Yes, samurai swords can become dull over time with regular use or if they are not properly maintained. The sharpness of a sword's blade depends on several factors, including the quality of the steel, the sharpness achieved during the initial forging, and how the sword is used and cared for.

Here are a few reasons why a samurai sword may become dull:

1. Wear and use: The act of cutting or striking objects, even under controlled training conditions, can gradually wear down the sharp edge of a sword. The repeated contact with targets can cause microscopic damage and blunting of the blade.
2. Improper technique: Using a sword with incorrect cutting angles or striking surfaces can result in increased friction and blunting. Proper technique, including maintaining the appropriate angle and avoiding hitting hard or unsuitable surfaces, can help preserve the sharpness of the blade.
3. Insufficient maintenance: Regular maintenance is essential for keeping a sword sharp. If a sword is not cleaned, oiled, and stored correctly, the blade can be exposed to moisture, rust, and other forms of corrosion. These factors can contribute to the dulling of the blade.
4. Normal wear and aging: Over time, even with proper care and maintenance, a sword's blade can naturally dull due to the wear and tear of use, the effects of oxidation, and changes in the structure of the steel.

To maintain the sharpness of a samurai sword, it is recommended to:

1. Clean the blade after use, removing any debris or residues.
2. Oil the blade regularly to prevent rust and corrosion.
3. Store the sword in a dry and controlled environment to avoid exposure to moisture.
4. Seek professional sharpening from a skilled swordsmith or a specialist in sword maintenance when needed.

Proper care and maintenance play a vital role in preserving the sharpness and longevity of a samurai sword. Regular inspection and professional maintenance can help ensure that the blade remains in optimal condition.