WPF datagrid - database not updating after cell change

(the underlines are for my benefit only.  It's hard to keep the data-thingy's straight)

I cannot get the database to update after a cell changed in a wpf datagrid. Can someone tell me what I'm doing wrong?

Code to set dataadapter and datatable:

cmd = New SqlCommand(sSelect, conn)
sda = New SqlDataAdapter(cmd)
dt = New DataTable("xxxx")
sda.Fill(dt)

Code to determine if cell changed and write back to database:

    Private Sub dgDentalAppointments_CellEditEnding(sender As Object, e As System.Windows.Controls.DataGridCellEditEndingEventArgs) Handles dgDentalAppointments.CellEditEnding

        'These 2 rows of code here and CurrentCellChanged borrowed from http://www.scottlogic.com/blog/2009/01/21/wpf-datagrid-committing-changes-cell-by-cell.html
        Dim rowView As DataRowView = TryCast(e.Row.Item, DataRowView)
        rowBeingEdited = rowView

        CommitEdit()

    End Sub

    Private Sub dgDentalAppointments_CurrentCellChanged(sender As Object, e As System.EventArgs) Handles dgDentalAppointments.CurrentCellChanged

        If rowBeingEdited IsNot Nothing AndAlso dgDentalAppointments.CurrentCell.Item IsNot rowBeingEdited Then
            rowBeingEdited.EndEdit()
        End If

    End Sub

    Private Sub CommitEdit()

        'code borrowed from http://codefluff.blogspot.com/2010/05/commiting-bound-cell-changes.html

        If Not isManualEditCommit Then
            isManualEditCommit = True

            dgDentalAppointments.CommitEdit(DataGridEditingUnit.Row, True)

            Dim Row As DataRow = dt.Rows(0)
            dt.AcceptChanges()


            Dim builder As SqlCommandBuilder = New SqlCommandBuilder(sda)

            sda.UpdateCommand = builder.GetUpdateCommand

            sda.Update(dt)

            isManualEditCommit = False
        End If

    End Sub

At this point, I'm trying to update existing rows in the database only.  I'll try adding and deleting rows when I get this figured out.

The datagrid is binding to the datatable successfully.

The datatable is being updated successfully.

I just can't get the database to update successfully.  I expect it to update at   sda.Update(dt)

Thanks for any help or advice.  Let me know if I need to post more code.

Kris Hood