I don't mean to be blunt or dismissive, but the pressure in the veins/arteries has nothing to do with (a) the thickness/elasticity of the wall tissue, (b) the diameter of the arteries/veins, or (c) the number of (branches of) arteries/veins.
This can either be caused by a more prominent maxilla (upper jaw) or a retruded mandible (lower jaw further back than it should be). This causes a discrepancy in how all teeth contact, and can manifest as an increased overjet. An increased overjet can also be caused by a discrepancy in the number of teeth, or the length of the arch.
Possible causes of mitral valve regurgitation include: 1  Mitral valve prolapse. 2  Damaged tissue cords. 3  Rheumatic fever. 4  Endocarditis. 5  Heart attack. 6  Abnormality of the heart muscle (cardiomyopathy). 7  Trauma. 8  Congenital heart defects. 9  Certain drugs. 10  Radiation therapy.