An assessment of the passivity of the fit of multiunit screw-retained implant frameworks manufactured by using additive and subtractive technologies

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.

Marginal fit and fracture resistance of polyetheretherketone, zirconia, and titanium implant-supported prosthesis frameworks for a partially edentulous arch after thermomechanical aging

STATEMENT OF PROBLEM

Although polyetheretherketone (PEEK) and zirconia (Zir) have been used as implant-supported prosthesis (ISP) frameworks, the long-term effects of thermomechanical aging on the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with titanium (Ti) bases for patients with a partially edentulous arch are not clear.

PURPOSE

The purpose of this in vitro study was to determine the marginal fit and fracture resistance of PEEK and Zir ISP frameworks with Ti bases and Ti ISP frameworks for partially edentulous arches after aging.

MATERIAL AND METHODS

A total of 30 ISP epoxy resin casts were obtained from a typodont with 1 straight implant (Nobel Biocare) in the mandibular right canine region and 1 implant with a 30-degree distal tilt in the mandibular right first molar region. All frameworks (n=10) were fabricated on their own epoxy resin cast with multiunit abutment replicas by using a computer-aided design and computer-aided manufacturing system (exocad-Yenadent). The PEEK and Zir frameworks were fabricated with Ti-bases. Primer (MKZ) and resin cement (DTK adhesive) were used to cement the frameworks to the Ti-bases under a static load of 10 N. After thermomechanical aging (1.2×106 cycles, 120 N, 5 °C-55 °C), marginal gaps between the Ti-bases and cemented frameworks and vertical and passive fits between the Ti-bases and framework and multi-unit abutments were measured by using a stereomicroscope (Euromex) at ×100 magnification. Fracture resistances and types were then determined by using a universal test machine and a stereomicroscope at ×40 magnification. Data were analyzed by using 1-way analysis of variance (ANOVA) and the Tukey HSD and Fisher-Freeman-Halton tests (α=.05).

RESULTS

The marginal gaps of the PEEK and Zir frameworks were respectively 83.5 ±27.1 and 81.8 ±17.8 µm. PEEK (23.7 ±4.6) and Zir (32.9 ±8.7) had a better vertical fit (µm) than Ti (52.5 ±10.6) (P<.001). Zir (49.3 ±16.2) (P<.001) and PEEK (70.9 ±19.6) (P>.05) frameworks had better passive fit (µm) than Ti (91.3 ±24.2). Ti had the highest mean fracture resistance (N) (14800.2 ±3442.3) followed by Zir (7318.7 ±1385.1) and PEEK (3448.9 ±486.6) (P<.001). Fracture types were different in different groups (P<.001).

CONCLUSIONS

The PEEK and Zir frameworks with Ti bases had better vertical and passive fit than the Ti frameworks. All ISP frameworks represented mean marginal fit below 92 µm and withstood physiologic occlusal forces after thermomechanical aging.

Accuracy of Selective Laser Melted Bar Retaining Mandibular Implant-Assisted Overdenture: An In Vitro Comparison of Different Impression Materials and Techniques

This study aimed to assess the accuracy of the marginal fit of 2 implant-supported overdenture bars fabricated with selective laser melting technology, using polyvinyl siloxane and vinyl siloxane ether impression materials and different impression techniques. Two implants with multi-unit abutments were inserted in a 3D-printed mandibular model and used as a reference model, then duplicated into a stone cast to fabricate custom trays for obtaining impressions with polyvinyl siloxane and vinyl siloxane ether impression materials, using both open and closed-tray techniques. This resulted in a total of 4 groups, each with 8 specimens. The impressions were poured and scanned, and 32 cobalt-chromium bars were fabricated using selective laser melting technology. Each bar was screwed onto one abutment of the reference model, and a standardized digital periapical radiograph of the opposite unscrewed side was taken; this process was repeated to the other abutment. The vertical misfit was measured at 3 predetermined positions on the unscrewed side, and 6 values per bar were recorded. The mean gap distance was measured, and the data were subjected to statistical analysis; the present study found that the open-tray technique with vinyl polyether siloxane impression material may offer improved accuracy for obtaining impressions for 2 implant-supported bars. The open-tray technique groups also showed better marginal fit than the closed-tray groups. However, further clinical research is required to confirm these findings.

Additive manufacturing technologies in the oral implant clinic: A review of current applications and progress

Additive manufacturing (AM) technologies can enable the direct fabrication of customized physical objects with complex shapes, based on computer-aided design models. This technology is changing the digital manufacturing industry and has become a subject of considerable interest in digital implant dentistry. Personalized dentistry implant treatments for individual patients can be achieved through Additive manufacturing. Herein, we review the applications of Additive manufacturing technologies in oral implantology, including implant surgery, and implant and restoration products, such as surgical guides for implantation, custom titanium meshes for bone augmentation, personalized or non-personalized dental implants, custom trays, implant casts, and implant-support frameworks, among others. In addition, this review also focuses on Additive manufacturing technologies commonly used in oral implantology. Stereolithography, digital light processing, and fused deposition modeling are often used to construct surgical guides and implant casts, whereas direct metal laser sintering, selective laser melting, and electron beam melting can be applied to fabricate dental implants, personalized titanium meshes, and denture frameworks. Moreover, it is sometimes required to combine Additive manufacturing technology with milling and other cutting and finishing techniques to ensure that the product is suitable for its final application.

Accuracy of digital implant impressions in clinical studies: A systematic review

OBJECTIVES

The use of intraoral scanners (IOSs) for digital implant impressions in daily clinical practice is increasing. However, no structured literature review on the accuracy of digital implant impressions in clinical studies has been described to date. Therefore, this systematic review aimed to answer the PICO question: Which accuracy is described for digital implant impressions in clinical studies?

MATERIAL AND METHODS

An electronic database search was conducted in December 2021 using MeSH terms and free-text search. English-language studies addressing the accuracy of digital implant impressions in clinical studies involving at least 10 patients were included. All clinical indications were considered.

RESULTS

Eight publications between 2014 and 2021 matched the review criteria. However, the study designs showed considerable differences. The number of implants within the studies ranged from 1 to 6, and the number of patients ranged from 10 to 39. The oldest study (2014) revealed the highest deviation for linear distances at 1000±650 µm, whereas the other studies reported data in the range of 360±46 µm to 40±20 µm. In one study, no numerical data were reported and all studies compared digital and conventional implant impressions.

CONCLUSIONS

The number of clinical studies on the accuracy of digital implant impressions is low. Thus, the impact of different factors, such as the scanpath or scanbody, could not be identified. However, the accuracy of recent IOSs for digital implant impressions in patients was shown to be clinically acceptable. Nevertheless, the transfer error still needs to be considered when fabrication implant-supported restorations.