Locator abutments height: thoughts?

Think about reinforcing the over-denture with a type of cast framework or a Milled framework. create housing over the attachments and make sure the thickness of acrylic is adequate all around. lower OD on 4 implants is almost like a fixed appliance, so make sure there is no rocking with you pick up the attachments. I don't think the length of the attachment collar has anything to do the acrylic fracture, BUT if you don't have adequate clearance, then the height will make it even thinner, hence more risk of fracture. it is a mechanical issue, try to identify the is causing it by evaluating the Fracture line.

Locator abutments should have a cuff height of the sulcus depth to the implant platform plus 1mm which would place it so the metal housing and male do not contact the gingiva when seated. I would suggest in this case to place shorter Locator abutments and have the new denture made with metal mesh reinforcement in it.

Implant abutments create structural weak points in implant overdentures. There are two materials that are available to strengthen the dentures without the need for a milled reinforcement bar, though that would be ideal. First is Ribbond, added to the denture before the housings are placed. The second is Trilor, a composite available to be trimmed and fit to the overdentures, also before pickup of the housings.

Stock metal mesh won’t work but custom metal mesh cast to your model works.

I agree with dr Kurtzman: shorter abutments, thicker acrylic and metal mesh.

It is a bit hard to say without looking at the denture thickness and the bite. Normally the locator inserts in the denture are not a point of weakness but occasionally they are especially when the inserts take up most of the denture volume in the area where they are placed. Obviously you need enough bulk of acrylic to resist breakage. However if the bite is aggressive or there is extreme parafunction, then this can also cause issues. Having said this, I have not found denture breakage a major problem – even when the locators are placed high (which I purposely do sometimes because I feel it makes it easier to click the denture onto the locator sometimes). The main issue with a long locator is dealing with the undercuts which eventuate (thereby making it hard to get a reasonable path of insertion without removing a lot of acrylic from the impression side of the denture). It seems to me from your radiograph that the locators/implants are divergent (although this might be due to a distorted image – I would need to check clinically) and this would mean that probably there has been considerable acrylic removed to allow for the denture to be inserted into the mouth. If this is the case, then shorter locators will reduce the amount of acrylic removal required and thus result in a denture less likely to fracture. Irrespective, a metal reinforcement plate of some sort should solve the problem (although the height of the locators could make this tricky). Several ideas have been described, however I ask my laboratory to cast up a chrome cobalt palatal or lingual plate about 1-2 mm thick which starts at the palatal or lingual edge of the denture and follows the soft tissue contour about 5-10 mm before it rises above the gingiva to allow teeth and acrylic to be placed over the metal in the usual way (so it is almost like a special Cr/Co partial denture frame – lingual plate design). The metal surface can be smooth or stippled. The cost is the same as a normal Cr/Co partial denture frame.

How far distal to the distal implant does the denture go? Is the fracture at the distal half of the distal implant? Maybe your distal extension is too long?

You have to make sure when making and relining that you create no interference with the housings and you make a small hole when picking up on the lingual to allow the material to express out and not cause the housing to be high . Check bite for heavy areas either side to the implant abutments . This is a tissue born appliance and should not be supported by the implants . Follow design protocols for thickness

Shorter abut and Fiberforce reinforcement processes into the denture. Cast frameworks take up too much space and actually weaken the acrylic as you need bulk for attention acrylic.

Judging by the composite screw hole plugs seen on the X-rays, I bet the Upper is a Fixed Hybrid prostheses, and for some reason, a lower overdenture over LOCATORs was made in occlusion with it. I bet you the patient sleeps with both of them in at night and grinds his teeth to high heaven and back, the upper does not move, so the teeth just wear down, the lower rocks over the LOCATOR abutments, and cracks will form around each metal cap housing, which is always a weak link in an overdenture. Just my opinion, I could be wrong.

Your occlusion is distal to the distal lower implant. In function there is compression on the lower ridge that creates compression on the distal and tension on the anterior implant Im not sure when it became popular to place 4 implants with locators in fromt of the mental nerve , but the locator was not made for this and there is no prosthetic guidelines that support 4 independent implants in either arch that are not splinted. Locators don't compress and have very little rotation. Not only will you find that the resilient liners wear out quickly there will be one anterior abutment that prematurely wears because you can't get an axis of rotation that is balanced. In order for you to function here without a bar I think you should move to balls or a bar At least you will have some freedom of rotation and compression with the balls - the height of the locators is too high and this thins the acrylic Move to ball and O-rings and shorten the abutments.JMHO Bill