Statement of the problem. Implant failure due to poor biomechanical behavior is a common
problem in dentistry. Occlusal overloading is considered the primary cause of peri-implantitis,
implant and\or prosthesis fracture, and screw loosening or fracture.
Purpose. The purpose of this study was to investigate the effect of different restorative crowns
on the fracture resistance and stress distribution in single implants.
Materials and Methods. One implant was anchored in a measurement model based on a
real-life patient situation simulating (D3) bone density. Strain gauges (SGs) were fixed mesially,
distally, lingual and buccally adjacent to the implant. A total of 20 crowns were produced using a
CAD\CAM machine and divided into two equal groups according to the material type; Zirconia
and (PEEK) (n=10). The magnitude of strain was recorded in microstrains (με). Each specimen was
loaded to fracture in a universal testing machine with a crosshead speed of 0.5 mm/min. Data were
analyzed with 2-way univariate ANOVA and Tukey HSD test (α=.05).
Results. The mean strain values for the two groups at the different (SG) sites ranged from (26.0
to 1033.6 μm/m). The 2-way univariate ANOVA indicated statistically significant differences (P
<0.001) between the zirconia and the (PEEK) crowns .In addition, Mean (SD) failure loads were
2070.5(100.24) N for zirconia crowns, 950.75(34.61) N for (PEEK) crowns. The 2-way univariate
ANOVA showed a statistically significant difference for the fracture resistance between the zirconia
and (PEEK) crowns (P< 0.001).
Conclusions: Superstructure materials appear to have an influence on strain development in
single implant restorations.