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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en">Wear of double crown systems - electroplated vs. casted female
part</title><author><name sortKey="Bayer, Stefan" sort="Bayer, Stefan" uniqKey="Bayer S" first="Stefan" last="Bayer">Stefan Bayer</name><affiliation><nlm:aff id="aff01"> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany; Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland.</nlm:aff></affiliation></author><author><name sortKey="Kraus, Dominik" sort="Kraus, Dominik" uniqKey="Kraus D" first="Dominik" last="Kraus">Dominik Kraus</name><affiliation><nlm:aff id="aff02"> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Keilig, Ludger" sort="Keilig, Ludger" uniqKey="Keilig L" first="Ludger" last="Keilig">Ludger Keilig</name><affiliation><nlm:aff id="aff03"> Dr. Rer. Nat., Endowed Chair of Oral Technology, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Golz, Lina" sort="Golz, Lina" uniqKey="Golz L" first="Lina" last="Gölz">Lina Gölz</name><affiliation><nlm:aff id="aff04"> Dr. Med. Dent., Clinic for Orthodontics, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Stark, Helmut" sort="Stark, Helmut" uniqKey="Stark H" first="Helmut" last="Stark">Helmut Stark</name><affiliation><nlm:aff id="aff05"> Prof. Dr. Med. Dent. Head of Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Enkling, Norbert" sort="Enkling, Norbert" uniqKey="Enkling N" first="Norbert" last="Enkling">Norbert Enkling</name><affiliation><nlm:aff id="aff06"> Dr. Med. Dent., Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland; Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author></titleStmt><publicationStmt><idno type="wicri:source">PMC</idno><idno type="pmid">22858708</idno><idno type="pmc">3881770</idno><idno type="url">http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3881770</idno><idno type="RBID">PMC:3881770</idno><idno type="doi">10.1590/S1678-77572012000300015</idno><date when="2012">2012</date><idno type="wicri:Area/Pmc/Corpus">000609</idno><idno type="wicri:explorRef" wicri:stream="Pmc" wicri:step="Corpus" wicri:corpus="PMC">000609</idno></publicationStmt><sourceDesc><biblStruct><analytic><title xml:lang="en" level="a" type="main">Wear of double crown systems - electroplated vs. casted female
part</title><author><name sortKey="Bayer, Stefan" sort="Bayer, Stefan" uniqKey="Bayer S" first="Stefan" last="Bayer">Stefan Bayer</name><affiliation><nlm:aff id="aff01"> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany; Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland.</nlm:aff></affiliation></author><author><name sortKey="Kraus, Dominik" sort="Kraus, Dominik" uniqKey="Kraus D" first="Dominik" last="Kraus">Dominik Kraus</name><affiliation><nlm:aff id="aff02"> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Keilig, Ludger" sort="Keilig, Ludger" uniqKey="Keilig L" first="Ludger" last="Keilig">Ludger Keilig</name><affiliation><nlm:aff id="aff03"> Dr. Rer. Nat., Endowed Chair of Oral Technology, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Golz, Lina" sort="Golz, Lina" uniqKey="Golz L" first="Lina" last="Gölz">Lina Gölz</name><affiliation><nlm:aff id="aff04"> Dr. Med. Dent., Clinic for Orthodontics, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Stark, Helmut" sort="Stark, Helmut" uniqKey="Stark H" first="Helmut" last="Stark">Helmut Stark</name><affiliation><nlm:aff id="aff05"> Prof. Dr. Med. Dent. Head of Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author><author><name sortKey="Enkling, Norbert" sort="Enkling, Norbert" uniqKey="Enkling N" first="Norbert" last="Enkling">Norbert Enkling</name><affiliation><nlm:aff id="aff06"> Dr. Med. Dent., Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland; Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</nlm:aff></affiliation></author></analytic><series><title level="j">Journal of Applied Oral Science</title><idno type="ISSN">1678-7757</idno><idno type="eISSN">1678-7765</idno><imprint><date when="2012">2012</date></imprint></series></biblStruct></sourceDesc></fileDesc><profileDesc><textClass></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en"><sec><title>Objectives</title><p>The wear of telescopic crowns is a common problem often reducing the patient's
satisfaction with the denture and resulting in a renewal of the denture. The study
aims to compare the wear behavior of conical crowns using electroplated copings
(group E) with standard telescopic crowns with cast female parts (group C). </p></sec><sec><title>Material and Methods</title><p>10 conical crowns were milled for each group of a cast gold alloy. The specimen of
group E had a conicity of 2º. The cast secondary crowns of group C had a 0º
design. The electroplated coping was established by direct electroforming. An
apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive
forces and the correlating distance during insertion and separation were measured.
The wear test was separated in a start phase, an initial wear phase and the long
term wear period. The retention force value and the force-distance integral of the
first 0.33 mm of each cycle were calculated. </p></sec><sec><title>Results</title><p>The retentive forces were significantly higher for group E and the integrals were
significantly lower for this group except the integral at cycle 10,000. The
changes of retention force and integral did not differ significantly between both
groups in all phases. The change of the integrals as well as the integral at the
particular cycles showed higher interquartile distances for group C. </p></sec><sec><title>Conclusions</title><p>Within the limitations of this study the tested conical crowns showed clinically
acceptable retentive properties. The values reached a range comparable to
retentive elements tested in recent literature. The values of group C showed
higher ranges. The force measured for group E was significantly higher than for
group C but the integrals showed an opposite tendency. The results indicate that
an exclusive analysis of the force is not sufficient as the integral is not
equivalent to the force although it describes the retentive property of the system
in a better way than the force over a distance is described. Both systems seem to
be suitable for clinical practice.</p></sec></div></front><back><div1 type="bibliography"><listBibl><biblStruct><analytic><author><name sortKey="Bayer, S" uniqKey="Bayer S">S Bayer</name></author><author><name sortKey="Gruner, M" uniqKey="Gruner M">M Gruner</name></author><author><name sortKey="Keilig, L" uniqKey="Keilig L">L Keilig</name></author><author><name sortKey="Hultenschmidt, R" uniqKey="Hultenschmidt R">R Hültenschmidt</name></author><author><name sortKey="Nicolay, C" uniqKey="Nicolay C">C Nicolay</name></author><author><name sortKey="Bourauel, C" uniqKey="Bourauel C">C Bourauel</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Bayer, S" uniqKey="Bayer S">S Bayer</name></author><author><name sortKey="Stark, H" uniqKey="Stark H">H Stark</name></author><author><name sortKey="Mues, S" uniqKey="Mues S">S Mues</name></author><author><name sortKey="Keilig, L" uniqKey="Keilig L">L Keilig</name></author><author><name sortKey="Schrader, A" 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Ep" uniqKey="Dias E">EP Dias</name></author><author><name sortKey="Cestary, Tm" uniqKey="Cestary T">TM Cestary</name></author><author><name sortKey="Taga, R" uniqKey="Taga R">R Taga</name></author><author><name sortKey="Zanetti, Rv" uniqKey="Zanetti R">RV Zanetti</name></author><author><name sortKey="Zanetti, A" uniqKey="Zanetti A">A Zanetti</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Greco, Gd" uniqKey="Greco G">GD Greco</name></author><author><name sortKey="Jansen, Wc" uniqKey="Jansen W">WC Jansen</name></author><author><name sortKey="Landre, J" uniqKey="Landre J">J Landre</name></author><author><name sortKey="Seraidarian, Pi" uniqKey="Seraidarian P">PI Seraidarian</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Greco, Gd" uniqKey="Greco G">GD Greco</name></author><author><name sortKey="Jansen, Wc" uniqKey="Jansen W">WC Jansen</name></author><author><name sortKey="Landre, J" uniqKey="Landre J">J 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uniqKey="Engel E">E Engel</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Stancic, I" uniqKey="Stancic I">I Stancic</name></author><author><name sortKey="Jelenkovic, A" uniqKey="Jelenkovic A">A Jelenkovic</name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Weigl, P" uniqKey="Weigl P">P Weigl</name></author><author><name sortKey="Hahn, L" uniqKey="Hahn L">L Hahn</name></author><author><name sortKey="Lauer, H C" uniqKey="Lauer H">H-C Lauer </name></author></analytic></biblStruct><biblStruct><analytic><author><name sortKey="Wichmann, Mg" uniqKey="Wichmann M">MG Wichmann</name></author><author><name sortKey="Kuntze, W" uniqKey="Kuntze W">W Kuntze</name></author></analytic></biblStruct></listBibl></div1></back></TEI><pmc article-type="research-article"><pmc-dir>properties open_access</pmc-dir>
<front><journal-meta><journal-id journal-id-type="nlm-ta">J Appl Oral Sci</journal-id><journal-id journal-id-type="iso-abbrev">J Appl Oral Sci</journal-id><journal-id journal-id-type="publisher-id">J. Appl. Oral. Sci.</journal-id><journal-title-group><journal-title>Journal of Applied Oral Science</journal-title></journal-title-group><issn pub-type="ppub">1678-7757</issn><issn pub-type="epub">1678-7765</issn><publisher><publisher-name>Faculdade de Odontologia de Bauru da Universidade de São
Paulo</publisher-name></publisher></journal-meta><article-meta><article-id pub-id-type="pmid">22858708</article-id><article-id pub-id-type="pmc">3881770</article-id><article-id pub-id-type="doi">10.1590/S1678-77572012000300015</article-id><article-categories><subj-group subj-group-type="heading"><subject>Original Articles</subject></subj-group></article-categories><title-group><article-title>Wear of double crown systems - electroplated vs. casted female
part</article-title></title-group><contrib-group><contrib contrib-type="author"><name><surname>BAYER</surname><given-names>Stefan</given-names></name><xref ref-type="aff" rid="aff01">1</xref><xref ref-type="corresp" rid="c01"></xref></contrib><contrib contrib-type="author"><name><surname>KRAUS</surname><given-names>Dominik</given-names></name><xref ref-type="aff" rid="aff02">2</xref></contrib><contrib contrib-type="author"><name><surname>KEILIG</surname><given-names>Ludger</given-names></name><xref ref-type="aff" rid="aff03">3</xref></contrib><contrib contrib-type="author"><name><surname>GÖLZ</surname><given-names>Lina</given-names></name><xref ref-type="aff" rid="aff04">4</xref></contrib><contrib contrib-type="author"><name><surname>STARK</surname><given-names>Helmut</given-names></name><xref ref-type="aff" rid="aff05">5</xref></contrib><contrib contrib-type="author"><name><surname>ENKLING</surname><given-names>Norbert</given-names></name><xref ref-type="aff" rid="aff06">6</xref></contrib></contrib-group><aff id="aff01"><label>1</label> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany; Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland.</aff><aff id="aff02"><label>2</label> Dr. Med. Dent., Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Germany.</aff><aff id="aff03"><label>3</label> Dr. Rer. Nat., Endowed Chair of Oral Technology, University of Bonn, Bonn, Germany.</aff><aff id="aff04"><label>4</label> Dr. Med. Dent., Clinic for Orthodontics, University of Bonn, Bonn, Germany.</aff><aff id="aff05"><label>5</label> Prof. Dr. Med. Dent. Head of Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</aff><aff id="aff06"><label>6</label> Dr. Med. Dent., Clinic for Prosthetic Dentistry, University of Bern, Bern, Switzerland; Department of Prosthodontics, Preclinical Education and Dental Materials Science, University of Bonn, Bonn, Germany.</aff><author-notes><corresp id="c01"><bold>Corresponding address:</bold> Dr. Stefan Bayer - Department of Prosthodontics,
Preclinical Education and Dental Materials Science - Welschnonnenstr. 17, 53111 Bonn,
Germany - e-mail: <email>sbayer@uni-bonn.de</email> - Phone: +49-228-28722016 - Fax:
+49-228-287-22453</corresp></author-notes><pub-date pub-type="ppub"><season>May-Jun</season><year>2012</year></pub-date><volume>20</volume><issue>3</issue><fpage>384</fpage><lpage>391</lpage><history><date date-type="received"><day>29</day><month>10</month><year>2010</year></date><date date-type="rev-recd"><day>05</day><month>8</month><year>2011</year></date><date date-type="accepted"><day>11</day><month>8</month><year>2011</year></date></history><permissions><license license-type="open-access" xlink:href="http://creativecommons.org/licenses/by-nc/3.0/"><license-p>This is an open-access article distributed under the terms of the Creative
Commons Attribution License, which permits unrestricted use, distribution, and
reproduction in any medium, provided the original work is properly
cited.</license-p></license></permissions><abstract><sec><title>Objectives</title><p>The wear of telescopic crowns is a common problem often reducing the patient's
satisfaction with the denture and resulting in a renewal of the denture. The study
aims to compare the wear behavior of conical crowns using electroplated copings
(group E) with standard telescopic crowns with cast female parts (group C). </p></sec><sec><title>Material and Methods</title><p>10 conical crowns were milled for each group of a cast gold alloy. The specimen of
group E had a conicity of 2º. The cast secondary crowns of group C had a 0º
design. The electroplated coping was established by direct electroforming. An
apparatus accomplishing 10,000 wear cycles performed the wear test. The retentive
forces and the correlating distance during insertion and separation were measured.
The wear test was separated in a start phase, an initial wear phase and the long
term wear period. The retention force value and the force-distance integral of the
first 0.33 mm of each cycle were calculated. </p></sec><sec><title>Results</title><p>The retentive forces were significantly higher for group E and the integrals were
significantly lower for this group except the integral at cycle 10,000. The
changes of retention force and integral did not differ significantly between both
groups in all phases. The change of the integrals as well as the integral at the
particular cycles showed higher interquartile distances for group C. </p></sec><sec><title>Conclusions</title><p>Within the limitations of this study the tested conical crowns showed clinically
acceptable retentive properties. The values reached a range comparable to
retentive elements tested in recent literature. The values of group C showed
higher ranges. The force measured for group E was significantly higher than for
group C but the integrals showed an opposite tendency. The results indicate that
an exclusive analysis of the force is not sufficient as the integral is not
equivalent to the force although it describes the retentive property of the system
in a better way than the force over a distance is described. Both systems seem to
be suitable for clinical practice.</p></sec></abstract><kwd-group><kwd>Dental restoration wear</kwd><kwd>Denture retention</kwd><kwd>Dental prosthesis</kwd><kwd>Implant-supported denture</kwd><kwd>Overlay denture</kwd><kwd>Denture precision attachment</kwd></kwd-group></article-meta></front><body><sec><title>INTRODUCTION</title><p>There is a wide choice of different retentive elements that can be used for denture
retention<sup><xref ref-type="bibr" rid="r01">1</xref>-<xref ref-type="bibr" rid="r05">5</xref>,<xref ref-type="bibr" rid="r08">8</xref>,<xref ref-type="bibr" rid="r13">13</xref></sup>. Almost all of these systems consist of two main parts
used to connect teeth or implants to removable dentures. The male component is fixed on
the tooth or implant and the female component is integrated as part of the removable
denture. The systems differ in the particular material combination and the retentive
mechanism used for denture retention<sup><xref ref-type="bibr" rid="r01">1</xref>-<xref ref-type="bibr" rid="r05">5</xref>,<xref ref-type="bibr" rid="r12">12</xref></sup>.</p><p>The change of retention forces over the time of usage is one of the main problems each
system has to face. The change is caused by tribological processes affecting the surface
structures of the male and female parts<sup><xref ref-type="bibr" rid="r06">6</xref>,<xref ref-type="bibr" rid="r08">8</xref>,<xref ref-type="bibr" rid="r09">9</xref></sup>. The four most relevant tribological factors are tribochemical
reaction, abrasion, adhesion and surface disruption. They can appear separately or can
overlap each other<sup><xref ref-type="bibr" rid="r10">10</xref></sup>. The influence,
appearance and combination of these factors are affected by the material and
construction of the retentive element.</p><p>Concerning the double crown system as retentive element, two main techniques can be
considered. At first, the technique using electroplated female parts and at second the
technique using cast female components. The systems using electroplated copings as
female part gain importance by advantages in clinical practice. This technique is able
to connect implants and teeth in a denture compensating systematic misfits due to
impression and cast model techniques<sup><xref ref-type="bibr" rid="r07">7</xref></sup>.
So it is able to achieve a passive fit<sup><xref ref-type="bibr" rid="r08">8</xref></sup>. As aspects like cleaning ability, denture retention, extensibility
after abutment loss and patient satisfaction also show good results, the interest in
this system increases more and more. The technique using cast female parts shows the
advantage of a long term experience as the system is well known concerning survival,
maintenance and patient satisfaction<sup><xref ref-type="bibr" rid="r10">10</xref>,<xref ref-type="bibr" rid="r11">11</xref></sup>.</p><p>The data concerning the wear behavior of electroplated copings on conical crowns are
sparse. Weigl, et al.<sup><xref ref-type="bibr" rid="r28">28</xref></sup> (2000) showed
the advantages of electroplated copings on Empress ceramic crowns in denture retention
and wear development compared with the combination gold/gold and
titanium/titanium<sup><xref ref-type="bibr" rid="r16">16</xref></sup>. All three
combinations showed clinically acceptable results but the gold copings on ceramic
conical crowns showed less tribological effects and constant retentive forces.
Dillschneider, et al.<sup><xref ref-type="bibr" rid="r09">9</xref></sup> (2009) showed
that there was almost no difference in retentive forces when the cone angle was changed
from 0º to 2º<sup><xref ref-type="bibr" rid="r09">9</xref></sup>. Both studies measured
an overall median retentive force about 4-5 N. The literature concerning the wear of
systems using cast female parts is more comprehensive. The studies show clinically
acceptable median retentive forces of about 5 N and more sometimes reaching values
exceeding 100 N<sup><xref ref-type="bibr" rid="r10">10</xref>,<xref ref-type="bibr" rid="r17">17</xref>,<xref ref-type="bibr" rid="r18">18</xref></sup>.</p><p>The study presented here tries to compare systems using electroplated female parts
(group E) versus cast ones (group C). The point of interest is to examine whether there
are differences in retentive properties and their development or not. From these data
conclusions can be drawn concerning the wear behavior.</p></sec><sec sec-type="materials|methods"><title>MATERIAL AND METHODS</title><p>The primary crowns for group E were produced with a taper of 2º. The specimens of group
C showed a parallel walled design. Apart from that the primary crowns were manufactured
by the same production processes.</p><sec><title>Gold primary crowns</title><p>The primary crowns were modelled in wax (Yeti Fräswachs, Yeti Dental, Engen, Germnay)
on a prepared premolar-like metal tooth. The wax model was milled by a wax-milling
cutter (Group E with 2º: 496 KR-2º, Meisinger, Neuss, Germany; Group C with 0º: 497
RD-0º, Meisinger, Neuss, Germany). After that the wax was embedded in a casting mould
(Deguvest® SR Einbettmasse, DeguDent, Hanau, Germany) and cast in high gold alloy
(Degunorm, DeguDent). The surface of the crowns was milled with a dental milling
device (F3 Milling Device, DeguDent) and a milling cutter (Group E: HM460FR/PR-2º,
Meisinger; Group C: HM486 F-0º, Meisinger). The high glossy finish was reached by
using pumace and polishing paste (No. 103, Polirapid, Singen, Germany; Pariser Rot,
Dentaurum, Ispringen Germany). Each of the crowns had an oblong width with an
oro-labial distance of 6 mm, mesio-distal distance of 4 mm and a height of 6.5 mm.
The thickness reached 0.3 mm. Examples of both groups are shown in <xref ref-type="fig" rid="f01">Figure 1</xref>.</p><fig id="f01" orientation="portrait" position="float"><label>Figure 1</label><caption><p>Parts of the specimen. At left the specimen using an electroplated female part:
1: cast metal framework of non-precious alloy, 2: electroplated coping, 3: gold
alloy conical crown. At right a specimen using a cast female part: 4: gold
alloy female part and 5: primary crown made of the same gold alloy</p></caption><graphic xlink:href="jaos-20-03-0384-g01"></graphic></fig></sec><sec><title>Group E: Electroplated female parts and cast metal framework</title><p>The electroplated copings were produced for group E in combination with the 2º
conical primary crowns. The gold crowns had to be filled with pattern resin to avoid
disposal of electroplated gold onto the inner surfaces of the crowns (Pattern Resin,
GC, Alsip, USA). The conical crowns were spray-coated using an air-brush with 0.7 bar
(Airbrush, C.Hafner, Pforzheim, Germany) to obtain a homogenous thin layer of silver
lacquer (Solaris Conducting Silver Varnish, DeguDent) and placed in a fully automated
electroplater (Solaris, DeguDent). The gold copings were created by directly
electroplating the ceramic surfaces with gold<sup><xref ref-type="bibr" rid="r08">8</xref></sup>. Electroplating times and currents were selected to produce
layers of approximate 0.25 mm thickness. The Solaris system uses an 8-level
graduation for the adjustment of the electroplating process. For the specimens used
in this study the electroplating was performed at level 4 as this level should be
used for constructions showing a surface of about 115 mm<sup>2</sup>. The
electroplating at level 4 required 5 h. After removing the electroplated coping, the
remaining silver layer on their internal surface was completely removed by 53% nitric
acid. No retention force adjustment was required for this double-crown
system<sup><xref ref-type="bibr" rid="r28">28</xref></sup>. An example of the
electroplated copings is shown in <xref ref-type="fig" rid="f01">Figure 1</xref>.</p><p>A cast metal framework was necessary for supporting the electroplated female parts.
This framework was produced by using a 0.6 mm thermoforming foil (Ekolen, Erkodent,
Pfalzgrafenweiler, Germany) to reach a standardized strength. Before casting, the
screw for the axial insertion and separation was placed to be cast in one piece with
the framework (<xref ref-type="fig" rid="f01">Figure 1</xref>). In the wear test the
screw was used to fix the specimen holder for axial insertion and separation. The
modeled structure was then invested in a casting mould and burned out by the
manufacturer's instructions (Optivest<sup>®</sup>, DeguDent). Non precious metal
(Biosil, DeguDent) was used for casting the framework. Then the framework was thinned
out to 0.5 mm thickness. The gold copings were placed onto the conical crown. The
female part was finished by gluing the coping and the cast metal framework by a
composite cement (AGC® Cem, Wieland Dental, Pforzheim, Germany) (<xref ref-type="fig" rid="f02">Figure 2</xref>).</p><fig id="f02" orientation="portrait" position="float"><label>Figure 2</label><caption><p>Cross section diagram of a specimen with an electroplated coping: Composite
cement (blue) is used for the fixation of the electroplated coping (yellow) in
the cast metal framework (a); The conical crown (green) is fixed by resin
cement (red) onto the specimen holder (b)</p></caption><graphic xlink:href="jaos-20-03-0384-g02"></graphic></fig><p>The alignment of the screws and the connecting of the copings and the cast metal
frameworks were performed with the aid of the milling device. This step guaranteed an
alignment of the crown's axis parallel to the direction of insertion and
separation.</p></sec><sec><title>Group C: Cast female parts</title><p>The female part was modeled onto the parallel walled primary crown using Pattern
Resin<sup>®</sup> LS (GC, Tokyo, Japan). The thickness of the resin reached
approximately 0.4 -0.5 mm. As the primary crown was still positioned on the milling
device the screw needed to move the female part was placed in the appropriate
direction of insertion and removal. The resin female part was embedded and cast using
the same materials that were used for the primary crown production. After removal of
the specimen out of the casting mould the surface was sandblasted by using
aluminum-oxide (Korox<sup>®</sup>110, Bego, Bremen, Germany) and sodium-glass
(Perlablast<sup>®</sup> micro 50, Bego) at 2 bar pressure. The result was
controlled by 10 times magnification. Further finishing of the inner surfaces was
performed using burnishers of different roughness. The retention force was adjusted
at approximately 1 to 3 N by burnishing the inner surfaces of the female part and the
outer surfaces of the primary crown. The force was controlled using a measuring
instrument (Friktionstester, Krupp, Germany).</p></sec><sec><title>Wear simulator</title><p>The wear simulator is shown in <xref ref-type="fig" rid="f03">Figure 3</xref>. An
electric motor produced the force required for insertion and separation. The
positioning accuracy of the carriage driven by this motor was 2 µm. A load cell with
a measuring range of ±200 N was used to register the forces with an accuracy of 0.1
N. The control of the wear simulator and recording of the data was performed with
DASYLab32 (National Instruments, Munchen, Germany).</p><fig id="f03" orientation="portrait" position="float"><label>Figure 3</label><caption><p>Wear apparatus: Digitally controlled electric motor with (1); Light barrier
limiting the covered distance to the insertion and separation path (2);
Artificial saliva supply (3); Load cell (4); Specimen (5)</p></caption><graphic xlink:href="jaos-20-03-0384-g03"></graphic></fig></sec><sec><title>Wear test procedure</title><p>In group E, the electroplated coping was glued into the frame structure during the
production process. As this procedure was performed by using the milling device, the
longitudinal axis of the female structure was oriented towards the direction of
insertion and separation. The female part was screwed onto the specimen holder. The
conical crown was placed manually into the coping. After that this crown was glued
onto the male part mounting using polymethyl methacrylate (Palavit<sup>®</sup> G,
Heraeus Kulzer). As the specimen needed no retention force adjustment the wear
simulation started and no adjustment cycles were needed<sup><xref ref-type="bibr" rid="r28">28</xref></sup>.</p><p>In group C, the specimens were fixed at the screw, which was aligned during the
production process. The primary crown was fixed to the male part mounting as
described for group E.</p><p>During the entire wear test, the specimens were moistened with the lubricant at a
rate of 5.00 ml/h by a perfusion pump (PERFUSOR of secura Co. B. Braun type 871602/1,
B. Braun, Melsungen, Germany). As lubricant was used a mixture of distilled water and
saliva substitute (Glandosane<sup>®</sup>, Cell Pharm GmbH, Bad Vilbel, Germany) in a
mixing ratio of 1:2.</p></sec><sec><title>Retention force measurement:</title><p>All specimens were inserted without further retention force adjustment. In accordance
with recent literature, each sample was subjected to 10,000 insertion-separation
cycles, which corresponded to approximately 10 years of removing and inserting the
denture three times a day<sup><xref ref-type="bibr" rid="r04">4</xref>,<xref ref-type="bibr" rid="r06">6</xref></sup>. The retention force measurement was
performed after every 20 cycles of axial loading. The female part was joined
completely onto the male part with a force of 20 N. The female part was fixed to the
linear axis by an electromagnet and then moved. The inserting and separating of the
specimen is done three times under permanent recording of retention force and
position. The velocity of this movement was set at 2 mm/s.</p></sec><sec><title>Data evaluation</title><p>For each insertion and separation cycle the maximum retention force value of the
first 0.3 mm separation distance was recorded. Additionally, the force distance
integral of the first 0.3 mm separation was calculated as the value of the separation
work.</p></sec><sec><title>Statistical analysis</title><p>The statistical analysis was performed using Prism 4.0 (Graph Pad Software Inc., La
Jolla, CA, USA). The Mann-Whitney test was used for comparison of the median
retention force values and the force-distance integrals.</p></sec></sec><sec sec-type="results"><title>RESULTS</title><sec><title>Retention force at cycle 0, 50, 2,000 and 10,000</title><p>The initial retention force of the group E specimens reached a median value of 6.54 N
and an interquartile range of 2.25 N (<xref ref-type="table" rid="t01">Table
1</xref>, <xref ref-type="fig" rid="f04">Figure 4</xref>). The specimens of group C
reached an initial median value of 3.00 N and an interquartile range of 3.14 N.
During the wear test the values of group E increased up to 12.79 N at cycle 10,000
with an interquartile distance of 4.45 N. Group C also showed the same behavior of
the measured values. At cycle 10,000 the median reached 4.78 N. The statistical
comparison of the median values by the Mann-Whitney test showed that the values in
group E were significantly higher than the values of group C at all 4 points in time
(<xref ref-type="fig" rid="f04">Figure 4</xref>).</p><table-wrap id="t01" orientation="portrait" position="float"><label>Table 1</label><caption><p>Retention force [N] at 0, 50, 2,000 and 10,000 cycles - descriptive statistics
and p values of the comparison of the median values by the
Mann-Whitney-test</p></caption><table frame="hsides" rules="groups"><thead><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1"><bold>Cycle</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>0</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>50</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>2000</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>10000</bold></td></tr><tr><td rowspan="1" colspan="1"><bold>Group</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td></tr></thead><tbody><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Minimum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">5.57</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.88</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">6.05</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">2.17</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">8.40</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">2.08</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">9.38</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">2.72</td></tr><tr><td rowspan="1" colspan="1">25% Percentile</td><td align="center" rowspan="1" colspan="1">5.86</td><td align="center" rowspan="1" colspan="1">2.12</td><td align="center" rowspan="1" colspan="1">6.20</td><td align="center" rowspan="1" colspan="1">3.50</td><td align="center" rowspan="1" colspan="1">9.03</td><td align="center" rowspan="1" colspan="1">3.69</td><td align="center" rowspan="1" colspan="1">10.84</td><td align="center" rowspan="1" colspan="1">3.26</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Median</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">6.54</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">3.00</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">7.18</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">4.54</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">10.89</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">4.92</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">12.79</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">4.78</td></tr><tr><td rowspan="1" colspan="1">75% Percentile</td><td align="center" rowspan="1" colspan="1">8.10</td><td align="center" rowspan="1" colspan="1">5.27</td><td align="center" rowspan="1" colspan="1">9.47</td><td align="center" rowspan="1" colspan="1">6.49</td><td align="center" rowspan="1" colspan="1">12.99</td><td align="center" rowspan="1" colspan="1">5.98</td><td align="center" rowspan="1" colspan="1">15.29</td><td align="center" rowspan="1" colspan="1">6.10</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Maximum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">9.28</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">8.19</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">10.94</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">8.52</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">13.87</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">6.65</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">17.29</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">6.82</td></tr><tr><td rowspan="1" colspan="1">Interquartile distance</td><td align="center" rowspan="1" colspan="1">2.25</td><td align="center" rowspan="1" colspan="1">3.14</td><td align="center" rowspan="1" colspan="1">3.27</td><td align="center" rowspan="1" colspan="1">2.99</td><td align="center" rowspan="1" colspan="1">3.95</td><td align="center" rowspan="1" colspan="1">2.29</td><td align="center" rowspan="1" colspan="1">4.45</td><td align="center" rowspan="1" colspan="1">2.83</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">p-value</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0196</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0503</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0028</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0028</td></tr></tbody></table><table-wrap-foot><fn><p>E=electroplated female part, C=cast female part</p></fn></table-wrap-foot></table-wrap><fig id="f04" orientation="portrait" position="float"><label>Figure 4</label><caption><p>Retention force values measured at the 4 particular points in time (cycle 0;
50; 2,000; 10,000) for group E (electroplated female part) and group C (cast
female part)</p></caption><graphic xlink:href="jaos-20-03-0384-g04"></graphic></fig></sec><sec><title>Force distance integral at cycle 0, 50, 2,000 and 10,000</title><p>Concerning the initial force-distance integral, group E reached a median value of
0.335 N/mm with an interquartile range of 0.427 N/mm (<xref ref-type="table" rid="t02">Table 2</xref>, <xref ref-type="fig" rid="f05">Figure 5</xref>). Group C
reached a higher median value with 1.070 N/mm and an interquartile range of 0.620
N/mm. This ratio existed up to cycle 10000 with a median of 0.608 N/mm for group E
and 0.950 N/mm for group C although the statistical test could only reveal
significant difference for cycle 0, 50 and 2,000 (<xref ref-type="table" rid="t02">Table 2</xref>).</p><table-wrap id="t02" orientation="portrait" position="float"><label>Table 2</label><caption><p>Force distance integral [N/mm] at cycle 0, 50, 2,000 and 10,000 - descriptive
statistics and p values of the comparison of the median values by the
Mann-Whitney-test</p></caption><table frame="hsides" rules="groups"><thead><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1"><bold>Cycle</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>0</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>50</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>2000</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>10000</bold></td></tr><tr><td rowspan="1" colspan="1"><bold>Group</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td></tr></thead><tbody><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Minimum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.213</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.110</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.206</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.170</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.308</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.320</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.451</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.450</td></tr><tr><td rowspan="1" colspan="1">25% Percentile</td><td align="center" rowspan="1" colspan="1">0.228</td><td align="center" rowspan="1" colspan="1">0.735</td><td align="center" rowspan="1" colspan="1">0.224</td><td align="center" rowspan="1" colspan="1">0.765</td><td align="center" rowspan="1" colspan="1">0.396</td><td align="center" rowspan="1" colspan="1">0.845</td><td align="center" rowspan="1" colspan="1">0.481</td><td align="center" rowspan="1" colspan="1">0.775</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Median</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.335</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.070</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.263</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.050</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.549</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.990</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.608</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.950</td></tr><tr><td rowspan="1" colspan="1">75% Percentile</td><td align="center" rowspan="1" colspan="1">0.655</td><td align="center" rowspan="1" colspan="1">1.355</td><td align="center" rowspan="1" colspan="1">0.429</td><td align="center" rowspan="1" colspan="1">1.340</td><td align="center" rowspan="1" colspan="1">0.675</td><td align="center" rowspan="1" colspan="1">1.315</td><td align="center" rowspan="1" colspan="1">0.883</td><td align="center" rowspan="1" colspan="1">1.275</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Maximum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.800</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.800</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.575</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.890</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.736</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.420</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.061</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.320</td></tr><tr><td rowspan="1" colspan="1">Interquartile distance</td><td align="center" rowspan="1" colspan="1">0.427</td><td align="center" rowspan="1" colspan="1">0.620</td><td align="center" rowspan="1" colspan="1">0.205</td><td align="center" rowspan="1" colspan="1">0.575</td><td align="center" rowspan="1" colspan="1">0.277</td><td align="center" rowspan="1" colspan="1">0.470</td><td align="center" rowspan="1" colspan="1">0.402</td><td align="center" rowspan="1" colspan="1">0.500</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">p-value</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0290</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0336</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.0196</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.1986</td></tr></tbody></table><table-wrap-foot><fn><p>E=electroplated female part, C=cast female part</p></fn></table-wrap-foot></table-wrap><fig id="f05" orientation="portrait" position="float"><label>Figure 5</label><caption><p>Force distance integrals calculated at the 4 particular points in time (cycle
0; 50; 2,000; 10,000) for group E (electroplated female part) and group C (cast
female part)</p></caption><graphic xlink:href="jaos-20-03-0384-g05"></graphic></fig></sec><sec><title>Changes in retention force and force distance integral</title><p>If the changes in retention force and the force distance integral are examined,
different periods have to be regarded. <xref ref-type="fig" rid="f06">Figure 6</xref>shows the box-plot diagrams of the measured changes in the retentive force values and
<xref ref-type="fig" rid="f07">Figure 7</xref> shows the changes of the
force-distance integrals. The respective descriptive statistics are shown in <xref ref-type="table" rid="t03">Tables 3</xref> and <xref ref-type="table" rid="t04">4</xref>.</p><fig id="f06" orientation="portrait" position="float"><label>Figure 6</label><caption><p>Comparison of the retention force changes of the two groups (E=electroplated
female part, C=cast female part). The three phases are shown: start phase
(cycle 0-50), initial phase (cycle 50-2,000), wear period (cycle
2,000-10,000)</p></caption><graphic xlink:href="jaos-20-03-0384-g06"></graphic></fig><fig id="f07" orientation="portrait" position="float"><label>Figure 7</label><caption><p>Comparison of the changes of the force-distance integral of the two groups
(E=electroplated female part, C=cast female part). The three phases are shown:
start phase (cycle 0-50), initial phase (cycle 50-2,000), wear period (cycle
2,000-10,000)</p></caption><graphic xlink:href="jaos-20-03-0384-g07"></graphic></fig><table-wrap id="t03" orientation="portrait" position="float"><label>Table 3</label><caption><p>Descriptive statistics of the retention force changes of the two groups from
cycle 0-50, cycle 50-2,000 and 2,000-10,000 in N. Negative values stand for a
decrease in retention force, positive values for an increase. The p-value for
the Mann-Whitney test of the two groups is given</p></caption><table frame="hsides" rules="groups"><thead><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1"><bold>Phase</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>0-50</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>50-2000</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>2000-10000</bold></td></tr><tr><td rowspan="1" colspan="1"><bold>Group</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td></tr></thead><tbody><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Minimum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-1.27</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-2.57</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-2.44</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-2.34</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-4.83</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.53</td></tr><tr><td rowspan="1" colspan="1">25% Percentile</td><td align="center" rowspan="1" colspan="1">-0.68</td><td align="center" rowspan="1" colspan="1">-0.41</td><td align="center" rowspan="1" colspan="1">-1.70</td><td align="center" rowspan="1" colspan="1">-0.74</td><td align="center" rowspan="1" colspan="1">-2.32</td><td align="center" rowspan="1" colspan="1">-0.38</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Median</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.20</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">2.13</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">2.05</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.22</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.80</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.16</td></tr><tr><td rowspan="1" colspan="1">75% Percentile</td><td align="center" rowspan="1" colspan="1">2.39</td><td align="center" rowspan="1" colspan="1">2.47</td><td align="center" rowspan="1" colspan="1">5.96</td><td align="center" rowspan="1" colspan="1">0.61</td><td align="center" rowspan="1" colspan="1">3.56</td><td align="center" rowspan="1" colspan="1">0.46</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">Maximum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">4.01</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">4.28</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">6.06</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.08</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">3.71</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.80</td></tr><tr><td rowspan="1" colspan="1">Interquartile range</td><td align="center" rowspan="1" colspan="1">3.07</td><td align="center" rowspan="1" colspan="1">2.88</td><td align="center" rowspan="1" colspan="1">7.66</td><td align="center" rowspan="1" colspan="1">1.35</td><td align="center" rowspan="1" colspan="1">5.88</td><td align="center" rowspan="1" colspan="1">0.84</td></tr><tr><td style="background-color:#CCCCCC" rowspan="1" colspan="1">p-value</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.7972</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.5185</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.3677</td></tr></tbody></table><table-wrap-foot><fn><p>E=electroplated female part, C=cast female part</p></fn></table-wrap-foot></table-wrap><table-wrap id="t04" orientation="portrait" position="float"><label>Table 4</label><caption><p>Descriptive statistics of the force-distance integral changes of the two groups
from cycle 0-50, cycle 50-2,000 and 2,000-10000 in N/mm. Negative values stand
for a decrease in retention force, positive values for an increase. The p-value
for the Mann-Whitney test of the two groups is given</p></caption><table frame="hsides" rules="groups"><thead><tr><td align="left" style="background-color:#CCCCCC" rowspan="1" colspan="1"><bold>Phase</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>0-50</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>50-2000</bold></td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1"><bold>2000-10000</bold></td></tr><tr><td align="left" rowspan="1" colspan="1"><bold>Group</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td><td align="center" rowspan="1" colspan="1"><bold>E</bold></td><td align="center" rowspan="1" colspan="1"><bold>C</bold></td></tr></thead><tbody><tr><td align="left" style="background-color:#CCCCCC" rowspan="1" colspan="1">Minimum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.225</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.340</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.102</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.630</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.026</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.370</td></tr><tr><td align="left" rowspan="1" colspan="1">25% Percentile</td><td align="center" rowspan="1" colspan="1">-0.178</td><td align="center" rowspan="1" colspan="1">-0.050</td><td align="center" rowspan="1" colspan="1">0.131</td><td align="center" rowspan="1" colspan="1">-0.055</td><td align="center" rowspan="1" colspan="1">0.039</td><td align="center" rowspan="1" colspan="1">-0.035</td></tr><tr><td align="left" style="background-color:#CCCCCC" rowspan="1" colspan="1">Median</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.092</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">-0.010</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.201</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.020</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.091</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.060</td></tr><tr><td align="left" rowspan="1" colspan="1">75% Percentile</td><td align="center" rowspan="1" colspan="1">0.016</td><td align="center" rowspan="1" colspan="1">0.165</td><td align="center" rowspan="1" colspan="1">0.295</td><td align="center" rowspan="1" colspan="1">0.560</td><td align="center" rowspan="1" colspan="1">0.234</td><td align="center" rowspan="1" colspan="1">0.340</td></tr><tr><td align="left" style="background-color:#CCCCCC" rowspan="1" colspan="1">Maximum</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.040</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.300</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.371</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">1.590</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.325</td><td align="center" style="background-color:#CCCCCC" rowspan="1" colspan="1">0.860</td></tr><tr><td align="left" rowspan="1" colspan="1">Interquartile range</td><td align="center" rowspan="1" colspan="1">0.194</td><td align="center" rowspan="1" colspan="1">0.215</td><td align="center" rowspan="1" colspan="1">0.164</td><td align="center" rowspan="1" colspan="1">0.615</td><td align="center" rowspan="1" colspan="1">0.195</td><td align="center" rowspan="1" colspan="1">0.375</td></tr><tr><td align="left" style="background-color:#CCCCCC" rowspan="1" colspan="1">p-value</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.2977</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.3636</td><td colspan="2" align="center" style="background-color:#CCCCCC" rowspan="1">0.6993</td></tr></tbody></table><table-wrap-foot><fn><p>E=electroplated female part, C=cast female part</p></fn></table-wrap-foot></table-wrap><p>Group E shows a slight increase in median retentive forces in the starting phase from
cycle 0-50 (0.20 N). In this period the retention force change is higher for group C
with a median value of 2.13 N, but the difference is not statistically significant.
During the further cycles of the initial phase (cycle 50-2,000) and the wear phase
(cycle 2,000-10,000) the values of group E show an increase in retention force
whereas the values of group C decrease slightly. The Mann-Whitney test reveals again
that this difference is not significant. During these two phases the interquartile
difference is higher for group E.</p><p>If the change in the retention force integrals is examined and regarded in relation
to the absolute values of force it is obvious that the values only change slightly.
This behavior was found in both groups. The values of both groups do not show
statistically significant difference when compared with each other.</p></sec></sec><sec sec-type="discussion"><title>DISCUSSION</title><p>Referring to the results of this study, it can be stated that the system of
electroplated copings on conical crowns and the technique of using cast female parts on
parallel walled primary crowns reach sufficient and reproducible retentive forces (<xref ref-type="fig" rid="f04">Figure 4</xref>). The electroplated (group E) and the cast
(group C) female parts both showed retentive forces comparable to the results of other
attachments for removable dentures<sup><xref ref-type="bibr" rid="r02">2</xref>,<xref ref-type="bibr" rid="r06">6</xref>,<xref ref-type="bibr" rid="r29">29</xref></sup>. Both systems showed a comparable behavior in the change of the
retentive properties over the 10,000 wear cycles. This concordance was found with the
retention force changes as well as with the change of the force distance integrals
(<xref ref-type="fig" rid="f06">Figure 6</xref>, <xref ref-type="fig" rid="f07">Figure 7</xref>). The difference between both systems is the level of the values
found in this study (<xref ref-type="fig" rid="f04">Figure 4</xref>, <xref ref-type="fig" rid="f05">Figure 5</xref>). The initial median retention force is
twice as high for the electroplated specimens (group E: 6.45 N, group C: 3.00 N). This
difference was statistically significant. As the specimens of group B were adjusted at
the Level of 1 to 3 N retention force, this cannot be assessed as disadvantage of the
cast system. On the contrary, achievement of this level shows the good potential of
retention force adjustment for the cast system. Whether the system could also be
adjusted and tested at a retention force twice as high should be examined in further
studies. Concerning the obviously higher range of the force distance integral found for
the system using cast female parts, there are two main aspects that could influence the
values. The cast system needs adjustment of the retention force of each specimen. This
manually performed adjustment results in a higher variability of the surfaces<sup><xref ref-type="bibr" rid="r28">28</xref></sup>. In combination with the telescopic
retentive operating mode, the contact between the surfaces persists during the
separation of the two parts of the system. This could explain why group C shows a wider
range of the values of the integral. The retentive properties of the electroplated
system are determined by the precise fit of the female part onto the primary crown and
the hydrodynamic effect of the saliva flowing into the space widened by the separation
of the two parts of the system<sup><xref ref-type="bibr" rid="r09">9</xref>,<xref ref-type="bibr" rid="r28">28</xref></sup>. As no manually retention force
adjustment is performed the surface is not as variable as assumed for the cast
specimens<sup><xref ref-type="bibr" rid="r28">28</xref></sup>.</p><p>In general, every <italic>in vitro</italic> wear test setup has to face the limitations
due to the enormous amount of different aspects affecting the <italic>in vivo</italic>wear processes<sup><xref ref-type="bibr" rid="r14">14</xref>,<xref ref-type="bibr" rid="r15">15</xref>,<xref ref-type="bibr" rid="r18">18</xref>,<xref ref-type="bibr" rid="r19">19</xref>,<xref ref-type="bibr" rid="r21">21</xref>,<xref ref-type="bibr" rid="r25">25</xref>,<xref ref-type="bibr" rid="r28">28</xref></sup>. The simulation is used to examine two different
material combinations under defined conditions regarding one considerable aspect, in
this study the wear stability. As a problem concerning the comparability of the results
with other studies there is no adequate ISO standard test set-up for the analysis of the
attachment wear processes.</p><p>The saliva substitute, the speed of insertion and the separation have to be discussed. A
mixture of Glandosane and distilled water was chosen as saliva substitute. This mixture
was used in different studies because of its lubricating properties. Other studies used
pure Glandosane or silicon oils and thus reach higher retentive forces as the viscosity
is higher. Whether the wear is affected by this fact or not has not yet been examined.
As both groups are examined under the same conditions the results should be comparable.
Concerning the speed of denture removal it has to be stated that there are only few data
from clinical trials<sup><xref ref-type="bibr" rid="r24">24</xref></sup>. The more
important question is the speed of the jaws during the chewing process, as the denture
should stay in place during this movement<sup><xref ref-type="bibr" rid="r23">23</xref></sup>. There is a connection between the speed of the denture's removal
and the retentive force due to the hydraulic system of the electroplated conical
crown<sup><xref ref-type="bibr" rid="r24">24</xref></sup>. As Rössler found, the
opening speed of the mouth during food chewing is about 760-2650 mm/min<sup><xref ref-type="bibr" rid="r23">23</xref></sup>. He also demonstrated that the retentive
force is not further increased by a removal speed exceeding 30 mm/min. There is no need
to accelerate the test speed any further<sup><xref ref-type="bibr" rid="r19">19</xref></sup>. The speed of 120 mm/min was a compromise for the test performed in
the present study, as it also allows performing the test in an acceptable span of
time.</p><p>For the simulation were performed 10,000 cycles of insertion and removal. Other studies
using many more cycles showed that the relevant retention force change is shown in this
period. Usually an almost constant force level is reached after 5,000 cycles<sup><xref ref-type="bibr" rid="r03">3</xref>,<xref ref-type="bibr" rid="r06">6</xref>,<xref ref-type="bibr" rid="r26">26</xref>,<xref ref-type="bibr" rid="r27">27</xref></sup>. So the study was constrained to the relevant space of time
simulating a wear period of about 5 years (5,000 cycles) plus a safety margin up to the
10,000<sup>th</sup> cycle.</p><p>For the analysis of the measured retentive forces and force-distance integrals separate
spans of time had to be defined, as the retentive force of a retentive element does not
develop in a linear modus<sup><xref ref-type="bibr" rid="r01">1</xref>,<xref ref-type="bibr" rid="r03">3</xref>,<xref ref-type="bibr" rid="r25">25</xref></sup>. As the first few cycles often dramatically change the retentive
properties of a retentive element, is shown the period of cycle 0-50. This is the period
in which the restoration is inserted and removed in the dental laboratory during the
fabrication of the denture and during the intraoral integration of the denture<sup><xref ref-type="bibr" rid="r06">6</xref>,<xref ref-type="bibr" rid="r25">25</xref></sup>. After this the denture is inserted at the patient and an initial wear
period starts which normally occurs in the first 2,000 cycles<sup><xref ref-type="bibr" rid="r03">3</xref>,<xref ref-type="bibr" rid="r26">26</xref></sup>. After this
period the most retentive elements do not change any further the retention force in wear
tests<sup><xref ref-type="bibr" rid="r03">3</xref>,33</sup>.</p><p>The results of this study indicate that the tested two double crown techniques tested
reach suitable retentive forces for denture retention. This retention should be
sufficient, as the forces of group C reach and those of group E exceed the values
measured for standard clinically used cast gold telescopic crowns<sup><xref ref-type="bibr" rid="r11">11</xref>,<xref ref-type="bibr" rid="r27">27</xref></sup>. As the force is not higher than for other attachments there should
be no risk of negative influences due to the level of retention force<sup><xref ref-type="bibr" rid="r01">1</xref>,<xref ref-type="bibr" rid="r03">3</xref>,<xref ref-type="bibr" rid="r06">6</xref></sup>. Compared with other retentive elements,
the two systems tested in this study allow a good reproducibility of retentive forces as
they show a small interquartile range of the measured values. Other attachments show a
much wider range of retention force resulting in a less predictable result<sup><xref ref-type="bibr" rid="r11">11</xref>,<xref ref-type="bibr" rid="r22">22</xref>,<xref ref-type="bibr" rid="r25">25</xref></sup>. The retention force
development does not differ significantly between the two groups. Whether the smaller
range of the integral for the electroplated female parts is clinically relevant or not
can only be clarified by a clinical study.</p></sec><sec sec-type="conclusions"><title>CONCLUSIONS</title><p>Within the limitations of this study it can be stated that the two double crown systems
tested reach sufficient retention forces. The electroplated system showed a higher level
of retention force. The lower values of the cast specimens are caused by the retention
force adjustment aiming at a force of 1-3 N. Concerning the development of the retentive
properties, the comparison revealed no statistically significant differences between the
two groups. Both systems seem to be suitable in clinical practice.</p></sec></body><back><ack><sec><title>ACKNOWLEDGEMENTS</title><p>The study was supported by DeguDent<sup>®</sup> (Hanau, Germany).</p></sec></ack><ref-list><title>REFERENCES</title><ref id="r01"><label>1</label><element-citation publication-type="journal"><person-group person-group-type="author"><name><surname>Bayer</surname><given-names>S</given-names></name><name><surname>Gruner</surname><given-names>M</given-names></name><name><surname>Keilig</surname><given-names>L</given-names></name><name><surname>Hültenschmidt</surname><given-names>R</given-names></name><name><surname>Nicolay</surname><given-names>C</given-names></name><name><surname>Bourauel</surname><given-names>C</given-names></name><etal>et al</etal></person-group><article-title> Investigation of the wear of prefabricated attachments - an
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