Implant Overdenture Case: What’s the best location to place the two implants?

nice case. Looking at prosthetic point of view, the best choise is to place implants in lower second incisors position (i am not very good with this american tooth numbering system) and you are thinking of placing implants at premolar area. to make a dentures with implant position in premolar area, with my experience is very nasty case to deal with, you will need to use ball attachments, because of dentures movement. Another problem you may finde lack of fixed gingiva. and another problem when relining a lot of saliva ( you going to finde yourself at the midle of the pool, full of saliva) my suggestion to you - look at it with well documented other expierence: 1.make an imediat dentures (or you may already have one, so skip this one) 2.extract teeth 3.level the anterior manible region 4.mark implant position using dentures, or 7mm from center to both sides 5. drill implants 3.8 or wider diameter. 6. after 6 weeks (if there is good primary stability) select proper height Locators attachments, reline or remake dentures and if patient wants to go with fixed prosthetics (all on 4 or 6 or 8) you always have a space for implants. for best info read this: quintpub "Mandibular Suction-Effective Denture and BPS" and "Implant Overdentures The Standard of Care for Edentulous Patients"

I recommend maximizing the a-p spread, premolars site is fine. If you are contemplating an all on four, then 18mm of inter arch distance is required otherwise the prosthesis will break. If you mean having a denture supported or retained by 4-6 implants then a bar over denture can be used or locators. All on four uses tilted posterior implants to increase a-p spread and avoid grafting with an immediate prosthesis screwed in. I personally don't like removing all that bone unless it is a last resort, you just married the patient when the implants fail or the prosthesis needs to be repaired. If the soft tissue is managed correctly the prosthesis should be maintained by removal for hygiene and access to the implants. I like the canine and first molars for locators or 3-4 implants anterior to the mental foramen.

Locators should be in the 2nd lower incisors position. You can go as far as the canine. No more then that. I mean if you are using 2 locators of course.

When is the indications using 4 instead of 2 locators for lower implant retain denture?

Any implant insertion depends mostly on antagonists' location to balance occlusion. In removable denture case the main rule remains stable: the farther implant posterior support the better.

Avoid placing more posteriorly, this will create an anterior cantilever and thus tipping of the denture in function. Also, bicuspid placement eliminates the option for a future fixed hybrid as the AP spread is compromised. Locators or any overdenture attachments provide retention and stability but not support which must come from the load bearing structures; in this case the buccal shelf. To create support, at least four must be placed but at a considerable AP spread to eliminate the posterior cantilevering; you want to create the legs of a table. Placement of more than two implants/attachments results in multiple axes of rotation, creating leverage by which the denture is loosened; a lot of good literature to support this argument. Therefore, more than two locators is often less retentive than two unless they are very far apart. I always treatment plan these cases as "all-on-4" just to determine the spread and angles necessary for fixed, this creates the parameters for placement of the two middle implants. If the plan is two, you know where they should be placed, typically between the lateral incisors and the canines. If the patient later wants or van afford fixed, you have planned for it.

With the remaining teeth being so much out of the bone, and with so much residual bone below the teeth, there is really no problem in placing the implants in the first premolar region. Further distally would generate too much "rock" potential over the implants. Too much further anteriorly you would get less B-L stability, less counter-rotation stability from the anterior region and you would have more difficulty in placing the implants axially.

When using only 2 implants for an over-denture the attachments must allow the tissues to be load bearing. If the attachments bear the vertical load they function as a fulcrum upon which the denture will rock. O-ring attachments will allow the movement for the denture so it becomes supported by tissue loading like a regular full denture. Locator attachments if placed anywhere except under the incisor teeth will bottom out and the result will be a denture that rocks. This is likely to occur with any attachment that does not allow sufficient vertical movement when loaded so to prevent the denture from bottoming out on it. Two implants will work for a mandibular over denture but plan the treatment with care or the attachment parts will have to be frequently replaced and implant failure could occur from overloading.

After extraction place the denture. Don't suture -don't do any surger just allow the tissue to granulate in over the holes . This will give you better soft tissue. After the tissue matures 4-6weeks you can return to place the implant at the 2nd incisor position. This position limits the anterior lift of the prosthesis which is the biggest aggravation of denture wearers. This also allows you to later upgrade with 2-3 other implants for a supported prosthesis. You can now do all on four or a traditional hybrid. At surgery you should level the bone down to where the trajectory of the anterior mandible changes to a more lingual inclination. This will assure a lingual emergent position of the implants for your prosthesis and you will have the prosthetic space you need. Doing the bone reduction at extraction requires removal of bone to the root apices and Then the primary soft tissue closure resulting in significant loss of keratinised soft tissue. Locators have no compressive ability. Their only function when soft tissue supported should be retention and allowing rotation. In my opinion , if you use 4 locators they need to be at the corners of the occlusal forces canine and first molars. Removable forces are different because of soft tissue compression and different thought processes need to be used in implant positoning. With 4 implant anterior to the foramenand having locators will create a compressive force on the posterior locators and lifting on the anterior and premature wear and loosening. It's just forces and movement