5 year clinical follow up of prefebricated precision attachments a comparison of uni and bilateral...

8/3/2019 5 Year Clinical Follow Up of Prefebricated Precision Attachments a Comparison of Uni and Bilateral Removable Dent

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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


3Associate Proessor, Dental Clinic 2, Department o


4Private Practice, Karlsruhe, Germany.

Correspondence: Dr Johannes Schmitt, Dental Clinic 2,

Department o Prosthodontics, University Clinic Erlangen,

Glueckstr 11, 91054 Erlangen, Germany. Email: johannes.

[email protected]

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:


(toal no. of aachmens = 43)

Class ii:



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:



Class ii:



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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