Abutment Selection

Abutment selection

John Beumer III DDS, MS
Division of Advanced Prosthodontics, Biomaterials and
Hospital Dentistry, UCLA

This program of instruction is protected by copyright ©. No portion of
this program of instruction may be reproduced, recorded or transferred
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Restoration connection to abutment
and/or implant fixture
Biologic and technical issues
v  Screw retained systems
v  Cement retained systems
v  Screwless - cementless system (UCLA II)
v  Platform reduction (ie platform switching)

Treatment Planning
Surgical Placement
Faciolingual position of the anterior implant
should be aligned under the cingulum of the
proposed crown for screw retained restorations
and under the incisal edge for cement retained
restorations. Posterior implant should be centered
faciolingually for reducing the potential for
overloading.

Implant along the
incisal edge for
Implant was aligned cement retained PFM
Implant is centered. under the cingulum for
screw retained PFM

Implant Placement
v  Perpendicular to the occlusal
plane
v  Tooth positions
v  Avoid proximal positions
v  Screw access channel should
exit in the central fossa

Advantages of Proper Implant
Positioning
l  Proper emergence profiles can be
developed
l  Space available interproximally for
hygiene access (arrow)
l  Control of occlusal anatomy (narrowed
occlusal table and flat cusp angles)
l  Occlusal loads delivered axially
l  Abutment selection simplified

Misalignment of Implants - Custom abutments
The implants placed in the right mandible
were inclined towards the lingual

Misalignment of Implants - Custom abutments
This technique permits the clinician to control two key occlusal factors –
width of the occlusal table, and the cusp angles. Result: Reduced load
magnification and less chance of implant overload.

Arguments commonly
used in favor of cementation
v  It’s
a common procedure in the dental office: No
“Implant” knowledge necessary?
v  Implants for dummies
v  The screw access hole is through the labial or buccal
v  Other options - Lingual set screws-lab expense and lab expertise

v  Simple traditional impression techniques?
v  Packing gingival retraction cord vs screw retained impression copings
v  Better esthetics?
v  Permits the use of zirconium abutments. Predictability of Zirconium
abutments?
v  Fit isn’t as critical
v  Really? The assumption is that a misfit is just a passive cement gap
with no negative consequences

Cement Retained Restorations
Advantage
v Simple
Problems
v Risk o subgingival cement
accumulation
v Lack of retrievability

Preformed nonprepable abutments

Considerations for use:
v Tissue height essentially the same 360 degrees around the
abutment
v Abutment cement margin just subgingival
v Sufficient clearance for sufficient axial wall height for predictable
cement retention
v Angulation allows reasonable draw with adjacent teeth

The final restoration


v  The margin between the crown and the abutment does not
follow the gingival margin. Note that the proximal margins are
4-6 mm below the gingival margin.
v  In this situation there is significant risk of trapping cement
beneath the gingival tissues upon cementation.

This patient presented with severe peri-implantitis 3 years
post insertion of the crown.

A subsequent
x-ray, taken at
right angles to
the long axis of
the implant,
The initial x-ray revealed that
appeared to the crown, was
indicate that the not seated.
crown was seated.

Inability to completely seat the crown onto the abutment is a
common complication associated with prefomed abutments.
Lingual access holes may help relieve the hydraulic pressure and
enable seating of the crown.


Cement was trapped
beneath the gingiva during
delivery of the crown and
was not detected.

Note the inflammation associated with the peri-implant
gingiva 2 1/2 years post insertion.


Issues of concern
v  Position
of the cement margin in relation to
the gingival margin
v Particularly significant in the anterior region
v  Impaction of cement into the gingival sulcus
v  Difficulty in seating the crown because of
hydraulic pressure

Prepable abutments

Abutment prepared on the master cast
Impressions are made in the
usual manner. The prepable
abutment is secured to the
implant fixture and prepared on
the cast.

Prepable abutments

The abutment was prepared and the crown
fabricated in the usual manner.

Prepable abutment and the risk of
subgingival cement accumulation

v The prepable abutment was secured in position with an
abutment screw and the crown cemented.
v The patient was not pleased with the esthetics and so a hole
was drilled into the occlusal surface and the abutment
screw removed.
v Note the accumulation of cement on the abutment.

Subgingival cement accumulation
Sulcus Epithelium

Implant Surface
Why is there a greater risk of
cement accumulation in the
sulcus of implant crowns?

Peri-implant
tissues are
more easily
displaced from
Circumferential
the surface of
collagen fibers
the restoration.

Bone

Packing cord to prevent
subgingival cement accumulation

v  Subgingival cement accumulation can be limited by
packing gingival retraction cord prior to cementation
v  Zirconium abutment allows the creation of an all ceramic
restoration from the implant to the incisal edge. Is there an
esthetic advantage?

Custom abutments with
screw retained restorations

Advantages
v  Control thickness
of labial porcelain
v  Used when the
Waxing implant is inclined
sleeve excessively to the
labial.
v  Retrievable

Full contour wax
pattern is developed


Wax cut back
Sprued
wax
pattern

Lingual retention screw channel


Cast
custom
abutment

Note lingual retention screw orifice

Coping

Completed and
sprued wax pattern

Lingual retention
screw channel Labial index
fabricated following
the full contour wax
pattern.


Completed
crown
Retention
screw
Abutment
screw

Custom
abutment

Completed restoration
compares favorably with
zirconium abutment
retained crown
Lingual
retention screw


Healing Full contour
abutment wax pattern

Completed
Wax pattern of custom abutment
custom abutment


Completed
restoration.
Note the level of
the gingiva


Gingival levels do
not match but the
the patient does
not display his
gingiva during a
high smile.

Custom abutments allows the use of pink porcelain

Porcelain has been baked onto the custom abutment

Excessive labial inclinations

The axial wall lengths are
frequently inadequate for
effective cement retention


Labial axial walls are insufficient to retain a cemented restoration.

Limits of Cement Retention
Implants angled excessively to the labial or
buccal
v  Axialwall height limits the retention
v  Shortest wall determines retention
v  Minimum height of axial wall – 4 mm.

Zirconium custom abutments
Cement retained

v  Allows the creation of an all ceramic restoration
from the implant to the incisal edge. Is there an
esthetic advantage? Probably not
v  The main issue is positioning of the cement
margin
v  Incidence of fracture has yet to be determined.

Zirconium custom abutments
Cement retained
Courtesy Dr. A. Sharma

v  Allows the creation of an all ceramic restoration from
the implant to the incisal edge. Is there an esthetic
advantage? Probably not.
v  The main issue is positioning of the cement margin
v  Incidence of fracture has yet to be determined.

Fit isn’t as critical ?
Really? The assumption is that a misfit is just a passive
cement gap with no negative consequences

The restoration appears
to precisely fit the
master cast. However,
will it fit the patient?

Really? The assumption is that a misfit is just a
passive cement gap with no negative consequences

Unfortunately, this was not the case. If you cement this case
there will be a sizable cement margin and you may overload the
implants.

Really? The assumption is that a misfit is just a passive cement
gap with no negative consequences

When the impression is made
with linked open tray
impression copings and the
original restoration placed on
the master cast the misfit is
profound.

Really? The assumption is that a misfit is just a passive
cement gap with no negative consequences

New Bridge on accurate model

Emergence Profile Compromises
Screw vs Cement Retained
v  Cemented crown contour v  Screw retained crown
begins ideally just apical to the can carry ideal contour
marginal soft tissue, which can
all the way to the head
produce the classic “pancake”
crown. of the implant (arrow)

Summary: Limits of Cement Retention
v  Axial wall height limits the retention
v  Shortest wall determines retention
v  Minimum height – 4 mm.
v  Restoration not easily retrieved
v  Subgingival cement accumulation
v  Compromised emergence profiles when interocclusal
space is lacking

Arguments in favor of screw retained restorations
v  Carry restoration more subgingivally than we can
predictably remove cement.
v  Formore ideal emergence profile and contour.
v  Avoid trapping cement subgingivally

v  More predictable seating of bridge pontic or even
single tooth given the gingival contour.
v  Better retention particularly when a cemented
restoration would have a very short axial wall.
v  Easier to restore when there is limited inter-
occlusal or restorative space

Next Generation of the UCLA Abutment
Shape Memory Sleeve (Seo and Wu)

❖  The treatment procedure is similar to current methods

The Next Generation of the UCLA
Abutment
Shape Memory Sleeve

“Nitinol”
(Nickel titanium alloy)

(Seo and Wu)
Issues
v Is Nitinal biocompatible?
v Will the increase in temperature during
activation be transmitted to the fixture,
abutment and underlying tissues?
v What is the quality of the retention?
v Will it stand up to repeated occlusal
loading
v Galvanic reactions?

Safety of Shape Memory Alloy, “Nitinol”
(Nickel titanium alloy)
‣  Nitinol is safe and bio-compatible

‣  Many devices are approved by FDA

‣  Economical to manufacture

Heart balloon

Arch bars
Heart stent

Release of the crown

Shape memory device is activated by heat

Activation brings the temperature up to 55
degrees Centigrade. It’s a shape change

Measurement of Temperature Rise in Abutment and
Implant Fixture During Heat Activation

Measurement of Temperature Rise in Abutment
and Implant Fixture During Heat Activation
ΔT, implant ﬁxture (°C)
ΔT, abutment (°C)

Passive air cool
1.4
2.8

Forced air cool
0.3
2.1

Measurement of Retention Strength

Temperature
Chamber


- Set up -

Assembly: implant
Saline chamber: body temperature
ﬁxture + abutment +
RODO sleeve


Results

Min - Max. (N)

Provisional cement
30 - 250

Zinc phosphate
330 - 346

RODO Device! 275 - 1,500!

Shape memory sleeve after the test

Measurement of Maximum Compressive
Strength
ISO 14801 Guideline
- Set up -
Assembly: implant ﬁxture + Saline Chamber
abutment + RODO sleeve
(Body Temperature)

Measurement of Maximum
Compressive Strength

Results

Maximum Abutment Strength
Failed at abutment- *No failure in the RODO Device
implant ﬁxture interface

750 N

Failure of Conventional Abutments : 800 ~ 1,000 N

Screw fractured

ISO 14801:2007-11-15
Dynamic Fatigue Test for Endosseous Dental
Implants
Failed at abutment- Displacement controlled fatigue performance
implant ﬁxture interface
*No failure in the RODO Device

50 - 400
Screw failed at 6000 cycles Minimum # of cycles

(Seo ,Wu and Shah)
Upcoming Studies
v  Galvanic testing
v  Short term IRB trial at UCLA School of Dentistry
(Kumar Shah and Neil Garrett)
v  Long term IRB trials at UCLA, other universities
and private clinics in the US commenced
summer 2011.
Patients with known nickel allergies not candidates

Platform Reduction and Etiology of Marginal
Bone Loss around Implants
Original Branemark design lost bone down to the first
thread. Why?

v  Thread design?
v  Surface topography?
v  Conical implant seal?
v  Design of the neck?
v  Platform reduction?
(switching)

Etiology of the initial bone loss
around implants
v  Almost immediately the
original “Branemark”
design lost bone down to
the first thread.
v  Other designs such as the
“Astra” design appear to
retain their bone levels
v  What is the evidence?

What are the likely explanations
for this difference?

Etiology of initial bone loss around implants
Angulation of the neck
v An implant is torqued into position with 45 Newtons
v However, the torque values around the neck of the
implant imbedded in the cortical bone is probably
closer to 100 Newtons.
v Will these values predispose to resorption to the
cortical bone around the neck of the implant when the
angle of the implant is acute?

Etiology of initial bone loss around implants
v Angulation of the neck
v Whenocclusal loads are applied will the implants
with acute angles atop of the implant overload
the bone in this area precipitating a resorptive
remodeling response and bone loss?

Platform reduction (platform switching)
Courtesy G. Perri Courtesy C. Stanford

v Note the bone levels atop the implant.
v Is it the result of the horizontalization of the
biologic width (platform reduction)?

Platform reduction (platform switching)

The evidence is far from clear.
v In these examples the angulation of the top of the
implant may be the more important factor
v In addition in both these implant systems the micro-rough
surface was extended to the top of the implant. This also,
may contribute to the maintenance of bone levels atop
the implant.

Angulation of the neck

v  Some authors have maintained that the angulation
atop the implant is the most important factor.
(Braun, et al, 2006; Iacono et al , 2006)
v  They attribute the maintenance of bone atop of the
implant to the so-called “negative” slope (dotted
lines).

The presence of micro-threads

Is it the result of the microthreads
around the neck of the implant?

Internal interlocking vs external hex
system
Conical seal
v  Allabutment – implant fixture interfaces demonstrate gaps
upon loading from 10-50 microns. The original external hex
systems demonstrates the largest gaps during flexure.
v  Do these gaps harbor micro-organism which in turn precipitate
an inflammatory response leading to bone loss around the
neck of the implant?

Marginal Bone Loss
Based on a Med Line search, a review of the literature
indicated that no implant system, surface or design
was found superior with regards to marginal bone loss
(Abrahamsson and Berhlundh, 2009)

Platform Switching (Reduction)
Will this type of implant fixture – abutment configuration
minimize the bone loss around the neck of implants?

Based on a review by Bateli and Strub (2011) “the current
literature provides insufficient evidence about the effectiveness
of any specific modification in the implant neck area in preserving
marginal bone or preventing marginal bone loss”

One piece systems
Nobel direct and similar one piece systems
There are no gaps developing between an
abutment and fixture. Why the bone loss?
Most have modern surfaces.

Many were immediately provisionalized and
loaded with cement retained restorations. In
many cases the cement extended down to
the boney levels
v Aninflammatory response was initiated which was
progressive and irreversible leading to extensive
bone loss.

Zirconium Implant Fixtures
(Strub et al, 2010)

v  Has been promoted for use in the esthetic zone
v  Biocompatible
" Histology similar to titanium – about 60% bone implant contact area
" Anchorage is similar to titanium
v  Microrough surfaces the best
v  Success rates equivalent to titanium
v  UV exposure makes the surface more bioreactive
v  Fractures
" One piece system – fractures at ¼ the load compared to titanium
" Two piece systems fracture at 1/6th the load compared to titanium
" Alumina reinforced zirconium is stronger

Not ready for clinical use. Some people believe that zirconium
implants will eventually disappear from the market.

Zirconium abutments and frameworks
Used in the esthetic zone
Abutments
l  Less plague adherence
l  More esthetic
l  Higher fracture rate
Frameworks
l  High incidence of chipping of porcelain
off the zirconium frameworks
l  Not recommended for posterior teeth

Courtesy Dr. A. Sharma

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