Foreword: Please beware that I ask this question only for mouthwash with NO alcohol whatsoever; so please omit alcoholic mouthwashes (which can cause cancer).
Since my grandmother continues to develop cavities, she twice daily brushes, flosses, then flosses again with interdental brushes, and concludes with a Crest mouthwash with 0 alcohol (see the footnote). She also abstains from any added sugar or sweeteners.
Question 1: How does saltwater compare with non-alcoholic mouthwash for daily lifelong use? Her dentist does not know of any relevant research, and only recommends saltwater for short-term use. So her dentist agrees with some of the claims here by Dentist David Kerr (B.DSc (Hons) BSc (Hons), University of Queensland).
Question 2: But is Dentist Kerr perfectly right in his criticism (of saltwater) below?
Longer term, the salt water is acidic, so there would be a problem if you were to use it every day, it could erode the teeth, but is not necessarily abrasive to the teeth. It is the acidity of the salt water that could eat away and soften the enamel on the teeth making them more susceptible to wearing, chipping and cavities.