CAM
Fatigue resistance of 1mm thickness CAD/CAM crowns: monolithic lithium disilicate, monolithic Leucite-based glass-ceramics and zirconia reinforced lithium silicate Mohanad Abumelha BDS, Anthony Randi DDS, Thomas Hill MSc,PhD, William Randi
Introduction Ceramic restorations have shown a high level of success as a restorative material1. The leucite-reinforced glass ceramic IPS Empress (Ivoclar-Vivadent) marketed since 1990 is indicated for inlays/onlays and anterior crowns. Recently, lithium disilicate and zirconia dominate the marketplace for ceramic restorative materials. Lithium disilicate with higher translucency, predictable ceramic layering and adhesion to resin cements make it an ideal restorative material in areas of low to moderate stress2,3. Conversely, zirconia with a modulus of elasticity of 210 Gpa and flexural strength of 1200Mpa make it an ideal material in regions of high occlusal load. However, zirconia demonstrates issues with ceramic layering and adhesive luting to resin cements2,3. There have been continuous efforts to improve physical and mechanical properties of ceramics. Minimally invasive prosthetic principles require the use of high strength ceramic materials which can be predictabley bonded to both enamel and dentin substrates. It has been demonstrated using CAD/CAM monothlithic ceramic restorations of 1mm thickness can withstand simulated occlusal stresses at high loads4. Zirconia reinforced lithium silicate is a new ceramic material recently introduced to the dental market. There are minimal published studies comparing fracture toughness, biaxial flexure strenthg and fatigue strength of CAD/CAM monolithic zirconia reinforced lithium silicate (both polished unfired and fired).
Purpose The purpose of this in vitro study is to investigate the fatigue resistance of CAD/CAM lithium disilicate (E.max,), monolithic Leucite-based glass-ceramic (IPS Empress) and zirconia reinforced lithium silicate (ZrLiSi) both polished and fired for 1 mm full contour crowns adhesively luted to composite resin abutments. • The first null hypothesis is that there is a difference between the ZrLiSi in the fired and unfired states for the fatigue test. • The second null hypothesis is that the fatigue test is different between the leucite and LiDi reinforced ceramics compared to the ZrLiSI glass ceramic.
Division of Post Graduate Prosthodontics, College of Dental Medicine, Columbia University, New York, NY Testing Materials and Methods SAMPLE FABRICATION: Ninety-six standardized maxillary molar crowns were CAD/CAM milled using three different materials(Table1); monolithic lithium disilicate [IPS e.max®CAD], monolithic Leucite-based glass-ceramics [IPS Empress®CAD] and zirconia reinforced lithium silicate [CELTRA® DUO (ZLS) Polished and Crystallized] then adhesively luted on CAD/CAM milled [Lava™ Ultimate] abutments using dual cure cement [Multilink® Automix] Fig2. Specimens were divided into 4 groups according to the material and each group was subdivided into 6 groups according to the applied force.
Fig.1: CAD/CAM resin nano-ceramic abutment
Results The fatigue resistance measurements revealed that the monolithic lithium disilicate was superior to zirconia reinforced lithium silicate and monolithic Leucite-based glass-ceramics respectively.
Wear Facet
Discussion
Crack Fig.5: Willytec chewing simulator
Fig.6:Post fatigue fractured CAD/CAM crown
Fig.2: Dual-cure resin cement
Results
Treatment of samples can lead to a high variability of results for fatigue test and biaxial flexural strength. Therefore, testing is indicative of material performance but not necessarily related to clinical success. Fracture toughness testing gives intrinsic value to the material to resist catastrophic failure therefore they are not subject to material treatment variables and deliver results that are clinically relevant. The results of this study confirm LiDi fracture toughness (2.2 K1C) meets ISO guidelines for single unit restoration while ZrLiSi (1.4 K1C) results fail to do so. The ZrLiSi uses 10% by weight zirconia oxide as a nucleating agent, the zirconia remains in solution and yields a dual microstructure. The primary difference between ZrLiSi and LiDi resides in the nature of the crystalline phase. Therefore the results of this study reveal no potential clinical advantages of the ZrLiSi compared to the LiDi. Results of this research demonstrate no advantage to firing the ZrLiSi versus polishing.
Conclusion
Fatigue Test 200000
• Monolithic CAD/CAM lithium disilicate demonstrate improved fracture fatigue compared to ZrLiSi (fired and polished) and leucite reinforced ceramics.
180000
Fig.3: Mounted CAD/CAM crown
Fig.4: CAD/CAM crown in Willytec chewing simulator
160000 140000
Material IPS Empress®CAD CELTRA® DUO (Fired) CELTRA® DUO (Unfired) IPS e.max®CAD
Ceramic composition Leucite-Glass-ceramics Zr Reinforced LiSi Zr Reinforced LiSi Lithium Disilicate
Manufacturer Ivoclar Vivadent Dentsply Dentsply Ivoclar Vivadent
Lot # L43354 1802683 18021683 W09477
Table(1): Tested materials
120000
• The first null hypothesis regarding the ZrLiSi polished and fired specimens was rejected.
100000 80000 60000
• The second null hypothesis regarding the LiDi and ZrLiSi samples was accepted.
40000 20000 0
37oC
All specimens stored at for 24h. Crowns were loaded applying an eccentric force in a Willytec chewing simulator Fig.4,5 (steel stylus, cusp to fossa movement) with stepwise decrease in load (23.3 , 21.3 , 19.3 , 17.3 , 15.3,13.3,11.3 and 9.3 kg, 200,000 cycles each, 0.8 Hz). A one-way ANOVA and Tukey’s post hoc test will be used, P>0.05 level of significance.
23.3
21.3
19.3 Empress
17.3 Celtra Unfired
15.3
13.3
Celtra Fired
11.3
9.3
E.max
Contrary to previously reported results, both the unfired and fired ZrLiSi revealed values that were not statistically significant (P
Introduction Ceramic restorations have shown a high level of success as a restorative material1. The leucite-reinforced glass ceramic IPS Empress (Ivoclar-Vivadent) marketed since 1990 is indicated for inlays/onlays and anterior crowns. Recently, lithium disilicate and zirconia dominate the marketplace for ceramic restorative materials. Lithium disilicate with higher translucency, predictable ceramic layering and adhesion to resin cements make it an ideal restorative material in areas of low to moderate stress2,3. Conversely, zirconia with a modulus of elasticity of 210 Gpa and flexural strength of 1200Mpa make it an ideal material in regions of high occlusal load. However, zirconia demonstrates issues with ceramic layering and adhesive luting to resin cements2,3. There have been continuous efforts to improve physical and mechanical properties of ceramics. Minimally invasive prosthetic principles require the use of high strength ceramic materials which can be predictabley bonded to both enamel and dentin substrates. It has been demonstrated using CAD/CAM monothlithic ceramic restorations of 1mm thickness can withstand simulated occlusal stresses at high loads4. Zirconia reinforced lithium silicate is a new ceramic material recently introduced to the dental market. There are minimal published studies comparing fracture toughness, biaxial flexure strenthg and fatigue strength of CAD/CAM monolithic zirconia reinforced lithium silicate (both polished unfired and fired).
Purpose The purpose of this in vitro study is to investigate the fatigue resistance of CAD/CAM lithium disilicate (E.max,), monolithic Leucite-based glass-ceramic (IPS Empress) and zirconia reinforced lithium silicate (ZrLiSi) both polished and fired for 1 mm full contour crowns adhesively luted to composite resin abutments. • The first null hypothesis is that there is a difference between the ZrLiSi in the fired and unfired states for the fatigue test. • The second null hypothesis is that the fatigue test is different between the leucite and LiDi reinforced ceramics compared to the ZrLiSI glass ceramic.
Division of Post Graduate Prosthodontics, College of Dental Medicine, Columbia University, New York, NY Testing Materials and Methods SAMPLE FABRICATION: Ninety-six standardized maxillary molar crowns were CAD/CAM milled using three different materials(Table1); monolithic lithium disilicate [IPS e.max®CAD], monolithic Leucite-based glass-ceramics [IPS Empress®CAD] and zirconia reinforced lithium silicate [CELTRA® DUO (ZLS) Polished and Crystallized] then adhesively luted on CAD/CAM milled [Lava™ Ultimate] abutments using dual cure cement [Multilink® Automix] Fig2. Specimens were divided into 4 groups according to the material and each group was subdivided into 6 groups according to the applied force.
Fig.1: CAD/CAM resin nano-ceramic abutment
Results The fatigue resistance measurements revealed that the monolithic lithium disilicate was superior to zirconia reinforced lithium silicate and monolithic Leucite-based glass-ceramics respectively.
Wear Facet
Discussion
Crack Fig.5: Willytec chewing simulator
Fig.6:Post fatigue fractured CAD/CAM crown
Fig.2: Dual-cure resin cement
Results
Treatment of samples can lead to a high variability of results for fatigue test and biaxial flexural strength. Therefore, testing is indicative of material performance but not necessarily related to clinical success. Fracture toughness testing gives intrinsic value to the material to resist catastrophic failure therefore they are not subject to material treatment variables and deliver results that are clinically relevant. The results of this study confirm LiDi fracture toughness (2.2 K1C) meets ISO guidelines for single unit restoration while ZrLiSi (1.4 K1C) results fail to do so. The ZrLiSi uses 10% by weight zirconia oxide as a nucleating agent, the zirconia remains in solution and yields a dual microstructure. The primary difference between ZrLiSi and LiDi resides in the nature of the crystalline phase. Therefore the results of this study reveal no potential clinical advantages of the ZrLiSi compared to the LiDi. Results of this research demonstrate no advantage to firing the ZrLiSi versus polishing.
Conclusion
Fatigue Test 200000
• Monolithic CAD/CAM lithium disilicate demonstrate improved fracture fatigue compared to ZrLiSi (fired and polished) and leucite reinforced ceramics.
180000
Fig.3: Mounted CAD/CAM crown
Fig.4: CAD/CAM crown in Willytec chewing simulator
160000 140000
Material IPS Empress®CAD CELTRA® DUO (Fired) CELTRA® DUO (Unfired) IPS e.max®CAD
Ceramic composition Leucite-Glass-ceramics Zr Reinforced LiSi Zr Reinforced LiSi Lithium Disilicate
Manufacturer Ivoclar Vivadent Dentsply Dentsply Ivoclar Vivadent
Lot # L43354 1802683 18021683 W09477
Table(1): Tested materials
120000
• The first null hypothesis regarding the ZrLiSi polished and fired specimens was rejected.
100000 80000 60000
• The second null hypothesis regarding the LiDi and ZrLiSi samples was accepted.
40000 20000 0
37oC
All specimens stored at for 24h. Crowns were loaded applying an eccentric force in a Willytec chewing simulator Fig.4,5 (steel stylus, cusp to fossa movement) with stepwise decrease in load (23.3 , 21.3 , 19.3 , 17.3 , 15.3,13.3,11.3 and 9.3 kg, 200,000 cycles each, 0.8 Hz). A one-way ANOVA and Tukey’s post hoc test will be used, P>0.05 level of significance.
23.3
21.3
19.3 Empress
17.3 Celtra Unfired
15.3
13.3
Celtra Fired
11.3
9.3
E.max
Contrary to previously reported results, both the unfired and fired ZrLiSi revealed values that were not statistically significant (P
