Maximum Masticatory Forces Research Articles

Influence of the margin design on the fracture resistance of implant supported monolithic zirconia crowns: An “In Vitro” Study

Introduction: The purpose of this in vitro study was to test the influence of the margin design of implant supported monolithic zirconia crowns and test if monolithic zirconia crowns with extra fine finish line thickness cemented on zirconia implant abutments can bare the maximum masticatory forces on molars and hence be used in the posterior region. Methods: Fourteen identical monolithic zirconia crowns cemented on zirconia implant abutments mounted on titanium bases and fixed on implant replicas embedded in PMMA resin were divided into two groups: group I designed with a 0.5 mm CFL (CFL) and group II with a feather-edge finish line (FEFL) of 0.3 mm. All specimens underwent static load until fracture in order to determine the break force. Break forces in N were recorded for each group. Results: The CFL group exhibited slightly higher fracture resistance (1879.14 ± 322.28 N) compared to the feather-edge finish line group (1685.00 ± 362.18 N). However, statistical analysis revealed that the observed difference between the two groups (194.14 ± 183.24; p = 0.310) was not significant. Conclusions: Within the limitations of this study, both monolithic zirconia crowns with 0.5 mm chamfer and 0.3 mm feather edge margins cemented on zirconia implant abutments can be used in the posterior region as their resistance to fracture is similar and surpasses the maximum masticatory force applied on molars.

Comparative Fracture Resistance Analysis of Translucent Monolithic Zirconia Dioxide Milled in a CAD/CAM System

The aim of this study was to evaluate and compare the fracture resistance of definitive zirconia dioxide restorations obtained using a computer-aided design and manufacturing (CAD/CAM) system. Methods: Two groups of ten samples were analyzed for each material (n: 20); the first group was Zolid Gen X Amann Girrbach (ZGX) and the second group was Cercon HT Dentsply Sirona (CDS). The restorations were designed with identical parameters and milled with a CAD/CAM system. Each specimen was load tested at a speed of 0.5 mm/min, with a direction parallel to the major axis of the tooth and with an initial preload of 10 N until fracture using a universal testing machine (Universal/Tensile Testing Machine, Autograph AGS-X Series) equipped with a 20 kN load cell. The results obtained were recorded in Newtons (N), using software connected to the testing machine. Results: Statistically significant differences were found, and the fracture resistance of the monolithic zirconia crowns was lower in the CDS group (1744.84 ± 172.8 N) compared to the ZGX group (2387.41 ± 516 N). Conclusions: The monolithic zirconia CAD-CAM zirconia crowns showed sufficient fracture resistance when used in posterior molar and premolar zones with either material, as they withstood fracture loads greater than the maximum masticatory force.

Stability of different fixation methods after reduction malarplasty under average and maximum masticatory forces: a finite element analysis

BackgroundAlthough titanium plates/screws are effective fixation methods (FM) after L-shaped osteotomy reduction malarplasty (LORM), the ideal FM remains controversial. This first finite element analysis (FEA) aimed to study the effect of various zygomatic body/zygomatic arch FM combinations and their placement vectors on the zygoma complex stability after virtual LORM under the effect of both average (150 N/mm2) and maximum (750 N/mm2) forces and three-dimensional (3D) mapping of stress and strain parameters distribution over the zygomatic bone, fixation methods, and total model.ResultsThe fixation methods about the short-arm of the L-shaped osteotomy showed lower stress, strain, and displacement values than those across the long-arm osteotomy site. Combined with any zygomatic arch fixation methods (ZAFm), the two bicortical screws group (2LS) on the zygomatic body osteotomy site resulted in smaller displacements and the lowest zygoma bone stress and displacement when combined with Mortice–Tenon structure (MT) as zygomatic arch fixation method. Applied forces caused statistically significant differences in zygomatic bone stress (P < 0.001 and P = 0.001) and displacement (P = 0.001 and P = 0.002).ConclusionAll FMs both on the zygomatic body and zygomatic arch provide adequate zygomatic complex stability after LORM. The 2LS group showed better resistance than rectangular plate (RP) and square plate (SP) with lower stress concentrations. The L-shaped plate with short-wing on the maxilla (LPwM) is more stable than having the short-wing on the zygoma bone (LPwZ). Future prospective clinical studies are required to validate the current findings.

64 Finite Element Analysis of a Porous Dual Component 3D-Printed Bone Graft for Alveolar Ridge Augmentation

OBJECTIVES/GOALS: Our goal was to assess the ability of a 3D-Printed dual cover-core design alveolar ridge bone graft, to withstand the average maximum masticatory force of a healthy person. To this end, we characterized the materials, ran a finite element analysis (FEA) model, and validated it using a resin 3D-printed version tested under compression with strain gauges. METHODS/STUDY POPULATION: A tricalcium-phosphate/hydroxyapatite paste and mixed methacrylated alginate-gelatin were used for the core, and polycaprolactone for the cover. These were characterized using ASTM standards D695 and D638 for compression, tensile, and rheological testing. Then we converted cone CT-scan images of a mandibular alveolar ridge defect to an .stl file, and designed the cover and core in Meshmixer. The model was then imported into ANSYS 11.0, and a downward compression force of 500 N, the maximum masticatory force of a healthy adult, was applied on the graft and mandible’s top ridge. The different models included solid and porous covers and cores, as well as comparing screws on one or both sides of the cover, then validated by compressing a resin 3D-printed versions. RESULTS/ANTICIPATED RESULTS: The FEA model provided maximum displacements, Von Mises stress (VMS), and stress/strain values for each model. The highest maximum displacement was found on the solid covers with a combination of both buccal and lingual screws, at 0.162 mm. The lowest maximum displacement was found in the porous cover at 0.085 mm. All VMS values were below the tensile yield strength, meaning that the materials would not yield. The highest maximum stress was found on the porous cover at 13.52 MPa, the lowest was 1.06 MPa on the cover with no screws. The highest strain was found on the porous model at 0.010, which was 5.6x higher than the solid cover. The porous cover also showed less stress shielding, thus allowing a beneficial mechanical stimulation of the bone, and the lowest maximum displacement, possibly due to flexion through the pores. DISCUSSION/SIGNIFICANCE: Preliminary FEA models demonstrated that for the considered materials, a cover-core design of the mandibular implant would sustain the desired 500 N of force without yielding. The porous cover provides the most benefits, causing the least stress shielding and allowing diffusion of biological factors to support the osteoinductive role of the core.

Comparative evaluation of digitally fabricated complete dentures versus conventional complete dentures: A randomized, single-blinded, cross-over clinical trial

Statement of problemClinical trials comparing outcomes associated with digital complete dentures (CDs) fabricated from intraoral scan data with those of CDs fabricated by using the conventional workflow are lacking. PurposeThe purpose of this randomized clinical trial was to evaluate the clinical performance of and patient satisfaction associated with digitally versus conventionally fabricated CDs. Material and methodsEight participants requiring CDs were enrolled in this study. Two sets of CDs were fabricated for each participant. One set was fabricated by using a digital workflow, which involved digital scanning with an intraoral scanner, whereas the other set was made by using the conventional workflow. The participants were given 1 set of CDs for 1 month and another set for the next month. The order of placing CDs was randomly selected for each participant. The internal adaptation, masticatory force, and masticatory efficiency of the CDs in each group were evaluated for objective analysis. Additionally, a questionnaire was provided to the participants, and the responses were evaluated for subjective satisfaction analysis. All parameters were analyzed by using t tests (α=.05). ResultsThe internal adaptation did not statistically significantly differ between the conventional and digital CDs with regard to the maxillary arches (P=.406) and mandibular arches (P=.412). The average masticatory force (P=.051) and maximum masticatory force (P=.110) likewise did not statistically significantly differ between the 2 types of CDs. Masticatory efficiency, expressed via the mixing ability index, was statistically better for conventional CDs than the digital CDs (P=.009). No statistically significant differences were observed between the 2 types of CDs in terms of overall patient satisfaction as assessed by using the study questionnaire (P=.172 for maxillary CD and P=.161 for mandibular CD). However, the conventional CDs were statistically significantly better than the digital CDs with regard to subjective satisfaction with pronunciation ability (P=.006). ConclusionsThe digital CDs were inferior to the conventional CDs in terms of masticatory efficiency and pronunciation. However, internal adaptation and overall patient satisfaction were comparable between conventional and digital CDs. This finding suggests that intraoral scanning and additively manufactured CDs may be suitable for edentulous patients, at least for interim use.

Influence of Margin Designs on Crack Initiation of High Translucency Monolithic Zirconia Crowns.

Zirconia crowns often crack at the margin. This study determined the loads and the times at which cracks are initiated in high-translucency monolithic zirconia crowns with different margin designs. A total of 90 crowns were fabricated from Zirconia blanks. The fabricated crowns had different margin thicknesses (light-chamfer, CL and heavy-chamfer, CH ) and collar heights (no-collar, NC ; low-collar, LC ; high-collar, HC ). They were grouped as CL NC , CL LC , CL HC , CH NC , CH LC , and CH HC (15 crowns/group). The crowns were seated on a metal model and loaded vertically through round end punch (Φ = 10 mm) at 0.2 mm/min crosshead speed until cracks began to be seen. Videos of the crack initiation were recorded at the rate of 50 frames/second. Load-initiated cracks and durability time were compared for significant differences using analysis of variance. The mean ± standard deviation values of load (N) and time (s) taken to initiate cracks were 3190 ±775, 212 ±47 for CL NC ; 2754 ±1109, 180 ±42 for CL LC ; 2887±832, 191±27 for CL HC ; 4082 ±896, 241 ±36 for CH NC ; 4180 ±1029, 220 ±28 for CH LC ; 4119 ±1124, 222 ±39 for CH HC . This indicates that the thickness of the margin has a significant influence on load-withstanding crack initiation capacity and durability time (p < 0.05). No significant impact of collar height was observed on either load-withstanding capacity or durability time (p > 0.05). No interaction was observed among these factors. Heavy chamfer margin provided a stronger zirconia crown than the light chamfer margin, but both of them were capable of withstanding crack-initiated load higher than the theoretical maximum masticatory force. The presence or absence of a collar did not have any impact on the crack initiation. Fabrication of zirconia crowns with either a heavy or light chamfer margin and with or without the presence of a collar should be generated by considering the relevant emergence profile.

Effect of Marginal Designs on Fracture Strength of High Translucency Monolithic Zirconia Crowns.

Introduction Monolithic zirconia is able to achieve certain aesthetic, but its durability in resisting fracture has been questioned, as fractures often originate from margins of restoration. This study determined fracture resistance of highly translucent monolithic zirconia crowns with different margin designs in terms of marginal thickness and collar height. Materials and Methods Zirconia blanks (Ceramill® Zolid HT+) were selected for the fabrication of zirconia crowns according to different designs, including varying margin thicknesses (light chamfer, CL; heavy chamfer, CH) and collar heights (no collar, NC; low collar, LC; high collar, HC), which resulted in CLNC, CLLC, CLHC, CHNC, CHLC, and CHHC groups (15 crowns each). The crowns were seated on a metal die and loaded vertically through round end punch (θ = 10 mm), contacting with inclined planes of cusp in a testing machine with crosshead speed of 0.2 mm/min until fracture. Videos with a rate of 50 frames/second were used to record fracture. Fracture load (N) and durable period (s) were compared for significant differences using ANOVA and Bonferroni test (α = 0.05). Results The mean ± sd of fracture load (N) and durable time (s) were 3211 ± 778 and 212 ± 47 for CLNC; 3041 ± 1370 and 188 ± 53 for CLLC; 2913 ± 828 and 192 ± 27 for CLHC; 4226 ± 905 and 245 ± 35 for CHNC; 4486 ± 807 and 228 ± 29 for CHLC; and 4376 ± 1043 and 227 ± 37 for CHHC. This indicated that marginal thickness had a significant influence on load-bearing capacity and durable time (p < 0.05). No significant impact of collar height was shown, either on load-bearing capacity or durable time (p > 0.05). No interaction between two factors was presented (p > 0.05). Conclusions Heavy chamfer margin provided stronger zirconia crown than light chamfer, but both were capable of withstanding fracture load higher than maximum masticatory force. Neither presence nor absence of collar indicated any impact on strength. Fabrication of zirconia crowns with either heavy or light chamfer margin and either presence or absence of collar, with the consideration of emergence profile, should be considered.

Influence of different surface treatments on two-body wear and fracture load of monolithic CAD/CAM ceramics.

To investigate two-body wear (2BW) and fracture load (FL) of monolithic ceramics after different surface pretreatments. Zirconia (MOZ), lithium-disilicate (LIT), and leucite-reinforced (LEU) specimens (n = 60/group) were manufactured with CAD/CAM-technology and underwent (n = 15/subgroup): 1) grinding + polishing (GrPo), 2) grinding + glazing (GrGz), 3) grinding (Gr), or 4) glazing (Gz). Scanning electron microscope (n = 3/subgroup) and 3D measurements of the ceramic crowns and antagonists (N = 180) were performed to determine 2BW before and after 120,000/1,200,000 masticatory cycles. FL was examined for all specimens (N = 180). Data were analyzed using Kolmogorov-Smirnov, one-way ANOVA, Scheffé post hoc, Kruskal-Wallis, Mann-Whitney-U, and Wilcoxon (p < 0.05). MOZ presented the highest FL independent on pretreatment (6960-9250N), while LEU (1405-2320N) showed the lowest (p < 0.001). Ceramic and antagonist wear increased between 120,000 and 1,200,000 masticatory cycles (p < 0.001). For pretreatments GrPo, GrGz, and Gz, MOZ showed the lowest wear of the ceramic, while causing the highest antagonist wear (p < 0.001). GrPo resulted in the lowest wear for MOZ (p < 0.001), with Gr leading to the highest antagonist wear (p = 0.008). LIT specimens presented the highest wear of the ceramic and antagonist after Gz (p < 0.001), while GrPo resulted in the lowest antagonist wear (p < 0.001). GrGz led to the highest antagonist wear for LEU (p < 0.001). With FL exceeding maximum masticatory forces, the three tested ceramics can be recommended for restorations, even in posterior regions. While glazing resulted in higher wear and impaired FL, polishing improved mechanical properties while largely preserving the antagonist. While surface pretreatment after grinding is vital to ensure a ceramic's optimal mechanical properties, glazing and polishing varies with regard to material properties, costs, and time.

Fracture Resistance of Pressed and Milled Lithium Disilicate Anterior Complete Coverage Restorations Following Endodontic Access Preparation.

This in vitro study evaluated the fracture resistance and clinical prognosis of anterior lithium disilicate crowns (e.max Press and e.max CAD), following endodontic access and repair. The research design simulates intraoral loading conditions to produce clinically applicable results. Monolithic anterior crowns, based on #8 anatomy, were fabricated from e.max Press ingots and e.max CAD blocks and adhesively bonded on identical dies milled out of a dentin analog material (NEMA G10). Specimens were divided into 4 groups: intact pressed, repaired pressed, intact milled, and repaired milled (n=15/group). Repaired pressed and repaired milled were prepared with a standardized endodontic access and repaired using a porcelain repair system and composite resin. All crowns were cyclically loaded under simulated oral conditions and then loaded to failure in water, using a universal testing machine. Data were interpreted using ANOVA/Tukey post-hoc test (α=0.05). Mean loads to failure ranged from 758.9 to 931.4 N for the 4 groups, indicating that both fabrication techniques, pressed and milled, yielded restorations that could reasonably withstand maximum masticatory forces. The pressed groups (923.7 N) exhibited significantly higher fracture resistance than the milled groups (797.5 N), p=0.0002. When milled and pressed groups were categorized into intact and repaired subgroups, no difference was found in fracture resistance between the subgroups. Differences were noted in the modes of fracture, where the milled groups (intact and repaired) exhibited higher frequency of catastrophic fractures than the pressed groups. Endodontic access preparation does not appear to affect fracture resistance of an anterior lithium disilicate restoration, suggesting that replacement may not be necessary. Fabrication technique had a significant effect on fracture resistance and fracture mode of lithium disilicate restorations. The pressed fabrication technique resulted in significantly greater crown strength and fracture resistance than the milled technique.

Fracture Resistance of Endodontically Treated Teeth Restored with Lithium Disilicate Crowns Retained with Fiber Posts Compared to Lithium Disilicate and Cerasmart Endocrowns: In Vitro Study

Purpose: The purpose of this in vitro study was to compare the effect of endocrowns and glass fiber postretained crowns on the fracture resistance of endodontically treated maxillary premolars made of different ceramics materials. Materials and Methods: Thirty sound maxillary premolars were endodontically treated. They were randomly assigned into 3 groups (n=10), in which, teeth were prepared to receive all- ceramic restorations. GP: fiber post and resin core and ferrule with all-ceramic (IPS E-max CAD, Ivoclar-Vivadent) conventional crown. GE: Endocrown with butt joint finish line design made of (IPS E-max CAD, Ivoclar-Vivadent). GC: Endocrown with butt joint finish line design made of hybrid nanoceramic (CERASMART, GC Dental, USA). The lithium disilicate (IPS E-max press, Ivoclar-Vivadent) and hybrid nanoceramic (CERASMART, GC Dental, USA) all-ceramic restorations were made by CAD/CAM system (CEREC MC XL SW 4.0) and adhesively cemented with dual-cure resin cement (BisCem Bisco, Inc, USA). Specimens were mounted in a universal testing machine (Model 3345; Instron Industrial Products, Norwood, MA, USA). Each specimen was loaded to failure at a crosshead speed of 5.0 mm / min. Mode of failure was also examined. Data were analyzed using one way analysis of variance (ANOVA) and Tukey’s post hoc significance difference tests. Differences were considered significant at P<0.05. Results: One way ANOVA test showed that group (GC) recorded statistically significant (p 0.05) difference between GP and GC groups. Conclusions: Within the limitations of this study, all fracture resistance loads obtained in this study were far beyond the maximum masticatory forces and the presence of hybrid nanoceramic increased the fracture resistance of endodontically treated maxillary premolars restored with endocrown than those restored with lithium disilicate endocrowns, in failure mode hybrid nanoceramic showed favorable fracture pattern than lithium disilicate.

Fatigue limits of different PEEK materials for dental implants

The increasing use of PEEK (poly-ether-ether-ketone) as a substitute for metal implant components has led to the suggestion that it could also be used as an alternative to titanium in the field of dental implants. A major requirement for dental implant materials is their resistance to cyclic loading due to mastication.A special fatigue test was designed to evaluate the elastic behavior and long-term form stability of cylindrically shaped PEEK specimens of 4, 5 and 6mm in diameter, using 11 different PEEK materials of various grades: unfilled, filled with titanium dioxide or barium sulfate powder, reinforced with short carbon fibers or short glass fibers, and reinforced with continuous carbon fibers. The samples were exposed to cyclic loads of up to 2000N.The elastic limits ranged between 46.57±6.44MPa for short carbon fiber reinforced specimens of 6mm diameter and 107.62±8.23MPa for samples of a different short carbon fiber reinforced PEEK compound of 4mm diameter. The elastic limits of the two PEEK grades containing continuous carbon fibers could not be observed because they exceeded the limits of the test specification.The elastic moduli ranged between 2.06±0.18GPa for barium sulfate powder filled PEEK-specimens of 6 mm diameter and 57.53±14.3GPa for continuous carbon fibers reinforced PEEK-specimens of 4 mm diameter.In terms of the elastic limit all the PEEK materials in consideration were able to resist the pressure caused by maximum masticatory forces.

Stress distribution in the cervical region of an upper central incisor in a 3D finite element model

The aim of this study was to evaluate the stress distribution in the cervical region of a sound upper central incisor in two clinical situations, standard and maximum masticatory forces, by means of a 3D model with the highest possible level of fidelity to the anatomic dimensions. Two models with 331,887 linear tetrahedral elements that represent a sound upper central incisor with periodontal ligament, cortical and trabecular bones were loaded at 45 masculine in relation to the tooth's long axis. All structures were considered to be homogeneous and isotropic, with the exception of the enamel (anisotropic). A standard masticatory force (100 N) was simulated on one of the models, while on the other one a maximum masticatory force was simulated (235.9 N). The software used were: PATRAN for pre- and post-processing and Nastran for processing. In the cementoenamel junction area, tensile forces reached 14.7 MPa in the 100 N model, and 40.2 MPa in the 235.9 N model, exceeding the enamel's tensile strength (16.7 MPa). The fact that the stress concentration in the amelodentinal junction exceeded the enamel's tensile strength under simulated conditions of maximum masticatory force suggests the possibility of the occurrence of non-carious cervical lesions such as abfractions.

Comparison of two types of ceromer molar crowns on their fracture resistance: An in-vitro study

GC Gradia and Signum+ are two different types of ceromer available for clinical use in the last few years. They showed an excellent esthetic and clinical success; however, their fracture strength needed further investigation. The aim of this study was to compare the fracture resistance of these two ceromers in a situation that simulates clinical conditions. Twenty extracted human mandibular molars, similar in their dimensions, were selected and prepared. After tooth preparation, impressions were taken and casts were made. Ten molar crowns were fabricated with GC Gradia and the other 10 molar crowns were made of Signum+ at random. All the molar crowns were luted on human molars with a resin cement named Dual-Cement. After all samples were thermally cycled, they were loaded mechanically to fracture using a universal testing machine (Instron). At the fracture moment, data were registered. Statistical analysis was performed and the results showed that the fracture resistance of GC Gradia (2652/75±511N) is higher than Signum+ (2106/09±304N). A Mann-Whitney test showed statistically significant differences between the two systems ( P = 0.029). Since both systems exceeded the fracture strength required to withstand the maximum masticatory force in the molar region, they can be used to fabricate single molar crowns, but probably GC Gradia can be used with more confidence in the clinic.

Comparison of three types of fiber-reinforced composite molar crowns on their fracture resistance and marginal adaptation

Three types of fiber-reinforced composite (FRC) molar crowns were tested on their fracture resistance and marginal adaptation under simulated oral stress conditions. Two glass fiber systems, one processed with a vacuum/pressure system, the other by manual fiber adaptation, and a polyethylene fiber system were evaluated. Every group consisted of 12 crowns. All crowns were luted adhesively on human molars and exposed to thermal cycling and mechanical loading (TCML: 6000×5°C/55°C; 1.2×10 6×50 N; 1.66 Hz). The marginal adaptation was evaluated through dye-penetration and analyzed semi-quantitatively with a scanning electron microscope. The fracture resistance was measured using a Zwick universal testing machine. The highest fracture resistance was observed on the glass-fiber systems (FibreKor/Sculpture 1875 N±596; Vectris/Targis 1726±542), though statistically, the polyethylene system (belleGlass/Connect 1388±620) was not significantly weaker. All systems exceeded the fracture resistance required to withstand the maximum masticatory forces expected in the molar region. The marginal adaptation generally had a tendency towards larger gaps after TCML. The crown/composite-cement bond deteriorated significantly after TCML with the manual fiber adaptation and the polyethylene fiber system. The cement/tooth bond strength depended on which composite-cement/dentin-adhesive system was used. Conclusion: The fracture resistance of molar crowns made of glass-fiber reinforced composite was higher than those of polyethylene fiber-reinforced composite crowns. However, there was no statistically significant difference. The marginal adaptation seems to depend on the fiber systems and composite-cement/dentin adhesive system used.

Patterns Observed in the First Chew of Foods with Various Textures.

Pressure distribution during the chewing of food with molars was measured using a multiple-point sheet sensor, and compared with results from an instrumental compression test. The sensor system detected the masticatory pressure with many sensing cells so that masticatory force and contact area between food materials and the lower teeth were directly measured. Masticatory pressure of five foods (white bread, raw carrot, cracker, rice cracker and Yokan) for fourteen healthy adults was measured, and the different pressure patterns related to the texture were discussed. Masticatory force versus time curves were characterized by each sample, although they varied largely by subject. Two peaks appeared in the masticatory curves of carrot and Yokan, more peaks were shown in cracker and rice cracker, but the first peak was missing for the bread mastication. The first peak corresponded to sample rupture, therefore the active pressure defined as the force divided by the contact area was found to reflect the breaking stress of the samples. Similar to the results of mechanical tests, brittle cracker and rice cracker showed a lower breaking force within a short time at the first peak. The last peak appearing just before teeth opening was similar to the maximum masticatory force for bread, cracker, rice cracker and Yokan, and did not correspond with the breaking force of samples. The order of the active pressure at the last peak was similar to that of stress values at very high strain measured in a compression test. The maximum force detected during one chew is not always measured in a normal instrumental test.