38. 1)All ionizing radiations are harmful and produce biologic changes in living tissue. 2)The amount of radiation used in dental radiography is small, but biologic damage does occur. a. Both statements are true b. Both statements are false c. The first statement is true; the second statement is false d. The first statement is false; the second statement is true A B C D 34. Which of the following statements is true regarding the direct theory of radiation injury? a. It involves absorption of an x-ray photon by water within a cell b. It involves the combination of free radicals to form toxins c. It involves a direct hit and absorption of an x-ray photon within a cell d. Both a b A B C D

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38. 1)All ionizing radiations are harmful and produce biologic changes in living tissue. 2)The amount of radiation used in dental radiography is small, but biologic damage does occur. a. Both statements are true b. Both statements are false c. The first statement is true; the second statement is false d. The first statement is false; the second statement is true A B C D 34. Which of the following statements is true regarding the direct theory of radiation injury? a. It involves absorption of an x-ray photon by water within a cell b. It involves the combination of free radicals to form toxins c. It involves a direct hit and absorption of an x-ray photon within a cell d. Both a b A B C D

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**38.** **A*** **Statement 1 is true:** All ionizing radiation, by its very nature, has the potential to cause biological changes. This is because ionizing radiation has enough energy to remove tightly bound electrons from atoms, creating ions and free radicals. These can damage DNA and other cellular structures.* **Statement 2 is true:** While the amount of radiation used in dental radiography is indeed small and the risks are low, it's important to acknowledge that some biological damage does occur, even at low doses. The principle of ALARA (As Low As Reasonably Achievable) is followed in dentistry to minimize this risk.**34. C**The direct theory of radiation injury proposes that cell damage results when ionizing radiation directly hits critical areas within the cell, such as DNA. Let's look at why the other options are incorrect:* **a. Incorrect:** Absorption of an x-ray photon by water within a cell describes the *indirect* theory of radiation injury, where the interaction produces free radicals that then damage the cell.* **b. Incorrect:** The combination of free radicals to form toxins is also part of the *indirect* theory.* **d. Incorrect:** Since 'a' and 'b' are incorrect, 'd' is also incorrect.

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