 mm2 (951 N) compared with 12 mm2 (638 N). For the zirconia material with a higher biaxial flexural strength, the fracture load values were increased from 751 to 838 N, but more implant fractures occurred. The position within the zirconia disk did not influence the fracture load. Conclusions: A connector size of 9 mm2 and a zirconia material with a lower strength should be considered when designing ICFDPS on zirconia implants to reduce the risk of fractures along the intraosseous implant portion.

Fracture resistance of Endodontically treated teeth restored with Metal and Composite Endocrowns luted with two different luting agents : An in vitro study

Background: Endodontically treated teeth should be properly restored to ensure longevity of the teeth. Many methods to restore ETT are reported in the literature. Endo crowns are a viable method of restoring ETT. There are no reports in the literature related to endo crowns fabricated with metal alloys and lab processed composite resins Aim: The aim of the study is to evaluate in vitro, the fracture resistance of the endodontically treated teeth restored with Endo crowns fabricated using two different materials and luted with two different cements. Material and method: Forty freshly extracted maxillary premolars were used as specimens for this in-vitro study. The specimens were endodontically treated with access opening in a class-I configuration. These specimens were randomly divided into four groups: MG, MR, CG and CR. The specimens were mounted in self-cure acrylic resin and tested for load-to-failure using universal testing machine with cross head speed of 0.5mm/sec. Results: The data obtained were tabulated and statistically analyzed using one way ANOVA and Student ‘t’ test. The fracture pattern and failure modes were classified and analyzed with chi square test. The results of this study showed that the mean fracture load for group-MG is 2816.5N; group-MR is 2709N; group-CG is 679N; group-CR is 642.5N, with very high significant difference between metal and composite material and no significant difference between the luting agents among similar restorative material groups. Regarding the modes of failure, the maximum number of favorable fractures was observed in group-CG, group-CR and catastrophic failure among the metal endocrown groups. Conclusion: Endo crowns fabricated with metal and luted with Glass ionomer cement exhibited superior fracture resistance and hence can be considered as a restorative option for ETT.

COMPARATIVE STUDY OF THE FLEXURAL STRENGTH OF MAXILLARY DENTURE BASES MADE IN CONVENTIONAL AND HIGH IMPACT HEAT CURE ACRYLIC RESIN

OBJECTIVE: To compare the flexural strength of maxillary denture bases made in high impact and conventional heat cure acrylic resin. METHODS: This experimental laboratory-based study was conducted in Peshawar Dental College, Materials Research and Centralized Resource Laboratories University of Peshawar, Pakistan. Total 120 edentulous maxillary casts, sixty each of conventional acrylic (30 in subgroup-IA for shallow palate and 30 in subgroup-IB for deep palate and high impact acrylic (30 in subgroup II-A for shallow palate and 30 in subgroup II-B for deep palate) were made. These were then tested for flexural strength using universal testing machine. The load was applied at the rate of 5.0 mm/min. Independent samples t-test was applied for statistical analysis. RESULTS: Mean values of deflection at fracture, fracture load and flexure strength were 0.309±0.059 cm, 87.729±22.497 Kg and 13.645± 4.453 kg/cm² respectively. Mean Flexure Strength (kg/cm2) was 8.30±1.27, 16.54±1.77, 10.88±1.01 and 18.85±1 in subgroups I-A, I-B, II-A and II-B respectively (&lt;0.001). Mean deflection at fracture (cm) was 0.24±0.04, 0.29±0.03, 0.35±0.03 &amp; 0.368±0.03 in subgroups I-A, I-B, II-A and II-B respectively (&lt;0.001).Mean Fracture Load (Kg) was 69.97±3.12, 114.9±6.75, 63.28±7.05 &amp; 102.8±5.5 in in subgroups I-A, I-B, II-A and II-B respectively (&lt;0.001).CONCLUSION: High impact acrylic resin was found to have significantly higher flexure strength as compared to conventional acrylic resin

Effects of Cuspal Inclination and Luting Agent on Fracture Load Values in Composite Resin CAD/CAM Crowns.

The purpose of this study was to evaluate whether change in cuspal inclination influences the fracture load values of composite resin computer-aided design/computer-aided manufacturing (CAD/CAM) crowns. Abutment teeth and CAD/CAM crowns were prepared as they would be for treating a mandibular first premolar with two cusps. The CAD/CAM crowns were designed so that 1) the principal stress lines would be radially distributed from the two points of contact with the indenter to the occlusal area of the abutment (Type I), or 2) the principal stress lines would pass outside the occlusal area of the abutment (Types II and III). The CAD/CAM crowns were mounted on the abutments using one of two types of resin or polycarboxylate cement. Fracture load values were measured using a universal tester. The Type I CAD/CAM crowns exhibited the highest mean fracture load value, followed by the Type II crowns and then the Type III crowns, with significant differences seen between all types (p<0.05). The luting agent used (resin or polycarboxylate cement) showed no effect on the fracture load value. With the Type II and Type III crowns, significant differences in the fracture load value were observed between the Super-Bond and Hy-Bond polycarboxylate cement groups (p<0.05).

O9 - Fatigue Analysis of Restored Teeth Longitudinally Cracked Under Cyclic Loading

To investigate the fatigue behavior of restored teeth, in particular the mechanisms of longitudinal dentinal cracking under cyclic mechanical loading, using finite element analysis (FEA) and the stress-life (S-N) approach. Ten root-filled premolars restored with resin composites were subjected to step-stress cyclic loading to produce longitudinal cracks. Fracture loads and number of cycles completed at each load level were recorded. Finite element analysis (FEA) was used to predict the stress amplitude of each component under the global cyclic load. Both intact and debonded conditions were considered for the dentin-composite interface in the FEA. The predicted stress concentrations were compared with the fracture patterns to help elucidate the failure mechanisms. The stress-life approach was further used to predict the lifetimes of the different components in the restored teeth. Cumulative fatigue damage was represented by the sum of the fractions of life spent under the different stress amplitudes. Longitudinal cracks were seen in ~50% of the samples with a mean fracture load of 77045 N and a mean number of cycles to failure of 3229712624. The longitudinal dentinal cracks seemed to start near the line angle of the cavity, and propagated longitudinally towards the root. The sum of fractions of life spent for the dentin-composite interface exceeded 1 after ~7000 cycles when that for dentin was much lower that 1, indicating that interfacial debonding would occur prior to dentin fracture. This was confirmed by micro-CT images showing widened interfacial space in the cracked samples. In the debonded tooth, FEA showed dentinal stress concentrations at the gingival wall of the cavity, which coincided with the longitudinal cracks found in the cyclic loading test. The sum of fractions of life spent for dentin was close to 1 at ~30000 cycles, similar to the experimental value. Debonding of the dentin-composite interface occurred prior to longitudinal cracking of dentin in root-filled teeth under cyclic loading. The approximate time of occurrence for these events could be estimated using fatigue analysis with stresses provided by FEA.

In Vitro Fatigue and Fracture Load of Monolithic Ceramic Crowns Supported by Hybrid Abutment

Objective: This study evaluated the performance of zirconia and lithium disilicate crowns supported by implants or cemented to epoxy resin dies. Methods: Eigthy zirconia and lithium disilicate crowns each were prepared and assigned in four groups according to the crown material and supporting structure combinations (implant-supported zirconia, die-supported zirconia, implant-supported lithium disilicate, and die-supported lithium disilicate). Ten crowns in each group acted as control while the rest (n=10) underwent thermocycling and fatigue with 100 N loading force for 1.5 million cycles. Specimens were then loaded to fracture in a universal testing machine. Data were analysed using one-way ANOVA and Tukey multiple comparison test with a 95% level of significance. Results: No implants or crown failure occurred during fatigue. The mean fracture load values (control, fatigued) in newton were as follows: (4054, 3344) for implant-supported zirconia, (3783, 3477) for die-supported zirconia, (2506, 2207) for implant-supported lithium disilicate, and (2159, 1806) for die-supported lithium disilicate. Comparing the control with the corresponding fatigued subgroup showed a significantly higher fracture load mean of the control group in all cases. Zirconia showed a significantly higher fracture load mean than lithium disilicate (P=0.001, P&lt;0.001). However, comparing crowns made from the same material according to the supporting structure showed no significant difference (P=0.923, P=0.337). Conclusion: Zirconia and lithium disilicate posterior crowns have adequate fatigue and fracture resistance required for posterior crowns. However, when heavy fatigue forces are expected, zirconia material is preferable over lithium disilicate. Zirconia and lithium disilicate implant-supported crowns cemented to hybrid abutments should have satisfactory clinical performance.

Fatigue analysis of restored teeth longitudinally cracked under cyclic loading

ObjectiveTo investigate the fatigue behavior of restored teeth, in particular the mechanisms of longitudinal dentinal cracking under cyclic mechanical loading, using finite element analysis (FEA) and the stress-life (S-N) approach. MethodsTen root-filled premolars restored with resin composites were subjected to step-stress cyclic loading to produce longitudinal cracks. Fracture loads and number of cycles completed at each load level were recorded. FEA was used to predict the stress amplitude of each component under the global cyclic load. Both intact and debonded conditions were considered for the dentin-composite interface in the FEA. The predicted stress concentrations were compared with the fracture patterns to help elucidate the failure mechanisms. The S-N approach was further used to predict the lifetimes of the different components in the restored teeth. Cumulative fatigue damage was represented by the sum of the fractions of life spent under the different stress amplitudes. ResultsLongitudinal cracks were seen in ~50% of the samples with a mean fracture load of 770 ± 45 N and a mean number of cycles to failure of 32,297 ± 12,624. The longitudinal dentinal cracks seemed to start near the line angle of the cavity, and propagated longitudinally towards the root. The sum of fractions of life spent for the dentin-composite interface exceeded 1 after ~7000 cycles when that for dentin was much lower than 1, indicating that interfacial debonding would occur prior to dentin fracture. This was supported by micro-CT images showing widened interfacial space in the cracked samples. In the debonded tooth, FEA showed dentinal stress concentrations at the gingival wall of the cavity, which coincided with the longitudinal cracks found in the cyclic loading test. The sum of fractions of life spent for dentin was close to 1 at ~30,000 cycles, similar to the experimental value. SignificanceDebonding of the dentin-composite interface may occur prior to longitudinal cracking of dentin in root-filled teeth under cyclic loading. The approximate time of occurrence for these events could be estimated using fatigue analysis with stresses provided by FEA. This methodology can therefore be used to evaluate the longevity of restoration designs for root-filled teeth.

Experimental analysis of early periprosthetic femoral fractures with uncemented straight hip stems

BackgroundThe periprosthetic femoral fracture is one of the most severe complications after total hip arthroplasty and is associated with an increased mortality. The underlying causes and the patient- and implant-specific risk factors of periprosthetic femoral fractures remain insufficiently understood. The aim of this study was to gain a more profound understanding of the underlying fracture mechanisms and to provide experimental datasets for validation of computational models. MethodsSix cadaveric femurs were implanted with straight hip stems (Zweymueller design) and loaded until fracture reproducing the clinically relevant load cases stumbling and sideways fall. Displacements and the strain distribution on the surface of the femurs and implants, as well as the fracture load and implant subsidence were measured. FindingsFor the load case stumbling the mean fracture load was 6743 N and two different mechanisms leading to fracture could be identified: high subsidence with low femoral bending and small subsidence with high femoral bending. For the load case sideways fall the mean fracture load was 1757 N and both tested femurs fractured due to a rotation of the hip stem around its own axis. The detailed datasets provided by this study can be used in future computational models. InterpretationWe demonstrated that the underlying fracture mechanisms of periprosthetic femoral fractures can be fundamentally different in the load case stumbling. The seating and exact position of the hip stem in the femur may correlate with implant subsidence and therefore lead to different types of fracture mechanisms resulting in different patient-specific fracture risks.

Effect of dynamic loading on fracture resistance of gradient zirconia fixed partial denture frameworks

Statement of problemThe new strength-gradient zirconia composed of 3-mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and 5-mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) has been claimed to have superior mechanical properties. However, data on the fracture resistance of 3-unit gradient 5Y-TZP and 3Y-TZP fixed partial denture frameworks are lacking. PurposeThe purpose of this in vitro study was to evaluate the effect of dynamic loading on the fracture resistance of gradient zirconia fixed partial denture frameworks. Material and methodsTwo standardized stainless-steel master dies were designed to simulate a mandibular left second premolar and second molar prepared to receive zirconia frameworks. The frameworks were designed with a 0.6-mm uniform wall thickness. The mesiodistal width of the connectors was 3 ±0.02 mm, and the occlusogingival height was 3 ±0.02 mm. Forty zirconia frameworks were fabricated and divided into 2 groups according to the tested materials (n=20): 3Y-TZP and gradient 5Y-TZP and 3Y-TZP. The frameworks were cemented onto their corresponding dies with a conventional glass ionomer cement. Half of the cemented frameworks in each group underwent 600 000 cycles of dynamic loading in a mastication simulator (n=10). The other half was fractured without dynamic loading (n=10). Fracture resistance measurements (N) for each framework were recorded by using a universal testing machine at a crosshead speed of 1 mm/min. A fractured framework from each group was examined by using a scanning electron microscope (SEM) at ×100 magnification. The data obtained were statistically analyzed by using 2-way ANOVA, the pairwise Tukey honestly significant difference (HSD), and simple main effect tests to detect the difference between group mean values (α=.05). ResultsThe mean ±standard deviation of fracture load value before dynamic loading was 1919 ±193 N for the 3Y-TZP group and 908 ±99 N for the gradient 5Y-TZP and 3Y-TZP group. In addition, the mean fracture load value after dynamic loading was 1418 ±163 N for the 3Y-TZP group and 716 ±85 N for the gradient 5Y-TZP and 3Y-TZP group. The interaction between the effects of the zirconia material and dynamic loading on the fracture resistance was statistically significant (P=.002). The 3Y-TZP group had a statistically significant, higher fracture load mean value the gradient 5Y-TZP and 3Y-TZP group before and after dynamic loading (P<.001). ConclusionsThe fracture resistance of 3Y-TZP frameworks was significantly higher than that of gradient 5Y-TZP and 3Y-TZP frameworks before and after dynamic loading. Dynamic loading significantly reduced the fracture resistance of 3Y-TZP and gradient 5Y-TZP and 3Y-TZP frameworks.

Optimal bone biopsy route to the proximal femur evaluated by computed tomography-based finite element modeling

IntroductionThe proximal femur (PF) is one of the most common locations of benign cystic lesions. A fracture after bone biopsy is a rare but severe complication. However, the risk of fracture after biopsy of this lesion has not been well-studied. Computed tomography (CT)-based finite element (FE) modeling estimates the elastic modulus and compressive strength enables fracture prediction. This study investigated strength of PF after biopsy by CT-FE modeling and determined the optimum biopsy level and size. Materials and methodsSix male bone tumor patients’ (15–38 years) total femur CT data (slice thickness, 0.8–1.0 mm) of the healthy side were obtained. Three different cylindrical bone defect (BD) diameters (10, 15, and 20 mm) were set on the lateral surface of PF at the following levels: level 1, insertion of the gluteus minimums; level 2, lower end of the greater trochanter (GT); level 3, origin of the vastus lateralis; level 4, center of the lesser trochanter (LT); and level 5, lower end of LT using Mechanical Finder software (version 8.0). Virtual loads were applied with incremental increases of 100 N until fracture occurred and the fracture load (FL) was evaluated. ResultsFor BD with a diameter of 15 and 20 mm, there was a significant difference in the decrease of the mean FL, with an average of 22% at level 4 and 5, and 33%–44% at levels 3 to 5, respectively. At level 1 and 2, no significant decrease in the mean FL was observed regardless of the diameter of BD. ConclusionBiopsies at level 1 and 2 showed no significant decrease in bone strength. However, biopsy at level 1 may contaminate the GT bursas. Therefore, biopsy at level 2 (lower end of GT) can avoid contamination and minimize the effect on bone strength.

A novel insertion design of fiber materials for the adhesive reattachment in vertically fractured teeth.

ObjectiveThis ex vivo study aimed to evaluate the strengthening effect of different ferrule and reattachment designs with fiber and adhesive materials on vertically fractured teeth.MethodsNinety extracted single-root premolars were instrumented and divided into nine groups (two control groups and seven experimental groups; n = 10). The negative control (NC) group comprised of intact teeth, while the positive control (PC) group comprised of root canal-treated teeth. The roots of the teeth in the experimental groups were vertically fractured into two equal fragments. The fragments were reattached with one of the followings: 4-methacryloxyethyl trimellitate anhydride/methacrylate-tri-n-butyl borane (4-META/MMA-TBB) resin, 4-META/MMA-TBB + quartz fiber post, 4-META/MMA-TBB + glass fiber bundles, 4-META/MMA-TBB + quartz fiber post + 1 mm ferrule, 4-META/MMA-TBB + glass fiber bundles + 1 mm ferrule, 4-META/MMA-TBB + quartz fiber post + 2 mm ferrule, and 4-META/MMA-TBB + glass fiber bundles + 2 mm ferrule. The core build-ups were made with composite resin. The specimens were subjected to compressive loading until failure occurred. Mean load necessary to fracture each sample and the fracture types of these samples were recorded.ResultsThe highest mean fracture load was recorded in the NC group (1,036.7 N), which was not significantly higher than the PC group (989.66 N) (p > 0.05). The roots reattached with quartz fiber post demonstrated significantly less fracture strength (871.9 N) as compared to the other test and control groups (p < 0.05). There was no significant difference between the PC group and reattached fragments with different ferrule designs in terms of fracture resistance (p > 0.05).ConclusionsThe customized fiber bundles may be more suitable for reattachment of vertically fractured teeth than the rigid fiber posts. For reattachment procedures, the ferrule design may be preferred to increase the fracture strength of vertically fractured teeth.

Pulsatile Lavage Improves Tibial Cement Penetration and Implant Stability in Medial Unicompartmental Arthroplasty: A Cadaveric Study.

Cemented unicompartmental knee arthroplasty (UKA) shows good survivorship and function. However, implant failure, causing the need for revision, can occur. Aseptic loosening is still among the most common reasons for revision. The purpose of this study was to assess the influence of preimplantation lavage technique on tibial cement penetration depth, tibial cement volume, and load to fracture in the tibial component of mobile-bearing UKA. In 10 pairs of fresh frozen human tibiae, cemented UKA was implanted by an experienced surgeon. Tibial components were then implanted, left and right tibiae were randomly allocated to group A or B. Prior to implantation, irrigation was performed with either syringe lavage or pulsatile jet lavage in a standardized manner. Cement surface was 4170.2 mm2 (3271.6-5497.8 mm2) in the syringe lavage group, whereas the jet lavage group showed 4499.3 mm2 (3354.3-5809.1 mm2); cement volume was significantly higher as well (4143.4 mm3 (2956.6-6198.6 mm3) compared with 5936.9 mm3 (3077.5-8183.1 mm3)). Cement penetration depth was 2.5 mm (1.7-3.2 mm) for the jet lavage, and 1.8 mm (1.2-2.4 mm) for the syringe lavage. The mean fracture load was 4680 N in the jet lavage group and 3800 N in the syringe lavage group (p = 0.001). Subsidence was significantly higher for syringe lavage. This study suggests a correlation of cement penetration depth and cement volume to implant failure in the tibial component of a UKA using a cadaveric model. The type of bone lavage most likely influences these two key parameters.

Novel CAD-CAM zirconia coping design to enhance the aesthetics and strength for anterior PLZ crowns.

The aesthetics and strength of anterior porcelain layered zirconia (PLZ) crowns are mainly affected by the zirconia (Zr) coping design. There is a need for a modified design to enhance aesthetics with strength. The purpose of this study was to compare the fracture resistance of anterior PLZ crowns having modified CAD-CAM Zr coping designs (in terms of thickness and marginal collar designs) with standard Zr copings. Fifty PLZ crowns were fabricated and divided into two groups: Gr 1: Standard Zr Coping (SZC) (control gr) with 0.5 mm thickness (Facial-F, Mesial-M, Distal-D, incisal-I, and Palatal-P) without a collar; Gr 2: Collar Zr Coping (CZC) (test gr) with 2.5 mm collar height on M, D, P and 0.2 mm F and variable facial wall thickness. Subgroups: Gr 2a: (CZC-0.5 mm) facial wall thickness 0.5 mm; Gr 2b: (CZC-0.4 mm) facial wall thickness 0.4 mm; Gr 2c: (CZC-0.3 mm) facial wall thickness 0.3 mm; Gr 2d: (CZC-0.2 mm) facial wall thickness 0.2 mm. The fracture load was determined and analysed using One-way ANOVA and Dunnet test. The minimum fracture load was 927.36 ± 127.80 N observed for Gr 2c (CZC at 0.3 mm) while the maximum fracture load was 1373.61 ± 146.54 N observed for Gr 2a (CZC at 0.5 mm). A highly significant difference in mean fracture load among various Zr coping groups (p< 0.001) was determined. Novel Zr coping design for anterior PLZ crowns can provide better aesthetics with strength. Reducing the thickness of Zr coping in the aesthetic zone to 0.2 mm and providing a modified collar design (2.5 mm collar height on M, D, P, and 0.2 mm F) would provide strength without jeopardizing aesthetics.

Laboratory simulation of longitudinally cracked teeth using the step-stress cyclic loading method.

To simulate in a laboratory setting longitudinal cracking in root filled premolar teeth, using cyclic mechanical fatigue. Mesial-occlusal-distal (MOD) cavities were prepared in twenty root filled, single-rooted, mandibular premolars restored with fibre posts and resin composites. The samples were randomly divided into two groups based on the loading approaches: static loading with a crosshead speed of 0.5mm/min and step-stress cyclic loading (1Hz) with increasing amplitude. The loads and numbers of cycles to failure were recorded. Micro-CT was also used to identify the fracture modes. Statistical analysis was performed using Student's t-test. The level of significance was set at 0.05. The mean fracture loads for the static loading and cyclic loading groups were 769±171N and 720±92N, respectively. There was no significant difference between the two groups (P>0.05). The proportions of longitudinal, cuspal and mixed-mode fractures under cyclic loading were 50%, 20% and 30%, respectively. Longitudinal fractures occurred with larger numbers of cycles and higher average loads per cycle compared with the other fractures. Static loading produced only cuspal fractures. Longitudinally cracked premolar teeth with root fillings were successfully produced using the step-stress cyclic loading method. This provides a more clinically representative methodology for studying cracked teeth in a laboratory setting.