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Cement Vs. Screw Retention

posted in Restoration of Dental Implants, Techniques and Procedures, Dental Implant Materials, Active Posts

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Dr. Collins asks:

In all the courses on dental implants that I have taken this year, the instructors recommend using custom abutments and cementing the crowns and bridges. Some recommend temporary cement and others use permanent cement.

One lecturer provided some vivid demonstrations of what can happen if you torque down a bridge with screws when it does not fit exactly. I am just about to start my first dental implant case – a maxillary second premolar. Should I use cement or screw retention? Is the prevailing opinion in the restoration of dental implants moving in the direction of cement retention? If so, why? I’d be interested in others philosophy and protocols on this subject. Thanks.

22 Responses to “ Cement Vs. Screw Retention ”

• Alejandro Berg October 10th, 2006

  
  

  Dear Dr Collins:
  The prevailling tendency in europe is to screw down the restorations(Branemark style) and in the USA the orientation is to cement them (temporary for retrievability or definitive when that is not an issue or when its not adviseable like in some full ceramic crowns).
  In my personal experience if the implant is correctly placed there should not be a statistical difference in the effectiveness between both types of retention….(actually I am conducting a study in the subject now for ten years) my opinion is simple,cemented restorations are more suitable when you have a bad emergency angle (i.e. vestibular emergence of the screw)or when you desperately need a permanent contact point where the screw hole would be(i.e. oclusal of some molars because the closing resin will wear down and you will lose contact or support in time )and screw retained in probably the rest of the cases. Bridges are no exception, if you take a good impresion and insure the correct fit(I usually ask for two or three part understructure and I fix it with Pattern Resin in the mouth after placing and the lab does laser welding of it), both systems will also work(I tend to do screw retained bridges, they are easier to retrieve if you need to fix something like a chipped ceramic or else)
  In a maxillary second premolar if you have a well placed implant, go with an aesthetic abutment(zirconia) with ceramic directly cooked on top of it and you can do an easy close of the access hole with resin and nobody will ever see it.
  best of luck to you

• Richard Wiggs, DDS October 10th, 2006

  
  

  Personal experience over decades is to use screw-in type for bridges and individual restorations. I restore with Cristobal. These two techniques provides maximum short term and long term control over most troublesome incidents.

• Dr. Berk October 10th, 2006

  
  

  Dr. Collins,
  I am a general dentist and have been restoring implants for about 15 years but in my small practice that amounts to about 150 or so. My sense is that early on we screwed down our restorations thinking it might provide better access to salvage a compromised implant or simply to tighten a loosened restoration. However as we have rightly gained confidence in the long term success of implant cases we have moved on to the concept of providing cases of optimal esthetics. It is my belief that you and your patient will be well served by a custom abutment, properly torqued, and a cemented porcelain fused to gold crown. Should you eventually restore an anterior unit, the zirconia abutments with an all ceramic crown using the system you and your lab prefer, will be a very nice option.

• MS October 10th, 2006

  
  

  Dr Collins,
  Never forget that when your abutment/crown margin is rather deep in the peri-implant sulcus, it might be quite difficult to remove access cement which may, at a later stage, lead to inflammation of the soft tissues. That seems a clear advantage of a screw-retained restoration whereas screw-retention is more expensive to the patient and usually screw-access holes are not always that simple to close in a perfect manner. However, for a single-crown posterior restoration a cemented crown should be the standard.

• Don Callan October 11th, 2006

  
  

  I have found if you treat the implant abutment as a tooth it will work great. Do we use temp cement on natural teeth?? If a screw is used to place the crown on the abutment, there will be a microgap for periodontal pathogens to harbor–thus problem WILL occur later.

• Anonymous October 11th, 2006

  
  

  There is no one way to do it.Keep both types in mind. Primarily in my practice if there is an issue with interocclusal space I use a screw reatained restoration. Custom abutments seem to be all the rage when we are talking to labs, but remember a stock abutment is a machined abutment ( if it can be used)is precisely made to fit the given implant. A cast custom abutment will have a greater chance to leak do to the inherent nature of the fabrication process similar to what Dr.Callan stated with the temp. cement.issue. Custom abuts. are also much more expensive and many times not needed.

• Dr. Dennis Fair October 11th, 2006

  
  

  Over the eighteen years that I have been placing and restoring implants, I have seen many trends come and go and I see this increasing popularity of cemented implant restorations as a trend that will likely lose its favored status some years down the line as dentists have to replace restorations over implants. Anyone who has had to cut off an implant crown whose underlying abutment screw has loosened will attest to the unpleasant task. I have found that cementing restorations, while may be necessary in some situations, does not give a predictably retrievable result, no matter what cement and how temporary its nature. I truly feel that the widespread push for the use of cemented restorations has come in a large part from implant manufacturers seeking to increase the use of implant therapy in the hands of otherwise inexperienced general dentists, encouraging them to think that implant restorations are just like regular crown and bridge (”C&B&I”).

  Whenever I find it necessary to cement restorations over implants, I use all porcelain restorations. These are easier and more predictable to cut off if they cannot be loosened with a tapper or GC pliers (even Procera cores can be cut using diamond burs) We cement Procera crowns permantly due to the increased cement space that these crowns seem to be constructed with and the fact that Improv or TempBond does not adequately hold.

  I feel that screw retaining is best if at all possible, and, failing that,porcelain crowns would be the best choice for a cemented restoration.

  Good luck….I am sure that the debate will continue.

• Michael Johnson October 12th, 2006

  
  

  I am a board certified prosthodontist and have done both screwed and cemented crowns. Screw access holes are a pain. They are unsightly, wreck your occlusal scheme and create a weakness in the porcelain to metal interface.A premolar should be made with a prepped prefab or custom abutment. The custom abutments these days are cast to a titanium connection which indexes into the internal of the implant so the old sloppy fit of custom abutments of old is a moot point. I still temporarily cement my crowns. Screws rarely if ever loosen with the internal connections, but I have seen proximal contacts open up over years of use. Teeth are a dynamic system, and constantly react to muscular forces on them. Implants are not. Therefore, at times, teeth may shift, opening the contact between implant and tooth. It is reassuring to tap the crown off, add the contact and recement rather than cutting it off and starting again.

  Always make sure the lab positions the finish line of the abutment no more that 1-1.5mm subgingival so you can easily remove excess cement.

  Best of luck. You will enjoy restoring implants!

• Ira Langstein, DDS, FICOI October 14th, 2006

  
  

  Re: deep cement lines:

  To overcome this, the custom abutment should flare and emerge up to provide a 1-2mm deep shoulder and that’s where the new cement line would be. To me, screw retained prostheses should be reserved for cases with complications(lack of vertical height) etc.

• randall October 16th, 2006

  
  

  The question to cement or not cement depends on several factors
  1. anterior maxilla typically are better to be cemented due to esthetic and bone constraints placing an implant as lingual as you need in this type of case causes one to create cantalievers no to mention it is hard to opaque out the access port.
  2. on full arch cases with all implants well then by all means use screw retention
  3. all on 4 cases must be screw retained. you will never get an impression at the fixture level with an implant tilted 30-45 degrees.
  the use of angled multiunit abutments is imparative.
  4. with porcelain full arch cases if you screw retain then make individual crowns to fit over the screw accesses this of course requires precise placement of the implants.
  5. minimal interocclusal space may mandate screw retention over cementables.
  6. with most posterior implants, and bridges I prefer cementable to prevent fracturing of the porcelain near the access holes.
  7. never cement acrylic restorations you cannot guarantee retreavability no matter what cement you use, and without a doubt acrylics will need replaced. Porcelain has a much longer life expectancy. I am sure I have not covered all case senarios but good judgement bases on experience and knowledge can not be given in such a limited forum
  Randall

• ira dickerman, cdt March 27th, 2007

  
  

  We have been restoring implants since 1984. When treatment planning implant prosthetics screw retained for retreivability is always a viable option. We always suggest it when there is a lack of implant number, implant size or poor implant position to adequately carry the load. Bruxers, grinders, any time retreivability is important. As we are all aware today, all implant systems require tightening to a required torque value. Without this torque value there is inadequate preload applied to the implant system to maintain screw tightness for a long term. There is a problem however even with properly tightened screws, cyclic loading. Many of us have driven rattle traps (cars) at some point in our lives. All of the screws, nuts and bolts in our automobiles are tightened to a spec too, yet they can loosen. There have been studies done documenting dental implant component deformation over time, preload loss, and screw loosening. Long term ease of retreivability is critical to patient satisfaction and maintenance.
  NobelBiocare has Procera Titanium and Zirconia Screw retained proshthesis, Biomet 3i has Archtiect PSR Hybrid Titanium Frames, and now AstraTech has Cresco Precision Screw retained frames in almost any alloy. On all of the major implant platforms Cresco can be utilized, even reangulating the access holes up to 17 degrees! Screw retained prosthesis are here to stay……..

• Sharon March 27th, 2007

  
  

  Most of my posterior crowns are screw retained; any good information on the “most ideal” technique for covering the screw holes for retention and cosmetics?

• Dennis Nimchuk March 28th, 2007

  
  

  20 years ago I only did screw retained prosthetics. Today it is almost the reverse. I completely agree with the comments made by my fellow Prosthodontist Michael Johnson. Screw retained prosthetics add more complications than the advantage of supposedly easy retrievability. Today’s excellent engaging interfaces and torque wrench protocols have all but eliminated screw loosing as a reason for having an access opening. Contrary to comments above, actually the least complex location in the mouth for screw-retained abutments or crowns are the maxillary anterior teeth but only if the implants can be ideally placed so that the access hole is in lingual fossa.
  As to temporary cements, there are a number of low soluble, resin based cements such as NeoTemp by Teledyne and others by Premier and by Nobel which are retentive but usually can be reverse malleted off, or if single crowns, can be pulled off with contour gripping devices.

• Dr. Mehdi Jafari March 28th, 2007

  
  

  Screw-retained implant restorations have an advantage of predictable irretrievability but demand precise placement of the implant for optimal location of the screw access hole. Deviation from this optimal direction can lead to an unesthetic restoration if screw retention is to be used. Also, obtaining passivity of frameworks that are screw-retained is difficult due to dimensional discrepancies inherent in the fabrication .To eliminate the presence of the screw access hole in esthetically demanding areas, other methods have been used to connect implant restorations to implant abutments or implants. These include the use of pre-angled abutments, which allow screw-retained restorations; cemented implant restorations to angled or custom abutments; and lateral set screws in the restoration, which allow for retention to the abutment. Unfortunately, none of these methods are ideal, and each exhibits advantages and disadvantages. Pre-angled abutments can redirect screw access openings to the occlusal or cingulum areas of implant restorations. However, to allow the abutment to be retained on the implant and still provide sufficient abutment structure to house a retention screw for an implant restoration, the long axis of the implant and the path of the retention screw for the restoration must diverge sufficiently.
  At present, the minimum amount of divergence required to permit the use of a screw-retained pre-angled abutment is 17 degrees .If the divergence of the screw path is less than 17 degrees, the use of pre-angled abutments for screw-retained restorations is not possible.
  Cementation of implant restorations eliminates unesthetic screw access holes. Cemented restorations also have the potential to compensate for any minor dimensional discrepancies in the fit of restorations to abutments, which can contribute to lack of passivity .Minor dimensional discrepancies may be compensated for by using cement and cement space.
  Preformed titanium or ceramic abutments can be secured to the implant and prepared in much the same way that teeth are prepared for fixed restorations. Custom abutments can also be formed by waxing and casting to premachined cylinders that are screw-retained on the implant. Restorations can then be fabricated and cemented to the abutments, similar to conventional fixed restorations.
  When cemented abutments are considered, it is imperative that the cement margin is shaped to maintain a relationship with the mucosal margin. With many manufactured abutments the cement margin is circular, which can lead to deeply located cement margins. Cement removal becomes difficult, if not impossible, and it can lead to soft tissue irritation. The ability to cement implant-supported restorations using techniques similar to conventional fixed prostheses simplifies treatment planning and the restoration of implants. However, a disadvantage of cementing implant-supported restorations is the potential difficulty in retrieving the restoration. Should an abutment loosen or any repair of the restoration become necessary, the restoration may be destroyed during the removal procedure if the cement seal cannot be easily broken. Further, when an abutment screw loosens under a cemented multiunit implant restoration, the restoration is usually uncemented from abutments firmly seated to implants and firmly attached to the loosened abutment(s). Any force applied to a restoration on a loosened abutment has the potential to damage the internal threads of the implant.
  The use of set screws allows a retrieval screw to be placed in a position where a displacing force can be applied in the direction of the abutment to break the cement seal and allow removal of the restorations .The access hole can be placed in a variety of positions, independent of the direction and position of the implant body. Cement can be mixed without using lubricant and still allows the predictable retrieval of the restoration. This technique has the potential to reduce stress to splinted implants, since the effects of minor misfit of the framework are not transferred directly to the implants, as is the case with prosthesis-retaining screws. In addition, the exposure of screw access holes in esthetic areas of the mouth can be avoided.
  The predictable retention and retrieval of screw-retained implant restorations must be weighed against the passivity and lack of screw access of cemented restorations. In my experience, the ability to predictably retrieve restorations and confidently retain them leads me to choose a screw-retained restoration whenever the implant position permits. From a facial and buccal view, esthetics can be achieved with either screw or cement retention. When cemented restorations are required, a mechanism to predictably separate them from the abutment should be incorporated.
  The single advantage of a screw-retained implant system is that of irretrievability. This includes removal of the prosthesis to retighten bridge or abutment screws, replace failed or fractured components, or to perform routine hygiene. The disadvantages of a screw-retained implant system are numerous. First, there is the problem of a lack of esthetics at the screw access channel, particularly if the channel is cast in metal. Second, if the metal is cut back to hide the non-esthetic metal, porcelain fracture around the screw access channel may occur. Third, screw-retained prostheses generally require both the abutment screws and bridge screws to be tightened using a torque driver to effect preload of the screws. This torquing appears to have lowered but not eliminated the incidence of screw loosening. Finally, screw-retained systems generally leave a micro-gap beneath the gingival crest, resulting in chronic gingival inflammation.
  An evaluation of the literature suggests that screw fracture and screw loosening are common occurrences in the traditional hex-top implant systems, regardless of whether the prosthesis is cemented or screw-retained. Various studies indicate an incidence of screw loosening or fracture of between 10 and 56%. The cost of long-term maintenance of these prostheses has not been investigated; nor have comparative studies of the effects of screw versus cement retention of prostheses been performed. Clearly, unless other provisions are made to successfully recover a cemented prosthesis (use of temporary cement, lateral retaining screw, etc), screw loosening in the abutment remains an ongoing concern for traditional hex-top systems.

• Ron Haas March 30th, 2007

  
  

  As a Prosthodontist who has been restoring implants for 20 years, I would say that my views are mostly similar to Dennis Fair. Even with our torque drivers and best efforts, if you restore enough implants, abutment screws will loosen, porcelain will fracture, solder and solid connections will break, abutment screws will break and implants will fail. Even with well chosen provisional cements, some cemented cases will either loosen too frequently or not come off intact, even with the best hydraulic removal devices. Why use screw retention for multiunit implant cases? To ensure predictable retrievability so we can more easily manage these inevitable problems. We have all heard: “Why do we do we screw retain implant cases when we don’t do this for natural teeth? Answer: Because we can!
  Anyone who has had to cut off an extensive cemented implant case (which includes most people who have restored many implants) will agree that it is both frustrating and avoidable. Having the ability to manage the inevitable complications when placing extensive fixed prostheses in multiple patients instills confidence in our patients and helps make practicing less stressful, more predictable and more enjoyable.
  I understand that there are other points of view. Certainly there are reasons to prefer cementable cases including easier fabrication, dificulty in finding labs proficient making screw retained prostheses, and avoiding screw holes. Like most clinical decisions in our practices, we pick the procedures we choose based on weighing the advantages vs. the disadvantages and basically ‘pick our poison’. For the above reasons, I choose screw retention whenever possible for multiunit implant prostheses.

• Gary D Kitzis, DMD April 4th, 2007

  
  

  I agree with Dr. Haas. Furthermore, the most common reason for screw loosening is a non-passive framework. Truly passive frameworks that pass the “Quarter turn test,” (the screw reaches full torque from initial contact with the gold cylinder to full torque in less than 1/4 turn on all the screws) rarely if ever get loose. As far as the screw hole ruining the occlusal scheme is concerned, the access hole isn’t that large, and a tiny composite placed at the top of the access (not on the screw head itself) is durable, easy to remove and can be blended well with the surrounding porcelain. Cement retained frameworks are much more forgiving with regard to impression making/casting/machining accuracy than screw retained frameworks because the cement will take up the slack in a misfit.

• William Nadler July 21st, 2007

  
  

  I am my domestic partner of 20 yrs, both of us have nr. 18, 19 teeth extracted because of cavities, and abscissas. One can not see the spacing just by looking at our mouths.

  We are both 75 yrs old. Do you think we should have a bridge or implant done? Also can we do a cement tooth procedure, without the bridge or implant?

  Which is the best and which is the cheapest way to go.

• Larry Mogen DDS August 1st, 2007

  
  

  I am a general dentist, and have been restoring implants for over 20 years back in the days when the abutment posts were cemented with comspan. I would have to agree that cutting off a restoration when an abutment loosens is a real pain, but you haven’t lived till you try to get out a broken screw. After a trial period with a soft cement, my preference is to cement on the restoration and never look at it again except at the periodic recall visits. Even though problems do occur, implant dentistry is so predictable that if designed and executed well, I would anticipate a long term success.

• Dr John Berne August 28th, 2007

  
  

  I couldn’t agree more with Larry Mogen.Having practised implant dentistry for over 30 years now, and having played golf for longer than that, I have come to the belief that there are 3 fundamental rules in life. 1. Your golf ball will never land next to a distance marker, 2 Given an opportunity a screw will always come loose and 3 a crown cemented temporarily will always come loose when you don’t want it to, and never come off when you want it to.
  So a solution to the last 2 rules is torque and lock in the screw to prevent any possibility of it coming loose and never cement a crown on temporarily unless it is meant to be there temporarily.To use screw retained prostheses means you have to be able to unscrew the screw which inevitably means the screw is not permanently locked in, thereby giving ample opportunity for the screw to come loose. From my extensive experience they do just that, and inevitably in the wrong place at the wrong time.Why is it that practitioners who cement crowns on natural teeth don’t complain that they can’t remove them easily? Because the need to remove them easily is so infrequent that it is rarely a problem. The same applies to implants properly constructed.Remember a crown cemented onto an implant can always be removed with a bur if it has to be.
  I’m not sure I have a solution to the 1st rule in life, other than perhaps to play more golf and become more proficient.Without the need to continually tighten screws and recement crowns there would probably be greater opportunity to do this.

• rob barron May 30th, 2008

  
  

  What is minimum interocclusal height required to restore an implant in the posterior areas? How would you restore a molar tooth implant which has 5mm interocclusal space available?

• bernardA February 11th, 2009

  
  

  dear rob,
  increase the interocclusal clearance first as much as possible (i.e. reduce opposing, even if you have to do endo tx for that opposing tooth), then restore both by pfms - the other one with an implant abutment of minimal ht. If you dont want to reduce the opposing, then reduce/flatten residual ridge bone ht, let heal, then insert implant to desired level (if amount of residual ridge allow). If none of the above is feasible, then don’t be a hero.

• Mark Psillakis April 5th, 2009

  
  

  Having porcelain fracture off a recently issued screw-retained pre-molar early on in my carreer, and the ease and low cost with which it was repaired, IT’S SCREW RETAINED wherever possible! If angulation doesn’t allow for lingually placed access/aesthetics, I usually go for cross-pinning!
  Comments on cross-pinning?

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