**Core Concept**
Filled sealants are a type of restorative material used in dentistry to prevent tooth decay and promote oral health. They consist of a resin matrix filled with silica or ceramic particles that provide additional mechanical properties. The main advantage of filled sealants is their ability to withstand the forces of mastication and resist wear and tear.

**Why the Correct Answer is Right**
The correct answer, low abrasion, is due to the presence of filler particles in filled sealants. These particles, typically made of silica or ceramic, help to reduce the coefficient of friction between the sealant and the tooth surface. As a result, filled sealants exhibit lower abrasion rates compared to unfilled sealants. This is because the filler particles act as a buffer, reducing the wear and tear on the sealant and the tooth surface. Additionally, the filler particles also help to improve the mechanical properties of the sealant, such as its compressive strength and durability.

**Why Each Wrong Option is Incorrect**
**Option A:** High viscosity is not the primary reason why filled sealants are better than unfilled sealants. While filled sealants may have a higher viscosity due to the presence of filler particles, this is not the main advantage of using filled sealants.

**Option B:** High strength is not a unique property of filled sealants. Unfilled sealants can also exhibit high strength, especially when cured properly. However, the high strength of unfilled sealants does not necessarily translate to better performance in the oral environment.

**Option C:** Cotton application is not related to the properties of filled sealants. Cotton is a separate material used in dentistry for various purposes, including as a base or as a means of applying sealants. The correct answer has nothing to do with cotton application.

**Clinical Pearl / High-Yield Fact**
When using filled sealants, it is essential to ensure that the filler particles are evenly distributed throughout the resin matrix. This can be achieved by using a suitable mixing technique and by following the manufacturer's instructions. Failure to do so may result in a sealant that is prone to cracking or debonding from the tooth surface.

**✓ Correct Answer: D. Low abrasion. Filled sealants exhibit lower abrasion rates compared to unfilled sealants due to the presence of filler particles that reduce the coefficient of friction between the sealant and the tooth surface.**