歯かす is sometimes used with the same meaning as 歯垢, but it is not commonly heard in everyday conversation.
Common mixed kanji-kana spelling; the kanji 歯 means 'tooth' and かす is kana for 'dregs'.
Rare kanji spelling using 滓 (dregs/lees); not commonly used in modern writing.
Compound of 歯 (tooth) and かす (dregs, lees), literally 'tooth dregs'. The kanji 滓 is a rare ateji for かす.