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Aus der Universitätsklinik für Zahn-, Mund-, und Kieferheilkunde der
Albert-Ludwigs-Universität Freiburg
Abteilung für Zahnärztliche Prothetik
(Ärztl. Direktor: Prof. Dr. J. R. Strub)


Survival rate and fracture strength of maxillary incisors,
restored with different kinds of full veneers.
An in-vitro study


INAUGURAL-DISSERTATION
zur Erlangung des
Zahnmedizinischen Doktorgrades
Der Medizinischen Fakultät der Albert-Ludwigs-Universität
Freiburg


Vorgelegt 2003
Von
Nektaria Stathopoulou
Geboren in Athen, Griechenland















Dekan: Prof. Dr. med. J. Zentner
1. Gutachter: Prof. Dr. J. R. Strub
2. Gutachter: PD. Dr. P. Hahn
Jahr der Promotion: 2003


























To my parents and my brother
Table of contents:

1. Introduction...................................................................................................... 1
2. Literature review ............................................................................................. 2
2.1 Historic perspective .................................................................................... 2
2.2 Indications and contraindications of porcelain veneers........................ 3
2.3 Classification of currently available all-ceramic systems for porcelain
veneers................................................................................................................ 5
2.3.1. Sintered ceramics.................................................................................................... 5
2.3.2. Infiltrated ceramics................................................................................................. 7
2.3.3. Castable ceramics 8
2.3.4. Pressable ceramics ................................................................................................ 10
2.3.5. Machining techniques .......................................................................................... 11
2.3.5.1. Copy-milling technique.............................................................. 11
2.3.5.2. CAD/CAM Systems ................................................................... 12
2.4. Preparation design................................................................................... 14
2.5. Luting procedure ..................................................................................... 18
2.5.1. Conditioning of the ceramic surface .................................................................. 18
2.5.2. Conditioning of the tooth surface....................................................................... 19
2.5.3. Luting composite .................................................................................................. 21
2.5.4. The adhesion complex: tooth/luting composite/porcelain ........................... 22
2.6. Survival rate and fracture strength of porcelain veneers................... 22
2.6.1. Biting forces and range of temperature on anterior dentition ....................... 22
2.6.2. Survival rate of porcelain veneers...................................................................... 23
2.6.3. Fracture strength of porcelain veneers .............................................................. 24
3. Aim of the study ............................................................................................ 27
4. Materials and Methods ................................................................................ 28
4.1. Materials.................................................................................................... 28
4.1.1. Abutment teeth ..................................................................................................... 28
4.1.2. Ceramic system 28
4.1.3. Luting agent........................................................................................................... 29
4.1.4. Impression materials ............................................................................................ 31
4.1.5. Die materials.......................................................................................................... 31
4.1.6. Additional materials used ................................................................................... 32
4.2. Methods..................................................................................................... 32
4.2.1. Teeth ....................................................................................................................... 32
4.2.1.1. Selection of the abutment teeth ................................................. 32
4.2.1.2. Diagnostic Wax-up...................................................................... 33
4.2.1.3. Tooth preparation........................................................................ 33
4.2.2. Fabrication of the master models ....................................................................... 36
4.2.2.1. Impression .................................................................................... 36
4.2.2.2. Fabrication of the master dies.................................................... 36
4.2.3. Fabrication of the veneers 36
4.2.3.1. Wax-up.......................................................................................... 36
4.2.3.2. Investment 37
4.2.3.3. Preheat and Pressing................................................................... 37
4.2.3.4. Divestment ................................................................................... 38
4.2.3.5. Glazing 38
4.2.4. Cementation of the veneers................................................................................. 39
4.2.4.1. Pre-treatment of the veneers (Fig. 4.5) ..................................... 39
4.2.4.2. Pre-treatment of the abutments (Fig. 4.6) ................................ 39
4.2.4.3. Bonding procedure (Fig. 4.7) ..................................................... 40
4.2.5. Preparing the test specimens for the artificial-mouth ..................................... 41
4.2.5.1. Artificial periodontal membrane .............................................. 41
4.2.5.2. Fabrication of the master models for the artificial mouth..... 41
4.2.6. Dynamic loading in the artificial mouth ........................................................... 42
4.7. Examination of post-bonding cracks..................................................... 46
4.8. Fracture strength test (Fig. 4.12)............................................................. 46
4.9. Statistic analysis of data .......................................................................... 47
5. Results ............................................................................................................. 47
5.1. Dynamic loading in the artificial oral environment............................ 47
5.1.1. Survival rate .......................................................................................................... 47
5.1.2. Crack development .............................................................................................. 50
5.1.2.1. Crack formation rate (Fig. 5.3)................................................... 50
5.1.2.2. Crack pattern of porcelain veneers (Table 5.1)........................ 52
5.2. Fracture strength test............................................................................... 54
5.2.1. Fracture strength of individual samples ........................................................... 54
5.2.2. Statistical evaluation of data 57
5.2.3.1. Component of the restoration that failed................................. 60
5.2.3.2. Position of the restoration where fracture occurred .............. 62
6. Discussion....................................................................................................... 64
6.1. Discussion of the materials..................................................................... 64
6.1.1. Extracted human teeth as abutments................................................................. 64
6.1.2. The storage solution ............................................................................................. 65
6.1.3. EPC as a material for the fabrication of full veneers ....................................... 65
6.2. Discussion of the methods...................................................................... 66
6.2.1. Preparation of the specimens for the artificial mouth..................................... 66
6.2.1.1. Preparation................................................................................... 66
6.2.1.2. Cementation ................................................................................. 68
6.2.1.3. Artificial membrane .................................................................... 69
6.2.2. Dynamic loading in the artificial mouth ........................................................... 70
6.2.2.1. Angulation in the artificial mouth ............................................ 70
6.2.2.2. Contact point of the applied force in the artificial mouth ..... 71
6.2.2.3. Artificial ageing and its clinical relevance on the survival rate
of ceramic veneers.................................................................................... 71
6.2.3. Load-to-fracture testing ....................................................................................... 73
6.2.3.1. Angulation in the Zwick testing machine................................ 73
6.2.3.2. Contact point of the load-to-fracture applied force................ 73
6.2.3.3. Clinical relevance of the fracture strength tests of ceramic
veneers ....................................................................................................... 74
6.3. Discussion of the results ......................................................................... 75
6.3.1. Dynamic loading in the artificial mouth ........................................................... 75
6.3.1.1. Survival rate ................................................................................. 75
6.3.1.2. Crack formation........................................................................... 76
6.3.2. Load-to-fracture testing ....................................................................................... 78
6.3.2.1. Fracture strength of the specimens in the Zwick universal
machine...................................................................................................... 78
6.3.2.2. Fracture pattern of the specimens in the Zwick universal
machine 79
7. Conclusions .................................................................................................... 81
8. Summary ......................................................................................................... 82
9. Zusammenfassung ........................................................................................ 83
10. References..................................................................................................... 84
11. Curriculum vitae.......................................................................................... 97
12. Acknowledgements .................................................................................... 98 Introduction 1
1. INTRODUCTION
The publics demand for the treatment of unaesthetic anterior teeth is
steadily growing. Accordingly, several treatment options have been
proposed to restore the aesthetic appearance of the dentition. For many
years, the most predictable and durable aesthetic correction of anterior
teeth has been achieved with full crowns. However, this approach is
undoubtedly the most invasive, requiring removal of large amounts of
sound tooth structure and resulting in possible adverse effects on the pulp
and adjacent periodontal tissues.
The introduction of multi-step total-etch adhesive systems, along with the
development of high-performance hybrid resin composites has led to a
more conservative restorative technique. Resin composite veneers can be
used to mask tooth discoloration and/or to correct unaesthetic tooth form
and/or position. However, such restorations still suffer from a limited
longevity, since resin composites remain suspect to discoloration, wear
and marginal fractures.
In search for more durable aesthetics, porcelain veneers have been
introduced. Several studies have proven their long time prognosis in-vivo
and high level of patient acceptance (Rucker et al. 1990; Calamia 1993;
Fradeani 1998; Friedman 1998; Kihn and Barnes 1998; Peumans et al. 1998b;
Dumfahrt and Schaffer 2000). The failure rate ranged in these studies ranged
between 0% (Rucker et al. 1990) and 33% (Shaini et al. 1997). Additionally,
in-vitro studies demonstrated long term retention of porcelain veneers
(Magne and Douglas 1999c; Castelnuovo et al. 2000; Hahn et al. 2000).
Despite the promising results, there are certainly limits to the possibilities
that veneers can offer. Key factors for prognosis are the material and the Literature review 2
kind of preparation used for such restorations. There are limited studies
concerning the design and thickness of the preparation. Regarding the
design of the preparation, four basic types have been described: the
window, the feather, the bevel and the overlapped incisal edge
preparation. As far as the thickness of preparation is concerned, the early
concepts suggested minimal or no tooth preparation. Nevertheless,
current beliefs support removal of varying amount of tooth structure.
Further studies are required to evaluate the influence of ceramic materials
and different types of preparation on the survival rate and fracture
strength of laminate porcelain veneers.
2. LITERATURE REVIEW
2.1 Historic perspective
Dr Charles Pincus (1938) was the first to describe the use of veneers to
enhance the appearance of actors for close-ups in the movie industry.
They were temporarily held in place with adhesive denture powder while
the actors were before a camera. The fragile restorations then had to be
removed, because no adhesive system existed at that time to provide a
permanent attachment of veneers to tooth structure.
Buonocore´s (1955) research on acid-etch techniques, combined with
Bowen´s (1978) later use of filled resin, enabled the mechanical bonding
between etched tooth and filled resins. The use of direct resin veneers was
now possible. The limitation of the self-curing technique was the limited
working time for the dentist to recreate a labial surface before the
composite resin chemically cured itself. The introduction of light-cured
composite resins allowed the dentist greater flexibility, due to a greater
working time and improved chemistry. Literature review 3
Faunce and Meyers (1976) described a one-piece acrylic resin prefabricated
veneer as an improved alternative to a direct acid-etched bonded veneer.
By using a chemical primer applied to the veneer and a composite resin to
lute the veneer onto an etched tooth, both chemical and mechanical
bonding contributed to the attachment.
The concept of acid-etching porcelain was cited in the dental literature,
when Rochette described the restoration of a fractured incisor with an
“etched silanted porcelain block” (1975). Essential to the attachment of
porcelain veneers is the ability of porcelain to be etched and bonded to
composite resin as reported by Horn (1983) and Simonsen and Calamia
(1983). Continued research by Calamia (1985) also showed that the
treatment of the etched porcelain veneer with a silane coupling agent
produced a chemical bond that enhanced the porcelain-composite resin
mechanical bond.
From the moment porcelain veneers could be adhesively luted, the clinical
and laboratory techniques have continued to be refined. Today we have at
our disposal long term in-vivo and in-vitro studies focusing on porcelain
veneers, performed during the last 10 to 15 years (Karlsson et al. 1992;
Nordbo et al. 1994; Jäger et al. 1995; Fradeani 1998; Friedman 1998; Peumans et
al. 1998b). Furthermore, new preparation designs and extensions of
porcelain veneers are tested (Magne and Douglas 1999c).


2.2 Indications and contraindications of porcelain
veneers
According to the last classification of Belser et al. (1997), the three principal
indications for porcelain veneers are: