Restoring strength of incisors with veneers and full ceramic crowns.
OBJECTIVE
The aim was to determine the in vitro fracture resistance of incisors restored with veneers and full ceramic crowns compared to unrestored teeth.


METHODS
Seventy intact, extracted human maxillary central incisors were randomized and assigned to 7 groups (n = 10). The teeth in group 1 remained intact (control). The teeth in groups 2 to 6 were prepared and IPS Empress restorations were conditioned and bonded using an adhesive luting cement, Variolink II/Syntac (group 2: labial veneer with incisal overlap, group 3: 3/4 veneer with margin in enamel, group 4: 3/4 veneer with margin in dentin, group 5: crown with margin in enamel, group 6: crown with margin in dentin group 7: veneer on worn tooth. After finishing and polishing, specimens were stored in water and thermocycled for 2000 cycles between 5 degrees C and 55 degrees C. The maximal fracture load of the specimens (40-degree inclination) was determined using the universal testing machine (Zwick) at a constant crosshead speed (0.5 mm/min). The statistical analysis was performed using the Kruskal-Wallis test with Bonferroni correction (p < 0.05). Fracture surfaces were qualitatively analyzed by SEM.


RESULTS
All restored teeth with cervical preparation margins in enamel showed a fracture load not significantly different from the intact teeth (control). Restored teeth with cervical preparation margins in dentin showed a significantly lower fracture load. All restorations showed a fracture load far above 400 N, serving as functional reference for anterior teeth. The failures were predominantly cohesive.


CONCLUSIONS
For the restoration of tooth strength, defining the finishing lines of veneers and crowns in enamel is recommended. Restorations with finishing lines in dentin resulted in significant loss of strength. Three-quarter veneers with finishing lines in enamel are functionally equal to crowns with the advantage of conserving tooth structure.
Biologic and Materials Sciences, University of Michigan, Ann Arbor, MI 48108, USA. ychun@umich.edu
Yong-Hee P
YH
Chun
Constanze
C
Raffelt
Hanjo
H
Pfeiffer
Mozhgan
M
Bizhang
Gunnar
G
Saul
Uwe
U
Blunck
Jean-François
JF
Roulet
D000134:Acid Etching, Dental / Q000379:methods; D003442:Crowns; D001840:Dental Bonding; D003776:Dental Porcelain; D017267:Dental Prosthesis Design; D003793:Dental Restoration, Permanent / Q000379:methods; D003799:Dental Stress Analysis; D003801:Dental Veneers; D006801:Humans; D007180:Incisor; D019279:Resin Cements; D014082:Tooth Fractures / Q000517:prevention & control*; D019231:Tooth Preparation, Prosthodontic / Q000379:methods*
D019279:Resin Cements; D003776:Dental Porcelain