Finite element analysis in implant dentistry: State of the art and future directions.

OBJECTIVE: To discuss the state of the art of Finite Element (FE) modeling in implant dentistry, to highlight the principal features and the current limitations, and giving recommendations to pave the way for future studies. METHODS: The articles' search was performed through PubMed, Web of Science, Scopus, Science Direct, and Google Scholar using specific keywords. The articles were selected based on the inclusion and exclusion criteria, after title, abstract and full-text evaluation. A total of 147 studies were included in this review. RESULTS: To date, the FE analysis of the bone-dental implant system has been investigated by analyzing several types of implants; modeling only a portion of bone considered as isotropic material, despite its anisotropic behavior; assuming in most cases complete osseointegration; considering compressive or oblique forces acting on the implant; neglecting muscle forces and the bone remodeling process. Finally, there is no standardized approach for FE modeling in the dentistry field. SIGNIFICANCE: FE modeling is an effective computational tool to investigate the long-term stability of implants. The ultimate aim is to transfer such technology into clinical practice to help dentists in the diagnostic and therapeutic phases. To do this, future research should deeply investigate the loading influence on the bone-implant complex at a microscale level. This is a key factor still not adequately studied. Thus, a multiscale model could be useful, allowing to account for this information through multiple length scales. It could help to obtain information about the relationship among implant design, distribution of bone stress, and bone growth. Finally, the adoption of a standardized approach will be necessary, in order to make FE modeling highly predictive of the implant's long-term stability.

Lithium disilicate and zirconia reinforced lithium silicate glass-ceramics for CAD/CAM dental restorations: biocompatibility, mechanical and microstructural properties after crystallization.

OBJECTIVES: The objective of this study was to define the impact of heating rate on the crystal growth, the mechanical properties, and the biocompatibility of three different kinds of CAD/CAM glass-ceramics treated with a conventional furnace. METHODS: Lithium disilicate (IPS EMax-CAD, Ivoclar Vivadent) (LS2) and two zirconia reinforced lithium silicate (ZLS) ceramics (Vita Suprinity PC, VITA Zahnfabrik; Celtra Duo, Dentsply Sirona) (ZLSS; ZLSC) were used. The mechanical properties and the crystal growth were evaluated on 42 specimens (n = 14 per group). The thermal treatments recommended by the manufacturers were carried out. All groups were tested for fracture toughness (Ft) and Vickers hardness (Hv). Scanning electron microscope (SEM) images were taken after a slight surface etching with hydrofluoric acid solution (1% for 20 s). Differential Thermal Analysis (DTA) was performed and cellular adhesion with human periodontal ligament stem cells (hPDLSCs) culture was qualitatively assayed. Data were analyzed with Repeated Measurements ANOVA and ANOVA followed by Tukey post hoc test. RESULTS: The crystals' mean size (±SD) after heat treatment was 1650.0 (±340.0) nm for LS2, 854.5 (±155.0) nm for ZLSS and 759.9 (±118.4) nm for ZLSC (p < 0.05 among the groups). As consequence of crystallization, the Hv was 6.1 ± 0.3 GPa for LS2, 7.6 ± 0.7 GPa for ZLSS and 7.1 ± 0.5 GPa for ZLSC (p < 0.05 for LS2 vs ZLSS and ZLSC), while the Ft was 2.2 ± 0.1 MPa m1/2 for LS2, 4.7 ± 0.8 MPa m1/2 for ZLSS and 3.8 ± 0.6 MPa m1/2 for ZLSC (p < 0.05 among the groups). The DTA curves showed a crystallization process for LS2, ZLSS and ZLSC at a temperature range 810-840 °C. The amount of adherent hPDLSCs was superior on LS2 than on ZLS. CONCLUSIONS: All the CAD/CAM materials can be properly crystallized if heat treated following the manufacturers' instructions. The crystallization process highly depends on temperature. ZLS glass ceramics show significantly inferior crystals dimensions and higher fracture toughness and Vickers hardness than LS2 ceramic. hPDLSCs cultured on LS2 have a superior adhesion than those cultured on ZLS. CLINICAL SIGNIFICANCE: The value of this study relies on the demonstration that a proper heat-treatment of CAD/CAM lithium disilicate and ZLS glass ceramics generates products that are suitable for clinical use . The differences highlightable in mechanical properties and biocompatibility behavior do not affect their successful clinical application.

Water-Airborne-Particle Abrasion as a Pre-Treatment to Improve Bioadhesion and Bond Strength of Glass-Ceramic Restorations: From In Vitro Study to 15-Year Survival Rate.

The purposes of this study were to evaluate the efficacy of water-airborne-particle abrasion (WAPA) as pre-etching procedure for tooth surfaces to increase bond strength, and to compare the survival rate of WAPA vs. non-WAPA glass-ceramic restorations with a 15-year follow-up. The occlusal surfaces of 20 human molars were sectioned and flattened. The prepared surfaces areas were subdivided into two parts: one received WAPA treatment (prophy jet handpiece with 50 µm aluminium oxide particles) followed by acid etching (37% phosphoric acid for 20 s/3-step etch-and-rinse); the other one was only acid-etched. In total, 108 specimens were obtained from the teeth, of which 80 were used to measure the micro-tensile bond strength (µTBS) in the WAPA (n = 40) and control (n = 40) groups, while the remaining specimens (n = 28) were investigated via SEM to evaluate the micromorphology and roughness (Ra) before and after the different treatment steps. The survival rate (SR) was performed on 465 glass-ceramic restorations (131 patients) comparing WAPA treatment (n = 183) versus non-WAPA treatment (n = 282). The bond strength was 63.9 ± 7.7 MPa for the WAPA group and 51.7 ± 10.8 MPa for the control group (p < 0.001). The Ra was 98 ± 24 µm for the enamel control group, 150 ± 35 µm for the enamel WAPA group, 102 ± 27 µm for the dentin control group and 160 ± 25 µm for the dentin WAPA group. The Ra increase from the WAPA procedure for enamel and dentin was statistically significant (p < 0.05). Under SEM, resin tags were present in both groups although in the WAPA they appeared to be extended in a 3D arrangement. The SR of the WAPA group (11.4 years) was 94%, while the SR of the non-WAPA group (12.3 years) was 87.6% (p < 0.05). The WAPA treatment using aluminium oxide particles followed by a 3-step etch-and-rinse adhesive system significantly improved bioadhesion with an increased bond strength of 23.6% and provided superior long-term clinical performance of glass-ceramic restorations.

Collagen Fibres Orientation in the Bone Matrix around Dental Implants: Does the Implant's Thread Design Play a Role?

The aim of this study was to analyse the influence of different thread shapes of titanium dental implant on the bone collagen fibre orientation (BCFO) around loaded implants. Twenty titanium dental implants, divided for thread shapes in six groups (A-F) were analysed in the present study. All implants were immediately loaded and left in function for 6 months before retrieval. The parameters evaluated under scanning electron microscope were the thread width, thread depth, top radius of curvature, flank angle, and the inter-thread straight section. Two undecalcified histological sections were prepared from each implant. Birefringence analysis using circularly polarized light microscopy was used to quantitively measure BCFO. For groups A-F, respectively, transverse BCFO was 32.7%, 24.1%, 22.3%, 18.2%, 32.4%, and 21.2%, longitudinal BCFO was 28.2%, 14.5%, 44.9%, 33.1%, 37.7%, and 40.2%. The percentage differences between transverse and longitudinal orientation were 4.50% (A), 9.60% (B), -22.60% (C), -14.90% (D), -5.30% (E), and -19.00% (F). Following loading, the amount of transverse and longitudinal BCFO were significantly influenced by the thread shape. The greater flank angles and narrower inter-thread sections of the "V" shaped and "concave" shaped implant threads of groups A and B, respectively, promoted the predominance of transverse BCFO, compared to groups C-F (p < 0.05). A narrow inter-thread straight section promotes transverse BCFO, as do "V" shaped and "concave" shaped threads, which can thus be considered desirable design for implant threads.

The Plant Nuclear Envelope and Its Role in Gene Transcription.

Chromosomes are dynamic entities in the eukaryotic nucleus. During cell development and in response to biotic and abiotic change, individual sections as well as entire chromosomes re-organise and reposition within the nuclear space. A focal point for these processes is the nuclear envelope (NE) providing both barrier and anchor for chromosomal movement. In plants, positioning of chromosome regions and individual genes at the nuclear envelope has been shown to be associated with distinct transcriptional patterns. Here, we will review recent findings on the interplay between transcriptional activity and gene positioning at the nuclear periphery (NP). We will discuss potential mechanisms of transcriptional regulation at the nuclear envelope and outline future perspectives in this research area.

In Vitro Fumonisin Biosynthesis and Genetic Structure of Fusarium verticillioides Strains from Five Mediterranean Countries.

Investigating the in vitro fumonisin biosynthesis and the genetic structure of Fusarium verticillioides populations can provide important insights into the relationships between strains originating from various world regions. In this study, 90 F. verticillioides strains isolated from maize in five Mediterranean countries (Italy, Spain, Tunisia, Egypt and Iran) were analyzed to investigate their ability to in vitro biosynthesize fumonisin B1, fumonisin B2 and fumonisin B3 and to characterize their genetic profile. In general, 80% of the analyzed strains were able to biosynthesize fumonisins (range 0.03-69.84 µg/g). Populations from Italy, Spain, Tunisia and Iran showed a similar percentage of fumonisin producing strains (>90%); conversely, the Egyptian population showed a lower level of producing strains (46%). Significant differences in fumonisin biosynthesis were detected among strains isolated in the same country and among strains isolated from different countries. A portion of the divergent FUM1 gene and of intergenic regions FUM6-FUM7 and FUM7-FUM8 were sequenced to evaluate strain diversity among populations. A high level of genetic uniformity inside the populations analyzed was detected. Apparently, neither geographical origin nor fumonisin production ability were correlated to the genetic diversity of the strain set. However, four strains from Egypt differed from the remaining strains.

Effects of 10-MDP Based Primer on Shear Bond Strength between Zirconia and New Experimental Resin Cement.

To date, numerous materials in the dental field are marketed to ensure stable adhesive cementation of zirconia ceramics (Y-TZP). The aims of this study were to assess the shear bond strength of the new experimental cement Surgi Dual Flo' Zr to Y-TZP compared to Panavia V5 cement, and to evaluate the effect of 10-MDP (10-methacryloyloxydecyl dihydrogen phosphate) containing primer on their bond strength. Twenty composite cylinders and Y-TZP disks were adhesively luted and divided into four groups based on cement type used and application or not of 10-MDP. The groups (n = 5 each) were S 10MDP (Surgi Dual Flo' Zr with 10-MDP); S no 10MDP (Surgi Dual Flo' Zr without 10-MDP); P 10MDP (Panavia V5 with 10-MDP); P no 10MDP (Panavia V5 without 10-MDP). Maximum load resistance (ML) and shear bond strength (SBS) were tested and mode of failure qualitative documented via scanning electron microscopy. The data were analyzed with one-way ANOVA, Holm-Sidak method, and Bayesian analysis. ML and SBS were significantly higher in S 10MDP than in S no 10MDP; and in P 10MDP than in P no 10MDP (p < 0.05). No significant differences were found between S 10MDP and P 10MDP; S no 10MDP and P no 10MDP (p > 0.05). Cohesive, adhesive, and mixed failure occurred among the groups. Bond strength between the experimental resin-based cement and Y-TZP was adequate for clinical application when 10-MDP was added. 10-MDP containing primer was effective improving the bond strength to Y-TZP more than the different type of resinous cement.

Three-dimensional analysis of dental arch forms in Italian population.

BACKGROUND: The aim of this study was the comparison of male and female upper and lower dental arch form in untreated Italian patients by 3D analysis, to find differences in shape, in transversal and longitudinal diameters between sexes, and to give a representative set of population's dental arch to clinicians in order to provide suitable orthodontic treatment. METHODS: The sample consisted of 3D scans of dental casts deriving from 104 Italian untreated patients (Male = 35, Female = 69) in permanent dentition. An evaluation of the arch form was performed by angular and linear values on every patient using a 3D software (SolidWorks®). A Student's two-tailed t test was used to determine if the differences in measurements between the male and female groups were significant and the level of significance was set at P < 0.05. RESULTS: Statistically significant differences in upper and lower transversal and longitudinal diameters were found. Male arch widths were significantly larger than those of females. Male intercanine, intermolar, and interpremolar diameters were significantly greater than females. Dental arch depth was significantly smaller in the female group. Anterior upper dental arch form was flatter, wider, and less sharp in the female group. CONCLUSIONS: Basing on the anatomical arches differences found between sexes concerning Italian patients, it is suggested to have regard to each patient pre-treatment arch form, width, and depth during orthodontic treatment according to gender.

Accuracy of computer-aided oral implant surgery: a clinical and radiographic study.

PURPOSE: Computer-aided oral implant surgery offers several advantages over the traditional approach. The purpose of this study was to evaluate the in vivo accuracy of computer-aided, template-guided oral implant surgery by comparing the three-dimensional positions of planned and placed implants. MATERIALS AND METHODS: Oral implant therapy was performed in two treatment centers on eligible patients using computerized tomography (CT)-based software planning and computer-aided design/computer-assisted manufacture stereolithographic templates. A second CT scan was obtained after surgery. Preoperative and postoperative CT images were compared (planned vs actual implant positions), and the accuracy of this type of image-guided therapy was assessed. RESULTS: Twenty-five adult patients were included in this retrospective study; 17 (11 partially and eight fully edentulous arches) were treated in center 1, and eight (six partially and two fully edentulous arches) in center 2. Of the 104 implants inserted with the computer-aided method, 100 integrated, giving a cumulative survival rate of 96% (mean follow-up, 36 months). There were no major surgical complications. With regard to accuracy, 89 implants were available for comparison; mean lateral deviations at the coronal and apical ends of the implants were 1.4 mm and 1.6 mm, respectively. Mean depth deviation was 1.1 mm and mean angular deviation was 7.9 degrees. There was a statistically significant correlation in the accuracy of any implants placed with the same guide. There was no difference in accuracy data from the two private centers; nor could a learning curve be demonstrated. CONCLUSIONS: Based upon this clinical study of 25 patients, the following observations were made: (1) computer-aided oral implant surgery used in two treatment centers provided a high likelihood (96%) of implant survival, and (2) deviations from planned implant positions existed in the coronal and apical portions of the implants as well as with implant angulation. Mean deviations were less than 2 mm in any direction and less than 8 degrees.