Different ideas are difficult to test in dental and medical fields because clinical trials on human beings are ethically limited. Many inspiring thoughts are, therefore, frequently ignored, that is, clinicians and researchers in those fields are generally conservative against the new ideas, and are dependent on traditional methods and opinions with long experience histories. However, such thoughts, ignored at present, may prove to be right, becoming major concepts or theories in the future. That is why some different viewpoints need to be reviewed. This book provides new perspectives and...