The words dents, dense sound the same but have different meanings and spellings. Why do dents, dense sound the same even though they are completely different words?
The answer is simple: dents, dense are homophones of the English language.
Slow to apprehend; thickheaded.
Having relatively high density.
Crowded closely together; compact: a dense population.
Hard to penetrate; thick: a dense jungle.
Plural form of dent.
Third-person singular simple present indicative form of dent.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.