Which of the following is NOT a cause of a midline diastema?

A midline diastema refers to a space or gap between the two upper front teeth (central incisors) and can have various causes.

When considering the causes of midline diastema, small teeth can contribute because if the teeth are smaller than the average size, the space between them can appear larger. Frenum attachment, particularly if the labial frenum extends low between the two incisors, can pull on the gum tissue and create or exacerbate a gap. Supernumerary teeth, or extra teeth, can lead to midline spacing as well, since these additional teeth may cause displacement or change the alignment of the central incisors.

In contrast, excessive dental plaque itself does not directly cause a diastema. While plaque can lead to periodontal issues and may contribute to recession that could indirectly alter tooth position, it is not a primary or direct cause of a midline diastema in the way that the other options can create space between the teeth. Therefore, excessive dental plaque is accurately identified as not being a cause of midline diastema.