Tooth-cusp preservation with lithium disilicate onlay restorations: A fatigue resistance study

Area of Science:

• Dental Materials Science
• Biomaterials Engineering
• Restorative Dentistry

Background:

• Maxillary premolars often require restoration due to extensive caries or fractures.
• Lithium disilicate ceramic onlays offer a conservative alternative to full coverage restorations.
• Understanding the in vitro fatigue resistance of these restorations is crucial for clinical longevity.

Purpose of the Study:

• To evaluate the in vitro fatigue resistance of maxillary premolars restored with lithium disilicate onlays.
• To compare the influence of preserved functional versus nonfunctional cusp thickness (2mm or 3mm) on restoration survival.
• To assess the effect of retentive preparation features on onlay debonding and fracture resistance.

Main Methods:

• Forty-eight maxillary premolars were restored with lithium disilicate onlays, varying cusp preservation and retentive features.
• Restorations underwent simulated aging via thermocycling (10,000 cycles) and mechanical loading (1.2 million cycles).
• Samples were evaluated for onlay debonding, cusp fracture, or onlay fracture.

Main Results:

• Failure rates varied significantly: 75% for 3mm functional cusp preservation, 0% for 2mm functional cusp preservation, and 12.5% for 3mm nonfunctional cusp preservation.
• No cusp or onlay fractures occurred; all failures were attributed to onlay debonding.
• Preserving functional cusps resulted in a statistically significant higher failure rate (37.5%) compared to nonfunctional cusps (6.3%).

Conclusions:

• Adhesively bonded lithium disilicate onlays can restore teeth with thin cusps without inducing fracture.
• Retentive preparation designs that prevent lateral displacement are critical for preventing onlay debonding, even with direct occlusal contact.
• These findings challenge traditional concepts of preparation resistance and retention form for ceramic partial coverage restorations.