screw versus cement for implant prosthesis installation part 1

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

November 12, 2015

1

© Dr. Emil Svoboda PhD, DDS 2015

Next View Part 2: The Game Changer that tips the balance to Favour Intra-oral Cementation.

© Dr. Em

il Svoboda PhD, DDS 2015

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

http://www.reversemargin.com/

“Many advances in the field of Dentistry have improved the quality of care we can offer our patients.”


3

There is still a significant problem with the deterioration of the

Foundation of our restorations due to the loss implant osseointegration

© Dr. Em


4Review 2013 of Peri-implant Disease

Mucositis 30.7% of Implants 63.4% of the patientsPeri-implantitis 9.6% of Implants 18.8% of the patients

Based on 6,283 implants and 1,497 patients Average 4.2 Implants /Patient

Average time 8.9 years ( Range 5 to 13 years)

Atieh MA et al. The Frequency of Peri-implant diseases: A systemic review and meta-analyses. J Periodontol 2013:84(11):1586-1598

© Dr. Em


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


© Dr. Em


7Data Re-Interpretation Peri-implant Disease

Conclusion 1With the Cementation System used

32% had no Residual Subgingival 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

“Not every cementation case ends up with Residual Excess Cement”

© Dr. Em


8Data Re-Interpretation Peri-implant Disease

Conclusion 2About 60% of the peri-implant disease cases

Were helped by removingResidual Subgingival Cement

And appeared to be disease free after 30 days Thomas G Wilson Jr. The Positive Relationship Between Excess

Cement and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-1392

“Some cases get better when Residual Excess Cement is removed”

© Dr. Em


9Data Re-Interpretation Peri-implant DiseaseConclusion 3

About 40% of the peri-implant disease caseshad NO Residual Subgingival Cement!

(Sample Size Small) Perhaps this group of patients already had less problems related to

implant-abutment misfit, because of the process of intra-oral cementation

Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A Prospective Clinical

Endoscopic Study. J. Periodont 2009;1388-1392“There is much more to the story than Residual Excess Cement”

© Dr. Em

il Svoboda PhD, 2015

10Review 2014 of Peri-implant Disease

Systematic Review included 2882 Dental Implants - 25 papers

Major failures ( implant or prosthesis failure )No Significant Difference in Implant Survival, related to

Installation Technique - Screw versus Cement

Sherif S et al. A Systematic Review of Screw- versus Cement-Retained Implant Supported Fixed Restorations. J of Prosthodontics 2014 (23)1-9

There are still Significant Weaknesses in the Implant-Prosthesis Complex


11

1) Implant-Abutment Connection at the alveolar bone level

2) Prosthesis-Abutment Connection at the more superficial gingival level

Screw-in Technique


12

Abutment-Prosthesis Complex is Cemented Together Extra-

orallyinto a rigid complex,

that fits on a physical model, and then screwed into the mouth


Abutments are individually screwed into the mouth

and then the Prosthesis is Cemented onto the Abutments Intra-orally.

Cementation Technique

© Dr. Em


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*

© Dr. Emil Svoboda PhD, DDS 2015 * New Information Below

© Dr. Em


16What about Screwed-in Prosthetics?

They do have Benefits too!1. Easy to remove and reinsert2. Avoid problems related to residual

subgingival cement

We will discuss these Relative Benefits again later ….

© Dr. Em


17Further Analysis of the Process ofScrewing-in

Assembled Abutment-Prosthesis Complexes

© Dr. Em


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

© Dr. Em


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.


21Reducing torque to 35 to 20 NCm

reduces clamping force by a whopping 43%

Many of our smaller diameter implants, commonly used for incisors, specify a 15 or 20 NCm insertion torque for the Implant-Abutment Screw

Prosthetics screwed into place at these lower torques would be much less able to resist displacement by tight contacts or indeed functional load.


222. What About Prosthesis Contact Position?

Class 1 Lever Mechanics ApplyEg. Load Force (LF) – Screw Clamping Force = 741 N

Radius of 4.5 mm Implant Top (D1) = 2.25 mmLength of Lever Arm (D2) = 10 mmEffort Force (EF) = the minimum Resistance that the

Contact must provide to keep the abutment from seating

EF = LF X D1/D2 = 167N Effort Force needs to be only 22.5% of the Clamping Force to keep the Abutment from

seating!

LF

EF

D1

D2

Google Lever Mechanics - https://en.wikipedia.org/wiki/Lever© Dr. Emil Svoboda PhD, DDS 2015

23Varied Lever Arm Lengths and Implant Diameters

EF

LF

D1

D28 mm 10 mm 12 mm0

20406080

100120140160

Force Threshold (N) Exerted Against Proximal Contact that could keep Abutments from Seat-

ing (Abutment Screw Torque 20 NCm, 423 N

Clamping Force)

3 mm 3.5 mm 4.5 mm 5.7 mm

As Distance from Implant-Abutment Connection Increases, the risk of open connections also increases.


24

423 7410

50

100

150

200

250

Force Threshold (N) Exerted Against 10 mm High Proximal Contact that could keep

Abutments from Seating during Installation

3 mm 3.5 mm 4.5 mm 5.7 mmImplant Diameter

Newtons

3. Varied Abutment Clamping Screw Torque and Implant Platform Diameter

D1

EF

D2

LF


Many implants reduce implant radius for perceived benefits of “Platform Switch”. This also reduces the mechanical advantage of the clamping screw.

254. What about Effect of a 3 mm Cantilever on Various Implant

Diameters.EF implant implant D2 LF Abutment Mechnical

diameter radius (D1) Screw Torque Disadvantage

N mm mm mm N NCm371 3.0 1.50 3 741 35 50%

432 3.5 1.75 3 741 35 58%

494 4.0 2.00 3 741 35 67%556 4.5 2.25 3 741 35 75%618 5.0 2.50 3 741 35 83%679 5.5 2.75 3 741 35 92%741 6.0 3.00 3 741 35 100%

Fulcrum

D2=3 mm

EF

“We often create cantilevers to accommodate lingual access holes for anterior teeth and think we can extend huge posterior cantilevers without

risk!”© Dr. Emil Svoboda PhD, DDS 2015

26What about Effect of a 3 mm Cantilever on Various Implant Diameters.

Fulcrum

D2=3 mm

EF

“With Screwed in Prosthetics we often create cantilevers to accommodate lingual access holes for anterior teeth??”


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!

© Dr. Em

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

© Dr. Em


Figure of implants above from “Dental Implant Prosthetic, Carl E. Misch, Elseier Mosby, 2005 Pg 417

Even the theoretical suggestion of “not more than 10 microns”, by PI

Branemark in 1985, could be considered sloppy when considering that

periodontal pathogens are only 1 micron in diameter and less.

© Dr. Em


30Overdenture retaining “Screwed-on framework” removed - Smells Bad!!

Undersurface of framework and tops of intra-oral abutments reveal the extent of a noxious

Biological Brew!

© Dr. Em


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


I wonder what happens to the screw threads inside the implants after 10-20 years …. 10-20X removal and tightening?

I know this removal process is expensive to do …. Does this service even have a remote chance of being effective???

© Dr. Em


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.

http://youtu.be/AssjiYjmTLE

© Dr. Em


34“Intra-oral Function”

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!


© Dr. Em


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

© Dr. Em


37What about the Benefits of Screwed-in Prosthetics?

1. Easy to remove and reinsert2. Avoid problems related to residual

subgingival cement

We will discuss these Relative Benefits again later ….

© Dr. Em



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.


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??

© Dr. Em


40Intra-oral Cementation onto already installed Abutments allows

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

41


Go to View

screw versus cement for implant prosthesis installation part 1

Health & Medicine