You definitely need to demonstrate basic mathematical skills, so not just addition, subtraction, multiplication and division, but an understanding of decimals and fractions.
As a dental assistant you will need to be able to stocktake and to know an understand the differences between cubic centimetres, millilitres, grams, micrograms and milligrams because you may be asked to measure out medications, fill syringes or just choose the correct size of syringe for any given task. You’ll also need to know that 1/4 is the same as 0.25 and that 1/2 is the same as 0.5, that 0.1 is the same as one-tenth and to understand which of those values is highest and which is lowest. Being able to add one-quarter to one-half is also important.
None of that is difficult: it’s all elementary level mathematics which you should be able to do accurately without a calculator but you may need to refresh yourself and practice it to gain (or to regain) confidence.