What appearance does a "reverse smile line" indicate on a radiograph?

A "reverse smile line" on a radiograph typically indicates that the chin is tipped up during the exposure. This causes the occlusal plane of the teeth to appear concave or inverted, resembling a smile that is upside down. When the chin is tipped up, the maxillary teeth can appear elongated, while the mandibular teeth may be foreshortened, resulting in this distinctive radiographic feature.

In contrast, when the chin is tipped down, the radiograph would often show a more natural or positive smile line, where the occlusal plane appears straight or convex. Similarly, positioning the teeth too far back or too far forward on the bite-block would lead to distortion or other positioning errors rather than creating a reverse smile line specifically. Understanding the relationship between head positioning and the resultant appearance on radiographs is crucial for accurate interpretation and for ensuring optimal radiographic quality.