What instrument is used to check that the floor of the cavity is caries free?

The spoon excavator is designed with a rounded, scooped end that effectively removes decayed tissue from the cavity while allowing the dental professional to assess the condition of the tooth structure beneath. When checking the floor of a cavity, the spoon excavator can be gently scraped along the surface to check for any remaining carious dentin.

In contrast, other instruments like the explorer are typically used to detect decay through probing and tactile feedback but are less effective for removing debris or confirming a caries-free state within the cavity. The dental probe serves similar functions, with a focus on measuring pocket depths in periodontal assessments and is not specifically tailored for examining cavity floors. The scalpel is mainly used for cutting soft tissues rather than for assessing the condition of tooth structures.

Thus, the spoon excavator is the most appropriate tool in determining whether the cavity floor is free of caries, making it the correct choice.