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4 Core Concepts of Mandibular Implant Overdentures
by Chris
One of the most satisfying services I can provide a patient is stabilizing their complete denture with implants. I’ve done many of these and I’d like to share with you my thoughts on how I use them successfully.
(1) Implant-Retained, Tissue-Supported
This is a critical concept! The implants are offering retention that is far superior to suction and gooey adhesives, no question about that. But the prosthesis is still supported by the soft tissue. That means traditional denture concepts must be respected. A good implant overdenture always begins with a stable, well-fitting complete denture. Preferably I will make a brand new CD for the patient that I will fit for implant attachments. However if I have to use the patients existing denture I will at least consider a new chair-side reline before beginning treatment. If the CD does not fit well then there will be unexpected forces acting on the implant attachments which will compromise retention.
(2) Implant Location and Number
The standard of care is a minimum of two in the mandible. The mandibular implants are placed between the mental foramina due to the high quality of bone that is found there. It’s best to place them close together, roughly in the lateral incisor areas, rather than spread out in the canine areas. Why? Because the first option is better at resisting anterior-posterior rocking of the prosthesis.
The placement on the left will better resist A-P rocking of the denture.
Alternatively you can place a third implant in between the first two for additional retention. I’ll do this if the patient’s force factors are high (bruxer, strong bite, etc.)
Implant placement for an overdenture retained by three implants. The healing abutments are still in place.
Can you place more implants than three? Sure. But once you start getting to four and five implants, you’ll probably be leaning more towards a fixed, implant-supported prosthesis.
Two Locator abutments for an implant overdenture.
(3) Attachment Selection
There are O-rings, Hader clips, bars, and all sorts of mechanisms for making your overdenture click and snap into place. Personally, my method of choice is the Locator attachment. It’s simple to use and quite effective. I’ll use a bar if the implants have a severe angle discrepancy (greater than 20 degrees between implants) that would prohibit seating of the Locators. In that case, a bar would zero out the angles and provide a clean slate for other attachments to connect to. For more information on Locators, check out my next post.
(4) Delivery
You could take impressions and send everything to the lab for fabrication, but I think it’s better to do this procedure chair-side. Not only will it save you money, but you will be able to get a dynamic fit. A lab doesn’t have the benefit of muscled attachments, lips, and functional movement; all they have is a model. It’s super easy to pick up Locators chair-side.
Locator Attachments for Implant Overdentures: Part 1
In a prior post I discussed the”4 Core Concepts for Mandibular Implant Overdentures“. One of those concepts is that Locator attachments are a simple and effective way to retain your overdenture. Incorporating these babies into a well-fitting denture is easy once you know how. Let’s dive in!
So the patient arrives in your office with healing abutments and full integrated implants. Where do we start? We don’t need any impressions since we’ll be doing everything chair-side.
Measure the deepest part of the tissue with a perio probe to determine your minimum collar height for the Locator abutment.
(1) Take off the healing abutments. Measure with a perio probe from the platform to the height of the gingival collar. If the tissue depth is not uniform all the way around we record the deepest measurement. This is what determines the collar height of the Locator abutment. If you’re not sure, err on the side of a taller abutment. The goal is to have the abutment completely clear the soft tissue so that the male attachment doesn’t pinch the tissue.
If you’re concerned about the angulation, insert some impression copings and make sure they are less than 20 degrees divergent. Locator makes an attachment that will also work with up to 40 degrees of divergence if you need it. Replace the healing abutments and we’re done. That’s all we need for the first visit.
(2) Order Locator abutments. You can get this through your implant company sales representative. We’ll need the correct size platform for the implant diameter, of course. We’ll also need the appropriate collar height for the depth of tissue. Make sure you also order the attachments.
(3) Okay, it’s your second visit. Show time! Remove the healing abutments and insert your Locator abutments. These are inserted with the special Locator driver and torqued to 10 Ncm (or implant manufacturer’s instructions).
Locator driver… don’t leave home without it. This should be interchangeable between implant systems.
Now we’ll snap on the metal housing. Look at your tube of attachments and take out the silver and black thing and the white ring. The metal part is what will become encased in acrylic inside the denture. The black part is a weak male attachment used to snap into the Locator abutment during processing. The white ring just fills in any space between the metal collar and the abutment to keep acrylic from flowing where it doesn’t belong.
So we place the ring on and snap on the metal housing. You will feel a snap!
Locator attachments. The white block-out ring is place around the abutment and then the metal collar and black processing male attachment are snapped on.
(4) Next we need to modify the denture to make room for the metal housing and Locator abutment. I like to paint the housing with a Thompson’s marking stick to show what areas of the denture need grinding. Go to town with that acrylic bur until the denture seats fully over all the abutments/housings.
A Thompson’s Marking Stick applied to the housing will show us where we need to adjust the denture.
(5) You may choose to poke a hole through the acrylic to the other side. This will allow excess acrylic to escape. Now it’s time to pick up the metal housings. DO THIS ONE AT A TIME! I do not recommend trying to pick up all the attachments at once. It’s harder to control the final fit. So we’ll mix a small batch of acrylic and place it in a relived area. As we seat the denture, we’ll see the excess spill out the other side. You can remove the excess at this stage or wait until the end. Have the patient bite into gentleocclusion; not a heavy bite. Once the material is set, remove the denture and pop out the white block-out collar. Trim any excess and fill in gaps with more acrylic.
The relieved area is filled with hard acrylic. As it is seated, excess flows through a hole on the other side. After setting, the white block-out collar is shown retained with the denture.
Repeat the process for the additional Locator abutments/housings. I like to leave the patient with the black processing male attachments initially. This gives them a chance to get accustomed to the added retention. Older patients with diminished dexterity may find that the black male attachments are perfectly suitable and won’t request an upgrade. Bring the patient back in a week to see how they’re doing. The denture will fit them differently now, so don’t be surprised if they develop a sore spot somewhere.
Now that we’ve learned how to treatment plan an implant overdenture and also how to insert a Locator attachment, let’s look at how to increase the retention force. When a patient’s implant overdenture is well-supported by tissue and the attachment apparatus is functioning properly, there still may be a need for additional retention. The process for swapping out the old attachment and swapping in a stronger one couldn’t be simpler. Expect a 10 minute appointment.
In order to increase retention we must use the Locator Tool. Here it is:
The head is unscrewed a few twists for coring out the old attachment (bottom left). It can then be screwed down fully to pop off the attachment (bottom right).
For now, just know that the head can be unscrewed or screwed down. When it’s screwed down, a metal pin is firmly exposed. You’ll see why in a moment…
Removing an old attachment from the implant overdenture.
(1) Out with the old… In this case the patient is still wearing the black processing attachments. Remember that these are the ones that come in the metal housing for use while picking up the apparatus. They are the lowest strength attachment but they can actually work pretty well for some patients with low chewing forces. I like to leave them in for a few weeks while the patient gets accustomed to inserting and removing the prosthesis.
Well now we want to pop that out. Loosen the head of the Locator tool a few twists and insert it into the attachment. Scrape the side and the cutting edge of the tool will cleanly pull out the attachment. The metal housing will still be in the overdenture awaiting a brand new attachment. Tighten down the head of the Locator tool and the old attachment will pop off.
This is pretty straight forward, folks. Not much to say here.
(2) … in with the new. Now we can completely unscrew the head of the tool to find a smooth part without any cutting edges. Take the male attachment of the next level of strength, which is blue in this case, and apply it to the tool. Place the overdenture on a hard surface like a counter top and just push it in. There’s no special technique here; just snap it in.
That’s basically everything you need to know to get started on your Locator cases. In Locator Attachments for Implant Overdentures: Part 3 I’ll review a technique for picking up the attachments that’s a lot cleaner than just smearing some hard acrylic all over the place.
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