Removing a cement-retained abutment-supported crown?

Trying to remove a cemented crown off an implant abutment can damage the abutment screw, abutment and or implant itself. An implant is not a tooth. If the porcelain is damaged in a posterior tooth, I would patch it via many of the composite techniques, but in an esthetic area the crown and abutment need to be removed by drilling nd finding the abutment screw. I strongly recommend screw retained crowns whenever possible for this reason of being retrievable. The implant systems are engineered this way with the screw being the weakest link to fracture instead if the implant. It is just the way it is. Often when an crown is cemented it is due to less than ideal placement due lack of bone, which can often be corrected with grafting and a good surgical stent. Trying to use techniques that work on a natural tooth is circumventing the system. Next time have the screw come thru the cingulum and you won't have this issue. There is no substitute for good planning and a surgical stent. These things can't be eyeballed, one can get burned when there is a problem. It is not rocket science, so this needs to be the first choice. Cement retained does work but it should be a second choice since it is not retrievable. Implants are not forgiving most of these posts deal with the above issues I don't make the rules I just follow them to stay out if trouble. Good luck now remove the abutment and crown hopefully the implant won't be damaged and the implant wasn't overheated with the ultrasonic. Also check the occlusion and try to determine why the porcelain broke off, patient habit etc.

I fully understand your take on screw-retained crowns due to many factors, however, I did not place this implant or restore it. My question still remains, is it ok to prep the metal substructure of the crown, after removal of all the ceramic, and take a traditional PVS imp to just cement a new crown on?

I think it could be a solution but isn't removing all the ceramic as much work as cutting off the abutment and starting over? Also would there be an issue with thickness and color?

Thank you. I really appreciate your input. I'll definitely make sure the patient understands.

Dear Linda, remove the crown, cut it, first the porcelain with a Diamond bur, then use a bur for metal. All along the vestibular face. Be carefull and pay attention to detect when you are on the cement. Using a lot of irrigation. The goal is to save the implant, then the abutment. Maybe you cut and do a canal or groove on the vestibular face of the abutment, if it's not too deep, it doesn't matter, most of the times I do a vestibular canal to avoid the rotation of the crown. Just pay attention to avoid the damage of the screw. If the abutment is damaged then the patient should buy another one, any way the patient sholud buy a healing screw. And yes, maybe the patient has to pay an analog, impression post or even screw drivers if it is a brand that you are not using. Don't do another crown over the metal structure as you were asking. Don't do a bad treatment trying to save some money.

Could you explain what you mean by that being "bad treatment"? If it's a well adapted crown and the cement has been fully removed why would that be ba treatment?

Overcontoured crown, good luck.

drill a hole through the palatal surface of the crown till you locate the abutment screw , unscrew the abutment and remove the crown along with the abutment ,insert new abutment and construct a new crown recement it and pay attention to the occlusion . if you want to save the abutment and you have enough time and your turbine is strong and the carbide bur is sharp and with copious amount of cooling water cut off the crown into tow pieces and sluff it off the abutment , check the torque of the screw and proceed . again check the occlusion

I get what you mean, Omar. Thanks for the technique you use. I appreciate your input. So, if I cut the crown into two pieces then have to pry the pieces apart with a crown separator? Is that what you meant Nasee? Due to cement bonding metal to metal I don't think that would work. I guess cement retained crowns just need to be replaced, abutment and crown.

I think it depends on the age of the crown, how long it has been cemented and what cement was used. Also, how retentive the abutment is. The last time this came up, I was able to get a spoon excavator under the crown margin and pop the crown off quite easily. But it was an old crown, with a soft cement. I retorqued, recemented with a soft cement, and told her we may end up doing this again in 10 years.

Cut the crown off or get access to the abutment screw by cutting through the crown to the access channel in the abutment, then unscrew it. Consult your old models for where to grind. Replace the crown by a lab that does a proper cut back for adequate porcelain thickness to avoid future fractures.

Let's not speculate on the how or why the porcelain fracture, it's not the issue and we don't have enough information to discuss it. Instead, let's trust that Linda has determined the crown needs to be replaced and answer her question. 1) Attempt to pull the crown off using rubber tip pliers, using a slight rotating pull. Because many abutments are nearly cylindrical, the turning action may loosen the crown. Heating the crown before hand may be helpful; because it is #9, stick compound is an easy way to heat it. 2) Cut it off with a high speed using a porcelain cutting diamond followed by a metal cutting bur. when cutting through the metal, use a gentle painting motion to avoid damaging the abutment. Remember, abutments are typically smaller than abutment teeth and therefore either the porcelain, metal or both are bound to be thicker than usual. The cut must be through either the buccal or lingual wall and through the incisal edge. This will allow you to flex the coping and remove it. Before flexing, remove the inter proximal porcelain to create room for the flexing. Use a straight separator, wedge the coping open. Once done, any damage to the abutment can be easily polished without problem. 3) Cut an access hole to the screw. I don't recommend this unless all else fails because you have to find the screw chamber and that may result in severe damage to the abutment. If you are lucky and can unscrew the whole thing, put the crown-abutment into an oven (even a toaster oven) at about 350 degrees F; this will melt the cement and you can separate the unit. Allow it to bench cool after separating. I always try 1) and then 2); I've cut hundreds of crowns off, it's no big deal and you will preserve the abutment. Good luck.

Rand, this was a first time patient. I didn't have old models to refer back too. Mark, that's great advice. I would never think to stick the abutment and crown in an oven to melt off the cement! However, I'm still curious if there would be any harm to just leave the metal substructure attached to the abutment and just remove all the porcelain and prep the metal substructure ( not the abutment just the metal from the previous crown), make sure I have enough reduction and just take an impression of that? Thanks for all the great advice on how to remove the crown.

drill a hole through the palatal surface and then unscrew the abutment. remove it along with the crown. remove the internal screw. now hold the abutment with tweezers and heat the whole assembly (crown fixed to the abutment) the cement will disintegrate and the separate the crown from abutment. use the abutment again.. hope it hepls

This definitely helps! Thank you

Dr. Deora, what if the screw access is through the MB cusp, or the mid-buccal or anywhere other than the direction you choose? When heating, avoid using a flame as uneven temp increase will frit the porcelain. Linda, prepping metal is an option but not fun. Also, prepped metal reproduces poorly when impressed, you have to polish it to impress it.

Thank you, Dr. Montana. I really appreciate your input and will take your advice.

Locating the screw is not so tough. Since the aim is to save the abutment and redo the crown, so removing the ceramic with a bur or heating over flame will not make any difference

Dr. Montana has the most logical technique. I totally disagree with the surgeon saying anteriors should be screw retained. I agree that it is ideal to have them retrievable via screw retention but due to the flare of the anterior maxilla it is very difficult to get the screw to exit the cingulum without almost tilting the implant palatally. This will put the apex of the implant into the labial concavity. cement retention creates the most predictable esthetics since the implant can be placed in the long axis of the tooth and parallel to the flare of the anterior maxilla. if you look at the anatomy of a natural extracted central incisor, the labial surface of the crown is in two planes and if you follow the root trajectory from its apex, in a straight line (like an implant), the long axis of the tooth root exits the facial of the tooth. It is difficult to have an anterior retrievable, you need to use a very soft cement like Temrex or some other real weak cement or tempbond with vaseline. Now, on to the question at hand. Unless the crown is cemented with a very soft cement it will not come off. Even tempbond by itself has nearly the retention of zinc phosphate when used on a parallel sided custom abutment. Therefore unless you know it's on with a soft cement, it will probably not be removable. To try and remove the crown, use an almore crown remover (aka a gummy bear). Heat the gummy square in hot water, dry the crown then push the softened gummy bear onto the tooth wrapping it as far facial and lingual as possible. Chill the gummy bear with ice or ice water until it is firm again. Then grab the gummy bear with a hemostat, embed the hemostat firmly into the gummy bear and gently rock facial/lingual and pull like the devil! If it is going to come off it will come off with this technique. If not, sacrifice the crown by drilling into the incisal edge (that's the most likely spot for the access hole of the abutment, not the cingulum) and remove the crown and abutment together. Then use Dr. Montanas technique to get the crown off the abutment. Or, under magnification, you can cut the crown off the abutment on the bench top. Good luck! Also, repairing the porcelain can be an option if the chip is small and the metal is not exposed.

Don't all of our patients deserve the best? Why patch things up unless finances are an issue? Get a good pair of loops and a light. Any dentist that can cut an access opening for an endo can cut an access through the lingual of the crown, locate the access hole in the abutment and take out the screw. Advise the patient that you will do everything you can to preserve the existing abutment, but no guarantees. Take everything off and start over. You are not patching anything up and you have the confidence of a new abutment, screw and crown.

Thank you Dr. Johnson for your input. Great advice! MPEDDS, I understand your train of thought, unfortunately, finances are an issue.

There is a lot of chair time being used here to fx a problem which I 'm assuming you are not charging for, if you enjoy this sort of thing I guess it's okay. However a well placed implant with a screw retained crown is the way these things are engineered to be retrievable. They are recommended to be screw retained for this reason. I don't know how much a lab bill is for a new abutment is but it has hot to be less than the rent, overhead, staff salaries and doctors time being a hero. If the porcelain is fractured some time after placement the patient needs to pay something towards this , also bear in mind that modifying an abutment or heating and grinding on an abutment or crown is not the best for an implant, it is not a natural tooth. When there is an additional problem the patient will not have any trouble finding a lawyer regardless of finances or will expect another free crown when they refracture the porcelain I would fix it the right way and charge for it appropriately. Compromising treatment due to finances is not a good idea nor is going out on a limb based on blog posts, I would be leary of someone who has fixed hundreds of these things it is not a mainstream technique. But it's your call, good luck and thanks for reading .

You will have to cut through the crown an remove the crown from the abutment with a crown splitter. Then remove the abutment and start over with a new impression, bite registration and shade. Fabricate a night guard after delivery. Good luck! I have done about three of these, but for bruxers that make abutment screws lose. With these people I remake with a screw access hole, but on posteriors.

Two Comments. The first is about heating to degrade the cement so the crown will separate from the abutment. Do not use flame, place in ceramic furnace at 350 degrees centigrade for 10 minutes and after cooling cooling the units will pull apart. Secondly: if there is sufficient porcelain material you can prep within the ceramic to bond a veneer. This is simple, inexpensive compared to remaking and very dependable with etch bond technique. Esthetics is usually readily easy to match.

I normally provide the Transfer Key for all cement retained abutment case. This key will be used when doctor wants to retrieve the crown and abutment. The Transfer Key provides the exact position where the screw access hole is. It is about 2mm below the occlusal table. Once, doctor drills it, he/she can remove the abutment screw and the retrieve the crown without damage it.