Researches proves that fruit juices markedly decreased hardness and increased roughness of tooth enamel.
The acid what juices contain is so strong that the tooth is literally washed away.  The orange juice decreased enamel hardness by 84 percent. No significant change in hardness or surface enamel was found for example from whitening.

Weakened and eroded enamel may speed up the wear of the tooth and increase the risk for tooth decay to quickly develop and spread.  Most soft drinks, including sodas and fruit juices, are acidic in nature. As an example orange juice, can potentially cause significant erosion of teeth.

It's long been known that juice and sodas have high acid content, and can negatively affect enamel hardness.
It's potentially a very serious problem for people who drink sodas and fruit juices daily.

 
Dentist  advises that consumers be aware of the acidic nature of beverages, including sodas, fruit juices, sports and energy drinks. The longer teeth are in contact with the acidic drinks, the more severe the erosion will be.  People who sip their drinks slowly over 20 minutes are more likely to have tooth erosion than those who finish a drink quickly. It's also very important to keep good oral hygiene practices,  brushing twice daily with fluoride toothpaste especially before going to bed , floss daily and see a dentist for a fluoride treatment at least once a year if you are at risk.