Objectives: To evaluate the fracture resistance, fracture modes, and crystalline phase changes of zirconia one-piece implants (OPI) and bone-level (BLTPI) or tissue-level, two-piece implants (TLTPI), with ceramic (C) or titanium (T) abutment screws after dynamic preloading in a moist environment. Materials and Methods: Dynamic preloading under moist conditions and subsequent static load-to-fracture testing were performed to evaluate fracture resistance and fracture mode. Scanning electron microscopy (SEM) analysis of fracture surfaces was employed to supplement the observations of macroscopic fracture modes. Crystalline phase changes were assessed using micro-Raman spectroscopy. Specimen preparations were performed in accordance with ISO 14801:2016. Five different ceramic (zirconia) implant designs were divided into the following groups: OPI, BLTPI (BLC, BLT), TLTPI (TLC, TLT). One-way and two-way ANOVA tests were used for comparisons and factor effect analysis. Results: Fracture resistance (N) and bending moment (N cm) differed significantly among the implant groups (p < 0.001), following the order TLTPI (775.2 ± 71 N) > OPI (605.7 ± 37 N) > BLTPI (498.3 ± 93 N). Within the two-piece implants (TPI), tissue-level designs (TL) outperformed bone-level designs (BL), while designs with different abutment screw materials showed no significant difference (p = 0.982). Conclusions: Within the limitations of this in vitro study, the evaluated zirconia-based OPI, BLTPI, and TLTPI systems demonstrate sufficient fracture resistance to support further clinical investigation. Implant-level design (TL vs. BL) influences mechanical performance, whereas the influence of abutment screw material (ceramic vs. titanium) is less pronounced and varies according to the implant-level design.

Purpose: Surface treatment of zirconia before cementation can be performed using different methods, e.g. airborne particle abrasion (APA) or various etching protocols. This study evaluated the effect of storage time between surface treatment and cementation on the surface free energy (SFE) of zirconia, the bond strength of composite cement, and failure mode. Materials and Methods: Rod-shaped zircon is specimens were fabricated and assigned to two surface treatment groups: APA (n = 80) and hot etching with potassium hydrogen difluoride (KH F-2, n = 80). Each group was divided into four storage time subgroups: immediate, 24 h, 1 week, and 1 month. After storage, specimens were either analyzed forSFE (n = 10) or cemented for shear bond strength (SBS) testing and failure mode evaluation (n = 10). Results: Two-way analysis of variance (ANOVA) showed a significant effect of both surface treatment and storage time on SFE (P < 0.05), with KHF2-etched zirconia exhibiting the highest values across all time points. In both groups, SFE gradually decreased with increased storage. Surface treatment did not significantly affect SBS (P > 0.05). Storage time significantly influenced SBS (P < 0.05), specifically for KH F2-etched zirconia; post-hoc comparisons showed higher SBS after 1 week than at immediate testing (P <0.05). Although adhesive failures to cement increased with longer storage time for KHF2-etched specimens, this trend was not significant (P > 0.05). For APA specimens, the highest incidence of adhesive failures (n = 9) to cement occurred after 24 h of storage. Conclusion: Given the significant decrease in SFE with prolonged storage and adhesive failures to zirconia tended to increase overtime, minimizing the interval between surface treatment and cementation is recommended.

Purpose: To systematically evaluate and compare the clinical performance of translucent zirconium dioxide 3-, 4-, and 5-unit fixed dental prostheses (FDPs) in the posterior dentition with either a monolithic design or with veneered buccal cutbacks (semimonolithic). Materials and Methods: A total of 31 patients treated by general practitioners received 31 translucent zirconium dioxide FDPs, randomized to be either monolithic or semimonolithic with a porcelain-veneered buccal cutback. The design choice was blinded. Clinical evaluations were made using the California Dental Association (CDA) criteria, and a questionnaire was used to obtain patient-reported outcomes and to compare them to ratings from the dentists. Results: Mean follow- up time was 48.7 months (SD = 7.7). No FDP fractured during the observation period, and no chip- off fractures could be detected. The overall success rate was 85.2%. One monolithic FDP was found with caries, and one semimonolithic FDP was endodontically treated, giving an overall survival rate of 92.6%. Two FDPs, both semimonolithic, failed due to loss of retention and caries. Both patients and dentists rated the FDPs favorably regarding the esthetic outcome and function, but the patients scored them higher than the dentists in this respect. Conclusions: Within the limitations of the study, both monolithic and semimonolithic yttria-stabilized zirconium dioxide FDPs seem to be a reliable choice of treatment for 3- to 5-unit restorations in the posterior dentition. The esthetic advantages of a porcelain veneer compared to a monolithic design might, however, be of less importance in the posterior regions for most patients.

OBJECTIVE: To evaluate the clinical outcome of different designs of zirconia dental implants.

DATA: This systematic review adhered to the PRISMA checklist and followed the PICO framework. The protocol is registered in PROSPERO (CRD42022337228).

SOURCES: The search was conducted in March 2023 through four databases (PubMed, Web of Science, Cochrane Library, and Google Scholar) along with a search of references in the related reviews. Three authors reviewed on title, and abstract level and analysed the risk of bias, and all authors reviewed on a full-text level.

STUDY SELECTION: Clinical studies excluding case reports for patients treated with different designs of zirconia dental implants were included. From a total of 2728 titles, 71 full-text studies were screened, and 27 studies were included to assess the risk of bias (ROBINS-I tool) and data extraction. After quality assessment, four studies were included, and the remaining 23 excluded studies were narratively described.

RESULT: The included prospective studies with moderate risk of bias reported success and survival rates of one-piece implants that ranged between 95 and 98.4 % with no difference between different lengths and diameters. The acid-etched roughened surface showed higher clinical outcomes compared to other surface roughness designs.

CONCLUSION: Promising 5-year clinical outcomes were found for one-piece zirconia implants with no difference between different diameters and lengths. Concerning surface roughness, better outcomes were found when using the acid-etched implant surface. However, due to the limited available studies, further high-quality clinical studies comparing zirconia one-piece and two-piece implants with different diameters, lengths, and surface roughness are needed.

CLINICAL SIGNIFICANCE: Based on this systematic review, under suitable clinical situations, the one-piece zirconia implants with diameters of 4.0 mm, 4.5 mm, or 5.5 mm and lengths of 8 mm, 10 mm, 12 mm, or 14 mm have similar promising clinical outcomes. Additionally, the acid-etched roughened implant surface may be preferable.

Objectives: To assess the impact of implantoplasty (IP) on maximum implant failure strength of narrow diameter implants of different type/design and material, with simulated advanced bone loss.

Materials and Methods: Narrow, parallel-walled implants (3.3 mm in diameter x 10 mm long) with an internal connection of different type/design [bone level (BL), tissue level (TL)] and material [Titanium grade IV (Ti), Titanium-Zirconium alloy (TiZr)] from one specific manufacturer were used. Half of the implants were subjected to IP in their coronal 5 mm; the remaining were used as controls (seven implants per group). Dynamic loading prior to maximum load strength testing was included.

Results: During dynamic loading, the fracture rate of BL implants was low and independent of IP, while that of TL implants increased significantly with IP compared with controls (p = .001). Maximum implant failure strength reduction (in %) due to IP, was 1.3%-25.4%; TiZr BL implants were least affected. Implants subjected to IP compared to those without IP as well as TL implants compared to BL implants showed a significantly lower maximum implant failure strength (p < .002); implant material was not significant (p = .845).

Conclusions: Based on data from implants of one specific manufacturer, IP has a significant negative impact on the fracture strength of narrow implants suffering from advanced peri-implantitis. TL implants have been more severely affected compared to BL implants and presented an increased risk for failure during normal chewing forces. In addition, this negative impact of IP on TL implants was independent of the implant material (i.e., Ti or TiZr).

Clinical Relevance: Narrow single TL implants with advanced horizontal bone loss (e.g., 5 mm), when subjected to IP, appear to have an increased fracture risk during normal function.

Purpose: To evaluate the effect of different placing strategies performed in the connector area on fracture resistance and fracture behaviour of monolithic multi-layered translucent zirconia fixed dental prostheses (FDPs).

Materials and Methods: Thirty 3-unit monolithic FDPs were produced and divided into three groups (n = 10) based on the different strategies for placing the connector area of FDPs in multi-layered zirconia blank with varying contents of yttria ranging from 4 to 5 mol%. The groups were as follows: FDPs with connectors placed in dentin layer with 4 mol% yttria content, FDPs with connectors placed in gradient layer, and FDPs with connectors placed in translucent layer with 5 mol% yttria content. A final group (n = 10) of conventional monolithic zirconia with a monolayer of yttria content (4 mol%) has been used as a control group. The specimens were artificially aged using thermocycling and pre-loading procedures and subsequently loaded to fracture using a universal testing machine. Fracture loads and fracture behaviour were analyzed using one-way ANOVA and Fisher's exact tests and statistically evaluated (p ≤ 0.05).

Results: There were no significant differences in fracture loads among the groups based on the placing strategies of the connector area of the FDPs in the multi-layered translucent zirconia blank (p > 0.05). There was no significant difference in fracture loads between monolithic multi-layered translucent zirconia and conventional monolithic translucent zirconia materials (p > 0.05). Fracture behaviour of FDPs with connector area placed in translucent layer differed significantly compared to FDPs with connector area placed in dentin layer and FDPs in control group (p = 0.004).

Conclusion: The placing strategies of the connector used in the computer aided design and manufacturing procedures do not considerably affect fracture resistance of monolithic FDPs made of multi-layered translucent zirconia. Monolithic FDPs made of multi-layered translucent zirconia show comparable strength to FDPs made of conventional translucent zirconia, but with different fracture behaviour.

OBJECTIVES: A crucial step in the preparation of yttria-stabilized zirconia materials (YSZ) is the final sintering step. Sintering parameters affect phase composition, grain growth and porosity of the material which, in turn, influence both mechanical and optical properties. Discrepancies of + /- 5% are common between actual and displayed firing temperatures depending on sintering furnace brand and condition. The aim of this study was therefore to investigate how such sintering temperature deviations in dental furnaces compared to the recommended firing protocols affected certain material properties of different yttria-stabilized zirconia materials.

METHODS: Disc-shaped specimens were made from four different translucent and high translucent YSZ-powders and analysed regarding crystal structure; unit cell volume for the c, t, and t' -phases along with the tetragonality for the t and t' phases. Biaxial flexure strength and the spectral transmittance through the ceramic specimens were also measured.

RESULTS: Deviations of 5% from the sintering temperature recommended for YSZ materials with different yttria content influenced material properties such as light transmittance, flexural strength, crystal phase fractions, tetragonality, and grain growth. Too low temperature resulted in decreased strength for some of the translucent zirconia materials, while others where less affected. Light transmittance varied depending on several factors such as grain size, crystal phase fractions and binder content in the start material prior to pre-sintering.

SIGNIFICANCE: The use of high quality, wellcalibrated furnaces is crucial when sintering YSZ materials to avoid unwanted material changes.

CONCLUSIONS: Deviations of 5% from the sintering temperature recommended for YSZ materials with different yttria content influence material properties such as light transmittance, flexural strength, crystal phase fractions, tetragonality, and grain growth. Too low temperature results in decreased strength for some translucent zirconia materials, while others are less affected. Light transmittance varies depending on several factors such as grain size, crystal phase fractions and binder content in the start material prior to pre-sintering. Consequently, the use of high quality, well-calibrated furnaces is crucial when sintering YSZ materials to avoid unwanted material changes.

Objective

To assess whether the impact of implantoplasty (IP) on the maximum implant failure strength depends on implant type/design, diameter, or material.

Methods

Fourteen implants each of different type/design [bone (BL) and tissue level (TL)], diameter [narrow (3.3 mm) and regular (4.1 mm)], and material [titanium grade IV (Ti) and titanium-zirconium alloy (TiZr)] of one company were used. Half of the implants were subjected to IP in a computerized torn. All implants were subjected to dynamic loading prior to loading until failure to simulate regular mastication. Multiple linear regression analyses were performed with maximum implant failure strength as dependent variable and IP, implant type/design, diameter, and material as predictors.

Results

Implants subjected to IP and TL implants showed statistically significant reduced implant failure strength irrespective of the diameter compared with implants without IP and BL implants, respectively. Implant material had a significant impact for TL implants and for regular diameter implants, with TiZr being stronger than Ti. During dynamic loading, 1 narrow Ti TL implant without IP, 4 narrow Ti TL implants subjected to IP, and 1 narrow TiZr TL implant subjected to IP were fractured.

Conclusion

IP significantly reduced the maximum implant failure strength, irrespective implant type/design, diameter, or mate- rial, but the maximum implant failure strength of regular diameter implants and of narrow BL implants remained high.

Clinical Relevance

IP seems to have no clinically relevant impact on the majority of cases, except from those of single narrow Ti TL implants, which may have an increased risk for mechanical complications. This should be considered for peri-implantitis treatment planning (e.g., communication of potential complications to the patient), but also in the planning of implant installation (e.g., choosing TiZr instead of Ti for narrow implants).

Purpose: To systematically evaluate and compare the clinical performance of lithium disilicate (LDS)and zirconium dioxide (ZrO2)-based ceramic monolithic crowns in the posterior dentition. Materials and Methods: Treatment was administered by two experienced general dental practitioners in two public dental health care clinics. Forty-four patients received 60 crowns randomized to be either LDS or ZrO2 and cemented with resin cement. Evaluations were performed after 3 years using California Dental Association criteria. Results: The mean follow-up time was 40 months (range: 31 to 50). No crown fractured during the observation time, and no chip-off fractures occurred. The success rate for ZrO2 was 80%, and the survival rate was 93.3%. For LDS, the success rate was 89.7%, and the survival rate was 100%. Survival after 3 years for all crowns together was 96.6%, and success was 84.7%. There was no significant difference between the two materials. Conclusion: Crowns made of monolithic translucent ZrO2 and LDS show equal and promising clinical results from a short-term perspective. There seems to be a difference between how patients and professionals rate crowns concerning esthetics (color and shape), with patients rating the restorations more favorably.