Effect of cavity design and material type on fracture resistance and failure pattern of molars restored by computer‑aided design/ computer‑aided manufacturing inlays/onlays

Abstract

Background: The maximum conservation of tooth structure and the use of restorative
materials with elastic modulus close to the dental structure may promote greater longevity of
the tooth/restoration complex. This study was conducted to evaluate the effect of cavity design
and material type on fracture resistance and failure pattern of molars restored by computer‑aided
design/computer‑aided manufacturing (CAD/CAM) inlays/onlays.
Materials and Methods: In this in vitro study, 55 human maxillary molars were embedded
in resin blocks and divided into control group (CG) and five main groups: Group 1: Inlay,
Group 2: Conventional onlay/mesiobuccal (MB), Group 3: Conservative onlay/MB, Group 4:
Conventional onlay/MB and distobuccal (DB), and Group 5: Conservative onlay/MB and
DB. Then, each group was divided into two subgroups: (A) CeraSmart (CS) and (B) Katana
Zirconia (KZ). Restorations were cemented by RelyX Ultimate and then thermocycled. The
universal testing machine was used to measure fracture loads. Failure was determined using
a magnifying lens. Data were statistically analyzed using ANOVA followed by Tukey’s post hoc
test (P < 0.05).
Results: Group 5 showed the highest significant fracture load, whereas the least significant value
was recorded in Group 2. KZ recorded higher significant fracture loads than CS in all tested groups.
Groups 1, 2, and 3 restored by CS showed lower fracture load than CG, but the difference was
insignificant with Group 1. CS restorations showed restorable failure, while unrestorable pattern
was predominant in KZ restorations (P < 0.05).
Conclusion: KZ inlays and onlays can be used safely in terms of fracture resistance as both
have values exceed the physiologic requirements. CS inlays and onlays/MB and DB are of fracture
resistance comparable to intact teeth. The use of conservative onlay design with more cusp coverage
guarantees better resistance of CS restorations. Being force absorbing material, the predominant
failure of teeth restored by CS was restorable.
Key Words: Ceramics, computer‑aided design, onlays