Digital and conventional impression die accuracy

128 Pages·2009·5.61 MB·English

DIGITAL AND CONVENTIONAL IMPRESSION
DIE ACCURACY

by

PRANITA KADAM

JOHN O. BURGESS, COMMITTEE CHAIR
DANIEL A. GIVAN
MARK S. LITAKER

A THESIS

Submitted to the graduate faculty of The University of Alabama at Birmingham,
in partial fulfillment of the requirements for the degree of
Master of Science

BIRMINGHAM, ALABAMA

2009
Copyright by
Pranita P. Kadam
2009
DIGITAL AND CONVENTIONAL IMPRESSION
DIE ACCURACY

PRANITA P. KADAM

MASTER OF SCIENCE

ABSTRACT

Computer technology is being incorporated in-office offering increased accuracy
and additional comfort to the patient for dental crown and bridge procedures. Three-
dimensional (3D) digital scanners are an integral part of many industries as computer-
aided design (CAD) and computer-aided manufacturing (CAM) units. This technology
enables intra-oral digital scanners capture 3D virtual images of tooth preparations from
which restorations can be fabricated directly (i.e. CAD/CAM systems) or indirectly (i.e.
creation of accurate master models). These machines may totally eliminate the need for
impression materials and trays, shipping of the disinfected impression to the laboratory
and other tedious conventional means of manufacturing a crown and bridge prosthesis.
A key determinant of the quality of any fixed prosthesis is intimate internal and
marginal adaptation of the crowns. To achieve that, the impression technique should
produce accurate and precise replicas of the teeth. In this thesis, a computer-aided
analysis method was applied to one of the stages involved in the production of fixed
dental prostheses. The general aim was to measure the accuracy of digital and
conventional impressions to reproduce dental dies from a single master die. Multiple
digital and conventional impressions were made from the master cast, dies from the
digital impressions were milled from pre-polymerized blocks of polyurethane and dental
stone dies were poured from the conventional impressions. The dies were then scanned
using a non-contact 3D digitizer, point-clouds resulting from the digitization of dies
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produced virtual 3D models and the use of computer-aided analysis gave accurate values
for their individual area. The 3D models were then superimposed to show color-
difference-maps showing the average difference between the scans. This data was
statistically analyzed for accuracy of the two impression techniques compared to the
master die by t-test. There was no statistical difference between dies fabricated from
either technique to the master die.
This thesis provided a validation of intra-oral scanners by answering a critical
question in fabrication of a successful restoration - ability of the digital impressioning
machine to create an exact replica of the dental tissues precisely.

Keywords: Accuracy, Computer-Aided Analysis, Computer-Aided Design, Computer-
Aided Manufacturing; Intra-Oral Digital Scanner, Non-Contact 3D Digitizer.
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DEDICATION
This thesis is dedicated to my parents and sisters who offered me unconditional
love and support. Without them lifting me up when this thesis seemed unattainable, I
doubt it should ever have been completed.
Also, this thesis is dedicated to Amrish, who has been a great source of
motivation and inspiration.
Finally, this thesis is dedicated to all those who believe in the power of education.

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ACKNOWLEDGEMENT
I am indebted to the many individuals who contributed to my learning and in
achieving this Master of Science degree. I would like to thank my supervisor, Dr. John
Burgess, who has shown extraordinary amounts of patience along with confidence in my
work. Dr. Givan who gave me assistance and advice and kept me motivated to complete
this degree in time. I would also like to thank my thesis committee, Dr. Litaker and Dr.
Javed whose guidance throughout proved helpful.
Another person without whom this project would never be completed is Phillip
Corey Shum, who spent many tireless hours helping with the peculiarities of the rapid
prototyping machine. I also acknowledge the contribution made by my teachers at UAB,
particularly the astonishingly vast knowledge and experience of Mr. Preston Beck that he
never hesitated in sharing, and Dr. Cakir and Dr. Anabtawi, who have been, and will
remain, much more than just teachers.
I would also like to thank all my colleagues and fellow residents, including
Ramtin, Taneet and Ian for making it possible to keep going when it seemed toughest. I
reserve a special mention for Laura and Robbie, who have never failed to help in any way
whenever I needed it. Finally, I would like to thank my family and friends in India,
especially my parents, without whom none of this would have been possible. To attempt
to thank them with a few words would be a travesty.
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TABLE OF CONTENTS
Page

ABSTRACT ....................................................................................................................... iii

DEDICATION .....................................................................................................................v

ACKNOWLEDGMENTS ................................................................................................. vi

LIST OF TABLES ........................................................................................................... viii

LIST OF FIGURES ........................................................................................................... ix

LIST OF ABBREVIATIONS ..............................................................................................x

INTRODUCTION ...............................................................................................................1

Conventional Impression Technique ............................................................................1
Polyvinyl Siloxane Impression Material ..............................................................3
Mixing Impression Material ................................................................................6
Impression Tray and Tray Adhesive ...................................................................7
Impression Technique .........................................................................................9
Limitations of Conventional Impression Technique .........................................12

Intra-oral Digital Impression Technique .....................................................................13
iTero Digital Impression System ......................................................................16

Accuracy of Die Fabrication ......................................................................................19
Fabrication of Dental Stone Die from Conventional Impression .....................19
Dimensional Change in Die Material ...............................................................20
Fabrication of Polyurethane Dies from Intra-oral Digital Impression ..............22
Computer-Aided Analysis of Die .....................................................................23

HYPOTHESIS AND AIMS ..............................................................................................26

MATERIALS AND METHODS .......................................................................................28
Conventional Impression Technique ................................................................29
Digital Impression Technique ...........................................................................32
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Computer-Aided Analysis ................................................................................35

RESULT ……... ................................................................................................................50

DISCUSSION .................................................................................................................51

REFERENCES .................................................................................................................65

APPENDIX A -Images of iTero Digital Impression………………………………….....85

APPENDIX B –Study I – Measurement of Surface Area of the Dies…………………...90

APPENDIX C –Study II – Measurement of Average Linear Discrepancy by Color-
Difference Maps ……………………………………………………….…………..…...105

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LIST OF TABLES

Tables Page

1 Table 1. Materials required for making conventional impressions
and dental stone models .........................................................................................29

2 Table 2. Mean surface area of the samples (mm2) ................................................44

3 Table 3. Average linear distance between the merged master mesh (MMM)
and the digital and conventional impressions measured in microns...…………..49

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LIST OF FIGURES

Figure Page

1. Figure 1. Flowchart of manufacturing process – intra-oral digitization vs.
conventional impression technique, lost wax technique vs. CAD/CAM ...........…14

2. Figure 2. Intra-oral digitizer: E4D DentistTM (D4D Technologies),
LAVA C.O.S. (3M ESPE), iTero (Cadent) and CEREC (Sirona) .....................…16

3. Figure 3. Columbia Dentoform Ivorene Model Tooth #30 in Simulated
Clinical Occlusion used for Standardized Impression Technique ....................…28

4. Figure 4. COE Nickel- plated metal perforated impression tray and
Caulk Tray Adhesive .........................................................................................…29

5. Figure 5. Aquasil Ultra Heavy (DECA), Pentamix 2 Automatic mixing
unit, Aquasil Ultra LV (Cartridge) and Heraues Kulzer dispensing gun .........…30

6. Figure 6. Dual-phase single step impression technique .....................................…31

7. Figure 7. Patient’s laboratory chart on the iTero Intra-oral Digitizer screen .....…33

8. Figure 8. Occlusal image of the prepared tooth is taken first. ..........................…33

9. Figure 9. Completed quadrant scan of the typodont model, with tooth .........…34

10. Figure 10. CAD/CAM assisted milling of dental casts from
pre-polymerized blocks of polyurethane. .........................................................…34

11. Figure 11. Master die, Digital die and Conventional die. ..................................…35

12. Figure 12. Konica Minolta VIVID 9i, non-contact laser scanner angled
at 54° to the rotary table. Powder coated specimen placed on the rotary
table. Plate used for calibration. Computer screen running the
RapidForm XOR2 software ...............................................................................…36

13. Figure 13. Calibration of the Konica Minolta VIVID 9i to the rotary table ....…36
x