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 degrees to the vertical axis. Results: Occlusal force application at 30 degrees 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. (C) 2011 American Association of Oral and Maxillofacial Surgeons J Oral Maxillofac Surg 69: 2990-2994, 2011