The concentration of professional whitening agents, typically 2540% hydrogen peroxide, is dramatically higher than anything available over the counter, which is why professional treatment produces results that consumer products simply cannot match
Bak, Universit de Lorraine Mark Bernard, Carson-Newman College Larry Blades, Independent scholar Darrell Bourque, University of Louisiana, Lafayette Will Brantley, Middle Tennessee State University Robert Bray, Middle Tennessee State University Mary F
Majority of participants were aged 1517 years (68.3%), female (56.7%), Chinese ethnicity (93.8%), had qualifications above secondary education (55.8%) and were non-smokers (96.7%) and had experience of indoor passive smoking (78%)
In the modern era a frequently used metric in cost equivalence calculations is The Economists Big Mac index interactive currency-comparison tool [4]