development of porcelain restorative material by …

Republic of Iraq

Ministry of Higher Education and Scientific Research

University of Technology

Laser and Optoelectronics Engineering Department

DEVELOPMENT OF PORCELAIN

RESTORATIVE MATERIAL BY

USING CO2 LASER

A Thesis

Submitted to the Laser and Optoelectronics Engineering

Department, University of Technology in Partial Fulfillment

of the Requirements for the Degree of Master of Science in

Laser Engineering

By

Nawras Mohsin Kadhim B. Sc. Laser Eng.

2006

Supervised by

Asst.Prof. Dr. Kadhim A.Hubeatir

2008 A. D. 1429A. H.

جمھورية العراق مي لعوزارة التعليم العالي والبحث ال

الجامعة التكنولوجية قسم ھندسة الليزر والبصريات الالكترونية

ليزر تطوير حشوات البورسلين بأستخدام

ثنائي أوكسيد الكربون

إلىرسالة مقدمة قسم ھندسة الليزر والبصريات الالكترونية الجامعة التكنولوجية

الليزرنيل درجة الماجستير علوم في ھندسة من متطلبات كجزء

المھندس تقدم بھا

نورس محسن كاظم

بإشراف

كاظم عبد حبيترالدكتور

ھ١٤٢9 م ٢٠٠8

Supervisor Certification I certify that this thesis entitled (Development of Porcelain

Restorative Material by Using CO2 Laser) was prepared by

(Nawras Mohsin Kadhim) under my supervision at the Laser and

Optoelectronics Engineering Department University of

Technology as a partial fulfillment of the requirements for the

degree of Master of Science in Laser Engineering. Signature:

Supervisor: Dr. Kadhim A.Hubeatir

Title: Asst Professor Date: / 10 / 2008

Certification of the Linguistic Supervisor I certify that this thesis entitled (Development of Porcelain

Restorative Material by Using CO2 Laser) was prepared under my

linguistic supervision.

Its language was amended to meet the style of the English Language

Signature:

Name: Sabah Aziz Dhahir Title: Lecture

Date: / 10 / 2008

Acknowledgment

First of all, praise and thank be to ALLAH the most beneficent, the

most merciful who enabled me to achieve this research.

Who has given me the greatest pride to carry out my research work

under the supervision of Asst. Prof. Dr. Kadhim A.Hubeatir whose valuable

advice, guidance, constructive criticism, encouragement and cooperation

throughout all the stages of preparing this study are gratefully appreciable. I

am greatly indebted to him and wish to express my deep gratitude and sincere

thanks to my supervisor.

Special greater thank to Asst. Prof Dr. Sheahab Ahmad Zeidan. for his

help and his scientific advice during the project.

Would like to thank Asst. prof. Khalid Salim. For his advice and help

Special great thank to Dr. Hisham Al-Raawi. For his scientific advice

Would like to thank Ministry of Science and Technology. Material

researches Directorate. To help for achieve this project.

Would like to thank Material Engineering and Material Science.

University of Technology. To help for achieve this project

A great thank to Dentists Maha Adnan for her help and good advice.

Greater Full thanks to all staff of Laser and Optoelectronic

Engineering department special Head of the department Asst.Prof.

Dr.Mohamed Hssain.

I would like to thank my Family for their encouragement and help me by pray for me. I am deeply indebted to my friends and colleagues for their

encouragement and help.

Nawras Mohsin

Examination Committee Certification We certify that we have read the thesis entitled “Development Of

Porcelain Restorative Material By Using CO2 Laser”, and as an

examination committee examined the student “Nawras Mohsin Kadhim”

in its content, and that in our opinion it is adequate for the partial

fulfillment of the requirement for the degree of Master of Science in laser

Engineering.

Signature: Name: Dr Mohammed Abdul-Wahab Title: Assist Professor Address: Laser and Optoelectronics Eng. Dep. University of Technology. (Member) Date: / 10 / 2008

PP

Signature: Name: Dr. Sheahab Ahmad Zeidan Title: Assist Professor Address: Material Dep. School of Applied Science. University of Technology. (Chairman) Date: / 10 / 2008

Signature: Name: Dr. Kadhim A.Hubeatir Title: Assist Professor Address: Laser and Optoelectronics Eng. Dep. University of Technology. (Supervisor) Date: / 10 /2008

Signature: Name: Dr. Mohamed K. Dhaher Title: lecturer Address: laser institute for postgraduated studies . Baghdad University. (Member) Date: / 10 / 2008

Approved by Department of Laser and Optoelectronics Engineering,

University of Technology.

Signature: Name: Dr. Mohammed Hussain Ali Title: Assist Professor Address: Head of Laser and Optoelectronics Eng. Dep. University of Technology. Date: / 10 / 2008

II

Abstract This thesis deals with Development of Porcelain Restorative Material

by Using CO2 Laser.

(10) specimens of porcelain material are prepare. They divided into two

groups with dimensions (4*10mm) & (6*10mm) respectively.

Eight of these specimens are irradiated by CO2 laser device with powers

(2,3,4, &5) Watt at a fixed time (20 sec).

After irradiation by laser beam these porcelain specimens tested to

know influence of the laser beam on the physical and mechanical properties.

Using X-Ray diffraction technique to know the unknown crystalline phase

consisting in the porcelain specimens which is called Leucite phase, which

found that there are three peaks consisted in the porcelain specimens after

irradiation by laser, and when irradiation by different laser power density

these peaks are growth at (2W) laser and decreased at (3W) laser and

beginning to rise again at (4 & 5) Watt laser. The mechanical properties test

such as Micro-hardness, Diametrical strength, density and porosity, showed

that the specimens irradiation by (2W) laser is better value.

Its found that the porcelain specimen irradiated by (3W) laser internal

deformation occur inside the specimen, this lead to decrease the micro-

hardness, diametrical strength and density, but when the temperature from

(4,5) Watt laser strike the specimens, its lead to build a glazed surface layer on

the internal deformation which increase the mechanical and physical

properties after irradiation by (3W) laser. Also its found that the specimen

irradiation by (2W) laser is the perfect specimen because of the improvement

of the mechanical and physical properties obtained without internal

deformation occur. Finally Ansys 5.4 programs was used to show the

temperature distribution on the specimens at different laser power density.

III

الخلاصة

.حشوات البورسلينعلى خواص (CO2)دراسة تأثير شعاع الليزر يتضمن البحث

و ) ملم 10*4(قسمت إلى مجموعتين بقياس .عينات من مادة البورسلين) 10( تم تحضير

باستخدام جھاز ليزر ثنائي اوكسيد الكربون ثمانية من ھذه العينات شععت. على التوالي) ملم 10*6(

).ثانية 20(وزمن تشعيع ثابت مقداره ) واط 2,3,4,5(بقدرات

لمعرفة تأثير شعاع الليزر على الخواص الفيزيائية العيناتتلك تفحص بالليزربعد التشعيع

لمعرفة الطور المجھول في العينات والذي تبين إن ھذا باستخدام تقنية الحيود السيني .والميكانيكية

. (Leucite)الطور ھو

وعندما , التشعيع بالليزر د ثلاث قمم متكونة في العينات بعدالأشعة السينية وجوأظھرت نتائج

) اطو 3(وقلت عند القدرة ) اطو 2(عند القدرة شععت باستخدام قدرات ليزر مختلفة نمت ھذه القيم

وعندما تم اختبار الصلادة الدقيقة والكسر ). طوا 4,5(ومن ثم بدأت بالصعود مرة أخرى عند القدرات

أحسنخذت أ) طوا 2(إن العينات المشععة بالقدرة شاھدنا ,والمسامية الكثافة المحوري للقوة واختبار

.قيمة

بقيمة تقليلأدى إلى , حصل بھا تشوه داخلي )اطو 3(لاحظ إن العينة المشععة بالقدرة ن

أدت إلى بناء ) طوا 4,5(لكن الحرارة المتولدة من القدرات لكثافةالدقيقة والكسر المحوري واالصلادة

في العينة مما أدى إلى الصعود التشوه الداخليأي تزجيج التشوه الداخليطبقة رقيقة ملأت

.للعينة ةوالفيزيائي ةبالخصائص الميكانيكي

الميكانيكية ھي الأفضل من جانب الخصائص) اطو 2(ذلك وجد إن العينة المشععة بالقدرة ك

.في العينة تشوه داخليوالفيزيائية والتي تم الحصول عليھا من دون حدوث أي

التوزيع الحراري على العينات عند استخدام قدرات لدراسة(Ansys 5.4) برنامج وأخيرا استخدم

.ليزر مختلفة

Appendix (B) (B-7)

Appendices

Appendix (B) (B-7)

Appendix (A)

Appendix (B) (B-7)

Appendix (B) (B-7)

Appendix (B)

Ansys user Guide.

Can used the following point to operate Ansys 5.4 programs:

1.Operate the programs by press Run, then the programs is ready to work, then

press OK.

2. From Utility menu select File (Change Title), her can be write the project

name, such as (Laser and Porcelain), then press OK.

3. From Main menu select preferences and choice (Thermal), then press OK.

Appendix (B) (B-7) 4. From Main menu select preprocessor and choice (element type, add, solid,

axi-hra 4 node 75), then press OK.

5. From Main menu select preprocessor and choice (material properties,

Isotropic) her we can enter the value of Thermal conductivity, Specific heat,

and Density of specimens, then press OK.

6. From Main menu select preprocessor and choice (modeling, create,

rectangular, by two corners), her can be enter the value of specimens size like

Height and width such as (4*10 and 6*10 mm), then press OK.

Appendix (B) (B-7)

7. From Main menu select preprocessor and choice (mesh tool, mesh, pick

all), then press OK.

8. From Main menu select preprocessor and choice (load, apply, initial

condition, define, pick all), her enter the value of room temperature (300K).

then press OK.

Appendix (B) (B-7)

9. From Main menu select preprocessor and choice (load, Time/Time

frequency, Time-Time stepping) her can be enter the irradiation time (20 sec),

then press OK.

10. From Main menu select preprocessor and choice (load, Apply, Heat flux,

On Line) gives all side of specimens (0) except the top of specimens, then

press OK.

Appendix (B) (B-7)

11. From Main menu select preprocessor and choice (load, Apply, Temperate,

On Node) and select the top side of the specimens and give the difference

temperature effect on the surface like (818.76K, 904.41K, 973.73K,

1028.74K), them press OK.

12. From Main menu select preprocessor and choice (load, New Analysis.

Transit) them press OK.

Appendix (B) (B-7)

13. From Main menu select Solution, Current LS, then if the solution is

correct the programs is gives done commend.

Appendix (B) (B-7)

14. From Main menu select Prostproc, Plot result, Nodal solution, these gives

the temperature distribution figures.

Appendix (B) (B-7)

Chapter One Introduction and Historical Review 1

Chapter One Introduction and Historical Review

1.1 Introduction Since its invention in 1960, the laser has found diverse application in

engineering and industry because of its ability to produce high power beams. In the field of metal processing, laser applications include welding, drilling,

cutting, scribing, machining, heat treatment, cladding and alloying. In other

fields, such as medical surgery, laser are also used extensively [1]. Laser are used in a wide rang of applications, from laser surgery to

marking golf clubs, from welding car parts to drilling holes into baby bottle

nipples. The number and type of applications increase daily [2].

In fact, because of their wide applications, are still stories of success

within materials processing and manufacturing. These developments show

that there is still a huge potential for new beam source, which of course set the

demand for additional system technology developments [3].

Porcelain is a specific type of ceramic. It is made up of white clay

(kaolin), quartz, and feldspar. The ingredients are pulverized, blended, shaped

and finally baked. The porcelain has been playing an important role in

restorative dentistry because they allow efficient restorations with great color

stability and resistance [4].

Porcelain has been used in various forms throughout the centuries.

Although it is impossible to know when porcelain was first used successfully,

the Chinese began working with it as early as the 9th century. Around 1700,

France and, somewhat later, England used refined porcelains for the

fabrications of dinner plates and various artistic objects. In dentistry, it was

Alexis Duchateau, a Parisian apothecary, who first used the material for the

fabrication of denture bases in the 18th century.


Today porcelain plays a vital role in restorative dentistry. Common uses

include full coverage as crowns, inlays and onlays, porcelain bridges,

veneering agent, and porcelain-fused-to-metal restorations [5].

1.2 Review of Literature.

1.2.1 Laser in Dentistry The first experiment with laser in dentistry was reported in study about

the effect of a pulse Ruby laser on human caries (Goldman et al, 1964). The

results of that study showed that the effects varied from small (2-mm) deep

holes to complete disappearance of the caries tissue, with some whitening of

surrounding rim of enamel, indicating extensive destruction of caries areas

along with create formation and melting of dentine. Further work in the 1970

focused on the effects of (Nd: YAG) and (CO2) lasers on dental tissues [6].

During the next few years, dental researches studied possible

applications of this visible laser energy. Dr Leon Goldman a dermatologist

had been experimentally with tattoo removal using the Ruby laser focused two

pulses of the red light on a tooth of his dentist brother in 1965. The result was

painless surface crazing of the enamel. The medical community in the mid to

late 1970 had begun to incorporate lasers for soft-tissue procedures, and oral

surgeons added the technology in the early 1980.

Frame, Pecaro, and Pick cited the benefits of CO2 laser treatment of oral

soft-tissue lesions and periodontal procedures, a portable tabletop model was

made available in 1987, and two years later. Since that time, numerous

instruments have been made available for use in dental Patrice, and more are

being developed [7].

The demand for adult orthodontic treatment has been gradually

increasing. Because many adult patients have porcelain crowns or bridges.

Orthodontists are faced with the problem of bonding brackets onto porcelain


surfaces. Optimal bracket adhesion to a porcelain surface required that

orthodontic forces to be applied without bond failure during treatment and the

porcelain integrity not be jeopardized during the debonding procedure.

Porcelain is not appropriate for orthodontic bonding because of the physical

properties of glazed surfaces and the chemical properties of bonding resins.

Various techniques have been suggested for surface treatment of

porcelain before bonding attachments, including deglazing the porcelain by

roughening the surface with a diamond bur or micro-etching with aluminum

oxide particles and then bonding the brackets with or without coupling agent,

and chemical preparation of the previously deglazing porcelain surface by

etching with orthophosphoric acid (OFA) or hydrofluoric acid (HFA) and then

bonding the brackets with or without coupling agent.

However, previous studies have indicated that sandblasting and acid-

etching with OFA produces in sufficient bond strength for clinical

requirements. Bond strength with hydrofluoric acid etching has been shown to

have clinically acceptable values, but the danger of acid burns must be

considered. Lasers have also been used for processing dental materials

especially for fusing the materials on or onto tooth surfaces. In orthodontic,

various types of lasers Nd: YAG, CO2, and Er: YAG have been suggested for

preparing enamel surfaces for bracket adhesion.

Although, some researches found laser irradiation effective for bracket

adhesion on enamel surfaces, others have not found this action due to the bond

strength, more often; lasers are recommended for debonding orthodontic

brackets. Only a few studies have been performed on the laser treatment of

dental porcelain masses. The CO2 laser is well suited for the treatment of

porcelain materials because its emission wavelength is almost totally absorbed

by porcelain [8].


1.3 Aim of Work The aim of this work is to study the influence of CO2 laser on porcelain

restorative material using different laser powers on the mechanical and

physical properties such as micro-hardness, diametrical strength, degree of

crystalline, density and porosity, study the temperature distribution after

irradiation by different laser powers using Ansys 5.4 programs.

Chapter Two Theory Background 5

Chapter Two

Theory Background 2.1 Laser Applications

Laser can deliver very low power to extremely high power, focused

power with a precise spot size/dimension and interaction/pulse time on to any

kind of substrate through any medium.

Laser is distinguished from other electromagnetic radiation mainly in

terms of its coherence, spectral purity and ability to propagate in a straight

line. As a result, laser has wide applications from very mundane (bar code

scanner) to most sophisticated (3-dimensional holography), mere commercial

(audio recording) to purely scientific (spectroscopy), routine (printer) to

futuristic computer), and life saving (surgery) to life threatening

(weapons/guide). Laser is useful in metrology (length/velocity/ roughness

measurement), entertainment (laser light show), medical diagnostics and

surgery/therapy and optical communication/computation.

From printer to pointer, surgery to spectroscopy, isotope separation to

invisible surveillance and medical to material treatment, laser finds a

ubiquitous presence mainly for some unique combination of properties.

These important properties that justify the use of laser in such a wide

spectrum of applications which are:

Spatial and temporal coherence (i.e., phase and amplitude are unique).

Low divergence (parallel to the optical axis).

High continuous or pulsed power density.

Monochromatic.


Table (2-1) presents a brief overview of the application of laser in

different fields with diverse objective. Though the list is not exhaustive, it

serves to show the diversity of application of laser.

In some applications, the power output is of main concern, e.g. atomic

fusion and isotope separation. Sometimes, the main reason for using laser lies

in its spectral purity and coherence (pollution detection, length/velocity

measurement, interferometer, etc.), low divergence (laser show, pointer/guide,

audio-player), or a combination of all of them (communication, holography,

metrology). Accordingly, a host of lasers capable of delivering a wide variety

of wavelength, energy, temporal/spectral distribution and efficiency have been

developed over the last several decades. Table 2-1 Application spectrum of lasers [9].

By mid 1970 more reliable lasers were made available for truly

practical applications in the industrial applications such as cutting, welding,

drilling and marking. During the 1980 and early 1990 the lasers were explored

for surface related applications such as heat treatment, cladding, alloying,

glazing and thin film deposition.


Table (2-2) summarizes commercially available lasers and their main

areas of application. Depending on the type of laser and wavelength desired,

the laser medium is solid, liquid or gaseous.

Different laser types are commonly named according to the state or the

physical properties of the active medium. Consequently, it have crystal, glass

or semiconductor, solid state lasers, liquid lasers, and gas lasers.

The latter (gas lasers) can be further subdivided into neutral atom lasers,

ion lasers, molecular lasers and Excimer lasers.

The typical commercially available lasers for material processing are

(a) Solid-state crystal or glass laser – Nd:YAG, Ruby.

(b) Semiconductor laser – AlGaAs, and Diode lasers.

(c) Dye or liquid lasers solutions of dyes in water/alcohol and other

solvents.

(d) neutral or atomic gas lasers He:Ne laser, Cu or Au vapor laser.

(e) Ionized gas lasers or ion lasers – argon, and krypton lasers.

(f) Molecular gas lasers – CO2 or CO laser.

(g) Excimer laser XeCl, KrF, etc.

Wavelengths of presently available lasers cover the entire spectral range

from the far-infrared to the soft X-ray [9].


Table (2-2) Commercially available lasers and their industrial applications [9].

Laser Year discovery Commercialized Application

Ruby 1960 1963 Metrology, Medical applications,

inorganic material processing

Nd:Glass 1961 1968 Length and velocity measurement

Diode 1962 1965 Semiconductor processing, bio-

medical applications, welding

He:Ne 1962 Light-pointer, length/velocity

measurement, alignment devices

Carbon

Dioxide 1964 1966

Material processing- cutting/ joining,

atomic fusion

Nd:YAG 1964 1966 Material processing, joining

Argon ion 1964 1966 Powerful light, medical applications

Dye 1966 1969 Pollution detection, isotope

separation

Copper 1966 1989 isotope separation

Excimer 1975 1976 Medical application, material

processing, coloring

The advantages of lasers in industrial applications include:

Lasers do not suffer tool wear. They can cut extremely hard materials,

such as super alloy, diamond, ceramic, etc without being eroded.

Laser can be focused to very small areas, producing high energy

densities exactly where it is needed, without affecting the neighboring

areas of the work piece.

Laser radiation is clean. It does not introduce impurities into the work

piece, it can work in vacuum or in an inert gas environment during the

procedure.


Lasers can be easily (taught) to process two-dimensional or even three-

dimensional parts. That is lasers are fully compatible with computer-

controlled manufacturing.

When used for cutting, lasers can produce clean and sharp edges that

require little or no additional processing.

When used for drilling, lasers can produce small diameter and deep

holes that are otherwise unattainable by conventional tools.

Lasers are compatible with micromachining and nanofabrication, such

as cutting micro-gears, tiny ball bearing, etc up to hard difficult

materials [2 ] .

2.2 Laser Matter interaction When the electromagnetic radiation strikes a surface the wave travels as

shown in Figure (2-1).

Figure (2-1) The phase and amplitude of an electromagnetic ray striking an air/solid

interact and undergoing reflection and transmission[10].

Some radiation is reflected, absorbed, and transmitted. As it passes

through the new medium it will be absorbed according to Beer Lambert law : ZeII β−= 0 ……………….. ……………………………………. (2-1).

The absorption coefficient β, depend on the medium, wavelength of the

radiation and the intensity [10].


2.3 Laser Material Processing The increasing demand of laser in material processing can be attributed

to several unique advantages of laser namely, high productivity, automation

worthiness, non-contact processing, elimination of finishing operation,

reduced processing cost, improve product quality, greater material utilization

and minimum heat affected zone. Table (2-3) shows a general classification of

laser material processing techniques. Table (2-3) Classification of laser material processing [9].

In general, application of laser to material processing can be grouped

into two major classes, (a) Applications requiring limited energy/power and

causing no significant change of phase or state. (b) Applications requiring

substantial amount of energy to induce the phase transformations.


The first category includes semiconductor annealing and etching,

polymer curing, scribing/marking of integrated circuit substrates, etc.

The second type of application encompasses cutting, welding, fusion,

heat treatment, etc.

The average power and efficiency of lasers are not important for the

former category that involves no change in phase or state. Lasers suitable for

this group of applications include, but not limited to, Excimer lasers (KrF,

ArF), ion lasers (Ar+, Kr+), metallic vapor lasers (cadmium, selenium, copper,

gold), semiconductor lasers (gallium aluminum arsenide, etc), and molecular

lasers (CO2, CO, etc).

For the second category, laser power, efficiency and interaction time are

crucial as the processes involved single or multiple phase changes within a

very short time. Because of high energy requirement, for this class of

operations, CO2 and Nd: YAG lasers are practically the only choice [9] .

2.4 Carbon Dioxide Laser The carbon dioxide (CO2) laser is a molecular laser in which molecular

vibrations rather than electronic transitions provide the mechanism for lasing

action [11].

At an infrared wavelength around 10.6 µm, the beam is readily

absorbed by most materials and readily converted into heat. Power outputs

ranging from big (compared to most common lasers, such as He:Ne) to

enormous, with power outputs in excess of 50 kW possible. Even the smallest

lasers output with several watts, enough to burn many materials on contact

with the beam. Aside from high power outputs, the other distinguishes feature

is high efficiency, with typical efficiencies of industrial lasers being over 10%.

These features combine to mark the CO2 laser the defect to standard materials

processing laser, with application including cutting and welding of such

materials as hardened metals and ceramic.


There are a variety forms of CO2 lasers, based on tube design. Many

small lasers resemble any other gas laser. Being a glass tube with two cavity

optics, while larger lasers may resemble an Excimer structure, with long,

transverse electrodes [12].

2.4.1 Lasing Medium CO2 lasers use a mixture of carbon dioxide, nitrogen, and helium in the

approximate ratio 1:2:8, with each gas in the mixture assuming a specific role

in this laser. The quantum system of CO2 laser uses a scheme similar to that of

the He:Ne lasers, in which the pump level for this four-level system is in a

separate species from the lasing atom. Nitrogen (N2) becomes excited with

energy from the discharge and the first vibrational energy level of that

molecular provides a pump energy level that matches very closely the upper

laser level (ULL) in the CO2 molecular (the first asymmetric stretch mode,

001). This is identical to the role of helium in the He:Ne laser. A large

quantity of nitrogen (i.e., a higher percentage that CO2) ensures that CO2

molecules in the ground state are pumped rapidly to the ULL.

Lasing occurs as result of transition between two vibrational energy

levels in the carbon dioxide molecule, the levels resulting from the various

modes of vibrations possible. Transition can terminate at possible lower

levels, as shown in Figure (2-2), with the most common (and powerful)

transitions resulting in the production of radiation at 10.6µm.


Figure (2-2) Energy levels in the carbon dioxide laser [12].

From that level, depopulation take place in a two-step process by with

either lower laser level (LLL) decays to a lower energy state, corresponding to

the bending motion of the molecule (010) and finally, to ground state. The

addition of helium to the gas mixture ensures that CO2 molecules at the LLL

are depopulated quickly required for a sizable population inversion.

Helium also serves to conduct heat from the discharge to the walls of

the tube since helium conducts heat much better than most gases do. This

provides a means of decreasing the thermal population of energy levels of the

CO2 molecule (which lie quit close to ground state), again helping to ensure

that an inversion occurs. As well as (purely) vibration levels, rotational of the

CO2 molecule are responsible for the output of spectrum of this laser, since

rotational levels serve to split each major vibration level into a cluster of

multiple closely spaced levels. As a result, the actual laser output is a series of

closely spaced wavelengths covering the range 9.2 µm. to almost 11µm,

centered around 9.6µm and 10.6 µm. The 10.6 µm transition is a normal CW

laser, for example, consists of over 20 transitions in the wavelength range

10.44 to 11.02 µm. with a diffraction grating added to the cavity for tunability,

the range of outputs makes the laser useful as a source for IR spectroscopy,


water cooling is required for most CO2 lasers not just to remove discharge heat

but also to reduce the thermal population of the lower energy levels, which are

very close to ground level. The output power of most CO2 laser is quit

sensitive to plasma temperature, and a blocked or restricted cooling water line

can easily result in a decrease in output power. To reduce this effect, the laser

system should shutdown when the temperature reach 40 to 50 oC, while the

plasma tube would probably tolerate much higher temperature, laser output

would drop drastically at these temperature. There are two type of CO2 laser

tube (longitudinal and transverse) [12].

2-5 Dental Materials Ceramic defined as a class of inorganic nonmetallic solids that are

subjected to high temperature in manufacture and/or use. A ceramic is

therefore an earthy material usually of a silicate nature and may be defined as

a combination of one or more metals with non-metallic element, usually

oxygen. The atomic bonds in ceramic crystals have both covalent and ionic

characters. These strong bonds are responsible for the great stability of

ceramics and important very useful properties, such as hardens, high modulus

of elasticity and resistance to heat and chemical attacks. On the other hands,

the nature of this bonding creates difficulties for the dental ceramist since all-

ceramic materials are brittle. Ceramics were probably the first materials to be

artificially made by humans and porcelain was a many the first materials to be

the subject of early laboratory research by scientists.

Three basic types of ceramic materials were developed: Earthenware is

fired at low temperature and is relatively porous. Stoneware which appeared in

china in about 100 years BC is fired at a higher temperature than earthenware

which results in both higher strength and also renders the material impervious

to water. The third material is porcelain, which was obtained by fusing white

china clay with china stone to produce white translucent stoneware.


Many attempts at imitating Chinese porcelain were made in Europe in

seven teeth century. Attempts were also made to dispense white clay particles

in glass in the sixteenth century, however these attempts were not able to

simulate the Chinese porcelain.. The introduction into dentistry of the art of

fusing porcelain must be stated as one of the most important and significant

historical developments in dental material science. De cheman’s, all porcelain

dentures were far from the complete answer to full denture fabrications. By

the early 1800, complete porcelain denture has been a abandoned. However,

these all porcelain dentures did stimulate work on the manufacture of

individual porcelain teeth for attaching to a plate of ivory or metal, and were

quite different for earthenware, stoneware and domestic porcelain, as

indicated in Figure (2-3).

Figure (2-3) Relative composition of ceramic products based on feldspar, kaolin and

quartz [23].

Elia Wildman in 1838 was able to formulate much more translucent

porcelain with shades much closer to nature teeth. The commercial

manufacture of porcelain teeth is understood to have commenced in France in

early 1800. The industry was later introduced into America in 1817. Porcelain

teeth were not manufactured in England until 1870.


Amber Tess improved the design of the dental coke burning porcelain

ovens in 1880, using gas , oil and finally the electric furnace was introduced at

the end of the century. Fauchard, (French dentist) is considered the father of

modern dentistry and authors at the second half of the eighteenth century

attempted to use porcelain for dental applications. Their efforts working in the

demanding and potentially destructive intraoral environment were largely

unsuccessful. Ceramic materials are being increasingly as dental biomaterials

in the form of the veneers, crowns, inlays and bridges. The appeal of ceramics

as structure dental materials is based on their esthetics, low density, high

hardness, chemical inertness, and wears resistance. A major goal of ceramics

research and development is to produce stronger, tougher ceramics that are

structurally reliable in dental applications [13].

2.6 Composition of Dental Porcelain The composition of the various types of porcelain is summarized in

table (2-4). Table 2-4 Composite of various types of porcelain [13].

Material Clay (kaolin) silica feldspar Glass

Decorative

porcelain 50 25 25 0

High-fusing

(dental) 5 15 80 0

Low-fusing

(dental) 0 25 60 15


It can be seen that there are considerable difference in composite

between the dental porcelains and decorative porcelain. Indeed the dental

porcelains contain little or more clay and possible would be more aptly

described as a dental glass. Conventional dental porcelain is a vitreous

ceramic based on silica (SiO2) network and potash feldspar (K2O. Al2O3.

SiO2) or soda feldspar (Na2O. AlO2. SiO2) or both, pigments opacifiers, and

glasses are added to control the fusion temperature, sintering temperature,

thermal contraction coefficient and solubility. The feldspar used for dental

porcelains are relatively pure and colorless. Thus pigments must be added to

produce the hues of nature teeth on the color appearance of the tooth colored

restorative materials that may exist in adjacent teeth.

Dental porcelain is produced from a blend of quartz (SiO2), feldspar

(potassium aluminum silicate), sodium aluminum silicate, and other oxides.

The typical composition is given in table (2-5). Table( 2-5) Composition of high, medium and low fusing porcelain [13].

Composition High-fusing Medium-fusing Low-fusing

SiO2 72.9 63.1 66.5

Al2O3 15.9 19.8 13.5

Na2O 1.68 2.0 4.2

K2O 9.8 7.9 7.1

B2O3 - 6.8 6.0

ZnO - 0.25 -

ZrO2 - - -


Although, the actual composition will very depending on the proposed

use of the end products. Dental porcelain is usually received from the

manufacture in powder form, which is mixed with either water or water based

glycerin containing liquid to form a past of workable consistency. The modern

dental materials are in fact basically a borosilicate feldspathic glass. Thus

improved translucency was mainly achieved by the lowering of the kaolinites

content or its complete removal from the composition. This resulted in the

composition moving away from the mullets zone and into the lenzite zone.

“Kerls handbook” of 1907 gives the following mineral composition for

the early dental porcelain developed by Stockton table (2-6). Table (2-6) Mineral composition for the early dental porcelain [13].

Composition Percentage

Feldspar 78.0

Kaolinite 15.3

Potash silicate 4.7

Dehydrated borax 2.9

The average dental porcelain will therefore contain a minimum content

of about 60 percent SiO2. Typical low fusing dental porcelain should rarely be

referred to as dental glass and would have a composition as in table (2-7). Table (2-7) Typically low fusing dental porcelain composition [13].

Composition Weight percent

SiO2 69.36

B2O3 7.53

CaO 1.85

K2O 8.33

Na2O 4.81

Al2O3 8.11


Such as a fluxed glass would have a maturing temperature of 900oC to

930oC.Conventional feldspathic porcelain is composed premature of SiO2

64%, Al2O3 18% with various amount of K2O and Na2O 8-10 % to control

expansion [13].

2.6.1 Silica

Pure quartz crystals (SiO2) are used in dental porcelain, and are ground

to the grain size possible, silica remains unchangeable at the temperature

normally used in firing porcelain, and this contributes stability to the mass

during heating by providing a framework for other ingredients.

The stability of the glass is highly dependent on the silicon-oxygen

lattice and the covalent bonds must not be reduced too much, otherwise,

diversification may arise. The average dental porcelain will therefore contain a

minimum content of the a bout 60% SiO2 [14].

2.6.2 Feldspar

Nature feldspars are mixtures of albeit Na2Al3Si6O16, and orthoclase

K2Al7Si6O16 with free crystalline quartz. These feldspars are never pure and

the ratio of soda (Na2O) to potash (K2O) may very quit considerably. For

dental purposes, high potash content feldspar is generally selected because of

its increased resistance to pyroplastic flow. Feldspar contains oxides of both

potassium and sodium, these break down the Si-O network and thus are

known as glass modifies.

Two desirable consequences result:

1. The softening temperature of the glass is reduced.

2. The coefficient of thermal expansion is increased the manufacture

adjusts the oxide content so that coefficient of thermal expansion of

dental porcelain will be close to the corresponding value for the

alloys used to make the substructure. Extensive breakdown of the


Si-O network may occur, and diversifications results from

crystallization of the glass.

This occurs of porcelain is fired too often, and it is typically associated

with loss of physical properties and appearance [13].

2.6.3 Kaolin

Kaolin is produced in nature by the weathering of feldspar, during

which the soluble potassium silicate is washed out by acid waters. The residue

is deposited in the form of clay. Only the purest clay or kaolin are used in

porcelain [15].

Kaolin gives porcelain its properties of opaqueness and which mixed

with water, it becomes sticky and acids in forming a workable mass of the

porcelain during molding [14].

2.7 Type of Dental Porcelain Dental porcelains are classified according to the firing temperatures.

1. High-fusing 1290 to 1370 oC.

2. Medium- fusing 1090 to 1260 oC.

3. Low- fusing 870 to 1065 oC.

4. Ultra- low fusing < 850 oC.

The medium- fusing and high-fusing types are used for the production

of denture teeth. The low- fusing and ultra- low fusing porcelains are used for

crown and bridged contraction [14].

High- fusing porcelains are considered superior in strength, solubility,

translucency, and maintenance of accuracy in form during repeated firing [15].

The low and medium- fusing porcelains manufactured by a process

called fritting, by which the raw constituents of porcelains are fused,

quenched, and ground back to an extremely fine powder. The powder fuses at

a lower temperature and undergoes no pyrochemical reaction [14].


Low firing temperatures are a definite assistance in the fusion of

porcelain to metal, since the differences in the coefficients of expansion of the

porcelain and metal can be tolerated better at lower temperature ranges [15].

Resent tests of low- fusing products indicate that they are essentially as

strong as the high- fusing types, and their solubility and translucency are

adequate. Some of the ultra-low- fusing porcelains are used for titanium and

titanium alloys because of their low-expansion coefficient that closely match

those of the metals and because the low firing temperature reduces of sag

formation in fixed partial denture frameworks.

Leinfelder in 2000 reported that low-fusing porcelain was developed to

offset the major disadvantages of traditional dental porcelains representing a

major change in direction, one of the basic differences between this

formulation and those that have been used for long periods of time is a

significant type (fincese) versus around 940oC for conventional type. He

mentioned that this 200oC differential has imparted a number of positive

characteristics to the final restorative.

Finesse low-fusing dental porcelain exhibited slightly lower wear

resistance than other porcelains. This could be clinical advantage as its wear

property comes closer to that of enamel [14].

Chapter Three Experimental Parts 22

Chapter three

Experimental parts 3.1 Introduction

This chapter deals with the measurement of a physical properties and

mechanical properties of the prepared specimens experimentally. It includes

specimens preparation methods, irradiation by CO2 laser, crystalline phase

deformation by using X-Ray diffraction technique, degree of crystalline

measurement, the mechanical properties measurement (density and porosity

measurement, micro-hardness, diametrical strength,). Also it would study the

temperature distribution on the surface and inside the specimens of different

laser power density by using Ansys 5.4 programs.

3.2 Specimens preparation method In this project (10) specimens of porcelain were prepare, which are

consists from the following components from Vita company as shown in table

(3-1). Table (3-1) Composition of dental porcelain.

Material Weight percent %

Silica 63

Alumina 17

Boroc oxide 7

Potash (K2O) 7

Soda (Na2O) 4

Other oxide 2


The porcelain powder was mixed with water to form a paste, this paste

divided into (10) specimens, each specimen put by using a syringe (5cc) to

form the final shape which is require.

Figure (3-1) The die

These (10) specimens have a cylindrical shape. These specimens are

moist and have a different dimension, so the dimension of these specimens

must be standardized by using another process to get the required. This

achieved by heating the specimens in a special programmable furnace type

IVOCLAR program X1 as shown in Figure (3-2).

Figure (3-2) The furnace

Putting all the specimens carefully in the furnace and turn ON adjusting

the temperature of the furnace on (600 oC) for a period time (15 min). Turned

OFF the furnace and let the specimens in the furnace to reach the room

temperature gradually.


This process was done to avoid instantiation any crack in the porcelain

specimens and to get a clear and clean surface and standard of all prepared

specimens.

To get a smooth and unique shape a polishing process would done by

using electrical diamond saw. The final shapes of the prepared specimens

which are needed in the project are (4*10 & 6*10 mm).

3.3 Specimens Irradiation by CO2 Laser

The prepared specimens irradiated by transverse sealed CO2 laser with

output (16W), the laser device which is used in this work is shown in Figure

(3-3), type DJG107-1518, input AC 220V, output V: 16kV/120 mA, it has

efficiency 10%.

Figure (3-3) CO2 laser system

Two group of the specimens irradiated by laser. Four specimens having

a dimension of (4*10mm). And four specimens having a dimension

(6*10mm).

Figure (3-4) shows the experimental setting for irradiation by CO2 laser.


Figure (3-4) Experimental setting for CO2 laser

The laser system produce output mentioned above (16W), but in present

work (2-5W) output power would be needed, so the laser system was

calibrated between input current to the laser tube and output power by using

(CO2) power meter device type SJG-100W as shown in Figure (3-5).

Figure (3-5) CO2 Power meter device

Table (3-2) show this calibration.


Table (3-2) Current/power calibration.

Current (mA) Power (W)

1.8 1

2 1.5

2.4 2

2.8 2.5

3 3

3.2 3.5

3.4 4

3.8 4.5

4 5

4.2 5.5

4.6 6

5 6.5

5.2 7

5.4 7.5

5.8 8

6 8.5

6.2 9

6.4 9.5

6.8 10

To get a perfect irradiation the specimens are put at the distance (5cm)

from the laser tube aperture. The laser tube aperture has (10mm) spot size

diameter. This spot cover the entire specimens surface.

Also to achieve a precise alignment between the porcelain specimens

and laser tube aperture.


Figure (3-6) Laser aperture alignment.

After the specimens aligned the CO2 laser device was turned ON the

specimens strikes in different laser power which are (2, 3, 4,5W) respectively,

at a fixed irradiation time which is (20sec).

3.4 Crystalline Phase Deformation by Using X-Ray Diffraction

Technique. The irradiation specimens were tested by using X-Ray device type

LabX.XRD-6000 Shimadzu as shown in Figure (3-7). Four specimens were

tested, (3) of them were irradiated by (2,3,4) Watt laser respectively and the

other one was not irradiated, to compared and show any change in the crystal

structure of these specimens.

Figure (3-7) X-Ray devices


3.4.1 Determination of Crystal Phase Method. In order to Bragg law the diffraction angle which limited the crystal

phase must be measured by using different parameter such as the intensity,

angle of diffraction, and d-spacing.

The angle range is (2θ) from (20-60) degree for all specimens. To get this

range using X-Ray technique for quantitative and qualitative analysis for

unknown crystalline component, then the diffraction mode considered as

idiosyncrasy of material property which limited by.

1. Using (2θ) value for all peaks which appear at diffraction.

2. Calculate the d-spacing for diffraction angle.

Listing each value for d-spacing value and relative intensity for diffraction

line, then considering the maximum value appear in each run as (100%)

intensity.

3. Compare all d-spacing value with higher intensity to know the

crystalline phase by using ASTM files to show the unknown phase is

appeared.

3.5 Degree of Crystalline Procedure To calculate the degree of crystalline, there are many methods that’s

depends on the changing in the physical properties of the matter by

appearance of crystalline of the matter.

The most important method and most available is the X-Ray diffraction

in which the spectrum or mode consist from peaks that produce from the

coherence scattering of the rays from the crystalline level of the specimens.

Assume that the intensity of the X-Ray scattering on radiated porcelain equal

to (Ip ) and (Ix) equal to the intensity of the scattering ray produce from the

non-radiated mode of porcelain, the following relation use to calculate the

percentage of crystalline of the porcelain specimens.


Degree of crystalline of irradiate porcelain from equation [16].

Degree of crystalline %100% ×−

=p

Xp

III

……………………………... (3-1)

3.6 Mechanical Properties Measurements

3.6.1 Micro-Hardness Procedure Hardness not considered as a physical property but as a complex

function of a group of a physical properties shared in different degrees

depends on the testing way and the environment in which the test done.

The basic principle of hardness not understand till now, the general idea

of hardness as a property of metals referred to rigidity and surface constancy

and its resistance to the external factors. In this work the Vickers method was

used which is called (indentation hardness). In Vickers method the top of the

diamond pyramid (that used to produce the indentation) strike the surface of

the porcelain specimens, this will leave identity on the place that strike, in

which its area represent the basic measure of hardness.

The terms hardness according to Vickers method as the exposed load by

(Kg) on the area of contact between diamond pyramid and the surface of the

specimens in (mm2).

Hardness is a key parameter in the choice of ceramic for abrasives, tool

bits, bearings, wear resistant applications, and resistance to particulate erosion

and ballistic impact.

The hardness of a material is related to the material characteristics

which give stiffness and strength. Hardness is an important characteristic of a

material, as it contributes to resistance to erosion/wear processes. At high

temperature, however, engineering alloys become "Softer" and so ceramics

are often used to give wear resistance.


The hardness of a material may be specified in terms of some standard

test involving indenting or scratching of the surface of the material, the harder

a material the more difficult it is to make an indentation or scratch.

Five specimens of dimension (4*10mm) were tested for micro-hardness

procedure. The specimens were tested in digital micro hardness tester HVS-

1000 by harden fixed time at 10 sec as shown in Figure (3-8).

Figure (3-8) Digital Micro-hardness device

Using Vickers method to calculate micro-hardness, considering one

specimen which not irradiated by CO2 laser beam and four specimens

irradiated by CO2 laser beam. These specimens were put in the micro-

hardness device to know the hardness value of each specimen.

3.6.2 Diametrical Strength Procedure. The Five specimens from the previous process were tested for the

diametrical strength. And this measurement will help to compare between the

micro-hardness and diametrical strength test. This test was done by using

Brazilian test device as shown in Figure (3-9).


Figure 3-9 Brazilin test device

Diametrical strength method is plagued by common problem of precise

machining of difficult to machine materials. Loading configuration is an

important fact in the diametrical compression disk; Figure (3-10).

Figure (3-10) Diametrical strength specimen [17].

The stress distribution should be independent of length, provided a

uniform compression stress applied. However, friction stress, as well as non

uniform stresses, ordinarily results at contact points.


The simple theory describing the stress distribution under a uniform diametric

load on a disk-shaped specimen predicts a uniform tension field at the center

of the disk [17]:

(Diametrical strength) DtF

D πσ 2

= ………………………………….……..(3-2).

where F is the applied load (N), D is the disk diameter and t is the thickness of

disk.

The stress field in the transverse direction is highly dependent on the

width of load application and becomes highly compressive the disk test has

therefore been used to attempt to study biaxial stress failure response.

3.7 Density and Porosity Five specimens of dimension (6*10) mm (four of them irradiated by

CO2 laser and the fifth one is not irradiated by CO2 laser ) were performed

density and porosity test.

Bulk density and open porosity are determined by using Archimedes

Method using distilled H2O. The mass of material in air is divided by its

buoyancy (reduction in weight) when suspended in a liquid medium to give a

measurement of density.

The density of a material is:

Density = Mass/ Volume ………………………….…………………….(3-3).

There are three volume expressions in common use:

1. Apparent volume or bulk volume: includes the volume of the solid

component, open pores and sealed pores, determined by the

difference between the soaked weight (S) and the immerse weight

(I) of the soaked piece.

2. True volume: The volume of the solid component only, is determined

by crushing the piece into powder form so that all the pores are

destroyed and using "Density Bottle" method.


3. Apparent solid-volume: The volume of the solid component and

sealed pores only, is obtained from the difference between the dry

weight (D) and the immersed weight (I) of the piece.

The densities and porosity expression are:

Apparent or bulk density (ρb) = mass/apparent volume

= D/S-I ………….……………….......… (3-4).

True density (ρt)= mass/true volume

Apparent-solid (sintered) density= mass/apparent-solid volume

= D/D-I …………………...……….…. (3-5).

Percentage apparent porosity= open pore volume/total volume *100%

A.P% = S-D/S-I *100 …………………………….(3-6).

Total (true) porosity %= 1- ρb/ρt *100 ………………………………….. (3-7).

3.8 Ansys Programs This programs study the different laser power density are used in the

previous testing which converted to the temperature value, and show the

temperature distribution inside and on the surface of specimens. Ansys 5.4

programs was used to show the temperature distribution irradiated by different

power (2, 3, 4, and 5) Watt of the CO2 laser device.

Chapter Four Results and Discussion 34

Chapter four

Results and Discussion 4.1 Introduction

This chapter presents both the calculation performed and the results

obtained. It also presents a discussion of all results obtained in the present

works. This project would concerned on the heat treatment of porcelain by

using CO2 laser at a fixed time and study the change in physical and

mechanical properties due to heat treatment.

This chapter divided into following;

1. Crystallographic Analysis.

2. Mechanical properties.

3. Density and Porosity calculation.

4. Temperature distribution using Ansys 5.4 programs.

4.2 Crystallographic Analysis

From X-Ray diffraction used the crystallographic analysis on tested

specimens which were irradiated by CO2 laser beam on a fixed time for all the

specimens (20 sec), a crystalline phase appear which is a dominate in all the

specimens and this phase called Leucite (KAlSi2O6).

Leucite- potassium alumina- silicate (KAlSi2O6) is the major crystalline phase

in most high-expansion dental porcelains.

Leucite crystalline was naturally occurring in the cubic form. On

cooling there is a phase transition to a tetragonal form.[18]

For dental porcelains this transformation occur between 700-

1300K.[19]

Leucite based ceramic materials are a subject of an extensive scientific interest

in recent year, especially in the field of dental prosthesis.[20]


Used in dental prosthesis in spit of a number of more advantageous

properties of porcelain (hardness, colorfastness, biological tolerance,

resistance to the oral environment, and also durability.[21]

Three peaks appear before the specimen irradiated by laser beam as shown in

Figure (4-1).

Leucite phase

Inte

nsity

I/I

o

2θ degree

Figure (4-1) X-Ray diffraction pattern for specimen without irradiation by laser

beam.


After irradiated the specimen with a (2W) power; these peaks of the

crystalline phase had been grown as shown in Figure (4-2).

Leucite phase

Inte

nsity

I/I

o

2θ degree

Figure (4-2) X-Ray diffraction pattern for specimen irradiation by 2W laser beam.


It’s found that the heat produced from (2W) laser when irradiated the

specimen was the best heat to relax and re-arrangement of the molecules and

atoms of the specimen, so the crystalline phase begin to grow. This heat not

causes re-conversion of the phase.

In (3W) laser these peaks decrease in intensity, because of internal

deformation occurred in the specimen which leads to decrease of the

mechanical properties of the specimens as shown in Figure (4-3).

Leucite phase

Inte

nsity

I/I

o

2θ degree



In (4W) laser these peaks started to grow again as shown in Figure (4-

4).

Leucite phase

Inte

nsity

I/I

o

2θ degree



This grow occur due to glazed on the internal deformation that appear

in (3W) power laser. These results obtained by using comparison between the

value of the diffraction angle and the intensity produced from the X-Ray

diffraction patterns.

The intensities of the peaks also the angles and d-spacing are shows in

Appendix A. It’s found that the angles of (3,4) Watt appear much closed to the

zero watt angles. While the angle that produced from (2W) laser is shifted,

comparing the results, its found that the process of crystal growth of the phase

not continue for long time because of the degree of crystalline lowered due to

relaxation of the crystalline mechanism at power (3W) by producing internal

deformation as shown in Figure (4-5), which shows the relation between

incident power and degree of crystalline.

Plot1

Power (W)

Deg

ree

of c

ryst

allin

e (%

)

0 0.5 1 1.5 2 2.5 3 3.5 460

62

64

66

68

70

72

74

76

78

Figure 4-5 Degree of Crystalline.


The degree of crystalline was calculated from equation (3-1), and listed

in table (4-1). Table 4-1 power and degree of crystalline.

Power (W) Degree of crystalline (%)

0 69

2 75

3 61.5

4 77

The result of the degree of crystalline shows that the higher degree of

crystalline at (4W) laser power and it’s equal to (77%).

Comparison present result with the previous researches (8, 18, 19, and

20), it shows a good agreement; also its found that the present method to

produce the Leucite phase as a perfect and rapid method and without produced

any damage to specimen. Compare it with M. Novotna and J. Maixner [20]

which was take several hours for the heat treatment to achieved this phase,

while the present method achieved this phase in (20 sec) only. Therefore, the

(2W) power laser consider as a best way to achieved the phase in compare

with reference [8,20] which was used different laser power up to (15W), also

its found that this method is best one with (2W) laser.

4.3 Micro-Hardness calculation

Measured the micro-hardness for both types of specimens irradiated by

laser with different powers (2, 3, 4, and 5) Watt and without irradiation to

compare the results and noticed the effects of crystal growth of Leucite phase

on the value of micro-hardness measurements.


The results from micro-hardness test device listed in table (4-2), and

Figure (4-6) shows the relation of laser irradiation on the micro-hardness

testing. Table 4-2 power and micro-hardness.

Power (W) Micro-hardness (HV)

0 580

2 660

3 630

4 663

5 670

Figure (4-6) show that as the values of power density increase the value

of micro-hardness is increased, also notice decrease in micro-hardness value

when used (3W) laser, due to the internal deformation which occurs in the

specimen after increase the value of micro-hardness at (4, 5) Watt caused

glazed in the specimens.

This glazed produced from the effect of the heat on the internal

deformation in the specimen, so its found that the specimen irradiated by (2W)

laser is the best power because of growing of the dominate crystalline phase

with out production of internal deformation and with hardness value near to

the values produced from irradiation of the specimens with (4 and 5) Watt

laser.


Plot1

Power (W)

Mic

ro-H

ardn

ess

(HV)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5580

590

600

610

620

630

640

650

660

670

Figure (4-6) Shows the relation between power and micro-hardness.

4.4 Diametrical strength calculation The results obtained by Brazilian test are the strength of each specimens

which are shown in Figure (4-7).


Plot1

Power (W)

Stre

ngth

(kN

)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 51.1

1.2

1.3

1.4

1.5

1.6

1.7

1.8

1.9

2

Figure (4-7) Shows the relation between power and strength.

The results from strength and diametrical strength listed in table (4-3). Table 4-3 power, strength, and diametrical strength.

Power (W) Strength (kN) Diametrical strength (MPa)

0 1.1 17.5

2 1.6 25.5

3 1.3 20.7

4 1.8 28.7

5 2 31.8


By using equation (3-2) to calculate the diametrical strength from the

strength values as shown in Figure (4-8).

Plot1

Power (W)

Dia

met

rica

l str

engt

h (M

Pa)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 516

18

20

22

24

26

28

30

32

Figure (4-8) Shows the relation between Power and Diametrical strength.

Compare Figure (4-8) with previous test of (3W) laser irradiated, the

specimen give a good similarity and has less value for diametrical strength .

Also the figure show that the value of the diametrical strength after

(3W) laser power is increase. But this is not mean that the specimen become

better, because from the pervious results and the result from this test see that

the power (3W) laser caused internal deformation in the specimen and (4 and


5) Watt laser temperature caused glazed in the specimens covered internal

deformation. And this gazed layer is weak not give a strength to the

specimens, it will be more exposed to break and this will weaken the

mechanical properties of the specimens, so that not choose the higher powers

over (2W) laser, but would considered (2W) laser stroked was the best power

at all.

The Figure (4-9) shows the shape of the specimens after the diametrical

strength was done.

2W 3W 4W 5W

Figure 4-9 Shows the broken specimen after diametrical loaded is applied.

4.5 Density and porosity calculation In this section firstly, calculate the porosity of the specimens which is

irradiated by (2, 3, 4, and 5) Watt laser power. In porosity measurement,

calculate the weight of the specimens when they are dry, soaked and

immersed, the results are shown in table (4-4). Table 4-4 Power and dry, soaked, immersed specimens weight.

Power (W) Dry specimens

weight (g)

Soaked specimens

weight (g)

Immersed specimens

weight (g)

0 1.22 1.25 0.72

2 1.48 1.53 0.88

3 1.34 1.37 0.81

4 1.40 1.43 0.83

5 1.43 1.45 0.87


Equation (3-6) was used to calculate the ratio of porosity listed in table (4-5). Table 4-5 power and apparent porosity.

Power (W) Apparent porosity (%)

0 5.73

2 7.69

3 5.53

4 5.28

5 3.53

Figure (4-10) shows this ratio.

Plot1

Power (W)

App

aren

t Por

osity

(%)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 53.5

4

4.5

5

5.5

6

6.5

7

7.5

8

Figure (4-10) Power and porosity.


The figure show a higher value of porosity at (2W) laser, because of no

internal deformation occur in the specimen. After (2W) laser the value of

porosity is decreased because of the internal deformation occur at (3W) laser

and glazed layer consisting in (4,5) Watt which make the specimens less

porous value.

Porosity is almost present in ceramics prepared by powder compaction

and heat treatment. Porosity is an important parameter to characterize ceramic

microstructures, as are grain size, grain shape and phase arrangement. Since

properties of materials depend on their microstructure, this article will recall

the main features of the porosity effects on the mechanical properties of

ceramics. Specific attention will be paid to technical ceramics and the main

interest will be devoted to thermal shock resistance, which largely determines

the in-service life time of these materials.

After calculate the porosity, apparent or bulk density was calculated by

using equation (3-4), the results were shown in Figure (4-11).

Plot1

Power (W)

App

aren

t or Bul

k Den

sity

(g/c

m3)

2.46

2.44

2.42

2.4

2.38

2.36

2.34

2.32

2.3

2.28

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 52.26

Figure 4-11 Power and apparent or bulk density.


Calculate the apparent-solid (sintered) density by using equation (3-5),

the results were shown in the Figure (4-12).

Plot1

Power (W)

App

aren

t-So

lid (s

inte

red)

Den

sity

(g/c

m3)

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 52.44

2.45

2.46

2.47

2.48

2.49

2.5

2.51

2.52

2.53

2.54

2.55

Figure (4-12) Power and apparent- solid (sintered) density.

The results from power and density test are listed in table (4-6).


Table 4-6 power , apparent or bulk density, and apparent solid density.

Power (W) Apparent or bulk

density (g/cm3)

Apparent- solid (sintered)

density (g/cm3)

0 2.3 2.44

2 2.28 2.47

3 2.39 2.53

4 2.33 2.46

5 2.46 2.55

4.6 Ansys programs calculation

Programs Ansys 5.4 was used to study the temperature distribution on

the surface of the porcelain specimens. Convert the powers that exposed on

the specimens to temperature values in order to use them in the programs and

this done by using the following equation [22].

W=σ T4………………………………………………...………..……….. (4-1).

where W is the power density, σ is the Stefan’s constant which equal 5.67*10-8

W/m2 K4, and T is the absolute temperature.

Calculate the power density for each specimen because it is the power

that exposed on the area specimen (r2π), and convert the power density in the

temperature by using equation (4-1). The result in the table (4-7).

Table (4-7) Power and power density and temperature conversion.

Power (W) Power density (W/m2) Temperature (K)

2 25.48*103 818.76

3 38.27*103 904.41

4 50.95*103 973.73

5 63.69*103 1028.74


To calculate the heat treated by using the programs, listed the values of

the density, thermal conductivity, and specific heat for specimen. The thermal

conductivity and specific heat were choose from standard tables which are

equal [0.07166 (W/m.K) and 578.611 (J/Kg.K)] respectively.

The density is calculated from the previous test, as shown in table (4-6).

The procedure and the Ansys user Guide show in appendix B.

Calculate the temperature distribution of the specimens with dimension

(4*10 mm) which have the same thermal conductivity and specific heat and

have density is 2.48 (g/cm3) from the standard table for all the specimens.

The results of the Ansys programs are show in the following Figures.

Figures (4-13, 14, 15, 16) are the result of (4*10mm) specimens irradiated by

(2, 3, 4, and 5) Watt respectively.

Figure (4-13) Temperature distribution of the specimen of 2W.



Figure (4-17, 18, 19, 20) show that the results of the (6*10mm)

specimen irradiated by (2,3,4, and 5)Watt respectively.

Figure (4-17) Temperature distribution of the specimen irradiated by 2W



Figure (4-19) Temperature distribution of the specimen irradiated by 4W


Figure (4-20) Temperature distribution of the specimen irradiated by 5W.

These Figures shown that the different area divided according to the

value of exposed heat which produced from strike of the laser beam on the

surface of the porcelain specimens. Its also observe that the red area was the

higher thermal area on the specimens surfaces, and this area increased

gradually due to the increase in the incident power that exposed on the surface

of the specimens.

Then a specimen was irradiated it by (10W) laser, which is equal to the

temperature value (1200 K), we observe that the specimen was broken

because the specimen withstand higher temperature and this is indicated that

the porcelain specimen break or crack may occur inside it in higher power

laser as it shown in (3,4,and 5) Watt laser, also (10W) laser the specimen was

break and this will support the present results it can be consider that the (2W)


laser is the best power exposed on the specimen and the rest of the power are

not useful and can not applied in practice.

Figure (4-21) (10W) laser broken the porcelain specimen.

The continually increase in the red area in the programs indicated that

the temperature generate on the surface start to penetrate inside the porcelain

specimens, this effect was useful in case of (2W) laser because this lead to

formation of crystalline phase inside the specimen, but it could explain that

the temperature was useful as we observed in the previous results because the

increased of red area lead to cause internal deformation and weaken in the

mechanical properties also lead to break the specimen as in (10W) laser. All

these results show that the atoms and molecules of the porcelain specimens

not withstand at higher temperature.

Chapter Five Conclusions and Future Works 56

Chapter Five Conclusions and Future Works

5.1 Conclusions The important facts derived from the practical results at this work can

be summarized as follows:

1. The laser surfaces Harding for porcelain material change the physical

and mechanical properties.

2. The CO2 laser is well suited for the treatment of porcelain materials

because its emission wavelength is almost totally absorbed by

porcelain.

3. The value of porosity decreased after irradiation by (2W) laser because

of the glazed layer.

4. By compare powers (2, 3, 4, 5) watt it is noted that the (2W) laser is the

better laser power than other power.

5. For laser Harding on other hand, the surface temperature should be as

high as possible with shortens time to complete the transformation and

to heat a sufficient thick surface layer in a short time. A short time and

high temperature gradients are also required to prevent heating of the

bulk material and avoid break in the porcelain specimens.

6. The specimens irradiated by (3W) laser internal deformation occur

inside the specimen will reduce the mechanical properties of the

material.

7. Ansys 5.4 programs showed effect of temperature distribution

instantaneous from the specimens surface and the temperature penetrate

inside the specimens.

Chapter Five Conclusions and Future Works 57

5.2 Future work A number of future works can be suggested depending on the practical

results of this thesis, these include the following points:

1. Using more than (10) specimens to irradiated by different laser power.

2. Study other laser device with different wavelength which can use in

temperature distribution to show a different influence on the porcelain

specimens.

3. Study the effect of changing irradiation time on the specimen for

different specimens size.

4. Study the surface morphology by using scanning electron microscope

(SEM).

5. Study the penetration depth of heat inside the specimens for different

specimens thickness.

III

CONTENTS

3.4.1 Determination of Crystal Phase Method. 28 3.5 Degree of Crystalline Procedure. 28 3.6 Mechanical Properties Measurements. 29 3.6.1 Micro-Hardness Procedure. 29 3.6.2 Diametrical Strength Procedure. 30 3.7 Density and Porosity. 32 3.8 Ansys Programs. 33

Acknowledgment. I Abstract. II Contents. III List of Figures. V List of Tables. VII List of Abbreviations. VIII List of Symbols. X

CHAPTER ONE : Introduction and Historical Review 1.1 Introduction. 1 1.2 Review of Literature. 2

1.2.1 Laser in Dentistry. 2 1.3 Aim of the Work. 4

CHPTER TWO : Theory Background 2.1 Laser Applications. 5 2.2 Laser matter interaction. 9 2.3 Laser Material Processing. 10 2.4 Carbon Dioxide Laser. 11 2.4.1 Lasing Medium. 12 2.5 Dental Materials. 14 2.6 Composition of Dental Porcelain. 16 2.6.1 Silica. 19 2.6.2 Feldspar. 19 2.6.3 Kaolin. 20 2.7 Type of Dental Porcelain. 20

CHAPTER THREE: Experimental Parts 3.1 Introduction. 22 3.2 Specimens Preparation Method. 22 3.3 Specimens Irradiation by CO2 Laser. 24

3.4 Crystalline Phase Deformation by Using X-Ray Diffraction Technique. 27

IV

CHAPTER FOUR : Results and Discussion 4.1 Introduction. 34 4.2 Crystallographic Analysis. 34 4.3 Micro-Hardness Calculation. 40 4.4 Diametrical Strength Calculation. 42 4.5 Density And Porosity Calculation. 45 4.6 Ansys programs Calculation. 49

CHAPTER FIVE: Conclusion and Future work 5.1 Conclusion. 56 5.2 Future Work. 57 REFRENCES. 58 APPENDICES.

VIII

List of Abbreviations.

AC Alternative Current.

AlGaAs Aluminum Garnet Arsenide.

ArF Argon Fluoride.

Au Gold.

CO Carbon Monoxide.

CO2 Carbon Dioxide.

Cu Copper.

D Dry Weight.

DC Direct Current.

Er:YAG Erbium doped Yttrium Aluminum Garnet.

FSR Free Spectral Range.

FWHM Full Width at Half Maximum.

He:Ne Helium Neon laser.

HFA Hydrofluoric Acid.

I Immersed Weight.

IR Infrared.

K Kelvin.

K2O Potash.

KrF Krypton Fluoride.

LASER Light Amplification By Stimulated Emission of Radiation.

LLL Lower Laser Level.

N Newton.

N2 Nitrogen.

Na2O Soda.

Nd:YAG Neodymium doped Yttrium Aluminum Garnet.

IX

OC Output Coupler. oC. Centigrade Degree

OFA Orthophosphoric Acid.

RF Radio Frequency.

S Soaked Weight.

SiO2 Silicate.

TEA Transversely Excited at Atmospheric pressure.

ULL Upper Laser Level.

UV Ultra Violet.

ρb Bulk Density.

ρt True Density.

X

List of Symbols.

∆υ The FWHM of the Output (Hz).

µm Micrometer.

c Speed of Light (3*108 m/s).

cm Centimeter.

D Specimens Diameter(mm).

F Applied Load (N).

I Incident Power Density (W/m2).

Io Absorbed Power Density (W/m2).

J Joule.

k Thermal Conductivity (W/mK).

kW Kilowatt.

L Cavity Length (m).

M Atomic Mass of atom or molecular.

m Meter.

mA Milliampre.

MHz Megahertz.

mm Millimeter.

q Heat Flux (W/m2).

T Temperature (oC or Kelvin).

t Thickness of Specimens (mm).

V Volt.

W Watt.

z Cross-section area (m2).

β Absorption coefficient.

ε Emissivity.

XI

Κ Boltzmann Constant (1.38*10-23 J/K).

λ Wavelength (µm).

σ Stefan-Boltzmann Constant (5.67*10-8 W/m2 K4).

V

List of Figures

2-1 The phase amplitude of an electromagnetic ray …………. 9

2-2 Energy level in the Carbon dioxide laser. 13

2-3 Relative composition of ceramic products based on feldspar 15

3-1 The die. 23

3-2 The furnace. 23

3-3 CO2 laser system. 24

3-4 Experimental setting for CO2 laser. 25

3-5 CO2 power meter device. 25

3-6 Laser aperture alignment. 27

3-7 X-Ray device. 27

3-8 Digital micro-hardness device. 30

3-9 Brazilian test device. 31

3-10 Diametrical strength specimens. 31

4-1 X-Ray diffraction figure for specimen not irradiate by laser. 35

4-2 X-Ray diffraction figure for specimen ….. 36

4-3 X-Ray diffraction figure for specimen …….. 37

4-4 X-Ray diffraction figure for specimen …… 38

4-5 Degree of Crystalline. 39

4-6 The relation between power and micro-hardness. 42

4-7 The relation between power and strength 43

4-8 The relation between power and Diametrical strength. 44

4-9 The broken specimen when diametrical loaded is applied. 45

4-10 Power and Apparent porosity. 46

4-11 Power and apparent or bulk density. 47

4-12 Power and apparent- solid (sintered) density. 48

VI

4-13 Temperature distribution of the specimen of 2W. 50





4-18 Temperature distribution of the specimen of 3W 53



4-21 (10W) Laser broken the porcelain specimen 55

VII

List of Table 2-1 Application spectrum of laser. 6

2-2 Commercially available lasers and their industrial applications.

8

2-3 Classification of laser material processing. 10

2-4 Composition of various types of porcelain. 16

2-5 Composition of high, medium, and low fusing porcelain. 17

2-6 Mineral composition for the early dental porcelain. 18

2-7 Typically low fusing dental porcelain composition. 18

3-1 Composition of dental porcelain. 22

3-2 Current/power calibration. 26

4-1 power and degree of crystalline. 40

4-2 power and micro-hardness. 41

4-3 power, strength, and diametrical strength. 43

4-4 Power and dry, soaked, immersed specimens weight. 45

4-5 power and apparent porosity. 46

4-6 power , apparent or bulk density, and apparent solid density. 49

4-7 Power and power density and temperature conversion. 49

REFRENCES 58

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Ed, Springer-Verlag Berlin Heidelberg, 1995.

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4. Sinan S. Al Banna “ Effect of the thermal cycling on shear Bond strength of

porcelain fused to titanium and Ni/Cr alloy using shear test (in Vitro study)”

MSc thesis submitted to Collage of Dentistry-University of Baghdad, 2005.

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Association. Vol. 131, June, 2000.

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Sciences, 2006.

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instruments” Dent Clin N Am 84, 2004.

8. Tolog Akova, Oguz Yoldes, M. Serdar Toroglu, and Hakan Uysal

“Porcelain surface treatment by laser for bracket-porcelain bonding”

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November, 2005.

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REFRENCES 59

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16. " للمواد الزجاجية المستخدمة في تثبيت النفايات المشعة ةدراسة الخواص الفيزيائي"كاظم عبد حبيتر

1986الجامعة التكنولوجية -م التطبيقيةرسالة ماجستير مقدمة إلى قسم العلو

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crystallization” European powder Diffraction conference, EPDIC9, 2006.

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development of porcelain restorative material by …

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