So you have to find living skin -peoples and living teeth!

Why laboratory? In laboratories there is cells and micro stuff, to see under microscope. Or laboratory animals, which do not have human skin! hahaha

Also you have to ask a specific questions. This question is not serious.

Because the tests are different for the specific product you wanna see the result.

In laboratory you can make researches only in particular cells how they will react with particular substances under microscope. For example reacting with some pathogenic microorganism.

For skin results, you have to reed a lot researches made until now, to find out what scientists real experiments say about the specific product.

The scientific approach to understanding whether a natural extract or product has the desired effect no matter how it is applied (on skin, topically, by supplements, or specific diet or combined) is doing research and experimentation. Because a skin health is not only by topical care. It is depend most from what peoples eat. The pollution, the allergies. etc.

So all the factors are connected.

This involve testing as many volunteers as possible, always divided into 2 groups. The first group is treated with the particular natural extract, the second group are treated with nothing - (something which does not give result - a "placebo".)

These treatments have to be applied topically principally every day, may be several times, dependent on the desired effect, and for at least about 3 or longer, up to 6 months, it still depends on the concert problem of the skin and the drug for what purpose it is applied to the skin.

So in the end of the experiment, there is a conclusions in whether actually the plant, extract or the drug have the real desired effect. Also whether have any or some side effects and how long has to be applied, so the relevant problem or the desired result to be achieved.

I would also suggest that you conduct a systematic review on the active ingredients you want to test efficacy for- that will give you an idea of what research has been conducted and if they have proven efficacy- if not what were the issues. Don't re-invent the wheel.

Without clinical trial efficacy can't be ascertained.