Unstable overdenture: suggestions?

I placed 2 Astra Tx ( 4x11mm) implants to try to stabilize a lower denture done at a different office. Zest R-Tx Locator abutments were used.

The first day the inserts were placed in the housing the overdenture was stable.  The next day the overdenture was rocking and not staying in place as if there were no attachments.

I would like to make the denture more stable.  What are your suggestions ? I am thinking of adding more implants ( 1 distal to every implant and one in the middle).  On the right side as you notice we don’t have enough vertical height unless we drill into the incise canal.  Your input is very much appreciated. Thank you in advance!

17 thoughts on: Unstable overdenture: suggestions?

  1. roadkingdoc says:

    I would pickup the female attachments again using LIGHT pressure on the denture. I would also make sure to have only posterior occlusion on the denture, an anterior open bite if you will. Your problem is not uncommon with two locators only.

  2. Dok says:

    All the forces on a 2 Locator overdenture should be tissue born, not implant born. The locators are only there to keep the denture from vertical displacement…… nothing more. May need to look at the denture more closely, not just the implant/locator stability.

  3. Timothy C Carter says:

    What level of retention are you using in the denture housings?? This may sound crazy but I see this situation fairly often and it is usually resolved by reducing the retention of the housing. I default to the 1lb (Red Extended Range for the conventional Locator, not sure the color for R-Tx). Usually the lighter retention allows for better seating of the denture and plenty of retention.

  4. Dale Gerke - BDS, BScDent(Hons), PhD, MDS, FRACDS, MRACDS (Pros) says:

    I have to say it is impossible to make an accurate diagnosis in such a case without careful clinical examination and more detailed information. In some cases, dentistry is more of an “art” form than a science, and therefore close clinical examination is required. So all I can do is offer my best guess.
    I treat many patients similar to the case you presented. They can be hard to obtain a satisfactory outcome.
    Adding more implants posteriorly would be tricky I suspect. Obviously there is little vertical bone height but I would bet there is not adequate width either. As such the case would be best referred to a specialist in regards to implant placement posteriorly.
    Adding a central implant might help the situation and I usually would recommend at least 3 lower implants to be placed for an implant retained denture (but more often 4 implants/locators). In this case adding one is probably the only easy option.
    However from what you have said, the denture was initially stable but is not any longer. If this is the case, you merely need to find out how to get the same situation as when you first inserted the denture. So let me deal with the likely issues.
    It may be that on initial insertion, you placed the denture and made sure the denture was seated properly on the locator retainers. After that, the patient may have not been able to locate the denture properly. This is a situation I have encountered before and it can be difficult to ascertain why. Presumably you have checked such a possibility.
    The next issues to check are the locator inserts in the denture. You will notice the implants are not parallel and the locators seem to be quite low (ie not much collar height).
    If you use inserts in the denture that are designed for parallel implants/locators (ie there is a central raised cylinder in the middle of the insert) then often these will work initially but not locate after a little time. I therefore have a stock of the full variety of inserts and I will try either the non parallel inserts (ie no central “cylinder” in the middle) or if I do not have them in stock I will carefully remove the central cylinder using a small high speed bur. However removing the central cylinder is not easy to do without damaging the insert, so changing to an off the shelf (factory made) one is much more sensible. The other consideration is what colour insert you use. Different colours provide different retaining tension on the locator. If the tension is too much, it is often difficult for the patient (and operator) to properly locate the denture onto the locators – particularly after a day or two (not sure why this is but presumably there is some slight dimensional change with the inserts after being in contact with moisture for 24 hours). As such I find I often have to replace a high tension insert with a lower tension one. So in regards to the inserts, try non parallel inserts and possibly lower tension ones.
    Further, if the locators do not protrude into the mouth enough (ie the collar height is insufficient) then it is often hard to get the denture to clip onto the locators. For this reason I now use locators that are a little higher than the recommended height. Unless there is a vertical dimension issue, having longer locators is less of a problem than them being too short. As best I can see from your radiograph, I suspect the locators are too short. This issue is often compounded by a little hypertrophic growth of the soft tissue around the locators after 24-48 hours post insert. This then makes it hard to properly locate the denture into place. So you might want to consider replacing the locators with longer ones (I recommend at least 3 mm above the gingiva).
    Lastly, I have noticed over the last 10 years that when locators are not parallel, in about 40% to 50% of cases – usually bruxers – there is considerable wear on the locators (ie they lose their retentive undercut) over several years. Exactly how this happens is a mystery to me since theoretically the only contact on the locator is the plastic insert – and plastic should not wear metal. Whatever the reason, I sometimes use tailor made stainless steel locators to reduce the wear factor.
    I hope some of these suggestions might help you with this case.

  5. Adil says:

    First The occlusal scheme needs to be evaluated. The upper right molars are over erupted. Tooth #1 is articulated with denture base, no room for teeth. Consider extraction. Teeth #2,#3 needs to be shaved to establish a line of occlusion. Reseat the denture and make sure the holes are lager than the locator housings the pick up again. If you decide to redo the denture after correcting the line of occlusion. Ask the lab to do a reinforced processed denture base , make big holes and use powder and liquid “acrylic “to weld the housing while the denture base seated in place with no interferences. Place the wax for vertical dimensions then proceed with the rest of the steps. And you can add a mini implant in the center to have Anterior posterior distance. Hope that help
    You can add

  6. Montana says:

    Pretty basic really, the implants provide assistance but no support. The maxillary posterior teeth create too much rotation for the attachments to handle. You might get by with O-rings, but really it’s an overload situation.

  7. Jeff Shnall DDS says:

    If the denture is attached to the locators does the denture rock when you press downward on the lower incisors or the posterior teeth? If so I would add softliner or mucosoft in the anterior and /or posterior undersurface of the denture. This could stop the rocking.
    Add the reine material to the underside of the denture, insert it into the mouth making sure the abutments are engaged to the locator housings. You could have the patient bite down gently to make sure the upper teeth are occluding evenly against the lower teeth but don’t have the patient bite hard or allow the denture to settle in anteriorly or posteriorly….you want to maintain a bulk of soft reline under the anterior (and if necessary posteriorly) of the denture, Hold the denture in position until the material has set. In my experience when only two implants are used to stabilize a lower denture, soft reline in the lower anterior can solve the problem you are having.

  8. Dr. Gerald Rudick says:

    My preference to stabilze a lower denture is with ball attachments. …. in my limited experience with Locator Attachments, I have encountered the same problem, and what I have noticed is that food particles may get lodged into the female portion of the locator, and prevent the denture attachment to be fully seated and engaged……. call the patient in again, and check this out….

  9. Uk Prostho says:

    Has your denture base covered all the available denture load bearing surfaces/ Have you confirmed the vertical dimensions is correct? have you checked and adjusted the occlusion as needed seeing as you are opposing natural dentition and a removable partial denture? You can see on the right side especially over eruption of the upper teeth and t he impact on curves of Spee and Moson. The Locators stop the denture lifting away from the supporting tissues but you need to check if you denture base is providing full coverage before you start to change inserts, place more implants etc. I think its more of an occlusion rather than a “pink or clear inserts problem”. If you already using clear inserts and the denture is not stable then what would you do?

  10. Andy says:

    One thing I see regularly with Locator Attachments in patients who have previously worn a denture is that, when I ask them to demonstrate placement of their overdenture, they throw the overdenture into their mouth and BITE IT INTO POSITION. This is a surefire killer of Locator male components, no matter how many. Even with patients whom I have instructed to carefully place their overdenture with their fingers only feeling lightly for the correct position before seating completely WITH THEIR FINGERS NOT BITING, some still eventually “FORGET”. Then there is the cleaning (or lack thereof) of any food impaction in the male components. There is also the potential issue of redundant loose gingiva as in Combination Syndrome lending to instability of the overdenture. These issues as well as all mentioned above, especially occlusion

  11. Frank Avason says:

    1) Reline
    2) Suspect no ridge remaining intraorally. Consider a 3rd fixture between the 2 as you are dealing with 2 implants holding the whole thing in….
    3) Full arch fixed option….?

  12. Dudley says:

    I am a family dentist on Western edge of rural Virginia. I do a lot of removable pros in my practice. I have my own remo lab. I use ZEST locators frequently as overdenture attachments on canines or with implants. I have seen the problem you describe in my practice. Question is: ‘What happened?’ Look at the ZEST attachments with your loops. Do they look mis-shaped or mutilated? Im thinking the edges of the ZEST attachment may have folded over. Sometimes I find older patients have trouble lining up the denture to the implants and will damage the snaps. This patient has a crooked plane of occlusion, If he/she puts the lower denture in and bites down, that can damage your attachments. I typically get pretty good results with two ZEST while I prefer 4. On one case, the patient had tremendous trouble getting the implant snaps aligned properly. We went through a lot of snaps and were both very frustrated. To remedy the problem, I placed two mini implants just distal to the ZEST attachments. The mini implant with the ball attachment will stick up about 7 mm above the gingiva. I find the attachments for the mini’s are more resistant to damage. An older patient with some arthritis in the fingers may need something like a couple of mini’s to get the alignment right for your conventional implants and those ZEST attachments.

  13. Ash says:

    On the right side as you notice we don’t have enough vertical height unless we drill into the incise canal.
    What would be the ” incise canal”?.

  14. Rick Herrick CDT says:

    The retentive element of the locator must be supragingival 360 degrees. I suspect you would need to place taller locators. Grind the metal housings out of the denture. Place the housings on the taller locators. Take a reline impression capturing the metal housings inside the impression. Make sure to capture all borders in the reline. Send to a lab to have a hard reline and housings processed in. This design is tissue supported and implant retained.

  15. Bill McFatter says:

    Bad Tx plan . If you think that this will work with the natural upper teeth you are wrong and this will be a common occurrence going forward. Personally after doing dentures as a main component of my practice for over 30 years this case is a failure and the patient haas been put in the position of severe posterior mandibular atrophy. You will continue to have this problem and the pt will begin to loose confidence. You can not support the occlusion on a lower denture against maxillary posterior teeth. You should remove the maxillary teeth and create a new U/L denture level the occlusion then your implants will do there job. Forces too great JMHO

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