In vitro comparison of accuracy between conventional and digital impression using elastomeric materials and two intra-oral scanning devices.

AIM: The aim of this study was to compare the accuracy of full-arch conventional implant impressions using two different materials (A-silicone and polyether) to full-arch digital implant impressions produced from two intraoral scanning devices. MATERIALS AND METHODS: A master model was fabricated representing an edentulous mandible with four implants with internal connection placed at the sites of canines and first molars. The anterior implants were parallel to the residual ridge, while the two posterior implants had an angulation of 15° to the distal and 15° to the lingual respectively. The conventional technique was performed with open-tray of non-splinted impression copings. Two different impression materials were used, A-silicone and polyether at monophase medium body consistencies. The digital impressions were obtained with the use of two different intraoral scanners, after the connection of scan bodies. A total of 10 impressions were produced for each of the four experimental groups. The conventional models as well as the master model were digitized using a high-resolution laboratory scanner. The STL files of the models and of the intraoral impressions were imported in a powerful superimposition software, for the conduction of measurements in pairs of files. The software calculated the 3D deviations, as well as the linear and angular displacements among scan bodies at the digital files. For "trueness" measurements every STL file of each experimental group was superimposed to the digital master model, while for "precision" measurements all STL files of each experimental group were superimposed to each other. RESULTS AND CONCLUSIONS: The accuracy of full arch mandibular implant impressions was influenced both by the impression technique used (conventional vs. digital) and the impression material used (A-silicone vs. polyether) or the intraoral scanner used (Trios vs. Heron). In terms of "trueness," A-silicone showed the highest impression accuracy with the lowest deviation values, followed by polyether and Trios, but the differences between the three groups were in the majority not statistically significant. Heron showed statistically lower accuracy results in all measurements compared to the other groups. In terms of "precision", conventional impressions with the use of A-Silicone or polyether were statistically significantly superior to digital impressions with either scanner. A-Silicone and polyether showed no statistically significant difference between them.

Surface, microstructural and mechanical characterization of contemporary implant abutment screws.

OBJECTIVES: The aim of the present work was to evaluate six commercially available abutment screws by characterising roughness parameters, microstructure and mechanical properties. METHODS: Six abutment screws from each implant system, were used. The surface roughness parameters (Sa, Sq, Ssk, Sku, Spk, Sk and Svk) were identified by an optical interferometric profiler. Microstructural observations and crystallographic analysis were performed using a scanning electron microscope (SEM) equipped with an energy dispersive X-ray spectroscopy (EDX) device for elemental analysis and an X-ray diffractometer (XRD), respectively. The Martens Hardness (HM), Indentation Modulus (EIT), elastic index (ηIT) and Vickers hardness (HV) of all specimens were determined by instrumented indentation testing (IIT). The results were analyzed by one-way ANOVA and Tukey multiple-comparison tests (a=0.05). RESULTS: EDX and XRD showed the abutment screws to be mixed α- and ß-phase titanium alloys. Microstructural analysis revealed a fine homogeneous microstructure without porosity, consisting of fine dispersoid rods of ß-phase embedded in a continuous α-phase matrix. Statistically significant differences were found among the mechanical properies and surface roughness parameters apart from Sq, Spk and Svk. CONCLUSIONS: The tested abutment screws showed significant differences in the probed properties, and, thus, differences in their clinical behaviour are anticipated.

Characteristics of intraoral scan bodies and their influence on impression accuracy: A systematic review.

OBJECTIVE: The aim of this systematic review was to evaluate the influence of the characteristics of intraoral scan bodies (ISBs) on the accuracy of intraoral scanning. MATERIALS AND METHODS: An electronic search was conducted through PubMed (MEDLINE), Scopus and Cochrane Library, up to March 2023. The literature search intended to retrieve all relevant clinical and in vitro studies about the effect that the various properties of ISBs may have on the accuracy (trueness and precision) of intraoral scanning. Only publications in English language were selected with animal studies, case reports, case series, technique presentation articles and expert opinions being excluded. RESULTS: A total of 28 studies met the inclusion criteria and were included in this systematic review. They were published between 2019 and 2023 and were all in vitro studies. Among the parameters described, the scan body material, position, geometry, height, diameter, and fixation torque were evaluated. The most common materials used for ISBs were polyetheretherketone (PEEK) and titanium alloys. The diameter and position of ISBs seemed to affect the trueness of implant impressions. Subgingival implant position and decreased ISB height affected negatively the trueness of scanning. Geometrical characteristics of ISBs also affect the implant impression accuracy, especially the bevel location and the types of designing modifications. CONCLUSIONS: The characteristics of the currently used ISBs vary widely and the available scientific evidence is not yet conclusive about the optimal design of ISB. The implant impression accuracy achieved by any of the studied parameters is encouraging. Clinical studies are however necessary for more concrete conclusions. CLINICAL SIGNIFICANCE: ISBs play a vital role in the digital workflow and influence significantly the accuracy and fit of implant restorations. More clinical trials are needed in order to conclude to the optimal characteristics of ISBs which would further enhance the success of the restorations.

Impact of maxillofacial growth on implants placed in adults: A narrative review.

OBJECTIVE: To determine the effect of lifetime maxillofacial changes on dental implants placed in adults, analyze the clinical implications of these changes, identify prognostic factors, and offer possible solutions. OVERVIEW: The relationship between implant placement and maxillofacial changes, occurring during not only the active growth period but also the entire span of adulthood, has not been extensively examined. Vertical differences between implants and adjacent teeth due to the ankylotic behavior of the former might be observed at any age and endanger restoration biologically, functionally, and esthetically. Regarding interproximal contacts, firm contact loss may occur within a few months after restoration, resulting in food impaction. Many prognostic factors have been reported, but most do not exhibit a statistically significant association with implant infraocclusion and interproximal contact loss. Incorporation of alternative solutions, accurate treatment planning, strict recall protocols, and retrievability of implant-supported restorations can facilitate efficient management of complications. CONCLUSION: Maxillomandibular changes throughout adulthood may lead to complications such as implant infraocclusion and interproximal contact loss. Rehabilitation of edentulism should be characterized by well-designed and flexible treatment plans to resolve long-term complications efficiently. Further long-term clinical studies are needed to identify other risk factors. CLINICAL SIGNIFICANCE: Treatment plans for implant therapy should be reconsidered for adults. Careful patient monitoring and early intervention are essential for securing treatment outcomes.

Qubit vitrification and entanglement criticality on a quantum simulator.

Many elusive quantum phenomena emerge from a quantum system interacting with its classical environment. Quantum simulators enable us to program this interaction by using measurement operations. Measurements generally remove part of the entanglement built between the qubits in a simulator. While in simple cases entanglement may disappear at a constant rate as we measure qubits one by one, the evolution of entanglement under measurements for a given class of quantum states is generally unknown. We show that consecutive measurements of qubits in a simulator can lead to criticality, separating two phases of entanglement. Using up to 48 qubits, we prepare an entangled superposition of ground states to a classical spin model. Progressively measuring the qubits drives the simulator through an observable vitrification point and into a spin glass phase of entanglement. Our findings suggest coupling to a classical environment may drive critical phenomena in more general quantum states.

Entanglement Phase Transition with Spin Glass Criticality.

We define an ensemble of random Clifford quantum circuits whose output state undergoes an entanglement phase transition between two volume-law phases as a function of measurement rate. Our setup maps exactly the output state to the ground space of a spin glass model. We identify the entanglement phases using an order parameter that is accessible on a quantum chip. We locate the transition point and evaluate a critical exponent, revealing spin glass criticality. Our Letter establishes an exact statistical mechanics theory of an entanglement phase transition.

Immediate Dentin Sealing: A Literature Review.

PURPOSE: The immediate application of a dentin-bonding agent after tooth preparation and before impression-taking (immediate dentin sealing [IDS]) has been suggested to provide several advantages concerning bacterial microleakage, hypersensitivity, and bonding quality. We reviewed the literature and clarified certain aspects related to each step of IDS application. MATERIALS AND METHODS: The search strategy comprised an electronic research in MEDLINE, Cochrane, Ovid and Scopus for studies published from January 1990 to December 2020 regarding the IDS technique and including both in vitro and clinical studies. RESULTS: After exclusion of irrelevant or duplicate articles, 88 articles focusing on aspects of the IDS technique were assessed. IDS seems to be advantageous with regard to bond strength, gap formation, bacterial microleakage, and dentin hypersensitivity. However, issues arising from interaction with impression materials, the provisional phase, and conditioning methods before cementation require further investigation. CONCLUSION: There are no documented reasons preventing clinicians applying IDS in their everyday practice. On the contrary, the presented technique seems to be beneficial in certain aspects regarding indirect restorations.

In vitro validation of Digital Image Analysis Sequence (DIAS) for the assessment of the marginal fit of cement-retained implant-supported experimental crowns.

BACKGROUND: The replica technique with its modifications (negative replica) has been used for the assessment of marginal fit (MF). However, identification of the boundaries between prosthesis, cement, and abutment is challenging. The recently developed Digital Image Analysis Sequence (DIAS) addresses this limitation. Although DIAS is applicable, its reliability has not yet been proven. The purpose of this study was to verify the DIAS as an acceptable method for the quantitative assessment of MF at cemented crowns, by conducting statistical tests of agreement between different examiners. METHODS: One hundred fifty-one implant-supported experimental crowns were cemented. Equal negative replicas were produced from the assemblies. Each replica was sectioned in six parts, which were photographed under an optical microscope. From the 906 standardized digital photomicrographs (0.65 µm/pixel), 130 were randomly selected for analysis. DIAS included tracing the profile of the crown and the abutment and marking the margin definition points before cementation. Next, the traced and marked outlines were superimposed on each digital image, highlighting the components' boundaries and enabling MF measurements. One researcher ran the analysis twice and three others once, independently. Five groups of 130 measurements were formed. Intra- and interobserver reliability was evaluated with intraclass correlation coefficient (ICC). Agreement was estimated with the standard error of measurement (SEM), the smallest detectable change at the 95% confidence level (SDC95%), and the Bland and Altman method of limits of agreement (LoA). RESULTS: Measured MF ranged between 22.83 and 286.58 pixels. Both the intra- and interobserver reliability were excellent, ICC = 1 at 95% confidence level. The intra- and interobserver SEM and SDC95% were less than 1 and 3 pixels, respectively. The Bland-Altman analysis presented graphically high level of agreement between the mean measurement of the first observer and each of the three other observers' measurements. Differences between observers were normally distributed. In all three cases, the mean difference was less than 1 pixel and within ± 3 pixels LoA laid at least 95% of differences. T tests of the differences did not reveal any fixed bias (P > .05, not significant). CONCLUSION: The DIAS is an objective and reliable method able to detect and quantify MF at ranges observed in clinical practice.

Effect of fiber-reinforcement on the strength of polymer materials for provisional restorations: An in vitro study.

OBJECTIVE: The purpose of this study was to evaluate the effect of three different methods of fiber reinforcement (glass fibers preimpregnated, glass fibers nonpreimpregnated, and polyethylene fibers) on the flexural strength and modulus of elasticity of poly-methyl-methacrylate resin (PMMA) and Bis-Gma materials. MATERIALS AND METHODS: A total of 60 specimens of autopolymerizing PMMA resin specimens were fabricated using a stainless steel matrix with dimensions of (37.5± 2) × (3 ± 0.1) × (3 ± 0.1) mm according to the standards of ISO 10477. The autopolymerizing resins used in this study were: (a) JET, (b) TRIM, (c) PROTEMP. The fibers used in this study were STICK (Glass fiber preimpregnated), POLYDENTIA (Glass fiber nonpreimpregnated), RIBBOND (Polyethylene fiber). The specimens were tested by three-point bending test and the flexural strength and modulus of elasticity were recorded. The data of each resin type were analyzed by analysis of variance using a significance level of 0.05 to determine the mean differences. RESULTS: The integration of reinforcing fibers in the mass of resins for provisional restorations increased both the flexural strength and the modulus of elasticity in all tested combinations compared to control groups. After the three-point bending test, the specimens were not completely fractured and the parts remained together due to the fibers. CONCLUSIONS: Fiber reinforcement is an effective method to increase mechanical properties of provisional restorative resins. Reinforcement with fibers enhances the flexural strength and the modulus of elasticity of the specimens compared to unreinforced (control) group. CLINICAL SIGNIFICANCE: The reinforcement of resin materials used for provisional restorations with fibers can increase mechanical strength and may improve the clinical performance and the longevity of provisional restorations during their clinical function.

Evaluating the Jones polynomial with tensor networks.

We introduce tensor network contraction algorithms for the evaluation of the Jones polynomial of arbitrary knots. The value of the Jones polynomial of a knot is reduces to the partition function of a q-state anisotropic Potts model with complex interactions, which is defined on a planar signed graph that corresponds to the knot. For any integer q, we cast this partition function into tensor network form, which inherits the interaction graph structure of the Potts model instance, and employ fast tensor network contraction protocols to obtain the exact tensor trace and thus the value of the Jones polynomial. By sampling random knots via a grid-walk procedure and computing the full tensor trace exactly, we demonstrate numerically that the Jones polynomial can be evaluated in time that scales subexponentially with the number of crossings in the typical case. This allows us to evaluate the Jones polynomial of knots that are too complex to be treated with other available methods. Our results establish tensor network methods as a practical tool for the study of knots.

The influence of impression coping splinting on the accuracy of the open-tray technique.

The objective of this study was to examine the effect of splinting of the impression copings on the accuracy of the cast when the open-tray technique is used. An epoxy master cast with 3 implants was fabricated. The first 2 implants were parallel to each other and perpendicular to the horizontal plane (implants A and B), and the third implant (implant C) had a 25-degree inclination. A passively fitting metal framework that was fabricated over this master cast was used to measure accuracy of fit. Ten casts were fabricated from this epoxy resin master cast with the use of polyether material and the open-tray technique. For the first 5 casts, the impression copings were splinted with dental floss and autopolymerizing acrylic resin; in the next 5 casts, the impression copings were not splinted. The metal framework in the master cast was fixed in the new specimens, and the microgap between this prosthesis and the implant analogs was evaluated. The specimens were observed under an optical microscope, and microgap measurements were made on photographs taken at a standardized magnification of 40×. The inclined implant C had the smallest mean microgap among the 3 implants, but the differences were not statistically significant. Microgaps for all 3 implants were smaller when they were splinted, but the difference from the mean of the nonsplinted counterpart was statistically significant only for the inclined implant. The results suggest that there is no clinical advantage in splinting the impression copings for parallel implants. On the other hand, when the implants are not parallel, splinting of the impression copings can result in greater accuracy of the fabricated cast.

Rehabilitation of the edentulous mandible with implant-supported overdentures on telescopic abutments and immediate loading. A controlled prospective clinical study.

The rehabilitation of the edentulous mandible with implant-supported overdentures is an established clinical procedure but immediate loading of implants supporting mandibular overdentures has not been equally documented. AIM: The aim of this prospective clinical study was to evaluate the rehabilitation of the edentulous mandible with immediate loading and implant-supported overdentures. MATERIALS AND METHODS: 10 patients were restored with immediate loading of the implants and 5 with delayed loading. The treatment planning included placement of four implants in the interforaminal area of the mandible. Prefabricated titanium abutments with 4 degrees of conical inclination were fixed on the implants and the telescoping conical caps were connected to the base of the mandibular denture. Bone loss was assessed by comparison of panoramic x-rays at baseline 3, 6, and 36 months by visual observation from clinicians. RESULTS: A total of 60 implants were restored, 40 with immediate and 20 with delayed loading. The follow-up period ranged from 4 to 10 years with 72 months mean observation time. Prosthetic complications appeared with low frequency and no implant loss occurred during the follow-up period. No statistical significance was observed in the bone loss in the cervical area of the immediate and late loaded implants. CLINICAL SIGNIFICANCE: The rehabilitation of the edentulous mandible with implant-supported overdentures and telescopic copings is a viable clinical solutions with multiple clinical advantages both for the clinician and the patient. . Immediate loading can be applied in cases where increased initial stability can be achieved. More extended long-term clinical studies with increased number of patients and implants are needed, however, to verify the efficacy of the treatment method.

Tensor network method for reversible classical computation.

We develop a tensor network technique that can solve universal reversible classical computational problems, formulated as vertex models on a square lattice [Nat. Commun. 8, 15303 (2017)2041-172310.1038/ncomms15303]. By encoding the truth table of each vertex constraint in a tensor, the total number of solutions compatible with partial inputs and outputs at the boundary can be represented as the full contraction of a tensor network. We introduce an iterative compression-decimation (ICD) scheme that performs this contraction efficiently. The ICD algorithm first propagates local constraints to longer ranges via repeated contraction-decomposition sweeps over all lattice bonds, thus achieving compression on a given length scale. It then decimates the lattice via coarse-graining tensor contractions. Repeated iterations of these two steps gradually collapse the tensor network and ultimately yield the exact tensor trace for large systems, without the need for manual control of tensor dimensions. Our protocol allows us to obtain the exact number of solutions for computations where a naive enumeration would take astronomically long times.

A detailed decision tree to create, preserve, transfer, and support the emergence profile in anterior maxillary implants using custom abutments.

Rehabilitation with implants in the esthetic zone is one of the most demanding tasks due to the importance of obtaining an optimum esthetic result. The aim of this article was to present a workflow to create, preserve, transfer and support the emergence profile in anterior maxillary implants. Different methods are used surgically as well as prosthetically to construct an ideal restoration. When immediate loading can be applied in cases of increased primary stability, a provisional restoration is placed with occlusal contacts. In cases not permitting the above procedure and requiring extensive augmentation, a resin-bonded partial coverage fixed partial denture can be a predictable and reliable treatment option until the final restoration is delivered. Creating or preserving the emergence profile at immediate post-extraction and delayed implants, respectively, is achieved through customized provisional, healing abutments, a combination of prefabricated healing abutments and partial coverage provisional restoration, or utilization of the patient's own tooth crown. Transferring the individualized soft tissue contour to the final restoration can be achieved by modifying the impression coping intraorally with composite resin, fabricating a cast mimicking the soft tissue contour in the laboratory, or by the use of CAD/CAM technology. A customized abutment is necessary in order to maintain the emergence profile that has been created during the previous stages. The objective of this paper was to present a detailed workflow for the restoration of anterior maxillary implants focused on the creation, preservation, support, and transfer of the emergence profile of the soft tissues through a series of clinical cases.

Loosening of the fixing screw in single implant crowns: predisposing factors, prevention and treatment options.

The problem of technical complications in implants and implant-supported restorations has existed for decades. The most frequent complication is the loosening of the fixing screw, which although is not catastrophic, if it occurs repeatedly, it may affect the success of the implant therapy and the patient satisfaction. Factors that affect the frequency of prosthetic complications include: the implant-abutment connection, para-functional habits, cantilevers, and the type of restoration. Regarding the implant-abutment connection, the first systems were those with an external hexagon. Because of their small height and the disadvantages that this entails, other connection types were developed, such as those of hexagonal and conical connection, which decreased the complication rates, including the loosening of the fixing screw. On the dilemma "cement- or screw-retained restoration", the choice depends on biological, technical, and aesthetic factors. Cement-retained restorations are simpler in construction with lower cost and clinicians are more familiar with the clinical procedure. On the other side, if the fixing screw of the abutment is loosened in a cement-retained restoration, it may be a difficult and demanding clinical task to fix this prosthetic complication. Screw-retained restorations are more prone to loosening of the fixing screw, but allow easy retrievability and repair. Their use however, is often restricted because of diverting or unfavorable inclination of the alveolar ridge and the implant. The aim of this article was to present clinical solutions for the complication of screw-loosening through clinical examples and discuss the factors that may predispose to its occurrence. CLINICAL SIGNIFICANCE: The problem of technical complications in implants and implant-supported restorations has existed for decades. The most frequent complication is the loosening of the fixing screw which, although is not catastrophic, if it occurs repeatedly, it may affect the success of the implant therapy and the patient satisfaction. Factors that affect the frequency of prosthetic complications include: the implant-abutment connection, para-functional habits, cantilevers and the type of restoration. The treatment options for the clinician are limited but certain preventing measures during construction of the restoration may be helpful to overcome this clinical problem.

Surgical and prosthetic dental rehabilitation through a complete digital workflow - A case report.

Several aspects of digital dentistry have recently been improved, including new materials, navigated implant placement, digital impression in combination with virtual articulation, and the computer-aided processes of designing and manufacturing of prosthetic restorations. In this case report, the prosthodontic treatment of a patient through a complete digital workflow is presented. A 39-year-old male patient presented for restoration of missing teeth in the posterior maxilla and mandible. In a single-tooth narrow gap (region 15), a Straumann NNC implant was placed by computer-assisted planning and navigation. For the rest of the missing teeth, ZrO2 fixed dental prostheses (FDPs) were manufactured by a computer-aided design/computer- aided manufacturing (CAD/CAM) system after optical impression with an intraoral scanner (iTero), and data transferal to a virtual articulator (Ceramill Artex). Rehabilitation through a complete digital workflow is a promising technology in terms of accuracy, reduced workload, greater control over the final product, and minimally invasive procedures. These advantages may have a potential positive effect with regard to patient satisfaction compared with conventional methods.

Treatment Options for Anterior Teeth with Questionable Prognosis: Critical Factors in Determining Whether to Maintain or Extract.

UNLABELLED: Implants nowadays have conquered the majority of prosthetic restorations in the everyday clinical practice. As a result there has been a tendency among many clinicians to believe that implant therapy is the best solution in every clinical case, even if extraction of natural tooth with questionable prognosis is necessary. The value of natural teeth has been recently reconsidered. An implant not placed under ideal circumstances, may lead to a compromised result especially in the anterior maxillary region. Conversely natural teeth, even in a compromised clinical condition, maintain proprioception and can be adapted to the stresses of functional loading. The most demanding task in daily clinical practice is the treatment plan. The role of the clinician is more complicated for the anterior teeth where the patient's expectations and the esthetic criteria complicate the objective way of thinking. Therefore, a frequent dilemma in dental practice is whether to maintain an anterior tooth with a questionable prognosis or to extract it and replace it with an implant. The aim of this article is to approach the dilemma of extraction or maintenance of anterior teeth with a questionable prognosis through a series of clinical cases focusing on the factors that should be taken under consideration. CLINICAL SIGNIFICANCE: Dental implants offer increased possibilities in the restoration of the anterior maxillary teeth. In specific clinical cases however a satisfying clinical result can be achieved by maintaining the existing natural teeth even if they have a questionable prognosis and a more complicated treatment plan may be needed. (J Esthet Restor Dent, 2016).

Restoration of divergent implants with a 2-piece screw-retained fixed, complete dental implant prostheses.

Restoring a severely resorbed maxilla is challenging because of poor bone quality and the resorptive pattern that follows tooth loss. When bone augmentation is not possible, implants are placed in suboptimal positions, making the prosthetic rehabilitation more complex. This report presents the steps used to rehabilitate a severely resorbed maxilla with divergent implants, using an implant-supported 2-piece screw-retained prosthesis.

Combined topological and Landau order from strong correlations in Chern bands.

We present a class of states with both topological and conventional Landau order that arise out of strongly interacting spinless fermions in fractionally filled and topologically nontrivial bands with Chern number C=±1. These quantum states show the features of fractional Chern insulators, such as fractional Hall conductivity and interchange of ground-state levels upon insertion of a magnetic flux. In addition, they exhibit charge order and a related additional trivial ground-state degeneracy. Band mixing and geometric frustration of the charge pattern place these lattice states markedly beyond a single-band description.

Fractional Chern insulators with strong interactions that far exceed band gaps.

We study two models for spinless fermions featuring topologically nontrivial bands characterized by Chern numbers C=±1 at fractional filling. Using exact diagonalization, we show that, even for infinitely strong nearest-neighbor repulsion, the ground states of these models belong to the recently discovered class of quantum liquids called fractional Chern insulators (FCI). Thus, we establish that FCI states can arise even if interaction strengths are arbitrarily larger than the noninteracting band gap, going beyond the limits in which FCI states have been previously studied. The strong-coupling FCI states, therefore, depart from the usual isolated-band picture that parallels the fractional quantum Hall effect in Landau levels and demonstrate how a topologically ordered state can arise in a truly multiband system.