Architecture and design of a robotic mastication simulator for interactive load testing of dental implants and the mandible.

STATEMENT OF PROBLEM: Determination of interactive loading between a dental prosthesis and the host mandible is essential for implant prosthodontics and to preserve bone. PURPOSE: The purpose of this study was to develop and evaluate a robotic mastication simulator to replicate the human mastication force cycle to record the required interactive loading using specifically designed force sensors. MATERIAL AND METHODS: This robotic mastication simulator incorporated a Stewart parallel kinematic mechanism (PKM) controlled in the force-control loop. The hydraulically operated PKM executed the wrench operation, which consisted of the combined effect of forces and moments exhibited by the mastication process. Principal design features of this robotic simulator included PKM kinematic modeling, static force analysis to realize the masticatory wrench characteristics, and the architecture of its hydraulic system. Additionally, the design of a load-sensing element for the mandible and implant interaction was also incorporated. This element facilitated the quantification of the load distribution between implants and the host bone during the masticatory operation produced by the PKM. These loading tests were patient-specific and required separate artificial mandibular models for each patient. RESULTS: The simulation results demonstrated that the robotic PKM could replicate human mastication. These results validated the hydraulic system modeling for the required range of masticatory movements and effective forces of the PKM end-effector. The overall structural design of the robotic mastication simulator presented the integration of the PKM and its hydraulic system with the premeditated load-recording mechanism. CONCLUSIONS: The developed system facilitated the teeth-replacement procedure. The PKM accomplished the execution of mastication cycle involving 6 degrees of freedom, enabling any translation and rotation in sagittal, horizontal, and vertical planes. The mechanism can simulate the human mastication cycle and has a force application range of up to 2000 N. The designed load-sensing element can record interactive forces within the range of 200 N to 2000 N with fast response and high sensitivity to produce a robotic mastication simulator with custom-made modules.

Orthodontic miniscrews: an experimental campaign on primary stability and bone properties.

OBJECTIVE: To evaluate the primary stability of different shaped miniscrews through the acquisition of data regarding maximum insertion torque, pullout force, and a radiodiagnosic evaluation of bone characteristics. MATERIALS AND METHODS: Sixty fresh porcine bone samples were scanned by computed tomography (CT) and cone-beam computed tomography (CBCT). By means of a dedicated software, CT and CBCT images were analysed to measure the insertion-site cortical thickness, cortical density, and marrow bone density. Sixty miniscrews of 12 different types were implanted with no predrilling pilot hole in the bone samples. Every device was tightened by means of a digital torque screwdriver and torque data were collected. Subsequently, pullout tests were performed. Spearman and Pearson correlations were employed to compare any relationship between continuous variables. RESULTS: Different types of miniscrews did not show statistically significant differences in their torque value (P = 0.595), instead a significant difference was revealed by considering their load measures (P = 0.039). Cortical bone thickness resulted strongly correlated both with value of load (P < 0.001), and modestly with torque measures (P = 0.004). A strong positive correlation was found between CT and CBCT both for cortical density (P < 0.001) and marrow bone density (P < 0.001). CONCLUSION: Bone characteristics play the major role in miniscrews primary stability.

Tackling Inequalities in Oral Health: Bone Augmentation in Dental Surgery through the 3D Printing of Poly(ε-caprolactone) Combined with 20% Tricalcium Phosphate.

The concept of personalized medicine and overcoming healthcare inequalities have become extremely popular in recent decades. Polymers can support cost reductions, the simplicity of customized printing processes, and possible future wide-scale expansion. Polymers with ß-tricalcium phosphate (TCP) are well known for their synergy with oral tissues and their ability to induce osteoconductivity. However, poor information exists concerning their properties after the printing process and whether they can maintain an unaffected biological role. Poly(ε-caprolactone) (PCL) polymer and PCL compounded with TCP 20% composite were printed with a Prusa Mini-LCD-®3D printer. Samples were sterilised by immersion in a 2% peracetic acid solution. Sample analyses were performed using infrared-spectroscopy and statical mechanical tests. Biocompatibility tests, such as cell adhesion on the substrate, evaluations of the metabolic activity of viable cells on substrates, and F-actin labelling, followed by FilaQuant-Software were performed using a MC3T3-E1 pre-osteoblasts line. PCL+ß-TCP-20% composite is satisfactory for commercial 3D printing and appears suitable to sustain an ISO14937:200937 sterilization procedure. In addition, the proper actin cytoskeleton rearrangement clearly shows their biocompatibility as well as their ability to favour osteoblast adhesion, which is a pivotal condition for cell proliferation and differentiation.

Multipotent Mesenchymal Cells Homing and Differentiation on Poly(ε-caprolactone) Blended with 20% Tricalcium Phosphate and Polylactic Acid Incorporating 10% Hydroxyapatite 3D-Printed Scaffolds via a Commercial Fused Deposition Modeling 3D Device.

As highlighted by the 'Global Burden of Disease Study 2019' conducted by the World Health Organization, ensuring fair access to medical care through affordable and targeted treatments remains crucial for an ethical global healthcare system. Given the escalating demand for advanced and urgently needed solutions in regenerative bone procedures, the critical role of biopolymers emerges as a paramount necessity, offering a groundbreaking avenue to address pressing medical needs and revolutionize the landscape of bone regeneration therapies. Polymers emerge as excellent solutions due to their versatility, making them reliable materials for 3D printing. The development and widespread adoption of this technology would impact production costs and enhance access to related healthcare services. For instance, in dentistry, the use of commercial polymers blended with ß-tricalcium phosphate (TCP) is driven by the need to print a standardized product with osteoconductive features. However, modernization is required to bridge the gap between biomaterial innovation and the ability to print them through commercial printing devices. Here we showed, for the first time, the metabolic behavior and the lineage commitment of bone marrow-derived multipotent mesenchymal cells (MSCs) on the 3D-printed substrates poly(e-caprolactone) combined with 20% tricalcium phosphate (PCL + 20% ß-TCP) and L-polylactic acid (PLLA) combined with 10% hydroxyapatite (PLLA + 10% HA). Although there are limitations in printing additive-enriched polymers with a predictable and short half-life, the tested 3D-printed biomaterials were highly efficient in supporting osteoinductivity. Indeed, considering different temporal sequences, both 3D-printed biomaterials resulted as optimal scaffolds for MSCs' commitment toward mature bone cells. Of interest, PLLA + 10% HA substrates hold the confirmation as the finest material for osteoinduction of MSCs.

Miniscrew design and bone characteristics: an experimental study of primary stability.

INTRODUCTION: The purpose of this study was to evaluate the correlations between bone characteristics, orthodontic miniscrew designs, and primary stability. METHODS: Four different miniscrews were placed in pig ribs. The miniscrews were first scanned with a scanning electron microscope to obtain measurable images of their threads. Subsequently, the maximum insertion torque of the screws and the maximum load value in the pullout force tests were measured; furthermore, bone specimen characteristics were analyzed by using cone-beam computed tomography. For each bone sample, the insertion site cortical thickness as well as both cortical and marrow bone density were evaluated. The nonparametric Kendall rank correlation (tau) was used to evaluate the strength of the associations among the characteristics measured. The nonparametric Kruskall-Wallis test was used to evaluate the differences among the groups, and post-hoc comparisons were assessed by using the Nemenyi-Damico-Wolfe-Dunn test. RESULTS: A significant dependence was found between pitch and maximum insertion torque (tau, -0.49). Positive correlations were also found between pullout force and maximum insertion torque (tau, 0.64), cortical thickness (tau, 0.36), and marrow bone density (tau, 0.35). CONCLUSIONS: In this in-vitro experimental study, strong correlations were observed among miniscrew geometry, bone characteristics, and primary stability.

Immediate Implants in the Aesthetic Zone: Is Socket Shield Technique a Predictable Treatment Option? A Narrative Review.

(1) Background. Dental implant placement in the anterior region requires extreme precision due to relatively high aesthetic demand. This narrative review aimed to analyse some of the available clinical studies of the socket-shield technique and determine its viability for dental implant survival/success and complication rates. (2) Methods. An electronic search for publications was performed using the Cochrane, PubMed-MEDLINE, Web of Science, and Google Scholar databases. All electronic searches included human clinical and animal studies and were performed by three independent examiners. (3) Results. A total of 1383 records were identified with the initial search strategies, but only 25 full texts + five abstracts clinical studies were kept after the recruitment criteria screening. The technical details, advantages, and limitations of the techniques were illustrated. (4) Conclusion. Within the limitations of the present review, it would be merely justified that immediate dental implant placement in conjunction with the socket-shield technique can be a promising strategy for dental implant therapy.

Mechanical characterisation of multi vs. uni-directional carbon fiber frameworks for dental implant applications.

OBJECTIVES: The aim of the present study was to investigate the mechanical characteristics of dental implant frameworks made of unidirectional carbon fiber composite (UF) and to compare them with those provided by multidirectional carbon fiber composite (IF). METHODS: 8 identical UF samples were used. The samples were initially evaluated by optical microscope and SEM then non-destructive and destructive mechanical tests were performed on 4 samples in order to evaluate dynamic, static elastic modulus, wettability and ultimate strength. The outcomes were compared with those of IF samples tested following the same protocol - data reported in a previous published paper. The remaining 4 samples were aged for 60 days in isotonic saline solution at 37 °C simulating the human saliva. The same tests reported before were performed on the aged samples. RESULTS: The dynamic elastic modulus was lower for UF (78.1 GPa for UF vs. 92.2 GPa for IF) as well as the static elastic modulus (71.0 GPa for UF vs. 84.5 GPa for IF). The ultimate strength value was 582 MPa for the IF samples and 700 MPa for the UF. The aging process of the UF samples did not show any appreciable variation, with small differences that falls within the experimental error. SIGNIFICANCE: Unidirectional carbon fiber-reinforced composite appears suitable for the fabrication of frameworks for implant-supported full-arch dentures. The dynamic elastic modulus was higher for UF while the static elastic modulus was higher for IF. The aging process seems not able to significantly alter the mechanical properties of the material. Further research is needed to evaluate the clinical significance of such outcomes.

Torque efficiency of a customized lingual appliance : Performance of wires with three different ligature systems.

PURPOSE: Torque control in lingual orthodontics is key to obtain optimal esthetic results. The aim of this in vitro experimental study was to verify the efficiency of the ligature-archwire-slot system in torque control using a customized lingual appliance. METHODS: An idealized cast with eight extracted human teeth was created and a set of customized lingual brackets was obtained. Tests were performed with the following wires: 0.016â€³â€¯× 0.022″ nickel-titanium (NiTi), 0.016â€³â€¯× 0.024″ stainless steel (SS), 0.017â€³â€¯× 0.025″ ßIII titanium (ßIIITi), 0.0182â€³â€¯× 0.0182″ ßIIITi, 0.018â€³â€¯× 0.025″ SS, 0.018â€³â€¯× 0.025″ NiTi, 0.018â€³â€¯× 0.025″ ßIIITi, and three types of ligatures were tested using a universal testing machine to calculate the efficiency in torque control. A blind statistical analysis was performed. RESULTS: Based on post hoc multiple comparisons, differences were found for two of the three ligatures when using the 0.016â€³â€¯× 0.022″ NiTi wires (p < 0.001 for both ligatures). When considering all ligatures, 0.018â€³â€¯× 0.025″ SS and 0.018â€³â€¯× 0.025″ ßIIITi were significantly different from all other wires (p < 0.001 in all cases). With a moment of 5 Nmm, the 0.016â€³â€¯× 0.022″ NiTi wire developed median angles of 26.7, 29.8, and 38.7° with the three ligatures, respectively, while the 0.018â€³â€¯× 0.025″ SS developed median angles of 12.9, 10.7, and 12.7°, respectively. CONCLUSIONS: The ligature type and geometry did not affect the efficiency of torque control, except for the 0.016â€³â€¯× 0.022″ NiTi wire. The wires generating the greatest moments were the 0.018â€³â€¯× 0.025″ SS and 0.018â€³â€¯× 0.025″ ßIIITi.

Evaluation of Adhesion Between Carbon Fiber Frameworks and Esthetic Veneering Materials.

PURPOSE: To assess bond strength and failure patterns of carbon fiber-reinforced composite (CFRC) and veneering materials. MATERIALS AND METHODS: A total of 20 samples were prepared: 10 veneered with polymethylmethacrylate (group A) and 10 with composite resin (group B). Shear bond strength (SBS) was measured, and failed samples were microscopically observed. RESULTS: The mean ± standard deviation (SD) SBS of specimens in group A was slightly higher (7.39 ± 0.24 MPa) than specimens in group B (5.68 ± 0.29 MPa). Microscopic observation showed an adhesive fracture pattern at the CFRC-adhesive interface in both groups. CONCLUSION: Adhesion between CFRC and veneering material is reliable and predictable, although a specific protocol needs to be developed to improve adhesion.

"Green-reduced" graphene oxide induces in vitro an enhanced biomimetic mineralization of polycaprolactone electrospun meshes.

A novel green method for graphene oxide (GO) reduction via ascorbic acid has been adopted to realize bio-friendly reduced graphene oxide (RGO)/polycaprolactone (PCL) nanofibrous meshes, as substrates for bone tissue engineering applications. PCL fibrous mats enriched with either RGO or GO (0.25 wt%) were fabricated to recapitulate the fibrillar structure of the bone extracellular matrix (ECM) and the effects of RGO incorporation on the structural proprieties, biomechanics and bioactivity of the nano-composites meshes were evaluated. RGO/PCL fibrous meshes displayed superior mechanical properties (i.e. Young's Modulus and ultimate tensile strength) besides supporting noticeably improved cell adhesion, spreading and proliferation of fibroblasts and osteoblast-like cell lines. Furthermore, RGO-based electrospun substrates enhanced in vitro calcium deposition in the ECM produced by osteoblast-like cells, which was paralleled, in human mesenchymal stem cells grown onto the same substrates, by an increased expression of the osteogenic markers mandatory for mineralization. In this respect, the capability of graphene-based materials to adsorb osteogenic factors cooperates synergically with the rougher surface of RGO/PCL-based materials, evidenced by AFM analysis, to ignite mineralization of the neodeposited matrix and to promote the osteogenic commitment of the cultured cell in the surrounding microenvironment.

Biological and mechanical characterization of carbon fiber frameworks for dental implant applications.

OBJECTIVES: The aim of the present study was to investigate the biocompatibility and mechanical characteristics of dental implant frameworks made of carbon fiber composite. METHODS: The biocompatibility of intact samples and fragments was evaluated by cell count and MTT test according to EN-ISO 10993-5:2009 directions. Destructive and non-destructive mechanical tests were performed in order to evaluate: porosity, static and dynamic elastic modulus of carbon fiber samples. These tests were conducted on different batches of samples manufactured by different dental technicians. The samples were evaluated by optical microscope and by SEM. A compression test was performed to compare complete implant-supported fixed dentures, provided with a metal or carbon fiber framework. RESULTS: Carbon fiber intact and fragmented samples showed optimal biocompatibility. Manufacture technique strongly influenced the mechanical characteristics of fiber-reinforced composite materials. The implant-supported full-arch fixed denture provided with a carbon fiber framework, showed a yield strength comparable to the implant-supported full-arch fixed denture, provided with a metal framework. SIGNIFICANCE: Carbon fiber-reinforced composites demonstrated optimal biocompatibility and mechanical characteristics. They appear suitable for the fabrication of frameworks for implant-supported full-arch dentures. Great attention must be paid to manufacture technique as it strongly affects the material mechanical characteristics.

Torque Loss After Miniscrew Placement: An In-Vitro Study Followed by a Clinical Trial.

To evaluate torque loss a week after insertion, both in an in vivo and an in vitro experimental setup were designed. In the in vivo setup a total of 29 miniscrews were placed in 20 patients who underwent orthodontic treatment. Maximum insertion torque (MIT) was evaluated at insertion time (T1). A week later, insertion torque was measured again by applying a quarter turn (T2); no load was applied on the screw during the first week. In the in vitro setup a total of 20 miniscrews were placed in pig rib bone samples. MIT was evaluated at insertion time (T1). Bone samples were kept in saline solution and controlled environment for a week during which the solution was refreshed every day. Afterwards, torque was measured again by applying a quarter turn (T2). The comparison of MIT over time was done calculating the percentage difference of the torque values between pre- and post-treatment and using the parametric two independent samples t-test or the non-parametric Mann-Whitney test. After a week unloaded miniscrews showed a mean loss of rotational torque of 36.3% and 40.9% in in vitro and in in vivo conditions, respectively. No statistical differences were found between the two different setups. Torque loss was observed after the first week in both study models; in vitro experimental setup provided a reliable study model for studying torque variation during the first week after insertion.

Tensile test and interface retention forces between wires and composites in lingual fixed retainers.

INTRODUCTION: In daily orthodontic clinical practice retention is very important, and lingual retainers are part of this challenge. The failure of lingual retainers may be due to many factors. The aim of this study was to assess the retention forces and mechanical behavior of different types of wires matched with different kinds of composites in lingual retainers. METHODS: A tensile test was performed on cylindrical composite test specimens bonded to orthodontic wires. The specimens were constructed using four different wires: a straight wire (Remanium .016×.022″ Dentaurum), two round twisted wires (Penta One .0215″ Masel, Gold Penta Twisted .0215″ Gold N'braces) and a rectangular braided wire (D-Rect .016×.022″ Ormco); and three composites: two micro-hybrids (Micro-Hybrid Enamel Plus HFO Micerium, and Micro-Hybrid SDR U Dentsply) and a micro-nano-filled composite (Micro-Nano-Filled Transbond LR 3M). The test was performed at a speed of 10mm/min on an Inström device. The wire was fixed with a clamp. RESULTS: The results showed that the bonding between wires and composites in lingual fixed retainers seemed to be lowest for rectangular smooth wires and increased in round twisted and rectangular twisted wires where the bonding was so strong that the maximum tension/bond strength was greater than the ultimate tensile strength of the wire. The highest values were in rectangular twisted wires. Concerning the composites, hybrid composites had the lowest interface bonding values and broke very quickly, while the nano- and micro-composites tolerated stronger forces and displayed higher bonding values. The best results were observed with the golden twisted wire and reached 21.46 MPa with the Transbond composite. With the rectangular braided wire the retention forces were so high that the Enamel Plus composite fractured when the load exceeded 154.6 N/MPa. When the same wire was combined with the Transbond LR either the wire or the composite broke when the force exceeded 240 N. CONCLUSIONS: The results of this study show that, when selecting a lingual retainer in daily clinical practice, not only must the patient's compliance and dependability be considered but also the mechanical properties and composition of different combinations of composites and wires.

Effect of Framework in an Implant-Supported Full-Arch Fixed Prosthesis: 3D Finite Element Analysis.

PURPOSE: The aim of this study was to analyze through a three-dimensional finite element analysis (3D-FEA) stress distribution on four implants supporting a full-arch implant-supported fixed prosthesis (FFP) using different prosthesis designs. MATERIALS AND METHODS: A 3D edentulous maxillary model was created and four implants were virtually placed into the maxilla and splinted, simulating an FFP without framework, with a cast metal framework, and with a carbon fiber framework. An occlusal load of 150 N was applied, stresses were transmitted into peri-implant bone, and prosthodontic components were recorded. RESULTS: 3D-FEA revealed higher stresses on the implants (up to +55.16%), on peri-implant bone (up to +56.93%), and in the prosthesis (up to +70.71%) when the full-acrylic prosthesis was simulated. The prosthesis with a carbon fiber framework showed an intermediate behavior between that of the other two configurations. CONCLUSION: This study suggests that the presence of a rigid framework in full-arch fixed prostheses provides a better load distribution that decreases the maximum values of stress at the levels of implants, prosthesis, and maxillary bone.

Internal bone temperature change during guided surgery preparations for dental implants: an in vitro study.

PURPOSE: The aim of this pig model study was to verify whether the use of devices (surgical templates) or procedures (flapless or flap) of guided surgery may cause a potentially pathologic increase of temperature during the bone preparation. MATERIALS AND METHODS: In this in vitro study, pig ribs with mean cortical thickness of 1.90 mm were used. Open-flap and flapless guided surgery (experimental groups OGS and FGS) and open-flap and flapless conventional technique (control groups OSS and OFS) were performed. Temperature changes were recorded at a distance of 0.5 mm from the final test osteotomy by 2 thermocouples at depths of 1.5 (point A) and 12 mm (point B). Data were collected from 80 measurements, 10 for each group. RESULTS: A statistically significant increase of temperature was reported for the FGS and OGS groups considering the measurement at point A (mean Δt 4.81 degrees and 4.21 degrees, respectively). The measurement at Point B for the FGS group compared to the FSS group did not differ significantly for the 3-mm drill, nor did the OSS group with the 2-mm drill. CONCLUSIONS: Site preparation with surgical stents generated higher bone temperature than conventional drilling. However, this heat generation did not reach temperature levels dangerous for the bone.