If you are an employee of a dental firm, you would click on the income tab and scroll down to employment expenses. You will need to get a T2200 Conditions of employment form from your employer in support of your claim for travel expense. Uniforms are generally not deductible.
If you are a contract worker, you will be able to enter the income under self-employment, but clothing is still not deductible. Deductible items for self-employment are here: