Today, two different types of CAD-CAM fabrication methods for complete denture bases are available besides the conventional protocols: a subtractive milling process from a prepolymerized block of polymethylmethacrylate and an additive manufacturing process that built the denture base using a light-cured liquid in a VAT-polymerization process. The aim of this study was to evaluate and to compare the accuracy and precision of denture prosthetic bases made with subtractive and additive manufacturing technologies and to compare them with a denture base with the conventional method in muffle. From the results obtained, 3D printing dentures show a statistically significant higher accuracy than milled prosthetic bases. Milled prosthetic bases have similar accuracy than conventional fabricated dentures.

The aim of this study was to evaluate the stability of prosthetic screws after applying cyclic loadings in an “all-on-four” rehabilitation model with the OT Bridge system. The model was tested both with and without anterior screws. Four implant analogues following the “all-on-four” concept were inserted in an edentulous mandibular resin model. An OT Bridge system with a Cr–Co prosthetic framework was fabricated. Depending on the presence or absence of one or two anterior screws on the implant analogues, three groups were created, i.e., Gr.1: three tightening screws, Gr.2: two tightening screws, Control Group: four tightening screws. Each single group underwent subsequent 400,000 cyclic loads, simulating approximately a year of chewing by using a dynamometer machine. This cycle was repeated five times for each group, and preload loss values were evaluated on each prosthetic screw after each cycle. All the data obtained were analyzed by one-way ANOVA and Student’s t-test. No statistically significant differences after intragroup analysis were found. A statistically significant difference within the Gr.1 between the screws in positions 33 and 36, equal to 15.2% (p-value = 0.0176), was found. The OT Bridge seems a useful system to maintain the retention of a prosthesis during mechanical stress conditions even in the absence of one screw in an “all-on-four” rehabilitation. This could represent a good solution to solve the esthetic problem of the screw buccal access hole for fixed solutions.

In full-arch implant rehabilitations, when the anterior screw abutment channel compromises the aesthetic of the patient, the OT-Bridge system used with its Seeger rings may provide the necessary retention of the prosthesis. However, no studies have evaluated the forces generated at the Seeger level during loading. This Finite Element Analysis aims to investigate the mechanical behavior of Seeger rings in a mandibular model with four implants and an OT-Bridge system, used without one or two anterior prosthetic screws. A 400 N unilateral load was virtually applied on a 7 mm distal cantilever. Two different variables were considered: the constraint conditions using two or three screws instead of four and the three different framework materials (fiberglass reinforced resin, cobalt-chrome, TiAl6V4). The FEA analysis exhibited tensile and compressive forces on the Seeger closest to the loading point. With the resin framework, a tension force on abutment 3.3 generates a displacement from 5 to 10 times greater than that respectively expressed in metal framework materials. In a full-arch rehabilitation with four implants, the case with three prosthetic screws seems to be a safer and more predictable configuration instead of two. Considering the stress value exhibited and the mechanical properties of the Seeger, the presence of only two prosthetic screws could lead to permanent deformation of the Seeger in the screwless abutment closest to the loading point.

During professional hygiene procedures, different instruments used may cause various damage to dental prostheses. Deplaquing and scaling with curettes and ultrasonic instruments may inadvertently increase the surface roughness of the material and the risk of future bacterial adhesion and/or also compromise the marginal seal of the prosthesis. Hence, the aim of this study was to assess the qualitative effects of two types of curettes and one piezoelectric instrument with a stainless-steel tip on three types of metal-free samples. After treating the samples with different instrumentations, they were analyzed using the scanning electron microscope and then underwent a qualitative microanalysis by using a spectroscopy machine. All the materials tested in this study have undergone significant changes of their superficial structure after instrumentation both with mechanical and manual instruments. Plastic curettes appeared to be less aggressive than the other instruments. Disilicate samples show a significantly lower degree of surface glazing erosion compared to the zirconia sample with all the instruments used.

The aim of the present in vitro comparative study is to validate a novel composite polymer, named “ONLY”, developed to overcome the mechanical drawbacks of conventional, metal-reinforced poly(methyl methacrylate) (PMMA) interim restoration. Ten interim restorations were designed and fabricated (five in the composite “ONLY” group, and five in the metal-reinforced PMMA group). All the samples were screwed into the prototype models, simulating a complete edentulous mandible rehabilitated with six straight implants. Outcome measures were break point (load, N) and displacement (mm) through a static compression test, and material behavior through a dynamic cyclic test method (fatigue test). A total of 20 samples were tested (10 for static and 10 for dynamic). In each group, five samples (test and control) were used. All the specimens completed the mechanical tests, as planned. There was no statistically significant difference between groups for any test. In the test group, the break point was 1953.19 ± 543.73 N, while it was 2031.10 ± 716.68 N in the control group (p = 0.775). The displacement was 1.89 ± 0.34 mm in the test group and 1.98 ± 0.75 mm in the control group (p = 0.763). Using the dynamic cyclic test method, in the control group the mean load was 2504.60 ± 972.15 N, while in the test group the mean load was 3382.00 ± 578.50 N. The difference between groups was 877.40 ± 579.30 N (p value = 0.121). Within the limitations of this in vitro study, the novel composite polymer can be used to immediately load dental implants. Further clinical research is needed to confirm these preliminary results.

Metal-reinforced polymethyl-methacrylate (PMMA) is considered the gold standard material for immediate loading on dental implants. However, mechanical problems under loading cycles can occur, such as fractures. To overcome these drawbacks, a novel polymer-based material has been proposed. The aim of the present in vitro comparative research is to validate a novel composite polymer developed to replace metal-reinforced PMMA interim restoration due to its advantages of good mechanical proprieties, easier manufacturing, and handling. Ten interim restorations were CAD/CAM designed and fabricated (five in the composite "ONLY" group, and five in the metal-reinforced PMMA group). All the samples were screwed into the prototype models, simulating a complete edentulous mandible rehabilitated with six straight implants. Outcome measures were breakpoint (load, N) and displacement (mm) thought a static, compression test and material behavior under dynamic cyclic test method (fatigue test). A total of twenty samples were tested. Ten samples were used for each test (10 for static and 10 for dynamic), five samples were used in each group (test and control). All the specimens completed the mechanical tests, as planned. There was no statistically significant difference between groups for all, breakpoint, displacement and fatigue tests. Breakpoint in the test group was 1953.19 ± 543.73 N, while, it was 2031.10 ± 716.68 N in the control group, with no statistically significant difference (P=0.775). The displacement was 1.89 ± 0.34 mm in the test group and 1.98 ± 0.75 mm in the control group, again, with no statistically significant difference (P=0.763). Under dynamic cyclic test method, in the control group the mean load was 2504.6 ± 972.15 N, while, in the test group the mean load was 3382 ± 578.5 N. The difference between group was 877.4 ± 579.3 N (p value=0.121). With the limitation of this in vitro study, the novel composite polymer can be used to immediately load dental implants. Further clinical researches are needed to confirm this preliminary results.