Purpose: The purpose of this study was to evaluate the fracture strength of monolithic FDPs of multi-layered zirconia (YML) with different connector dimensions and placement in the disc. Material and method: Forty 3-unit monolithic anterior FDPs were produced, 212223, and divided in four groups (n=10) based on the different connector dimensions and strategies for placement in KATANATM Zirconia Yttria Multi-Layered (YML)-disc. The groups were as follows: EB12, produced with 12 mm  connector dimension and EB7, with 7 mm  connector dimension which were both placed in Enamel layer and Body layer 1 (flexural strength: 750 and 1000 MPa, respectively) in the disc, BB12, with 12 mm  connector dimension and BB7, produced with 7 mm  connector dimension both placed in Body layer 2 and 3 (both with 1100 MPa) in the disc. The specimens were artificially aged by 10 000 cycles in thermocycling. Then, one random specimen was selected from each group (4 in total) and cemented onto the model, subsequently loaded to fracture using a universal testing machine. The result was compiled and reported descriptively. Result: The FDP in group BB12 remained intact and fracturing only occurred in this model at 893 N. The FDP in group BB7 demonstrated the highest fracture strength (972 N), followed by EB12 (842 N) and EB7 which showed the lowest fracture strength (465 N). All these three FDPs broke mesially on the pontics. Conclusion: Within the limitations of this pilot study, the following conclusions can be drawn: the fracture strength of monolithic FDPs of multi-layered zirconia is affected by the connector dimension. Placement of FDPs with a small connector area should be avoided in the layers with lower strength. The choice of model material affects the result. / Syfte: Syftet med föreliggande pilotstudie var att undersöka brotthållfastheten påmonolitiska broar av flerskiktad zirkonia (YML) med olika konnektordimensioneroch placering i disken. Material och metod: Totalt framställdes 40 stycken 3-leds monolitiska anteriorabroar, 212223. Broarna delades in i 4 grupper (n=10) efter olikakonnektordimensionering och placering i KATANATM Zirconia YttriaMulti-Layered (YML)-disken. Grupperna var enligt följande: EB12 med 12 mm²konnektordimension och EB7 med 7 mm² konnektordimension där broarnaplacerades i både Enamel Layer och Body Layer 1 (med 750 respektive 1000 MPai böjhållfasthet) i disken. Broarna i grupperna BB12 med 12 mm²konnektordimension och BB7 med 7 mm² konnektordimension placerades i BodyLayer 2 och Body Layer 3 (med 1100 MPa böjhållfasthet för respektive lager) idisken. Broarna genomgick termocykling, 10 000 cykler. Därefter valdes fyrabroar slumpmässigt ut, en bro från varje grupp, och cementerades på modell.Slutligen genomfördes ett brotthållfasthetstest med en universaltestmaskin tillsfraktur uppstod. Resultatet sammanställdes och redovisades deskriptivt. Resultat: Bron i grupp BB12 förblev intakt och fraktur skedde enbart i modellen(893N). Bron i grupp BB7 visade högst brotthållfasthet: 972N, följt av bron igrupp EB12 som visade brotthållfasthet på 842N och bron i grupp EB7 påvisadeden lägsta brotthållfastheten: 465N. Dessa tre broar frakturerade mesialt på dethängande ledet. Slutsats: Inom ramen för föreliggande pilotstudies begränsningar kan följandeslutsatser dras: brotthållfastheten på monolitiska broar i flerskiktad zirkoniapåverkas av konnektordimensioneringen. Placering av broar med mindrekonnektorarea än rekommendationen ska undvikas i skikten med lägre hållfasthet.Valet av modellmaterial har betydelse och påverkar resultatet.

This study aimed to determine the effects of grinding and low temperature aging on the surface micromorphology (roughness measurement, Scanning Electron Microscopy and Atomic Force Microscopy), phase transformation (t→m), biaxial flexural strength and structural reliability (Weibull analysis) of an yttrium-stabilized tetragonal zirconia polycrystalline ceramic. One hundred and eighty ceramic discs (15.0 × 1.2 ± 0.2 mm, VITA In-Ceram YZ) were prepared and randomly assigned into six groups according to 2 factors (n = 30): grinding (Ctrl without treatment, as-sintered; Xfine grinding with extra fine diamond bur - 30 μm; Coarse grinding by coarse diamond bur - 151 μm), and aging (without or with aging: CtrlLTD; XfineLTD; CoarseLTD). Grinding was performed in an oscillatory motion with a contra-angle handpiece under constant water-cooling. Low temperature degradation (LTD) was simulated in an autoclave at 134 °C, under 2 bar pressure, for 20 h. The roughness (Ra and Rz parameters) significantly increased after grinding in accordance with bur grit-size (Coarse > Xfine > Ctrl), and aging promoted distinct effects (Ctrl = CtrlLTD; Xfine > XfineLTD; Coarse = CoarseLTD). Grinding increased the m-phase, and aging led to an increase in the m-phase in all groups. However, different susceptibilities to LTD were observed. Weibull analysis showed a significant increase in the characteristic strength after grinding (Coarse = Xfine > Ctrl), while aging did not lead to any deleterious impact. Neither grinding nor aging resulted in any deleterious impact (no statistical decrease in the Weibull moduli) on material reliability. Thus, neither grinding nor aging led to a deleterious effect on the mechanical properties of the evaluated Y-TZP ceramic although a high m-phase content and roughness were observed. / Este estudo avaliou o efeito do desgaste com brocas diamantadas de diferentes granulações (Grossa G e Extrafina FF), associado ou não ao envelhecimento em autoclave (LTD) na micromorfologia superficial, na transformação de fase (tetragonal para monoclínica, t→m), e nas propriedades mecânicas de uma zircônia policristalina parcialmente estabilizada por óxido de ítrio. Foram confeccionados 180 discos (15,0 Ø x 1,2 mm de espessura) conforme a ISO 6872-2008, que foram divididos em 6 grupos (n=30) de acordo com dois fatores em estudo: desgaste da superfície (controle C - sem desgaste; desgaste com broca G ou FF); e envelhecimento em autoclave (CLTD, GLTD FFLTD); Os desgastes foram executados por um operador treinado sob refrigeração constante; e a LTD em autoclave a 134ºC, sob 2 bar de pressão, por 20 horas. Os resultados indicam que o envelhecimento em autoclave associado ou não ao desgaste não foram prejudiciais às propriedades mecânicas da zircônia. Entretanto cabe ressaltar que estes estímulos promoveram grande aumento de fase monoclínica, o que pode ser um indício de degradação do material. A análise de Weibull (Módulo de Weibull) demonstrou que os tratamentos avaliados (desgaste, envelhecimento em autoclave) não promoveram efeitos deletérios, não resultando em maior variabilidade da resistência mecânica. Logo, não há indícios de que os diferentes tratamentos realizados impactem negativamente na resistência à flexão biaxial da Y-TZP. Adicionalmente, nota-se que as superfícies desgastadas com brocas diamantadas têm uma menor susceptibilidade à LTD (menor aumento de fase m).