Handpiece size /Back of 3rd molar repair accessr?

A have a cavity located on the back surface of a third molar in my mandible.  A sideways impacted wisdom tooth was removed, and the cavity is located down - bordering or possibly under where the gumline will heal to.  

The tooth is healthy, and the oral surgeon said my regular dentist should just put a filling in.  But my dentist says that there is no space to work back there.  He says the handpiece is too big to work back there.

He suggests either:

remove the top of the tooth,  do root canal, and place crown

or

cut down the tooth from the top, then place a large restoration.

1.  Are there special mini handpieces that another dentist might use to just clean, prepare, and fill this cavity.
2. Is it common for dentists to work in that area?

Thanks for reading, and hopefully for your reply...

John B

[Jerome Tsang, DDS]

Your dentist should be able to do a filling back there but he may be concerned about the depth of the cavity below the gum which would be difficult to do as moisture and blood could mix into the filling causing it to fail early.  If your mouth is small and there isn't much room to work, I believe there are pediatric handpieces but your dentist may not have them available.  You could always seek a second opinion with another dentist as well.