Localised shrinkage porosity is seen when there is
**Core Concept**
Localised shrinkage porosity is a type of porosity that occurs in dental restorations due to the contraction of the restoration material during the setting process. This contraction creates shrinkage stresses that can lead to the formation of pores or voids in the restoration.
**Why the Correct Answer is Right**
Localised shrinkage porosity is a common issue in dental restorations, particularly in materials like composite resins. As the restoration material polymerises, it contracts and shrinks, creating stresses that can lead to the formation of pores. This type of porosity is characterised by the presence of small, localised pores or voids that can compromise the integrity of the restoration. The formation of localised shrinkage porosity is often influenced by factors such as the type of restoration material, the thickness of the restoration, and the presence of any surface irregularities.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe localised shrinkage porosity.
* **Option B:** This option is incorrect because it does not specify the type of porosity being referred to.
* **Option C:** This option is incorrect because it describes a different type of porosity.
**Clinical Pearl / High-Yield Fact**
To minimise the risk of localised shrinkage porosity, dentists should use restoration materials that have a low shrinkage rate, and should also use techniques such as incremental filling and use of a matrix system to help control the shrinkage stresses.
**Correct Answer: D.**