Objectives: To examine the effects of soft and hard occlusal splints in vitro on the cervical tooth area, while considering PDL-simulating medium and position of the splint (maxillary/mandibular).
Materials and methods: A morphological model of the first maxillary and mandibular molars was used. Strain gauges were bonded to the buccal and lingual aspects of the mandibular molar. Teeth were embedded in acrylic material, with and without root coverage by denture lining material (GC RELINE Soft) simulating the PDL. Teeth were placed in a special jig in Intercuspal Position. Four types of occlusal splints were adjusted: acrylic (hard) occlusal splints on the maxillary and mandibular teeth, and soft vacuum-formed (Mouthguard) maxillary and mandibular splints. Teeth were loaded via a loading machine up to 500N while acquiring strains as a function of force. Maximal strain, maximal bending strain and energy absorption values were determined.
Results: PDL uniformly influenced all models, regardless of splint material or position: PDL increased compressive strains and reduced tensile strains when these existed (hard, maxillary) compared to no-PDL. The presence of PDL-simulating material decreased the absolute buccal and lingual strains (40% and 20%, respectively, p<0.003). A 40% decrease in absolute energy absorption on both the lingual and buccal aspects (p < 0.001) and a 40% decrease in absolute developing bending strain (p<0.001) were found compared to no PDL. Soft splints significantly reduced all measured parameters (p<0.001). Increased bending strain was observed with maxillary splint placement (p<0.001).
Conclusions: PDL should be simulated in in vitro models. Although these findings do not consider the potential effect of splints on bruxism, the soft maxillary splint seems to offer maximal protection concerning cervical tooth strains.