||Using NIR activated phosphors to enhance polymerization of light-curable dental composites
||Institute of Oral Medicine
degree of conversion
under tooth substances
首先，將螢光粉研磨至1.8、0.5以及0.3 μm大小，分別檢測螢光粉紅外光和經轉換激發光的發光強度。並選用0.5 μm顆粒大小為接下來實驗使用。為評估適當的螢光粉比例，將螢光粉與Z100牙科樹脂以不同的比例混和成3個組別：Z100 (0% 螢光粉)、 UP5 (混和5wt% 螢光粉)及UP10 (混10wt% 螢光粉)進行測試。為檢測不同光照的影響，使用紅外線1至10分鐘或結合藍光照射在UP5上，評估樹脂固化程度。照射方式為將樣品填入模具槽內透過開口照射藍光、紅外光或藍光加紅外光。檢測不同組別在不同深度的微硬度來評估其轉換度，以及檢測其聚合深度和聚合度。接著做溫度分析觀察紅外線對溫度的影響。最後測試樹脂在牙齒的遮蔽下 (牙釉質、牙本質及牙釉質+牙本質雙層體 )，不同光照方式之微硬度測試。
在適當比例的實驗中，UP5/紅外線加藍光這個組別在不同深度有最高的微硬度，而藍光輔助紅外線大約比藍光增加1mm的聚合深度。在不同光照影響中，20秒藍光至少加上5分鐘紅外線才會明顯改變樹脂表面微硬度，且照射10分鐘紅外線後微硬度明顯增加。單純照射紅外光10分鐘表現最低的微硬度。在金屬模具的溫度分析實驗顯示，紅外光會造成2 mm深處溫度上升大約12 oC，4 mm深處大約7.1 oC。 在牙齒模型的溫度分析實驗顯示，紅外光會造成距離樹脂2 mm遠，且2mm深處溫度上升大約16.4 oC。在穿透齒質聚合測試中，牙釉質+牙本質雙層體影響藍色光穿透比牙釉質和牙本質大。不論在牙釉質、牙本質及牙釉質+牙本質雙層體遮蔽下藍光照射600秒顯示最高的微硬度。
Light-curing composite resins have been widely used in restorative dentistry for several decades. Despite the fact of their wide application, there are clinical problems due to limitations of blue light penetration in 2-3 mm depth. Their applications are restricted in cavities exposed to the light source, where layered filling is still required.
The near-infrared light may penetrate tissue deeper than blue light does. A novel resin polymerization reaction has been proposed by adding upconversion phosphor (UP) particles into dental composite and conversion via the excitation of near-infrared light. The purpose of this study is to examine the novel curing pathway of dental composites, and to compare its property of polymerization with traditional light-cured dental composites.
The efficacy of UPs in upconverted luminous intensity of the fluorescence was first characterized. The UP particles were ground into sizes of 1.8, 0.5, and 0.3 μm. The excitation spectra of these UPs were examined, and their mixtures with dental composite were evaluated, thus to determine the proper UP particle size. With the result, 0.5-μm UP was chosen as adjunct filler for further examination. UP was mixed into Z100 microhybrid composites at different conditions to generate three composites: Z100 (0% UP), UP5 (the mixture of 5 wt% UP), and UP10 (the mixture of 10 wt% UP). To examine the effect of curing protocols, UP5 received either 3-10 min NIR irradiation or the combination with BL (BL+NIR), and subsequently received a microhardness test to compare the degree of conversion of composites at different depths. The depths of cure in different composite materials were also evaluated. These materials also received FTIR analysis for degrees of conversion. A temperature analysis was performed to measure the temperature rise during NIR irradiation. Finally, these UP tuned composites were evaluated about their applications to enhance the polymerization under tooth substances (enamel, dentin, and enamel + dentin bilayer).
For the proper UP ratio, UP5/BL+NIR showed higher microhardness at each depth compared to UP10/BL+NIR and Z100. The adjunct NIR increased the depths of cure about 1 mm compared to blue light alone. For the curing protocol, 10-min NIR significantly improved the top microhardness. However, 10-min NIR alone showed the lowest top microhardness. The temperature analysis showed NIR irradiation on UP5 for 10 min raised temperature about 12 oC and 7.1 oC at 2mm and 4mm depth in metal mold. The temperature raised was about 16.4 oC in teeth mold.
For the polymerization under tooth substances, the enamel + dentin bilyaer affected the blue light penetration most compare with enamel and dentin. The BL600 irradiation group was higher than others under enamel, dentin and enamel + dentin bilyaer.
According to these findings, NIR activated phosphors could be a new way to cure the dental composite deeply to enhance the degree of conversion. Accordingly, this study will provide some information for the future development in another direction of the dental composites.
List of figures IX
List of Tables XI
List of Equation XI
Chapter 1 Introduction 1
1.1. Dental composite resins 1
1.1.1. Polymerization reaction of dental composite resin 4
1.1.2. Degree of conversion 6
1.1.3. Problems of dental composite resins 6
1.1.4. Depth of cure 8
1.2. Blue light curing system 8
1.2.1. Problems of blue light curing 10
1.3. Near infrared upconverted illumination 10
1.3.1. Near infrared 10
1.3.2. Upconversion phosphors 11
1.4. Application of UP in curing dental composites 12
1.5. Motivation and objectives 13
Chapter 2 Materials and methods 14
2.1. NIR laser 15
2.2. Upconversion phosphors preparation and characterization 16
2.3. Preparation of UP tuned composite resin 16
2.4. Effect of UP size on composite polymerization. 17
2.5. Effects of irradiation protocol on composite polymerization 20
2.6. Effects of UP ratio on composite polymerization 21
2.6.1. Microhardness at irradiated surface 22
2.6.2. Microhardness along depth 22
2.6.3. Depth of cure 22
2.7. Temperature analysis 24
2.8. Effect of resin degree of conversion through the tooth substances by UP composite. 26
2.8.1. Power decay 26
2.9. Data analysis 27
Chapter 3 Results 28
3.1. Electric current and NIR power relationship 28
3.2. The characteristic of UP 29
3.3. Effect of different UP size on composite polymerization. 32
3.4. Effects of irradiation protocol on composite polymerization 32
3.5. Effects of UP ratio on composite polymerization 33
3.5.1. Microhardness at irradiated surface 33
3.5.2. Microhardness along depth 34
3.5.3. Depth of cure 37
3.6. Temperature analysis 38
3.7. Effect of resin degree of conversion through the tooth substances by UP composite. 40
3.7.1. Power decay 42
3.7.2. Under enamel 42
3.7.3. Under dentin 43
3.7.4. Under enamel + dentin bilayer 44
Chapter 4 Discussions 45
Chapter 5 Conclusions 50
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