Update Textbox values in sql

No. The easiest way is to use the Tag property. Set all of your textboxes Tags to either a false, or the starting string, and then:
If you use the Tag as a bool, handle the Textboxes.TextChanged Event and set them all to the same method:

private void MyTextBoxes_TextChanged(object sender, EventArgs e)
    {
    TextBox tb = sender as TextBox;
    if (tb != null)
        {
        tb.Tag = true;
        }
    }

You can then look at the tags when you save and decide if it needs to be updated.

If you use a string, then just compare the current value against the Tag value and only save if different.

Why are you using 50 textboxes? Wouldn't a grid of some form be a better solution?