With the increasing use of implants in replacing missing teeth, their use can also be extended to retaining and supporting removable prosthesis. If the patient already has an existing removable denture, one way is to convert the denture to an implant supported one. There are many ways to achieve this goal. You can do that through laboratory processed procedures or you can do that through chairside attachment pick up procedures. The latter one can be done provided the existing denture is in good reasonable shape with proper retention, support and stability. The advantages of the technique are the instant delivery of the prosthesis to the patient and possibly the decrease in laboratory cost.
On the internet, the different implant companies and practitioners have provided very resourceful information on step by step procedures of how to perform a chairside attachment pick up procedure. Below are few of the links that I came across that you may find useful.
On this blog, I want to talk about some of the things I think about when I am considering this type of procedure. In my practice, I have done both laboratory processed conversion and chairside conversion. But when I do, these are some of the things I consider before delivering the prosthesis:
1/Diagnostic evaluation and Patient Expectation
Before I decide whether I want to convert the denture through laboratory processed procedures or chairside procedures, I have to evaluate if the implants are relatively parallel to one another. This is heavily influenced by the available bone anatomy and the skills of the surgeon placing the implants. If the implants are relatively parallel to one another, then I am more inclined to consider the direct chairside conversion procedures. If the implants’ angulations are not parallel, then I am more likely to consider the laboratory processed procedures so I can evaluate the angulations better and select the right retentive element for the prosthesis.
I also would like to review the limitations and advantages of this method as opposed to other implant supported prosthesis. With the individual stud abutment supported implant prosthesis versus other bar supported implant prosthesis, the amount of retention expected from each abutment may be different. That means, you may not always hear the “click” to all the abutments; some abutments click better than others, some abutments get worn out faster than others requiring replacement of the components. Therefore, the expectation is there may be some movement of the prosthesis depending on the path of insertion, the number of implants involved and the distribution of the implants in the arch. The more implants involved, the less of the issue. In one scenario, with only two implants in the anterior region of a large mandible, I will explain to the patient this is still a tissue-supported prosthesis with some “help” from the two implants in the front. There may be a need to replace the components more frequently and a need to reline the denture. In another scenario with four well parallel, well distributed implants, the implants serve more like a four legged table and the risk of denture rocking and tissue-ward movement will be much less. I want to review these possible issues so the patient understands what to expect and the need for future maintenance should they be required.
2/Closed mouth technique versus open mouth technique
In most of the videos and techniques I reviewed over the internet, they have demonstrated an open mouth chairside technique in direct chairside conversion procedure. This means the pickup of the attachments is done while the prosthesis is seated but patient’s mouth is wide open. Contrary to how I normally perform my chairside conversion, I treat the procedure very much like a direct chairside reline where I will pick up the attachment with the patient’s mouth closed into occlusion. This ensures that I have a tangible reference point that the prosthesis is seated the same way before and after conversion. Prior to the conversion, I place the prosthesis in the mouth and pay close attention to the type of overlap, overbite, and midline orientation of the maxillary and mandibular teeth. In fact, when I place the components and have to relieve the intaglio surface so that the denture seats again, this is how I check if I have relieved enough. Without this reference, I may be changing the way the denture seats without even realizing it. This is an important point to me because if you don’t have this reference, you may end up converting the denture in a slightly different orientation such that the denture is entirely implant supported without any tissue support. To me, this can be a source of attachment wear, more denture rocking and a need for more change of components and reline in the future.
3/Relieve just enough and pick up all attachments together
Traditionally, when doing a chairside conversion procedure, you have to relieve some acrylic to allow the abutments to seat and to allow room to pick up the attachments using auto-polymerizing acrylic. This use of self-curing or auto-polymerizing acrylic is what makes it feasible to perform a closed mouth chairside attachment conversion procedures I talked about previously. However, if you understand the chemistry of this material, this material is often an exothermic reaction and subjected to a 7% of polymerization shrinkage. For this reason, I try to minimize the use of this material to minimize the amount of shrinkage and to minimize the amount of heat released during this chemical reaction. In other words, do not over relieve the intaglio surface too much but just enough so the denture seats well before and after the placement of your stud abutments so you use just the minimum amount of self-curing acrylic for the conversion procedure.
Recently, there are newer materials out there that are light cured and designed for chairside attachment pick up procedure. The use of light cured acrylic may be less messy and provide less risk of monomer exposure. But the need to light cure means the conversion has to be performed as a open mouth technique. In my previous discussion, this may cause the denture to be seated slightly differently before and after the conversion. In any case, it is still a material that can be used as long as the practitioner recognizes the potential pitfalls in an open mouth technique conversion.
I also tend to pick up all the attachments together in one try rather than picking them up one at a time. I find that if I pick up one attachment at a time, it increases the amount of processing error causing the denture to rock more between attachments. However, if the implants are not very parallel to one another, I would either consider a laboratory processed method for the pick up of attachments or to consider picking the attachments one at a time. The reason for this is if the implants are very much divergent, if I pick up the attachments all at the same time, I run the risk of the attachments getting locked in the freshly cured acrylic even if the undercuts have been blocked out. The risk is high if the implants are very divergent. I would prefer a laboratory processed conversion so there is time to decide on what retentive elements work best for the case based on the existing angulations of the implants. For chairside procedure, you may not have the resources or the time to try out different components before deciding what works best for the case. Therefore, I would only consider direct chairside conversion if the implants are all relatively parallel to one another.
I hope you find this material useful and I welcome any comments you may have at firstname.lastname@example.org. Thank you so much for reading.
Please check out my other posts too.