The role of welding techniques in the biomechanical behavior of implant-supported prostheses

Recent development and applications of electrodeposition biocoatings on medical titanium for bone repair

Bioactive coatings play a crucial role in enhancing the osseointegration of titanium implants for bone repair. Electrodeposition offers a versatile and efficient technique to deposit uniform coatings onto titanium surfaces, endowing implants with antibacterial properties, controlled drug release, enhanced osteoblast adhesion, and even smart responsiveness. This review summarizes the recent advancements in bioactive coatings for titanium implants used in bone repair, focusing on various electrodeposition strategies based on material-structure synergy. Firstly, it outlines different titanium implant materials and bioactive coating materials suitable for bone repair. Then, it introduces various electrodeposition methods, including electrophoretic deposition, anodization, micro-arc oxidation, electrochemical etching, electrochemical polymerization, and electrochemical deposition, discussing their applications in antibacterial, osteogenic, drug delivery, and smart responsiveness. Finally, it discusses the challenges encountered in the electrodeposition of coatings for titanium implants in bone repair and potential solutions.

An in vitro study using confocal laser scanning microscopy to evaluate the marginal misfits of different implant-supported frameworks

PURPOSE

This study aimed to develop and evaluate a simple, non-destructive method for assessing the misfit and passivity of implant-retained prostheses frameworks.

MATERIALS AND METHODS

To simulate the rehabilitation of a mandible posterior partially edentulous area using 3-unit screw-retained frameworks supported by two implants were fabricated and divided into the following five groups (n = 10 in each group): OP = one-piece framework cast in Co-Cr with the conventional method (control-group); Co-Cr frameworks sectioned and welded by laser (=LAS) or tungsten inert gas (=TIG); Co-Cr CAD-CAM = milled Co-Cr framework; Zir CAD-CAM = milled zirconia framework. The horizontal |X| and vertical |Y| misfits were measured using confocal laser scanning microscopy with one or both screws tightened. Data were analyzed by a two-way ANOVA with repeated measures and Bonferroni correction (α = 0.05).

RESULTS

The greatest |X| misfit was observed in the OP group with both screws tightened (290 µm) and one screw tightened (388 and 340 µm). The conventional casting groups sectioned and welded by laser or TIG had lower mean values (235.35 µm, both screws tightened; and 275 µm, one screw tightened) than the OP framework. However, these values still exceeded those of the milled Co-Cr and zirconia frameworks (190 and 216 µm with both screws tightened). Across all reading conditions, every framework subjected to testing consistently maintained vertical |Y| misfit levels below the threshold of 53 µm; however, the milled frameworks exhibited higher vertical misfits than the frameworks obtained by the conventional cast method.

CONCLUSIONS

The frameworks, whether cast and sectioned with laser welding or milled from Co-Cr, exhibit improved marginal misfit and enhanced passive fit when compared to other fabrication methods. Additionally, the use of confocal laser scanning microscopy is highly effective for passivity and misfit analysis.

Differences between the Fittings of Dental Prostheses Produced by CAD-CAM and Laser Sintering Processes

Digital dentistry and new techniques for the dental protheses' suprastructure fabrication have undergone a great evolution in recent years, revolutionizing the quality of dental prostheses. The aim of this work is to determine whether the best horizontal marginal fit is provided by the CAD-CAM technique or by laser sintering. These values have been compared with the traditional casting technique. A total of 30 CAD-CAM models, 30 laser sintering models, and 10 casting models (as control) were fabricated. The structures realized with chromium-cobalt (CrCo) have been made by six different companies, always with the same model. Scanning electron microscopy with a high-precision image analysis system was used, and 10,000 measurements were taken for each model on the gingival (external) and palatal (internal) side. Thus, a total of 1,400,000 images were measured. It was determined that the CAD-CAM technique is the one that allows the best adjustments in the manufacturing methods studied. The laser sintering technique presents less adjustment, showing the presence of porosities and volume contraction defects due to solidification processes and heterogeneities in the chemical composition (coring). The technique with the worst adjustments is the casting technique, containing numerous defects in the suprastructure. The statistical analysis of results reflected the presence of statistically significant gap differences between the three manufacturing methods analyzed (p < 0.05), with the samples manufactured by CAD-CAM and by traditional casting processes being the ones that showed lower and higher values, respectively. No statistically significant differences in fit were observed between the palatal and gingival fit values, regardless of the manufacturing method used. No statistically significant differences in adjustment between the different manufacturing centers were found, regardless of the process used.

Fracture Resistance of Endodontically Treated Premolars Reconstructed by Traditional Casting and CAD-CAM Milling Post and Cores

Purpose. Restoration of endodontically treated premolars has always been considered as a challenging procedure. This study compared the fracture strength and mode of failure of root canal treated premolars reconstructed with various post and core systems. Materials and Methods. Twenty healthy extracted premolars were selected and underwent root canal treatment and then randomly assigned into 4 groups (n = 5). The teeth in group 1 restored with amalgam, whereas others reconstructed with post and cores made by cobalt-chromium (Co-Cr) casting (group 2), nonprecious gold (NPG) casting (group 3), or computer-aided design (CAD) and computer-aided manufacturing (CAM) milling (group 4). The force at fracture was measured in a universal testing machine, and the failure mode was recorded as repairable or nonrepairable. Results. ANOVA revealed a significant difference in fracture resistance between groups ( $P=0.001$ ). The control group displayed significantly lower strength than that of the CAD-CAM or CO-Cr groups ( $P<0.05$ ). The CAD-CAM posts were also more resistant to fracture than the NPG group ( $P<0.05$ ). The frequencies of repairable fracture in the control, Co-Cr, NPG, and CAD-CAM groups were 40%, 20%, 20%, and 60%, respectively. The chi-square test revealed no significant difference in the distribution of failure modes between groups ( $P=0.415$ ). Conclusion. The teeth reconstructed with post and cores were more resistant to fracture than those restored with amalgam alone. CAD-CAM milling could be considered as the best system for reconstruction of endodontically treated teeth, as it provided the highest fracture strength with less risk of nonrepairable tooth fracture.

Evaluation of misfit and stress distribution in implant-retained prosthesis obtained by different methods

This study evaluated the vertical misfit, passivity, and stress distribution after tightening the screws of different prosthesis. Two implants were used to simulate the rehabilitation of partially edentulous mandible space from the second premolar to the second molar. 40 three-element screw-retained fixed dental prosthesis with distal cantilever were fabricated and divided into four groups according to the method of production of framework (n = 10): G1 = conventional casting one-piece framework, G2 = conventional casting sectioned and laser welding, G3 = conventional casting sectioned and tungsten inert gas (TIG) welding and G4 = framework obtained by CAD/CAM (computer-aided design/computer-aided manufacturing) system. The vertical misfits (both screws tightened) and the passive fit (one screw tightened) were measured under a comparator optical microscope. The data was submitted to Shapiro-Wilk test to enable comparison with ANOVA followed by Tukey with Bonferroni adjust (α = .05). The qualitative analysis of the stress distribution was performed by the photoelastic method. The vertical misfit (both screws tightened) of the G2 (24 μm) and G3 (27 μm) were significantly higher than G4 (10 μm) (p = 0,006). The passive fit (for the non-tightened) of the G1(64 μm) and G3 (61 μm) were significantly higher than the G4 (32 μm) (p=0,009). G1 showed high stress between the implants in the photoelastic analysis and G4 presented lower stress. In conclusion, CAD/CAM method results in less vertical misfit, more passivity, and consequently better stress distribution to the bone.

The Role of Digital X-Ray in Curative Effect and Nursing Evaluation of Cervical Spondylotic Radiculopathy

The present study attempted to analyze the features of atlanto-occipital radiograph in patients with cervical spondylotic radiculopathy or vertebral artery type. In order to reduce the interference of human factors and the measurement error as much as possible, this experiment adopts the blind design and analyzes the digital format X-ray films by using the computer software ImageJ. Because the tangent line between the outer plates of the anterior and posterior margin of the foramen magnum was not accurately located on the X-ray film, the angle formed by the line between the saddle dorsal slope and the center point of the anterior and posterior nodule with a clear display was selected as the measurement method of the angle between the atlanto-occipital joints. The results showed that the lateral cervical curvature of the VCS group was 0.43 ± 0.51, and the lateral cervical curvature of the CSR group was 0.46 ± 0.49, both of which were significantly lower than the normal value (1.2 ± 0.5 cm). Patients in both groups had the characteristic of cervical curvature straightening. The changes of cervical curvature in overflexion and overextension positions can indirectly reflect the state of cervical motion. The anterior flexion neck curve of the VCS group was less than that of the CSR group (P < 0.05). Compared with the CSR group, VCS showed limited cervical anterior flexion movement. In this study, X-ray films of both CSR and VCS showed occipitocervical flexion and extension disorders, cervical curvature straightening, and lower cervical instability. In VCS, occipitocervical flexion and extension disorders were mainly manifested in atlantoaxial flexion disorders, while in CSR, atlanto-occipitocervical flexion and extension disorders were mainly manifested in atlantoaxial flexion disorders.

Can ceramic veneer spark erosion and mechanical cycling affect the accuracy of milled complete-arch frameworks supported by 6 implants?

STATEMENT OF PROBLEM

Milling is a well-established method for manufacturing prosthetic frameworks. However, information about the influence of ceramic veneer and spark erosion on the accuracy of the all-on-six complete-arch fixed frameworks manufactured from different materials is lacking.

PURPOSE

The purpose of this in vitro study was to compare the accuracy of milled complete-arch fixed frameworks with zirconia, cobalt-chromium, and titanium at different steps of their manufacturing process and the influence of mechanical cycling.

MATERIAL AND METHODS

Fifteen milled complete-arch fixed frameworks, supported by 6 implants, were made in zirconia, cobalt-chromium, and titanium (n=5). The fit was measured by the single-screw test protocol. Stress was measured by photoelastic analysis. The loosening torque was evaluated by tightening the screws, retightening them after 10 minutes, and then evaluating the loosening torque 24 hours later. Thereafter, all frameworks received ceramic veneer, and the previous tests were repeated. Cobalt-chromium and titanium frameworks received spark erosion after ceramic veneer, and all analyses were repeated. Before and after mechanical cycling, loosening torque was evaluated. The results were subjected to 2-way repeated-measures ANOVA and the Bonferroni test (α=.05).

RESULTS

Titanium presented higher fit values than zirconia (P=.037) and similar to cobalt-chromium frameworks (P>.05) at baseline. After ceramic veneer, higher fit levels were observed for zirconia (P=.001) and cobalt-chromium (P=.008). Titanium showed higher stress values (P<.05) regardless of time. Baseline for all materials presented lower stress values (P<.05). Higher loosening torque values were found for the titanium group at baseline (P<.001) and after ceramic veneer (P<.001). Spark erosion improved fit and loosening torque values only for cobalt-chromium (P<.05). Mechanical cycling did not influence the loosening torque (P>.05).

CONCLUSIONS

Titanium milled complete-arch fixed frameworks presented poorer fit values than zirconia, although the loosening torque at baseline was higher. Ceramic veneer increased the fit levels for zirconia and cobalt-chromium, decreased the loosening torque values for cobalt-chromium, and enhanced stress levels. Spark erosion can be a reliable technique to improve fit and loosening torque for cobalt-chromium frameworks. Mechanical cycling did not decrease loosening torque.

Influence of the CAD-CAM Systems on the Marginal Accuracy and Mechanical Properties of Dental Restorations

The aim of this study was to compare the quality of different computer-assisted-design and computer assisted manufacturing systems (CAD-CAM) generated by only one scanner, focusing on vertical fit discrepancies and the mechanical properties. A master model was obtained from a real clinical situation: the replacement of an absent (pontic) tooth, with the construction of a fixed partial denture on natural abutments with three elements. Nine scans were performed by each tested and 36 copies were designed using a dental CAD-CAM software (Exocad). The frameworks were manufactured using three-axis and five-axis, with the same batch of the chrome-cobalt (CrCo) alloy. The frameworks were not cemented. A focus ion beam-high resolution scanning electron microscope (FIB-HRSEM) allowed us to obtain the vertical gap measurements in five points for each specimen. Roughness parameters were measured using white light interferometry (WLI). The samples were mechanically characterized by means of flexural tests. A servo-hydraulic testing machine was used with a cross-head rate of 1 mm/min. One-way ANOVA statistical analysis was performed to determine whether the vertical discrepancies and mechanical properties were significantly different between each group (significance level p < 0.05). The overall mean marginal gap values ranged: from 92.38 ± 19.24 µm to 19.46 ± 10.20 µm, for the samples produced by three-axis and five-axis machines, respectively. Roughness was lower in the five-axis machine than the three-axis one, and as a consequence, the surface quality was better when the five-axis machine was used. These results revealed a statistically significant difference (p < 0.005) in the mean marginal gap between the CAD-CAM systems studied. The flexural strength for these restorations range from 6500 to 7000 N, and does not present any statistical differences’ significance between two CAD-CAM systems studied. This contribution suggests that the number of axes improves vertical fit and surface quality due to the lower roughness. These claims show some discrepancies with other studies.

Systematic review and meta-analysis of welding procedures in one-piece cast implant-supported frameworks

The objective of this systematic review and meta-analysis was to evaluate the effect of welding techniques on implant-supported prostheses and determine whether they contribute to a better adaptation compared with a one-piece cast. A search was conducted using the PubMed/MEDLINE, Embase, and Cochrane Library databases, and articles published until November 2017 were obtained from these databases. This review followed the PRISMA criteria and is registered on the PROSPERO platform (CRD42017081865). The PICO question was "Do welding procedures in one-piece cast implant-supported frameworks influence implant/abutment-framework marginal misfits?" Eleven studies were selected for a qualitative analysis, and seven studies were selected for a quantitative analysis. A total of 189 specimens were fabricated using different materials (cp-Ti, Ni-Cr, Cr-Co, and noble alloys), and welding techniques such as laser welding, conventional welding, tungsten inert gas, and brazing were applied. A vertical marginal misfit was measured using an optical microscope, a stereomicroscope, and/or a scanning electron microscopy. The qualitative analysis in the studies demonstrated a positive effect of the welding techniques on the adaptation of the infrastructures. The meta-analysis confirmed the results (p < 0.00001; MD: -36.14; 95%CI: -48.69 to -23.59). Within the limitations of this study and regarding the heterogeneity of the samples, we conclude that the soldering point technique is effective for obtaining relatively low values of marginal misfit, with laser welding as the most effective technique. However, additional studies were recommended due to the heterogeneity of different variables (alloys, connection, and misfit evaluation) in the included studies.