What percent relative humidity is preferred for strong impressions?

For obtaining strong impressions, a relative humidity of 100% is preferred because it minimizes dimensional changes in the impression materials. When the humidity is at this level, the moisture content in the air helps to maintain the properties of the impression material, thereby ensuring it captures details accurately without warping or drying out.

Higher humidity prevents the material from losing moisture, which can occur in lower humidity environments and negatively impact the impression's accuracy and stability. This is particularly important with certain materials that can be sensitive to changes in moisture and temperature, thus ensuring that the final model produced from the impression is as precise as possible.

The other options, which include lower percentages of humidity, can lead to issues such as shrinkage or distortion of the impression material, making the accuracy of the final dental restoration compromised. Hence, 100% relative humidity is ideal for achieving strong, reliable impressions.