Bruxism is excessive grinding of the teeth or clenching of the jaw. It can lead to tooth wear, tooth mobility, hypersensitivity, aching jaw muscles, and headaches. Occlusal splints, commonly called bite guards, can be prescribed to reduce wear on teeth. In a clinical study of occlusal splints in the treatment of childhood bruxism, Restrepo et. al. used a nondimensional measure called the D factor (the ratio of the square root of the area to the perimeter) to evaluate the form of dental wear. The 32 subjects ranged in age from three to six years old. The researchers randomly assigned 19 and 13 children to the experimental and control groups, respectively. Assume that the researchers randomly recruited all subjects from a population with a normally distributed D factor. Because they drew all subjects from the same population, the researchers assumed that the variances would be equal for each group. The mean baseline D factor for the experimental group was 13.35 ; the mean baseline D factor for the control group was 10.91 . For each group, the sample standard deviation of the D factor was 2.51 . Select the appropriate distribution to test for the difference between the two means.