Biomechanical behavior of all-on-4 concept and alternative designs under different occlusal load configurations for completely edentulous mandible: a 3-D finite element analysis.

The aim of this study was to evaluate the effect of the All-on-4 design and 4 alternative implant-supported fixed prosthesis designs on stress distribution in implants, peri-implant bone, and prosthetic framework in the edentulous mandible under different loading conditions using three-dimensional finite element analysis (3D-FEA).Five different experimental finite element models (Model A (unsplinted 6), Model B (splinted 6), Model C (All-on-4), Model D (axial; 2 anterior, 2 posterior), and Model E (4 interforaminal)) were created. Three different loading conditions were applied (canine loading, unilateral I-loading, and unilateral II-loading). The highest minimum (Pmin) and the maximum (Pmax) principal stress values were acquired for cortical and trabecular bones; the highest von Mises (mvM) stress values were obtained for implants and metal frameworks. Model B and Model D showed the most favorable stress distribution. The All-on-4 design (Model C) also showed acceptable stress values close to those of Model B and Model D in the cortical and trabecular bones. In accordance with the stress values in the bone structure, the lowest stress values were measured in the implants and Co-Cr framework in Model B and Model D. The highest stress values in all structures were measured for unilateral loading- II, while the lowest values were found for canine loading. It was concluded that Model B and Model D experimental models showed better biomechanical performance in all structures. Furthermore, the use of a splinted framework, avoiding cantilevers, results in lower stress transmission. On the other hand, canine loading and unilateral loading-I exhibited the best loading conditions.

Biomechanical Analysis of One-Piece Postand- Core: High-Performance Polymers vs Conventional Materials.

PURPOSE: To evaluate the stress distribution along a premolar's root dentin, its post, and its post-luting agent when materials with different elastic moduli are used to fabricate one-piece post-and-cores in two different designs. MATERIALS AND METHODS: Two 3D virtual models (for cylindrical and conical post designs) of a mandibular premolar restored with one-piece post-and-core restorations were obtained using a software. A total of eight post-and-core materials were tested: polyetheretherketone (PEEK), polyetherketoneketone (PEKK), glass fiber-reinforced polyetheretherketone (GFR-PEEK), carbon fiber-reinforced polyetheretherketone (CFR-PEEK), gold-palladium alloy (Au-Pd), titanium (Ti), zirconia (Zi), and chromium-nickel (Cr-Ni). Maximum principals stress (MPS) in the post, post-luting agent, and root dentin were determined. A load of 150 N was applied to the buccal cusp in the linguo-labial direction at an angle of 45 degrees oblique to the longitudinal axis of the crown. RESULTS: The highest MPS value in post structure was observed with Cr-Ni material for both post designs. Similarly, the highest MPS value in the post-luting agent was observed for Cr-Ni, the material with the highest elastic modulus. However, in the root dentin, the highest value was observed in PEEK, the material with the lowest elastic modulus. CONCLUSIONS: Post material and design influenced the stress concentration in the post, post-luting agent, and root dentin. The stress at the root dentin was slightly higher for polymeric materials. Cylindrical post design revealed lower stresses than conical post design at root dentin for all post-and-core materials tested.

Comparative analysis of denture base adaptation performance between pour and other conventional fabrication techniques.

STATEMENT OF PROBLEM: Studies assessing the comparative denture base adaptation performance of the pour technique for various palatal vault depths are sparse. PURPOSE: The purpose of this in vitro study was to investigate the denture base adaptation performance of the pour technique compared with other conventional fabrication techniques (light-polymerization, injection, compression molding) for shallow and deep palatal vault depths. MATERIAL AND METHODS: Edentulous maxillary study models with 2 palatal vault depths were prepared. Based on the power analysis, the sample size of each conventional fabrication technique was 12 (N=96). After denture bases for each technique had been fabricated on the casts according to the manufacturers' recommendations, the casts and the intaglio surfaces of the denture bases were scanned by using a laboratory scanner (InEos X5). The standard tessellation language (STL) files of the casts and the intaglio surfaces of acrylic resin bases were transferred into a software program (Romexis, version 5.0), and the software superimposed each cast and its corresponding denture base scan with the reference pyramids semi-automatically. After superimposition, the mean gap distances (mm) were calculated by using the software and recorded from the identified 4 specific regions (denture border apex, palate, ridge crest, and posterior palatal seal). A statistical analysis was performed by using the 3-factor factorial ANOVA. Post hoc comparisons among the subgroups were performed by using the Tukey HSD test. RESULTS: Two- and 3-way interactions among palatal vault depth, polymerization technique, and location variables were statistically significant (P<.05). For shallow palatal vault depth, injection and pour polymerization techniques demonstrated similar mean gap distances irrespective of location (P>.05). The light-polymerization technique showed the highest mean gap distances among the tested polymerization techniques in all regions except for the posterior palatal seal area (P<.05). CONCLUSIONS: The pour technique showed similar denture base adaptation to compression molding and injection. Light-polymerization exhibited the highest mean gap distance between the denture base and the cast for both palatal vault depths for most of the locations. A deep palatal vault depth led to inferior denture base adaptation performance for light-polymerization in the ridge crest and compression molding in the posterior palatal seal location.

Resin Nanoceramic CAD/CAM Restoration of the Primary Molar: 3-Year Follow-Up Study.

This case report presents the clinical use of a resin nanoceramic CAD/CAM restoration of a primary second molar without successor in the form of a permanent second premolar tooth in a patient. Three-year follow-up of the case revealed that resin nanoceramic CAD/CAM restoration of the primary molar without successor achieved both aesthetics and function. Despite the high cost of treatment, this type of restoration should be considered if the retained tooth is expected to maintain functionality over the long term.

Strain characteristics of Marburg double crown-retained implant overdentures compared with bar and ball-retained implant overdentures, with and without a rigid major connector.

STATEMENT OF PROBLEM: It is hard to identify the most favorable retainer type and the denture design when considering strain levels around implants and in edentulous ridges for implant overdentures (IOVD). PURPOSE: The purpose of this study was to evaluate the strain transmitted to the implants and edentulous ridges by Marburg double crown (MDC)-retained IOVD as opposed to bar and ball-retained IOVD and the efficiency of a rigid major connector in the maxilla. MATERIAL AND METHODS: An in vitro maxillary model was prepared with 4 implants, with strain gauges placed distally to each implant and also in the anterior and posterior edentulous ridges. Five overdentures were fabricated for each MDC and each ball and bar attachment retainers. Vertical loads of 280 N were applied bilaterally on the first molar region. Then the palatal bars of each IOVD were disconnected, and loading procedures were repeated for the prostheses. RESULTS: No significant difference was observed among the MDC and the bar and ball-retained IOVD, with and without a rigid bar according to the data taken from both the implants and edentulous ridges. However, when the strain values attained from each strain gauge separately were considered, a slight difference was observed around the implants of ball-retained overdentures and in the edentulous ridges of MDC-retained overdentures. CONCLUSIONS: Within the limitations of this in vitro study, MDC-retained maxillary overdentures with 4 parallel and symmetrically placed implants can be used safely without a rigid major connector as with bar and ball-retained IOVD with regard to the strains generated in the edentulous ridge and around implants.