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ASSESSMENT OF CLINICAL AND IN VITRO WEAR OF A NANO-HYBRID

COMPOSITE RESIN BY NON-CONTACT PROFILOMETRY

by

Courtney Michelson

Dr. John Burgess, CHAIR

Dr. Daniel Givan

Dr. Jack Lemons

Dr. Mark Litaker

Dr. Amjad Javed

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

2010

ii

Copyright by

Courtney Michelson

2010

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ASSESSMENT OF CLINICAL AND IN VITRO WEAR OF A NANO-HYBRID

COMPOSITE RESIN BY NON-CONTACT PROFILOMETRY

Courtney Michelson

MASTER OF SCIENCE IN CLINICAL DENTISTRY

ABSTRACT

The purpose of this study was to measure and compare the volumetric wear loss

(mm3) and linear depth (μm) values of in vitro specimens and in vivo restorations of a

highly filled BisGMA nano-hybrid composite resin system using a 3-D non-contact

surface profilometer. Twenty-one restorations were placed in a clinical trial. Impressions,

casts, and scans (PROSCAN 2000) were made at baseline and one year. Images were

superimposed (PROFORM Software) and values were obtained for volume and depth

loss. Sixteen wear specimens of the same material used in the clinical trial were prepared

in the laboratory under standardized conditions. The specimens were subjected to

200,000 or 400,000 (n=8) cycles in the Alabama Wear Testing Device. The specimens

were scanned (PROSCAN 2000) before and after wear and the images were

superimposed (PROFORM Software) to determine volumetric and depth wear loss

values.

Results showed that the wear patterns varied greatly between the two groups

which the investigators concluded were due to the large amount of confounding variables

present in a clinical study. It was inappropriate to analyze the differences between the

two groups and therefore, the data was analyzed within groups. Conclusions were made

on how to better standardize future clinical trials and ways the in vitro testing device can

more accurately portray conditions in the oral cavity.

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ACKNOWLEDGMENTS

Dr. John Burgess –Thank you for taking a chance on me. I am forever grateful for

the opportunities that you have given me and the things that you have exposed me to, to

say the least. You are an incredible teacher, mentor, and inspiration. Your constant

optimism and eagerness to better the dental research field has made this an exciting place

to work the past two years. You have shown me how to be a knowledgeable and

insightful researcher. I have a passion that I will continue. You have taught me so much

and I am honored to be one of your students.

Dr. Daniel Givan – You have taught me so much (don’t panic!) and guided me

through this thesis so much. I am so thankful for your constant support and guidance

when I needed it the most throughout this process. You were always available and

excited to discuss wear processes or create apparatuses with me. I will never forget you

taking the time to give me one-on-one lessons of dentistry 101 to make sure I would be

on the same page (or close enough to it) as everyone else so that I could actively

participate in discussions.

Dr. Jack Lemons – It is an honor to be one of your students. You have taught me

new ways to think about and approach a concept or situation. Your humbleness is

inspiring. You are always so proud of us and encouraging. Thank you for teaching me

how to be a better researcher and writer.

Dr. Mark Litaker – Thank you so much for teaching me about statistics and

helping me over the past two years. Thank you for your patience in these final weeks of

re-working and re-running data.

Dr. Amjad Javed – Thank you for your guidance on making sure that everything

with the graduate school and thesis has gone on without any problems. Your input and

kindness is much appreciated.

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Dr. Deniz Cakir – Thank you for your patience and understanding with all of my

questions. You have always been a wonderful teacher and friend. You were such a big

part of my experience here and I am grateful for all of your assistance through it all

Preston Beck – You have been such an integral part of my thesis. You have been

so encouraging and always offering to help in any way possible. Thank you for your

insightful knowledge on every machine we possess in the lab. If it was not for you, the

Proscan probably would have been dead a few months ago along with my thesis. Thank

you for keeping all of the above alive.

Ian and Gowri –Two of my best friends. I was so intimidated when I started this

program. Instead of making me feel like I was in over my head, you took my under your

wings and taught me so much; not only tremendous amounts of dental knowledge, but

also so much about your unique cultures. We are such an incredible team. Anytime I

ever doubted myself, you both were there encouraging me and keeping me on track with

you both. I am at this point because of you.

Nate, Ben, Ann, and Unger – Thank you for being such wonderful friends and

resources throughout this entire process. Thank you for always being there for me and

teaching me so much during this experience.

To My Incredible Family: Mom, Dad, Jennifer, and Mama Elaine – Thank you for

your patience and understanding through this entire process (especially towards the end).

You have been so supportive. Thank you for always loving me and having confidence in

me. You continue to make everything possible for me. Thank you for everything, and I

love you all so very much.

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DEDICATION

This thesis is dedicated to everyone who encouraged, supported, and believed in

me throughout this entire process and made this such an incredible and wonderful

experience for me.

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TABLE OF CONTENTS

Page

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

ACKNOWLEDGMENTS .............................................................................................. iv

DEDICATION ............................................................................................................... vi

LIST OF TABLES ......................................................................................................... ix

LIST OF FIGURES ......................................................................................................... x

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

Composite Background ............................................................................................. 1

Wear Background ..................................................................................................... 5

Methods of Measuring Wear ..................................................................................... 9

Contact vs. Non-Contact Profilometers ................................................................... 11

Accuracy and Precision ........................................................................................... 12

In Vitro Devices ...................................................................................................... 14

In Vitro vs. In Vivo .................................................................................................. 19

OBJECTIVES AND HYPOTHESES ............................................................................ 21

MATERIALS and METHODS ...................................................................................... 23

In Vivo Protocol ..................................................................................................... 23

Impressions ............................................................................................................ 28

Disinfection ........................................................................................................... 29

Casts ...................................................................................................................... 29

Bases ..................................................................................................................... 30

Measuring Wear .................................................................................................... 32

In Vivo Data Analysis ............................................................................................ 34

In Vitro Specimen Preparation ............................................................................... 34

Determination of In Vitro Wear.............................................................................. 36

In Vitro Data Analysis............................................................................................ 37

RESULTS ..................................................................................................................... 38

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TABLE OF CONTENTS (Continued)

Page

DISCUSSION ............................................................................................................... 40

SUGGESTIONS FOR FUTURE RESEARCH .............................................................. 44

LIST OF REFERENCES ............................................................................................... 46

APPENDICES

A IRB APPROVAL ........................................................................................ 51

B In Vivo Scans at Baseline, 1 year, and Superimposition of Restoration ........ 55

C In Vitro SUPERIMPOSITION .................................................................... 77

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LIST OF TABLES

Page

1 Study Characteristics .......................................................................................... 23

2 Inclusion Criteria ............................................................................................... 24

3 Exclusion Criteria .............................................................................................. 24

4 Materials used in vivo......................................................................................... 27

5 Materials used in vitro ........................................................................................ 34

6 Results ............................................................................................................... 38

7 In Vivo Results ................................................................................................... 38

8 In Vitro Results .................................................................................................. 39

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LIST OF FIGURES

Page

1 Movement of muscles and mandible during chewing .......................................... 5

2 Two-Body Wear .................................................................................................. 7

3 Three-Body Wear................................................................................................. 7

4 OHSU Wear Simulator ...................................................................................... 15

5 BIOMAT Wear Simulator .................................................................................. 15

6 Minnesota Wear Simulator ................................................................................. 16

7 ACTA Wear Simulator....................................................................................... 16

8 Zurich Wear Simulator ....................................................................................... 17

9 Original Drawings of Alabama Wear Simulator ................................................. 18

10 Alabama Wear Machine ..................................................................................... 18

11 Sandwich Technique .......................................................................................... 26

12 Polyvinyl Siloxane Impression ........................................................................... 29

13 Final Cast ........................................................................................................... 30

14 Dental surveyor with acrylic .............................................................................. 31

15 Apparatus to standardize bases ........................................................................... 31

16 Final standardized bases ..................................................................................... 32

17 Proscan 2000...................................................................................................... 32

18 Composite build-up ............................................................................................ 35

19 Prepared Wear Specimen ................................................................................... 36

20 Specimen after subjection to wear ...................................................................... 36

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INTRODUCTION

Composite Background

Concerns with the release of mercury toxicity from amalgam and the demand for

more esthetic tooth-colored restorations led to the introduction of polymer matrix

reinforced composite resins in the early 1960’s1. Composites were introduced as an

alternative to silicate cements and unfilled acrylic resin materials, since restorations

composed of these materials had limited clinical longevity2. A dental composite is a

highly cross linked polymeric material reinforced by a dispersion of amorphous silica,

glass, crystalline, or organic resin filler particles bonded to the matrix by a coupling agent

that can be transformed from a fluid or putty-like material into a tooth-like solid for direct

or indirect restorations3. Since the creation of bisphenol glycidyl dimethacrylate (bis-

GMA) by Bowen in 1962, composite resins have been used as the primary choice for

many esthetic dental restorations4. Currently more than 50% of all directly placed

posterior restorations are composites5.

Applications of early composites showed significant problems with secondary

caries and wear4. The first clinical trials performed in the early 1970’s that measured the

effectiveness of composite resin as posterior restorations reported that composites had

poor wear resistance and did not last more than 3-5 years3. Early generations of

composites were highly susceptible to three-body wear, occlusal contacts, and attrition

showing higher rates of wear across the entire restoration6.

Composites can be classified by their monomer (BisGMA, TegDMA, UDMA),

filler loading (size of filler particles-macro, micro, nano, or hybrid), curing type (light,

visible, or dual), or viscosity (condensable or flowable). Composites are most commonly

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classified based on their filler particle size in a system created by Lutz7. These

classifications are as follows: macro 1-100μm, micro 0.04-0.1 μm, and nano 0.01-0.04

μm7.

First generations of dental composites were traditional macro-filled. They were

prepared by crushing large inorganic quartz, glass with barium, strontium, borosilicate, or

ceramics into 8-100µm particles2. The early structural dental composites were 60-75%

filler by weight, were easily stained, and accumulated plaque easily8. Their coefficient of

thermal expansion was 2-10 times greater than tooth structure leading to micro-leakage,

post-operative sensitivity, and recurrent decay2. All macro-filled composites lost filler

particles while polishing, which made it difficult to attain and maintain smooth surfaces.

Early generations of composites were unable to withstand occlusal forces in the oral

cavity and had poor wear resistance.

In an attempt to improve the polishability and wear resistance of composites, in

1977 Vivadent introduced micro-filled composites with 0.01-0.1μm fused silica particles

made from silicon dioxide where the dental composite was 40-50% filler by weight4.

Micro-filled composite resin had organic silica particle fillers and organic

prepolymerized particles. They had pre-cured filler particles included in the matrix which

decreased the amount of shrinkage and improved polishing properties. These softer, less

resistant particles showed reduced wear rates by staying partially embedded in the surface

as opposed to the macro-fillers that were plucked from the surface2. The search for an

ideal composite resin continued.

The late 1980’s saw a transition to hybrid composites, which were a combination

of macro-fillers and 7-15% micro-filler particulates, producing 75-80% filled by weight4.

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Adding microfills hardened the matrix which decreased fracture crack formation. The

higher filler loading of hybrids decreased interparticle distance which improved wear.

They had good polishability and better wear resistance. Hybrids became the first

composites judged to be broadly successful for use in posterior regions.

Nano-filled composites are composed of particles that are less than 0.1μm average

diameter. They have been introduced more recently as a way to increase the amount of

filler loading and increase physio-mechanical properties. Nano-hybrids are a blend of

nano filler and smaller grinds and give a wider range of fillers. They allow for higher

filler loading and therefore have lower shrinkage rates of 1.8-2.3% volume, are easier to

polish, and retain gloss long but not as long as the microfilled resins.

Other categories of composites are based on their viscosity: flowable and

condensable. Flowable, low viscosity, composites are composed of inorganic fillers and

dimethacrylates4. They have high polymerization shrinkage rates and decreased wear

resistance due to their low filler content.

As composite resins have evolved and the filler particle size decreased, wear

resistance and polishability increased. Therefore, some say that the ideal composite

would be highly filled with small particles; however this is hard to obtain since a larger

surface area could cause an increase in viscosity and altered properties for clinical

placement. This is the problem with fillers and is why they have to have a range in

addition smaller particles. The nanoscale has low fracture toughness which is why

nanoclusters were developed.

Since dental composites were created, they have been evolving and have

continued to improve their physio-mechanical properties. Over the past decade, the main

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focus has turned to minimizing polymerization shrinkage as it is one of the main clinical

concerns because it can lead to microleakage, adhesion failure, enamel microcracks, gap

formation, and post-operative sensitivity. To reduce shrinkage and stresses, several

methods have been tested (increment placement techniques, bulk curing, light curing

methods). However none of these proved to be affective. Therefore, manufacturers have

manipulated the chemistries to create low-shrink/low-stress materials. Though they have

been very promising in the shrinkage aspect, they need improvement in physical and

mechanical properties (toughness, hardness, wear).

One of these low-shrinkage materials is Surefil SDR (DENTSPLY Caulk). Surefil

SDR is a stress decreasing resin that is a typical BisGMA composite resin, yet it has a

polymerization modulator that increases the polymerization time and reduces the stresses

produced while polymerizing. It is a translucent flowable composite that has a 4mm

depth of cure. It is designed to be placed as a base beneath a conventional composite

resin restoration, such as Esthet-X HD, a high definition micro matrix restorative

material. Esthet-X HD was designed for replacement of missing occlusal/facial enamel. It

is a visible cured, radiopaque composite restorative material for anterior and posterior

restorations of primary and permanent teeth. It has handling characteristics typical of a

conventional microhybrid composite, allowing easy placement and anatomic

sculptability, which provides a durable and esthetic surface. The resin matrix consists of a

Bis-GMA adduct, a Bis-EMA adduct, and triethylene glycol dimethacrylate,

Camphorquinone (CQ), photoinitiator, stabilizer pigments. The filler combination

consists of barium fluoroborosilicate glass with a mean particle size below 1μm and

nanofiller silica (particle size 0.04μm). According to the manufacturer, Esthet-X HD has

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the polishability of a microfilm and the resin matrix of an advanced hybrid. By reducing

the size of particles of glass fillers and precisely controlling the particle distribution,

Esthet-X HD gives better polish properties throughout the material in less time with less

effort. This increases the visual display of the restoration and increases the gloss score.

This material was chosen for inclusion in this study because there was a clinical trial

going on looking at the physio-mechanical properties of Esthet-X HD placed on top of

SurefilSDR in the Biohorizons Research Clinic at the University of Alabama School of

Dentistry.

Wear Background

Muscles of mastication have been shown to produce active forces that are

perpendicular and tangential to the occlusal surfaces of teeth by guiding the movement of

the mandible in relation to the upper jaw (Figure 1). These forces are responsible, in part,

for the wear of composite resins in the mouth. The ratio of the force of friction between

the two surfaces and the force pressing them together is the coefficient of friction9. The

coefficient of friction changes with materials, and during mastication, the coefficient can

be lower due to lubrication from foods, drinks, and saliva10

.

Figure 1. Movement of muscles and mandible during chewing

Wearing of tooth surfaces has significant clinical consequences both esthetically

and functionally. Increasing levels of tooth wear are significantly associated with age.

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The predicted percentage of adults presenting with severe tooth wear increased from 3%

at 20 years old to 17% in patients 70 years old and older11

. The teeth most severely

affected by wear are mandibular molars, but the most commonly affected teeth are

anteriors11

.

Wear of materials at occlusal surfaces can lead to systemic and functional

complications, e.g., worn micro- or nano-size fill particles can be swallowed or inhaled

and can accumulate into tissues which can further lead to diseases12

. During mastication

most composite particles that are disintegrated have a diameter smaller than 100μm,

which was found to be the critical threshold values for the absorption of particles in the

lungs and intestines12

. However, no published studies were found reporting that the

absorbed particles from composites put patients at a health risk with regard to toxic or

mutagenic effects.

Wear is a very complex process that involves extrinsic and intrinsic factors.

Excessive wear may lead to premature failure and replacement of the restorations.

Therefore, it is imperative that restorative composite materials be wear resistant. Wear is

defined as the progressive loss of material through the contact of two or more surfaces in

motion. The general wear equation is defined as:

Wear = Volume loss = (k x F x d) / H

where k is a dimensionless constant, F is the occlusal force perpendicular to the surfaces

at contact, d is the sliding distance, and H is the indentation hardness of the contacting

surfaces13

.

Wear is sometimes classified as either adhesive, abrasive, fatigue, or corrosive.

Adhesive wear occurs when two smooth surfaces contact and slide across each other, as

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when an occlusal cusp contacts a composite restoration. The loss of material occurs when

electrostatic bonds form between the two surfaces and the softer material adheres to the

harder material.

Another type of wear is abrasive wear which is produced when asperities on the

harder surface fracture asperities on the softer surface. Abrasive wear is categorized as

either two- or three-body. Two-body wear is surface to surface wear and occurs at

occlusal contact points (Figure 2). Three-body wear occurs during mastication when

particles are free to translate and rotate between the two surfaces (Figure 3). A third-body

such as a particle of food can be caught between the maxillary and mandibular teeth

during chewing. When the food bolus is broken down, the particles may become trapped

between the teeth. This is more commonly seen in occlusal contact-free areas.

Figure 2. Two-Body Wear

Figure 3. Three-Body Wear

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Other forms of wear can be classified as fatigue and corrosive processes. Fatigue

is the loss of material due to cyclic loading which produces microcracks at or below the

surface of the material. These cracks grow as the material is repeatedly deformed over

time. Corrosive wear is caused by the chemical alteration of a surface. In the oral

environment, this may be caused by acidic drinks, food, saliva, microorganisms, or acidic

bodily fluids in the oral cavity sometimes introduced in patients with bulimia. The

chemicals present in the oral cavity may also breakdown the matrix of the composite

restorative material and make the composite more susceptible to wear.

The control of occlusal wear for composites has improved over the years. When

early and more recent clinical trials are compared, it is seen that current posterior

composites wear at a rate of 10-50μm/year compared to 80-100μm/year as shown in

clinical trials taken place two decades ago14

. Prospective studies on clinical wear have

shown logarithmic curve patterns with magnitudes decreasing with time, which

demonstrate more wear early in the life of the restoration which decreases as a function

of time15

. As the composite has less occlusal contact due to wear out of occlusion, the

composite resin wears less. The teeth still contact which holds the occlusion and allows

this separation and slowing of the wear. According to the ADA Specification adaptation

to the ISO Standard for composite wear, a composite should not lose more than

0.05mm/year along occlusal surfaces16,17

.

Wear has been shown to occur mostly in three regions on teeth: occlusal contact

areas (OCA), contact-free areas (CFA), and at inter-proximal areas (IP). Most clinical

and in vitro studies measure wear in OCA and CFA regions. Wear that takes place in

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contact free areas is referred to as generalized wear. Wear that occurs at occlusal contacts

is referred to as localized wear.

Limited data dealing with interproximal wear in the laboratory are available

Interproximal wear has been shown to be a problem in Class II restorations. It can lead to

the loss of proximal contact areas which can result in food impaction, periodontal

attachment, and loss of bone. Schmidlin, et. al, reported aproximal wear loss on two

composite materaials using a two-body wear simulator18

. Wendt et. al, found that wear at

proximal contacts existed at a higher rate than occlusal surfaces. He proposed that this

was caused by the restoration always being in contact with the adjacent tooth and with

little access for the curing light to polymerize all of the material19

. However, other

prospective clinical trials do not support the observations that interproximal wear results

in open proximal contacts20,21

.

Methods of Measuring Wear

Wear loss can be quantified using depth, area, and volume. Depth is associated

with loss of vertical height, and has been shown to be dependent on occlusal forces and

varies with time. Historically, depth was used to compare wear because early composite

showed rapid wear which exposed the cavosurface margin which was then used as a

measurement reference. The most indicative laboratory parameters for comparing resin

composites using simulated localized wear is loss of vertical height and the total

volumetric loss of the restorative material22

.

Most clinical trials measuring posterior composite resin wear have utilized the

United States Public Health Service (USPHS) direct method or the indirect Leinfelder

method23

. Each method has its own limitations, for example, the USPHS, also known as

10

the Ryge criteria, is the most universally used method for measuring wear because this

procedure does not require special equipment24

. This is a non-parametric test based on

three well-defined categories (Alpha, Bravo, Charlie) to visually assess wear where:

Alpha indicates that there is no wear present; Bravo signifies that there is visible wear;

and Charlie represents excessive wear. The restoration should be replaced for a Charlie

rating. 3 years after placement of restoration, no more than 10% of the restorations can be

rated Charlie25

. The main disadvantages of using this system to assess wear loss are that it

is time consuming and subjective26

. The USPHS approach does not detect minor loss in

wear and gives values that are not parametric and therefore cannot be analyzed by some

statistical methods25

.

Another widely used measure is the Leinfelder method, which has been listed as

quick and inexpensive27

. A series of calibrated standard casts with preset increasing wear

depths of 100μm are used. The relative amount of wear is determined by comparing the

cast of the restored tooth to the standardized casts to find which one is most similar. The

accuracy of this method depends on uniform wear across the surface of the restoration

and provides a measure of altered vertical height. Disadvantages of the Leinfelder

method are that wear tends to be underestimated28

and the inter-evaluator error can be

around 0.05mm29

. Studies have shown that most clinical evaluators detect occlusal

cavosurface margins after 150-175μm of material has been worn away27

.

Moffa and Lugassy expanded on the Leinfelder method. The M-L system used 18

cylinder-shaped specimens with carefully machined offsets in 25μm increments in the

center of the dies30

. Vivadent combined the Leinfelder and M-L scales to create better

precision when identifying wear.

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In a study performed by Leinfelder et. al, results from the USPHS system

indicated significant wear loss between the 3rd

and 4th

year after placement of some

restorations while the Leinfelder method showed that the majority of wear was observed

in the first two years27

. This finding indicated that 2 year clinical studies were sufficient

for measuring wear of composites. Taylor, et. al confirmed that high initial wear rates and

early changes could not be detected by the USPHS system26

.

Results show that wear is underestimated during visual depth evaluations such as

the USPHS and Leinfelder methods31,32

. Recent advances in technology offer faster and

more accurate methods which have been developed to quantify wear loss such as

stereomicroscopes, scanning electron microscopes, computerized 3-D microscopes, and

contact and non-contact profilometers33,34,35

. These methods utilize before and after 3-D

images of the restorations that are superimposed by maximizing the overlap of common

based on the unaltered surface topography of the overall images. The overlap from the

aligned surfaces is then subtracted to reveal the amount of material loss representing

wear. However, these methods require specialized software and instrumentation.

Contact vs. Non-Contact Profilometers

Various types of surface profilometers are listed to be accurate and easy to use36

.

Scanners that profile the topography of occlusal surfaces of teeth are classified as contact

or non-contact. Most contact profilers use different sized (0.1mm or larger) spherical

tipped styli. This scanning system has high accuracy, high repeatability, low cost, and is

not affected by the color and light reflecting properties of the material37

. However, this

method is time consuming, and has the potential for the stylus to alter the surface of the

material being scanned38

.

12

Most non-contact profilometers use a laser or light source for analyses. They

require an opaque and reflecting material surface. A digital camera-like system in the

profilometer captures images as the light source moves across the surface. Non-contact

profilers can also be categorized as line, area, point, and volume scanners (CT scans).

Non-contact line laser systems scan the surface using a straight line path along the

surface. Area scanners are similar to line scanners except that they develop a pattern

covering an area of the surface and use triangulation, interferometry, and phase shifting

to calculate surface points. Point scanners have the highest resolution but because of

repeated images, take the longest time to scan. Volume scanners are called computer

tomography (CT) scans with radiographic systems exposing patients to radiation. CT

systems are relatively expensive.

Accuracy and Precision

Accuracy is defined as how close the measured value is to the actual

(international standard) value. Precision is defined as the degree of repeatability of the

measurement technique. Ideally a system will be both accurate and precise. However, if a

methodology introduces a bias, it can be a precise method that is not accurate. Biases can

be corrected through several methods for calibration. Accuracy is necessary when

measuring clinical wear because dental restoration wear is measured on such a small

scale.

If measurements are done indirectly using stone cast replicas, then the accuracy of

the impression and replica materials must also be considered along with the scanner

accuracy as part of the overall system accuracy determination39

. Factors that limit the

accuracy of impressions are limited working time, material dimensional stability, use or

13

not of tray adhesives, selection of tray type, material tear resistance, and disinfection

methods. According to ANSI/ADA Specification No. 25 (ISO 6873), there are four types

of pure gypsum products: Type II (model plaster), Type III (dental stone), Type IV (high-

strength stone), and Type V (high-strength/high-expansion stone). Type IV is listed as the

dental stone most widely used for the fabrication of casts and dies because of higher

strength and lower setting expansion magnitudes. According to the ADA Specification

25, 2 hours after mixing, the setting expansion should be 0.0-0.10%. However delayed

linear expansion and contractions of gypsum products have been measured up to 120

hours after mixing and setting. The accuracy of the casts therefore is dependent on a

known and predictable amount of long-term stability and expansion magnitudes.

The accuracy of the scanner is just as important as the accuracy of the surface

being scanned. During scanning, the measurement of each of the data points collected

depends on the shape of the surface and the angle that the beam from the scanner makes

to the surface40,41

. The greater the angle the surface makes to the scanner’s line of sight

the less accurate the measurement42

. It is important to know how well the digitized

surface represents the true surface. The reproducibility of the alignment method for the

test surfaces also has been shown to affect accuracy. This is a very important factor,

especially where distortion can occur during the impression step or when creating the

replica models. If distortion occurs, it is unlikely that they will be identical on both the

baseline and one year model surfaces; therefore, the quality of alignment will be

decreased.

14

In Vitro Devices

As manufacturers try to develop or improve existing materials, materials are

placed in clinical trials, which are expensive and can last up to two to three years to

obtain meaningful clinical data. By the time a study has been carried out, newer products

could have been developed. Consequently, numerous investigators have tried to develop

in vitro devices that are capable of predicting clinical performance in a timelier manner.

Several mechanical testing systems (machines) have been created to simulate in

vivo occlusal wear on the influence of test materials. The FDA established guidelines for

non-clinical laboratory studies including: equipment should be calibrated and its

maintenance defined and ensured so that the generation, measurement, and assessment of

data should be adequately tested, calibrated, and/or standardized (No. 58.63)43

.

Machines for the simulation of dental wear provide reproducible chewing patterns

where force, gliding path, and number of chewing cycles are controlled. The machines

and support systems offer controls to vary pH, temperature, antagonist material, contact

area, frequency of load cycles, load/force, slurry medium, lubrication and friction,

duration of tooth contact, sliding speed, and wear measurement technique. All of which

have been shown to affect wear rates. However, available machines do not take into

account the presence/absence of a periodontal ligament which absorbs some of the forces

and influences motions during mastication. Due to the complexities of recreating the

mechanisms and properties of the oral cavity, no in vitro device can fully simulate in vivo

conditions. Therefore,an important purpose of these machines is to serve as a comparison

of materials and to rank restorative materials according to their wear resistance.

15

Literature review shows that many have created machines to induce wear, e.g., OHSU,

BIOMAT, Minnesota, ACTA, Zurich, Willytec, and Alabama.

The Oregon Health Sciences University Oral Wear Simulator (OHSU) simulates

wear by loading at 70N for attrition and at 20N abrasion44

(Figure 4). The machine also

includes a multi-mode simulator, poppy seeds + polymethylmethacrylate (PMMA) bead

medium, enamel and a conical stylus. Studies with the OHSU suggest 50,000 to 100,000

cycles at a frequency of 1.2 Hz44

.

Figure 4. OHSU Wear Simulator

The BIOMAT wear simulator uses independent weights for applications of force

(loading), 37°C water as the medium, and 304SS alloy counter-body as the

stylus45

(Figure 5). A 20 MPa force is exerted to produce a contact stress, and a variable

shock absorbing layer is present45

.

Figure 5. BIOMAT Wear Simulator

16

The Minnesota wear simulator (MTS) uses enamel as the stylus, water as the

medium, and a hydraulic system for controlled loading46

(Figure 6). Contact stress and

speed can all be adjusted on this machine. A force of 13.35 N is exerted during loading46

.

Figure 6. Minnesota Wear Simulator

The ACTA machine uses two metal discs that rotate against each other at

different speeds using 15-20N force47

(Figure 7). Rice/millet seeds are used in the

medium and the machine is spring loaded47

.

Figure 7. ACTA Wear Simulator

The Zurich computer-controlled masticator exerts a 49N force at a frequency of

1.7Hz48

(Figure 8). Specimens are set in a water medium using enamel as the antagonist.

Loading is by electro-magnetic control and includes an impact sliding movement48

.

17

Figure 8. Zurich Wear Simulator

The Willytec Munich wear machine produces a variable load profile and wear

path and has been used to simulate abrasive and attrition wear49

. A 50N force is exerted,

thermocycling is optional, and weights are used for loading. It is normally run with water

as the medium using enamel as an antagonists49

.

The University of Alabama Wear Simulator is a modification of the Leinfelder

type three-body wear device50

(Figures 9 and 10). Over the years there have been many

modifications of the original machine. In the first publication in 1989, a polyethylene

tape was used as intermediate substance, driven by a tape advancing system. The tape

was subsequently replaced by PMMA slurry. PMMA beads have been shown to produce

the maximum loss of material in the shortest amount of time. Also, they do not degrade in

water and they transfer the masticatory energy to the surface of the composite resin rather

than absorb it. The initial force used was 55N (12.4 lbs) which was increased to 75N

(16.8 lbs) during each cycle. This was consistent with conventional biting forces of 16.0

lbs51

. A 30° clockwise rotation was initiated as soon as the stylus touched the specimen

which was staged with the loading cycle. Originally, the restorative materials were

incorporated into extracted molars that were trimmed flat, which simulated generalized

wear. More recently, localized wear has been simulated by using ceramics (alumina and

zirconia) and stainless steel balls as the actuator against 4mm deep restorations that are

18

set into brass holders filled with acrylic resin50,52

. Most studies using the Alabama wear

machine are run from 100,000 to 400,000 cycles. The Alabama wear simulator in vitro

wear device is the most cited as determined by literature review.

Figure 9. Original drawings of Alabama Wear Simulator

Figure 10. Alabama Wear Machine

In overview, each of the machines varies in the way that they load and simulate

wear. Testing protocols and methods for measuring wear fluctuate for each machine and

testing site. Therefore, it is difficult to compare results from different machines. In 2006,

Heintz performed a round robin test with the ACTA, OHSU, Willytec and Zurich wear

devices using eight different composites53

. Prepared specimens were exchanged between

testing sites with each collecting and analyzing the data. This study concluded that the

relative ranks of the materials differed significantly between the wear devices53

.

19

In Vitro vs. In Vivo

Attempts to correlate in vivo and in vitro wear rates and magnitudes are difficult

because of the complexities of recreating the mechanisms and properties of the oral

cavity54

. In 1989, the Council on Dental Materials stated that in vitro (laboratory) and in

vivo (clinical) correlations have not yet been established from these machines. No in vitro

test can fully simulate in vivo conditions55

.

On the other hand, there have been articles published showing how well wear

simulation methods correspond to actual in vivo situations. In the early 1980’s, the

Minnesota wear simulator became the first in vitro wear machine to have a publication

correlating the two56

. After testing Brilliant D.I. composite and Dispersalloy amalgam,

they showed that 250,000 cycles corresponded to a year of in vivo function. Later, Lutz

and Krejci claimed that 1,200,000 cycles using the Zurich simulator corresponded to 5

years in vivo57

. They based their results on 4 year clinical data for 14 amalgam

restorations and 6-month data for 12 composite inlays57

. In the late 80’s, Leinfelder, et. al

reported that a modified Roulet simulator produced wear patterns similiar to generalized

wear in vivo50

. In 1999, Leinfelder and Suzuki reported that 400,000 cycles in the

Alabama wear simulator exhibiting generalized wear corresponded to 3 years of in vivo

function. They used a profilometer to trace the surfaces of the worn specimens51

. Depth

loss values for the specimens were compared to results obtained in previous clinical

studies with the same materials58

. Barkmeier, et. al, used a modified Leinfelder wear

simulator to produce localized wear59

. They used a MTS 3-D Profiler and AnSur3D

software to obtain values for P50 and Z100 composites after being cycled 100,000,

200,000, 300,000, and 400,000 times. Depth values from clinical trials performed at

20

Creighton University using the same materials were used for comparison. They

concluded that in vitro localized wear could be correlated to wear in the oral cavity52

. In

another study out of Creighton University, investigators compared specimens of P50 and

Z100 subjected to 100,000, 400,000, and 800,000 cycles in a generalized wear model.

Volume loss, maximum depth, and mean depth were all investigated. They reported that

simulated generalized wear correlated to clinical CFA wear22

.

In each of these studies, the investigators compared the results they obtained in

the laboratory to data from previous clinical trials using the same material. Although

these correlations were found, it is questionable how reliable they are. Therefore, this

goal of this study was to investigate the differences in the wear patterns and values of a

nano-hybrid composite resin system after one year of placement in an ongoing clinical

trial to controlled specimens prepared in the laboratory of the same material subjected to

200,000 and 400,000 cycles of three-body wear using the Alabama wear testing device.

21

OBJECTIVES AND HYPOTHESES

Objective: To measure and compare volumetric wear loss (mm3) and linear depth (μm)

values of in vitro specimens and in vivo restorations of a highly filled BisGMA nano-

hybrid composite resin system using a 3-D non-contact surface profilometer.

Hypothesis 1: Volume loss of wear (mm3) does not differ among tooth types, arches, or

face sides of in vivo restorations of a highly filled BisGMA composite resin system after

one year of placement.

Hypothesis 2: Linear depth of wear (μm) does not differ among tooth types, arches, or

face sides of in vivo restorations of a highly filled BisGMA composite resin system after

one year of placement.

Specific Aims 1 and 2: Casts of in vivo restorations of the same material were compared

at baseline and one year by a 3-D non-contact light profilometer. Volume loss (mm3) and

mean linear depth (μm) data were obtained for tooth type, arch, face side, and restoration

type and were compared and statistical differences were determined by

Hypothesis 3: There is no difference in volumetric wear loss of wear (mm3) of in vitro

specimens of a highly filled BisGMA composite resin system subjected to 200,000 and

400,000 cycles of wear.

22

Hypothesis 4: There is no difference in linear depth or wear (μm) of in vitro specimens

of a highly filled BisGMA composite resin system subjected to 200,000 and 400,000

cycles of wear.

Specific Aims 3 and 4: Using the same material, in vitro specimens subjected to 200,000

or 400,000 cycles of localized wear in the modified Alabama wear testing machine were

measured by a 3-D non-contact light profilometer. Volume loss (mm3) and mean linear

depth (μm) data were obtained and statistical differences were determined using pooled t-

tests if not significantly different (p > 0.10) and Sattertwaite adjustments if significantly

different (p < 0.10).

23

MATERIALS and METHODS

In Vivo Protocol

Subjects for the proposed follow-up study were recruited from the University of

Alabama at Birmingham dental clinics (University of Alabama at Birmingham

Institutional Review Board with a protocol number of #20072034-See Appendix 1). The

study was a single-center, non-blinded clinical trial with clinical evaluations at baseline

and 12 months. Thirty-one patients were enrolled and received treatment including 63

composite restorations. Details for 12 of these patients receiving treatment and 21

restorations were available for portions of this study.

Table 1. Study Characteristics

Study Characteristics (n=21)

Overall Count Percentage

Tooth type

1st Premolar 4 19

2nd Premolar 5 24

1st Molar 7 33

2nd Molar 5 24

Arch

Maxillary 14 67

Mandibular 7 33

Face Side

Right 12 57

Left 9 43

Restoration Type

Class I 4 19

Class II 17 81

An oral examination was conducted to determine the adequacy of inclusion and

exclusion criteria which were meant to reduce the confounding variables in oral hygiene.

24

Table 2. Inclusion criteria.

Inclusion criteria

1 19 years of age and older

2 Must have given written consent to participate in the trial

3 Must be in need of at least one posterior restoration (replacement restorations

are acceptable)

4 Must be in good general health

5 Must be available for the required post-operative follow-up visits

6 Restorations must have at least one contact in habitual closure with an opposing

natural or crowned tooth or a fixed bridge

7 Restorations must have a buccal to lingual/palatal width equal to or greater than

1/3 the distance from buccal to lingual/palatal cusp tips

Table 3. Exclusion criteria.

Exclusion criteria.

1 Does not meet all inclusion criteria

2 Has rampant uncontrolled caries or advanced untreated periodontal disease

3 Presents with any systemic or local disorders that contra-indicate the dental

procedures included in this study

4 Evidence of xerostomia

5 Evidence of systemic bruxing or clenching or in need of TMJ related therapy

6 Teeth with periapical pathology or exhibiting symptoms of pulpal pathology

25

7 Teeth exhibiting hypersensitivity that would not be expected to be relieved by

placement of restoration

8 Teeth that have been pulp capped

9 Teeth with near exposures (caries approaching the pulp)

10 Teeth with exposures during tooth preparation

11 Teeth requiring cusp replacement – buccal and lingual/palatal extensions are

acceptable

12 Women who are known to be pregnant or who are intending to become pregnant

over the duration of the study will not be excluded from the study. No

pregnancy test will be performed.

Investigators who performed the clinical assessments were trained in the method

of clinical examination. Investigators were trained on how to manipulate the material in

extracted or model teeth to become familiar with its handling properties. All study

procedures were explained to every subject, and every subject was provided written

consent to participate in the study. Each subject was screened for compliance with

inclusion/exclusion criteria specified in Tables 1 and 2. The patient was appointed for a

restorative appointment. Digital images were taken before restoration preparation. The

tooth to be restored was isolated with a rubber dam. The restoration was prepared using

330 and 245 burs. Any cavity preparations judged to be within 1mm of pulpal tissue

either clinically or radiographically were lined with a Ca(OH)2 containing-liner.

Phosphoric acid etchant was applied to enamel first and then dentin and agitated for 15

seconds, rinsed for 10 seconds, and dried with a high volume suction until enamel etch

26

pattern was seen. A total etch bonding system (Prime and Bond NT, DENTSPLY Caulk)

was applied to thoroughly wet all the tooth surfaces for 20 seconds. Excess solvent was

dried gently with dry air from dental syringe for 5 seconds until glossy surface appeared.

Bonding agent was cured for 20 seconds using G Light. Light output was checked

frequently to make sure it was greater than 750 mW/cm2. Sectional matrix or Tofflemire

retainer was used. Wedge and burnish matrix band were placed adjacent to contact. Low

viscosity Surefil SDR base material (DENTSPLY Caulk) was inserted and bulk filled (up

to 4mm) to within 1.5-2mm of the occlusal surface and cured with G Light (GC America)

for 20 seconds. Esthet-X HD was placed to complete the restoration and was photo-

initiated for 20 seconds with G Light. The method of placing a flowable composite under

a more wear-resistant capping material is referred to as the sandwich technique (Figure

11).

Figure 11. Sandwich Technique

Matrix band was removed and excess material was removed for gingival area

using a 12 blade. 3M finishing strips were used below the contact area. The gross contour

was removed with a 7404 bur or OS 2 (red, then yellow, and finally white). Anatomy was

27

established and refined with OS 1 bur. Embrasure areas were finished with Sof-Lex (3M

ESPE) discs. Rubber dam was removed and occlusion was adjusted with 7404, 7901, or

OS 2 burs. Finally, restoration was polished with Enhance POGO. Impressions were

disinfected using Biotrol and stored under ideal climatic conditions. First recall (baseline)

evaluation was within 10-15 days after restoration. A conventional impression was made.

Two trained examiners performed clinical assessments of the following at baseline:

fracture, proximal contact, marginal discoloration, marginal integrity, recurrent caries,

retention, sensitivity, and gingival index according to USPHS. The second recall

evaluation took place after twelve months of restoration. Conventional impression was

made. The same examiners performed the same clinical assessments as performed at the

baseline appointment.

Table 4: Materials used in vivo

Materials Manufacturer Lot No Expiration Date Shade

Curing time

Esthet-X HD DENTSPLY/Caulk

080718

R1039-1

080717

07/2011

02/2010

07/2011

A1

A2

A3

20 seconds

Material Manufacturer

Surefil SDR DENTSPLY Caulk

Prime & Bond NT DENTSPLY Caulk

Self adhesive Directed Flow Impression Tray 3M ESPE

Aquasil Ultra Heavy: Type 2: Medium bodied consistency DENTSPLY Caulk

Aquasil Ultra XLV: Type 3: Light-bodied DENTSPLY Caulk.

28

Fujirock Type 1V Die & model stone GC America

Mounting Stone Whip Mix Coroporation

Putty impression material 3M ESPE

Biotrol disinfectant solution Biotrol International

Impressions

The patient was comfortably seated in the dental chair and adjusted to a

convenient position. The dental assistant was instructed to load the Self adhesive

Directed Flow Impression Tray (3M ESPE St. Paul, MN) with Aquasil (DENTSPLY

International Inc. York, PA) Ultra Heavy: Type 2: Medium bodied consistency PVS

impression material starting from left molar area and following dentate region of the arch

through the right molar area avoiding entrapment of any air. The impression material was

dispensed from Pentamix 2 (3M ESPE St. Paul, MN) an automated machine. An air

spray was used to dry the teeth while the assistant was loading the impression tray, and

the facial surfaces of the teeth of interest were covered with Aquasil (DENTSPLY

International Inc. York, PA) Ultra XLV: Type 3: Light-bodied impression material

(cartridge) prior to insertion of the tray. Over the heavy body impression material, a

layer of light body was added in areas of interest to capture fine details. The impression

tray was inserted from the left side, and rotated into the mouth while retracting the cheek.

The impression tray was seated and slowly moved in contact with the teeth, using the

central incisors as guidance. This was done to avoid the entrapment of air into the

material. The tray was positioned using the subject’s nose as the reference point. Three

29

and half minutes after seating the tray, the impression was removed and disinfected

(Figure 12).

Figure 12. Polyvinyl Siloxane Impression

Disinfection

Biotrol disinfectant solution (Biotrol International, Salt lake City, UT) was

sprayed on the impression. The impression was then placed in a plastic bag with a code

written on it. The impressions were stored in a dry area.

Casts

The impressions were washed under tap water, and dried with air water syringe to

ensure there was no excess liquid. One hundred mg of Fujirock (GC America Alsip, IL)

Type IV Die & model stone was spatula mixed for 10 sec and followed by vacuum

mixing (Whip Mix Corporation, Model # 6500, Louisville, US) under 27 psi/ hg for 30-

40 sec with 20ml of tap water measured in a measuring cylinder at 23 ± 2 º C. According

to the manufacturer, Fujirock sets in 12 minutes and expands .08%. The color topaz was

chosen because it gave the best intensity during preliminary tests on the Proscan2000.

The mix was poured at an ambient temperature of 23 ± 2 º C and humidity of 34 ±1 %.

30

Using the stone vibrator set in slow mode the mixed stone was slowly poured into the

impression. The tray with the impression was placed in a slanting position with one

corner touching the vibrator. Care was taken not to touch the impression but the tray on

the vibrator to prevent distortion. A small amount of the stone was vibrated through the

impression to provide a thin wash of stone in the impression covering the depressions.

Subsequent stone was slowly added in small increments to fill the impression while

vibrating the impression. The impressions were not inverted. The casts were separated

from the impression trays after setting for 30 to 40 minutes (Figure 13). Patient codes

were assigned and written on the casts.

Figure 13. Final Cast

Bases

Since ProForm software was unable to compensate for more than a 6° difference

between the before and after images, the investigators in this study created an apparatus

to standardize the angulation between the bases of the baseline and one year casts. A

dental surveyor was used as the base for the apparatus. Acrylic was added to the end of

the pole and three distinctly different lines were cut into the acrylic (Figure 14).

31

Figure 14. Dental surveyor with acrylic

A base was poured up for the baseline cast using white Mounting Stone (ISO

type 3, Whip Mix Corporation). One hundred grams of Mounting Stone was spatula

mixed for 30-45 seconds with 26mL of tap water measured in a measuring cylinder at 23

± 2ºC. The Mounting Stone set in 5 minutes and expanded 0.08%. After the base had set,

putty impression material was placed on the occlusal surface extending lingually and

buccally over the cast. The acrylic covering part of the dental surveyor was lowered until

the acrylic lines were in the putty (Figure 15). This allowed the impressions of the same

patient to be standardized in the same angle along the Z axis.

Figure 15. Apparatus to standardize bases

After the putty had set, the baseline cast was removed from the apparatus and

replaced by the one year cast. The one year cast was then situated into the putty. The base

32

was then poured up for the one year using the same material as the baseline base (Figure

16). After setting, the casts were stored in plastic containers.

Figure 16. Final standardized bases

Measuring Wear

The casts were scanned using a non-contact 3-D surface profilometer measuring

instrument (Proscan2000, Scantron Industrial Products Ltd. Taunton, England) (Figure

17).

Figure 17. Proscan2000

33

The following are features of the Proscan2000:

1. Uses non-contact sensor technology which measures surfaces sensitive to the

influence of a contact technology and it does not experience problems with

penetration.

2. Has a resolution in height measurement as low as 5nm, measured at a rate of up to

1,000 points per second.

3. Proscan2000 scans the top surface of specimens over an area of up to 150mm x

100mm.

4. Uses a confocal multiplexing sensor with up to 0.005μm resolution.

5. Safe white light is transmitted through a lens, which has spectral aberration built

in. Takes the white light and divides it into the full spectral field, focusing each

different color frequency at a slightly different point through a defined measuring

range. When an object is placed within this range, only one particular color

frequency reflects back from the surface.

6. Information passes back into processor where a spectrometer analyzes the signal

and converts it to a measurement. Proscan combines these measurements with the

precise location of a moving X and Y linear table, giving three co-ordinates from

which a three dimensional profile is created.

7. Results of the surface profile appear immediately on the computer monitor and an

image of the graphical 3-D representation can be saved on the computer.

The cast was placed under the scanner with the point of interest tooth being

perpendicular to the field of vision. The step size was set at 20 μm. Then the sample rate

34

was set at 300Hz. The S29/12 sensor model was chosen because that is the best sensor for

measuring multiple teeth or a full arch. The S29/12 sensor has a measuring range o12mm,

resolution of .28μm, and uses chromatic, not triangulation, technology.

The image produced for each tooth was cropped so that only the area of the

restoration was used in the analysis (See Appendix 2). Scans for both assessment periods

for each restoration were superimposed on top of each other to determine the volumetric

wear of the material (ProForm software, Scantron Industrial Products Ltd. Taunton,

England). To achieve the goal of selecting the same points all the times, surface features

were selected and the casts were aligned to these features. This technique reduced the

error along the XY axes. The measurements were repeated two times on the same tooth

and recorded to check the operators’ reliability. Each of the casts was positioned carefully

to be able to reproduce the same axis orientation.

In Vivo Data Analysis

The statistical method used was mixed-model analysis of variance. Separate

analyses were conducted for volume and for depth, and for each of the potential predictor

variables tooth type, arch, face side, and restoration type. Patient was included as a

random effect in each model in order to account for correlation among multiple

measurements made on the same patient. Least-squares means were calculated in order to

adjust for unequal numbers of observations per patient.

In Vitro Specimen preparation

Table 5: Materials used in vitro

Materials Manufacturer Lot No Expiration Curing time Shade

35

Date

Group 1 (n=8)

200,000 cycles

Esthet-X HD

DENTSPLY/

Caulk

0907171 July 2012 20 seconds Y-E

Group 2 (n=8)

400,000 cycles

Esthet-X HD

DENTSPLY/

Caulk

0812301

December

2011

20 seconds A2

A cylindrical mold made of an impression material with diameter of 8mm and

height of 5mm was used to prepare the composite samples, 8 for each group. Composite

specimen was built up in 2 increments, 2mm each and cured with visible curing light

FusionTM

(Dentlight, TX, USA) 530mW/cm2, according to the required curing time by

the manufacturer (Figure 18). The specimens were prepared in a room with 40%

humidity and a temperature of 25°C. The top layer was cured through a glass slide which

was placed on composite to create a flat surface.

Figure 18. Composite build-up

Specimens were stored in the incubator at 37ºC for 24 hours after which they

were embedded in the center of brass holders (d=15mm) using a self curing acrylic

material (Flash Acrylic), creating a flat surface (Figure 19). They were polished using

600, 1200-grit SiC abrasive paper under water spray (for 2 minutes rotating 90° every 30

seconds) followed by finishing with 0.05µ alumina slurry and a polishing cloth using a

36

rotational polishing device for one minute (No: 233-0-1997, Buehler Ltd, Evanston, IL).

They were cleaned with an ultrasonic bath for 5 minutes using distilled water.

Figure 19. Prepared wear specimen

Determination of in vitro wear

The specimens were then subjected to wear using the Alabama Wear Testing

Device. The specimens were mounted in a water bath and a cylinder was placed around

each sample. A water-slurry of PMMA (15 grams of PMMA for 9 grams of water) was

poured into each cylinder, covering the specimens. The stainless steel antagonists (Type

440C; diameter=4.70mm; Rockwell hardness=58-65, Small Parts Inc.) were mounted in

spring-loaded styli and used with the PMMA slurry to simulate localized wear. The styli

were calibrated to be 75N using an Instron machine (INSTRON Model no:5565). At a

rate of 1.2 Hz (72cycles/min), the stainless steel stylus was vertically loaded onto the

specimen under a load of 75N (16.8 pounds). As soon as the maximum load was

achieved, the stylus rotated clockwise 30 degrees and then counter-rotated. The stylus

then moved vertically up into its original position. The entire cycling procedure was

carried out 200,000 and 400,000 times for 8 specimens (Figure 20).

37

Figure 20. Specimen after subjection to wear

Specimens were scanned using a non-contact 3D surface profilometer

(PROSCAN 2000, Scantron Industrial Products Ltd. Taunton, England). The pre- and

post-test surfaces were compared using ProForm software (Scantron Industrial Products

Ltd. Taunton, England-See Appendix 3). ProForm software provides conditions for

determining volume loss (mm3), the total volumetric loss of material from the profiled

surface, and maximum depth (μm), the lowest or deepest points from al the individual

scans. The wear measurements were based on differences observed between the before

and after data sets.

In Vitro Data Analysis

The volume and depth was compared between the two groups using t-tests.

Pooled t-tests were used when the group variances were not significantly different (p >

0.10). Satterthwaite adjustment was used when group variances were significantly

different (p < 0.10).

38

RESULTS

Table 6. Results (mean ± standard deviation)

Volume Loss (mm3) Mean Depth (μm)

In Vivo 1.791±.7583 489.25±236.73

In Vitro – 200,000 cycles .011±.0019 58.69±8.47

In Vitro – 400,000 cycles .017±.0025 76.38±16.53

Table 7. In Vivo Results (See Appendix 2 for Images)

Restoration

# Tooth Type Arch

Face

Side

Restoration

Type

Pt

Number

Volume

(mm3)

Depth

(μm)

1 1st Premolar Maxillary Right Class 2 1 0.484 279.46

2 2nd Premolar Maxillary Left Class 2 1 0.797 187.36

3 2nd Molar Mandibular Left Class 2 2 2.849 357.05

4 1st Premolar Maxillary Left Class 2 3 1.982 403.45


6 1st Molar Maxillary Right Class 2 4 1.428 268.01

7 1st Molar Mandibular Right Class 2 4 2.748 540.53

8 2nd Molar Mandibular Right Class 2 4 2.804 370.11


10 2nd Premolar Maxillary Right Class 2 5 1.309 519.12

11 2nd Molar Maxillary Right Class 1 6 2.156 900.45


13 1st Premolar Mandibular Left Class 2 7 1.339 372.2

14 2nd Premolar Mandibular Right Class 2 7 1.672 438.5

15 1st Molar Maxillary Left Class 2 8 1.846 538.35

16 1st Premolar Maxillary Left Class 2 9 1.849 546.84

17 1st Molar Maxillary Left Class 1 9 1.327 445.63





39

Table 8. In Vitro Results (See Appendix 3 for Images)

Specimen Group

Volume

(mm3)

Depth

(μm)

1 200,000 cycles 0.013 59.28

2 200,000 cycles 0.013 51.46

3 200,000 cycles 0.013 64.15

4 200,000 cycles 0.01 59.26

5 200,000 cycles 0.009 54.88

6 200,000 cycles 0.008 44.59

7 200,000 cycles 0.012 63.78

8 200,000 cycles 0.012 72.13

9 400,000 cycles 0.014 61.52

10 400,000 cycles 0.02 96.68

11 400,000 cycles 0.019 100.78

12 400,000 cycles 0.018 62

13 400,000 cycles 0.014 60.03

14 400,000 cycles 0.02 80.85

15 400,000 cycles 0.015 84.19

16 400,000 cycles 0.016 65.01

40

DISCUSSION

In this study, the investigators found that it was inappropriate to compare in vivo

and in vitro data due to the large amount of different parameters between the two groups.

Observations from the Proscan2000 images showed different wear patterns between the

two groups. The specimens that were prepared in the laboratory were standardized and

controlled. Therefore, their wear patterns consistently showed the same conical shape. On

the other hand, the restorations from the clinical trial showed varied amounts of wear

throughout the entire surface of the restorations. The Proscan images shoed inconsistent

wear patterns with different shapes and sizes. It was concluded that there were different

mechanisms of wear being exhibited and was therefore inappropriate to compare the two

groups statistically.

Clinical trials are expensive and time consuming, so companies rely on results

from laboratory testing. It is easier and less expensive yet less accurate to work outside of

the mouth where conditions are standardized. Researchers cannot take wear results

straight from in vitro studies and use them to predict the amount of in vivo wear. Results

from in vitro studies can only be used to rank and compare materials.

In this study, even with 21 restorations, there were too many variations in the

restorations to accurately correlate wear between the clinic and the standardized

laboratory specimens. There are many factors that limit the outcome of the results in a

clinical trial, especially one measuring wear. Patients ranged in age, sex, dietary and

smoking habits, chewing habits and patterns, dominate chewing side, caries risk

assessment, size of restoration, location of restoration, and bite force, all of which have

been proven to affect the amount of wear. Although all of the restorations were placed in

41

the posterior region, most of them were class 2 and only a few were class 1. Each

restoration varied in size and depth depending on how deep the caries extended. Another

factor that varies from individual to individual is biting force. It is generally found that

males can bite with more force (118-142 lbs) than can females (79-99 lbs)60

. There was a

mixture of males and females included in this study. The location of the restoration can

also have an effect on how much wear will occur. The current study included 1st and 2

nd

molars along with 1st and 2

nd premolars. It has been noted that the maximum amount of

force applied to a molar (91-198 lbs) is usually several times that which can be applied to

an incisor (29-51 lbs)61

. Another variable that influenced the analysis was the amount of

restorations each patient received. Some patients had up to three restorations placed in

their mouths. This multiple observations/patient influenced the results. Furthermore,

patients’ variations in dietary and chewing habits influence the wear resistance of the

restorative material. Food consistencies can have a significant impact on force. Anderson

measured bite force on carrots (30 lbs) versus mean (16 lbs)62

. Other confounding

variables in this study were amount of clinicians placing restorations, and the accuracy

and precision of impressions and casts. Due to all of these discrepancies between patients

and restorations, it was concluded that the in vivo and in vitro values could not properly

be compared to each other. Instead, the investigators made comparisons within the two

groups.

The 1st and 2

nd hypotheses looked at comparisons of volume and depth loss values

between tooth type, restoration type, arch, and face side of in vivo restorations. The 3rd

ad

4th hypotheses looked at the differences between volume and depth loss in the two in

vitro groups.

42

For the clinical data, the within-subject (intraclass) correlations ranged from 0,

which did not affect the results, to 0.2720, which is a substantial ICC and even with the

relatively small number of observations per person (mean = 1.75) resulted in a design

effect of approximately 1.2, corresponding to a reduction of power by approximately

20% relative to having the same number of observations on independent units (people).

Least-squares means accounted for bias due to the unequal numbers of observations. The

investigators failed to reject null hypothesis 1 that volume loss (mm3) does not differ

among tooth types, arches, or face sides of in vivo restorations. Also, the investigators

failed to reject null hypothesis 2 that linear depth (μm) does not differ among tooth types,

arches, or face sides of in vivo restorations. Not finding significant differences does not

argue for there being no association. The small sample size does not provide sufficient

power to justify a statement of equivalence. The magnitude of the differences was judged

by looking at the least square means for each analysis.

The investigators rejected null hypothesis 3 that there is no difference in

volumetric wear loss (mm3) of in vitro specimens of a highly filled BisGMA composite

resin system subjected to 200,000 and 400,000 cycles of wear. They also rejected null

hypothesis 4 that there is no difference in linear depth (μm) of in vitro specimens of a

highly filled BisGMA composite resin system subjected to 200,000 and 400,000 cycles of

wear. There were significant differences found between the two groups in both volume

and depth loss. This conclusion goes along with what was expected when the amount of

cycles was doubled.

Although it has been successfully used many times to scan and measure the wear

loss of in vitro specimens, this was the first time that the Proscan2000 was used for

43

clinical wear. The only time the Proscan2000 was found to be cited in the literature was

in a study where it was used to determine the surface roughness values of different

enamel conditioning techniques63

. In the beginning of this study, the goal was to scan all

of the restorations (baseline and one year) in the DENTSPLY/Caulk clinical trial. Due to

technical and time issues, in the end, a representative sample of the restorations was able

to be included in this study. On the other hand, this study did allow the investigators the

ability to see that the Proscan2000 could properly quantify wear loss in vivo.

44

SUGGESTIONS FOR FUTURE RESEARCH

After performing this study, the investigators suggest that the following variables

should be isolated in future clinical trials to make them more controlled: bite force,

dominant chewing side, occlusion (where occlusal cusps contact restoration), amount of

restorations per patient, age, and sex.

In the clinical portion of this study, the material being investigated was placed on

top of a flowable low-stress/shrinkage composite resin, Surefil SDR, which has a higher

modulus than Esthet-X HD. It would be interesting to investigate the role that the

flowable material played on the wear of the capping material. Since Surefil SDR was

filled in 4mm increments up to the CEJ, not every restoration was filled with the same

amount of Esthet-X HD. Some were capped over the Surefil SDR in 1, 2, or even 3 mm

increments. In the laboratory, the specimens were prepared by being set into acrylic

inside of brass holders. Future studies could include both materials being placed in the

brass holders.

It is important to note that improvements and modifications can be made to design

a device that will more accurately portray what is going on in the oral cavity and produce

comparable wear deficits to the ones found in vivo. This can be done by cycling of

medium, temperature, and pH. Future investigators should also look at changing the

mechanisms of the Alabama Wear Testing Device to a twist and slide rotation that would

closely simulate the chewing patterns in the oral cavity.

Future investigators can state that in 2010 Michelson, et. al tried to assess

differences in clinical and in vitro wear and found that the generation of the Alabama

45

Wear Testing Device used in this study does not directly correlate to what is occurring in

the mouth.

46

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Appendix 1: IRB Approval Forms

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Appendix 2: In Vivo Scans at Baseline, 1 year,

and Superimposition of Restoration

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Restoration #1

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Restoration #2

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Restoration #3

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Restoration #4

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Restoration #5

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Restoration #6

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Restoration #7

63

Restoration #8

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Restoration #9

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Restoration #10

Restoration #1

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Restoration #11

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Restoration #12

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Restoration #13

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Restoration #14

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Restoration #15

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Restoration #16

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Restoration #17

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Restoration #18

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Restoration #19

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Restoration #20

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Restoration #21

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Appendix 3: In Vitro Superimposition

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Specimen 1 – 200,000 cycles


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