Influence of restoration height and masticatory load orientation on ceramic endocrowns

Aim: Endocrown restorations are an alternative to restore endodontically treated teeth. Due to the fact that in the literature it is recommended a remnant of 1.5 mm, different heights of endocrown were elaborated and analyzed, obtaining possible faults and their location. This study aimed to evaluate the mechanism of stress distribution in the tooth/restoration set, varying two factors: "restoration height"-three levels, and load application-two levels (oblique or axial), totaling six groups. Materials and methods: For finite element analysis (FEA), a maxillary premolar was modeled with an endodontic treatment. Then, this template was triplicated and each copy received an endocrown restoration of different heights: G6 (4.5 mm), G7 (5.5 mm), and G8 (6.5 mm). The models were exported in STEP format to analysis software (ANSYS 17.2, ANSYS Inc.). During preprocessing, the solids were considered isotropic, linearly elastic, and homogeneous. Initially, a load (300 N) was axially applied in the central fossa region. For a second evaluation, an oblique load (300 N) was applied on the grinding slope of functional cusp. System fixation occurred at the base of polyurethane cylinder. Results were evaluated through maximum principal stress (MPS). Results: For axial load, lower stress values were generated in all groups. For oblique load, G8 showed a higher stress concentration in the cement layer and root dentin. Conclusion: When an endocrown restoration is performed, there is a tendency of failure in the cement line and in the root directly proportional to its size. However, regardless of the size of the element to be reconstituted, the axial direction of the masticatory loads tends to decrease stress concentration. Clinical significance: When performing an endocrown restoration, care must be taken with its high regardless the tooth remnant high, altering even the anatomical angulations of the occlusal face, when necessary, to avoid stress concentration in thick areas

In vitro evaluation of multi-walled carbon nanotube reinforced nanofibers composites for dental application

The goal of this study was to evaluate the mechanical properties of an experimental composite resin filled with nylon-6 nanofibers (N6), nylon-6 nanofibers with multi-walled carbon nanotubes (N6-MWCN) or with pre-polymerized resin at different concentrations. The fillers/particles were obtained from nanofibers produced by electrospinning technique or from pre-polymerized composite resin. The fillers were distributed in the composite resin in four different mass fractions (2.5, 5.0, 10.0, and 20.0%), totaling 12 groups. The volumetric polymerization shrinkage (VPS), composite film thickness (CRFT), flexural strength (FS) and elastic (E) modulus of the composite resins were calculated. The data were evaluated using two-way ANOVA and Tukey test (p <.05). The interaction concentration*filler material was statistically significant for the VPS (p =.0008) and for FS (p =.0001). The smallest VPS was observed in 20% concentration without a difference to 10% for N6-MWCN particles. For FS, N6-MWCN in 2.5 and 5.0% presented the highest values (116.4 ± 9.32; 118.5 ± 7.72). Both factors (p =.0001) were significant for CRFT. Higher concentration (20%) showed a higher film thickness. E modulus was similar for all conditions, with p =.0590 for filler material and p =.3987 for concentration. The most indicated composite reinforcement in order to achieve suitable flexural strength with decreased polymerization shrinkage is the use of pre-polymerized composite-based material at a concentration of 20%. N6-MWCNT particles in 2.5 or 5% concentrations should be incorporated to produce a composite resin presenting adequate strength associated with reduced film thickness

Effect of pH variation on the subcritical crack growth parameters of glassy matrix ceramics

The goals of our study were to calculate the subcritical crack growth (SCG) parameters of two veneering ceramics stored in water or Streptococcus mutans (S. mutans) biofilm and remineralizing medium, with indentation flaws. Feldspar (VM7) and leucite-reinforced (VM13) glass ceramic disks (Vita Zahnfabrik, Bad Säckingen, Germany) were made according to ISO 6872. Some specimens were indented with a Vickers diamond and the crack dimensions were measured. The specimens were fractured for a calculation of inert strength or further stored in water or submitted to pH variation, under preloading tension. Finally, the SCG parameters were calculated after the specimens were fractured under four stressing rates (MPa/s). Weibull analysis was conducted on non-indented specimens. XPS was performed as qualitative analysis. The subcritical crack of leucite ceramic did not vary with the media storage, but the glass-ceramic experienced a retarded growth after pH variation. The materials presented low Weibull modulus. Qualitative elemental analyses showed chemical modification on both ceramics. Therefore, the crack growth of leucite-reinforced ceramic was less affected by the environment pH than glass-ceramic

Short communication: Influence of retainer configuration and loading direction on the stress distribution of lithium disilicate resin-bonded fixed dental prostheses: 3D finite element analysis

The present study elucidates the mechanical performance of different designs of resin-bonded fixed dental prostheses made of lithium disilicate simulating masticatory loads of anterior or canine guidance. A three-dimensional model of maxilla was constructed containing central incisor and canine teeth, with edentulous space of the lateral incisor. Three designs of prosthesis were created: retained in central incisor (1-I), retained in canine (1-C) and fixed in both teeth (2-IC). The computational analysis was performed for load in canine and central incisor separately (100N, 45°). The tensile and shear stresses were calculated for the resin-bonded fixed dental prosthesis, bonding surface of each retainer and cement layer using 3D finite element analysis. The 20 highest stress values were analyzed using two-way ANOVA and post-hoc Tukey test, all with α = 5%. The computational analysis showed that 2-retainer resin-bonded fixed dental prosthesis presented the worst prognosis regardless of the mandibular movement. ANOVA showed that Mandibular movement*Retainer interaction influenced on the tensile and shear stresses values (p < 0.01). Higher stresses were observed in the connector region for all groups (13-82.2 MPa; 11-70.2 MPa). In order to reduce the stress concentration in the resin-bonded fixed dental prosthesis and the retainer made of lithium disilicate, the occlusion may serve as the selection criteria of the unitary abutment for better sustainability