First-degree | 1/3 dorsum of the tongue and thin |
Second-degree | 2/3 dorsum of the tongue and thin or 1/3 dorsum of the tongue and thick |
Third-degree | 2/3 or more dorsum of the tongue and thin or 2/3 dorsum of the tongue and thick |
Fourth-degree | 2/3 or more dorsum of the tongue and thick |