Why use 有 in 只要前排的牙齿有脱落... about shark teeth?
"前排的牙齿脱落" means "the entire front row of teeth drops off"
前排的牙齿有脱落 is short for "前排的牙齿有脱落(的部分)" which
means "the front row of teeth has dropped off (parts)" 


脱落 in the second sentence is in effect a noun for "脱落(的部分)" - "dropped off (parts)"

If you don't want "前排的牙齿" to imply it is "the entire front row of teeth "  it  has to be changed to "前排有牙齿" (the front row has some teeth)

Unlike in English, Chinese language doesn't use verb tenses. For example, both 'is' and 'was'  is written as '是' in Chinese.