Abstract
The objective of this study is to investigate the influence of veneering technique (hand-layering vs. milling) on the fracture resistance of bi-layer implant-supported zirconia-based hybrid-abutment crowns. Mandibular molar copings were anatomically designed and milled. Copings were then veneered by hand-layering (HL) (n = 20) and milling using the Cad-On technique (LD) (n = 20). Crowns were cemented to zirconia hybrid-abutments. Ten samples of each group acted as a control while the remaining ten samples were subjected to fatigue in a chewing simulator. Crowns were loaded between 50 and 100 N for 1.2 million cycles under simultaneous temperature fluctuation between 5 and 55 °C. Crowns were then subjected to static load a to fracture test. Data were statistically analysed using the one-way ANOVA. Randomly selected crowns from each group were observed under scanning electron microscopy to view fractured surfaces. Study results indicate that during fatigue, LD crowns had a 100% survival rate; while HL crowns had a 50% failure rate. Fracture resistance of LD crowns was statistically significantly higher than that of HL crowns at the baseline and after fatigue (p ≤ 0.05). However, fatigue did not cause a statistically significant reduction in fracture resistance in both LD and HL groups (p > 0.05). Copings fractured in the LD crowns only and the fracture path was different in both LD and HL groups. According to the results, it was concluded that milled veneer implant-supported hybrid-abutment crowns exhibit significantly higher fracture resistance, and better withstand clinical masticatory loads in the posterior region compared to the hand-layered technique. Also, fatigue application and artificial aging caused no significant strength reduction in both techniques. Clinical significance: Different veneering techniques and materials (hand-layering or milling) act differently to clinical forces and environment and may be prone to early chipping during service. Therefore, practitioners are urged to consider the appropriate veneering protocol for posterior implant-supported hybrid-abutment restorations.
Highlights
Being the toughest of all dental ceramics [1], zirconium dioxide has been in clinical use for over 10 years
This study aimed to evaluate the fracture resistance and post fatigue fracture load of zirconia copings veneered with computer aided design/computer aided manufacturing (CAD/CAM) milled lithium disilicate structures compared to hand-layered veneered copings when
Such significant difference in fracture load values between both veneering techniques might be due to differences in both veneering materials and fabrication techniques used; while a lithium disilicate veneer has a flexural strength of 360 MPa, the veneering ceramic used in the hand-layering technique has a flexural strength of 90 MPa making the later more prone to failure at low loads during mastication [53]
Summary
Being the toughest of all dental ceramics [1], zirconium dioxide has been in clinical use for over 10 years. It is reported that the fracture resistance of a hybrid-abutment all-ceramic crown is influenced by the crown’s structure (monolithic vs bi-layered) [32], crown’s material [32] and the abutment’s material, manufacturer and design [33]. Elshiyab et al [34,35] studied the influence of ageing on implant-supported crowns fabricated from zirconia and lithium disilicate and cemented to hybrid abutments. They reported a good performance of this implant-abutment design with no fracture for any of its components. This study aimed to evaluate the fracture resistance and post fatigue fracture load of zirconia copings veneered with CAD/CAM milled lithium disilicate structures compared to hand-layered veneered copings when. Wlitehihuympodthiseisliicsaetdetcheartaimmipclawnot-usludpepxohritbedit hsiymbirliadr-asbuurvtmiveanbtilictryowasnswveellneaesrefdracwtuitrhe mloialldesd tloithfaiuilmuredicsoilmicpataerecdertaomhicybwriodu-ladbuetxmheibnitt csrimowilnars svuernveievraebdilbityyhaasnwde-llalyaesrferdacntaunreo-lfoluadorsatpoaftaitielucreeracommicp. aWreedatlosohhyybpriodt-haebsuistemdetnhtactrfoawtignusevetenseteinregdinbya hsiamndu-lalatyedereodranl aennov-iflrounomraepnattiwteocuelrdamnoict. sWigenaifliscoanhtylypoatfhfeecsitsferdactthuartefalotiagduseftoerstcirnogwinnsa msimaduelaintedeitohrearl etencvhinroiqnumee. nt would not significantly affect fracture loads for crowns made in either technique
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