Final answer:
The first sign of gingival over-extension when placing a temporary crown is usually gum inflammation, leading to swelling, discomfort, and potentially bleeding if not addressed promptly.
Step-by-step explanation:
The first sign of gingival over-extension when placing a temporary crown can often be inflammation of the gums. This may occur if the margin of the temporary crown extends too deep beneath the gumline, irritating the surrounding soft tissues. Symptoms may include gum swelling, discomfort, or changes in color. If left unaddressed, this could progress to more severe issues, such as gum erosion or bleeding. Early intervention is crucial to prevent further complications like infection or damage to the periodontal tissues.