Re: trouble with molar number 18
the lower second molar does not need to be replaced in all cases. there are a couple of important considerations though.
first, do you have a first lower molar and is it in good condition? and does that first molar have an opposing top molar (also healthy) so that you gat full chewing (mashing) function on that side. a person does not need all 6 molars on one side in order to have adequate chewing function, thank goodness!
second, if you still have the wisdom tooth on that side, just know that it will start to drift frontward, possibly at an angle that matches to the other top molars without causing some interference. relatedly, and third, is whether or not you have an opposing tooth for 18. that upper could start to "super errupt" if there is no lower tooth in contact with it at all. (typically, 18 is in contact with both 15 and 16, and so 15 and 19 can "hold each other in place if 18 must be extracted.) there are other occusal patterns, and yours may be a little different. so the dentist will be able to tell you whether a "place holder" (implant) is adviseable (and show you why) for either function or to prevent drifting. it all depends on the layout and condition of your other remaining teeth and can be easily determined from casts and xrays. good luck and hope this helps!