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Aim: To investigate the effect of using different materials for the fabrication of implant abutments and crowns on the mechanical behavior of implant-supported single crowns after artificial aging. The materials were tested in different combinations to reveal whether using stiff or resilient materials as an abutment or a crown material might influence the fracture strength of the whole structure. Materials and Methods: A total of 40 implants (blueSKY, bredent GmbH & Co. KG) were restored with identical custom-made CAD/CAM abutments milled out of lithium disilicate or ceramic-reinforced PEEK and were divided into 5 test groups (n = 8 each). Forty crowns made of three different materials (zirconia, lithium disilicate, and ceramic-reinforced PEEK) were used to restore the abutments. Specimens were subjected to mechanical load up to 1,200,000 cycles in a chewing simulator (Kausimulator, Willytech) with additional thermal cycling. The surviving specimens were subjected to quasi-static loading using a universal testing machine (Z010, Zwick). Results: PEEK abutments with zirconia crowns showed the highest median failure load (3890.5 N), while PEEK abutments with lithium disilicate crowns exhibited the lowest (1920 N). Fracture and deformation occurred in both crowns and abutments. Conclusion: The failure load of the restorations was influenced by the material of the abutment and the crown. Restoring PEEK abutments with zirconia crowns showed a high failure load and no screw loosening. Keywords: CAD/CAM, Custom-made implant abutment, implant abutment, Lithium disilicate, PEEK, Zirconia

Ziel der in diesem Beitrag beschriebenen Studie war es, die Bruchfestigkeit vollanatomischer Kronen aus drei verschiedenen Zirkonoxidtypen mit unterschiedlichem Gehalt an Yttriumoxid zu bestimmen. Es zeigte sich, dass die mechanischen Eigenschaften der Zirkonoxidkeramik darunter leiden können, wenn der Yttriumoxidgehalt erhöht wird, um die optischen Eigenschaften zu verbessern. Das transluzentere 5Y-TZP wies dennoch eine sehr hohe Bruchfestigkeit auf, die 3000 N überstieg. Die Ergebnisse dieser Studie legen nahe, den Einsatz von Zirkonoxid mit hohem Yttriumoxidgehalt in Bereichen oder Situationen mit hohen Belastungen sorgfältig abzuwägen. Keywords: Zirkonoxid, Keramik, künstliche Alterung, Yttriumoxid

Manuskripteingang: 10.09.2023, Manuskriptannahme: 16.10.2023 Keywords: Elektrotomie, Hochfrequenz (HF)-Chirurgie

Purpose: To investigate the influence of contamination and different cleaning methods on resin bonding to cobalt-chro- mium (CoCr) alloy disks. Materials and Methods: A total of 160 CoCr disks were divided into 3 groups. The first group (N = 64) was air abraded with alumina particles and contaminated with a silicone disclosing agent and saliva; the second group (N = 64) was air abraded but not contaminated; the third group (N = 32) was neither air abraded nor contaminated. The first two groups were di- vided into 4 subgroups (N = 16) according to the cleaning method: ultrasonic bath in 99% isopropanol, use of a cleaning suspension of zirconium oxide particles, use of a cleaning suspension based on 10-MDP salt, and treatment with atmo- spheric plasma. The third group was divided into 2 subgroups (N = 16): treatment with atmospheric plasma and no treat- ment. All CoCr specimens were bonded to plexiglas tubes filled with a bonding resin that contained phosphate monomer. Tensile bond strength (TBS) was examined by tensile testing after 3 and 150 days of water storage plus 37,500 thermal cy- cles (N = 8). Results: After contamination, TBS was significantly reduced after 150 days of water storage. Groups without air abrasion showed initially low TBS and debonded spontaneously after 150 days of water storage. Conclusion: None of the cleaning methods was able to remove saliva and silicone disclosing agent on CoCr-alloy sur- faces. Surface activation by plasma treatment has no long-term effect on the bond strength. Keywords: alloy, contamination, cleaning, bonding, plasma treatment

Purpose: To evaluate the effects of post length, post material, and substance loss on the fracture resistance of endodontically treated mandibular premolars. Materials and Methods: A total of 96 extracted human mandibular first premolars were endodontically treated and divided into 12 test groups (n = 8 each) based on the number of residual walls (one/two), post material (glass-fiber/titanium), and post length (5 mm, 7.5 mm, and 10 mm). After luting the posts, specimens received a composite resin core and a crown preparation with a 1.5-mm ferrule. Cast cobalt-chromium crowns were cemented using glass-ionomer cement. After 1,200,000 chewing cycles with a load of 49 N and simultaneous thermocycling (5°C to 55°C), specimens were quasi-statically loaded at 30 degrees to the longitudinal axis of the tooth until fracture. Fracture loads were analyzed using three-way, two-way, and one-way ANOVA (α = .05). Fracture modes were examined under a stereomicroscope (×25 magnification) and recorded. Results: The mean ± SD fracture loads ranged from 642 ± 190 N (one wall, glass fiber, 5 mm) to 1,170 ± 130 N (two walls, titanium, 7.5 mm). The mean fracture load of titanium posts was significantly higher than that of glass-fiber posts (P < .001), and the 7.5-mm post length exhibited significantly higher fracture loads than groups with 5-mm and 10-mm post length (P = .008). Conclusions: Teeth restored with titanium posts revealed considerably higher fracture resistance than teeth restored with glass-fiber posts, especially if 7.5-mm–length posts were used.

Purpose: To evaluate the effect of thermomechanical dynamic loading on the retention of telescopic mandibular overdentures with different metallic and nonmetallic material combinations. Materials and Methods: Four groups were tested: (1) ZP (zirconia abutments/PEEK framework); (2) PP (PEEK abutments/PEEK framework); (3) TP (titanium abutments/PEEK framework); and (4) TG (titanium abutments/gold copings/cobalt-chromium framework). Each specimen contained four implants positioned over a polyvinylchloride-cylindrical base. After 10,000 removal/insertion cycles, the specimens were subjected to thermomechanical dynamic load in a chewing simulator for 1,200,000 loading cycles, corresponding to 5-year clinical fatigue. A screw was used to receive the chewing load, and 0.5 mm was permitted between the screw and the metal top fixed into the base to simulate the resilience of the posterior residual ridge tissues. Vertical chewing loads of 60 N were applied at a speed of 30 mm/second. Thermocycling was applied with a temperature ranging between 5°C and 55°C. The retentive force was measured using a universal testing machine 10 times before and after the thermomechanical dynamic loading test with a speed of 8 mm/second. Results: The mean retentive force increased significantly from 13.2 (± 4.6) N to 16.4 (± 6.1) N in group ZP (P = .002), while in group TP, it decreased significantly from 4.9 (± 2.1) N to 3.3 (± 1.7) N (P = .046). There was no statistically significant change in the retentive force for groups PP and TG. Conclusions: The investigated metallic and nonmetallic combinations of double-crown-retained mandibular overdentures maintained acceptable levels of retention after thermomechanical dynamic loading. Further laboratory and clinical studies are needed before their routine clinical use can be recommended.

Ziel dieses Beitrags ist es, eine minimalinvasive und ästhetische Therapieoption für den Ersatz fehlender Zähne im teilbezahnten Kiefer mithilfe von monolithischen Adhäsivattachments aus Zirkonoxidkeramik vorzustellen. Die Adhäsivattachments wurden digital konstruiert, mit CAD/CAM-Technik aus monolithischer 3Y-TZP-Zirkonoxidkeramik gefräst und dicht gesintert. Die Attachments wiesen ein für Zirkonoxidkeramik optimiertes Attachmentdesign mit Stabgeschiebe und integrierten Schubverteiler auf. Die Präparation der Pfeilerzähne erfolgte minimalinvasiv, rein schmelzbegrenzt mit einer abgerundeten approximalen vertikalen Rille. Die Restaurationen wurden nach sorgfältiger Konditionierung aller Oberflächen unter absoluter Trockenlegung mithilfe eines Positionierungsschlüssels und Phosphatmonomer-haltigen Kompositklebers eingegliedert. Die vorgestellte prothetische Arbeit hat sich bisher über 30 Monate hinweg klinisch ohne Komplikationen bewährt. Der Patient ist mit dem vorgestellten minimalinvasiven Behandlungsverfahren sehr zufrieden. Vollkeramische Adhäsivattachments mit einem optimierten Design erlauben eine ästhetische und minimalinvasive Versorgung von teilbezahnten Kiefern. Bei positiver klinischer Bewährung könnten monolithische Adhäsivattachments zu einer minimalinvasiven und metallfreien Therapieoption zu Versorgung von teilbezahnten Patienten avancieren. Manuskripteingang: 15.03.2023, Manuskriptannahme: 17.03.2023 Englischsprachige Erstpublikation: Becker M, Sad Chaar M, Kern M. Resin-bonded attachments made of monolithic zirconia ceramic: A minimally invasive and esthetic treatment approach. Quintessence Int 2023;54(3):220–226; Übersetzung des vorliegenden Beitrags aus dem Englischen ins Deutsche: Dr. Merlind Becker Keywords: Adhäsivattachments, herausnehmbare Teilprothesen, Vollkeramik, Zirkonoxid

Objective: The aim of this case report was to present a minimally invasive and esthetic treatment approach for the replacement of missing teeth removable partial dentures retained by zirconia ceramic resin-bonded attachments. Method and materials: The resin-bonded attachments were digitally designed and milled using CAD/CAM technology from monolithic 3Y-TZP zirconia ceramic. The resin-bonded attachments had an optimized attachment design approved for zirconia ceramic. The preparation was based on general preparation guidelines for resin-bonded attachments and resin-bonded fixed dental prostheses (RBFDPs). After placement of rubber dam, the resin-bonded attachments were bonded with a phosphate monomer-containing luting resin. Results: The presented resin-bonded attachment-retained removable partial denture was successful over 30 months of clinical observation without any complications. The patient was satisfied with the minimally invasive treatment procedure. Conclusion: Zirconia ceramic resin-bonded attachments fabricated with a special attachment design are an esthetic and minimally invasive treatment approach. However, clinical data on the long-term outcome of zirconia resin-bonded attachments are still needed. (Quintessence Int 2023;54:220–226; doi: 10.3290/j.qi.b3819523) Keywords: all-ceramic, precision-retained removable dental prostheses, resin-bonded attachments, zirconia

Aim: The aim of the present article is to describe a new method to reduce the undesirable loss of material thickness that results from overmilling due to the tool diameter compensation correction of common CAD/CAM software. Materials and methods: Today’s CAD/CAM software (eg, 3Shape or Exocad) specifies the same tool diameter compensation for different ceramics. In the case of zirconia ceramics milled in the raw state, this leads to excessive milling of the inner surfaces of crowns, which results in unnecessarily large cementation gaps and a restoration that is thinned out from the inside. By manually reducing the preset correction in the digital design process by the volumetric sintering shrinkage factor specified by the manufacturer, excessive thinning of the zirconia can be avoided. Results: The inner geometry of the restorations changes only slightly after manually reducing the preset tool diameter compensation correction. Consequently, a design of the restoration with the required minimum interocclusal thickness yet with accurate passive seating and marginal fit is possible without any further interventions. Conclusions: Understanding the specifics of the subtractive fabrication process as well as the properties of the restorative materials is a key factor in achieving optimal clinical outcomes with all-ceramic restorations fabricated with CAD/CAM technology. The use of monolithic zirconia combined with a calculated reduction in the preset tool diameter compensation correction might be beneficial in cases with thin or uneven geometry. Keywords: all-ceramic restorations, CAD/CAM, tool diameter compensation, monolithic zirconia, minimum thickness, subtractive manufacturing