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.

Impact of radiographic field-of-view volume on alignment accuracy during virtual implant planning: A noninterventional retrospective pilot study.

OBJECTIVE: To evaluate the impact of reducing the radiographic field of view (FOV) on the trueness and precision of the alignment between cone beam computed tomography (CBCT) and intraoral scanning data for implant planning. MATERIALS AND METHODS: Fifteen participants presenting with one of three clinical scenarios: single tooth loss (ST, n = 5), multiple missing teeth (MT, n = 5) and presence of radiographic artifacts (AR, n = 5) were included. CBCT volumes covering the full arch (FA) were reduced to the quadrant (Q) or the adjacent tooth/teeth (A). Two operators, an expert (exp) in virtual implant planning and an inexperienced clinician, performed multiple superimpositions, with FA-exp serving as a reference. The deviations were calculated at the implant apex and shoulder levels. Thereafter, linear mixed models were adapted to investigate the influence of FOV on discrepancies. RESULTS: Evaluation of trueness compared to FA-exp resulted in the largest mean (AR-A: 0.10 ± 0.33 mm) and single maximum discrepancy (AR-Q: 1.44 mm) in the presence of artifacts. Furthermore, for the ST group, the largest mean error (-0.06 ± 0.2 mm, shoulder) was calculated with the FA-FOV, while for MT, with the intermediate volume (-0.07 ± 0.24 mm, Q). In terms of precision, the mean SD intervals were ≤0.25 mm (A-exp). Precision was influenced by FOV volume (FA < Q < A) but not by operator expertise. CONCLUSIONS: For single posterior missing teeth, an extended FOV does not improve registration accuracy. However, in the presence of artifacts or multiple missing posterior teeth, caution is recommended when reducing FOV.

Fracture resistance and crystal phase transformation of a one- and a two-piece zirconia implant with and without simultaneous loading and aging-An in vitro study.

OBJECTIVE: To evaluate the influence of artificial aging on the transformation propagation and fracture resistance of zirconia implants. METHODS: One-piece (with integrated implant abutment, 1P; regular diameter [4.1mm]; n = 16) and two-piece (with separate implant abutment, 2P; wide diameter [5 mm]; n = 16) zirconia implants were embedded according to ISO 14801. A two-piece titanium-zirconium implant (Ti-Zr; 4.1 mm diameter) served as a control (n = 16). One subgroup (n = 8) of each system was simultaneously dynamically loaded (107 cycles; 98N) and hydrothermally aged (85°C, 58 days), while the other subgroup (n = 8) remained untreated. Finally, specimens were statically loaded to fracture. Potential crystal phase transformation was examined at cross sections using scanning electron microscopy (SEM). A multivariate linear regression model was applied for statistical analyses. RESULTS: The fracture resistance of 1P (1,117 [SD = 38] N; loaded/aged: 1,009 [60] N), 2P (850 [36] N; loaded/aged: 799 [84] N), and Ti-Zr implants (1,338 [205] N; loaded/aged: 1,319 [247] N) was not affected significantly by loading/aging (p = .171). However, when comparing the systems, they revealed significant differences independent of loading/aging (p ≤ .001). Regarding the crystal structure, a transformation zone was observed in SEM images of 1P only after aging, while 2P showed a transformation zone even before aging. After hydrothermal treatment, an increase of this monoclinic layer was observed in both systems. CONCLUSIONS: The Ti-Zr control implant showed higher fracture resistance compared to both zirconia implants. Loading/aging had no significant impact on the fracture resistance of both zirconia implants. The wide-body 2P zirconia implant was weaker than the regular body 1P implant.

Dimensional accuracy of extrusion- and photopolymerization-based 3D printers: In vitro study comparing printed casts.

STATEMENT OF PROBLEM: Reliable studies comparing the accuracy of complete-arch casts from 3D printers are scarce. PURPOSE: The purpose of this in vitro study was to investigate the accuracy of casts printed by using various extrusion- and photopolymerization-based printers. MATERIAL AND METHODS: A master file was sent to 5 printer manufacturers and distributors to print 37 identical casts. This file consisted of a standardized data set of a maxillary cast in standard tessellation language (STL) format comprising 5 reference points for the measurement of 3 distances that served as reference for all measurements: intermolar width (IMW), intercanine width (ICW), and dental arch length (AL). The digital measurement of the master file obtained by using a surveying software program (Convince Premium 2012) was used as the control. Two extrusion-based (M2 and Ultimaker 2+) and 3 photopolymerization-based printers (Form 2, Asiga MAX UV, and myrev140) were compared. The casts were measured by using a multisensory coordinate measuring machine (O-Inspect 422). The values were then compared with those of the master file. The Mann-Whitney U test and Levene tests were used to determine significant differences in the trueness and precision (accuracy) of the measured distances. RESULTS: The deviations from the master file at all 3 distances for the included printers ranged between 12 µm and 240 µm (trueness), with an interquartile range (IQR) between 17 µm and 388 µm (precision). Asiga MAX UV displayed the highest accuracy, considering all the distances, and Ultimaker 2+ demonstrated comparable accuracy for shorter distances (IMW and ICW). Although myrev140 operated with high precision, it displayed high deviations from the master file. Similarly, although Form 2 exhibited high IQR, it did not deviate significantly from the master file in the longest range (AL). M2 performed consistently. CONCLUSIONS: Both extrusion-based and photopolymerization-based printers were accurate. In general, inexpensive printers were no less accurate than more expensive ones.

Does ambient light affect the accuracy and scanning time of intraoral scans?

STATEMENT OF PROBLEM: Intraoral scanners (IOSs) are based on light-optical imaging methods. However, little is known about whether the ambient light in dental practices influences the accuracy and scanning time of the IOS. PURPOSE: The purpose of this in vitro study was to investigate the influence of different illuminations on the accuracy of 4-unit and complete-arch scans of 6 IOSs. In addition, the required scanning time was evaluated. MATERIAL AND METHODS: A reference structure was attached to the first premolars (P) and second molars (M) in both quadrants (L/R) of a maxillary model. The resulting measured distances were M1-P1, M2-P2, P1-P2, and M1-M2. The investigation included 6 IOSs: TRIOS 3 (TRI), Cerec Omnicam (OC), iTero Element (ITE), CS 3600 (CS), Planmeca Emerald (EME), and GC Aadva (AAD). With each IOS, 17 scans at different illuminances (100, 500, 1000, and 5000 lux) were performed (N = 408). The precision and trueness for all distances were determined, and the scanning time was recorded. For statistical analyses, the Levene tests (precision) and 1-way analysis of variance with the post hoc Tukey honestly significant difference and Games-Howell tests (trueness) were calculated. RESULTS: Illuminance significantly influenced the trueness of 4-unit scans for OC, EME, and AAD. TRI, OC, ITE, and CS demonstrated comparable results. AAD (>96 ±22 µm; 1000 lux) and EME (>248 ±88 µm; 500 lux) revealed greater deviations. For complete-arch scans, illuminance did not influence TRI and AAD, but significant variations were detected for ITE, CS, EME, and AAD. The least deviations were achieved with TRI and OC. The scanning time was extended for all IOSs except ITE at more than 500 lux. The shortest scanning times with OC and EME were recorded at 100 lux; with TRI, CS, and AAD at 500 lux; and with ITE at both 100 and 5000 lux. At all illuminances, the fastest scans were obtained with TRI. CONCLUSIONS: Ambient light was found to influence the accuracy and scanning time of IOSs. This influence varies depending on the device. For 4-unit scans, the effect was not clinically relevant, but for complete-arch scans, accuracy and scanning time can be improved with appropriate lighting.

Zirconia implants restored with single crowns or fixed dental prostheses: 5-year results of a prospective cohort investigation.

AIM: To evaluate the clinical and radiological outcomes of one-piece zirconia implants restored with single crowns (SCs) or fixed dental prostheses (FDPs) over an observation period of 5 years in function. MATERIALS AND METHODS: In a prospective cohort investigation with two investigational centers, one-piece zirconia implants were placed in anterior and posterior sites. After a healing period of at least 2 months in the mandible and 4 months in the maxilla with immediate provisional reconstructions, the final all-ceramic SCs or three-unit FDPs were cemented. Patients were followed for 5 years. Clinical parameters and radiological measurements of the implants and the neighboring teeth were assessed. For the statistical analysis, linear mixed models were applied. RESULTS: A total of 71 implants were placed in 60 patients. Sixty-three implants in 53 patients could be evaluated at the 5-year follow-up. Six patients with a total of seven implants were counted as dropouts. One implant did not achieve adequate osseointegration and had to be removed 5 weeks after implantation. The 5-year survival rate was calculated as 98.4% (95% CI 91.6, 99.9). The mean overall marginal bone loss from implant placement to the 5-year follow-up was 0.7 ± 0.6 mm. After an initial mean marginal loss before loading the implants (0.7 mm), no further statistically significant change in marginal bone level (p = .458) could be observed. CONCLUSION: The investigated one-piece zirconia implant showed a high survival rate, very stable marginal bone, and mucosal margin levels after 5 years in function. Therefore, it can be considered safe and reliable for the reconstruction of implant-supported SCs or FDPs over a mid-term period.

Pandemic-Driven Development of a Medical-Grade, Economic and Decentralized Applicable Polyolefin Filament for Additive Fused Filament Fabrication.

A polyolefin with certified biocompatibility according to USP class VI was used by our group as feedstock for filament-based 3D printing to meet the highest medical standards in order to print personal protective equipment for our university hospital during the ongoing pandemic. Besides the chemical resistance and durability, as well as the ability to withstand steam sterilization, this polypropylene (PP) copolymer is characterized by its high purity, as achieved by highly efficient and selective catalytic polymerization. As the PP copolymer is suited to be printed with all common printers in fused filament fabrication (FFF), it offers an eco-friendly cost-benefit ratio, even for large-scale production. In addition, a digital workflow was established focusing on common desktop FFF printers in the medical sector. It comprises the simulation-based optimization of personalized print objects, considering the inherent material properties such as warping tendency, through to validation of the process chain by 3D scanning, sterilization, and biocompatibility analysis of the printed part. This combination of digital data processing and 3D printing with a sustainable and medically certified material showed great promise in establishing decentralized additive manufacturing in everyday hospital life to meet peaks in demand, supply bottlenecks, and enhanced personalized patient treatment.

All-ceramic single crowns supported by zirconia implants: 5-year results of a prospective multicenter study.

OBJECTIVES: To assess survival/success rates and patient-reported outcome of zirconia-based posterior single crowns (SCs) supported by zirconia implants in a prospective two-center study after five years of observation. MATERIAL AND METHODS: Forty-five patients were restored with 45 zirconia implant-supported posterior SCs composed of zirconia frameworks hand-layered with a leucite-reinforced feldspathic ceramic. Survival rates of SCs were assessed and technical success was evaluated according to modified United States Public Health Care (USPHS) criteria. Furthermore, patient-reported outcome measures (PROMs) were assessed by applying visual analog scales (VAS). Wilcoxon matched-pairs signed-rank test, mixed-effects ordered logistic regression, and linear mixed models were used to evaluate time effects on response variables. RESULTS: Forty patients were available after a mean observation period of 61.0 ± 1.4 months. One SC had to be replaced, resulting in a Kaplan-Meier (KM) survival estimate for the SCs of 97.5 ± 2.47%. Since nine reconstructions showed at least in one category a major deviation from the ideal (five major chippings, four with increased occlusal roughness, one significant crevice, and one pronounced over-contouring), the KM success estimate was 79.3 ± 5.8%. Incidence of chipping (n = 19) and occlusal roughness (n = 35) was frequent (p < 0.001). All PROMs at prosthetic delivery except for speech (p = 0.139) showed significantly improved VAS scores (81%-94%; p < 0.001) compared to pre-treatment evaluations. Thereafter, no decrease in satisfaction could be observed until the 5-year follow-up (93%-97%). CONCLUSION: Veneered zirconia-based SCs supported by zirconia implants showed high survival rates and highly satisfied patients' needs. However, significant incidence of technical complications is compromising the clinical long-term outcome for this indication.

One-piece zirconia oral implants for single-tooth replacement: Three-year results from a long-term prospective cohort study.

AIM: This 3-year report of a prospective long-term cohort investigation aimed to evaluate the clinical and radiographic outcomes of a one-piece zirconia oral implant for single-tooth replacement. MATERIALS AND METHODS: Sixty-five patients received a 1-stage implant surgery with immediate temporization. Standardized radiographs were taken at implant insertion, after 1 year, and after 3 years to monitor peri-implant bone levels. A univariate analysis of the association of different baseline parameters on marginal bone loss from implant insertion to 36 months was performed. Soft-tissue parameters were evaluated at prosthesis insertion, after 6 months, after 1 year, and at the 3-year follow-up. RESULTS: After 3 years, six posterior site implants were lost, giving a cumulative survival rate of 90.8%. The mean marginal bone loss was 1.45 mm; 35% of the implants lost at least 2 mm bone, and 22% more than 3 mm. The univariate analysis did not identify any parameter associated with marginal bone loss. Probing depth, clinical attachment level, and bleeding index increased over 3 years, and plaque index decreased. CONCLUSIONS: The low survival rate of the presented ceramic implant and especially the high frequency of advanced bone loss are noticeable but remain unexplained.

Three-year analysis of zirconia implants used for single-tooth replacement and three-unit fixed dental prostheses: A prospective multicenter study.

AIM: The aim of the present investigation was to evaluate clinically and radiographically the outcome of zirconia oral implants after 3 years in function. MATERIALS AND METHODS: In 60 patients in need of either a single-tooth replacement or a three-unit fixed dental prosthesis (FDP), a total of 71 one-piece zirconia implants were placed and immediately restored with temporary fixed prostheses. After a period of at least 2 months in the mandible and at least 4 months in the maxilla, zirconia-based reconstructions were cemented. The implants were clinically and radiologically examined at implant insertion, prosthetic delivery, at 6 months and then yearly up to 3 years. A linear mixed model was used to analyze statistically the influence of prognostic factors on changes in the marginal bone level. RESULTS: Seventy-one implants (48 in the mandible, 23 in the maxilla) inserted in 60 patients were restored with 49 crowns and 11 FDP. One patient lost his implant after 5 weeks. Five patients with one implant each could not be evaluated after 3 years. Based on 55 patients with a total of 66 implants, the mean survival rate was 98.5% after 3 years in function. A statistically significant mean marginal bone loss (0.70 mm ± 0.72 mm) has been detected from implant insertion to the 3-year follow-up. The largest marginal bone loss occurred between implantation and prosthetic delivery (0.67 mm ± 0.56 mm). After delivery, no statistically significant bone level change was observed (0.02 mm ± 0.59 mm). None of the investigated prognostic factors had a significant influence on changes in the marginal bone level. CONCLUSIONS: After 3 years in function, the investigated one-piece zirconia implant showed a high survival rate and a low marginal bone loss. The implant system was successful for single-tooth replacement and three-unit FDPs. Further investigations with long-term data are needed to confirm these findings.

Reconstructive aspects: Summary and consensus statements of group 3. The 5th EAO Consensus Conference 2018.

OBJECTIVES: The tasks of this working group were to evaluate the existing evidence on the efficiency and efficacy of the digital and conventional workflows for the fabrication of fixed implant reconstructions, to assess the performance of all-ceramic fixed implant reconstructions and, finally, to evaluate the outcomes of internally and externally connected implant abutments and reconstructions. METHODS: Four reviews were available analyzing the current literature on the respective topics. One review dealt with the efficiency and efficacy of digital and conventional fabrication workflows. Two reviews analyzed the outcomes of all-ceramic fixed implant reconstructions, one focusing on single-implant reconstructions and the other evaluating multiple-unit implant fixed dental prostheses (FDPs). The fourth review evaluated the clinical outcome on external, respectively, internal implant-abutment connections. These reviews were the basis for the discussions within the group and at the plenary sessions. RESULTS: The present consensus report gives the consensus statements, the clinical recommendations, and the implications for future research as discussed and approved by the plenum of the consensus conference. The four manuscripts by Mühlemann et al., Rabel et al., Pieralli et al., and Pjetursson et al. are published as part of the journal supplement of the present EAO consensus conference.

Direct or Indirect Restoration of Endodontically Treated Maxillary Central Incisors with Class III Defects? Composite vs Veneer or Crown Restoration.

PURPOSE: The aim of this ex-vivo study was to evaluate the load capacity of direct or indirect endodontically restored maxillary central incisors with Class III defects, with or without glass-fiber posts. MATERIALS AND METHODS: Seventy-two extracted human maxillary central incisors were endodontically treated and bi-proximal Class III cavities were prepared. Specimens were randomly allocated to six groups (n = 12): direct restoration with composite (C); direct restoration with composite and additional glass-fiber post (CP); ceramic veneer restoration (V), ceramic veneer restoration and additional glass-fiber post (VP), ceramic crown restoration (Cr), ceramic crown restoration and additional glass-fiber post (CrP). Specimens were exposed to thermomechanical loading (TML: 1.2 million cycles, 1 to 50 N; 6000 thermal cycles between 5°C and 55°C for 1 min each), and subsequently linearly loaded until failure (Fmax [N]) at an angle of 135 degrees 3 mm below the incisal edge on the palatal side. Statistical tests were performed using the Kruskall-Wallis and Mann-Whitney U-Test. RESULTS: During dynamic loading by TML, one early failure occurred in group C, CP, and CrP. Subsequent linear loading resulted in mean fracture load values [N] of C = 483 ± 219, CP = 536 ± 281, V = 908 ± 293, VP = 775 ± 333, Cr = 549 ± 258, CrP = 593 ± 259. The Kruskal-Wallis test showed significant differences of load capacity between groups (p < 0.05). Mann-Whitney U-test revealed significantly lower maximum fracture load values of group C compared to group V (p = 0.014), after Bonferroni-Holm correction. Non-restorable root fracture was the most frequent type of failure. CONCLUSION: Endodontically treated maxillary central incisors with Class III defects directly restored with composite are as loadable as indirect crown restorations. Compared to full-coverage restorations, less invasive veneers appear to be more beneficial. Additional placement of glass-fiber posts shows no positive effect.

Contemporary Digital Restorative and Minimal-Invasive Preservative Surgical Techniques in the Esthetic Zone: A Case Report.

When immediately temporizing an implant, relining and cementation of the provisional can be a challenging, time-consuming, and contaminating procedure. Excess resin and cement need to be carefully removed from the fresh wound. This can be overcome by digitally backward planning the treatment with subsequent production of a surgical guide to be used by both the technician and the dentist. In this report, a patient with a fractured and hopeless central incisor and an apical radiolucency at his compromised (root-canal treated, post and core build-up) contralateral counterpart was treated using guided implant installation, immediate placement of a prefabricated screw-retained provisional, and apicoectomy. Dehiscence of the buccal plate after tooth extraction resulting in the need for hard- and soft-tissue grafting and delayed surgery did not affect the clinical outcome.

CAD/CAM-fabricated implant-supported restorations: a systematic review.

OBJECTIVES: The aim of this systematic review was to identify and summarize the available literature related to CAD/CAM-fabricated implant-supported restorations. MATERIALS AND METHODS: A systematic review of the literature was conducted using the Cochrane Library and the US Library of Medicine, National Institute of Health databases (Pubmed). Several search runs with specific search terms were performed and combined. All published papers available on the databases up to January 15, 2015 were considered with primarily no restrictions. RESULTS: About 12 of 3484 identified papers met the inclusion criteria and were analyzed in the present review. One paper reported results on implant-supported single crowns (SCs), one on partial fixed dental prostheses (FDPs), and 10 papers reported results on full-arch screw-retained FDPs. Publications on SCs and FDPs were very limited but it was possible to identify 10 papers reporting adequate results on full-arch screw-retained FDPs. Survival rates ranged between 92% and 100% with observation times of 1-10 years. CONCLUSION: The available data provided promising results for CAD/CAM-fabricated implant-supported restorations; nonetheless, current evidence is limited due to the quality of available studies and the paucity of data on long-term clinical outcomes of 5 years or more. In the sense of an evidence-based dentistry, the authors recommend further studies designed as randomized controlled clinical trials and reported according to the CONSORT statement.

Accuracy of additively manufactured and steam sterilized surgical guides by means of continuous liquid interface production, stereolithography, digital light processing, and fused filament fabrication.

Different printing technologies can be used for prosthetically oriented implant placement, however the influence of different printing orientations and steam sterilization remains unclear. In particular, no data is available for the novel technology Continuous Liquid Interface Production. The objective was to evaluate the dimensional accuracy of surgical guides manufactured with different printing techniques in vertical and horizontal printing orientation before and after steam sterilization. A total of 80 surgical guides were manufactured by means of continuous liquid interface production (CLIP; material: Keyguide, Keyprint), digital light processing (DLP; material: Luxaprint Ortho, DMG), stereolithography (SLA; Surgical guide, Formlabs), and fused filament fabrication (FFF; material: Clear Base Support, Arfona) in vertical and horizontal printing orientation (n = 10 per subgroup). Spheres were included in the design to determine the coordinates of 17 reference points. Each specimen was digitized with a laboratory scanner after additive manufacturing (AM) and after steam sterilization (134 °C). To determine the accuracy, root mean square values (RMS) were calculated and coordinates of the reference points were recorded. Based on the measured coordinates, deviations of the reference points and relevant distances were calculated. Paired t-tests and one-way ANOVA were applied for statistical analysis (significance p < 0.05). After AM, all printing technologies showed comparable high accuracy, with an increased deviation in z-axis when printed horizontally. After sterilization, FFF printed surgical guides showed distinct warpage. The other subgroups showed no significant differences regarding the RMS of the corpus after steam sterilization (p > 0.05). Regarding reference points and distances, CLIP showed larger deviations compared to SLA in both printing orientations after steam sterilization, while DLP manufactured guides were the most dimensionally stable. In conclusion, the different printing technologies and orientations had little effect on the manufacturing accuracy of the surgical guides before sterilization. However, after sterilization, FFF surgical guides exhibited significant deformation making their clinical use impossible. CLIP showed larger deformations due to steam sterilization than the other photopolymerizing techniques, however, discrepancies may be considered within the range of clinical acceptance. The influence on the implant position remains to be evaluated.

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.

Dimensional accuracy and simulation-based optimization of polyolefins and biocopolyesters for extrusion-based additive manufacturing and steam sterilization.

Polyolefins exhibit robust mechanical and chemical properties and can be applied in the medical field, e.g. for the manufacturing of dentures. Despite their wide range of applications, they are rarely used in extrusion-based printing due to their warpage tendency. The aim of this study was to investigate and reduce the warpage of polyolefins compared to commonly used filaments after additive manufacturing (AM) and sterilization using finite element simulation. Three types of filaments were investigated: a medical-grade polypropylene (PP), a glass-fiber reinforced polypropylene (PP-GF), and a biocopolyester (BE) filament, and they were compared to an acrylic resin (AR) for material jetting. Square specimens, standardized samples prone to warpage, and denture bases (n = 10 of each group), as clinically relevant and anatomically shaped reference, were digitized after AM and steam sterilization (134 °C). To determine warpage, the volume underneath the square specimens was calculated, while the deviations of the denture bases from the printing file were measured using root mean square (RMS) values. To reduce the warpage of the PP denture base, a simulation of the printing file based on thermomechanical calculations was performed. Statistical analysis was conducted using the Kruskal-Wallis test, followed by Dunn's test for multiple comparisons. The results showed that PP exhibited the greatest warpage of the square specimens after AM, while PP-GF, BE, and AR showed minimal warpage before sterilization. However, warpage increased for PP-GF, BE and AR during sterilization, whereas PP remained more stable. After AM, denture bases made of PP showed the highest warpage. Through simulation-based optimization, warpage of the PP denture base was successfully reduced by 25%. In contrast to the reference materials, PP demonstrated greater dimensional stability during sterilization, making it a potential alternative for medical applications. Nevertheless, reducing warpage during the cooling process after AM remains necessary, and simulation-based optimization holds promise in addressing this issue.

Analysis of soft tissue integration-supportive cell functions in gingival fibroblasts cultured on 3D printed biomaterials for oral implant-supported prostheses.

To date, it is unknown whether 3D printed fixed oral implant-supported prostheses can achieve comparable soft tissue integration (STI) to clinically established subtractively manufactured counterparts. STI is mediated among others by gingival fibroblasts (GFs) and is modulated by biomaterial surface characteristics. Therefore, the aim of the present work was to investigate the GF response of a 3D printed methacrylate photopolymer and a hybrid ceramic-filled methacrylate photopolymer for fixed implant-supported prostheses in the sense of supporting an STI. Subtractively manufactured samples made from methacrylate polymer and hybrid ceramic were evaluated for comparison and samples from yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP), comprising well documented biocompatibility, served as control. Surface topography was analyzed by scanning electron microscopy and interferometry, elemental composition by energy-dispersive x-ray spectroscopy, and wettability by contact angle measurement. The response of GFs obtained from five donors was examined in terms of membrane integrity, adhesion, morphogenesis, metabolic activity, and proliferation behavior by a lactate-dehydrogenase assay, fluorescent staining, a resazurin-based assay, and DNA quantification. The results revealed all surfaces were smooth and hydrophilic. GF adhesion, metabolic activity and proliferation were impaired by 3D printed biomaterials compared to subtractively manufactured comparison surfaces and the 3Y-TZP control, whereas membrane integrity was comparable. Within the limits of the present investigation, it was concluded that subtractively manufactured surfaces are superior compared to 3D printed surfaces to support STI. For the development of biologically optimized 3D printable biomaterials, consecutive studies will focus on the improvement of cytocompatibility and the synthesis of STI-relevant extracellular matrix constituents.

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.

Method development for the intraoral release of nanoparticles from dental restorative materials.

OBJECTIVE: The aim of this study was the development of a novel in-vitro method to evaluate the intraoral release of wear particles with a diameter< 1 µm from dental restorative materials. METHODS: Test fixtures for a dual-axis chewing simulator (CS-4.8, SD Mechatronik, Feldkirchen-Westerham, Germany), consisting of three components to mount the specimens and a solvent (distilled water) as well as a zirconia antagonist to transfer the masticatory forces onto the specimen was developed. Ceram.x Spectra™ ST HV (CS) and Filtek™ Supreme XTE (FS) specimens (n = 3) were fixed into the mounts and immersed in 25 ml solvent. All specimens were subjected to 500.000 wear cycles with a load of 49 N. The particle size distribution of the suspensions were examined by dynamic light scattering (DLS). The collected particles were characterised by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). For wear quantification, the surfaces of the specimens were photo-optically scanned and the wear was measured. For the statistical analysis, one-way ANOVA and post-hoc Scheffé tests were applied. RESULTS: DLS showed particle diameters< 1 µm (CS: 18.06 nm-1.64 µm, FS: 72.30 nm-2.31 µm). SEM/EDS indicated an association between the detected elements and the materials' composition. FS showed significantly higher volume loss (p = 0.007) and maximum depth of the wear profile (p = 0.005) than CS, but no significant differences in the surface loss (p = 0.668). SIGNIFICANCE: The novel method is able to detect material dependent particles to the size of nanoscale after in-vitro abrasion.