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No-- a torn mid-line frenulum would not affect the amount of tooth or gum tissue that normally shows with the lip at rest. If a frenulum is particularly short and thick, it can theoretically limit the range of motion of the lip, and the removal of the frenum may allow a slight amount of increased lip range of motion-- which is a good thing. In fact, a "frenulectomy"-- a surgical excision of the frenum--is sometimes intentionally performed if it creates a mechanical obstruction between the two upper central incisors
, and is sometimes implemented prior to orthodontic treatment. However, these virtues of frenulum removal are not relevant to your question.
A "gummy smile"-- i.e., a smile in which more than the usual amount of upper gum tissue shows during smiling, is due to one factor and one factor only: the length and position of the upper lip relative to the position of the gum lines of the upper incisors
. The presence or absence of a maxillary labial midline frenulum has no influence on this factor. What does influence it is the length of the lip and the positions of the teeth, and this is related to growth patterns that are variably linked to facial traits that run in families. It is not linked to the presence or absence of a frenulum.
It should be emphasized that because of the typically prominent upper jaws and short teeth in young children with primary teeth, gummy smiles are the rule rather than the exception, and do not have any predictive value when projecting what to expect in the adult dentition. The gumminess of the smile does tend to diminish as normal growth patters progress.
More importantly, your child's dentist should monitor those growth patterns and be vigilant for any hints of deviation from the norm, so that orthodontic or orthopedic intervention can be initiated if needed at an appropriate time. But the issue of a gummy smile is really a non-issue, and can be safely ignored.
Hope this helps...