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teeth adjacent to treated or untreated pos-terior-bounded edentulous spaces, teeth
restored with fixed dental prostheses had a
10-year survival estimate of 92% compared
with spaces that remained untreated (81%
survival of adjacent teeth). However, the
application of removable dental prostheses
resulted in only a 56% survival rate.2
The advantages of using attachment-
retained removable dental prostheses are
improved esthetics, readjustable retention
force, and a reduced incidence of second-
ary caries that is often observed with clasp-
retained dentures.3 While some clinical
studies of precision attachmentretained
removable dental prostheses report good
results with 80% of the prostheses function-
ing properly after a 3-year period,4 other
studies observed failure rates of 35% to
40% after 5 years and only a 30.1% clinical
survival rate after 8 years.5 In longitudinal
studies, the lack of success of extracoronal
attachments was attributed primarily to bio-
logic and secondly to technical factors.6,7
A shortened dental arch or distal free-endsituation is defined as a dentition with
intact anterior teeth and a reduction of
occluding pairs of posterior teeth that affect
the premolars and molars.1 Restorative
solutions include fixed tooth- or implant-
retained restorations and removable dental
prostheses. A removable dental prosthesis
can be retained by clasps or extracoronal
attachments or be designed as an over-
denture retained by telescopic copings.
When evaluating the long-term survival of
1Assistant Proessor, Dental Clinic 2, Department o
Prosthodontics, University Clinic Erlangen, Erlangen, Germany.
2Dean and Clinical Director, Dental Clinic 2, Department o
Prosthodontics, University Clinic Erlangen, Erlangen, Germany.
3Associate Proessor, Dental Clinic 2, Department o
Prosthodontics, University Clinic Erlangen, Erlangen, Germany.
4Private Practice, Karlsruhe, Germany.
Correspondence: Dr Johannes Schmitt, Dental Clinic 2,
Department o Prosthodontics, University Clinic Erlangen,
Glueckstr 11, 91054 Erlangen, Germany. Email: johannes.
Five-year clinical follow-up of prefabricated
precision attachments: A comparison of uni-
and bilateral removable dental prostheses
Johannes Schmitt, DMD1/Manfred Wichmann, PhD, DMD2/
Stephan Eitner, PhD, DMD3/Jrg Hamel, DMD4/
Stefan Holst, PhD, DMD3
Objcvs: To evaluate the clinical long-term success of prefabricated precision attach-
ments in retaining uni- or bilateral removable dental prostheses. Mo Mrs:
Twenty-three patients with uni- or bilateral shortened dental arches received removable
dental prostheses attached to the residual dentition with two types of precision attach-
ments. Rss: After 5 years, 70% of bilateral and 25% of unilateral removable dental
prostheses remained clinically functional. The most frequent cause of clinical failure was
fracture of the abutment teeth for bilateral partial dentures and irreversible wear of the pre-
cision attachment for unilateral prostheses. Oral hygiene status significantly improved, and
the mean pocket depth of the abutment teeth did not increase after 5 years. Cocso:
Removable partial denture prostheses, retained bilaterally with precision attachments,
are a reliable treatment modality without negative long-term effects on periodontal health,
whereas unilateral removable dental prostheses cannot be recommended because of high
clinical failure rates. (Quintessence Int 2011;42:413418)
Ky ors: distal free end, precision attachment, removable dental prosthesis,
unilateral
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To achieve long-term clinical success with
precision attachments, at least two abut-
ment teeth should be splinted,8 and a
number of technical improvements have
been developed in recent years. Theseinclude adjustable retentive forces with set
screws and interchangeable plastic inserts
that allow for easy recovery of retention and
eliminate problems associated with wear of
components.
Despite the number of studies of preci-
sion attachments available, no data are avail-
able comparing the clinical performance
and success of precision attachments in
uni- or bilateral edentulous situations. The
rationale of the present prospective clinical
investigation was to assess the long-term
outcome of unilaterally retained removable
dental prostheses or bilaterally retained
removable dental prostheses with regard to
their technical and biologic complications.
It was hypothesized that bilaterally
retained removable dental prostheses
would positively affect long-term stability
and longevity of the prosthesis, whereas
unilaterally retained removable dental pros-
thesis retention would be more susceptible
to technical complications.
MethOd and MateRialS
Patients presenting with uni- or bilateral
shortened dental arches were informed of
the study and gave their written consent.
The study protocol was approved by thelocal ethical committee (IRB no. 2783). A
total of 23 patients participated in the study
in 2000 and 2001 and received a total of
20 bilaterally retained removable dental
prostheses and eight unilaterally retained
removable dental prostheses retained
by precision attachments (Swiss Mini-SG
System, Cendres & Meteaux).
The Mini-SG system is a prefabricat-
ed precision attachment system based on
one universal male and several different
female components. For all Kennedy Class
II situations, splinting of abutment teeth was
performed. In addition, bracing arm con-
structions were planned (Fig 1). In Kennedy
Class I cases, splinting of abutment teeth
was carried out for all but three dentures (Fig
2). For Kennedy Class I bilateral situations,
extracoronal attachments with interchange-
able plastic inserts that are adjustable with
an activation screw or by replacing the
insert itself were used, whereas the uni-
lateral removable dental prostheses were
anchored with spring bolt attachments.
The first examination was conducted2 weeks after the prosthesis was inserted
(baseline). Follow-up examinations were
performed annually for 3 years and after 5
years of clinical function. To evaluate oral
hygiene status and gingival inflammation,
Plaque Index (PI) and Gingival Index (GI)
scores were assessed.9,10 Periodontal prob-
ing depths were measured at six locations
near each abutment tooth. Data analysis
consisted of descriptive statistics and the
Wilcoxon test for paired data (P .05).
ReSultS
Prostheses survival rates after 3 and 5 years
of clinical function are shown in Table 1. For
bilaterally retained removable dental pros-
theses, the most common complication and
cause for prosthesis failure was fracture
of abutment teeth, whereas for unilaterally
retained removable dental prostheses, irre-
Fig 1 Removable dental prostheses or Kennedy Class II occlusion.
Unilateral prosthesis or Kennedy Class II with splinted teeth (mandibularcentral and lateral incisors and right canine and frst premolar). The insetimage shows the emale part o the Mini-SG attachment with spring boltand activation screw.
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versible mechanical wear of the male part
of the attachment occurred (Table 2 and Fig
3). Four nonsplinted abutment teeth (two
vital, one endodontically treated) fractured
in the bilateral group.
For bilaterally retained removable dental
prostheses, the attachment retention force
could usually be restored with screw activa-
tion, but exchange of the plastic insert was
necessary in one-third of all attachments
Fig 2 Removable dental prostheses or Kennedy
Class I occlusion. Bilateral prosthesis or Kennedey ClassI, and the unsplinted single abutment teeth (maxillaryright frst premolar and let canine). The inset imageshows the emale part o the Mini-SG attachment withthe plastic insert and activation screw.
Fig 3 Irreversible mechanical wear on the male attachment part.The inset image shows a new male attachment part.
table 1 Prosheses survival raes
Year
Class i:
Blaeral dsal exensons
(baselne, n = 20)
Class ii:
unlaeral dsal exensons
(baselne, n = 8)3 80.0% 62.5%
5 70.0% 25.0%
table 2 Reasons for proshesis failure
Class i:
Blaeral dsal exensons
(toal no. of aachmens = 43)
Class ii:
unlaeral dsal exensons
(toal no. of aachmens = 8)
Irreversible mechanical wear of attachment 4
Fracture of abutment splinting 1
Fracture of abutment tooth 4 1
Caries 2
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during the 5-year observation period. In four
clinical cases, the male part of the spring bolt
attachment for the Kennedy Class II situations
showed irreversible mechanical wear after 4
years of clinical function, and the restoration
had to be replaced (Table 3).
The mean probing depth values ranged
from 2.1 to 3.1 mm for the abutment teeth
after 5 years and did not increase com-
pared with baseline values (.023 P .850).
Data for PI and sulcus bleeding index (SBI)
showed a statistically significant decrease
(P < .001) and dropped to 52.1% and
50.2%, respectively, in both groups after 5
years.
diSCuSSiOn
The observed survival rate of precision
attachmentretained bilateral removable
dental prostheses was comparable to the
reported survival rates of clasp-retained
removable dental prosthesis after 5 years,
but inferior to the 95.1% survival rate report-
ed for telescopic crownretained den-
tures.11,12 Despite the vitality of the teeth,
three of the observed abutment tooth frac-
tures, all of which led to failure of bilateral
dentures, occurred on nonsplinted attach-
ments and are in accordance with data
reported in the literature.13 Thus, the low
survival rate of 70% after 5 years refers par-
tially to nonsplinted abutment teeth, which
created a lack of uniformity in the bilater-
ally retained removable dental prosthesis
group. Nonsplinted abutment teeth with a
removable dental prosthesis design without
reciprocation elements in patients with a
reduced vertical dimension may put this
type of restoration at risk for failures.
In vitro investigations showed that these
attachments tend to introduce significantly
more stress at the terminal abutment tooth
compared with clasp-retained dentures.14
With the use of the extracoronal attach-
ment systems, fracture of unsplinted abut-
ment teeth or caries on splinted abutments
can lead to irreversible prosthesis failure.
Therefore, use of the extracoronal attachment
system requires at least two splinted, vital,
and periodontally healthy abutment teeth.8,13
The survival rate for the unilaterally
retained removable dental prostheses was
25.0% after 5 years; using the miniaturized
attachment system for this indication is
highly questionable. An in vitro investigation
demonstrated that movement of the abut-
ment tooth and denture base of unilaterally
stabilized dentures is significantly greater
than with the bilateral design.15 Jin et al rec-
ommended positioning occlusal contacts
exactly on top of the crest of the alveolar
ridge and not extending the restorations
distally to the first molar.15 The observed
destructive and irreversible wear of the
miniaturized male attachment part and the
fracture of a vital and splinted abutment
tooth in the present investigation is a strong
indicator of prosthesis movement during
clinical function. It can be assumed that the
design of a unilaterally retained removable
dental prosthesis without crossarch stabi-
lization and extended cantilever lengths
creates significant stress on the fixed dental
table 3 technical complicaions occurring during he 5-year observaion period
Class i:
Blaeral dsal exensons
(toal no. of aachmens = 43)
Class ii:
unlaeral dsal exensons
(toal no. of aachmens = 8)
Attachment screw activation 20 3
Change of plastic insert 17
Irreversible mechanical wear of attachment 4
Fracture of ceramic veneering 3
Decementation 1 1
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prosthesis. The additional lack of control
on the lateral and vertical forces on both
the removable and fixed dental prosthesis
may be the primary reason for the observed
technical failures.
As suggested by other authors, bilateralstabilization should be recommended for
Kennedy Class II situations if removable
dental prostheses are used.1517 A remark-
able finding of this study was the need to
change the plastic insert in the female part
of the bilaterally retained removable dental
prosthesis attachments, confirming previ-
ous in vitro findings that showed only neg-
ligible amounts of wear on plastic female
inserts in comparison with metal-alloy matrix
and patrix components.18
Improvement in periodontal parameters
is a positive result of this study, contrast-
ing with reports of clasp-retained remov-
able dental prostheses that described
increased plaque accumulation and peri-
odontal inflammation.19 Our results showing
that inflammatory signs improved and peri-
odontal probing depths generally appeared
quite stable over time led to the conclusion
that precision attachmentretained remov-
able dental prostheses contribute less to
formation of dental plaque compared with
clasp-retained removable dental prosthe-
ses. Furthermore, a precise attachmentbetween the prosthesis and abutment teeth
with adjustable retentive forces seems to be
useful in maintaining periodontal health.
It can be argued that the reduced num-
ber of patients in the unilaterally retained
removable dental prosthesis group is inad-
equate to draw definitive conclusions about
the attachments performance. However, the
observed failure parameters (destructible
wear) were identical in all patients and pre-
sented a general reason for failure that can
also be expected in larger samples sizes.
Therefore, it can be concluded that the
Mini-SG attachment is suitable for anchoring
bilaterally retained removable dental pros-
theses, whereas in unilateral distal free-end
situations, the design of removable dental
prostheses should include crossarch sta-
bilization if alternative fixed restorations are
not feasible. Unilaterally retained removable
dental prostheses cannot be recommended
because of high clinical failure rates.
aCKnOwledgMentS
The authors express their gratitude to dental techni-
cian Erwin Schtz or his outstanding collaboration
and excellent technical expertise during years o clini-
cal teamwork. The study was supported by Cendres &
Meteaux.
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