Analysis of the mesh resolution of an .STL exported from an intraoral scanner file.

OBJECTIVES: This study aimed to provide information on the accuracy of exported digital files with the different resolutions available in the CEREC 4.6.2 software obtained by means of an intraoral scanner (IOS), in addition to establishing differences between materialized models with different exported resolutions, and how these different exported files can influence finite element analysis (FEA) simulations. MATERIALS AND METHODS: The upper complete arch of 10 patients was scanned through an IOS (CEREC Omnicam 1.0/Dentsply Sirona). Files of three resolution meshes digitalized by a CAD software (Cerec SW, 4.6.2) high, medium and low (IOSH, IOSM, and IOSL) were exported. Each file was evaluated by a software (NETFABB) about the number of triangles obtained and compared with the number announced by the manufacturer. Also, with a superimposition with a specialized software (GEOMAGIC X), the digital models were compared. The files of each resolution were printed (Sprintray 3D Printer), and the printed models were scanned with IOS (Omnicam 1.0) and compared with the control group (intraoral scanned high-resolution file, IOSH). FEA simulations were imported into COMSOL and analyzed under different loading conditions. RESULTS: The number of exported triangles coincided with that reported by the manufacturer. The digital models from files of different resolution did not show significant differences (less than 1.5 um) between each other. Models printed (H, M, L) from files of the same resolution mesh (H, M, L) did not show significant differences between them either in partial measures of the arch and neither in the complete arch. FEA showed significant differences in stress concentration between different exported models. CLINICAL SIGNIFICANCE: Digital models can be exported and printed in three resolutions of the mesh, without differences clinically significative. On the other hand, for future FEA applications further research should be performed in order to determine the optimal number of triangles.

Measurement of Three-Dimensional Internal Dynamic Strains in the Intervertebral Disc of the Lumbar Spine With Mechanical Loading and Golden-Angle Radial Sparse Parallel-Magnetic Resonance Imaging.

BACKGROUND: Noninvasive measurement of internal dynamic strain can be potentially useful to characterize spine intervertebral disc (IVD) in the setting of injury or degenerative disease. PURPOSE: To develop and demonstrate a noninvasive technique to quantify three-dimensional (3D) internal dynamic strains in the IVD using a combination of static mechanical loading of the IVD using a magnetic resonance imaging (MRI)-compatible ergometer. STUDY TYPE: Prospective. SUBJECTS: Silicone gel phantom studies were conducted to assess strain variation with load and repeatability. Mechanical testing was done on the phantoms to confirm MR results. Eight healthy human volunteers (four men and four woman, age = 29 ± 5 years) underwent MRI using a rest, static loading, and recovery paradigm. Repeatability tests were conducted in three subjects. FIELD STRENGTH/SEQUENCE: MRI (3 T) with 3D continuous golden-angle radial sparse parallel (GRASP) and compressed sensing (CS) reconstruction. ASSESSMENT: CS reconstruction of the images, motion deformation, and Lagrangian strain maps were calculated for five IVD segments from L1/L2 to L5/S1. STATISTICAL TESTS: Ranges of displacement and strain in each subject and the resulting mean and standard deviation were calculated. Student t-tests were used to calculate changes in strain from loading to recovery. The correlation coefficient (CC) in the repeatability study was calculated. RESULTS: The most compressive strain experienced by the IVD segments under loaded conditions was in the L4/L5 segment (-7.5 ± 2.9%). The change in minimum strain from load to recovery was the most for the L4/L5 segment (-7.5% to -5.0%, P = 0.026) and the least for the L1/L2 segment (-4.4% to -3.9%, P = 0.51). In vivo repeatability in three subjects shows strong correlation between scans in subjects done 6 months apart, with CCs equal to 0.86, 0.94, and 0.94 along principal directions. DATA CONCLUSION: This study shows the feasibility of using static mechanical loading with continuous GRASP-MRI acquisition with CS reconstruction to measure 3D internal dynamic strains in the spine IVD. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 1.

Glycosylation Fosters Interactions between Model Sea Urchin Spicule Matrix Proteins. Implications for Embryonic Spiculogenesis and Biomineralization.

The formation of embryonic mineralized skeletal elements (spicules) in the sea urchin requires the participation of proteins, many of which may interact with one another and assist in the creation of an extracellular matrix wherein mineral formation takes place. To probe this, we created a sea urchin spicule recombinant model protein pair system wherein we tested the interactions between two major spicule proteins, SpSM50 and the glycoprotein, SpSM30B/C. Both proteins are strong hydrogelators that manipulate early and later events in mineral formation. We discovered that the anionic glycan moieties of SpSM30B/C are required for interaction with the SpSM50 protein and that these interactions are Ca(II)-independent. In addition, when these proteins form a complex, they create hybrid hydrogel particles that are physically distinct from their individual counterparts. Thus, glycan-mediated interactions play an important role in in vitro spicule protein assembly and most likely within the spicule itself.

Selective Synergism Created by Interactive Nacre Framework-Associated Proteins Possessing EGF and vWA Motifs: Implications for Mollusk Shell Formation.

In the nacre layer of the Pinctada fucata oyster shell there exists a multimember proteome, known as the framework family, which regulates the formation of the aragonite mesoscale tablets and participates in the creation of an organic coating around each tablet. Several approaches have been developed to understand protein-associated mechanisms of nacre formation, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights we have created a proportionally defined combinatorial model consisting of two recombinant framework proteins, r-Pif97 (containing a von Willebrand Factor Type A domain (vWA)) and r-n16.3 (containing an EGF-like domain), whose individual in vitro mineralization functionalities are distinct from one another. We find that at 1:1 molar ratios r-Pif97 and r-n16.3 exhibit little or no synergistic activity regarding modifying existing calcite crystals. However, during the early stages of nucleation in solution, we note synergistic effects on nucleation kinetics and ACC formation/stability (via dehydration) that are not observed for the individual proteins. This selective synergism is generated by Ca2+-mediated protein-protein interactions (∼4 molecules of r-n16.3 per 1 molecule of r-Pif97) which lead to the formation of nucleation-responsive hybrid hydrogel particles in solution. Interestingly, in the absence of Ca2+ there are no significant interactions occurring between the two proteins. This unique behavior of the framework-associated n16.3 and Pif97 proteins suggests that the Asp/Glu-containing regions of the vWA and EGF-like domains may play a role in both nacre matrix formation and mineralization.

A Model Sea Urchin Spicule Matrix Protein, rSpSM50, Is a Hydrogelator That Modifies and Organizes the Mineralization Process.

In the purple sea urchin Strongylocentrotus purpuratus, the formation and mineralization of fracture-resistant skeletal elements such as the embryonic spicule require the combinatorial participation of numerous spicule matrix proteins such as SpSM50. However, because of its limited abundance and solubility issues, it has been difficult to pursue extensive in vitro biochemical studies of SpSM50 protein and deduce its role in spicule formation and mineralization. To circumvent these problems, we expressed a tag-free bacterial model recombinant spicule matrix protein, rSpSM50. Bioinformatics and biophysical experiments confirm that rSpSM50 is an intrinsically disordered, aggregation-prone C-type lectin-like domain-containing protein that forms dimensionally and internally heterogeneous protein hydrogels that control the in vitro mineralization process in three ways. The hydrogels (1) kinetically stabilize the aqueous calcium carbonate system against nucleation and thermodynamically destabilize the initially formed ACC in bulk solution, (2) promote and organize faceted single-crystal calcite and polycrystalline vaterite nanoparticles, and (3) promote surface texturing of calcite crystals and induce subsurface nanoporosities and channels within both calcite and vaterite crystals. Many of these features are also common to mollusk shell nacre proteins and the sea urchin spicule matrix glycoprotein, SpSM30B/C, and we conclude that rSpSM50 is a spiculogenesis hydrogelator protein that exhibits traits found in other calcium carbonate mineral-modification proteins.

Functional Prioritization and Hydrogel Regulation Phenomena Created by a Combinatorial Pearl-Associated Two-Protein Biomineralization Model System.

In the nacre or aragonitic layer of an oyster pearl, there exists a 12-member proteome that regulates both the early stages of nucleation and nanoscale-to-mesoscale assembly of nacre tablets and calcitic crystals from mineral nanoparticle precursors. Several approaches to understanding protein-associated mechanisms of pearl nacre formation have been developed, yet we still lack insight into how protein ensembles or proteomes manage nucleation and crystal growth. To provide additional insights, we have created a proportionally defined combinatorial model consisting of two pearl nacre-associated proteins, PFMG1 and PFMG2 (shell oyster pearl nacre, Pinctada fucata) whose individual in vitro mineralization functionalities are distinct from one another. Using scanning electron microscopy, atomic force microscopy, Ca(II) potentiometric titrations, and quartz crystal microbalance with dissipation monitoring quantitative analyses, we find that at 1:1 molar ratios, rPFMG2 and rPFMG1 co-aggregate in specific molecular ratios to form hybrid hydrogels that affect both the early and later stages of in vitro calcium carbonate nucleation. Within these hybrid hydrogels, rPFMG2 plays a role in defining protein co-aggregation and hydrogel dimension, whereas rPFMG1 defines participation in nonclassical nucleation processes; both proteins exhibit synergy with regard to surface and subsurface modifications to existing crystals. The interactions between both proteins are enhanced by Ca(II) ions and may involve Ca(II)-induced conformational events within the EF-hand rPFMG1 protein, as well as putative interactions between the EF-hand domain of rPFMG1 and the calponin-like domain of rPFMG2. Thus, the pearl-associated PFMG1 and PFMG2 proteins interact and exhibit mineralization functionalities in specific ways, which may be relevant for pearl formation.

A Model Sea Urchin Spicule Matrix Protein Self-Associates To Form Mineral-Modifying Protein Hydrogels.

In the purple sea urchin Strongylocentrotus purpuratus, the formation and mineralization of fracture-resistant skeletal elements such as the embryonic spicule require the combinatorial participation of numerous spicule matrix proteins such as the SpSM30A-F isoforms. However, because of limited abundance, it has been difficult to pursue extensive biochemical studies of the SpSM30 proteins and deduce their role in spicule formation and mineralization. To circumvent these problems, we expressed a model recombinant spicule matrix protein, rSpSM30B/C, which possesses the key sequence attributes of isoforms "B" and "C". Our findings indicate that rSpSM30B/C is expressed in insect cells as a single polypeptide containing variations in glycosylation that create microheterogeneity in rSpSM30B/C molecular masses. These post-translational modifications incorporate O- and N-glycans and anionic mono- and bisialylated and mono- and bisulfated monosaccharides on the protein molecules and enhance its aggregation propensity. Bioinformatics and biophysical experiments confirm that rSpSM30B/C is an intrinsically disordered, aggregation-prone protein that forms porous protein hydrogels that control the in vitro mineralization process in three ways: (1) increase the time interval for prenucleation cluster formation and transiently stabilize an ACC polymorph, (2) promote and organize single-crystal calcite nanoparticles, and (3) promote faceted growth and create surface texturing of calcite crystals. These features are also common to mollusk shell nacre proteins, and we conclude that rSpSM30B/C is a spiculogenesis protein that exhibits traits found in other calcium carbonate mineral modification proteins.

Microwave processing of a dental ceramic used in computer-aided design/computer-aided manufacturing.

Because of their favorable mechanical properties and natural esthetics, ceramics are widely used in restorative dentistry. The conventional ceramic sintering process required for their use is usually slow, however, and the equipment has an elevated energy consumption. Sintering processes that use microwaves have several advantages compared to regular sintering: shorter processing times, lower energy consumption, and the capacity for volumetric heating. The objective of this study was to test the mechanical properties of a dental ceramic used in computer-aided design/computer-aided manufacturing (CAD/CAM) after the specimens were processed with microwave hybrid sintering. Density, hardness, and bending strength were measured. When ceramic specimens were sintered with microwaves, the processing times were reduced and protocols were simplified. Hardness was improved almost 20% compared to regular sintering, and flexural strength measurements suggested that specimens were approximately 50% stronger than specimens sintered in a conventional system. Microwave hybrid sintering may preserve or improve the mechanical properties of dental ceramics designed for CAD/CAM processing systems, reducing processing and waiting times.

A Preliminary Model of the Wrist Midcarpal Joint.

Background A challenge to deciphering the effect of structure on function in the wrist involves difficulty in obtaining in-vivo information. To provide a platform to study wrist mechanics using in vivo acquired forces, we developed a model of the midcarpal joint based on computed tomography (CT) scans of normal wrists. Finite element analysis (FEA) can enable application of in vivo collected information to an ex vivo model. Objectives The objectives of this study are to (1) create a three-dimensional model of the midcarpal joint of the wrist based on CT scans and (2) generate separate models for the midcarpal joint based on two distinct wrist types and perform a pilot loading of the model. Methods CT scans from a normal patient database were converted to three-dimensional standard template library (STL) files using OsiriX software. Five type 1 and five type 2 wrists were used for modeling. A simulated load was applied to the carpometacarpal joints in a distal-to-proximal direction, and FEA was used to predict force transfer in the wrist. Results There were 33% type 1 and 67% type 2 wrists. The midcarpal joint dimensional measurements estimated from the model had intermediate agreement between wrist type as measured on CT scan and as predicted by the model: 56% Cohen's kappa (95% confidence interval) = 0.221 (0.05-0.5). Surface stress on the carpometacarpal joints is different in type 1 and type 2 wrists. On loading the neutral wrist, the capitolunate angle was 90 degrees in type 1 wrists and 107 degrees in type 2 wrists ( p < 0.0001). Conclusions The model predicted differences in movement and force transfer through the midcarpal joint dependent on structural type. This knowledge can improve our understanding of the development of disparate patterns of degeneration in the wrist.

Skeletal development in the sea urchin relies upon protein families that contain intrinsic disorder, aggregation-prone, and conserved globular interactive domains.

The formation of the sea urchin spicule skeleton requires the participation of hydrogel-forming protein families that regulate mineral nucleation and nanoparticle assembly processes that give rise to the spicule. However, the structure and molecular behavior of these proteins is not well established, and thus our ability to understand this process is hampered. We embarked on a study of sea urchin spicule proteins using a combination of biophysical and bioinformatics techniques. Our biophysical findings indicate that recombinant variants of the two most studied spicule matrix proteins, SpSM50 and SpSM30B/C (S. purpuratus) have a conformational landscape that include a C-terminal random coil/intrinsically disordered MAPQG sequence coupled to a conserved, folded N-terminal C-type lectin-like (CTLL) domain, with SpSM50 > SpSM30B/C with regard to intrinsic disorder. Both proteins possess solvent-accessible unfolded MAQPG sequence regions where Asn, Gln, and Arg residues may be accessible for protein hydrogel interactions with water molecules. Our bioinformatics study included seven other spicule matrix proteins where we note similarities between these proteins and rare, unusual proteins that possess folded and unfolded traits. Moreover, spicule matrix proteins possess three types of sequences: intrinsically disordered, amyloid-like, and folded protein-protein interactive. Collectively these reactive domains would be capable of driving protein assembly and hydrogel formation. Interestingly, three types of global conformations are predicted for the nine member protein set, wherein we note variations in the arrangement of intrinsically disordered and interactive globular domains. These variations may reflect species-specific requirements for spiculogenesis. We conclude that the molecular landscape of spicule matrix protein families enables them to function as hydrogelators, nucleators, and assemblers of mineral nanoparticles.

Mechanical Loading Promotes the Expansion of Primitive Osteoprogenitors and Organizes Matrix and Vascular Morphology in Long Bone Defects.

Elucidating the effects of mechanical stimulation on bone repair is crucial for optimization of the healing process. Specifically, the regulatory role that mechanical loading exerts on the osteogenic stem cell pool and vascular morphology during healing is incompletely understood. Because dynamic loading has been shown to enhance osteogenesis and repair, we hypothesized that loading induces the expansion of the osteoprogenitor cell population within a healing bone defect, leading to an increased presence of osteogenic cells. We further hypothesized that loading during the repair process regulates vascular and collagen matrix morphology and spatial interactions between vessels and osteogenic cells. To address these hypotheses, we used a mechanobiological bone repair model, which produces a consistent and reproducible intramembranous repair response confined in time and space. Bilateral tibial defects were created in adult C57BL/6 mice, which were subjected to axial compressive dynamic loading either during the early cellular invasion phase on postsurgical days (PSDs) 2 to 5 or during the matrix deposition phase on PSD 5 to 8. Confocal and two-photon microscopy was used to generate high-resolution three-dimensional (3D) renderings of longitudinal thick sections of the defect on PSD 10. Endomucin (EMCN)-positive vessels, Paired related homeobox 1 (Prrx1+) stem cell antigen-1 positive (Sca-1+) primitive osteoprogenitors (OPCs), and osterix positive (Osx+) preosteoblasts were visualized and quantified using deep tissue immunohistochemistry. New bone matrix was visualized with second harmonic generation autofluorescence of collagen fibers. We found that mechanical loading during the matrix deposition phase (PSD 5 to 8) increased vessel volume and number, and aligned vessels and collagen fibers to the load-bearing direction of bone. Furthermore, loading led to a significant increase in the proliferation and number of Prrx1+ Sca-1+ primitive OPCs, but not Osx+ preosteoblasts within the defect. Together, these data illustrate the adaptation of both collagen matrix and vascular morphology to better withstand mechanical load during bone repair, and that the mechanoresponsive cell population consists of the primitive osteogenic progenitors. © 2019 American Society for Bone and Mineral Research.

Insights into Mollusk Shell Formation: Interlamellar and Lamellar-Specific Nacre Protein Hydrogels Differ in Ion Interaction Signatures.

In the mollusk shell nacre layer, there exist hydrogelator proteomes that play important roles in the formation of the mineral phase. Two of these proteomes, the intracrystalline and the framework, reside in the interior and exterior, respectively, of the nacre tablets. To date there is no clear evidence of what distinguishes an intracrystalline protein from a framework protein regarding the nucleation process. Using Eu(III), phosphate anions, and recombinant versions of the intracrystalline protein, AP7 and the framework protein, n16.3 we probed each protein hydrogel for its interactions with these model ions. Fluorescence spectroscopy of Eu(III) interactions with both protein hydrogels revealed that r-AP7 exhibited enhanced effects on Eu(III) fluorescence compared to r-n16.3, and, 31P NMR experiments demonstrated that r-AP7 had a more significant impact on phosphate anions compared to r-n16.3. Thus, r-AP7 was found to be more of an ion "disruptor" than r-n16.3. Interestingly, these findings correlate with the particle size distributions and internal structure of the hydrogel particles themselves, suggesting that the physical and chemical properties of the hydrogels dictate hydrogel-ion interactions. In conclusion, we confirm that hydrogelator proteomes possess distinguishable ion interaction properties that may impact the nucleation processes in these regions and control the overall formation of mesoscale nacre tablets.

Intracrystalline incorporation of nacre protein hydrogels modifies the mechanical properties of calcite crystals: a microcompression study.

The fracture toughness of mollusk shell nacre has been attributed to many factors, one of which is the intracrystalline incorporation of nacre-specific proteins. Although mechanical force measurements have been made on the nacre layer and on individual calcium carbonate crystals containing occluded organic molecules and macromolecules, there are few if any studies which examine the impact of occluded proteins on the mechanical properties of calcium carbonate crystals. To remedy this, we performed microcompression studies of calcite crystals grown in the presence and absence of two recombinant nacre proteins, r-AP7 (H. rufescens, intracrystalline proteome) and r-n16.3 (P. fucata, framework proteome), both of which are known aggregators that form hydrogel nanoinclusions within in vitro calcite. We find that, relative to protein-free calcite, the intracrystalline inclusion of either r-AP7 or r-n16.3 nacre protein hydrogels within the calcite crystals leads to a reduction in strength. However, nacre protein-modified crystals were found to exhibit elastic deformation under force compared to control scenarios, with no discernable differences noted between intracrystalline or framework protein-modified crystals. We conclude from our in vitro microcompression studies that the intracrystalline incorporation of nacre proteins can contribute to fracture-resistance of the crystalline phase by significantly reducing both modulus AND critical strength.

Use of Ferrule Rings as Stress Dissipators in Temporomandibular Joint Intramedullary Implants: A Finite Element Analysis Study.

The use of temporomandibular joint (TMJ) implants is considered to be a reliable treatment for some TMJ disorders when TMJ anatomical integrity is compromised. Among all of the designs proposed for these devices, intramedullary approaches are relatively new, and they may offer several advantages compared to those of past models with a lateral approach. In this report, we use finite element analysis (FEA) to calculate stress forces of a TMJ implant featuring a ferrule ring, which is frequently used in engineering as a stress distractor to reduce the splinter effect. Our analysis suggests that the addition of a ferrule ring in the TMJ implant helps to reduce von Mises stresses in the device and displacement forces in the volume and surface of the implant. These results suggest that including a ferrule ring in a TMJ implant may contribute to the stability and outcome of a TMJ implant by reducing component stress and displacement forces.

Secrets of the Sea Urchin Spicule Revealed: Protein Cooperativity Is Responsible for ACC Transformation, Intracrystalline Incorporation, and Guided Mineral Particle Assembly in Biocomposite Material Formation.

The formation of the sea urchin spicule involves the stabilization and transformation of amorphous calcium carbonate (ACC) and assembly of ACC nanoparticle precursors into a mesoscale single crystal of fracture-resistant calcite. This process of particle assembly or attachment is under the control of a family of proteins known as the spicule matrix [Strongylocentrotus purpuratus (SpSM)] proteome. Recently, two members of this proteome, SpSM50 and the glycoprotein SpSM30B/C-G (in recombinant forms), were found to interact together via SpSM30B/C-G oligosaccharide-SpSM50 protein interactions to form hybrid protein hydrogels with unique physical properties. In this study, we investigate the mineralization properties of this hybrid hydrogel alongside the hydrogels formed by SpSM50 and SpSM30B/C-G individually. We find that the SpSM50 + SpSM30B/C-G hybrid hydrogel is synergistic with regard to surface modifications and intracrystalline inclusions of existing calcite crystals, the inhibition of ACC formation, and the kinetic destabilization of ACC to form a crystalline phase. Most importantly, the hybrid hydrogel phase assembles and organizes mineral particles into discrete clusters or domains within in vitro mineralization environments. Thus, the interactions of SpSM50 and SpSM30B/C-G, mediated by carbohydrate-protein binding, reflect the need for protein cooperativity for the ACC-to-crystalline transformation, intracrystalline void formation, and guided mineral particle assembly processes that are instrumental in spicule formation.

Sea Urchin Spicule Matrix Proteins Form Mesoscale "Smart" Hydrogels That Exhibit Selective Ion Interactions.

In the sea urchin embryo spicule, there exists a proteome of >200 proteins that are responsible for controlling the mineralization of the spicule and the formation of a fracture-resistant composite. In this report, using recombinant proteins, we identify that two protein components of the spicule, SM30B/C and SM50, are hydrogelators. Because of the presence of intrinsic disorder and aggregation-prone regions, these proteins assemble to form porous mesoscale hydrogel particles in solution. These hydrogel particles change their size, organization, and internal structure in response to pH and ions, particularly Ca(II), which indicates that these behave as ion-responsive or "smart" hydrogels. Using diffusion-ordered spectroscopy NMR, we find that both hydrogels affect the diffusion of water, but only SM50 affects the diffusion of an anionic solute. Thus, the extracellular matrix of the spicule consists of several hydrogelator proteins which are responsive to solution conditions and can control the diffusion of water and solutes, and these proteins will serve as a model system for designing ion-responsive, composite, and smart hydrogels.

Evaluation of apical debris extrusion and patency file in continuous and reciprocating rotary endodontic systems / Evaluación de la extrusión de residuos apicales y permeabilidad apical en sistemas endodónticos rotativos continuos y recíprocos

The aim of the study was to quantify and compare apical debris extrusion in two systems of continuous and reciprocating rotary instrumentation with, and without, the use of a patency file. An experimental study was carried out in 120 mesial roots of lower first molars, which were randomized in the following 4 groups: Group A. Reciproc (VDW) R25 without a patency file, Group B Mtwo (VDW) without a patency file, Group C Reciproc (VDW) R25 with a patency file and Group D Mtwo with a patency file. Groups A, B and C presented statistically significant differences in comparison to group D, Mtwo with the use of a patency file (p<0.008 to 95% reliability). In conclusion, the greater amount of debris extruded through the apex occurred in roots instrumented with the reciprocating rotary system; this difference was statistically significant in relation to teeth treated with the Mtwo continuous rotary system with the use of a patency file.

El objetivo del estudio fue cuantificar y comparar la extrusión de residuos apicales en dos sistemas de instrumentación endodónticos rotativos, continuo y recíproco, con y sin el uso de una lima de pasaje apical. Se realizó un estudio experimental en 120 raíces mesiales de primeros molares inferiores, que se aleatorizaron en los siguientes 4 grupos: Grupo A. Reciproc (VDW) R25 sin lima de pasaje apical, Grupo B Mtwo (VDW) sin lima de pasaje apical, Grupo C Reciproc (VDW) R25 con lima de pasaje apical y Grupo D Mtwo con lima de pasaje apical. Los grupos A, B y C presentaron diferencias estadísticamente significativas encomparación con el grupo D, Mtwo con el uso de una lima de pasaje apical (p<0.008 a 95% de confiabilidad). En conclusión, la mayor cantidad de residuos extruidos a través del ápice ocurrió en raíces preparadas con el sistema rotativo recíproco; Esta diferencia fue estadísticamente significativa en relación a los dientes tratados con el sistema rotativo continuo Mtwo con el uso de una lima de pasaje apical.

Crystal Modification on Lithium Disilicate Glass Ceramics Sintered Using Microwaves / Modificación de Cristales de Cerémicas de Vidrio de Disilicato de Litio Sinterizadas con Microondas

ABSTRACT: Microwaves are an interesting alternative to process dental ceramics. It is well documented that Microwave Hybrid Sintering (MHS) allows important savings in time and energy consumption. However, little is known about its effect on lithium disilicate glass ceramics, a popular material in dentistry today. We analyzed the microstructure of lithium disilicate glass ceramics sintered with MHS compared with conventional sintering. We sintered lithium disilicate glass ceramics using MHS and conventional furnaces, and we analyzed the samples using X-Ray diffraction and SEM. Samples sintered with MHS showed an increased crystalline phase, with an increased number of crystals. These crystals have larger perimeters compared with samples sintered in conventional furnaces. MHS produced a different crystallization pattern and crystal/ matrix ration in lithium disilicate glass ceramics when compared to conventional sintering. This can be associated with the improved mechanical properties of these materials reported previously.

RESUMEN: Las microondas son una interesante alternativa para procesar cerámicas dentales. Está bien documentado que el Sinterizado Híbrido por Microondas (MHS) permite ahorros importantes de tiempo y energía. Sin embargo, poco se ha publicado respecto a sus efectos en cerámicas de disilicato de litio, un material bastante popular en odontología en estos días. En este artículo analizamos la micro estructura de cerámicas de disilicato de litio sinterizada con MHS comparada con el sinterizado convencional. Sinterizamos muestras de cerámicas de disilicato de litio usando MHS y hornos convencionales, y analizamos las muestras usando difracción de rayos X y SEM. Las muestras sintetizadas usando MHS tienen una mayor fase cristalina, con mayor número de cristales. Estos cristales tienen además perímetros mayores, comparados con las muestras sinterizadas en hornos convencionales. MHS produce patrones de cristalización y proporción de cristal/matrix diferentes a las producidos por sinterizado convencional. Esto puede asociarse a las mejoras en propiedades mecánicas reportadas previamente.