[1] Univ Amsterdam, Dept Periodontol, Amsterdam, Netherlands
[2] Vrije Univ, Acad Ctr Dent Amsterdam ACTA, Amsterdam, Netherlands
[3] Univ Michigan, Dept Oral & Maxillofacial Surg, Ann Arbor, MI USA
[4] Univ Michigan, Sch Dent, Dept Periodont & Oral Med, Ann Arbor, MI 48109 USA