Effect of elastic gradients on the fracture resistance of tri-layer restorative systems.

Objectives: To assess the impact of elastic gradients formed among restorative material, cement, and substrate on the fracture resistance of tri-layer restorative systems.

Methods: Four CAD/CAM materials were utilized, two glass-ceramics (IPS e.max CAD, Vita Suprinity) and two resin-ceramic hybrids (Vita Enamic, Lava Ultimate).

A finite element study on the risk of bone loss around posterior short implants in an atrophic mandible.

Purpose: This study aimed to evaluate the risk of bone loss around single short molar crown-supporting implants in an atrophic mandible.

Methods: Implants of different lengths (L = 4 or 6 mm) and diameters (Ø = 4.1 or 4.

Intrusion of overerupted periodontally compromised posterior teeth using orthodontic mini implants: A mechanobiological finite element study.

Introduction: The intrusion of posterior teeth had been considered challenging up to the development of orthodontic mini implants. In periodontally compromised teeth, the challenge is even greater, because of the root resorption risk due to periodontal ligament over-compression. Still, the precise strategy to determine the force reduction level remains uncertain.

Effect of processing methods on the chipping resistance of veneered zirconia.

Objectives: To evaluate the edge chipping resistance (R) and the fracture toughness (K) of 3Y-TZP bilayers produced with the following materials/processing combinations: fluorapatite glass-ceramic applied on zirconia using the traditional layering and hot-pressing (press-on) techniques; feldspathic porcelain using rapid layer technology (RLT); and lithium disilicate glass-ceramic using CAD-on method. The influence of the cooling rate (slow and fast) was analyzed for layering and hot-pressing.

Methods: Bilayer bars (25x4x2 mm) were made following manufacturers' instructions.

Orthodontically induced root resorption: A critical analysis of finite element studies' input and output.

Introduction: Orthodontically induced inflammatory root resorption (OIIRR) constitutes an undesirable risk connected to orthodontic treatment. Finite element analysis (FEA) is a powerful tool to study the risk of OIIRR. However, its efficiency in predicting OIIRR depends on the insertion of the correct inputs and the selection of an output coherent with the clinical failure mechanism.

Can maxilla and mandible bone quality explain differences in orthodontic mini-implant failures?

This study aimed to compare the risk of orthodontic mini-implant (OMI) failure between maxilla and mandible. A critical analysis of finite-element studies was used to explain the contradiction of the greatest clinical success for OMIs placed in the maxilla, despite the higher quality bone of mandible. Four tridimensional FE models were built, simulating an OMI inserted in a low-dense maxilla, control maxilla, control mandible, and high-dense mandible.

Why a zero CTE mismatch may be better for veneered Y-TZP structures.

Objective: Compare residual stress distribution of bilayered structures with a mismatch between the coefficient of thermal expansion (CTE) of framework and veneering ceramic. A positive mismatch, which is recommended for metal-ceramic dental crowns, was hypothesized to contribute to a greater chipping frequency in veneered Y-TZP structures. In addition, the multidirectional nature of residual stresses in bars and crowns is presented to explore some apparent contradictions among different studies.

Influence of residual thermal stresses on the edge chipping resistance of PFM and veneered zirconia structures: Experimental and FEA study.

Objective: Chipping fractures of the veneering porcelain are frequently reported for veneered all-ceramic crowns. In the present study, the edge chipping test is used to measure the toughness and the edge chipping resistance of veneered zirconia and porcelain-fused-to-metal (PFM). The aim is to describe an edge chipping method developed with the use of a universal testing machine and to verify the accuracy of this method to determine the influence of residual thermal stresses on the chipping fracture resistance of veneering porcelain.

How mechanical stresses modulate enamel demineralization in non-carious cervical lesions?

Objective: To introduce an experimental non-carious cervical lesion (NCCL) model for studying the influence of presence and type of stress (tension or compression) on acid effects involved in NCCL formation on the enamel near the cement-enamel junction (CEJ).

Methods: 108 bovine incisors were cut into 18 × 3×3 mm beams, with a notch in the cervical region to generate a standardized area of stress concentration. Half of the specimens were immersed in distilled water and the other half in acetic acid solution (pH 4.

Experimental and finite element study of residual thermal stresses in veneered Y-TZP structures.

The main complications of zirconia-based laminated systems are chipping and delamination of veneering porcelain, which has been found to be directly associated with the development of residual thermal stresses in the porcelain layer. This study investigates the effects of cooling rate and specimen geometry on the residual stress states in porcelain-veneered zirconia structures. Bilayers of three different shapes (bars, semi-cylindrical shells, and arch-cubic structures) with 1.

Influence of physical assessment of different light-curing units on irradiance and composite microhardness top/bottom ratio.

The aim of this study was to evaluate the influence of the physical assessment of different light-curing units from 55 dental offices on the irradiance and composite microhardness top/bottom ratio, and the influence of the radiometers for LED or QTH light sources on irradiance measurement. The irradiance of each light-curing unit was evaluated with two radiometers, either for LED or QTH light. A questionnaire regarding the type of source (LED or QTH), time of use, date of last maintenance and light-curing performance assessment applied.

Association of orthodontic force system and root resorption: A systematic review.

Introduction: In this systematic review, we assessed the literature to determine which evidence level supports the association of orthodontic force system and root resorption.

Methods: PubMed, Cochrane, and Embase databases were searched with no restrictions on year, publication status, or language. Selection criteria included human studies conducted with fixed orthodontic appliances or aligners, with at least 10 patients and the force system well described.

Influence of fiber post cementation length on coronal microleakage values in vitro and finite element analysis.

Aim: This study aims to evaluate, the Influence of different fiber posts cementation lengths by finite element analysis (FEA) and coronal microleakage.

Materials And Methods: Fifty anterior bovine teeth were sectioned to obtain roots with 16 mm length. The coronal length of the post was 6 mm for all groups, while the radicular length were varied 6, 8, 10 or 12 mm.

Experimental and FE displacement and polymerization stress of bonded restorations as a function of the C-Factor, volume and substrate stiffness.

Objectives: To determine the free surface displacement of resin-composite restorations as a function of the C-Factor, volume and substrate stiffness, and to compare the results with interfacial stress values evaluated by finite element analysis (FEA).

Methods: Surface displacement was determined by an extensometer using restorations with 4 or 6mm diameter and 1 or 2mm depth, prepared in either bovine teeth or glass. The maximum displacement of the free surface was monitored for 5 min from the start of photoactivation, at an acquisition rate of 1s(-1).

Influence of specimen dimensions and their derivatives (C-factor and volume) on polymerization stress determined in a high compliance testing system.

Objective: To verify the null hypothesis that in a high compliance testing system stress magnitude was not influenced by specimen dimensions and, therefore, by its cavity configuration factor (C-factor) and volume.

Methods: Twelve experimental groups were defined according to the specimen height (0.5, 1, 2 or 4mm) and diameter (4, 6 or 8mm).

Residual stresses in Y-TZP crowns due to changes in the thermal contraction coefficient of veneers.

Objective: To test the hypothesis that the difference in the coefficient of thermal contraction of the veneering porcelain above (αliquid) and below (αsolid) its Tg plays an important role in stress development during a fast cooling protocol of Y-TZP crowns.

Methods: Three-dimensional finite element models of veneered Y-TZP crowns were developed. Heat transfer analyses were conducted with two cooling protocols: slow (group A) and fast (groups B-F).

A method to investigate the shrinkage stress developed by resin-composites bonded to a single flat surface.

Objectives: To purpose a method for predicting the shrinkage stress development in the adhesive layer of resin-composite cylinders that shrink bonded to a single flat surface, by measuring the deflection of a glass coverslip caused by the shrinkage of the bonded cylinders. The correlation between the volume of the bonded resin-composite and the stress-peak was also investigated.

Methods: A glass coverslip deflection caused by the shrinkage of a bonded resin-composite cylinder (diameter: d=8 mm, 4 mm, or 2 mm, height: h=4 mm, 2 mm, 1 mm, or 0.

Assessment of nose protector for sport activities: finite element analysis.

There has been a significant increase in the number of facial fractures stemming from sport activities in recent years, with the nasal bone one of the most affected structures. Researchers recommend the use of a nose protector, but there is no standardization regarding the material employed. Clinical experience has demonstrated that a combination of a flexible and rigid layer of ethylene vinyl acetate (EVA) offers both comfort and safety to practitioners of sports.

Adhesion to tooth structure: a critical review of "macro" test methods.

Objectives: Bond strength between adhesive systems and the tooth structure is influenced by a large number of variables, which makes the comparison among studies virtually impossible. Also, failure often times propagates into the dental substrate or the composite, deeming the results questionable at best. In spite of the increased popularity gained by micro-tensile and micro-shear tests, in vitro evaluations using specimens with relatively large bonding areas remain frequent.

A critical view on biaxial and short-beam uniaxial flexural strength tests applied to resin composites using Weibull, fractographic and finite element analyses.

Objective: To evaluate the biaxial and short-beam uniaxial strength tests applied to resin composites based upon their Weibull parameters, fractographic features and stress distribution.

Methods: Disk- (15 mm x 1 mm) and beam-shaped specimens (10 mm x 2 mm x 1 mm) of three commercial composites (Concept/Vigodent, CA; Heliomolar/Ivoclar-Vivadent, HE; Z250/3M ESPE, FZ) were prepared. After 48h dry storage at 37 degrees C, disks and beams were submitted to piston-on-three-balls (BI) and three-point bending (UNI) tests, respectively.

Elastic modulus of posts and the risk of root fracture.

The definition of an optimal elastic modulus for a post is controversial. This work hypothesized that the influence of the posts' elastic modulus on dentin stress concentration is dependent on the load direction. The objective was to evaluate, using finite element analysis, the maximum principal stress (sigma(max)) on the root, using posts with different elastic modulus submitted to different loading directions.

Vertical root fracture in upper premolars with endodontic posts: finite element analysis.

Upper premolars restored with endodontic posts present a high incidence of vertical root fracture (VRF). Two hypotheses were tested: (1) the smaller mesiodistal diameter favors stress concentration in the root and (2) the lack of an effective bonding between root and post increases the risk of VRF. Using finite element analysis, maximum principal stress was analyzed in 3-dimensional intact upper second premolar models.

Influence of local factors on composite shrinkage stress development--a finite element analysis.

Purpose: Using finite element analysis (FEA), to determine the nominal shrinkage stress of a composite under different restriction conditions defined by the longitudinal compliance (LC) and C-factor (C) of the testing system, and by the elastic modulus of the bonding substrate (E).

Materials And Methods: Eight axisymmetric models representing an experimental setup used to determine composite shrinkage stress were simulated. Composite thicknesses of 0.

Polymerization stress of resin composites as a function of system compliance.

Objectives: Evaluate the effect of testing system compliance on polymerization stress and stress distribution of composites.

Methods: Composites tested were Filtek Z250 (FZ), Herculite (HL), Tetric Ceram (TC), Helio Fill-AP (HF) and Heliomolar (HM). Stress was determined in 1-mm thick specimens, inserted between two rods of either poly(methyl methacrylate), PMMA, or glass.

The suitability of different FEA models for studying root fractures caused by wedge effect.

Finite element analysis (FEA) utilizing models with different levels of complexity are found in the literature to study the tendency to vertical root fracture caused by post intrusion ("wedge effect"). The objective of this investigation was to verify if some simplifications used in bi-dimensional FEA models are acceptable regarding the analysis of stresses caused by wedge effect. Three plane strain (PS) and two axisymmetric (Axi) models were studied.