Regarding the taper of a crown preparation, which statement is true?

The assertion that a preparation with equal height and diameter will have decreased resistance with greater taper is based on the understanding of the relationship between taper, resistance, and the mechanics of crown retention.

Taper refers to the angled reduction of the tooth structure in relation to the long axis of the tooth. A crown preparation that has excessive taper tends to have less surface area for adhesion with the cement, which can lead to a reduction in resistance to dislodgement. This means that as the taper increases, the ability of the crown to resist forces that could dislodge it decreases. Therefore, for a preparation that maintains the same height and diameter, an increase in taper will indeed result in decreased resistance.

This is critical in dental practice, as achieving the appropriate balance of taper is essential to ensure that crowns can withstand the forces of biting and chewing without coming loose. This is why it is often emphasized in dental education and practice to maintain a controlled, minimal taper that provides sufficient resistance without compromising the strength of the crown retention.

Thus, this understanding clarifies the mechanics at play in the preparation of crowns and highlights why maintaining a careful taper is vital in crown design and application.