A Luting Technique for Passive Fit of Implant-Supported Fixed Dentures

Fiber-Reinforced Composites for Full-Arch Implant-Supported Rehabilitations: An In Vitro Study

Background: Fiber-reinforced composites (FRCs) have been proposed as an alternative to traditional metal alloys for the realization of frameworks in full-arch implant-supported prostheses. The aim of the present in vitro study was to evaluate the deflection under load of seven prostheses endowed with frameworks made of different materials, including different types of fiber-reinforced composites (FRCs). Methods: A master cast with four implant analogues in correspondence with the two lateral incisors and the two first molars was used to create full-arch fixed prostheses with the same shape and different materials. Prostheses were made of the following different materials (framework+veneering material): gold alloy+resin (Au+R), titanium+resin (Ti+R), FRC with multidirectional carbon fibers+resin (ICFRC+AR), FRC with unidirectional carbon fibers+composite (UCFRC+C), FRC with glass fibers+resin (GFRC+AR), FRC with glass fibers+composite (GFRC+C), and resin (R, fully acrylic prosthesis). Flexural tests were conducted using a Zwick/Roell Z 0.5 machine, and the deflection of the lower surface of the prosthesis was measured in order to obtain load/deflection graphs. Results: Greater rigidity and less deflection were recorded for UCFRC+C and GFRC+C, followed by Ti+R and Au+R. The greatest deformations were observed for resin alone, ICFRC+R, and GFRC+R. The results were slightly different in the incisal region, probably due to the greater amount of veneering material in this area. Conclusions: When used to realize full-arch frameworks, Au and Ti allow for predictable mechanical behavior with gradual deformations with increasing load. UCFRC also demonstrated good outcomes and less deflection than ICFRCs when loaded. The GFRC full-arch framework may be a valid alternative, although it showed greater deflections. Further studies are needed in order to evaluate how different prosthesis designs and material thicknesses might affect the outcomes.

Application of Semipermanent Cements and Conventional Cement with Modified Cementing Technique in Dental Implantology

Objectives

The aim of this study was to evaluate the influence of artificial ageing on the retention force of original semipermanent cements, as well as the possibility of using conventional cements for semipermanent cementation with adequate modification of the cementing protocol.

Materials and methods

Forty CoCrMo alloy crowns were divided in four groups (each group n=10) and fixed with two semipermanent cements (resin-based and glass ionomer-based cements) and one conventional (zinc phosphate), using conventional and modified cementation techniques on titanium abutments. The samples were stored in humid conditions for 24 hours at 37°C and subjected to thermocycling (500 cycles) and mechanical cyclic loading (7 days, 3, 6, 9 and 12 months function simulation). The cast crowns were removed and the retention force was recorded.

Results

The highest initial retention force measured was for zinc-phosphate cement - conventional cementing (198,00±61,90 N), followed in descending order by zinc-phosphate cement - modified cementing technique (152,00±45,42 N), long term temporary cement - GC Fuji Temp LT (57,70±20,40 N), and semipermanent cement - Telio CS Cem Implant (56,10±18,68 N). After 12 months, the highest retention force measured was for zinc-phosphate cement - conventional cementing (88, 90±14, 45 N), followed by zinc-phosphate cement - modified cementing (48, 15±14,41N), semipermanent cement GC Fuji Temp LT (16,55±3,88 N) and Telio CS Cem Implant (15,55±5,52 N).

Conclusions

Zinc-phosphate cement - modified cementing technique and original semipermanent cements can be recommended for conditional permanent cementing of implant supported crowns.

Clinical relevance

The use of semipermanenet cements and zinc-phosphate cement - modified cementing technique provides a predictable retrievability of implant-supported crowns.

Framework Materials for Full-Arch Implant-Supported Rehabilitations: A Systematic Review of Clinical Studies

The purpose of this systematic review was to investigate the clinical outcomes of frameworks made of different materials in patients with implant-supported full-arch prostheses. A literature search was conducted on MEDLINE, Scopus and Cochrane Library, until the 1st of March 2021, with the following search terms: framework or substructure combined with "dental implants". The outcomes evaluated were: implant and prosthesis survival, bone resorption, biological and technical complications. The Cochrane Handbook for Systematic Reviews of Interventions was employed to assess the risk of bias in randomized clinical trials. The Newcastle-Ottawa quality assessment scale was used for non-randomized studies. In total, 924 records were evaluated for title and abstract, and 11 studies were included in the review: 4 clinical randomized trials and 7 cohort studies. The framework materials investigated were: gold alloy, titanium, silver-palladium alloy, zirconia and polymers including acrylic resin and carbon-fiber-reinforced composites. High implant and prosthetic cumulative survival rates were recorded by all included studies. Various materials and different fabrication techniques are now available as alternatives to traditional cast metal frameworks, for full-arch implant-supported rehabilitations. Further long-term studies are needed to validate the use of these materials and clarify their specific clinical indications and manufacturing protocols to optimize their clinical outcomes.

Accuracy of multi-unit implant impression: traditional techniques versus a digital procedure

OBJECTIVES

The objective of this study was to evaluate the accuracy of different impression techniques on multiple implants.

MATERIAL AND METHODS

A master cast simulating a jaw with four implants was used. Eight impression techniques were tested: open tray-polyether#1, open tray plus splint of impression copings with acrylic resin-polyether#1, closed tray-polyether#1, open tray-polyether#2, open tray-splint-polyether#2, closed tray-polyether#2, open tray-impression plaster, and digital impression (DI). Five impressions of the master cast were taken with each traditional impression (TI) technique, pouring 35 sample casts. Three different clinicians took 5 DI each (n = 15). A three-dimensional coordinate measurement machine (CMM) was used to measure implant angulation and inter-implant distances on TI casts. TI data and DI Standard Tessellation Language datasets were compared with the master cast. The best and the worst impressions made with TI and DI were selected to fabricate four milled titanium frameworks. Passive fit was evaluated through Sheffield test, screwing each framework on the master cast. Gaps between framework-implant analogs were measured through a stereomicroscope (×40 magnification).

RESULTS

Statistically significant differences in accuracy were found comparing the different impression techniques by CMM (p < 0.01). DI performed the best, while TI techniques revealed a greater variability in the results. Sheffield test revealed a mean gap of 0.022 ± 0.023 mm (the best TI), 0.063 ± 0.059 mm (the worst TI), 0.015 ± 0.011 mm (the best DI), and 0.019 ± 0.015 mm (the worst DI).

CONCLUSIONS

Within the limits of this in vitro study, the digital impression showed better accuracy compared to conventional impressioning.

CLINICAL RELEVANCE

The digital impression might offer a viable alternative to traditional impressions for fabrication of full-arch implant-supported prostheses with satisfactory passive fit.