**Core Concept**
The Chi-square test is a statistical method used to determine the independence of two categorical variables in a cross-tabulation. It assesses whether there is a significant association between the variables, which can be used to identify patterns or correlations. In the context of dental research, this test is often applied to analyze the relationship between various factors such as treatment outcomes, patient demographics, or disease prevalence.

**Why the Correct Answer is Right**
For the Chi-square test to be applicable, the cases must be mutually exclusive, meaning that each observation or data point belongs to only one category. This is crucial because the test relies on the assumption that the observed frequencies are independent and not influenced by any external factors. If the cases are not mutually exclusive, it can lead to biased or misleading results. The Chi-square test does not require equal numbers of cases (A) or normal distribution (C), as these are not necessary conditions for the test to be valid. Non-mutually exclusive cases (D) are actually a violation of the test's assumptions, making it an incorrect option.

**Why Each Wrong Option is Incorrect**
**Option A:** Equal number of cases is not a requirement for the Chi-square test. The test can be applied to datasets with varying numbers of cases, as long as the cases are mutually exclusive.

**Option C:** Normal distribution is not a prerequisite for the Chi-square test. The test is robust to non-normality and can be applied to categorical data, regardless of the distribution of the variables.

**Option D:** Non-mutually exclusive cases violate the test's assumptions and can lead to inaccurate or misleading results. This option is therefore incorrect.

**Clinical Pearl / High-Yield Fact**
When applying the Chi-square test, it's essential to ensure that the cases are mutually exclusive to avoid biased results. This can be achieved by carefully defining the categories and ensuring that each observation belongs to only one category.

✓ Correct Answer: B. Mutually exclusive cases