INTRODUCTION
Implant-supported fixed dental prostheses (FDPs) are a predictable treatment, which
allows to improve function and esthetics in partially and fully edentulous patients.[1 ]
Among the advantages of implant treatment, there is the possibility to apply an FDP
for single and multiunit replacement without grinding the neighboring teeth and to
have an FDP where formerly a removable denture would have been placed. However, the
long-term outcome is one factor guiding a clinician whether implant treatment or conventional
FDPs or removable partial dentures.
The third EAO consensus conference of 2012 focused on implant survival and complications
of single crowns and FDPs, partial and complete. Based on prospective and retrospective
cohort studies, the 10-year survival of conventional tooth-supported FDPs was 89.2%
compared to 86.7% for implant-supported FDPs. Despite high survival, biological and
technical complications were frequent too and were reported to be higher than for
implant-supported FDPs (38.7% compared to 15.7% for conventional FDPs). The increased
incidence of technical complications, such as veneer fractures, abutment rotation
and breakage, abutment and screw loosening, and loss of retention for implant-supported
FDPs, could be explained by the type of screw material, preload, abutment material,
and connection configuration.[2 ]
[3 ] Furthermore, the biologic complications such as increased microleakage, gingivitis,
and marginal bone loss (MBL) have been reported to result from a poorly adapted implant-abutment
interface (IAI).[4 ]
[5 ]
[6 ] However, there is still a lack of knowledge among clinicians regarding mechanical
behavior and marginal accuracy of the implant-abutment complex and its relationship
with technical complications as well as peri-implant bone loss (biologic complication).
In two-piece implants, microgaps at the IAI are unavoidable and are the consequences
of the microtolerances between components required during the industrial manufacturing.[7 ] The presence of this microgap allows microorganisms to proliferate close to the
epithelial attachment, which often results in bone resorption up to 2 mm apical to
the microgap.[5 ] In addition to infection caused by plaque and its by-products, numerous etiological
factors have been recognized to be specifically associated with peri-implantitis.[8 ] Plaque-induced and prosthetically and surgically triggered peri-implantitis have
been found to be different entities associated with distinguishing predictive profiles.[9 ] Prosthetically triggered peri-implantitis was defined to be associated with plaque
together with clinically evaluated cement remnants or together with incorrect finishing
line positioning with respect to soft tissue, presence of overloading, crown ceramic
chipping, abutment unscrewing (detected using periapical X-ray), and implant crack
or fracture (detected at the time of abutment removal).[9 ]
The aim of this consensus conference was to provide clinical guidelines for general
dentistry and dental practitioners to allow them to deliver long-term successful restorations.
The prosthetic variables and the incidence of technical and biological complications
were analyzed to recommend a prosthetic procedure as a standard for implant-supported
rehabilitations, based on the available evidence and on the author's daily practice
and experience.
MATERIALS AND METHODS
The first Osstem Advanced Dental Implant Research and Education Center (AIC) “close/consensus
meeting” was held in September 2017 at the Micerium S.p.A., Avegno (Ge), Italy. Dr.
Marco Tallarico, the Research Project Manager of Osstem AIC Italy, was the scientific
responsible of the consensus meeting, and Micerium was responsible for the organization
[Figure 1 ]. The Osstem AIC is a professional organization in implant dentistry. Outside funding
was utilized to cover the travel costs of the participants. No other costs were provided
for conducting the conference or for publishing the present results.
Figure 1: Osstem Advanced Dental Implant Research and Education Center participants. From left
to right: Mauro Billi, Marco Duvina, Martina Caneva, Nicola Baldini, Gaetano Iannello,
Ottaviano Miceli, Marco Tallarico, Fulvio Gatti, Silvio Mario Meloni, and Giacomo
Piacentini
Three groups of expert clinicians and expert dental technicians were invited to evaluate
all the scientific literature from 1967up to March 2017 to identify relevant studies
on the assigned topics and to prepare in advance narrative/systematic review to fulfill
the consensus statement criteria. The following electronic databases were consulted:
PubMed database of the US National Library of Medicine, Embase (Excerpta Medica database),
and the Grey Literature Database (New York Academy of Medicine Grey Literature Report).
The systematic reviews were written according to the Preferred Reporting Items for
Systematic Reviews and Meta-Analyses guidelines (http://www.prisma-statement.org ). Quality assessment of selected full-text articles was performed according to the
ARRIVE and CONSORT statement guidelines.
Assigned topics and group discussion
Work Group 1: Abutment/framework retentions (cemented- vs. screw-retained implant-supported
prostheses). Authors: Nicola Baldini, Gaetano Iannello, and Marco Duvina
Work Group 2a: Abutment/framework designs: original versus nonoriginal abutments;
macroarchitecture of the implant neck (implant shoulder design); and IAI. Authors:
Marco Tallarico, Silvio Mario Meloni, and Martina Caneva
Work Group 2b: Abutment/framework protocols: Abutment insertion protocol, such as
one-abutment/one-time and platform switching. Authors: Marco Tallarico, Silvio Mario
Meloni, and Martina Caneva
Work Group 3: Abutment/framework materials and customization (metal vs. metal-free
restorations). Authors: Fulvio Gatti, Mauro Billi, and Giacomo Piacentini.
The objective of the literature reviews of the different topics was to determine whether
a procedure could be recommended as a standard based on the available evidence and
on the author's daily practice and experience. The description of the technical aspects,
advantages or disadvantages of each procedure, technical and biological complications
and their management, esthetic outcomes, marginal bone level changes, costs, and retractability
had to be addressed by each group. The clinicians had 3 months to complete the reviews,
and all manuscripts had to be submitted to each participant at least 1 month before
the consensus.
During the first part of the consensus, all the expert clinicians presented their
results, and the lecture was followed by a first discussion. Similar topics of the
reviews, with insufficient clinical data to be defined as subjects, were used to stimulate
discussion among the consensus conference participants. During the second part, presentations
were discussed step-by-step by all the participants, starting from the proposed variables.
Some questions were answered by vote from the participants, and conclusions were provided.
Inclusion criteria
Written in English
Evaluate in their protocol the influence of the different analyzed variables on soft
and hard tissue levels around single or multiple implants, as well as biological or
mechanical complications
In vivo randomized controlled clinical trials of implants ≥1 year in function
In vivo case-control studies of implants ≥1 year in function
In vivo prospective and retrospective cohort studies of implants ≥1 year in function
In vivo cross-sectional studies ≥1 year in function
In vitro studies
Systematic reviews, narrative reviews, and consensus statements.
Exclusion criteria
Observational (prospective or retrospective) cohort studies without control group
Finite element analyses
Animal studies
Reports with <5 cases
Reports involving mini-implants, zirconia implants, or blade implants
Clinical reports on implants <1 year in function
Abstracts, commentaries, or editorials.
Terms definitions
According to the latest Glossary of Prosthodontic Terms[10 ] and Mesh terms (https://www.ncbi.nlm.nih.gov/mesh ):
Retention: The quality inherent in the implant-supported dental prosthesis acting
to resist the forces of dislodgement along the path of placement. The fixation of
an implant reconstruction can either be accomplished by screw retaining the reconstruction
on the implant or on a screw onto implant abutment or by cementing the reconstruction
on standardized or customized abutments, in the same manner as luting an FDP to natural
teeth
Original abutment: An abutment produced by the same implant manufacturer based on
original nominal dimensions. It can be stock (or standardized) or computer-aided design/computer-aided
manufacturing (CAD/CAM)
Nonoriginal abutment: An abutment produced by a different implant manufacturer (a
third-party company). It can be certified or compatible. Nonoriginal certified abutment
is an abutment produced by a third-party milling center, directly or indirectly certified
for certain implant companies. It can be gold cast or CAD/CAM. Nonoriginal compatible
abutment is an abutment produced by an implant company compatible with other implant
systems with which has the same IAI. It might also be manufactured by a generic producer
not directly involved in the implant manufacturing. It can be stock or CAD/CAM
Macroarchitecture of the implant neck: Dental implants come in a variety of designs
to adapt to the individual patient situation as well as the preferences of the dentist.
Regarding the implant neck design, there is a choice between two-piece (conventional
flat platform neck design with the same level on the 360°), one-piece (implant body
and abutment are manufactured as one piece), and scalloped or sloped implants (implant
neck designs aimed to mirror the natural alveolar ridge curvature)
Dental abutment: A tooth, tooth root, or implant component that serves as support
and/or retention for a dental prosthesis ([anatomic] healing abutment; angled/angulated
abutment; CAD/CAM abutment; castable abutment; ceramic/metal abutment; straight abutment;
rotating/nonrotating abutment; prefabricated/stock abutment; preparable abutment;
standard abutment; temporary abutment; transmucosal abutment; and Universal Clearance
Limited Abutment UCLA abutment)
One-abutment/one-time: Definitive abutments placed at implant insertion and never
removed
IAI: Common contact surface area between an implant abutment and the supporting implant
Platform switching: A design strategy including the connection of a smaller diameter
abutment relative to the platform diameter of the titanium implant.
RESULTS
In the effort to determine whether a prosthetic procedure could be recommended as
a standard for implant-supported rehabilitations, based on the available evidence
and on the author's daily practice and experience, a small national and independent
study group made up of nine established clinical experts was formed. Their collective
long-term clinical and research experience with implant-supported restorations would
provide scope for a prudent and objective synthesis of the relevant available literature
and of the clinical concerns related to this topic. Based on the literature reviews,
the participants of each group prepared consensus statements, clinical recommendations,
and implications related to their topic in written form that were approved during
the plenary session (second part of the consensus). These statements are presented
here in a condensed version. The keywords used to search the literature and the number
of final articles from which data are extracted, as described in [Table 1 ].
Table 1:
The keywords used to search the literature
Topic
Search strategy
Cemented versus screw-retained implant-supported prostheses
Original versus nonoriginal abutments
((“Dental Implant-Abutment Design” [Mesh] OR “Dental Implant-Abutment*” OR “Dental
Implant Abutment*”) AND (“Computer-Aided Design”[Mesh] OR “*original” OR “compatible”
OR “avatar”))
Macroarchitecture of the implant neck
((((“Dental implants”[Mesh] AND “dental implant abutment design”[Mesh]) OR “dental
implant abutment interface”[All Fields]) OR (one[All Fields] AND piece[All Fields]
AND implant[All Fields])) OR ((“scalloped”[All Fields]) AND implant[All Fields]) OR
(sloped[All Fields] AND implant[All Fields]) AND English[lang])
Implant abutment interface
(“dental implants” [MeSH] AND “bacterial contamination” OR “presence of bacterium”
OR “dental leakage/microbiology” [MeSH] OR “microleakage” OR “microbiological findings”
OR “microbiological colonization” OR “microbiota” OR “peri-implant microflora” AND
“peri-implantitis” [MeSH] OR “peri-implant pathology” OR “peri-implant disease” AND
“Dental Abutments*/microbiology” [MeSH]“connection, implant-abutment” OR “dental Implant-abutment
design” [MeSH] OR “implant-abutment junction” OR “implant-abutment microgap” OR “inner
space of dental implants” OR “inner part of dental implants”)
Abutment insertion protocol
(((((Dental Implant-Abutment*[Title/Abstract]) OR One-abutment*[Title/Abstract]) OR
abutment dis*[Title/Abstract]) AND (Immediate Dental Implant Loading[Title/Abstract])
OR Immediate loading[Title/Abstract]) OR Immediate abutment[Title/Abstract])
Platform switching
((“Dental implants”[Mesh]) OR (“dental” AND “implant*”) OR (“endosseous implant” AND
“dental”)) AND ((“dental implant-abutment design”[ALL] OR (“dental” AND “implant-abutment”
AND “design”) OR (“dental implant-abutment design”[ALL]) OR ((“dental” AND “implant”
AND “platform” AND (“switching” OR “platform switch*” OR “platform-switched” OR “platform
mismatch*” OR “platform shift*”))
Metal versus metal-free restorations
((“Dental Implants”[Mesh]) AND (“Dental Prosthesis, Implant-Supported”[Mesh] OR “Denture,
Partial, Fixed”[Mesh] OR “Dentures”[Mesh]) AND (“Complications” OR “Survival”))
Work Group 1: Abutment/framework retention (cemented- vs. screw-retained implant-supported
prostheses)
A total of 245 potentially relevant titles and abstracts were found after the electronic
and manual search. After the first and second stage of selection, a total of 40 manuscripts
were selected. Of these, three were randomized controlled trials (RCTs), eight were
observational comparative studies (3 retrospective and 5 prospective), 12 were systematic
review of the literature, and 17 were in vitro studies. Based on the selected studies, all the participants agreed that implant-supported
FDPs can be connected either by screw retention or cement retention. However, when
using a cemented protocol, extreme care must be taken to avoid residual cement. In
general, screw-retained restorations are suggested because they are easier to remove
and no cement is required. Nevertheless, they present more technical complications
(screw loosening, chipping of the veneering material). To reduce complications, skills
of the clinician and the dental technician are required.
All the participants agreed that prosthetic screws have to be tight at the recommended
torque. A second-time tightening (10 min later) is recommended to reduce the risk
of screw loosening. It is suggested that the dental technician uses the same driver
at the same torque of the clinician. There is still lack of evidence regarding the
efficacy of sealing agents on preload maintenance of screw-retained implant-supported
prostheses. Screw-retained restoration can be either with one or two prosthetic screws
(if multiple abutments have been used). Advantages of multiple abutments are one abutment
at one-time concept, correction of disparallelism between implants, and move inflammation
at tissue level. Disadvantages are only 15 Ncm of prosthetic torque, wide diameter
for esthetics, and reducing vertical space for restorations.
In case of cemented-retained restorations, the most important complications are biological
consequence of cement-retained and fracture of the prosthetic screw due to screw loosening.[11 ]
Single or multiple, cemented-retained, metal-free, lithium disilicate restorations
could be cemented on abutments or frameworks, out of the patients' mouth. Analyzed
data reported that single implant-supported restoration can be either screw- or cemented-retained,
with no significant differences in clinical parameters (MBL, bleeding on probing [BOP],
and pocket probing depth). Participants agreed that the final choice can be made based
on esthetics, tissue biotype, interarches space, implant disparellelism, and personal
expertise.
Similarly, multiple restorations can be either screw- or cemented-retained. In case
of partial restorations, authors reported no differences between screw- and cemented-retained
FDPs. Again, the choice can be made based on esthetics, tissue biotype, interarche
space, and implant disparellelism. All the participants agreed that CAD/CAM abutments
and/or frameworks should be preferred to improve esthetics and reduce potential biological
complications, in both single and multiple restorations.
In case of complete restorations, the most frequent technical complications were screw
fracture and chipping or fracture of the veneering material.[12 ] To reduce complications, an adequate number of implants and their correct position
are recommended. In fact, in case of multiple, implant-level restorations, the IAI
works as a flat-to-flat interface. Long-span, implant-supported FDPs should be at
abutment level (screwed on multi-abutment or cemented on stock or customized abutment).
The longer the span is, the greater the distortion and subsequently the misfit that
may occur. Hence, in case of complete restorations, the use of multi-abutments is
strongly suggested. Disadvantages of multi-abutments are wide emergence profile, maximum
15 Ncm of torque, and reduced interarch space for the prosthesis. Otherwise, the smaller
the inter-implant distance, the lower is the risk of prosthetic misfit. Hence, short-span
fixed partial prostheses can be at implant level. Implants parallelism is mandatory.
Work Group 2a: Abutment/framework design: Original versus nonoriginal abutments; macroarchitecture
of the implant neck (implant shoulder design); implant-abutment interface
Original versus nonoriginal abutments
After second-step selection and manual research, 16 full texts were included. Overall,
data from 255 original abutments (120 stock and 135 CAD/CAM) and 364 nonoriginal abutments
(211 stock and 153 CAD/CAM) were analyzed.
There is moderate evidence from in vitro studies that nonoriginal abutments provide worse mechanical behavior than originals.
Nevertheless, certified abutment with high-quality control seems to have similar outcomes
than original. Compatible abutments should not be used. Furthermore, little but positive
evidence is present on angled screw-channel solutions; nevertheless, they do not change
implants’ disparallelism.[13 ]
Macroarchitecture of the implant neck
After electronic and manual search, 16 manuscripts were selected. Of these, seven
were RCTs, four were observational comparative studies (2 retrospective and 2 prospective),
and five were systematic review of the literature. Overall, 221 one-piece implants
were placed in 107 patients, 139 scalloped implants placed in 96 patients, and 366
flat implants (same level on 360°) placed in 207 patients. No comparative studies
reporting data on sloped implants that fulfilled the inclusion criteria were found
in this research.
There is high evidence that different implant neck designs do not offer any clinical
or radiographic advantage.[14 ] Hence, it is preferable to have a two-piece implant with convergent or straight
neck design, with the same level on 360°. Nevertheless, other factors related to implant
neck design, such as the use of microthreads and modifications in implant surface
characteristics, could preserve peri-implant bone. In addition, some authors recently
demonstrated significantly higher MBL rates around implants with shorter compared
with longer prosthetic abutments, concluding that the height of the abutment plays
a critical role in the marginal bone maintenance in screw-retained prostheses, in
spite of the platform-switching distance.[15 ]
Implant-abutment interface
After electronic and manual search, 14 manuscripts, including 1126 implants, were
selected. Then, four in vitro studies and three in vivo RCTs were analyzed to find possible significant differences between internal and
external connections.
Bacterial colonization at the IAI seemed to be unavoidable.[16 ] Nevertheless, based on the selected studies, there is medium evidence that a stable
connection is essential to reduce micromovements and microleakage. Stable implant-abutment
connection depends on a several number of variables including, but not limited to,
the accuracy (manufacturing) of the implant’s components. In general, internal connections
are considered to be more stable than external. However, external connections can
provide prosthetic stability with the proper screw preload, and it could be suggested
in complete restorations.
Work Group 2b: Abutment/framework protocols: Abutment insertion protocol; platform
switching
Abutment insertion protocol (one-abutment/one-time)
After electronic and manual search, 14 manuscripts, including 535 patients with 994
implants, were selected. Of these, five were prospective cohort studies, three were
retrospective cohort studies, and six were RCTs with a parallel group design that
was included in the quantitative analysis. One-abutment one-time protocol has no clinical
influence on the esthetic outcome. Results from systematic review and meta-analysis
showed a reduction of 0.3 mm for MBL and 0.2 mm for buccal reduction.[17 ] The main limitation of this protocol is that a cemented-retained restoration is
required. Nevertheless, all the participants agreed that it is desirable to connect
and remove abutments as few times as possible.
Platform switching
After electronic and manual search, 12 manuscripts were selected for this consensus.
Of these, three were RCTs by the authors of this consensus and six were systematic
review with meta-analysis. Two were narrative reviews, and one was systematic review
of the literature.
There is medium evidence that an adequate platform switching tends to enhance tissue
volume and stability in the medium- and long-term follow-up.[18 ]
[19 ] Nevertheless, all the participants agreed to apply the platform switching concept.
Work Group 3: Abutment/framework materials and customization: Metal versus metal-free
restorations
After electronic and manual search, 13 manuscripts were selected for this consensus.
Based on RCTs, zirconia frameworks exhibited similar outcomes to metal-based FDPs.
The majority of technical and biologic outcome measures were not significantly different.
Chipping of the veneering material was the most frequent complication for both types
of restorations.[20 ]
[21 ]
All the participants agreed that in the presence of a thin phenotype, all ceramic
materials should be used for abutments and/or crowns. There is strong clinical evidence
that when all ceramic materials are used, the use of a titanium base connector is
advised. Regarding the production method, customized abutments can improve tissue
support compared with stock abutments. In addition, customized abutments improve cement
line position in cement-retained crowns, and hence, CAD/CAM abutments should be preferable.
The accuracy of the workflow depends mainly on physical material properties (impression,
master model, and casting) and human-related factors (timing and manual handling).
In the smile zone, a single, CAD/CAM zirconia abutment with a titanium base connector
is advised. Metal-free materials are advised as veneering material (i.e., lithium
disilicate). In the nonsmile zone, it is advisable to use a metal (titanium or Cr-Cb)
abutment (titanium) with a porcelain fused to metal (Cr-Cb) crown, cemented on the
top. Stock or CAD/CAM abutment can both be used. A custom UCLA-metal ceramic abutment
or a customized CAD/CAM abutment can be screwed at implant level and stratified with
porcelain. In this case, gold alloy or Cr-Cb is recommended as an abutment/framework
material. No statistically significant differences exist between metal and zirconia
as a framework material.
Data from the literature showed that most chipping of the veneering materials is observed
when using porcelain fused to zirconia. Nevertheless, all the participants agreed
that these complications can be reduced with technical experience and following an
accurate production protocol. Furthermore, participants highlighted that screw-retained
restorations are easy to remove in case of complications. Monolithic solution in the
posterior area and stratified restorations in the anterior could be another good solution
to reduce technical complications; nevertheless, there is still lack of scientific
evidence about monolithic reconstructions. For all of these reasons, all the participants
agreed that prevention and management of complications should be improved.
No scientific evidence is present for the new prosthetic solutions: single, partial,
or complete restorations bonded on metallic abutment; monolithic zirconia restorations;
and metallic ring for zirconia-based, screw-retained restorations. There is also no
evidence on dental composite as a restorative material (titanium-composite restoration).
DISCUSSIONS
It seems clear that, regardless of all the efforts to limit it, there are many factors
causing MBL around dental implants. The reformation of biologic width around dental
implants has been hypothesized as one of the most likely causes of early implant bone
loss.[22 ] Several factors, such as implant micro- and macro-design, as well as surgical and
prosthetic aspects, may all contribute to this process.[23 ]
[24 ]
[25 ] In many cases, adjunctive bone loss can be attributed to complications associated
with the implant and its components such as loose of abutment screws, broken components,
bacterial contamination of interfaces, and cement in the soft tissues. In fact, according
to an observational study from Canullo et al. , 30.4% of peri-implantitis can be classified as prosthetically triggered.[9 ]
According to the Seventh European Workshop on Periodontology,[8 ] peri-implantitis was defined as positive BOP and/or suppuration, in combination
with radiographic MBL ≥2 mm.[8 ] In a recent observational study, Galindo-Moreno et al. found that implants with increased MBL rates during the immediate postloading healing
period are more likely to reach MBL values that may compromise their mid-long-term
success and survival rates. The cutoff value suggested from this study was 2 mm at
18 months. Factors influencing MBL during this healing period are smoking, bone, age,
connection type, and plaque accumulation.[26 ] An open-cohort prospective study reported patients receiving bone level implants
with a rough surface (Ra of 2.5 ~ 3.0 μm) sandblasted with alumina and acid-etched
and featuring an internal hex and 11° conical connection (Osstem TSIII, XXX).[27 ] Following the results of this study, a physiological marginal bone remodeling of
0.37 mm within 1 year after loading can be expected in the daily practice.
It is well known that implant-supported FDPs are a safe and predictable treatment
method with high survival rates. However, biological and technical complications are
frequent (33.6%).[1 ]
[28 ]
[29 ] A recent systematic review by Pjetursson et al . suggested that a way to minimize the incidence of complications is to choose reliable
components and materials.[1 ] Moreover, the patients should be placed in well-structured maintenance systems immediately
after treatment.
During this consensus conference, in the effort to determine whether a prosthetic
procedure could be recommended as a standard for implant-supported rehabilitations,
the authors discussed and all agreed that retrievability and patient’s expectation
(function and esthetics) should guide the choice of the most adequate technique, component,
and material.
Although screw-retained reconstructions exhibit more technical problems compared with
cemented prostheses, screw-retained reconstructions are more easily retrievable and
show less biological complications (implant loss, bone loss >2 mm). Furthermore, eventual
technical and/or biological complications can be treated more easily.[12 ] At the same time, especially for posterior regions and/or in case of reduced mouth
opening, this prosthetic solution would make easier and faster the tightening procedure.
However, screw-retained restorations require a careful prosthetically driven planning,
performed according to the esthetic and functional needs, which could be achieved
using a computer-assisted template-guided implant placement. These approaches also
potentially reduce the risks for implant and prosthetic long-term failure.[30 ] Moreover, an angulated screw channel abutment may allow to further compensate divergence
up to 25°, in order not to affect esthetics.
Stability of the peri-implant soft and hard tissues is prerequisites for a long-term
esthetic and function of implant-supported restoration. In the last year, new implant
and abutment designs have been proposed to minimize the crestal bone loss. Platform
switching has been proposed as an effective prosthetic concept to reduce the amount
of peri-implant bone loss around dental implants.[20 ] On the contrary, there was sufficient evidence that implants with scalloped or sloped
marginal contour offer no benefit when compared to two-piece, conventional flat implants.[14 ]
If possible, repeated abutment dis/re-connections may be avoided due to significantly
increased MBL and buccal recession.[17 ] Placing a definitive abutment the day of the surgery presupposes that the definitive
restoration will be cemented above. Otherwise, screwing multiunit abutments immediately
on the day of the surgery (i.e., complete restorations) allow to deliver a screw-retained
restoration maintaining advantages of the one-abutment one-time concept.
Standardized titanium abutments still represent, worldwide, the gold standard for
implant reconstructions due to the good long-term success rates reported in clinical
studies.[31 ]
[36 ]
[37 ] Nevertheless, these abutments exhibit several shortcomings. First, metallic abutments
can provide grayish color when in contact with thin soft tissues which may lead to
esthetic problems.[31 ] Second, to develop a natural emergence profile of the reconstruction, the standardized
shape needs to be modified directly by a tooth-like shape of the crown. This situation
may lead to over-contouring the reconstruction. Finally, the standardized height of
the crown margin may impair the removal of the excess cement, leading to possible
biological complications. To overcome these problems, customized CAD/CAM abutments
have been developed. These may be made of either titanium or zirconia. It has been
shown that zirconia abutments exhibited the same survival and a similar esthetic outcome
as titanium abutments.[35 ]
[36 ]
[37 ]
[38 ]
[39 ]
[40 ] Moreover, zirconia abutments allow to improve esthetics leading to customized emergence
profile and cement line. One limitation of the zirconia abutments may be that their
material strength is lower than that of titanium, and hence, all the participants
agreed that a metallic ring for zirconia-based, screw-retained restorations is mandatory.
Because of their greater optical properties and esthetic results, the use of zirconia
abutments is suggested for smile regions even if more studies should be performed
to longitudinally analyze biological response.
