This document discusses various options for connecting dental restorations to abutments and implants, including the biologic and technical issues involved. It compares screw-retained, cement-retained, and screwless systems. It also discusses arguments in favor of cementation, potential problems like cement accumulation, and the limits of cement retention related to factors like abutment angulation and axial wall height. Finally, it covers custom abutments, platform switching, and the next generation of the UCLA abutment using shape memory alloys.

1. 9. Abutment selection
John Beumer III DDS, MS
George Perri DDS
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
by any means electronic, digital, photographic, mechanical etc., or by
any information storage or retrieval system, without prior permission.

2. 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)

3. 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

4. Major Problems
v Cement accumulation
v Lack of retrievability

5. Subgingival cement accumulation
Prepable abutment
These abutments can be prepared at the lab bench or
intraorally. An impression is made and the restoration
is cemented in the usual and customary fashion.

6. Subgingival cement accumulation
Prepable abutment
An impression was obtained with an impression coping
and the prepable abutment was attached to the fixture
analogue imbedded in the master cast.

7. Subgingival cement accumulation
Prepable abutment
v The abutment is prepared so that the margin is slightly sub gingival.
v An impression is made and the porcelain fused to metal crown was
completed in a customary fashion.
v The abutment is secured to the implant fixture and the crown is then
cemented.

8. Subgingival cement accumulation
Prepable abutment
v The patient was unhappy with the esthetic result and so a
hole was drilled into the occlusal surface in order to access the
abutment screw. The crown and abutment was then removed
v Note the accumulation of cement subgingivally.

9. 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
*

10. Anatomy & Biology
of Peri-Implant Soft Tissue
Similarities between
periodontal & peri-implant
soft tissues:
v Oral epithelium
v Sulcular epithelium
v Junctional epithelium
Differences in peri-implant
soft tissues include:
v Lack of CT attachment
v Hypovascular,
hypocellular CT zone adjacent
to the implant
v Absence of periodontal
ligament blood supply
Sclar AG, 2003

11. Cementation permits use
of a ceramic abutment
Excellent esthetic result
v Subgingival cement accumulation can be limited by packing gingival
retraction cord prior to cementation
v Allows the creation of an all ceramic restoration from the implant to
the incisal edge. Is there an esthetic advantage? Perhaps.
v The main issue is positioning of the cement margin
v Incidence of fracture of zirconium abutments is a concern but long
term followup data is not yet available.

12. Preformed nonprepable abutments
Issues of concern
v Positionof 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

13. Preformed nonprepable abutments
Considerations for use:
v Tissue height essentially the same 360 degrees around the
abutment
v Head of the implant or 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

14. Preformed
nonprepable abutments
v The margin between the crown and the
abutment does not follow the gingival margin.
v There is significant risk of trapping cement
beneath the gingival tissues upon cementation.

15. Preformed nonprepable abutments
This patient presented with severe peri-implantitis 3 years
post insertion of the crown.
The initial x-ray A subsequent
appeared to x-ray, taken at
indicate that the right angles to
crown was the long axis of
seated. the implant,
revealed that
the crown, was
not seated.
Inability to completely seat the crown onto the abutment is a
common complication associated with preformed abutments.
Lingual access holes may help relieve the hydraulic pressure and
enable seating of the crown.

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

17. UCLA Abutment
Indications:
a) Lack of interocclusal space
b) Restorations in the esthetic zone
c) Angulation problems
d) Soft tissue problems

18. UCLA Abutment Technique

19. Ucla Abutment Technique

20. 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

21. Custom abutments with
screw retained restorations
Wax cut back
Sprued
wax
pattern
Lingual retention screw channel

22. Custom abutments with screw
retained restorations
Cast
custom
abutment
Note lingual retention screw orifice

23. Custom abutments with screw
retained restorations
Coping
Completed and
sprued wax pattern
Lingual retention
screw channel Labial index
fabricated following
the full contour wax
pattern.

24. Custom abutments with screw
retained restorations
Completed
crown
Retention
screw
Abutment
screw
Custom
abutment

25. Custom abutments with screw
retained restorations
Completed
restoration
Lingual
retention screw

26. Custom abutments with screw
retained restorations

27. Custom abutments with screw
retained restorations
Healing Full contour
abutment wax pattern
Completed
Wax pattern of custom abutment
custom abutment

28. Custom abutments with screw
retained restorations
Completed
restoration.
Note the level of
the gingiva

29. Custom abutments with screw
retained restorations
Gingival levels do
not match but the
the patient does
not display his
gingiva during a
high smile.

30. Custom abutments allows
the use of pink porcelain
Porcelain has been baked onto the custom abutment

31. Custom abutments with
screw retained restorations
Excessive labial inclinations
The axial wall lengths are
frequently inadequate for
effective cement retention

32. Custom abutments with
screw retained restorations
Labial axial walls are insufficient to retain a cemented restoration.

33. Custom abutments with
screw retained restorations

34. Custom abutments with screw retained
restorations

35. 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.

36. 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?

37. Fit isn’t as critical ?
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.

38. Fit isn’t as critical ?
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

39. Fit isn’t as critical ?
Really? The assumption is that a misfit is just a passive
cement gap with no negative consequences
New Bridge on accurate model.

40. 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)

41. Summary: Limits of Cement Retention
v Axialwall height limits the retention
v Shortest wall determines retention
v Minimum height – 4 mm.

42. Cementation
The main issues are:
v Cement retention (pack retraction chord before cementation)
v Quality of retention (axial wall length)
v Lack of retrievability

43. 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

44. Next Generation of the UCLA Abutment
Shape Memory Sleeve (Seo and Wu)
❖ The treatment procedure is similar to current methods

45. The Next Generation of the UCLA
Abutment
Shape Memory Sleeve
“Nitinol”
(Nickel titanium alloy)

46. Next Generation of the UCLA Abutment
(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?

47. Next Generation of the UCLA Abutment
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

48. 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

49. Next Generation of the UCLA Abutment
Measurement of Temperature Rise in Abutment and
Implant Fixture During Heat Activation

50. Next Generation of the UCLA Abutment
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

51. Next Generation of the UCLA Abutment
Measurement of Retention Strength
Temperature
Chamber

52. Next Generation of the UCLA Abutment
Measurement of Retention Strength
- Set up -
Assembly: implant
Saline chamber: body temperature
fixture + abutment +
RODO sleeve

53. Measurement of Retention Strength
Results
Min - Max. (N)
Provisional cement
30 - 250
Zinc phosphate
330 - 346
RODO Device! 275 - 1,500!
Shape memory sleeve after the test

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

55. 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

56. Next Generation of the UCLA Abutment
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

57. Next Generation of the UCLA Abutment
(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

58. 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)

59. 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?

60. 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?

61. 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?

62. 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)?

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

64. 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).

65. The presence of micro-threads
Courtesy G. Perri Courtesy C. Stanford
Is it the result of the microthreads
around the neck of the implant?

66. 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?

67. 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)

68. Platform Switching (Reduction)
Will this type of implant fixture – abutment
configuration minimize the bone loss around the neck
of implants?
v Basedon 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”

69. 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.

70. 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.

71. 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

72. v Visitffofr.org for hundreds of additional lectures
on Complete Dentures, Implant Dentistry,
Removable Partial Dentures, Esthetic Dentistry
and Maxillofacial Prosthetics.
v The lectures are free.
v Our objective is to create the best and most
comprehensive online programs of instruction in
Prosthodontics