The phrase "addition to their substantive" is not correct in English.
Did you mean "in addition to their substantive"? You can use the corrected phrase when you want to indicate that something is being added to what is already considered substantive or significant.
Example: "In addition to their substantive contributions, the team also provided valuable insights during the project."
Alternatives: "besides their substantive" or "along with their substantive".
However, it was never assessed whether absorption of antibacterial agents in plaque could substantially contribute to the observed substantive effects in addition to their adsorption to oral surfaces.
Voters who care about restoring our prestige and influence internationally have serious, substantive disagreements with Trump (in addition to their legitimate concerns about his ignorance and erratic temperament) that will persist.
That's in addition to their tithe.
In addition to contributing their substantive knowledge, librarians would have an opportunity to develop a language and a system that reflect how they think about and look for information.
In addition to expanding their substantive knowledge of the field through a classroom component, students gain valuable experience through researching labor and employment law topics and providing advice and representation to unions.
In addition to the substantive content, there's clearly a tactical angle here: Mr McCain is trying to regain some of his squandered "maverick" credentials.
In addition to that substantive problem, there's a crisis of appearances here as well: Ailes is negotiating and issuing statements to protect Kelly, the host that Fox News promotes as an intrepid, thick-skinned cable brawler.
In addition to covering substantive areas of environmental law, Clinic seminars help students master the tools of effective environmental advocacy, including the abilities to research law and science, write and cite persuasively, navigate environmental organizations, and manage projects cooperatively.
In addition to its substantive content, the real value of this book to the researcher is its extensive bibliography of English-language sources, including books and scholarly articles, for each jurisdiction/legal system it covers.
