The frenum is a connective tissue membrane connecting one surface of the mouth to another. The three types of frena in the mouth are as follows: Lingual frenum – the vertical strip of thin tissue attaches the tongue to the bottom of the mouth. Labial frenum – a connective webbing that connects the lips to the gum above the top two front teeth and below the bottom two front teeth. Buccal frenum – thin threads of tissue linking the gums to the inside of the cheeks.