A two-year clinical trial of enamel wear opposing 5Y-TZP and lithium disilicate crowns.

Statement Of Problem: Clinical information on enamel wear opposing 5 mol% yttria-stabilized tetragonal zirconia polycrystal (5Y-TZP) or lithium disilicate crowns is lacking. Moreover, the effect of surface roughness on the wear of enamel antagonists remains unclear.

Purpose: The purpose of this clinical study was to quantify the vertical wear and total volume of wear while also measuring the surface roughness of antagonists at 6-month intervals over 2 years.

Material And Methods: A tooth-supported first molar 5Y-TZP Lava Esthetic Fluorescent Zirconia crown or an IPS e.max CAD lithium disilicate crown was randomly provided for 24 participants (n=12). The contralateral first molar and opposite teeth were the natural enamel controls. The crowns were fabricated using computer-aided design and computer-aided manufacturing (CAD-CAM) technology and then polished. The data were gathered every 6 months at recall appointments with an intraoral scanner and a polyvinyl siloxane impression. A 3-dimensional (3D) comparative software program was used to measure the maximum vertical and volume loss on opposing enamel, as well as on the enamel control on the opposite side of the mouth. The surface of epoxy resin replicas was analyzed using a scanning electron microscope. The surface roughness of the cusp replica was measured with a 3D laser microscope. The crown's antagonist enamel and natural enamel wear were compared using a 2-way repeated measure ANOVA (α=.05).

Results: No significant difference was found in the average volume loss between the crown's antagonist enamel (ZTE 0.042 ±0.005 mm, LTE 0.048 ±0.006 mm) and the enamel control (ZCE 0.046 ±0.004 mm, LCE 0.050 ±0.005 mm) (P>.05). No significant difference was found in surface roughness between the crown's antagonist enamel (antagonist enamel of zirconia group [ZTE] 0.7 ±0.3 µm, antagonist enamel of lithium disilicate group [LTE] 0.6 ±0.3 µm) and the enamel control (enamel control of zirconia group [ZCE] 0.7 ±0.3 µm, enamel control of lithium disilicate group [LCE] 0.5 ±0.2 µm) in both zirconia and lithium disilicate groups (P>.05). Also, no correlation was found between the amount of wear and the roughness of the surface. The wear patterns observed on the opposing enamel surfaces of the monolithic zirconia and lithium disilicate materials were found to be similar to those seen on natural enamel.

Conclusions: A 2-year clinical investigation found that polished lithium disilicate and 5Y-TZP crowns did not affect enamel wear more than enamel against enamel, contrary to laboratory studies. Another finding revealed that surface roughness did not significantly affect wear.