Factors affecting fracture of zirconia dental crowns : Laboratory studies on retrievals and crown-shaped specimens

Objektiv: De siste 20 årene har bruken av zirkonia som dentalt materiale har økt betydelig. Laboratorietester som undersøker materialstyrke, indikerer at de tilgjengelige zirkonia-materialene har tilstrekkelige mekaniske egenskaper til å tolerere klinisk bruk. Imidlertid, kliniske studier viser at zirkonia-baserte kroner svikter grunnet totalfraktur og mindre avskallinger. Det er lite informasjon tilgjengelig om den underliggende årsaken og mulige faktorer som påvirker en kronefraktur. Mål: Hovedmålet med denne oppgaven var å undersøke frakturdetaljer hos klinisk knekte zirkonia-baserte kroner og å identifisere faktorer som kan påvirke fraktur hos zirkonia-baserte kroner. Materialer og metoder: Klinisk knekte zirkonia-baserte kroner ble levert/sendt inn av allmenntannleger og undersøkt vha fraktografisk metode. I to laboratoriestudier ble det undersøkt hvordan ulike faktorer som kronematerialtykkelse, preparasjonstype, produksjonsmetode, materialsammensetning og aldringsprosedyrer påvirket bruddverdi ved belastning hos zirkonium-kroner. Konklusjoner: Fraktografisk analyse viste at de fleste knekte kronene hadde frakturstart ved kronekanten. Dette indikerer at kronekanten hos zirkonia-baserte kroner er utsatt for forhøyet belastning. Materialtykkelse og sammensetning hadde effekt på bruddverdien til zirkonia-baserte kroner. Aldringsprosedyrer som simulerte kortvarig klinisk bruk påvirket ikke bruddverdier, uavhengig av materialsammensetning.Objective: The use of zirconia material in dental use has increased significantly over the last 20 years. Laboratory tests that examine material strength and toughness indicate that the available zirconia materials have sufficient mechanical properties to tolerate clinical use. However, clinical studies show that zirconia-based crowns fail due to mechanical failure such as fracture and chipping. There is little information available on the underlaying cause and possible factors affecting a crown fracture. Aim: The main aim of this thesis was to examine fracture details of zirconia-based crowns fractured during clinical use and to identify factors that could affect fracture of zirconia dental crowns. Material and methods: A convenience sample of clinically fractured zirconia-based crowns submitted by general dentists were analyzed by fractographic method. Two laboratory studies assessed how different factors such as crown material thickness, preparation type, production method, material composition and aging procedures affected load at fracture for zirconia crowns. Conclusions: Fractographic analysis showed that most fractured crowns had fracture origin at the crown margin and thus indicating an area of increased load during clinical use. Zirconia material thickness and material composition had an effect on load at fracture. However, aging procedures simulating short-term clinical use did not affect the load at fracture values, regardless of material composition.Doktorgradsavhandlin

Effect of margin design on fracture load of zirconia crowns

Zirconia‐based restorations are showing an increase as the clinicians’ preferred choice at posterior sites because of the strength and esthetic properties of such restorations. However, all‐ceramic restorations fracture at higher rates than do metal‐based restorations. Margin design is one of several factors that can affect the fracture strength of all‐ceramic restorations. The aim of this study was to assess the effect of preparation and crown margin design on fracture resistance. Four groups of bilayer zirconia crowns (with 10 crowns in each group) were produced by hard‐ or soft‐machining technique, with the following four different margin designs: chamfer preparation (control); slice preparation; slice preparation with an additional cervical collar of 0.7 mm thickness; and reduced occlusal thickness (to 0.4 mm) on slice preparation with an additional cervical collar of 0.7 mm thickness. Additionally, 10 hard‐machined crowns with slice preparation were veneered and glazed with feldspathic porcelain. In total, 90 crowns were loaded centrally in the occlusal fossa until fracture. The load at fracture was higher than clinically relevant mastication loads for all preparation and margin designs. The crowns on a chamfer preparation fractured at higher loads compared with crowns on a slice preparation. An additional cervical collar increased load at fracture for hard‐machined crowns.publishedVersio

Fractographic analysis of 35 clinically fractured bi-layered and monolithic zirconia crowns

Objectives The aim of this retrieval study was to analyze the fracture features and identify the fracture origin of zirconia-based single crowns that failed during clinical use. Methods Thirty-five fractured single crowns were retrieved from dental practices (bi-layered, n = 15; monolithic, n = 20). These were analyzed according to fractographic procedures by optical and scanning electron microscopy to identify fracture patterns and fracture origins. The fracture origins were closely examined. The crown margin thickness and axial wall height were measured. Results Three types of failure modes were observed: total fractures, marginal semilunar fractures, and incisal chippings. Most of the crowns (23) had fracture origins at the crown margin and seven of them had defects in the fracture origin area. The exact fracture origin was not possible to identify due to missing parts in four crowns. The crown wall thickness was 20% thinner and wall height 30% shorter in the fracture origin area compared to the opposite side. Conclusions The findings in this study show that fractography can reveal fracture origins and fracture modes of both monolithic and bi-layered dental zirconia. The findings indicate that the crown margin on the shortest axial wall is the most common fracture origin site. Clinical significance Crown design factors such as material thickness at the margin, axial wall height and preparation type affects the risk of fracture. It is important to ensure that the crown margins are even and flawless.publishedVersio

Passform hos dentale kroner av ulike zirkonia materialer. En laboratoriestudie

Objective: All-ceramic restorations are becoming more common in prosthetic treatment. The material composition of the ceramics provides different properties in terms of strength, aesthetics, translucency. The aim of the study was to assess whether the variation in material composition and production methods affects the internal fit of monolithic zirconia crowns. The null hypothesis was that different material compositions and production methods will not affect the internal fit, given that all other factors such as preparation type, crown shape and crown thickness are the same. Material and methods: Sixty-six zirconia crowns were produced from five different commercial manufacturers to a premolar model tooth with shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. Results: There was a statistically significant difference in the occlusal internal fit values for the different groups (Kruskall Wallis, p = 0.0003). The soft machined crowns in three groups (BX, DD and ZZ) had a thicker occlusal cement space than all the other groups. There was no statistically significant difference in marginal and axial internal fit values among the different groups. Conclusion: The production method for monolithic zirconia crowns has an effect on internal fit. The largest variation was observed occlusally in soft machined crowns. Excess occlusal cement accumulation leads to increased axial discrepancy which can further give both technical and biological effect. Material composition did not had a clear correlation with the internal fit of the tested zirconia crowns

Factors affecting fracture of zirconia dental crowns : Laboratory studies on retrievals and crown-shaped specimens

Objektiv: De siste 20 årene har bruken av zirkonia som dentalt materiale har økt betydelig. Laboratorietester som undersøker materialstyrke, indikerer at de tilgjengelige zirkonia-materialene har tilstrekkelige mekaniske egenskaper til å tolerere klinisk bruk. Imidlertid, kliniske studier viser at zirkonia-baserte kroner svikter grunnet totalfraktur og mindre avskallinger. Det er lite informasjon tilgjengelig om den underliggende årsaken og mulige faktorer som påvirker en kronefraktur. Mål: Hovedmålet med denne oppgaven var å undersøke frakturdetaljer hos klinisk knekte zirkonia-baserte kroner og å identifisere faktorer som kan påvirke fraktur hos zirkonia-baserte kroner. Materialer og metoder: Klinisk knekte zirkonia-baserte kroner ble levert/sendt inn av allmenntannleger og undersøkt vha fraktografisk metode. I to laboratoriestudier ble det undersøkt hvordan ulike faktorer som kronematerialtykkelse, preparasjonstype, produksjonsmetode, materialsammensetning og aldringsprosedyrer påvirket bruddverdi ved belastning hos zirkonium-kroner. Konklusjoner: Fraktografisk analyse viste at de fleste knekte kronene hadde frakturstart ved kronekanten. Dette indikerer at kronekanten hos zirkonia-baserte kroner er utsatt for forhøyet belastning. Materialtykkelse og sammensetning hadde effekt på bruddverdien til zirkonia-baserte kroner. Aldringsprosedyrer som simulerte kortvarig klinisk bruk påvirket ikke bruddverdier, uavhengig av materialsammensetning

Internal fit in dental crowns of various zirconia materials.

Objective: All-ceramic restorations are becoming more common in prosthetic treatment. The material composition of the ceramics provides different properties in terms of strength, aesthetics, translucency. The aim of the study was to assess whether the variation in material composition and production methods affects the internal fit of monolithic zirconia crowns. The null hypothesis was that different material compositions and production methods will not affect the internal fit, given that all other factors such as preparation type, crown shape and crown thickness are the same. Material and methods: Sixty-six zirconia crowns were produced from five different commercial manufacturers to a premolar model tooth with shallow circumferential chamfer preparation. Internal fit was assessed by the replica method. Results: There was a statistically significant difference in the occlusal internal fit values for the different groups (Kruskall Wallis, p = 0.0003). The soft machined crowns in three groups (BX, DD and ZZ) had a thicker occlusal cement space than all the other groups. There was no statistically significant difference in marginal and axial internal fit values among the different groups. Conclusion: The production method for monolithic zirconia crowns has an effect on internal fit. The largest variation was observed occlusally in soft machined crowns. Excess occlusal cement accumulation leads to increased axial discrepancy which can further give both technical and biological effect. Material composition did not had a clear correlation with the internal fit of the tested zirconia crowns.Bakgrunn: Helkeramiske restaureringer blir stadig vanligere innen protetisk behandling. Materialsammensetningen til keramene gir ulike egenskaper i form av styrke, estetikk, gjennomskinnelighetsgrad noe som videre indikerer ulike anvendelsesområder. Formålet med studien var å vurdere om variasjon i materialsammensetning og produksjonsmetode påvirker monolitiske zirkoniakroners indre passformen. Nullhypotesen er at ulik materialsammensetning og produksjonsmetode ikke vil påvirke indre passform, gitt at alle andre faktorer som prepareringstype, kroneform og kronetykkelse er det samme. Material og metode: Det ble fremstilt sekstiseks zirkonia kroner fra fem ulike produsenter etter en premolar-modelltann med konkav preparering. Indre passform ble undersøkt med replika – metoden. Resultat: Det var statistisk signifikant forskjell i indre passform verdiene okklusalt for de ulike gruppene (Kruskall Wallis, p=0.0003). De mykmaskinerte materialene BX, DD og ZZ hadde tykkere okklusal sementspalte enn alle de andre gruppene. Det var ingen statistisk signifikant forskjell ved indre passform verdiene marginalt eller aksialt blant de ulike gruppene. Konklusjon: Produksjonsmetoden for monolitiske zirkoniakroner har en effekt på passform. Størst variasjon ble observert okklusalt på mykmaskinerte kroner. Opphoping av sement okklusalt fører til økt aksial diskrepans noe som videre kan ha både teknisk og biologisk effekt. Materialsammensetning hadde ikke en klar sammenheng med passformen til de testede zirkonia kronene.Prosjektoppgave / Integrert masteroppgaveOD3PROS

Effect of margin design on fracture load of zirconia crowns

Zirconia‐based restorations are showing an increase as the clinicians’ preferred choice at posterior sites because of the strength and esthetic properties of such restorations. However, all‐ceramic restorations fracture at higher rates than do metal‐based restorations. Margin design is one of several factors that can affect the fracture strength of all‐ceramic restorations. The aim of this study was to assess the effect of preparation and crown margin design on fracture resistance. Four groups of bilayer zirconia crowns (with 10 crowns in each group) were produced by hard‐ or soft‐machining technique, with the following four different margin designs: chamfer preparation (control); slice preparation; slice preparation with an additional cervical collar of 0.7 mm thickness; and reduced occlusal thickness (to 0.4 mm) on slice preparation with an additional cervical collar of 0.7 mm thickness. Additionally, 10 hard‐machined crowns with slice preparation were veneered and glazed with feldspathic porcelain. In total, 90 crowns were loaded centrally in the occlusal fossa until fracture. The load at fracture was higher than clinically relevant mastication loads for all preparation and margin designs. The crowns on a chamfer preparation fractured at higher loads compared with crowns on a slice preparation. An additional cervical collar increased load at fracture for hard‐machined crowns

Effect of cementation techniques on fracture load of monolithic zirconia crowns

The aim of this study was to evaluate the effect of cement on the fracture load of monolithic zirconia crowns with different yttria content (3 and 5mol%). A total of 62 monolithic zirconia crowns, 40 3Y-zirconia crowns (Prettau®Zirconia, Zirkonzahn) and 22 5Y-zirconia crowns (Prettau® 4 Anterior®, Zirkonzahn) were produced to a shallow chamfer molar preparation. The 3Y-crowns were divided into four groups and attached to composite abutment duplicates (SDR® flow+, Dentsply DeTrey GmbH) using the following four cementation techniques; 1: Self-adhesive resin-based cement, 2: Pre-treatment with air-abrasion and self-adhesive resin-based cement, 3: Zinc phosphate cement 4: Glass-ionomer cement. The 5Y-crowns were divided into two groups and attached to the duplicates with; 1: Self-adhesive resin-based cement, or 2: Air-abrasion pre-treatment and self-adhesive resin-based cement. All crowns were loaded axially (0.5mm/min) on the occlusal surface until fracture occurred. Among the 3Y-zirconia groups, the zinc phosphate cement group fractured at lower loads compared to the resin-based cement groups, with and without air-abrasion, (

Fractographic analysis of 35 clinically fractured bi-layered and monolithic zirconia crowns

Objectives The aim of this retrieval study was to analyze the fracture features and identify the fracture origin of zirconia-based single crowns that failed during clinical use. Methods Thirty-five fractured single crowns were retrieved from dental practices (bi-layered, n = 15; monolithic, n = 20). These were analyzed according to fractographic procedures by optical and scanning electron microscopy to identify fracture patterns and fracture origins. The fracture origins were closely examined. The crown margin thickness and axial wall height were measured. Results Three types of failure modes were observed: total fractures, marginal semilunar fractures, and incisal chippings. Most of the crowns (23) had fracture origins at the crown margin and seven of them had defects in the fracture origin area. The exact fracture origin was not possible to identify due to missing parts in four crowns. The crown wall thickness was 20% thinner and wall height 30% shorter in the fracture origin area compared to the opposite side. Conclusions The findings in this study show that fractography can reveal fracture origins and fracture modes of both monolithic and bi-layered dental zirconia. The findings indicate that the crown margin on the shortest axial wall is the most common fracture origin site. Clinical significance Crown design factors such as material thickness at the margin, axial wall height and preparation type affects the risk of fracture. It is important to ensure that the crown margins are even and flawless