Positive Replica Research Articles

The effect of two preparation designs on the fracture resistance and marginal adaptation of two types of ceramic crowns using CAD/CAM technology (In vitro study)

BackgroundRecently, prosthodontic approaches involve more conservative procedures that include less invasive finish line preparations that use less ceramic thickness.Aim of the studyThis in vitro study aimed to evaluate the effect of vertical preparation and modified vertical preparation designs on the marginal adaptation and fracture resistance of two types of ceramic crowns using CAD/CAM technology.Materials and methodsTwo typodont maxillary first premolars were embedded in acrylic resin. Forty positive replicas of epoxy resin dies were used that were divided into two groups depending on the preparation design (n = 20); Group V (Vertical): dies with feather edge finish line and Group MV (Modified vertical): dies with feather edge finish line, where a reverse shoulder of 1 mm depth was placed on the buccal surface 1.5 mm from the occlusal surface. Each group was further subdivided into two subgroups according to the type of ceramic material (n = 10): Subgroup Va and subgroup MVa for lithium disilicate (e.max CAD) and subgroup Vb and subgroup MVb for zirconia (zolid ht+). Crown restorations were made with CAD-CAM technology. The marginal adaptation was assessed using a stereomicroscope both prior to cementation and after cementation and aging. Fracture resistance was tested with a universal testing machine, and the data were statistically analyzed.ResultsMarginal adaptation showed no significant differences between subgroups before or after cementation and aging. Three-way ANOVA indicated that preparation design (p = 0.516) and material (p = 0.269) had no significant effect, but cementation had a significant effect (p < 0.0001) on the marginal adaptation. According to two-way ANOVA test, Subgroup (MVb) showed the highest result followed by subgroup (Vb) and subgroub (MVa) and the least was subgroub (Va). Fracture modes showed no significant differences among the subgroups (p = 0.982).ConclusionsMarginal adaptation of lithium disilicate and zirconia crowns remained clinically acceptable regardless of preparation design. While the modified vertical preparation with a reverse shoulder notably enhanced the fracture resistance of both materials, with zirconia demonstrating superior fracture resistance compared to lithium disilicate with average values exceeding premolar biting force.

Concave/Convex Curvature of Anisotropic Grooves Differentially Alters Cellular Morphology, Adhesion, and Proliferation.

Curvature is an integral part of the complex in vivo tissue architecture across various length scales. Therefore, several in vitro models with a patterned curvature in different length scales have been developed to understand the role of this in cellular behavior. At the subcellular scale, wavy patterns have been reported wherein concave and convex grooves are adjacently present. However, the independent effect of continuous subcellular concave and convex shapes has not been reported, mainly owing to the limitations in fabricating such patterns. In this study, we developed continuous concave and convex grooves on polydimethylsiloxane (PDMS) using a Dracaena sanderiana (bamboo) leaf as a template. The first (negative) replica from the abaxial side of the bamboo leaf, which imparted concave grooves on PDMS, was subsequently used as a template to fabricate a positive replica of the leaf, resulting in convex grooves of the same size and arrangement as the concave grooves. We examined the influence of the groove curvature on the morphology of bone marrow-derived human mesenchymal stem cells (BM-hMSCs) and skeletal muscle cells (C2C12). BM-hMSCs and C2C12 cells aligned on both concave and convex grooves as compared to the random orientation on a flat substrate. The significant difference was observed in the morphology of both cells, in terms of area, aspect ratio, number, and length of protrusions on concave and convex patterns. We found that the number of protrusions was also dependent on the ratio of cell to pattern length scale for convex-shaped grooves but independent of length scale for concave-shaped grooves. The proliferation of BM-hMSCs was also found to be different on concave and convex shapes. Therefore, this study shows the importance of (1) convex and concave curvatures of the subcellular length scale in cellular response, (2) dependence on the ratio of cell and curvature length scale, and (3) use of natural templates for overcoming fabrication challenges.

Anisotropic Superhydrophobic Properties Replicated from Leek Leaves.

A bio-inspired approach to fabricate robust superhydrophobic (SHB) surfaces with anisotropic properties replicated from a leek leaf is presented. The polydimethylsiloxane (PDMS) replica surfaces exhibit anisotropic wetting, anti-icing, and light scattering properties due to microgrooves replicated from leek leaves. Superhydrophobicity is achieved by a novel modified candle soot (CS) coating that mimics leek's epicuticular wax. The resulting surfaces show a contact angle (CA) difference of ≈30° in the directions perpendicular and parallel to the grooves, which is similar to the anisotropic properties of the original leek leaf. The coated replica is durable, withstanding cyclic bending tests (up to 10 000 cycles) and mechanical sand abrasion (up to 60g of sand). The coated replica shows low ice adhesion (10kPa) after the first cycle; and then, increases to ≈70kPa after ten icing-shearing cycles; while, anisotropy in ice adhesion becomes more evident with more cycles. In addition, the candle soot-coated positive replica (CS-coated PR) demonstrates a transmittance of ≈73% and a haze of ≈65% at the wavelength of 550nm. The results show that the properties depend on the replicated surface features of the leek leaf, which means that the leek leaf appears to be a highly useful template for bioinspired surfaces.

Time sequence variation of incoherent and coherent random laser based on positive replica of abalone shell

Besides the scattering structures, the energy transfer (ET) process in the gain medium plays a significant role in the competition between coherent (comprising strongly coherent components) and incoherent (consisting of weakly coherent or “hidden” coherent components) modes of random lasers. In this study, bichromatic emission random lasers were successfully created using polydimethylsiloxane (PDMS) replicas with grooved structures that imitate the inner surface of abalone shells as scattering substrates. The influence mechanism of the ET process from the monomer to dimer in the Rhodamine 640 dye on the competition of random laser modes was thoroughly investigated from both spectral and temporal dimensions. It was confirmed that the ET process can reduce the gain of monomers while amplifying the gain of dimers. By considering the dominant high-efficiency ET processes, an energy transfer factor associated with the pump energy density was determined. Notably, for the first time, it was validated that the statistical distribution characteristics of the time sequence variations in the coherent random laser generated by dimers closely resemble a normal distribution. This finding demonstrates the feasibility of producing high-quality random number sequences.

Understanding the petal effect: Wetting properties and surface structure of natural rose petals and rose petal-derived surfaces

The petal effect is identified as a non-wetting state with high drop adhesion. The wetting behavior of petal surfaces is attributed to the papillose structure of their epidermis, which leads to a Cassie-Baxter regime combined with strong pinning sites. Under this scenario, sessile drops are pearl shaped and, unlike lotus-like surfaces, firmly attached to the surface. Petal surfaces are used as inspiration for the fabrication of functional parahydrophobic surfaces such as antibacterial or water-harvesting surfaces. In this work, two types of rose petals were replicated by using a templating technique based in Polydimethylsiloxane (PDMS) nanocasting. The topographic structure, the condensation mechanism under saturated environments and the wetting properties of the natural rose petal and their negative and positive replicas were analyzed. Finally, we performed prospective ice adhesion studies to elucidate whether petal-like surfaces may be used as deicing solutions.

Assessment of the of fixed dental prosthesis impressions received at commercial dental laboratories in Aljabal-Alakhdar region, Libya0

Background: Crown and bridge prosthodontics needs an accurate and precise impression (positive replica) of the abutment teeth and the edentulous region to be rehabilitated for the dental technician to be able to construct the high quality and well adapted fixed dental restoration without mistakes. The aim of the current survey was to assess any visible mistakes commonly observed in fixed dental prosthesis impressions received at five commercial dental laboratories, frequency errors determination, and to determine any possible association between the preparation finish line errors and other assessed factors. Materials and methods: 150 fixed prosthodontic impressions were collected from five commercial dental laboratories located at Aljabal-Alakhdar region, Libya. All the fixed prosthodontic impressions which had been received by the visited commercial dental laboratories were assessed for many factors in relation to the accuracy such as the dental arch involved, prepared abutment teeth, dental impression materials used, and final techniques and viscosity of the impression, the type of impression tray, full-arch or segmental impression tray, the impression tray size, type of fixed dental restoration requested, mistakes in impression material or tray used, gingival tissue dilation errors, closed-mouth impression technique errors, and finish line errors. No attempts were made to determine the reason of the detected errors in each fixed prosthodontic impression assessed. Association between dental practitioner years of experience and gender and impression errors was evaluated. The association between categorical variables and the outcomes were examined by the use of Chi square and Fisher exact tests. Results: Condensation silicone was the most impression material used. Of the impressions evaluated 121(80.6%), 97% have at least one detectable error, 103(68.6%) had finish line errors, 53.9% had tooth preparation area errors. Visible contamination of impression with blood was seen in about 79(52.2%) of the assessed impressions. There was significant association between the type of dental impression material and errors in the preparation cervical finish line and tooth preparation area. Conclusion: In the present study, it has been found that a high frequency of recognizable errors was detected in crown and bridge impressions received by the five commercial dental laboratories. This can result in poorly fitted fixed restorations cemented for the fixed prosthodontic patients.

Comparison of the Anatomy and Adaptability of Reconstructed Teeth with Natural Teeth: An Innovative Approach in Forensic Dentistry

Abstract Background: Forensic tooth reconstruction is the technique of reconstructing the morphology of a missing tooth from the intra-alveolar morphology of dental sockets from skeletal remains. Aims and Objectives: The aim and objective of the study are to compare and investigate whether the anatomy and adaptability of reconstructed teeth simulate with the natural tooth and to investigate whether the dental materials have potential in reconstruction of teeth. Materials and Methods: An in vitro experimental study was undertaken on a human mandible. According to the Fédération Dentaire Internationale, charting will be done based on the number of teeth present. The entire study will be conducted in three phases using dental materials. Phase 1 comprised preparation for negative replica, where an impression will be taken, Phase 2 comprised preparation of a positive replica or cast, and Phase 3 comprised tooth reconstruction using the flowable composite. Results: The specimen tooth (which had been taken from its socket) and the newly constructed tooth were compared, and when the length of the newly constructed root was measured using digital vernier calipers, there was a disparity of 0.5–1 mm. The cone-beam computed tomography radiographs demonstrated the necessary flexibility. Conclusion: The present study demonstrated that dental information can be obtained even when teeth are absent postmortem by making an attempt to recreate the teeth using dental materials while documenting the intra-alveolar anatomy of the dental root socket.

DIGITAL IMPRESSIONS- PAVING PATH TOWARDS GREEN DENTISTRY: A REVIEW

The concept of making an impression has undergone a paradigm shift as a result of the development of highly accurate and novel impression systems based on new technologies.1 Digital intraoral imaging represents a cutting-edge technique that allows the dentist to create a virtual computer-generated replica of the hard and soft tissues. Digital impression-making techniques are highly accurate, and they will undoubtedly lessen the need for traditional techniques in the near future. The information is stored in specialized software to be utilized in the manufacture of appliances, positive replicas, or other restorations. Additionally, this makes it possible to access data at any moment for further research and follow-ups. The future of digital dentistry is bright, but there is still work to be done to make sure that the technology delivers significant benefits to practitioners and patients in terms of therapeutic outcomes, regardless of how beautiful the process itself maybe. At the same time, it must be kept affordable and investments should yield a solid return.1

Two-point functions of composite twist fields in the Ising field theory

All standard measures of bipartite entanglement in one-dimensional quantum field theories can be expressed in terms of correlators of branch point twist fields, here denoted by and . These are symmetry fields associated to cyclic permutation symmetry in a replica theory and having the smallest conformal dimension at the critical point. Recently, other twist fields (composite twist fields), typically of higher dimension, have been shown to play a role in the study of a new measure of entanglement known as the symmetry resolved entanglement entropy. In this paper we give an exact expression for the two-point function of a composite twist field that arises in the Ising field theory. In doing so we extend the techniques originally developed for the standard branch point twist field in free theories as well as an existing computation due to Horváth and Calabrese of the same two-point function which focused on the leading large-distance contribution. We study the ground state two-point function of the composite twist field and its conjugate . At criticality, this field can be defined as the leading field in the operator product expansion of and the disorder field µ. We find a general formula for and for (the derivative of) its analytic continuation to positive real replica numbers greater than 1. We check our formula for consistency by showing that at short distances it exactly reproduces the expected conformal dimension.

Ordered non-close packed colloidal array with morphology control.

Non-close packed (NCP) colloidal arrays find wide applications in the fields of photonics, optical chip fabrication, nano sphere lithography and so on. However, unlike their close packed counterparts, such arrays cannot be obtained by direct self-organization of colloidal particles and require specialized techniques involving plasma/reactive ion etching, electric field driven assembly, substrate stretching or precise positioning of the particles. In this article, we present a facile template guided approach for fabricating ordered NCP arrays of colloidal particles. First, we employ soft lithography to replicate self-assembled hexagonal close packed (HCP) arrays of 'larger colloidal particles' (LPs) to obtain a topographically patterned positive and/or negative replica of the initial array. These replicas are then used as templates to spin coat 'smaller colloidal particles' (SPs), which may even have some degree of poly-dispersity, to obtain ordered NCP arrays. We further show that pattern morphology can be modulated based on whether a single or a double replicated template is used to confine the SPs, the concentration (Cn) of the SPs in the casting solution as well as the relative commensuration of the diameter of the SPs (ds) with that of the LPs (dL). Finally, we show that such NCP arrays can be transferred onto any flat surface by UVO mediated colloidal transfer printing.

A universal replica molding strategy based on natural bio-templates for fabrication of robust superhydrophobic surfaces

Superhydrophobic surfaces (SHS) have been constructed and applied by multitudinous methods in the past two decades. However, it is still a challenge to fabricate the staunch SHS based on natural bio-template through a universal strategy. Herein, we develop a method to fabricate the stable SHS via a bio-template replica method assisted by candle soot and plant wax. The deposited candle soot coating can more easily separate replicate samples and increase the surface roughness of the positive replica. In addition, natural plant wax could act as a potential substitute to fluoride reagents, resulting from its cost-efficient, eco-friendly, repairable and hydrophobic properties. According to this technique, we successfully constructed an artificial SHS with self-cleaning properties or anisotropic wettability using the lotus leaf and rice leaf as biological templates, respectively. Significantly, the resultant SHS demonstrates outstanding mechanical durability and reparability. We envision that a green and universal fabrication strategy reported in this paper, which should be to construct SHS concerning other bio-templates, and provide new insights for the development of SHS possessing durability and restorability.

Dual-band random laser based on positive replica of abalone shell

Random lasing from a polydimethylsiloxane substrate prepared from abalone shell by soft lithography was investigated. The substrate has better scattering efficiency than abalone shell and its groove structure can support both incoherent and coherent random lasing when covered with a layer of dye solution. When employing rhodamine 640 dye as gain medium, a dual-band random laser signal based on the mechanism of optical feedback intensity and mode competition can be observed, where the signals of the two bands are shown as incoherent and coherent random lasing regimes respectively. Speckle-free imaging is achieved by using incoherent and coherent random lasers as illumination sources and imaging effects are compared. This research shall promote the development of random lasers in the fields of illumination and imaging.

High sensitivity, broad linearity range and low detection limit flexible pressure sensors based on irregular surface microstructure

Flexible pressure sensors have attracted great interest due to their application potential in healthcare monitoring, electronic-skin and human-machine interfaces. To satisfy the requirements from practical applications, the sensors with high sensitivity, broad linearity range and low detection limit are urgently desired. Here, flexible pressure sensors with the negative replica (N-Sensor) and the positive one (P-Sensor) of the irregular surface microstructures are systemically investigated to achieve high performances. As revealed by the in situ observation method, the positive replica which mainly contained convex microstructures exhibits smaller initial contact area and could be compressed more easily than the negative one with porous surface. Therefore, the performances of the P-Sensor including sensitivity, linearity range and detection limit are greatly improved. The P-Sensor exhibits high sensitivity of 163.4 kPa −1 over a broad linearity range of 0–140 kPa, low detection limit of 1.3 Pa, fast response time (<10 ms) and good stability (>8000 cycles), which is one of the best results for flexible pressure sensors. Attributed to these excellent performances, the P-Sensor well performs in the measurements of human pulse, tactility and plantar pressure, showing great application potentials in human daily life. • Using negative and positive replicas of irregular microstructures manipulate the performance of flexible pressure sensors. • The sensors with positive replica achieve high sensitivity over a broad linearity range. • The flexible pressure sensors show great application potentials in human daily life.

Assessment of accuracy of open tray and closed tray dental implant impression techniques: A comparative study

Background: A dental impression is a negative imprint of an oral structure utilized to produce a positive replica of the structure that can be used as a permanent record or in the production process of a dental restoration. Hence; the present study was undertaken for assessing the accuracy of two different dental implant impression techniques. Materials & methods: For reference model, an edentulous mandibular cast with four implant analogues in the anterior region was used. For the present study, two different types of impression trays were used as follows: Closed custom tray, and Open custom tray. The impressions were allowed to set for 10 minutes under a standard load of 500 gm. All the impressions were poured using the same quantity of Type IV dental stone. The casts were subjected to measurement after 24 hours to simulate clinical situation. All the results were recorded in Microsoft excel sheet and were analysed by SPSS software.Results: Mean error obtained in closed custom tray technique was 0.028 while mean error obtained in open custom tray technique was 0.23. While analysing statistically, significant results were obtained. Conclusion: Better results are obtained when open custom trays were used.

Evaluation of Various Tongue Patterns in Namakkal District-Role in Forensic Dentistry

Background: Human identification is one of the most challenging areas in forensic field that man has been confronted with. Identification of an individual plays an important role in any crime investigation, mass disaster and in deceased cases. Materials and Methods: Sixty healthy individuals, which included 30 males (Group I) and 30 females (Group II) in the age group of 11 to 60 years, were included in this study. An alginate impression of the dorsal surface and lateral borders of the tongue was also made in a pre-customized acrylic tray. Positive replica of the tongue was made by pouring type II dental stone on alginate impression and used for identification purpose. The various parameters that were recorded for each subject include shape of tongue (U/V shape), margins of the tongue (smooth/scalloped) and texture of tongue (normal, fissures, bifid/cleft). Results: The data collected was tabulated and statistical analysis was done using SPSS software (version 20). Pearson's chi"‘square test was performed to compare the results obtained from the different groups, and Cramer's V was determined to assess the relationship between gender and tongue morphological characteristics. Conclusion: The morphology of tongue margins, texture and shape showed significant variation among genders which can be reliable for personal identification.

Mimicking flower petals to fabricate self-cleaning and antireflective polymer surfaces

This work explored a facile way to fabricate superhydrophobic and antireflective polymer surfaces using Canna indica flower petals. A simple, inexpensive two-step soft-lithography technique was employed to replicate the surface structures of C. indica flower petals onto two different polymer surfaces namely, polydimethylsiloxane (PDMS) — a hydrophobic polymer and resorcinol–formaldehyde (RF) xerogel — a hydrophilic polymer. First, a negative replica was prepared in PDMS using the flower petal as a template. Second, the negative PDMS replica was later used as a stamp to prepare a positive replica in both PDMS and RF xerogel. These replicated structured surfaces greatly influenced the wettability properties. The contact angle of the replicated PDMS surfaces increased to the nearly superhydrophobic values of 145° (negative PDMS replica) and 144° (positive PDMS replica) compared with that of the plain surface, which is 101°. Interestingly, the contact angle of the replicated RF surface significantly increased to 151° (superhydrophobic) compared with that of the planar RF surface, which is hydrophilic (68°). Furthermore, the replicated polymer surfaces exhibited not only excellent superhydrophobic properties but also antireflective properties. These multifunctional surfaces with superhydrophobicity as well as an omnidirectional antireflective property may find a wide range of applications, such as solar energy harvesting, optical displays and marine applications.

Hierarchical patterns on laminated composite bilayer films via surface roughness-mediated buckling instability

This study describes buckling instabilities mediated via surface roughness to generate hierarchical structures on a metal (aluminum)/polymer (polystyrene) laminated composite bilayer film on a rigid substrate. Buckling instability is a non-lithographic approach to generate microscale features in thin films. Metals can buckle over the surface due to compressive stress arising from differences in thermal expansion of the individual layers. The topographies of the buckles characterized by wavelength and amplitude can be manipulated by varying the thickness of the layers and the extent of thermal annealing time. Here, the pre-buckled surface on the laminated composite bilayer film formed via two–step molding resulted in hierarchical patterns via surface roughness-mediated buckling instability. The negative replica of the buckles was generated by poly(dimethyl siloxane) (PDMS) and the positive replica of the buckles was fabricated via molding using a PDMS negative replica onto the PS film. The metal layer was subsequently formed on the PS film and the laminated composite bilayer film enabled patterns with hierarchical topography following thermal treatment. The hierarchically structured surfaces exhibit moderately enhanced hydrophilicity and the elastomeric replica with hierarchical buckles showed stretchable hydrophobicity up to 120% stretching due to partial preservation of the pre-structured buckles on the surface.

Replication of the Surface Wettability of Plant Leaves with Different Surface Morphologies Using Soft Lithography

Naturally occurring surfaces which display interesting surface wetting properties such as superhydrophobicity, superoleophobicity and directional wettability are found in most aquatic plants. These phenomena arise from the micro/nano structures present on these surfaces complimented by their surface chemistry. The replication of such surface structures is highly pursued due to their potential in applications such as self-cleaning (Lotus effect), microfluidic devices and antifouling surfaces. Soft lithography is a technique that has been used to replicate micro/nano structures with varying degrees of success. Nevertheless, in the context of natural surfaces, the technique has been mostly limited to the replication of the lotus leaf structure. Therefore, a systematic investigation could be fruitful since it has the potential to be scaled up to replicate different surface structures as well as large-area patterning. In this study, the feasibility of soft lithography technique on natural leaf surfaces was investigated using five plant species with different surface morphologies. The negatives of these primary molds were replicated using polydimethylsiloxane (PDMS) and the final positive replica was successfully replicated from PDMS while using hydroxypropyl methylcellulose (HPMC) as an anti-stick layer. The structures were characterized based on SEM images and contact angle measurements. Additionally, the effect of HPMC was also investigated. The technique can easily be extended to broader applications in other areas that require micro/nanostructured surfaces such as anti-reflection coatings, chemical sensors and anti-microbial surfaces.

Rapid Fabrication of Bio-inspired Antireflection Film Replicating From Cicada Wings

Inspired by cicada wings, a flexible film with self-cleaning and broadband antireflection properties was fabricated with a rapid, straightforward and cost-effective method. The cicada wing was selected as the original template, and a polymethyl methacrylate (PMMA) negative replica was obtained by evaporation solvent process. The original template was directly peeled off. Subsequently, the polydi-methylsiloxane (PDMS) was spread in the as-prepared PMMA negative replica. After curing and peeling processes, the PDMS positive replica was manufactured successfully. The morphologies and performances of cicada wings were perfectly inherited by the PDMS positive replica. What is more, the excellent optical property of cicada wing was investigated experimentally and theoretically. Compared with flat PDMS film, the average reflectivity of structural PDMS film was reduced from 9% to 3.5% in the wavelength range of 500 nm–900 nm. These excellent antireflection properties of bio-inspired antireflection film can be attributed to the nanostructures which achieve a gradient refractive index between air and the materials, and the mechanism of the antireflection properties was revealed via effective medium theory. Besides, the bio-inspired broadband antireflective film exhibited superhydrophobic property after the surface treatment (a 152.1°water contact angle), and it also displayed satisfactory flexibility. This work provided a universal method to fabricate the exquisite biological structures, realizing the transfer of structure and function. Moreover, the multifunctional antireflection film exhibited the potential value for applications in optical communications, flexible display screens, and anti-dazzle glasses.

Production of Hydrophobic Zein-Based Films Bioinspired by The Lotus Leaf Surface: Characterization and Bioactive Properties.

Hydrophobic zein-based functional films incorporating licorice essential oil were successfully developed as new alternative materials for food packaging. The lotus-leaf negative template was obtained using polydimethylsiloxane (PDMS). The complex surface patterns of the lotus leaves were transferred onto the surface of the zein-based films with high fidelity (positive replica), which validates the proposed proof-of-concept. The films were prepared by casting method and fully characterized by Scanning Electron Microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR) and Differential Scanning Calorimetry (DSC). The grammage, thickness, contact angle, mechanical, optical and barrier properties of the films were measured, together with the evaluation of their biodegradability, antioxidant and antibacterial activities against common foodborne pathogens (Enterococcus faecalis and Listeria monocytogenes). The zein-based films with the incorporation of licorice essential oil presented the typical rugosities of the lotus leaf making the surfaces very hydrophobic (water contact angle of 112.50°). In addition to having antioxidant and antibacterial properties, the films also shown to be biodegradable, making them a strong alternative to the traditional plastics used in food packaging.