My last post on how I manage broken screws was such a big hit that I think I covered a topic that many people are interested in. It gives me great pleasure to know the little tricks I learned from my mentors and the ones I discovered by myself can be beneficial to others. I thought the last post would be incomplete unless I discussed some of the possible causes for screw breakage so that we can all learn from them. After all, it’s not exactly something I like to do on a regular basis.
As I am thinking back all the implant screw rescue cases I have done, each one of them is really unique and a lesson to be learned. Some of them I can only rely on the patient’s limited history, some of them may be operator related and some of them are related to the quality and the design of the prosthesis. But if I can draw on some key points here for all to think and to explore, here are my observations and recommendations:
1/ Know the torque value of your screw from the implant company. I was approached by a dentist in a local study club once how I deal with broken screws. He confessed to me that those prosthetic screws from All on Four restorations are so small and hard to work with. Then I told him that the gold screws are only designed to be torqued to 15Ncm. He said he didn’t know it then so that was probably the cause of the screw breakage. So the morale of the story is to never assume what the torque value is. Even for the same implant company, the different line of products is designed differently and may have different torque values for the screws. One of the things I noticed my lab does is to always include a small note in the case regarding the recommended torque value of the screw. I guess with all the different products on the market, it’s hard to keep track of what the recommended torque value is and I find this reminder note to be a nice gesture from the lab.
2/ Confirm the abutment and the crown are seated before you apply the final torque. This is especially true when you are working with single tooth restoration. Depending on the access, the intra-occlusal clearance and the angulation of the adjacent teeth, inserting a single abutment or crown in an isolated site can be challenging. Being a single tooth restoration, its anti-rotational feature is built into the abutment and/or the crown. So getting the abutment/crown to seat is more than just lining up the access hole with the implant and tightening up the screw. It also has to engage the internal feature of the implant. If the implant is quite subgingival with abundant soft tissue surrounding it, there is a tendency for the tissue to push the implant crown or the abutment in an occlusal direction while the screw is being tightened. I have discussed this issue in previous post as well. My trick is to actually feel the internal engagement to the implant and holding it down with slight apical and slight rotational pressure while the screw is being tightened. The abutment/crown should have no movement while you are tightening the screw. If you feel there has been movement, it’s likely the soft tissue has pushed the component away from the implant while it is being tightened. Taking an x-ray is key to confirming the positive seat of your abutment or crown.
Abutment not seated all the way with a broken screw flush with the abutment
I know some lab will make a resin jig that helps the dentist to seat the abutment. Personally, I find that it adds an extra bulk to the area which may make access more difficult for me. The resin jig, if not properly adjusted, may prevent the abutment from being seated all the way on the fixture. But it can help the dentist to orient the abutment properly before the screw is tightened. I personally rely on the orientation groove that is usually placed on the buccal aspect of the abutment so I know how to position it in the mouth. Because the abutment can be seated in several positions, it is important the abutment is seated the same way on the model as in the mouth, otherwise, your final cementable crown will not seat.
Orientation Groove on the Buccal Aspect of Abutments
And if you are like me, I prefer to make screw retained restorations. So getting a single screw retained restoration to seat can be a little bit more difficult than a single cementable implant restoration. The more favorable scenario is when the implant angulation is parallel to the proximal contours of the adjacent teeth and it has a relatively short clinical crown height. When everything is working in your favour, the screw retained implant restoration goes into the implant like slam dunk with no interference. However, when you find yourself that it is not seating all the way, something is holding it occlusally, it has been my experience that it is the proximal contours that may be binding to the proximal contacts. But you don’t want to haphazardly adjust the contacts because otherwise by the time it is fully seated, you may find yourself with an open contact. The key is to start with adjusting the more gingival binding areas. To pick up these bindings areas can be difficult. I don’t’ have any fancy trick but to just use an articulating paper placed intra-orally between the adjacent teeth and the implant restoration and “rub the crown” against the proximal contours in buccal lingual and gingival occlusal direction. In order for this to work, both the restoration and the tooth have to be quite dry to pick up any marks. This can be challenging if you have a patient who salivates a lot. I suppose you can also use other indicating medium like occlude spray or pre-marking the area with a pencil to identify these binding areas. But for me, I haven’t had to adopt other tools beyond using my standard articulating paper. Continue to adjust the more gingival binding areas first before moving to adjust the more occlusal binding areas. Try to seat the implant restoration not just in the occlusal gingival direction but also in a buccal lingual direction until you can feel the crown slide further gingivally and engages the internal feature of the implant. Finger-tighten the screw if you think the crown is seated and take an x-ray to confirm that it is fully seated. Once it’s seated, go back to check all your usual things like proximal contacts, occlusion, contour and esthetics. To me, if you are not used to seating a screw retained restoration, this can be a more time-consuming procedure than your standard tooth supported crown. I have seen cases where the dentist tries to force it in and ended up getting the crown stuck in the site. The dentist thought the screw was stripped when in fact it was just wedged between the two teeth which was later removed by me. In my opinion, the proximal contacts are the more difficult aspect of seating screw retained restorations. When it is not done right, it is likely one of the sources of screw breakage.
The lines marked in red are areas most likely to be interfering with seating a screw retained restoration if the proximal contours are not parallel to the implant angulation.
Stay tuned for a continuation of this post. This topic becomes much bigger than I thought and I want to keep these posts short and useful without overloading you with too much information. Thanks again for your time in reading my post. I look forward to your comments.