Screw retained vs cement retained prosthesis.pptx

 Introduction
 Screw retained prosthesis
• Advantages
• Disadvantages
• Screw loosening
 Cement retained prosthesis
• One piece abutment
• Two piece abutment
2
Screw retained versus cement retained prosthesis

 Screw versus cement retained prosthesis
 Ease of fabrication and cost
 Passivity of the framework
 Retention
 Occlusion
 Esthetics
 Delivery
 Retrievability
3

• Summary
• Conclusion
• References and Bibiliography
4

5

 Screw-retained prostheses have a well-documented
history of successful application in completely edentulous
patients.
 As noted in the literature, “Screw-retained implant
restorations have an advantage of predictable
retrievability but demand precise placement of the
implant.
6

 However, with the increase in treatment of partially
edentulous patients, new restorative concepts have
evolved in the field of implant Prosthodontics.
 In screw-retained restorations, the fastening screw
provides a solid joint between the restoration and the
implant abutment which can be easily retrivable.
7

 Easy
 Safe efficient
 Retrievable
 No cement in soft tissue periimplant area
 Retention even for small dimensions
8
Carl E. Misch; Contemporary implant dentistry; 3rd Edition.

 Screw loosening under final cemented prosthesis
 Fracture
 Device not sealed(bacterial growth)
9

10
•Forces:Occlusion interferences
•Cantilever:offset loads
•Non passive fit of prosthesis

11

12

 Cement-retained prostheses have become, the
restoration of choice for the treatment of implant patients.
 This evolution started after a modification of the UCLA
abutment, i.e. fabrication of customized abutments to
overcome esthetic and angulation problems.
13

 Lewis and coworkers in 1988 were the first to describe a
new technique for the fabrication of implant-supported
restorations made directly on Brånemark System
implants (Nobel Biocare, Göteborg, Sweden), without the
use of traditional transmucosal abutment cylinders, so as
to overcome limited interocclusal space problems.
14

 In 1989, Lewis and associates described the fabrication
of telescopic crowns on customized abutments made
from UCLA abutments to solve problems with implant
angulation.
15

 Currently, there are numerous pre-machined cement-
retained abutments, as well as preparable titanium and
ceramic abutments.
 These abutments can be further modified in the mouth to
accommodate soft tissue changes.
16

 Two broad categories of abutments are used for cement
retained restorations.
• A single unit abutment (one piece abutment)
• Two piece abutment.
17

 The one piece abutment for cement is often the abutment
of choice for multiple splinted implants, provided no
transfer done with the laboratory.
18

 No torque wrench needed.
 Stronger.
 No screw loosening.
 Easy complete seating.
 No need to retighten under
restoration.
 Less expensive.
 Thicker walls to allow great freedom
of preparation.
19

 Only for multiple abutments.
 Not for single tooth restoration.
 Not for angled abutments.
 Weaker for fracture.
20

 An independent single tooth implant should be restored
with an anti rotational, two-piece abutment and abutment
screw screw system.
 The abutment should engage the hexagon or anti
rotational feature of implant body.
21

 Advantages:
• Anti rotational under shear forces.
• Angled abutments.
22

 Disadvantages:
• Screw loosening.
• Abutment loosening under restoration.
• Torque and counter torque devices needed for
preload.
• Proper seating with radiograph must be checked.
• Thinner walls limits freedom of preparation.
23

24

 The factors that are influenced by different methods of
fixation of the prostheses to the implants are:
• Ease of fabrication and cost
• Passivity of the framework
• Retention
• Occlusion
• Esthetics
• Delivery
• Retrievability
25

 The fabrication of cement-retained prostheses is easier
than that for screw-retained prostheses.
 The components used for this type of restoration are less
expensive and does not require special training for
technician.
 Restoration of implants with a divergence of less than 17
degrees is also easier with cement-retained prostheses.
26

 The screw retained restorations for same incidence is not
simple as it requires the fabrication of customized
abutments, a procedure that is technique-sensitive and
demanding.
27
W.Chee, Screw versus cemented implant supported Restoration, British dental journal volume 201 no. 8 Oct 21 2006 501

 The possible complications of non-passively fitting
frameworks can be categorized into 2 groups:
• Biologic complications: increased transfer of load to
the bone, bone loss, and development of micro flora at
the gap between the implant and the abutment.
• Prosthetic complications: loosening or fracture of the
fastening screw and implant fracture
28

 The fabrication of implant-supported restorations requires
many clinical and laboratory procedures that must be
very precise. Each stage in the fabrication procedure can
incorporate a small error, which will contribute to a
positional distortion of the prosthesis.
29

 Possible distortion can occur during the impression
procedure, during fabrication of the master cast, during
fabrication of wax patterns, during investing and casting
procedures, during firing of the porcelain, or during
delivery of the prosthesis.
30

 A truly passive screw retained dental restoration is
virtually impossible to fabricate.
 Screwed restorations may create permanent strain on
implants that can be 2to3 times greater than that of
cemented prosthesis.
 A passive fit is easier to accomplish in cemented
restorations due to die spacers.
31

 The die spacer creates an approximately 40 μm cement
space, which compensates for laboratory distortions and
permits a more passive casting.
 If the laboratory is utilizing CAD/CAM technology, the
cement space can be adjusted based on the
substructure.
32

 Occlusal material fracture is more common with implants
than natural teeth because of lack of periodontal stress
relief with implants.
 A decreased incidence of porcelain or acrylic fracture of
prosthesis has been observed with cement retained
restorations compared with screw retained restorations.
33

 In screw retained restorations, screw holes may increase
stress concentration to the restoring material and more
often leads to un supported porcelain.
 A cement retained prosthesis does not have a weak link
through the surface of the material.
34

 Access is more challenging in the posterior regions of
mouth for insertion of screw retained restorations.
 The manipulation of small screws and screw drivers is far
more time consuming and challenging than the
preparation and cementation of restoration.
35

 A long term complication of screw retained prosthesis is
fatigue failure of screw components.
 The narrow diameter of prosthesis screws reduces its
long term strength.
 Cemented prosthesis have no small diameter
components and no metal to metal wearing and such
similar complications were not observed.
36

 A screw retained prosthesis does not seal the abutment
to crown interface or margin, which harbors bacteria in
the crevice.
 The crevice may act as endotoxin pump, encouraging the
proliferation of microorganisms in the sulcular region.
 A cemented crown seals the crown abutment connection
and impairs bacterial penetration.
37

 Retention certainly influences the lack of complications
as well as the longevity of implant prostheses.
 The factors that influence retention of the cement
retained restorations are convergence of axial walls,
surface area and height, roughness of the surface, and
type of cement.
38

Roughness of surface:
 Roughness of axial walls offers greater retention to
cemented prosthesis.
 Implant abutments can be roughened by using diamond
bur or air borne particle abrasion.
39

Path of insertion:
 In ideal conditions the path of insertion of restoration
should be slightly different from direction of occlusal load.
 If the fixed partial denture path of insertion is identical to
direction of occlusal force then grater tensile forces were
placed on the cement.
 So, ideal suggestion is that the path of insertion should
be about 10 degrees divergent from the axial load of
implant during occlusion to prevent uncementation.
40

Type of cement:
 The cements used in fixed prosthodontics are either
definitive or provisional.
 The definitive cements are used to increase retention
and provide good marginal seal for the restorations.
Provisional cements are used primarily for interim
restorations to facilitate their removal.
 As no risk of decay for the abutments, provisional
cements can also be used for the cementation of implant
restorations, for easy retrivability.
41

 Zinc phosphate cements have excellent properties for
definitive implant restorative cement because they
cannot cause pulpal sensitivity on implants , have
adequate working time and excess material can be
removed without starching the surface of abutment.
42

 For screw-retained restorations, retention is obtained by
the fastening screw, which connects the implant with the
abutment and the abutment with the prosthesis.
 The screws most commonly used are the gold and the
titanium.
 Retention is obtained by the friction resistance
developed between the internal threads of the implant
and those of the fastening screws.
43

 In the case of titanium abutment screws, there can be
slight damage of both the implant and the fastening
screw threads, which results in their joining. This
phenomenon is called galling.
 Gold abutment screws have a smaller coefficient of
friction, allowing them to be tightened more effectively
than the titanium without risking galling between the
threads.
44

 Occlusion is another factor affecting the selection of the
restoration type-screw- or cement-retained.
 The bucco-lingual dimension of maxillary premolars and
maxillary 1st and 2nd molars would be 9mm and 11mm.
The occlusal table for above mentioned teeth is 4.5mm &
5-6mm.
 The heads of fastening screws have a diameter of 3mm,
thus requiring screw access hole diameter of 3mm.
45

 Esthetics is another factor to consider when deciding
between screw-retained and cement-retained crowns.
 In anterior screw-retained crowns, the implant is placed
lingually to allow screw emergence through the cingulum
area.
46

 An implant for an anterior cemented restoration is placed
under the incisal edge. An angulated abutment is then
used, which eliminates the ridge lap and replicates a
more natural emergence profile.
47

 In posterior screw-retained restorations, the access hole
will exit through the central fossa of the prosthetic tooth.
The cementable crown obviously has no entrance cavity.
Allowing the forces of occlusion to be distributed along
the axial inclination, congruent with the long axis of the
tooth, is easier.
48

 For screw retained restorations, only a radiographic
examination is required to verify the prices fit of the
prosthesis.
 However for cemented restorations, there is need for
careful removal of cement remnants in addition with
radiographic examination. The removal of cement
residues is critical for peri-implant health.
49

 The main advantage of screw retained prosthesis is
retrievability. The crown is not only recoverable, but no
damage occurs upon removal of the crown.
 In screw retained prosthesis, the access hole is covered
with composite. To retrieve the screw retained prosthesis,
the dentist must remove occlusal obturation, underlying
cotton pellet and coping screw.
50

 Once the prosthesis is reinserted, the screws may need
to be changed and torqued.
 The main disadvantage of cemented prostheses is the
difficulty of their retrievability.
 Although retrieval is needed less often because of the
dramatically increased survival rates for dental implants,
the need for future removal of FPDs should not be
overlooked. For this provisional luting cements are being
used.
51

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 It is to be stated that the decision to screw or cement
retain abutments remain an individual choice for dentists.
 Clinicians should be aware of the limitations and is
advantages of each type of prosthesis so as to select the
one that is most appropriate for a given clinical situation.
54

 Carl E. Misch; Contemporary implant dentistry; 3rd
Edition.
 Charles A. Babbush; Dental implants art & science; 2nd
Edition.
 Michalakis K.X, Hirayama .H; Cement retained versus
screw retained implant restorations- A critical review;
Int J Oral Maxillofacial implants 2003; 18; 719-728.
55

 W.Chee, Screw versus cemented implant supported
Restoration, British dental journal volume 201 no. 8 Oct
21 2006 501
 Hebel KS, Gajjar RC. Cementretained versus screw-
retained implant restorations: achieving optimal occlusion
and esthetics in implant dentistry.JPD 1997;77(1):20-35
 Sanath shetty,Principles of screw-retained and
cement-retained fixed implant prosthesis: A critical
review;Journal of Interdisciplinary dentistry,2014
56

 Giblin J; A Rationale for the successful retention of
implant supported restorations- to screw or cement;
Australian dental practice; 2009; 136-146.
 Roberta,Cement retained versus screw retained dental
prostheses:A literature review;Dental press
Implantology,April,2013
57

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