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Screw Versus Cement For Implant Prosthesis Installation. Part 1: The Logic Behind the Argument.
Emil L.A. Svoboda PhD, DDS,Published to www.ReverseMargin.com
2AbstractPart 1: The Logic Behind the Argument This subject has been reviewed many times, often with a bias to one side of the
story. Any side can be supported by showing selected clinical pictures. The literature shows no difference in survival of implants on the bases of prosthesis
insertion technique - screw or cement. Yes Residual Cement is not good. What is causing the implants with the Screwed-in
Prosthetics to Fail?Part 2: During 100 years of intra-oral cementation, nobody has published on the effect of
Gingiva, on flow of cement during the cementation process. Dr. Svoboda has created an “in vitro model”, that sheds New Light on the dynamics
of intra-oral cementation. This is a “Game Changer”. This presentation refers to design features and dental procedures that make intra-
oral cementation safer and thus tips the balance in favour of Intra-oral Cementation. See Both Slide Presentations at www.ReverseMargin.com
5Review 2015 of Peri-implant DiseaseMucositis 33% of Implants 48% of the
patientsPeri-implantitis 16% of Implants 26% of the patientsFailure Rate 8.3% of implants 13% of the patients
Based on 225 implants and 96 patients Average 2.3 Implants /Patient
Average time 10.9 years, implant survival rate 91.7%
Daubert DM et al. Prevalence and predictive factors for peri-implant disease and implant failure: a cross-sectional analyses. J Periodontol 2015:86(3): 337-347
6Pivotal Study - Peri-implant Disease All patients had received cemented single unit implant crowns 39 consecutive patients with 42 implants with peri-implant disease -
test 12 of the same patients had 20 implants without disease and
without subgingival cement – controls-- 32% 34 of 42 the test implants had Residual Subgingival Cement ( 81%)
and thus 8 (19%) had Peri-implant disease without subgingival cement.
After Cement Removal 25 of the 33 (lost one patient) no longer has signs of peri-implant disease after 1 month. (An additional 8 (20%) patients still had disease) - that’s 40% with peri-implant disease without residual cement !
Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-1392
14Extra-oral Cementation Makes the Implant-Abutment Connection Worse!
1. Solidifies Impression-Model Error2. Makes Abutment installation more complex3. Makes Prosthesis installation more complex4. Limits Use, as Implant Position More
Important5. Creates Technique Related Cantilevers for
Screw Access
15Screw-in versus Cement-in Prosthetics Prosthetic Insertion
TechniqueScrew-in Cement-in
Abutment-Crown Assembled on inaccurate model
before installation of abutment(s)
Assembled in mouth after installation of
Abutment(s)
Adjusting Contacts/Occlusion Difficult EasyOptimized Implant-Abutment Fit
Unknown/No Yes
Path of insertion considerations Yes NoScrew access hole considerations
Yes No
Cause Technique Related Cantilevers
Yes No
Removable Yes Yes/NoResidual Excess Cement No Yes/No*
18What about Problems related to Screwed-in Prosthetics?
The BIG PROBLEM is: They Cause a“MISFIT or OPENING at Implant-Abutment
Connection”at the deep subgingival bone level.
Dental Implant Prosthetics. Carl Misch, 2nd Edition, Elsevier-Mosby, 2015,Ch 28.Passive Fit in Screw Retained Multi-unit Implant Prosthesis Understanding and Achieving: A Review of the Literature. M.M.Buzaya and N.B. Yunus. J Indian Prosthodont Soc. 2014, Mar;14(1):16-23 – an elusive goal!Bacterial leakage of different internal implant/abutment connections. Nasar HI and Abdalla M. Future Dental Journal 2015
19What Puts the Retaining Screw at Risk of Failure to Prevent an Open Implant-Abutment Connection??
1. Lower torque levels2. Increased distance from implant-abutment to contact point3. Smaller implant platform diameters4. Cantilevers (off axis forces)5. Tight contacts 6. Multi-unit Prosthesis inaccuracies7. Function
Let’s Look at the above problems More Closely ………..
201. Using Lower Torque to Tighten Abutment Screws
When an abutment screw is tightened, it clamps the abutment to the implant base. Anything that reduces the Clamping Force (red arrow) reduces its ability to hold the Prosthesis onto the implant.
35 NCm torque can give 741 Newtons20 NCm torque can give 423 Newtons
Reducing Torque from 35 to 20 NCm
reduces clamping force by a whopping 43%
Size and shape, metal, thread shape, thread frequency and fit all affect the optimal magnitude of this force for specific clamping screws.
Even a Small Cantilever can reduce the ability of an Abutment Screw to effectively resist an occlusal load.
Many Implant Companies are reducing their platform diameters and thus rendering their Abutment Screws more susceptible to failure under load!
275. Tight Contacts Can Cause Misfits of the Implant-Abutment
Connections!This misfit can be very difficult to detect at the time of affixing the prosthesis. Tactile senses and x-ray imaging only detect gross misfits, even with perpendicular imaging.This misfit can cause early screw loosening and peri-implant disease!
Figure from “Dental Implant Prosthetics, Carl E. Misch,2nd Edition Elseier Mosby, 2015 Pg 739
286. Multiple unit screw retained prosthetics just amplify the effect of stress and misfit between
units!
The stress caused by the misfit of the individual retainers plus the pontic(s) between them, tends to push or pull the connected retainers and thus increases the amount of misfit and opening of their margins – at the bone level!
il Svoboda PhD, DDS 2015Figure of implants above from “Dental Implant Prosthetic, Carl E. Misch, Elseier Mosby, 2005 Pg 417
29Acceptable Levels of Misfit at the Implant–Abutment Interface - An error of 100 microns is
considered clinically acceptable*.
*Review: Passive Fit in Screw Retained Multi-unit Implant Prosthesis Understanding and Achieving: A Review of the Literature. M.M.Buzaya and N.B. Yunus. J Indian Prosthodont Soc. 2014, Mar;14(1):16-23Branemark PI, Zarb GA, Albrektsson T. Tissue -integrated prostheses. Chicago: Quintessence; 1985. p. 253
31Stress on Retainers keeps abutments from seating and creates misfit of components!
Abutment on Driver with
retaining screw facing upwards
Top of implant “external hex” showing residual
biological mass !
32Can You Imagine that“All-On-4” Screwed in Prosthetics are removed 1X /Year for Cleaning under
their Huge Non-cleanable Cantilevers!It takes only 4 hours for bacterial colonies to be seen on abutment surfaces.Nakazato, G., Tsuchiya, H., Sato, M.,Yamauchi, M., In vivo plaque formation on implant materials. Int J Oral Maxillofac Implants 1989; 4(4):321-6
337. What makes the fit worse? Intra-oral Function
The machining process for the mass produced dental implants and abutments creates irregularities between mating surfaces…. tiny hills and valleys …mating surfaces can settle as a result of intra-oral function and the resulting micromovement ….
This can loosen screws and create openings between implant components … these openings allow for the ingress and proliferation of bacteria which are known to be able to cause premature loss of osseointegrated dental implants.Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2005 Pg 453Zipprich Micro Movements on Implant Abutment Interfaces. Part 1&2. http://youtu.be/AssjiYjmTLE, June 12, 2013.
What do you think would resist the loads of function better??a) An optimized implant-abutment connection or
…..b) A stressed implant-abutment connection that
is already open due to misfit?I am sure your answer is a) – So make it your priority to optimize this important connection!
35“When a Prosthesis is Cemented together with its Abutment Outside of the mouth ….
it becomes a larger rigid – a more complex unit to manipulate. The models on which the prosthesis is assembled, are still not accurate enough
and thus the prosthesis can push or pull the abutments off their intended base(s) When installing into the mouth, it can be very difficult to determine “How tight
is too tight” for Contact(s) with adjacent teeth. Too tight creates misfits. When the abutment screw is finally torqued into place, the prosthesis can tend to
shift to accommodate the physical reality of the matching implant-abutment platforms. This can cause misfits and stress on the implant-abutment connection.
All of the above issues can cause damaging misfits at the implant-abutment junction at the bone level!
36What else causes misfit of screw retained prosthetics?
Adjacent structures (gingiva, alveolar bone, calculus, residual graft material) can get trapped between mating surfaces of abutments and dental implants.
This misfit is often very difficult to detect, especially with the larger pre-assembled units of screwed in prosthetics.
“Some dental implants with flat mating surfaces are probably worse than other abutment-implant designs at trapping tissues between them” – Dr. ES
38What about the Benefits of Screwed-in Prosthetics?
1. Easy to remove and re-insertion Many loose screws that require tightening are probably loose
because of abutment prosthesis misfits and design related cantilevers
Removal of most crowns and fixed bridges are for porcelain repair or open contacts. They are remakes anyway, so cutting a facing (if necessary) to engage an access screw is an alternate possibility for removal.
Removal and re-insertion will probably not make a multi-unit prosthesis fit better.
Multiple removals for hygiene is expensive and will probably wear out the inside of the implant that engages the clamping screws and cause a permanent deformation of the top of the implants (not so good for a replacement prosthesis)
Removal of a hybrid acrylic prosthesis for repair purposes is probably beneficial.
39What about the Benefits of Screwed-in Prosthetics?
2. Avoid problems related to residual subgingival cement
Yes, but do not forget Screwed in Prosthetics are cemented (assembled) in the lab and this causes additional inaccuracies and stress on the implant-abutment connection. They are also more difficult to install because of their complexity and contacts with adjacent teeth.
It’s a trade-off between Open Implant-Abutment Junction and Residual Cement
What if Intra-oral Cementation Just Became Safer??
for the creation of a Passive Fit between Retainers and the ProsthesisThe cement space (40 to 120 microns), created between the prosthesis and the retainer allows for some tolerance in the system.This allows the clinician to “Optimize the Fit” of the abutment-implant interphase. This is very important!
What if Intra-oral Cementation Just Became Safer??
Screw Versus Cement For Implant Prosthesis Installation. Part 2: The Game Changer that tips the
balance in Favour Intra-oral Cementation. Emil L.A. Svoboda PhD, DDS,
Published to www.ReverseMargin.comNovember 12, 2015