Screw Vs Cement for Dental Implant Prosthesis Installation Part 1: The Logic Behind the Argument

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

© Dr. Emil Svoboda PhD, DDS 2015

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

2AbstractPart 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 © Dr. Emil Svoboda PhD, DDS 2015

http://www.reversemargin.com/

“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.

© Dr. Em

il Svoboda PhD, DDS 2015

4Review 2013 of Peri-implant DiseaseMucositis 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)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

© Dr. Em


5Review 2014 of Peri-implant Disease

2,387 Cemented-in & 3,471 Screwed-in Prostheses5 years Survival Rates about 96%10 years Survival Rates about 92%

No Difference Between Cement or Screw InstalledProsthesis 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.

© Dr. Em

il Svoboda PhD, 2015

6Review 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

© Dr. Em


7Review 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%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

8Conclusions from the ReviewsConsidering 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

…….© Dr. Emil Svoboda PhD, DDS 2015

9Study by TG Wilson 2009

Residual Excess Cement & Peri-implant Disease

1. All patients received cemented single unit implant crowns2. 39 consecutive patients with 42 implants had peri-implant disease -

test3. 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


© Dr. Em


10Data Re-Interpretation “Incidence of Residual Cement”

Observation 1With 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“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.

11Peri-implant Disease“Some Get Disease without Cement”

Observation 2With 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


“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!”

© Dr. Em


12Peri-implant Disease Reduced by Cement Removal!Observation 3

About 60% of the peri-implant disease caseswere helped by removing

Residual Subgingival CementAnd 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

“Most cases get better when Residual Subgingival Cement is removed”

13Not Only Cement Causes Peri-implant Disease

Observation 4About 40% of the peri-implant disease caseshad 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


“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.

16Extra-oral Cementation Makes the Implant-Abutment Connection Worse!


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

18Screw-in versus Cement-in Prosthetics Prosthetic Insertion

TechniqueScrew-in Cement-in

Abutment-ProsthesisComplex

Assembled on and fit to an inaccurate

model before installation

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 & repair

Yes No

Cause Technique Related Cantilevers

Yes No

Removable Yes Yes/No*Residual Excess Cement No Yes/No**© Dr. Emil Svoboda PhD, DDS

2015*Many can be removed by creating an access hole. **Presentation Part 2: The Game Changer that tips the balance to Favour Intra-oral Cementation.

© Dr. Em


19What about Screwed-in Prosthetics?

They do have Benefits too! Easy to remove and reinsert Avoid problems related to residual

subgingival cementThey can be used in short crown situations

We will discuss these Relative Benefits later ….

© Dr. Em


20Further Analysis of the Process of

Screwing-in the Assembled Abutment-Prosthesis Complex

“The Screw-in Technique”

21What 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


22What Puts the Abutment Retaining Screw at Risk of “Failure to Prevent” an Open Implant-Abutment Connection?

1. Lower screw torque levels2. Tight contacts and Increased distance from implant-

abutment connection to contact point with adjacent teeth

3. Smaller implant platform diameters4. Cantilevers (off axis forces)5. Multi-unit Prosthesis inaccuracies6. Function

Let’s Look at the above problems More Closely ………..

231. 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 Force20 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.


24Reducing 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.


*see 2 below

252. 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!


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!”

26What 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 mmEffort 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


“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.”

27Varied Lever Arm Lengths to Contact Position

and Implant Diameters

8 mm 10 mm 12 mm020406080

100120140160

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

ing (Abutment Screw Torque 20 NCm, 423 N Clamp-

ing 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.© Dr. Emil Svoboda PhD, DDS 2015

LF

EF

D1

D2

28Varied Lever Arm Lengthsand 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 the Lever Arm Length Increases so does the risk of forces generated by function opening the implant-abutment

connection.© Dr. Emil Svoboda PhD, DDS 2015

29

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 Implant Platform Diameter


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!

304. What about Effect of a 3 mm

Lateral Cantilever on Various Implant Diameters.EF implant implant D2 LF Abutment Mechnical

diameter radius (D1)Horizonta

l 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!”© Dr. Emil Svoboda PhD, DDS 2015

31Example: 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.”© Dr. Emil Svoboda PhD, DDS 2015

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?

325. 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.

© Dr. Em


Figure of implants above from “Dental Implant Prosthetics, Carl E. Misch, Elseier Mosby, 2015 Pg 740

33Acceptable 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: 662-667Branemark PI, Zarb GA, Albrektsson T. Tissue -integrated prostheses. Chicago: Quintessence; 1985. p. 253

© Dr. Em


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.

© Dr. Em


34Overdenture 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!

© Dr. Em


35Stress 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 !This patient’s immune system was able to resist peri-implantits in spite of a massive bacterial inoculum.

36Can 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


“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?”

© Dr. Em


376. 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

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.


39How 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!


40In 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!


© Dr. Em


41What 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

© Dr. Em


42What about Screwed-in Prosthetics?

They do have Benefits too! Easy to remove and reinsert Avoid problems related to residual

subgingival cementThey can be used in short crown situations

We will now discuss these Relative Benefits ….

43What about the Benefits of Screwed-in

Prosthetics? 1. Easy to remove and re-insert


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.

44What 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 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??

45What about the Benefits of Screwed-in Prosthetics?

3. They can be used in short crown situations


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.

© Dr. Em


46Intra-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!

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.comUpdate January 2, 2016

41


Go to View the Very Exciting

Health & Medicine

Screw Vs Cement for Dental Implant Prosthesis Installation Part 1: The Logic Behind the Argument