Vectorial analysis of the equilibrium of forces transmitted to TMJ and Occlusal biteplane splints

SUMMARY A mechanical model (link quadrilateral bell crank) is used to demonstrate the equilibrium of normal force vectors transmitted to the masticatory system and maxillary occlusal biteplane splints with different designs. Occlusal contacts were imposed on the proposed models under the action of a masticatory force vector with an arbitrary value of 40 kgf. The consequence of this force action created different responses within the joint and at the level of the dentition. When compared to the intercuspal position in centric occlusion, intra-oral appliances with either smooth contacting surfaces or indentations, both with increased vertical dimension, forced the mandible to assume an anterior position with a con- current increase of joint forces. The bite-splint that produced the least amount of joint force was the stabilization type with minimal increase of vertical dimension.     

Retention of cast crown copings cemented to implant abutments

Background: The cementation of crowns to dental implant abutments is an accepted form of crown retention that requires consideration of the properties of available cements within the applied clinical context. Dental luting agents are exposed to a number of stressors that may reduce crown retention in vivo, not the least of which is occlusal loading. This study investigated the influence of compressive cyclic loading on the physical retention of cast crown copings cemented to implant abutments. Methods: Cast crown copings were cemented to Straumann synOcta titanium implant abutments with three different readily used and available cements. Specimens were placed in a humidifier, thermocycled and subjected to one of four quantities of compressive cyclic loading. The uniaxial tensile force required to remove the cast crown copings was then recorded. Results: The mean retention values for crown copings cemented with Panavia‐F cement were statistically significantly greater than both KetacCem and TempBond non‐eugenol cements at each compressive cyclic loading quantity. KetacCem and TempBond non‐eugenol cements produced relatively low mean retention values that were not statistically significantly different at each quantity of compressive cyclic loading. Compressive cyclic loading had a statistically significant effect on Panavia‐F specimens alone, but increased loading quantities produced no further statistically significant difference in mean retention. Conclusions: Within the limitations of the current in vitro conditions employed in this study, the retention of cast crown copings cemented to Straumann synOcta implant abutments with a resin, glass ionomer and temporary cement was significantly affected by cement type but not compressive cyclic loading. Resin cement is the cement of choice for the definitive non‐retrievable cementation of cast crown copings to Straumann synOcta implant abutments out of the three cements tested.