Physical-mechanical characterization of direct restorative dental materials by Pedro AA Vale ...

220 Pages·2012·42.05 MB·English

Physical-mechanical characterization of direct restorative dental materials
by Pedro A.A. Vale Antunes
Disserta¸c˜ao para a obtenc¸˜ao do grau de Doutor em Engenharia Mecˆanica na especialidade de
Constru¸c˜oes Mecˆanicas apresentada `a Faculdade de Ciˆencias e Tecnologia da Universidade de
Coimbra, sob a orientao do Professor Doutor Am´ılcar Lopes Ramalho
Universidade de Coimbra, 2011
ISBN: 978-972-8954-24-6
União Europeia

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To Matilde and Gonc¸alo,
who always stood by me and dealt with all my absences with a smile.

“By failing to prepare, you are preparing to fail.”
Benjamin Franklin

Acknowledgements
First and foremost, I would like to express my sincere gratitude to my advisor Prof. Am´ılcar
Ramalho for the continuous support of my Ph.D study and research, for his patience, motiva-
tion, enthusiasm, and massive knowledge. His guidance helped me throughout the research and
writing of this thesis. He has taught me, both consciously and unconsciously, how well exper-
imental research is done. I appreciate all his contributions of time and ideas to my Ph.D. His
support and guidance also occurred at a personal level which allowed me to grow as a person. I
could not have imagined having a better advisor and mentor for my Ph.D study.
Besides my advisor, I would also like to give thanks to: Prof. Martins Ferreira, Prof. Jos´e
Domingos and Prof. Fernando Antunes, as well as to my fellow laboratory colleagues. Thank
youalsotoJo˜aoCerejoforhisencouragement,insightfulcommentsandfellowshipinconferences
abroad.
I gratefully acknowledge the funding sources that made my Ph.D. work possible. I was
funded by the Fundac¸˜ao para a Ciˆencia e a Tecnologia (FCT — Portugal) under the frame-
work of the POCI — 2010 program — ERDF (European Regional Development Fund — POCI
project/CTM/59858/2004). In regards to this program, I thank Prof. Maria Helena Gil and
Prof. Jorge Rocha, members of the Department of Chemistry, University of Coimbra, for their
students supervision and excellent contribution for the matrix evolution. I would like to ac-
knowledge the valuable help of Prof. Eunice Carrilho, from the Faculty of Medicine of the
University of Coimbra, on the selection of commercial restorative dental materials, discussion as
well as for supplying the teeth used in the study. I appreciatively acknowledge the help in the
thesis editing with precious and helpful advices from my friends Joaquim Pinho da Cruz and
Filipe Teixeira-Dias. Thank you to Dr. Rui Marcelino my long time friend for his readiness and
support always demonstrated throughout the work.
My work was also supported by PRODEP III in the scope of the concourse 05.03/C/00195.
012/03 action 5.3 advanced training of teachers in higher education, through Escola Superior de
Tecnologia, of Castelo Branco’s Polytechnic. I would like to acknowledge my dear friend Prof.
Armando Ramalho. This Ph.D work could not be possible without the material supplier’s help,
by providing all tested materials, namely all essential commercial resin composite material,
thank you to: Dentsply DeTrey Iberica; 3M ESPE; Dentina (Bisco Inc.); Kerr sds; Colt`ene
Whaledent Portugal and Pentron Clinical.
Last but not the least; I would like to thank all my family, especially my parents Augusto
and Maria Teresa Antunes, for supporting me throughout my life and for the immense love that
they have always showed in every situation, thank you. I would like to thank my wife Matilde
and my son Gon¸calo for their support and limitless patience throughout this long process. Also,
thanks to my cousins Daniel and Karin for their great support and availability at all times.
Special thanks to Daniel for proofreading the manuscript using his precious time and helping in
the correction my defective English.
Finally, I would like to thank everyone who was important to the successful realization of
the thesis, as well as express my apologies that I could not mention personally one by one.
Pedro Vale Antunes
Coimbra University, 2011
Keywords
Dental composites, filler effect, pH and aging effect, mechanical properties, tribological charac-
terization.
Abstract
Direct restorative dental materials possess very special characteristics. These materials operate
in a singular environment that is the mouth. The factors at play are numerous and their
variation range is important. Humidity, load cycles, pH, temperature, bacteria, external agents,
environment, material properties and contact geometry, etc., are some examples. Teeth and
restorative materials are, therefore subjected to complex and numerous factors.
During the past decade clinicians and patients have developed an interest in to posterior
compositeresins. Thedemandforrestorationswithanaturalappearanceintheposteriorregion
and the controversy as to the mercury action of amalgam, although it’s excellent mechanical
properties, has attracted researchers to focus on the improvement of the resin composites to be
applied in posterior teeth.
Resin composites have been by far the most successful in dental applications by meeting
several stringent design requirements difficult to achieve with homogeneous materials such as
ceramics and metal alloys. When the intention is to repair cavities, the product needs to be
aesthetically matched in color and translucence with other teeth and retain its gloss. It must
match the hardness of the opposing tooth and be resistant to wear or fatigue fracture. It
must be dimensionally stable and withstand the largely varying thermal stresses in the mouth.
“Packable” composites have been termed as alternative to amalgam, for usage in posterior
restoration.
Criteria to select a composite in detriment of another are very complex and the few existent
standards do not allow for establishing a consensus as to which tests must be used to determine
and compare composites properties.
Mechanical and tribological properties of direct restorative filling materials are crucial not
onlytoserveandallowsimilaritywithhumanenamelanddentinebutalsotocomparecomposites
between them and determine objective criteria for their selection.
This work is focused on the mechanical and tribological characterization of posterior direct
commercial restorative materials. Due to their characteristics, commercial composites are ma-
terials which can not be altered (filler volume fraction, average particle dimension and matrix
composition are pre-fixed parameters), thus limiting the objectives of the initial study. With
the introduction of the production of a composite material which allowed variation of its con-
stituents, the initial work was complemented.
The mechanical properties assessment was done with the following tests: Vickers hardness,
Impulseexcitationofvibrationandfourpointbendingtests. Themechanicalpropertiesassessed
were: hardness, elastic modulus (static and dynamic), flexural resistance and work-of-fracture.
To determine the tribological behavior of composites reciprocating sliding tests was used.
Wearandthemechanismsinvolvedwereevaluatedonthecompositesaswellasontheantagonist
(humanteethandglassspheres). Aclassicalandanenergeticapproachwereusedtounderstand
the behavior of the composites and their antagonists. The use of glass sphere as antagonist
material was subjected to validation, by comparison to the material pair composite natural
tooth. Although difference in wear volumes of the distinct pairs does exist, extrapolation of
results is possible with similar and acceptable results.
Eight direct restorative commercial composites were tested against glass spheres, to deter-
mine wear resistance under different wear mechanisms: abrasion and attrition. The evaluation
of environment influence in these tests allows us to understand composites behavior under re-
ciprocating contact through the measuring of wear volumes and coefficients of friction of the
contact pair and analyzing the removal mechanisms involved in the wear process. In this analy-
sis, some composite-glass pair some materials showed some discrepancy regarding wear and the
coefficient of friction, thus a complementary study involving, only, three commercial composite
was done. A load-scanning test was used to understand and explain the wear regime transition
of these. This test permitted the perception of the wear/fracture mechanisms induced by the
different values of coefficient of friction.
The influence of external factors on the mechanical behavior of composites was also eval-
uated. Two types of environment in the reciprocating wear tests were introduced: artificial
saliva/distillate water and abrasive slurry. The other external parameters introduced in the
study were aging time and pH. Two batches of seven commercial composites were aged in 3, 7
and 9 pH buffer solutions during three periods 3, 6 and 22 months. The tribological and me-
chanical evaluation of these composites was done after each aging period. Generally and from
the point of view of application, it was possible to draw conclusions relatively to commercial
composite mechanical and tribological behavior. The effect of external factors on the behavior
of these commercial materials was also evaluated and the properties variation quantified.
Due to the nature of the study, parameterized evaluation, of produced composites brought
further progress, with clear conclusions as to volume content, filler dimension, matrix on the
mechanical and tribological properties studied.
Thetribologicalbehaviorwasevaluatedandremovalmechanismsenclosedinthewearprocess
arediscussed,takingintoaccountthesystematicSEMobservationstoevaluatethefailuremodes.