The effect of splinting implant-supported restorations on stress distribution of different crown-implant ratios and crown height spaces

Purpose: To assess whether splinting can counterbalance the detrimental effects of varying the crown-to-implant (C/I) ratio and crown height space (CHS) by decreasing nonaxial overload stresses. Materials and Methods: Three implants were inserted into a photoelastic block model. Two strain gauges were cemented onto the neck of each implant on the buccal and lingual aspects and provided a simultaneous direct reading of strain. Four groups of splinted cement-retained restorations with C/I ratios of 1:1, 1:1.5, 1:1.75, and 1:2 were used. CHSs were 10, 15, 17.5, and 20 mm, respectively. Fifteen static loadings were carried out simultaneously with 20-kg weights via a custom-built loading apparatus at 30° to the vertical axis. Results: Occlusal force application at 30° showed a statistically significant increase in both buccal (1,911.65 ± 110 vs 3,252.06 ± 150) and palatal (35.58 ± 7 vs 286.85 ± 15) microstrain values as the C/I ratio increased from 1:1 to 1:1.5 (P <.001). Force application at 30° in cases with C/I ratios of 1:1.75 and 1:2 resulted in fracture of the abutment screw followed by dislodgement of the crowns. Failures were noted at a CHS of 15 mm or greater. Conclusions: In this biomechanical mode, splinting does not prevent prosthetic failure when the CHS is 15 mm or greater. Vertical bone augmentation is highly recommended in cases with a CHS of 15 mm or greater.