Understanding charged particle adhesion forces is a critical step in the understanding and modeling of electrophotographic printing processes. Electrostatic and mechanical (Van der Waals) forces are both significant contributors to toner adhesion to substrates, and previous work has shown these to have roughly equivalent magnitudes in modern printer designs. Measuring distributions of toner adhesion as a function of multiple parameters including environmental and toner charge variation has revealed that there are additional interactions beyond Coulombic Attraction and dipole induced London-Van der Waals' forces which are significant contributors to system performance. A model for toner adhesion is presented, including a term which describes the increased adhesion resulting from particle deformation at higher temperatures. Experimental results show good correlation to the model.