How to manage open and close connections of SqlHelper class

Question

I am managing a code and when i had a code walkthrough i found that in many places SqlHelper class was used and i have a question regarding that. In many places connection.open() and connection.close() was not used, i am concerned as not closing connection explicitly might cause some issue in application. Should connection.close() be explicitly mentioned wherever sqlhelper is used?

SqlHelper.ExecuteNonQuery()
SqlHelper.Reader()
SqlHelper.Scalar()
SqlHelper.ExecuteDataSet()

With the above methods should i close connections explicitly?