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Screw Versus Cement
For Implant Prosthesis Installation.
Part 1: The Logic Behind the Arguments.
Emil L.A. Svoboda PhD, DDS,
Published to www.ReverseMargin.com
Update January 2, 2016
1
Next View Part 2: The Game Changer that tips the
balance to Favour Intra-oral Cementation.
Abstract
Part 1: The Logic Behind the Arguments
 This subject has been reviewed many times over many years. Some conclusions do not follow from the evidence presented in the articles, or they simply ignore pertinent
evidence from the literature. Ignoring evidence about problems in the system makes it difficult to make informed conclusions.
 The recent reviews are unable to show a difference in survival of implants on the bases of prosthesis insertion technique - screw or cement. It appears to be too difficult to
see through the many variables contained in the studies that are the foundations of the reviews. Let us say the failures using either system, are about 5% for 5 years and 8
% for 10years, and the implants require significant home and professional care to reduce the impact of peri-implant disease.
 What is causing the implants attached to Screwed-in Prosthetics to Fail? This is an important question. Let us review some of the less visible causes of these failures. Some
failures appear to be related to implant-abutment misfit and exacerbated by mechanical challenges created by a need for prosthesis retrievability. These problems of
screwed-in prosthetics appear to be very difficult to solve. They are discussed here.
 Intra-oral cementation can optimize the fit of the implant-abutment connection. However, subgingival residual excess cement is a known risk factor for peri-implant
disease. We know that it can be removed and thus reduce peri-implant disease by 60% (Slide #12). What if it could be prevented? That could surely reduce implant failure.
That will be discussed in Part 2 below.
Part 2: The Game Changer that tips the balance to Favor Intra-oral Cementation.
 During 100 years of intra-oral cementation, nobody seems to have published on the effect of Gingiva on the flow of cement during the intra-oral cementation process.
Understanding this process is the key to mitigating its negative effects.
 Dr. Svoboda has created an “in vitro model”, that sheds New Light on the dynamics of intra-oral cementation. This is a “Game Changer”. Understanding the “Gingival
Effects” changes the logic behind the approach to intra-oral cementation. This is the basis of a new Cement Control System™ that allows us to prevent the poorly
controlled injection of cement into the subgingival environment. This cement can be difficult to detect and remove.
 This presentation refers to design features of the abutment-prosthesis complex and the dental cementation process that can make intra-oral cementation safer. Safer
cementation also helps the clinician optimize the fit of the implant-abutment junction, unlike that seen with screw-in prosthesis techniques. The herein described
innovations will likely tip the balance in favor of intra-oral cementation and hopefully reduce the incidence of implant treatment failure. Failure is expensive for patients,
clinicians and the entire implant industry. It can be especially damaging to the patient-dentist relationship.
See Both Slide Presentations at www.ReverseMargin.com
2
“Many advances in the
Field of Implant Dentistry have improved the quality
of care we can offer our patients.”
3
There are still significant problems contributing
to the deterioration of the
Foundations
of our restorations through
loss of implant osseointegration.
Review 2013 of Peri-implant Disease
Mucositis 30.7% of Implants 63.4% of the patients
Peri-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)
No Difference Between Cement or Screw Installation
Atieh MA et al. The Frequency of Peri-implant diseases: A systemic
review and meta-analyses. J Periodontol 2013:84(11):1586-1598
4
Review 2014 of Peri-implant Disease
2,387 Cemented-in & 3,471 Screwed-in Prostheses
5 years Survival Rates about 96%
10 years Survival Rates about 92%
No Difference Between Cement or Screw Installed
Prosthesis Survival Rates
Whittneben et al. Clinical Performance of Screw- Versus Cement Retained
Fixed Implant-Supported Reconstructions: A Systemic Review. The Int J Oral
Maxillofac Implants; 2014:29(Suppl):84-98.
5
Review 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
6
Sherif S et al. A Systematic Review of Screw- versus Cement-Retained Implant
Supported Fixed Restorations. J of Prosthodontics 2014 (23)1-9
Review 2015 of Peri-implant Disease
Mucositis 33% of Implants 48% of the patients
Peri-implantitis 16% of Implants 26% of the patients
Failure 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%
No Difference Between Cement or Screw Installation
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
7
Conclusions from the Reviews
Considering that these Reviews seem to be “tilling the same old soil”, is there any
wonder that the results are similar?
The details differ, but success and failure of dental implants is where the “Rubber meets
the Road”
No Difference Between Cement or Screw Installation
However there is however One BIG Difference that I see!
With Peri-implant Disease, it is often possible to remove excess cement and expect an
improved result! How do you treat Peri-implant Disease when dealing with the
Screwed-in Technique? It is very difficult to correct the implant-abutment misfit! What
about implant distortion due to this misfit? Not even a remake will solve these
problems! Let’s look at this in more detail …….
8
Study by TG Wilson 2009
Residual Excess Cement & Peri-implant Disease
1. All patients received cemented single unit implant crowns
2. 39 consecutive patients with 42 implants had peri-implant disease - test
3. 12 of the same patients had 20 implants without disease and without detectable
subgingival cement – controls-- 32%
4. 34 of 42 the test implants had Residual Subgingival Cement ( 81%) and thus 8
(19%) had Peri-implant disease without subgingival cement.
5. 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) - Therefore 40% of peri-implant disease implants had no detectable
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
9
Data Re-Interpretation
“Incidence of Residual Cement”
Observation 1
With the Cementation System Used
45% had no Visible Residual Subgingival Cement!
(20+8 = 28, 28/62= 0.45)
Thomas G Wilson Jr. The Positive Relationship Between Excess Cement
and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J.
Periodont 2009;1388-1392
10
“Not every cementation case ends up with Residual Subgingival Cement”
This is also an underestimate, as the group was pre-selected to represent the work from clinicians who
had restored single cemented crowns to have at least 1 implant with peri-implant disease.
Peri-implant Disease
“Some Get Disease without Cement”
Observation 2
With the Cementation System Used
13% had No Visible Residual Subgingival Cement but had Peri-
implant Disease! (8/62= 0.13)
Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A
Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-92
11
“However the rate of peri-implant disease is much less than the 30-50% expected from
the Reviews cited.
Does cementation create a better fit of implant-abutment connection and thus decrease disease by
more than 50%? This could be very interesting!”
Peri-implant Disease Reduced by Cement
Removal!
Observation 3
About 60% of the peri-implant disease cases
were helped by removing
Residual 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
12
“Most cases get better when Residual Subgingival Cement is removed”
Not Only Cement Causes
Peri-implant Disease
Observation 4
About 40% of the peri-implant disease cases
had NO Residual Subgingival Cement!
(8+8=16, 16/42 = 0.40, Sample Size Small)
Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A
Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-92
13
“There is more to the story than Residual Subgingival Cement. The impact of the
implant-abutment fit and its stability under load conditions needs to be investigated
further under controlled conditions.”
There are still Significant Weaknesses in the
Implant-Prosthesis Connections
Affected by Installation Technique.
14
1) Implant-Abutment Connection at the
alveolar bone level
2) Prosthesis-Abutment Connection at
the more superficial gingival level
The Screw-in Technique 15
1. Abutments and prosthesis are cemented
together Extra-orally into a rigid Complex.
2. This complex is made to fit on a model
representing the mouth.
3. This Complex is then screwed onto dental
implants already in the mouth.
It is difficult to asses fit or adjust contacts during
prosthesis installation. The implant-abutment connection
can be prevented from seating properly by tight contacts
with adjacent teeth and inherent prosthesis-model
inaccuracies.
Extra-oral Cementation Makes the
Implant-Abutment Connection Worse!
16
1. Solidifies Impression-Model Error because is
assembled on the model not in the mouth. This
error in dimension is huge!
2. Makes Abutment Installation more complex
3. Makes Prosthesis Installation more complex
4. Limits Use. Implant Position more important
5. In the anterior, it often requires technique
related cantilevers for hiding screw access holes.
Screwed-in Prosthetics introduce unnecessary mechanical and biological risk factors that affect the
survival of implant treatment. These risk factors can be very difficult to mitigate.
17
1. Abutments are individually screwed onto
dental implants inside the mouth.
Implant-abutment connections are not affected
by contacts or prosthesis-model inaccuracies.
Their fit is optimized.
2. The prosthesis is cemented onto the custom
abutments.
It is relatively simple to adjust occlusion, fit and
contacts prior to cementation. Implant angle is
not so critical. The abutment-prosthesis
connection is easier to control than the implant-
abutment connection.
Cementation Technique
Screw-in versus Cement-in Prosthetics
Prosthetic Insertion Technique Screw-in Cement-in
Abutment-Prosthesis
Complex
Assembled on and fit to
an inaccurate model
before installation
Assembled in mouth
after installation of
Abutment(s)
Adjusting Contacts/Occlusion Difficult Easy
Optimized Implant-Abutment Fit Unknown/No Yes
Path of insertion considerations Yes No
Screw access hole considerations &
repair
Yes No
Cause Technique Related
Cantilevers
Yes No
Removable Yes Yes/No*
Residual Excess Cement No Yes/No**
18
*Many can be removed by creating an access hole.
**Presentation Part 2: The Game Changer that tips the balance to Favour Intra-oral Cementation.
What about
Screwed-in Prosthetics?
They do have Benefits too!
 Easy to remove and reinsert
 Avoid problems related to residual
subgingival cement
They can be used in short crown situations
19
We will discuss these Relative Benefits later ….
Further Analysis
of the Process of
Screwing-in the Assembled
Abutment-Prosthesis Complex
“The Screw-in Technique”
20
What 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
21
What Puts the Abutment Retaining Screw at
Risk of “Failure to Prevent” an Open
Implant-Abutment Connection?
1. Lower screw torque levels
2. Tight contacts and Increased distance from implant-abutment
connection to contact point with adjacent teeth
3. Smaller implant platform diameters
4. Cantilevers (off axis forces)
5. Multi-unit Prosthesis inaccuracies
6. Function
22
Let’s Look at the above problems More Closely ………..
1. 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 Newtons Clamping Force
20 NCm torque can give 423 Newtons Clamping Force
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.
23
Reducing torque to 35 to 20 NCm
reduces clamping force by a whopping 43%
 Many of our smaller diameter implants, including those 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 a functional load and by
*tight contacts with adjacent teeth.
24
*see 2 below
2. 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
optimal perpendicular imaging.
This misfit can cause early screw loosening and
peri-implant disease!
25
Figure from “Dental Implant Prosthetics, Carl E. Misch,2nd Edition
Elseier Mosby, 2015 Pg 739
“The final torqueing down of the retaining screw can tend to shift or realign the abutment on its base.
This can cause a tight contact on one side and a loose one on the other. At best, you will have a open
and/or tight contact, at worst the abutment will be prevented from seating!”
What About Prosthesis Contact Position?
Torque on Clamping Screw 35 NCm (20 NCm)
Load Force (LF) is Screw Clamping Force 741 N (423 N)
Radius of 4.5 mm (3.0) Implant Top (D1) = 2.25 mm (1.50 mm)
Length of Lever Arm (D2) = 10 mm
Effort Force (EF) = the minimum Resistance that the Contact must provide to
keep the abutment from seating
EF = LF X D1/D2 = 167 N (63 N)
Effort Force (Resistance offered by a tight contact with an
adjacent tooth) needs to be only 22.5% of the Clamping Force to
keep the Abutment from seating!
Class 1 Lever Mechanics - Google Lever Mechanics -
https://en.wikipedia.org/wiki/Lever
LF
EF
D1
D2
26
“It is not possible with office dental imaging or tactile techniques to detect such misfits in the 15 micron
range. Too bad since oral pathogens are about 1 micron in diameter and less.”
Varied Lever Arm Lengths to Contact Position
and Implant Diameters
0
100
200
8 mm 10 mm 12 mm
Force Threshold (N) Exerted Against Proximal Contact
that could keep Abutments from Seating
(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 to the contact increases, so does the
risk of a tight contact preventing an abutment from seating.
27
LF
EF
D1
D2
Varied Lever Arm Lengths
and Implant Diameters
EF
LF
D1
D20
100
200
8 mm 10 mm 12 mm
Force Threshold (N) Exerted Against Proximal Contact
that could keep Abutments from Seating
(Abutment Screw Torque 20 NCm, 423 N Clamping
Force)
3 mm 3.5 mm 4.5 mm 5.7 mm
As the Lever Arm Length Increases so does the risk of
forces generated by function opening the implant-abutment connection.
28
0
100
200
300
423 741
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 Implant Platform Diameter
29
Many implants reduce implant radius for perceived benefits of “Platform Switch”.
This also reduces the mechanical advantage of the clamping screw. This may not be ideal in
the posterior of the mouth!
4. What about Effect of a 3 mm Lateral Cantilever
on Various Implant Diameters.
EF implant implant D2 LF Abutment Mechnical
diameter radius (D1) Horizontal
Screw
Torque Disadvantage
N mm mm mm N NCm
*212 3.0 1.50 3 423 20 50%
245 3.5 1.75 3 423 20 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%
*33 3.0 1.50 3 423 20
+10mm
vertical lever
Fulcrum
D2
=3 mm
EF
“We often create cantilevers to accommodate lingual access holes for anterior teeth.
This puts the implant-abutment connection at additional risk!”
30
Example: Lets take a lateral incisor with a 3.0 mm abutment base and use a
20 NCm torque to seat it into place. There is a 10 mm distance from the
implant-abutment connection to the contact with an adjacent tooth and
we need to create a 3 mm cantilever to create abutment screw access from
the lingual.
Fulcrum
D2
=3 mm
EF
“We often create additional cantilevers to accommodate lingual screw access holes for anterior teeth.
This puts all the implant-abutment connections at increased risk of failure!
This additional risk of failure is technique related.”
31
 1. -Narrow Diameter 3 mm platform for incisors or platform switch purposes
 2. -Reduced 20 NCm torque force on screw. Clamping force that would seat crown is
423 Newtons
 3. -Effort Force (EF) by a tight contact that would keep the abutment from seating or the
functional force required to dislodge the crown from the abutment would be : EF=
423X1.5/10= 65 N *** Start Sweating!
 4. -Creating a 3 mm Lateral Cantilever for screw access reduces the Effort Force by 50%
to dislodge crown from abutment – 33N ***** Bingo! No Hope!
 Average Force often used to cement a crown is 40N – That finger pressure alone can
open the above implant-abutment connection! Is that not scary to you?
5. 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!
There is at least one major implant company that voids their “Warrantee” when
clinicians choose to insert a multi unit prosthesis in such a fashion!
They take this type of misfit seriously! You should too.
32
Figure of implants
above from “Dental
Implant Prosthetics,
Carl E. Misch, Elseier
Mosby, 2015 Pg 740
Acceptable Levels of Misfit at the Implant–Abutment Interface -
An error of 100 to 150 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):16-23
*Passive Fit could not be achieved with Screwed-in Prosthetics!
Comparison of the Accuracy of Different Transfer Impression Techniques for Osseointegrated Implants. Zen BM et al.
JOI Vol 41 No 6 2015: 662-667
Branemark PI, Zarb GA, Albrektsson T. Tissue -integrated prostheses. Chicago: Quintessence; 1985. p. 253
33
Figure of implants
above from “Dental
Implant Prosthetics,
Carl E. Misch, Elseier
Mosby, 2015 Pg 740
Even the theoretical suggestion of “not more than
10 microns error”, by PI Branemark in 1985, could
be considered sloppy when considering that
periodontal pathogens are only 1 micron in
diameter and less.
Overdenture retaining a “Screwed-on
framework” was removed - Smells Bad!!
Undersurface of framework and tops of intra-oral abutments reveal the
extent of a noxious Biological Brew!
34
Stress on Retainers keeps abutments from seating
and creates misfit of components!
Abutment on
Driver with
retaining screw
facing upwards
35
Top of implant “external
hex” showing residual
biological mass !
This patient’s immune system was able to resist peri-implantits in spite of a massive bacterial inoculum.
Can You Imagine that some
“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
36
“I wonder what happens to the screw threads inside the implants after 10-20 years ….
10-20X removal and tightening? Do the tops of the implants distort when loaded
unevenly? Can that be fixed? I know this removal process is expensive …. Does this
particular service even have a remote chance of being effective long term?”
6. 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.
37
Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2005 Pg 453
Zipprich Micro Movements on Implant Abutment Interfaces. Part 1&2.
http://youtu.be/AssjiYjmTLE, June 12, 2013.
“Intra-oral Function”
What do you think would resist the loads of function better?
a) An optimized implant-abutment connection or …..
b) A stressed and perhaps deformed 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! Today this can only be done by the
process of intra-oral cementation.
38
How do you correct an Implant-
Abutment Misfit?
How do you repair a deformed or
damaged Implant Platform?
Not Even A Remake Can Solve these
BIG Problems!
39
In Summary - When a Prosthesis is Cemented together
with its Abutment Outside of the Mouth ...
 It becomes a larger rigid and more complex unit that amplifies dimensional errors through
extended length, and it is difficult to manipulate intra-orally.
 The model on which the prosthesis is assembled, is not accurate enough. Thus the
assembled prosthesis will push or pull the abutments off their intended base(s) and cause
increase implant-abutment misfits when screwed into place inside the mouth.
 When installing the prosthesis into the mouth, it can be very difficult to create ideal
contacts with adjacent teeth. “How tight is too tight?” 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 a change in contact pressure and
cause additional stress and misfits of the implant-abutment connection.
All of the above issues are BiG PROBLEMS that can and do cause damaging
misfits at the implant-abutment junction that is at the deep alveolar bone level!
40
What else causes a 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
41
What about
Screwed-in Prosthetics?
They do have Benefits too!
 Easy to remove and reinsert
 Avoid problems related to residual
subgingival cement
They can be used in short crown situations
42
We will now discuss these Relative Benefits ….
What about the Benefits of Screwed-in Prosthetics?
1. Easy to remove and re-insert 43
Many loose screws that require tightening are probably loose because of abutment
prosthesis misfits and design related cantilevers.
A misfit may lead to a permanent deformation of the top of the retaining implants.
This is not so good for a replacement prosthesis. This is a disaster.
Removal of most crowns and fixed bridges are for porcelain repair or open contacts.
They are usually remakes anyway. Cutting them to engage an access screw is often
not such a disaster.
Removal and re-insertion will probably not make a multi-unit prosthesis fit better.
This is a disaster.
Multiple removals for hygiene is expensive and will probably damage the inside of the
implant that engages the clamping screws. This may become a disaster.
Removal of a hybrid acrylic prosthesis for repair purposes or an acute problem is
probably beneficial. Some procedures can also be done without removal.
What about the Benefits of Screwed-in Prosthetics?
2. Avoid problems related to residual subgingival cement.
44
 Yes, but do not forget, Screwed in Prosthetics are cemented (assembled) in the lab on inaccurate
models. 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.
 Unlike the non-assembled abutment and prosthesis, the assemblies are difficult to sterilize prior to
delivery, because the cement may degrade at high temperature. (see Part 2: all abutments, prosthetics
and models are sterilized (not sanitized) prior to delivery to patient’s mouth)
What if Intra-oral Cementation Just Became Safer??
It’s a trade-off between the misfits of the Implant-Abutment Junction and Residual
Subgingival Cement. Cement can often be accessed surgically or by endoscopic means
and cleaned away. What can you do about misfits??
What about the Benefits of Screwed-in Prosthetics?
3. They can be used in short crown situations
45
 Yes, the screw-in technique can be useful in these situations.
 As the adhesive properties of dental cements have improved, the definition of a short crown also
changes. Crowns are already cemented onto natural teeth without traditional mechanical retention.
With the screwed-in prosthesis technique, the crowns are already cemented onto their abutments in
the lab. They seem to hold.
 The Reverse Margin™ Design can add 1 or 2 mm to crown length by lowering the base of the margin.
The inflected part of the margin plus the additional central post length can effectively increase the
retentive surface area.
Adhesive technology and other properties of cement have improved dramatically over
the years. Margin designs have also improved. Short crowns are not so much of a
problem as before. However, it is always nice to have another tool in your toolbox to
handle site-specific problems.
Intra-oral Cementation
onto already installed Abutments allows for the
creation of an Optimal Passive Fit
between the Prosthesis and its Retainers
The cement space (40 to 120 microns), created between
the prosthesis and the retainer allows for some tolerance
in the system.
This is very important!
46
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.com
Update January 2, 2016
41
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Screw Vs Cement for Dental Implant Prosthesis Installation Part 1: The Logic Behind the Argument

  • 1. Screw Versus Cement For Implant Prosthesis Installation. Part 1: The Logic Behind the Arguments. Emil L.A. Svoboda PhD, DDS, Published to www.ReverseMargin.com Update January 2, 2016 1 Next View Part 2: The Game Changer that tips the balance to Favour Intra-oral Cementation.
  • 2. Abstract Part 1: The Logic Behind the Arguments  This subject has been reviewed many times over many years. Some conclusions do not follow from the evidence presented in the articles, or they simply ignore pertinent evidence from the literature. Ignoring evidence about problems in the system makes it difficult to make informed conclusions.  The recent reviews are unable to show a difference in survival of implants on the bases of prosthesis insertion technique - screw or cement. It appears to be too difficult to see through the many variables contained in the studies that are the foundations of the reviews. Let us say the failures using either system, are about 5% for 5 years and 8 % for 10years, and the implants require significant home and professional care to reduce the impact of peri-implant disease.  What is causing the implants attached to Screwed-in Prosthetics to Fail? This is an important question. Let us review some of the less visible causes of these failures. Some failures appear to be related to implant-abutment misfit and exacerbated by mechanical challenges created by a need for prosthesis retrievability. These problems of screwed-in prosthetics appear to be very difficult to solve. They are discussed here.  Intra-oral cementation can optimize the fit of the implant-abutment connection. However, subgingival residual excess cement is a known risk factor for peri-implant disease. We know that it can be removed and thus reduce peri-implant disease by 60% (Slide #12). What if it could be prevented? That could surely reduce implant failure. That will be discussed in Part 2 below. Part 2: The Game Changer that tips the balance to Favor Intra-oral Cementation.  During 100 years of intra-oral cementation, nobody seems to have published on the effect of Gingiva on the flow of cement during the intra-oral cementation process. Understanding this process is the key to mitigating its negative effects.  Dr. Svoboda has created an “in vitro model”, that sheds New Light on the dynamics of intra-oral cementation. This is a “Game Changer”. Understanding the “Gingival Effects” changes the logic behind the approach to intra-oral cementation. This is the basis of a new Cement Control System™ that allows us to prevent the poorly controlled injection of cement into the subgingival environment. This cement can be difficult to detect and remove.  This presentation refers to design features of the abutment-prosthesis complex and the dental cementation process that can make intra-oral cementation safer. Safer cementation also helps the clinician optimize the fit of the implant-abutment junction, unlike that seen with screw-in prosthesis techniques. The herein described innovations will likely tip the balance in favor of intra-oral cementation and hopefully reduce the incidence of implant treatment failure. Failure is expensive for patients, clinicians and the entire implant industry. It can be especially damaging to the patient-dentist relationship. See Both Slide Presentations at www.ReverseMargin.com 2
  • 3. “Many advances in the Field of Implant Dentistry have improved the quality of care we can offer our patients.” 3 There are still significant problems contributing to the deterioration of the Foundations of our restorations through loss of implant osseointegration.
  • 4. Review 2013 of Peri-implant Disease Mucositis 30.7% of Implants 63.4% of the patients Peri-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) No Difference Between Cement or Screw Installation Atieh MA et al. The Frequency of Peri-implant diseases: A systemic review and meta-analyses. J Periodontol 2013:84(11):1586-1598 4
  • 5. Review 2014 of Peri-implant Disease 2,387 Cemented-in & 3,471 Screwed-in Prostheses 5 years Survival Rates about 96% 10 years Survival Rates about 92% No Difference Between Cement or Screw Installed Prosthesis Survival Rates Whittneben et al. Clinical Performance of Screw- Versus Cement Retained Fixed Implant-Supported Reconstructions: A Systemic Review. The Int J Oral Maxillofac Implants; 2014:29(Suppl):84-98. 5
  • 6. Review 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 6 Sherif S et al. A Systematic Review of Screw- versus Cement-Retained Implant Supported Fixed Restorations. J of Prosthodontics 2014 (23)1-9
  • 7. Review 2015 of Peri-implant Disease Mucositis 33% of Implants 48% of the patients Peri-implantitis 16% of Implants 26% of the patients Failure 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% No Difference Between Cement or Screw Installation 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 7
  • 8. Conclusions from the Reviews Considering that these Reviews seem to be “tilling the same old soil”, is there any wonder that the results are similar? The details differ, but success and failure of dental implants is where the “Rubber meets the Road” No Difference Between Cement or Screw Installation However there is however One BIG Difference that I see! With Peri-implant Disease, it is often possible to remove excess cement and expect an improved result! How do you treat Peri-implant Disease when dealing with the Screwed-in Technique? It is very difficult to correct the implant-abutment misfit! What about implant distortion due to this misfit? Not even a remake will solve these problems! Let’s look at this in more detail ……. 8
  • 9. Study by TG Wilson 2009 Residual Excess Cement & Peri-implant Disease 1. All patients received cemented single unit implant crowns 2. 39 consecutive patients with 42 implants had peri-implant disease - test 3. 12 of the same patients had 20 implants without disease and without detectable subgingival cement – controls-- 32% 4. 34 of 42 the test implants had Residual Subgingival Cement ( 81%) and thus 8 (19%) had Peri-implant disease without subgingival cement. 5. 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) - Therefore 40% of peri-implant disease implants had no detectable 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 9
  • 10. Data Re-Interpretation “Incidence of Residual Cement” Observation 1 With the Cementation System Used 45% had no Visible Residual Subgingival Cement! (20+8 = 28, 28/62= 0.45) Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-1392 10 “Not every cementation case ends up with Residual Subgingival Cement” This is also an underestimate, as the group was pre-selected to represent the work from clinicians who had restored single cemented crowns to have at least 1 implant with peri-implant disease.
  • 11. Peri-implant Disease “Some Get Disease without Cement” Observation 2 With the Cementation System Used 13% had No Visible Residual Subgingival Cement but had Peri- implant Disease! (8/62= 0.13) Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-92 11 “However the rate of peri-implant disease is much less than the 30-50% expected from the Reviews cited. Does cementation create a better fit of implant-abutment connection and thus decrease disease by more than 50%? This could be very interesting!”
  • 12. Peri-implant Disease Reduced by Cement Removal! Observation 3 About 60% of the peri-implant disease cases were helped by removing Residual 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 12 “Most cases get better when Residual Subgingival Cement is removed”
  • 13. Not Only Cement Causes Peri-implant Disease Observation 4 About 40% of the peri-implant disease cases had NO Residual Subgingival Cement! (8+8=16, 16/42 = 0.40, Sample Size Small) Thomas G Wilson Jr. The Positive Relationship Between Excess Cement and Peri-implant Disease: A Prospective Clinical Endoscopic Study. J. Periodont 2009;1388-92 13 “There is more to the story than Residual Subgingival Cement. The impact of the implant-abutment fit and its stability under load conditions needs to be investigated further under controlled conditions.”
  • 14. There are still Significant Weaknesses in the Implant-Prosthesis Connections Affected by Installation Technique. 14 1) Implant-Abutment Connection at the alveolar bone level 2) Prosthesis-Abutment Connection at the more superficial gingival level
  • 15. The Screw-in Technique 15 1. Abutments and prosthesis are cemented together Extra-orally into a rigid Complex. 2. This complex is made to fit on a model representing the mouth. 3. This Complex is then screwed onto dental implants already in the mouth. It is difficult to asses fit or adjust contacts during prosthesis installation. The implant-abutment connection can be prevented from seating properly by tight contacts with adjacent teeth and inherent prosthesis-model inaccuracies.
  • 16. Extra-oral Cementation Makes the Implant-Abutment Connection Worse! 16 1. Solidifies Impression-Model Error because is assembled on the model not in the mouth. This error in dimension is huge! 2. Makes Abutment Installation more complex 3. Makes Prosthesis Installation more complex 4. Limits Use. Implant Position more important 5. In the anterior, it often requires technique related cantilevers for hiding screw access holes. Screwed-in Prosthetics introduce unnecessary mechanical and biological risk factors that affect the survival of implant treatment. These risk factors can be very difficult to mitigate.
  • 17. 17 1. Abutments are individually screwed onto dental implants inside the mouth. Implant-abutment connections are not affected by contacts or prosthesis-model inaccuracies. Their fit is optimized. 2. The prosthesis is cemented onto the custom abutments. It is relatively simple to adjust occlusion, fit and contacts prior to cementation. Implant angle is not so critical. The abutment-prosthesis connection is easier to control than the implant- abutment connection. Cementation Technique
  • 18. Screw-in versus Cement-in Prosthetics Prosthetic Insertion Technique Screw-in Cement-in Abutment-Prosthesis Complex Assembled on and fit to an inaccurate model before installation Assembled in mouth after installation of Abutment(s) Adjusting Contacts/Occlusion Difficult Easy Optimized Implant-Abutment Fit Unknown/No Yes Path of insertion considerations Yes No Screw access hole considerations & repair Yes No Cause Technique Related Cantilevers Yes No Removable Yes Yes/No* Residual Excess Cement No Yes/No** 18 *Many can be removed by creating an access hole. **Presentation Part 2: The Game Changer that tips the balance to Favour Intra-oral Cementation.
  • 19. What about Screwed-in Prosthetics? They do have Benefits too!  Easy to remove and reinsert  Avoid problems related to residual subgingival cement They can be used in short crown situations 19 We will discuss these Relative Benefits later ….
  • 20. Further Analysis of the Process of Screwing-in the Assembled Abutment-Prosthesis Complex “The Screw-in Technique” 20
  • 21. What 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 21
  • 22. What Puts the Abutment Retaining Screw at Risk of “Failure to Prevent” an Open Implant-Abutment Connection? 1. Lower screw torque levels 2. Tight contacts and Increased distance from implant-abutment connection to contact point with adjacent teeth 3. Smaller implant platform diameters 4. Cantilevers (off axis forces) 5. Multi-unit Prosthesis inaccuracies 6. Function 22 Let’s Look at the above problems More Closely ………..
  • 23. 1. 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 Newtons Clamping Force 20 NCm torque can give 423 Newtons Clamping Force 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. 23
  • 24. Reducing torque to 35 to 20 NCm reduces clamping force by a whopping 43%  Many of our smaller diameter implants, including those 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 a functional load and by *tight contacts with adjacent teeth. 24 *see 2 below
  • 25. 2. 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 optimal perpendicular imaging. This misfit can cause early screw loosening and peri-implant disease! 25 Figure from “Dental Implant Prosthetics, Carl E. Misch,2nd Edition Elseier Mosby, 2015 Pg 739 “The final torqueing down of the retaining screw can tend to shift or realign the abutment on its base. This can cause a tight contact on one side and a loose one on the other. At best, you will have a open and/or tight contact, at worst the abutment will be prevented from seating!”
  • 26. What About Prosthesis Contact Position? Torque on Clamping Screw 35 NCm (20 NCm) Load Force (LF) is Screw Clamping Force 741 N (423 N) Radius of 4.5 mm (3.0) Implant Top (D1) = 2.25 mm (1.50 mm) Length of Lever Arm (D2) = 10 mm Effort Force (EF) = the minimum Resistance that the Contact must provide to keep the abutment from seating EF = LF X D1/D2 = 167 N (63 N) Effort Force (Resistance offered by a tight contact with an adjacent tooth) needs to be only 22.5% of the Clamping Force to keep the Abutment from seating! Class 1 Lever Mechanics - Google Lever Mechanics - https://en.wikipedia.org/wiki/Lever LF EF D1 D2 26 “It is not possible with office dental imaging or tactile techniques to detect such misfits in the 15 micron range. Too bad since oral pathogens are about 1 micron in diameter and less.”
  • 27. Varied Lever Arm Lengths to Contact Position and Implant Diameters 0 100 200 8 mm 10 mm 12 mm Force Threshold (N) Exerted Against Proximal Contact that could keep Abutments from Seating (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 to the contact increases, so does the risk of a tight contact preventing an abutment from seating. 27 LF EF D1 D2
  • 28. Varied Lever Arm Lengths and Implant Diameters EF LF D1 D20 100 200 8 mm 10 mm 12 mm Force Threshold (N) Exerted Against Proximal Contact that could keep Abutments from Seating (Abutment Screw Torque 20 NCm, 423 N Clamping Force) 3 mm 3.5 mm 4.5 mm 5.7 mm As the Lever Arm Length Increases so does the risk of forces generated by function opening the implant-abutment connection. 28
  • 29. 0 100 200 300 423 741 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 Implant Platform Diameter 29 Many implants reduce implant radius for perceived benefits of “Platform Switch”. This also reduces the mechanical advantage of the clamping screw. This may not be ideal in the posterior of the mouth!
  • 30. 4. What about Effect of a 3 mm Lateral Cantilever on Various Implant Diameters. EF implant implant D2 LF Abutment Mechnical diameter radius (D1) Horizontal Screw Torque Disadvantage N mm mm mm N NCm *212 3.0 1.50 3 423 20 50% 245 3.5 1.75 3 423 20 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% *33 3.0 1.50 3 423 20 +10mm vertical lever Fulcrum D2 =3 mm EF “We often create cantilevers to accommodate lingual access holes for anterior teeth. This puts the implant-abutment connection at additional risk!” 30
  • 31. Example: Lets take a lateral incisor with a 3.0 mm abutment base and use a 20 NCm torque to seat it into place. There is a 10 mm distance from the implant-abutment connection to the contact with an adjacent tooth and we need to create a 3 mm cantilever to create abutment screw access from the lingual. Fulcrum D2 =3 mm EF “We often create additional cantilevers to accommodate lingual screw access holes for anterior teeth. This puts all the implant-abutment connections at increased risk of failure! This additional risk of failure is technique related.” 31  1. -Narrow Diameter 3 mm platform for incisors or platform switch purposes  2. -Reduced 20 NCm torque force on screw. Clamping force that would seat crown is 423 Newtons  3. -Effort Force (EF) by a tight contact that would keep the abutment from seating or the functional force required to dislodge the crown from the abutment would be : EF= 423X1.5/10= 65 N *** Start Sweating!  4. -Creating a 3 mm Lateral Cantilever for screw access reduces the Effort Force by 50% to dislodge crown from abutment – 33N ***** Bingo! No Hope!  Average Force often used to cement a crown is 40N – That finger pressure alone can open the above implant-abutment connection! Is that not scary to you?
  • 32. 5. 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! There is at least one major implant company that voids their “Warrantee” when clinicians choose to insert a multi unit prosthesis in such a fashion! They take this type of misfit seriously! You should too. 32 Figure of implants above from “Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2015 Pg 740
  • 33. Acceptable Levels of Misfit at the Implant–Abutment Interface - An error of 100 to 150 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):16-23 *Passive Fit could not be achieved with Screwed-in Prosthetics! Comparison of the Accuracy of Different Transfer Impression Techniques for Osseointegrated Implants. Zen BM et al. JOI Vol 41 No 6 2015: 662-667 Branemark PI, Zarb GA, Albrektsson T. Tissue -integrated prostheses. Chicago: Quintessence; 1985. p. 253 33 Figure of implants above from “Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2015 Pg 740 Even the theoretical suggestion of “not more than 10 microns error”, by PI Branemark in 1985, could be considered sloppy when considering that periodontal pathogens are only 1 micron in diameter and less.
  • 34. Overdenture retaining a “Screwed-on framework” was removed - Smells Bad!! Undersurface of framework and tops of intra-oral abutments reveal the extent of a noxious Biological Brew! 34
  • 35. Stress on Retainers keeps abutments from seating and creates misfit of components! Abutment on Driver with retaining screw facing upwards 35 Top of implant “external hex” showing residual biological mass ! This patient’s immune system was able to resist peri-implantits in spite of a massive bacterial inoculum.
  • 36. Can You Imagine that some “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 36 “I wonder what happens to the screw threads inside the implants after 10-20 years …. 10-20X removal and tightening? Do the tops of the implants distort when loaded unevenly? Can that be fixed? I know this removal process is expensive …. Does this particular service even have a remote chance of being effective long term?”
  • 37. 6. 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. 37 Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2005 Pg 453 Zipprich Micro Movements on Implant Abutment Interfaces. Part 1&2. http://youtu.be/AssjiYjmTLE, June 12, 2013.
  • 38. “Intra-oral Function” What do you think would resist the loads of function better? a) An optimized implant-abutment connection or ….. b) A stressed and perhaps deformed 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! Today this can only be done by the process of intra-oral cementation. 38
  • 39. How do you correct an Implant- Abutment Misfit? How do you repair a deformed or damaged Implant Platform? Not Even A Remake Can Solve these BIG Problems! 39
  • 40. In Summary - When a Prosthesis is Cemented together with its Abutment Outside of the Mouth ...  It becomes a larger rigid and more complex unit that amplifies dimensional errors through extended length, and it is difficult to manipulate intra-orally.  The model on which the prosthesis is assembled, is not accurate enough. Thus the assembled prosthesis will push or pull the abutments off their intended base(s) and cause increase implant-abutment misfits when screwed into place inside the mouth.  When installing the prosthesis into the mouth, it can be very difficult to create ideal contacts with adjacent teeth. “How tight is too tight?” 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 a change in contact pressure and cause additional stress and misfits of the implant-abutment connection. All of the above issues are BiG PROBLEMS that can and do cause damaging misfits at the implant-abutment junction that is at the deep alveolar bone level! 40
  • 41. What else causes a 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 41
  • 42. What about Screwed-in Prosthetics? They do have Benefits too!  Easy to remove and reinsert  Avoid problems related to residual subgingival cement They can be used in short crown situations 42 We will now discuss these Relative Benefits ….
  • 43. What about the Benefits of Screwed-in Prosthetics? 1. Easy to remove and re-insert 43 Many loose screws that require tightening are probably loose because of abutment prosthesis misfits and design related cantilevers. A misfit may lead to a permanent deformation of the top of the retaining implants. This is not so good for a replacement prosthesis. This is a disaster. Removal of most crowns and fixed bridges are for porcelain repair or open contacts. They are usually remakes anyway. Cutting them to engage an access screw is often not such a disaster. Removal and re-insertion will probably not make a multi-unit prosthesis fit better. This is a disaster. Multiple removals for hygiene is expensive and will probably damage the inside of the implant that engages the clamping screws. This may become a disaster. Removal of a hybrid acrylic prosthesis for repair purposes or an acute problem is probably beneficial. Some procedures can also be done without removal.
  • 44. What about the Benefits of Screwed-in Prosthetics? 2. Avoid problems related to residual subgingival cement. 44  Yes, but do not forget, Screwed in Prosthetics are cemented (assembled) in the lab on inaccurate models. 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.  Unlike the non-assembled abutment and prosthesis, the assemblies are difficult to sterilize prior to delivery, because the cement may degrade at high temperature. (see Part 2: all abutments, prosthetics and models are sterilized (not sanitized) prior to delivery to patient’s mouth) What if Intra-oral Cementation Just Became Safer?? It’s a trade-off between the misfits of the Implant-Abutment Junction and Residual Subgingival Cement. Cement can often be accessed surgically or by endoscopic means and cleaned away. What can you do about misfits??
  • 45. What about the Benefits of Screwed-in Prosthetics? 3. They can be used in short crown situations 45  Yes, the screw-in technique can be useful in these situations.  As the adhesive properties of dental cements have improved, the definition of a short crown also changes. Crowns are already cemented onto natural teeth without traditional mechanical retention. With the screwed-in prosthesis technique, the crowns are already cemented onto their abutments in the lab. They seem to hold.  The Reverse Margin™ Design can add 1 or 2 mm to crown length by lowering the base of the margin. The inflected part of the margin plus the additional central post length can effectively increase the retentive surface area. Adhesive technology and other properties of cement have improved dramatically over the years. Margin designs have also improved. Short crowns are not so much of a problem as before. However, it is always nice to have another tool in your toolbox to handle site-specific problems.
  • 46. Intra-oral Cementation onto already installed Abutments allows for the creation of an Optimal Passive Fit between the Prosthesis and its Retainers The cement space (40 to 120 microns), created between the prosthesis and the retainer allows for some tolerance in the system. This is very important! 46 What if Intra-oral Cementation Just Became Safer??
  • 47. 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.com Update January 2, 2016 41 Go to View the Very Exciting

Editor's Notes

  1. According to Wilson*, even cases with residual subgingival cement may take 4 months to 9 years to be discovered in cases with peri-implant disease.
  2. A Systematic Review of Screw- versus Cement-Retained Implant-Supported Fixed Restorations, Sami Sherif et al, J of Prosthodontics Vol 23, 2014 1-9. Conclusions – no difference in major or minor problems – cementation failure and fracture of porcelain – what type of cement, what was the material supporting the porcelain. Both cemented and screwed prosthetics have a screwed element. The Positive Relationship Between Excess Cement and Peri-Implant Disease: A Prospective Clinical Endoscopic Study Thomas G. Wilson Jr.*, J Periodontol 2009;80:1388-1392. Excess dental cement was associated with signs of peri-implant disease in the majority (81%) of the cases. Clinical and endoscopic signs of peri-implant disease were absent in 74% of the test implants after the removal of excess cement. If these findings are confirmed by other studies, they argue for increased diligence in cement removal at the time of cementation, as well as arousing suspicion of excess cement when signs of peri-implant disease are seen. In all cemented cases, due diligence should be paid to removing all excess cement at the time of placement of the fixed partial denture. The delay in the appearance of peri-implant disease is particularly troubling and indicates that cemented implant prostheses should be evaluated periodically for peri-implant disease. Four types of cement were used from five manufacturers (Table 1) Resin modified glass ionomers, zinc polycarboxylate, resin cement, Glass ionomer. Within the scope of this study, no difference could be detected in the initial presence of disease or response to treatment based on the type of cement used to lute the restoration. Peri-implant disease was first diagnosed in the test implants loaded from 4months to >9 years after ementation of the single-unit fixed partial dentures. a surgical flap procedure eliminated signs of inflammation after 1 month in most (25 of 33) of the treated implants. Mombelli A, Mu¨ ller N, Cionca N. The epidemiology of peri-implantitis, Clin. Oral Implants Res. 23(Suppl. 6), 2012, 67–76 doi: 10.1111/j.1600-0501.2012.02541.x © 2012 John Wiley & Sons A/S 67