||Addition of upconversion phosphors in dental resin cements to enhance polymerization
||Institute of Oral Medicine
degrees of conversion
現今的光聚合樹脂使用在牙科復形上有數十年的歷史，並應用於假牙所使用的樹脂黏著劑，使其可以經由藍光的照射而固化，以達快速固著的效果。但牙科樹脂黏著劑所面臨問題之一，是透過陶瓷之藍光強度降低，會使樹脂黏著劑聚合不完全，導致微滲透的產生。最近研究顯示，紅外光對陶瓷有較高的穿透性，且本實驗室也發現填加上轉換螢光粉(upconversion phosphors)於樹脂中，紅外光照射可提升牙科複合樹脂的聚合反應率。因此本研究目的是藉由將螢光粉添加於光聚合黏著樹脂，輔以紅外光照射以增加牙科樹脂黏著劑聚合反應程度。研究中將探討不同厚度及種類的陶瓷、不同的藍光-紅外光配合照射方式，對此樹脂黏著劑聚合程度的影響。實驗材料採用近紅外光照射會激發出藍光的上轉換螢光粉，以四部分進行。首先以光譜測量儀測量上轉換螢光粉經激發的藍光波長範圍與強度，以此計算光轉換率。第二部分為測量光透過陶瓷的穿透率，分別製備0.3, 0.5, 0.8, 1.0, 1.5, 2.0mm的二矽酸鋰陶瓷及氧化鋯試片，以藍光或紅外光隔著陶瓷照射，以光強度測量儀測量。第三部分以多光子顯微鏡檢測添加螢光粉樹脂激發與發射光性質，與螢光粒子分布的均勻度。第四部分測量以上轉換螢光粉改質樹脂黏著劑之聚合反應。將樹脂黏著劑透過不同厚度之二矽酸鋰、氧化鋯陶瓷，分別以藍光、藍光加紅外光照射聚合，以微小硬度測試機測量努式硬度(Knoop hardness)。
第一部分結果顯示，紅外-藍光的光轉換率為10.8%。第二部分，紅外光穿透兩種陶瓷0.5mm試片的穿透強度為藍光1.8倍，2 mm 試片穿透強度為藍光1.7 倍；此外，二矽酸鋰陶瓷的光穿透度比氧化鋯高。第三部分，經多光子顯微鏡觀測試片的表面及底部，粒子均勻分布於黏著劑中。第四部分，表面硬度測試結果，單純以NIR照射樹脂60秒無法硬化；但藍光20秒配合紅外光40秒、藍光40秒配合紅外光20秒兩組之表面硬度在不同厚度、不同種類陶瓷中都比單純藍光照射較高；且兩組在陶瓷厚度1.5 mm以上無統計差異。二矽酸鋰陶瓷組的表面硬度比氧化鋯高。本實驗研發的材料及光照技術應用在陶瓷假牙的黏著，黏著的強度及品質預期會有顯著的改善。
Light-cured (LC) composite resins are widely used in dental restorations, and are also applied as luting cements. Dental resin cements are polymerized by blue light irradiation, thus they are easily controlled, and fast cured in a short time. However, the polymerization of resin cements by blue light is hampered by the reduced transmission through the ceramics. Recently research reveals that Infrared (IR) light exhibits high transmission through dental ceramics. Our previous study also showed that the addition of upconversion phosphors (UPs) into LC composites could enhance the degrees of polymerization under NIR irradiation. The purpose of this study is to investigate if the addition of Ups into dental resin cements might enhance polymerization. The specific aims are to examine the thickness and type of dental ceramics, different combinations of blue light and IR, on the new polymerization pathway. The experimental material was Ups which absorbs NIR laser to emit blue light. First, the spectrum and irradiance of NIR laser and blue light emission were measured by a spectrometer. To examine the light transmission through ceramics, transmission of blue light and NIR through two ceramics (lithium disilicate ceramics and zirconia discs) of four thicknesses (0.3, 0.5, 0.8, 1.0, 1.5, and 2.0 mm) were measured by a powermeter. The experimental cement was prepared by adding 5% UPs into LC resin cement (VariolinkⅡA3 base). A multiphoton excitation microscopy was used to examine the excitation and emission lights of Ups and the particle distribution in resin cements. Subsequently, the blended cements were cured under two ceramics of different thickness with four blue light and adjunctive NIR combinations. The microhardness of cured cements was measured by a Knoop hardness test.
The result shows that the NIR-UP conversion rate was 10.8%. NIR light exhibited about 1.8 time transmitted power of BL through both ceramics at 0.5 mm, and 1.7 time of BL power through 2 mm thick ceramics. The lithium disilicate ceramic allowed more light transmission than zirconia did. The UPs particle distributed homogeneously from top to bottom layers of the cement. From the microhardness test, NIR60 did not polymerize the cement to detectable hardness. Both BL40+NIR20 and BL20s+NIR40s showed higher hardness than BL60s did. The lithium disilicate ceramic groups exhibited higher surface hardness than zirconia. When increased NIR irradiation time from 20s to 40s and decreased BL from 40s to 20s, there were no significance difference in surface hardness. The application of this new materials and light curing technique on clinical ceramic cementation well improve the adhesion strength and quality significantly.
List of tables IX
List of figures X
Chapter 1 Introduction 1
1.1 Dental ceramic restorations 1
1.1.1 Classification of dental ceramic materials 2
1.1.2 Lithium disilicate reinforced ceramics 3
1.1.3 Zirconia ceramics 4
1.2 Cementation of dental ceramic restorations 5
1.2.1 Dental resin cement 6
1.2.2 Polymerization of resin cement 8
1.2.3 Problems of insufficient polymerization 11
1.2.4 Light attenuation through ceramics 11
1.3 Near infrared upconverted illumination 14
1.3.1 Near infrared 14
1.3.2 Upconversion phosphors (UP) 14
1.4 Application of UP in dental composite polymerization 15
1.5 Motivation and objectives 17
Chapter 2 Materials and methods 18
2.1. Light source examination 21
2.1.1 Spectrum of light sources and UP-conversion light 21
2.1.2 Light conversion rate 22
2.2. Light transmission through ceramics 24
2.2.1 Fabrication of ceramic disks 24
2.2.2 Measurement of light transmission 25
2.3 Characterization of UP and its distribution in cements 26
2.3.1 UP particle size measurement and characterization 26
2.3.2 Preparation of UP tuned resin cements 27
2.3.3. Distributions of UP particles in cements 28
2.4. Knoop hardness of resin cement through ceramics 29
2.4.1. Effect of light sources 32
2.4.2. Effect of ceramic thickness 32
2.4.3. Effect of different cements 33
2.5. Data analysis 33
Chapter 3 Results 34
3.1 Light source examination 34
3.1.1 NIR-blue light conversion rate 35
3.2 Light transmission through ceramics 35
3.2.1 Light transmission rate with original maximum power 35
3.2.2 Light transmission rate with the same original power 36
3.3 Characterization of UP and its distribution in cements 37
3.3.1 UP particle examination with TEM and EDS 37
3.3.2 UP particle distribution in resin cement examined with Multiphoton Excitation Microscopy 39
3.4 Microhardness test 44
3.4.1 Microhardness of resin cement under lithium disilicate ceramics 44
3.4.2 Microhardness of resin cement under Zirconia ceramics 46
3.4.3 Microhardness of resin cements under lithium disilicate ceramic and zirconia ceramic 47
3.4.4 Microhardness of resin cement compare different light combination 48
3.4.5 Microhardness of UP5 and UP0 resin cement 49
Chapter 4 Discussion 52
Chapter 5 Conclusion 58
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