Fracture Resistance of a Bone-Level Two-Piece Zirconia Oral Implant System-The Influence of Artificial Loading and Hydrothermal Aging.

Preclinical and clinical research on two-piece zirconia implants are warranted. Therefore, we evaluated the in vitro fracture resistance of such a zirconia oral implant system. The present study comprised 32 two-piece zirconia implants and abutments attached to the implants using a titanium (n = 16) or a zirconia abutment screw (n = 16). Both groups were subdivided (n = 8): group T-0 comprised implants with a titanium abutment screw and no artificial loading; group T-HL was the titanium screw group exposed to hydro-thermomechanical loading in a chewing simulator; group Z-0 was the zirconia abutment screw group with no artificial loading; and group Z-HL comprised the zirconia screw group with hydro-thermomechanical loading. Groups T-HL and Z-HL were loaded with 98 N and aged in 85 °C hot water for 107 chewing cycles. All samples were loaded to fracture. Kruskal-Wallis tests were executed to assess the loading/bending moment group differences. The significance level was established at a probability of 0.05. During the artificial loading, there was a single occurrence of an implant fracture. The mean fracture resistances measured in a universal testing machine were 749 N for group T-0, 828 N for group Z-0, 652 N for group T-HL, and 826 N for group Z-HL. The corresponding bending moments were as follows: group T-0, 411 Ncm; group Z-0, 452 Ncm; group T-HL, 356 Ncm; and group Z-HL, 456 Ncm. There were no statistically significant differences found between the experimental groups. Therefore, the conclusion was that loading and aging did not diminish the fracture resistance of the evaluated implant system.

Gingival fibroblast response to (hybrid) ceramic implant reconstruction surfaces is modulated by biomaterial type and surface treatment.

OBJECTIVES: Surface characteristics of implant reconstructions determine the gingival fibroblast (GF) response and thus soft tissue integration (STI). However, for monolithic implant reconstructions it is unknown whether the (hybrid) ceramic biomaterial type and its surface treatment affect GF response. Therefore, this investigation examined the influence of the implant reconstruction biomaterials hybrid ceramic (HC), lithium disilicate ceramic (LS), 4 and 5 mol% yttria partially stabilized zirconiumdioxide ceramics (4/5Y-PSZ) and their surface treatment - machining, polishing or glazing - on surface characteristics and GF response. METHODS: After characterization of surface topography and wettability by scanning electron microscopy, interferometry and contact angle measurement, the adhesion, morphology, metabolic activity and proliferation of GFs from six donors was investigated by fluorescent staining and a resazurin-based assay at days 1, 3 and 7. Titanium (Ti) served as control. RESULTS: Biomaterial type and surface treatment affected the GF response in a topography-dependent manner. Smooth polished and glazed surfaces demonstrated enhanced GF adhesion and earlier proliferation onset compared to rough machined surfaces. Due to minor differences in surface topography of polished and glazed surfaces, however, the GF response was similar for polished and glazed HC, LS, 4- and 5Y-PSZ as well as Ti. SIGNIFICANCE: Within the limits of the present investigation, polishing and glazing of machined HC, LS and 4/5Y-PSZ can be recommended to support STI-relevant cell functions in GF. Since the GF response on polished and glazed HC, LS, 4- and 5Y-PSZ surfaces and the Ti control was comparable, this investigation proofed equal cytocompatibility of these surfaces in vitro.

Bonding Strength of Various Luting Agents between Zirconium Dioxide Crowns and Titanium Bonding Bases after Long-Term Artificial Chewing.

The use of hybrid abutment crowns bonded extraorally to a titanium bonding base has aesthetic and biological benefits for the prosthetic rehabilitation of oral implants. The objective of this study was to evaluate the effects of luting agents between a zirconium dioxide crown and the titanium bonding base on crown/abutment retention and the subsequent durability of the prosthetic superstructure. Fifty-six implant abutment samples, all restored with a lower first premolar zirconium dioxide crown, were used and divided into seven groups (n = 8/group) according to the type of luting agent used: group 1, SpeedCEM Plus; group 2, Panavia SA Cement Universal; group 3, Panavia V5; group 4, RelyX Unicem 2 Automix; group 5, VITA ADIVA IA-Cem; group 6, Ketac CEM; and group 7, Hoffmann's Phosphate Cement. All specimens were subjected to thermomechanical loading (load of 49 N, 5 million chewing cycles and 54.825 thermocycles in water with temperatures of 5 °C and 55 °C). The surviving samples were exposed to a pull-off force until crown debonding from the bonding base. Overall, 55 samples survived the thermomechanical load. Group 2 showed the highest mean pull-off force value (762 N), whereas group 6 showed the lowest mean value (55 N). The differences between the seven groups were statistically significant (ANOVA, p < 0.001). The debonding failure pattern was mainly adhesive and was noticed predominantly at the zirconium dioxide-luting agent interface. Within the scope of the present investigation, it was shown that most of the luting agents are suitable for "cementation" of a zirconium dioxide crown onto a titanium base since the debonding forces are above a recommended value (159 N).

Fracture Resistance of a Two-Piece Zirconia Implant System after Artificial Loading and/or Hydrothermal Aging-An In Vitro Investigation.

The purpose of the present study was to assess the fracture resistance of a two-piece alumina-toughened zirconia implant system with a carbon-reinforced PEEK abutment screw. METHODS: Thirty-two implants with screw-retained zirconia abutments were divided into four groups of eight samples each. Group 0 (control group) was neither loaded nor aged in a chewing simulator; group H was hydrothermally aged; group L was loaded with 98 N; and group HL was subjected to both hydrothermal aging and loading in a chewing simulator. One sample of each group was evaluated for t-m phase transformation, and the others were loaded until fracture. A one-way ANOVA was applied to evaluate differences between the groups. RESULTS: No implant fracture occurred during the artificial chewing simulation. Furthermore, there were no statistically significant differences (p > 0.05) between the groups in terms of fracture resistance (group 0: 783 ± 43 N; group H: 742 ± 43 N; group L: 757 ± 86 N; group HL: 740 ± 43 N) and bending moment (group 0: 433 ± 26 Ncm; group H: 413 ± 23 Ncm; group L: 422 ± 49 Ncm; group HL: 408 ± 27 Ncm). CONCLUSIONS: Within the limitations of the present investigation, it can be concluded that artificial loading and hydrothermal aging do not reduce the fracture resistance of the investigated implant system.

Accuracy of Computerized Optical Impression Making in Fabrication of Removable Dentures for Partially Edentulous Jaws: An In Vivo Feasibility Study.

The use of computerized optical impression making (COIM) for the fabrication of removable dentures for partially edentulous jaws is a rising trend in dental prosthetics. However, the accuracy of this method compared with that of traditional impression-making techniques remains uncertain. We therefore decided to evaluate the accuracy of COIM in the context of partially edentulous jaws in an in vivo setting. Twelve partially edentulous patients with different Kennedy classes underwent both a conventional impression (CI) and a computerized optical impression (COI) procedure. The CI was then digitized and compared with the COI data using 3D analysis software. Four different comparison situations were assessed: Whole Jaw (WJ), Mucosa with Residual Teeth (M_RT), Isolated Mucosa (IM), and Isolated Abutment Teeth (AT). Statistical analyses were conducted to evaluate group differences by quantifying the deviation values between the CIs and COIs. The mean deviations between the COIs and CIs varied significantly across the different comparison situations, with mucosal areas showing higher deviations than dental hard tissue. However, no statistically significant difference was found between the maxilla and mandible. Although COIM offers a no-pressure impression method that captures surfaces without irritation, it was found to capture mucosa less accurately than dental hard tissue. This discrepancy can likely be attributed to software algorithms that automatically filter out mobile tissues. Clinically, these findings suggest that caution is required when using COIM for prosthetics involving mucosal tissues as deviations could compromise the fit and longevity of the prosthetic appliance. Further research is warranted to assess the clinical relevance of these deviations.

Long-Term Stability of Hydrothermally Aged and/or Dynamically Loaded One-Piece Diameter Reduced Zirconia Oral Implants.

The aim of this in vitro study was to evaluate the long-term stability of one-piece diameter reduced zirconia oral implants under the influence of loading and artificial aging in a chewing simulator as well as the fracture load in a static loading test. Thirty-two one-piece zirconia implants with a diameter of 3.6 mm were embedded according to the ISO 14801:2016 standard. The implants were divided into four groups of eight implants. The implants of group DLHT were dynamically loaded (DL) in a chewing simulator for 107 cycles with a load of 98 N and simultaneously hydrothermally aged (HT) using a hot water bath at 85 °C. Group DL was only subjected to dynamic loading and group HT was exclusively subjected to hydrothermal aging. Group 0 acted as a control group: no dynamical loading, no hydrothermal ageing. After exposure to the chewing simulator, the implants were statically loaded to fracture in a universal testing machine. To evaluate group differences in the fracture load and bending moments, a one-way ANOVA with Bonferroni correction for multiple testing was performed. The level of significance was set to p < 0.05. In the static loading test, group DLHT showed a mean fracture load of 511 N, group DL of 569 N, group HT of 588 N and control group 0 of 516 N. The average bending moments had the following values: DLHT: 283.5 Ncm; DL: 313.7 Ncm; HT: 324.4 Ncm; 0: 284.5 Ncm. No significant differences could be found between the groups. Hydrothermal aging and/or dynamic loading had no significant effect on the stability of the one-piece diameter reduced zirconia implants (p > 0.05). Within the limits of this investigation, it can be concluded that dynamic loading, hydrothermal aging and the combination of loading and aging did not negatively influence the fracture load of the implant system. The artificial chewing results and the fracture load values indicate that the investigated implant system seems to be able to resist physiological chewing forces also over a long service period.

Effects of a disability-simulating learning unit on ableism of final-year dental students - a pilot study.

OBJECTIVES: This study aimed to describe a disability-simulating learning unit (DSLU) to raise dental students' awareness of the special needs of patients with disabilities as well as to measure the effect of the DSLU on ableism. METHODS: A DSLU among final-year undergraduate dental students (n = 33), was developed and evaluated. The students were randomly divided into two groups (Group I, n = 17; Group II, n = 16). Group II only received conventional teaching (control group), whereas Group I was additionally exposed to the DSLU (intervention group). In the DSLU, typical physical restrictions and the associated difficulties in attending dental appointments were simulated with the help of simulation suits. Four different stations offered the opportunity to experience typical signs of disability in a dental context. About 2 months after the DSLU, both groups were asked to answer the Symbolic Ableism Scale (SAS). An analysis was conducted to examine the participants' average total score and several subscores. The Mann-Whitney U Test was employed to control the differences between the study groups. RESULTS: Overall, the students in the intervention group had a significantly (p = .001) lower mean SAS summary score (median = .37; IQR .32-.42) than the students in the control group (median = .50; IQR .39-.53). For the components "individualism" (p < .0001) and "excessive demands" (p = .002) significant group differences could be observed. CONCLUSION: The DSLU is a potentially feasible and effective method for influencing students' ableism attitude.

One-Piece Zirconia Oral Implants for Single Tooth Replacement: Five-Year Results from a Prospective Cohort Study.

The intention of this 5-year prospective cohort investigation was to clinically and radiographically investigate the outcomes of a one-piece zirconia implant system for single tooth replacement. Sixty-five patients received a total of 66 single-tooth implants. All implants immediately received temporary restorations and were finally restored with all-ceramic crowns. Follow-ups were performed at the prosthetic delivery, after 1, 3, and 5 years. Peri-implant and dental soft-tissue parameters were evaluated and patient-reported outcomes recorded. To monitor peri-implant bone remodelling, standardised radiographs were taken at the implant insertion and at the 1-, 3-, and 5-year follow-ups. In the course of 5 years, 14 implants were lost, resulting in a cumulative implant survival rate of 78.2%. The mean marginal bone loss from the implant insertion to the 5-year follow-up amounted to 1.12 mm. Probing depth, clinical attachment level, bleeding, and plaque index increased over time. In 91.5% of the implants, the papilla index showed levels of 1 or 2, respectively. At the end of the study, the patient satisfaction was higher compared to the pre-treatment measurements. Due to the low survival rate after five years and the noticeably high frequency of advanced bone loss observed in this study, the implant has not met the launch criteria, as it would have not been recommended for routine clinical use.

HOW TO IDENTIFY SUBGROUPS IN LONGITUDINAL CLINICAL DATA: TREATMENT RESPONSE PATTERNS IN PATIENTS WITH A SHORTENED DENTAL ARCH.

BACKGROUND: When dental patients seek care, treatments are not always successful,that is patients' oral health problems are not always eliminated or substantially reduced. Identifying these patients (treatment non-responders) is essential for clinical decision-making. Group-based trajectory modeling (GBTM) is rarely used in dentistry, but a promising statistical technique to identify non-responders in particular and clinical distinct patient groups in general in longitudinal data sets. AIM: Using group-based trajectory modeling, this study aimed to demonstrate how to identify oral health-related quality of life (OHRQoL) treatment response patterns by the example of patients with a shortened dental arch (SDA). METHODS: This paper is a secondary data analysis of a randomized controlled clinical trial. In this trial SDA patients received partial removable dental prostheses replacing missing teeth up to the first molars (N = 79) either or the dental arch ended with the second premolar that was present or replaced by a cantilever fixed dental prosthesis (N = 71). Up to ten follow-up examinations (1-2, 6, 12, 24, 36, 48, 60, 96, 120, and 180 months post-treatment) continued for 15 years. The outcome OHRQoL was assessed with the 49-item Oral Health Impact Profile (OHIP). Exploratory GBTM was performed to identify treatment response patterns. RESULTS: Two response patterns could be identified - "responders" and "non-responders." Responders' OHRQoL improved substantially and stayed primarily stable over the 15 years. Non-responders' OHRQoL did not improve considerably over time or worsened. While the SDA treatments were not related to the 2 response patterns, higher levels of functional, pain-related, psychological impairment in particular, and severely impaired OHRQoL in general predicted a non-responding OHRQoL pattern after treatment. Supplementary, a 3 pattern approach has been evaluated. CONCLUSIONS: Clustering patients according to certain longitudinal characteristics after treatment is generally important, but specifically identifying treatment in non-responders is central. With the increasing availability of OHRQoL data in clinical research and regular patient care, GBTM has become a powerful tool to investigate which dental treatment works for which patients.

One-Piece Zirconia Oral Implants for the Support of Three-Unit Fixed Dental Prostheses: Three-Year Results from a Prospective Case Series.

The objective was to investigate the clinical and radiological outcome of one-piece zirconia oral implants to support three-unit fixed dental prostheses (FDP) after three years in function. Twenty-seven patients were treated with a total of 54 implants in a one-stage surgery and immediate provisionalization. Standardized radiographs were taken at implant placement, after one year and after three years, to evaluate peri-implant bone loss. Soft-tissue parameters were also assessed. Linear mixed regression models as well as Wilcoxon Signed Rank tests were used for analyzing differences between groups and time points (p < 0.05). At the three-year evaluation, one implant was lost, resulting in a cumulative survival rate of 98.1%. The mean marginal bone loss amounted to 2.16 mm. An implant success grade I of 52% (bone loss of ≤2 mm) and success grade II of 61% (bone loss of ≤3 mm) were achieved. None of the evaluated baseline parameters affected bone loss. The survival rate of the zirconia implants was comparable to market-available titanium implants. However, an increased marginal bone loss was observed with a high peri-implantitis incidence and a resulting low implant success rate.

Influence of loading and aging on the fracture strength of an injection-molded two-piece zirconia implant restored with a zirconia abutment.

OBJECTIVE: To investigate the fracture strength and potential phase transformation of an injection-molded two-piece zirconia implant restored with a zirconia abutment after loading and/or aging. METHODS: Thirty-two two-piece zirconia implants (4.0 mm diameter) restored with zirconia abutments were embedded according to ISO 14801 and divided into four groups (n = 8/group): Three groups were either exclusively hydrothermally treated (group HT; 85°C), dynamically loaded (group DL; 107 cycles; 98 N), or subjected to both treatments simultaneously (group DL/HT). One group remained untreated (group 0). A sample from each group was cross-sectioned and examined by scanning electron microscopy for possible crystal phase transformation. The remaining samples were then loaded to fracture in a static loading test. A one-way ANOVA was used for statistical analyses. RESULTS: During dynamic loading, three implants of group DL and six implants of group DL/HT fractured at a load of 98 N. The fracture strength of group DL/HT (108 ± 141 Ncm) was significantly reduced compared to the other groups (group 0: 342 ± 36 Ncm; HT: 363 ± 49 Ncm; DL: 264 ± 198 Ncm) (p < .05). Fractures from group 0 and HT occurred at both implant and abutment level, whereas implants from group DL and DL/HT fractured only at implant level. A shallow monoclinic transformation zone of approximately 2 µm was observed following hydrothermal treatment. CONCLUSIONS: Within the limitations of this study, it can be concluded that dynamic loading and the combination of loading and aging reduced the fracture strength of the implant abutment combination. Hydrothermal treatment caused a shallow transformation zone which had no influence on the fracture strength.

Identification of Zirconia Particle Uptake in Human Osteoblasts by ToF-SIMS Analysis and Particle-Size Effects on Cell Metabolism.

As the use of zirconia-based nano-ceramics is rising in dentistry, the examination of possible biological effects caused by released nanoparticles on oral target tissues, such as bone, is gaining importance. The aim of this investigation was to identify a possible internalization of differently sized zirconia nanoparticles (ZrNP) into human osteoblasts applying Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS), and to examine whether ZrNP exposure affected the metabolic activity of the cells. Since ToF-SIMS has a low probing depth (about 5 nm), visualizing the ZrNP required the controlled erosion of the sample by oxygen bombardment. This procedure removed organic matter, uncovering the internalized ZrNP and leaving the hard particles practically unaffected. It was demonstrated that osteoblasts internalized ZrNP within 24 h in a size-dependent manner. Regarding the cellular metabolic activity, metabolization of alamarBlue by osteoblasts revealed a size- and time-dependent unfavorable effect of ZrNP, with the smallest ZrNP exerting the most pronounced effect. These findings point to different uptake efficiencies of the differently sized ZrNP by human osteoblasts. Furthermore, it was proven that ToF-SIMS is a powerful technique for the detection of zirconia-based nano/microparticles that can be applied for the cell-based validation of clinically relevant materials at the nano/micro scale.

Computerized optical scanning of ears: An in vitro evaluation with an intraoral scanner.

STATEMENT OF PROBLEM: Making conventional facial impressions can be uncomfortable for the patient and complicated for the prosthodontist. Using facial scanners to digitize faces is an alternative approach. However, the initial costs of the equipment have prevented their widespread use in dental practice, and the accuracy of ear scanning is unclear. PURPOSE: The purpose of this in vitro study was to investigate the accuracy of a widely used intraoral scanner for digitizing an ear model. MATERIAL AND METHODS: For reference, a silicone model of an ear was scanned with an industrial scanner. Then, the model was scanned 5 times with an intraoral scanner. Five conventional impressions of the model were made with a hydrocolloid impression material and poured with dental stone. The stone casts were then digitized with a desktop scanner. The data sets acquired with the 3 approaches were analyzed by using a 3-dimensional (3D) evaluation software program. Trueness and precision values were calculated for each approach. Linear mixed models with random intercepts were fitted to each sample to evaluate the effects of the impression method on mean deviations (α=.05). RESULTS: Mean ±standard deviation trueness and precision values were 0.097 ±0.012 mm and 0.033 ±0.015 mm, respectively, for the digital scan, and 0.092 ±0.022 mm and 0.081 ±0.024 mm for the conventional impression, showing a significantly lower deviation in precision for the digital approach (P<.001). CONCLUSIONS: The feasibility of digitizing an ear efficiently by using the investigated intraoral scanner was demonstrated, and similar trueness and significantly better precision values were achieved than when using conventional impressions. These promising results suggest the need for clinical investigations.

Fatigue and Fracture Resistance Testing of Polyether Ether Ketone (PEEK) Implant Abutments in an Ex Vivo Chewing Simulator Model.

Polyether ether ketone (PEEK) has been introduced into implant dentistry as a viable alternative to current implant abutment materials. However, data on its physico-mechanical properties are still scarce. The present study sought to shed light on this topic utilizing an ex vivo chewing simulator model. A total of 48 titanium two-piece implants were allocated into three groups (n = 16 per group): (1) implants with PEEK abutments and an internal butt-joint connection (PBJ), (2) implants with PEEK abutments and an internal conical implant-abutment connection (PC), and (3) implants with zirconia abutments and an internal butt-joint connection (ZA). All abutments were restored with a non-precious metal alloy crown mimicking the upper right central incisor. A dynamic chewing simulation of half (n = 8) of the specimens per group was performed with 5 × 106 cycles and a load of 49 N at a frequency of 1.7 Hz with thermocycling between 5 and 55 °C. The other eight specimens served as unloaded controls. Surface roughness, implant-abutment connection microgaps (IACMs), and the titanium base-abutment interface microgaps (TAIMs) in the loaded groups were evaluated. Finally, a quasi-static loading test was performed in a universal testing machine with all samples to evaluate fracture resistance. Overall, 23 samples survived the artificial chewing process. One abutment screw fracture was observed in the PC group. The ZA group showed higher surface roughness values than PEEK abutments. Furthermore, ZA revealed lower TAIM values compared to PEEK abutments. Similarly, ZA was associated with lower IACM values compared to PBJ. Fracture loads/bending moments were 1018 N/704 N cm for PBJ, 966 N/676 N cm for PC, and 738 N/508 N cm for ZA, with no significant differences compared to the unloaded references. Artificial loading did not significantly affect fracture resistance of the examined materials. PEEK abutments were associated with better load-bearing properties than zirconia abutments, although they showed higher microgap values. PEEK abutments could, therefore, be feasible alternatives to zirconia abutments based on the present ex vivo findings resembling 20 years of clinical service.

Zirconia fixed dental prostheses fabricated by 3D gel deposition show higher fracture strength than conventionally milled counterparts.

Zirconia restorations, which are fabricated by additive 3D gel deposition and do not require glazing like conventional restorations, were introduced as "self-glazed" zirconia restorations into dentistry. This in vitro investigation characterized the surface layer, microstructure and the fracture and aging behavior of "self-glazed" zirconia (Y-TZPSG) three-unit fixed dental prostheses (FDP) and compared them to conventionally CAD/CAM milled and glazed controls (Y-TZPC-FDPs). For this purpose, the FDPs were analyzed by (focused ion beam) scanning electron microscopy, laserscanning microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and a dynamic and static loading test. For the latter, half of the samples of each material group (n = 16) was subjected to 5 million cycles of thermocyclic loading (98N) in an aqueous environment in a chewing simulator. Afterwards, all FDPs were loaded to fracture. Y-TZPSG-FDPs demonstrated a comparable elemental composition but higher surface microstructural homogeneity and fracture strength compared to Y-TZPC-FDPs. Microstructural flaws within the FDPs' surfaces were identified as fracture origins. The high fracture strength of the Y-TZPSG-FDPs was attributed to a finer-grained microstructure with fewer surface flaws compared to the Y-TZPC-FDPs which showed numerous flaws in the glaze overlayer. A decrease in fracture strength after dynamic loading from 5165N to 4507N was observed for the Y-TZPSG-FDPs, however, fracture strength remained statistically significantly above the one measured for Y-TZPC-FDPs (before chewing simulation: 1923N; after: 2041N). Within the limits of this investigation, it can therefore be concluded that Y-TZPSG appears to be stable for clinical application suggesting further investigations to prove clinical applicability.

Non-Precious Metal Alloy Double Crown-Retained Removable Partial Dentures: A Cross-Sectional In Vivo Investigation.

(1) Background: An alternative material to precious metal alloys are non-precious metal alloys. The material properties of these are different and, therefore, their clinical, biological and mechanical behaviors may also differ. Hence, the purpose of this in vivo investigation was to analyze the clinical and patient-reported outcomes of patients restored with non-precious metal alloy double crown-retained removable partial dentures (NP-D-RPDs). (2) Methods: Partially edentulous patients were restored with non-precious metal alloy partially veneered NP-D-RPDs. Survival rates, success rates, failures and patient-reported outcomes were investigated and statistically evaluated. (3) Results: A total of 61 patients (65.6 ± 10.8 years) were included and clinically and radiographically examined. The mean follow-up time was 25.2 ± 16.5 months. In total, 82 NP-D-RPDs and 268 abutment teeth were examined. The overall survival rate of the NP-D-RPDs was 100% after a mean follow-up time of 2.1 years. The overall success rate was 68.3%. The overall satisfaction with the NP-D-RPDs was 94.3%. (4) Conclusions: Non-precious metal alloy partially veneered NP-D-RPDs seem to be an efficient alternative to precious metal alloy RPDs with excellent patient-reported outcomes.

EAO Position Paper: Current Level of Evidence Regarding Zirconia Implants in Clinical Trials.

Titanium oral implants are still considered "state of the art" in implant dentistry, with well-documented survival rates. However, their grayish color and high prevalence of peri-implant infections have resulted in controversial discussion as to whether tooth-like-colored, metal-free zirconia ceramic implants provide sufficient potential to be considered equal regarding treatment outcomes. The present position paper has been composed upon invitation by the European Association of Osseointegration in order to provide an update on the current level of evidence regarding zirconia implants in clinical trials. To date, most available and scientifically documented zirconia implant systems are one-piece implants that require an experienced surgeon and prosthodontist due to the restricted flexibility in cases of compromised angulation or vertical positioning. Taking this limitation into account, there is evidence of a comparable outcome for one-piece zirconia implants compared to titanium implants for the fixed replacement of one to three missing teeth. In contrast, currently available clinical data evaluating two-piece zirconia implants with an adhesively bonded implant-abutment interface suggest an inferior outcome. Data evaluating the clinical applicability of screw-retained solutions, even if revealing sufficient fracture resistance in laboratory investigations, are still missing. High survival rates were reported for all-ceramic reconstructions supported by zirconia implants, but with increased technical complications; ie, fractures of the ceramic veneer in the case of bilayered restorations. Sufficient clinical evidence for recommending monolithic approaches is limited to single crowns.

3D printed zirconia dental implants with integrated directional surface pores combine mechanical strength with favorable osteoblast response.

Dental implants need to combine mechanical strength with promoted osseointegration. Currently used subtractive manufacturing techniques require a multi-step process to obtain a rough surface topography that stimulates osseointegration. Advantageously, additive manufacturing (AM) enables direct implant shaping with unique geometries and surface topographies. In this study, zirconia implants with integrated lamellar surface topography were additively manufactured by nano-particle ink-jetting. The ISO-14801 fracture load of as-sintered implants (516±39 N) resisted fatigue in 5-55 °C water thermo-cycling (631±134 N). Remarkably, simultaneous mechanical fatigue and hydrothermal aging at 90 °C significantly increased the implant strength to 909±280 N due to compressive stress generated at the seamless transition of the 30-40 µm thick, rough and porous surface layer to the dense implant core. This unique surface structure induced an elongated osteoblast morphology with uniform cell orientation and allowed for osteoblast proliferation, long-term attachment and matrix mineralization. In conclusion, the developed AM zirconia implants not only provided high long-term mechanical resistance thanks to the dense core along with compressive stress induced at the transition zone, but also generated a favorable osteoblast response owing to the integrated directional surface pores. STATEMENT OF SIGNIFICANCE: Zirconia ceramics are becoming the material of choice for metal-free dental implants, however significant efforts are required to obtain a rough/porous surface for enhanced osseointegration, along with the risk of surface delamination and/or microstructure variation. In this study, we addressed the challenge by additively manufacturing implants that seamlessly combine dense core with a porous surface layer. For the first time, a unique surface with a directional lamellar pore morphology was additively obtained. This AM implant also provided strength as strong as conventionally manufactured zirconia implants before and after long-term fatigue. Favorable osteoblast response was proved by in-vitro cell investigation. This work demonstrated the opportunity to AM fabricate novel ceramic implants that can simultaneously meet the mechanical and biological functionality requirements.

The Mechanical Behavior of a Screwless Morse Taper Implant-Abutment Connection: An In Vitro Study.

The use of screwless Morse taper implant−abutment connections (IAC) might facilitate the clinician's work by eliminating the mechanical complications associated with the retention screw. The aim of this study is to evaluate the effect of artificial chewing on the long-term stability of screwless Morse taper IACs. Thirty-two implant abutments restored with an upper central incisor zirconia crown were used and divided into four groups according to the implant−abutment assembling manner (C1,H: screw retained (20 Ncm); C2: tapped; or C3: torqued (20 Ncm; the screws were removed before the dynamic loading)). All specimens were subjected to a cyclic loading (98 N) for 10 million chewing cycles. The survived samples were exposed to a pull-off force until failure/disassembling of the connection. All the samples revealed a 100% survival. Regarding the pull-off test, the screw-retained internal hexagonal IAC revealed significantly higher resistance to failure/disassembling (769.6 N) than screwless conical IACs (171.6 N−246 N) (p < 0.0001). The retention forces in the Morse taper groups were not significantly different (p > 0.05). The screw-retained hexagonal IAC showed the highest retention stability. The screw preload/retention in the conical IAC was lost over time in the group where the screws were kept in place during loading. Nevertheless, the screwless Morse taper IACs were stable for an extended service time and might represent a valid form of treatment for single-tooth replacement.