行政院國家科學委員會專題研究計畫 成果報告

行政院國家科學委員會專題研究計畫 成果報告

口腔中氟離子對金屬矯正裝置之機械與生物學效應研究 (2/2)

研究成果報告(完整版)

計 畫 類 別 ： 個別型

計 畫 編 號 ： NSC 95-2314-B-040-004-

執 行 期 間 ： 95 年 08 月 01 日至 96 年 07 月 31 日 執 行 單 位 ： 中山醫學大學口腔材料科學研究所

計 畫 主 持 人 ： 高嘉澤 共 同 主 持 人 ： 黃翠賢

計畫參與人員： 臨時工：陳易駿、錢弘芝、林靜慧

報 告 附 件 ： 出席國際會議研究心得報告及發表論文

公 開 資 訊 ： 本計畫可公開查詢

中 華 民 國 96 年 08 月 29 日

行政院國家科學委員會補助專題研究計畫期中進度報告

（計畫名稱）

口腔中氟離子對金屬矯正裝置之機械與生物學效應研究

計畫類別：※ 個別型計畫 □ 整合型計畫

計畫編號：NSC 94 －2314 －B － 040 － 016 － 執行期間： 94 年 08 月 01 日至 96 年 07 月 31 日

計畫主持人：高嘉澤 共同主持人：黃翠賢

成果報告類型(依經費核定清單規定繳交)：精簡報告 ※完整報 告

本成果報告包括以下應繳交之附件：

□赴國外出差或研習心得報告一份

□赴大陸地區出差或研習心得報告一份

□出席國際學術會議心得報告及發表之論文各一份

□國際合作研究計畫國外研究報告書一份

處理方式：除產學合作研究計畫、提升產業技術及人才培育研究 計畫、列管計畫及下列情形者外，得立即公開查詢

□涉及專利或其他智慧財產權，□一年□二年後可公 開查詢

執行單位：中山醫學大學

中 華 民 國 九十六年 八 月 十五 日

目錄

中、英文摘要及關鍵詞(keywords)。

中文摘要--- III 英文摘要---V-

Introduction--- 1.

Materials and Methods--- 2.

Result --- 6.

Discussion --- 8.

Conclusion --- 14.

REFERENCES --- 15.

Figure and table --- 21.

中、英文摘要及關鍵詞(keywords)。

中文摘要

口腔是一個複雜的環境，氟化物常被用於預防蛀牙或牙菌斑之發生。金屬矯 正裝置的種類依支架內金屬各種元素含量的不同以及廠牌不同特性的要求而有 差異。本研究第一年目的：比較金屬矯正支架與金屬矯正線於含氟化物下之腐蝕 性速率變化。第二年研究目的；由腐蝕之金屬矯正裝置釋出物（即金屬離子溶 液），對於生物體之生物相容性。第一年研究方法與材料：本研究以不同之矯正 支架與不同尺吋之矯正金屬線經表面處理後，分別以電化學腐蝕方法處理，以不 同之電解液體（人工唾液、含氟溶液）分析其腐蝕之現象；以原子吸收光譜儀分 析經電化學處理後之電解液體其金屬離子釋放量。結果以ANOVA分析，以 Student newman Keul做事後分析比較。結果發現：於極化曲線下矯正支架與矯正 金屬線均會發生腐蝕現象。不同廠牌之金屬矯正支架有不同量之金屬離子釋出。

於pH 4人工唾液與pH3.5 APF條件下鎳離子、鉻離子與鐵離子之釋出量增加 (P<0.05)。於pH4 人工唾液和 pH 3.5 NaF溶液下， NiTi金屬線釋出之鎳離子濃 度較不銹鋼線釋出之鎳離子濃度高(P<0.05).。鉻離子濃度只於pH 3.5 NaF溶液 下，呈現出差異性(P<0.05)。鈦金屬離子只於pH 3.5 NaF溶液下，呈現出差異性 (P<0.05)。第二年研究方法與材料：將金屬矯正支架釋出溶液調整濃度為0.01, 0.1, and 1.0 μ l/ml.分別加入到primary human oral gingival fibroblast (HGF)和 Human osteogenic sarcoma cell line (U2OS )培養皿，以MTT分析細胞之存活 率及觀察細胞之型態變化。結果發現：於pH4條件下，Unitek (p=0.003)和Ormco (p=0.000)之U2OS和HGF細胞存活率有差異性，於pH7條件下，則Unitek (p=0.03) 和Dentaurum(p=0.021) 之U2OS和HGF細胞存活率有差異性。結語：含氟化物之溶 液對於矯正金屬具有腐蝕效應，會將金屬離子釋出。而矯正支架釋出之金屬離子 溶液隨廠牌不同而有不同之細胞毒性反應。後續之研究將可繼續進行該釋出物對 於牙齦之癌性反應，以利了解矯正治療過程中牙齦發炎之機轉。

關鍵詞：金屬矯正支架、金屬矯正線、氟化物、腐蝕效應、金屬離子、

細胞相容性

英文摘要

To prevent the dental caries and maintain the oral hygiene in orthodontic patient, fluoride prophylaxis material is routinely applied on them. The purpose of the first year study was to evaluate the corrosion of orthodontic metals under fluoride solution treatment. The purpose of the second year was to evaluate the cytotoxic effects of four different metal bracket immersion media on primary human oral gingival fibroblasts (HGFs) and one permanent human osteogenic sarcoma cell line (U2OS). Materials and methods: Different brands of metal bracket and different size of metal wire were treated by electrochemical method with various electrolytes. They were acidified NaF, pH4 and pH6.75 artificial saliva. The atomic absorption machine was to analyze the metal ions released from these corrosive electrolytes. In biocompatibility study, Four different metal brackets (Unitek, Tomy, Ormco, and Dentaurum) were immersed in buffer solutions of NaHNO3 (1 mM) with a pH of 4 or 7, as well as artificial saliva.

The concentrations for the experiments were 0.01, 0.1,and 1.0 μ l/ml.Attheend of the period of bracket immersion, morphological observations were conducted using light microscopy. The tetrazolium reduction assay was used to detect the survival rate of the target cells. Data were analyzed by one way analysis of variance (ANOVA), with Student-Newman-Kewul test to detect the difference under p<0.05. Results: the present study showed all test samples existed corrosion under different medium.

Different brands of metal brackets were released different amount of metal ions. In pH4 and pH3.5 NaF solution, Ni ion Fe ions and Cr ion concentrations increased.(p<0.05) In pH4 and pH3.5 NaF solution wire test, Ni ions release higher in NiTi wire than that in stainless steel wire. (p<0.05) Cr ion exist statistic difference on pH3.5 NaF condition. (p<0.05) Similar result existed on Ti ion as in Cr ion group.

(p<0.05) At pH 4, the survival rates of the U2OS cells and the HGFs differed statistically for the Unitek and Ormcogroups. ( P <0.05) At pH 7, the survival rate for the HGFs and the U2OS cells differed statistically for the Dentaurum and Unitek groups ( P <0.05). Conclusion: Fluoride material will corrode the orthodontic metal appliance and release different amount of metal ions. The elute solution will cause the HGF and U2OS cytotoxicity.

keywords:metal bracket, orthodontic wire, fluoride, corrosion, metal ions, biocompatibility, HGF, U2OS

Introduction

In the oral environment, orthodontic attachments are exposed to a number of potentially damaging physical and chemical agents, and such conditions possibly contribute to corrosion of the metal components of appliances.¹ Orthodontic bands, brackets, and wires are universally made of austenitic stainless steel containing approximately 8%~12% nickel and 17%~22% chromium.^2,3 Many studies on the corrosion resistance of metal appliances used for dental orthodontic applications have been conducted.^4-6A previous study demonstrated that metal ions are released from an orthodontic metal bracket at pH 4.⁷A number of studies have also demonstrated that metal ions are released by all dental alloys in vitro and in vivo.^8,9

Orthodontic patients are referred to general dentists for fluoride treatments once every 6 months during the course of orthodontic mechanotherapy. Increasingly, dental gels and resins containing fluoride are being applied to prevent dental caries. Fluoride levels in the oral cavity vary according to the prophylactic treatment. Fluoride levels in toothpastes and mouth rinses can reach 1%, and for eliminating enamel stains, can be close to 2%; these substances have a pH range of between about 3.5 and 7.0.¹⁰ Since the oral environment is particularly favorable for the biodegradation of metal due to its ionic, thermal, microbiological, and enzymatic properties, it can be presumed that to a certain extent, patients are exposed to the products of corrosion processes.¹¹

Nickel is one of the most-common causes of allergic contact dermatitis.¹² The incidence of nickel hypersensitivity within the general population is reported to be as high as 20%~30%, with case reports of nickel hypersensitivity commonplace within the biomedical literature.^12-14 Adverse reactions related to nickel-containing orthodontic devices such as arch wires, brackets, and buckles on headgear devices

have been observed.^15-17 Particularly interesting were two clinical studies which claimed that the use of nickel-titanium arch wires can convert nickel-nonsensitive subjects into nickel-sensitive subjects, with an approximately 20% conversion rate.^18,19

The purpose of the first year study was to evaluate the corrosion of orthodontic metals under fluoride solution treatment. The purpose of second year study was to compare the cytotoxic effects of four different orthodontic metal bracket immersion media on primary human oral gingival fi broblasts (HGFs) and one permanent human osteogenic sarcoma cell line (U2OS).

Materials and Methods

Four major orthodontic wires, namely, 0.016-in (0.41mm) nickel-titanium (NiTi) wire (Unitek, 3M, CA, USA), 0.016 x 0.022-in (0.41 x 0.56 mm) Ni-Ti wire (Unitek, 3M, CA, USA), 0.014-in (0.36 mm) stainless steel wire (SSW) (Unitek, 3M, CA, USA), and 0.016 x 0.022-in (0.41 x 0.56 mm mm) SSW (Unitek, 3M, CA, USA), and four major orthodontic brackets, namely, a Unitek DynaLock twin-torque bracket (Unitek, 3M, CA, USA), Tomy metal base bracket (Tomy Co, Tokyo, Japan), Ormco standard edgewise bracket (Ormco Co., CA, USA), and Dentarum Rickett bracket (Dentarum Co., Germany), were tested in this study. The wires were cut into 50-mm-long specimens. Each sample consisted of five pieces for testing. All materials were cleaned by swabbing with acetone and placing in an ultrasonic container with distilled water for 10 min before testing.

The electrochemical corrosive breakdown of the metal brackets and wires was initiated by applying a method based on Shih et al.'s description.²⁰ Three electrolytes were used in the corrosive reaction. First, artificial saliva (Table 1) containing 0.2%

acidulated phosphate fluoride (NaF; 0.2% NaF + 0.17% H₃PO₄, adjusted to pH 3.5 with lactic acid) was used as the electrochemical corrosive electrolyte and was

maintained at 37 °C. In the second and third cases, the electrochemical corrosive electrolytes were adjusted to pH 4 and pH 6 using lactic acid in artificial saliva. A cyclic potentiodynamic polarization machine was applied from -800 mV in the anodic direction with a scan rate of 1 mV/s after dipping the specimen into the electrolyte for 1 h. Each cyclic potentiodynamic polarization curve was printed out. The global polarization curves were assessed to determine the corrosion and breakdown potentials. One-way analysis of variance (ANOVA) was used to make the comparison with p < 0.05 accepted as showing a statistically significant difference. The Student-Newman-Keuls test was used for multiple comparisons. A scanning electron microscope (SEM) (ABT-150S, Topcon, Tokyo, Japan) was used to observe the surface morphologies of the metal brackets and wires.

Metal ions release analyses

The method was followed our previous study.²¹ Extracts were added to polypropylene tubes containing SS wire or NiTi wire. The solution was analyzed for nickel (Ni), chromium (Cr) and titanium (Ti) ions. Standards were prepared in equivalent solutions to counteract any buffer effects. The pre-treatment and atomization temperatures as recommended by Perkin-Elmer were used in the furnace programs to ensure that linear standard curves were obtained for each element. Each sample was analyzed for all three ions and concentrations, measured as μg/cm², averaged across the five replicates. Results were compared using the one-way analysis of variance (ANOVA). Differences in treatment means were analyzed using the Student-Newman-Keul’stestand wereconsidered to besignificantat

p < 0.05.

Sample preparation

Four different brands of metal bracket were analysed ( Table 1 ). The method of sample preparation followed that of a previous study ( Huang et al. , 2004 ). For each brand, a total of 160 brackets were tested. The brackets were immersed in the relevant

solutions and incubated at a temperature of 37°C for a period of 48 weeks. The buffer solutions included NaHNO 3 (1 mM), with a pH of 4 or 7, as well as artifi cial saliva (Sinphar, Taipei, Taiwan; Table 2 ). The concentrations for the experiments were 0.01, 0.1,and 1.0 μl/ml.

Cell cultures

Human primary gingival fi broblast culture. The research was approved by the ethical

board of Chung Shan Medical University Hospital. Following informed consent, gingival tissues were obtained by excision of premolar gingiva from a 12-year-old female patient undergoing orthodontic treatment. The resultant tissue was cut into 1- to 2-mm 3 sized pieces, washed twice with phosphate-buffered saline supplemented with penicillin (100 U/ml; Sigma Chemical Co., St Louis, Missouri, USA), streptomycin (100 μ g/ml,Sigma Chemical Co.), and placed into 25 cm 3 tissue-culture fl asks. The explants were incubated with culture medium consisting of alpha minimum essential medium (Sigma Chemical Co.), 30 per cent foetal bovine serum (FBS; Sigma Chemical Co.), penicillin (100 U/ml), and streptomycin (100 μ g/ml), at 37°C in a humidified atmosphere of 5 per cent CO 2 in air. When outgrowth cells were observed in the cultures, the medium was replaced twice, sequentially, and the cells were then reincubated until the proliferating cells had reached confl uence.

The cells were detached from the monolayer by brief treatment with 0.02 per cent trypsin/0.04 M ethylenediaminetetraacetic acid (EDTA) and recultured in 100 cm 2 tissue-culture fl asks until confl uent monolayers were again obtained. Cells between the fi fth and the seventh passages were used in the subsequent experiments.

Human osteogenic sarcoma cell culture.

The U2OS cell line (BCRC no. 60187, Food Industry Research and Development

Institute, Taiwan) was used. Briefl y, the cells were cultured in McCoy’smedium (Sigma Chemical Co.) containing 10 per cent FBS and penicillin, streptomycin, and fungizone, and L -glutamine (1 per cent; Sigma Chemical Co.). The cultures were maintained at 37°C in a humidified atmosphere of 5 per cent CO 2 in air. Confl uent cells were detached with 0.025 per cent trypsin and 0.05 per cent EDTA for a period of 5 minutes, following which, aliquots of separated cells were subcultured. Cells were cultivated as monolayers in plastic culture fl asks.

Cell viability test — tetrazolium reduction assay

The tetrazolium reduction (MTT) [3-(4,5-dimethylthiazol- 2-yl)-2,5-diphenyl tetrazolium bromide] colorimetric assay, a measure of succinic dehydrogenase activity, was performed following the method of Mossman (1983) . HGF and U2OS cells were inoculated into 96-well plates (Falcon, Teterboro, New Jersey, USA) at a density of 4 × 10 3 cells per well, and incubated at 37°C, in 5 per cent CO 2 -in-air for a period of 2 days. The cells were then incubated under identical conditions to the above for a further 3 days. Subsequent to incubation, the cells were treated with various concentrations of metal bracketextracts,following which MTT dye(50 μ g/l) was added to each well. The plates were incubated at 37°C, and 5 per cent CO 2 in air for a period of 4 hours. For each well, the degree of light absorbance at 570 nm was then measured using an enzyme-linked immunosorbent assay reader (U2000, Hitachi, Tokyo, Japan). The cell viability results were presented as the ratio (in per cent) of the absorbance at 570 nm in the experimental wells to that detected in the control wells.

Five replicates of each concentration were used for each test. All assays were repeated three times to ensure reproducibility. Statistical analysis was conducted using the SAS program for Unix 6.09 (SAS Institute, Cary, North Carolina, USA) using one-way analysis of variance, with a value of P <0.05 showing statistical difference.

Result

Results of the electrochemical analysis of metal bracket cyclic potentiodynamic polarization curves are shown in figure 1. The corrosion tendencies of different brands of brackets were statistically compared, and the corrosion potential (voltage, mean ± standard deviation) sequence from strong to weak was: Ormco, NaF (-0.451 ± 0.087 V) = pH 4 (-0.438 ± 0.093 V) > pH 6 (-0.324 ± 0.118 V) (F = 4.86, p = 0.016); Unitek, NaF (- 0.412 ± 0.095 V) = pH 4 (0.417 ± 0.192) > pH 6 (-0.082 ± 0.018 V) (F = 11.96,

p = 0.001); Dentaurum, NaF (-0.367 ± 0.069 V) = pH 4 (-0.407 ± 0.081 V ) > pH 6

(-0.286 ± 0.052 V) (F = 4.06, p = 0.045); and Tomy, pH 4 (-0.346 ± 0.063 V) > NaF (-0.271 ± 0.051 V) = pH 6 (-0.256 ± 0.046 V) (F = 4.02, p = 0.046) (Figure 1).

Results of the electrochemical analysis of wires using the cyclic potentiodynamic polarization curves are shown in figure 2. The corrosion tendencies of the different wires are indicated by the corrosion potential (voltage, mean ± standard deviation) sequence from strong to weak: 0.016 x 0.022-in SSW, pH 4 (-0.402 ± 0.101 V) = pH 6 (-0.397 ± 0.189 V) > NaF (-0.09 ± 0.013 V) (F = 10.39, p = 0.002); 0.014-in SSW, pH 4 (-0.425 ± 0.105 V) = pH 6 (0.401 ± 0.101 V) > NaF (-0.121 ± 0.009 V) (F = 20.11, p = 0.000); 0.016-in NiTi, pH 4 (-0.358 ± 0.097 V) = pH 6 (-0.345 ± 0.106 V)

> NaF (-0.126 ± 0.078 V) (F = 9.54, p = 0.003); and 0.016 x 0.022-in NiTi, pH 4 (-0.387 ± 0.095 V) = pH 6 (-0.316 ± 0.102 V) > NaF (-0.067 ± 0.019 V) (F = 21.41, p

= 0.000) (Figure 2).

Results of the SEM morphological observations of the different brands of brackets in different media are shown in figure 3. The bracket surface of all brands of the normal artificial saliva group indicated that surface defects were related to the bracket milling, pickling, or electropolishing procedures performed during the manufacturing process. In the pH 6 group, surface defects were similar to those of

normal artificial saliva group. In the pH 4 group, bracket surface defects and pitting corrosion were observed. In the NaF group, pitting corrosion and defects were similar to those of the pH 4 group.

Results of the SEM morphological observations of the different wires in different media are shown in figure 4. They indicated that the wire surface defects were related to the wire drawing, pickling, or electropolishing procedures performed during the manufacturing process. The wire surface of the normal salivary group, for both the stainless steel and nickel titanium wires, exhibited scratches and pits on the surface (Figure 4a). The surfaces of the nickel-titanium wires immersed in pH 4 and NaF media became rough and pitted because of corrosion. (Figure 4c and d for the 0.016 x 0.022-in NiTi and 0.016-in NiTi groups, respectively) The surfaces of the stainless steel wire groups exhibited scratches and pitting corrosion with pH 4 and NaF treatments (Figure 4).

Corrosive metal ions

The metal bracket release ions were shown in table 2 A to C. The results of atomic absorption analysis of different medium are presented in table 3 A to C. The release of ionic nickel was showed statistical difference in all groups (P<0.05). In pH 6.75 artificial saliva medium, the release of nickel ion was higher from the SSW than from the NiTi (P<0.05). In pH4 artificial saliva medium or pH 3.5 NaF medium, the release of nickel ion was higher from the NiTi than from the NiTi (P<0.05).

Analysis of released chromium ions revealed that there was only difference in pH 3.5 NaF medium group (P<0.05). Analysis of released titanium ions revealed that there was only difference in pH 3.5 NaF medium group (P<0.05).

Morphological observation

The morphology of the cells appeared to have been maintained subsequent to metal bracket immersion media exposure. Cell membranes appeared to be intact with no

obvious damage or apoptosis ( Figures 5 and 6 ).

Cytotoxicity of pH 4 metal bracket immersion media evaluated by MTT assay The dose-response curve showed a dose-dependent increase in toxicity for the Unitek ( P = 0.03) ( Figure 8 ) and Ormco ( P = 0) ( Figure 10 ) groups, but not for the Dentaurum ( P = 0.667) ( Figure 7 ) or Tomy ( P = 0.138) groups ( Figure 9 ). The greatest cell survival rate (in per cent) for the Unitek group was noted at a concentration of 0.01 μl/mlfortheHGF cellgroup (89.48 ± 5.37 percent)while the lowest survival rate was observed at a concentration of1 μ l/mlfortheU2OS cellline (74.76 ± 4.89 per cent). The greatest cell survival rate (in per cent) for the Ormco group was noted at aconcentration of0.01 μ l/mlfortheU2OS cell line (90.32 ± 8.99 per cent) while the lowest survival rate for the HGF cell group was observed at a concentration of1 μ l/ml(69.42 ± 4.77 percent).

Cytotoxicity of pH 7 metal bracket extracts evaluated by the MTT assay

The dose-response curve refl ecting the level of relative cytotoxicity of the metal bracket immersion media appeared Dentaurum ( P = 0.021) and Unitek ( P = 0.03) ( Figure 8 ) groups but not for the Tomy ( P = 0.054) ( Figure 9 ) or Ormco ( P = 0.06) groups ( Figure 10 ). The greatest cell survival rate for the Dentaurum group (110.43

± 8.38 per cent) ( Figure 7 ) was observed at a concentration of 0.01 μl/mlforthe U2OS cell group, while the test cell survival rate appeared to be similar for the other remaining metal bracket groups. The greatest cell survival rate (in per cent) for the Unitek group was observed at a concentration of0.01 μ l/mlfortheU2OS cell group (104.83 ± 10.74 per cent).

Discussion

It has been reported that various brands of new brackets exhibit differences in

corrosion behavior.²²The present results revealed similar findings, i.e., the surfaces of brackets and wires in different media exhibited various degrees of roughness. AISI type 316L austenitic stainless steel alloy is currently used for bracket manufacturing.²³ Stainless steel owes its corrosion resistance property to chromium, a highly reactive base metal. The alloy’s corrosion resistance depends on a passive film, which spontaneously forms (passivation) and reforms (repassivation) in air and under most tissue fluid conditions.²³ Oxygen is necessary to form and maintain the film, whereas acidity and chloride ions can be particularly detrimental to it.²⁴

From the potentiodynamic polarization curves, it is apparent that most brands of metal brackets showed higher corrosion tendencies in the pH 4 and NaF media (Figure 1). It is known that corrosion of orthodontic alloys occurs in the intraoral environment,regardlessofthealloy’smetallurgic structure,and itisalso known that the presence of manufacturing defects may accelerate the process.²⁴The morphologies of the brackets by SEM showed already existing surface defects in the normal artificial saliva group in the present study (Figure 2). In an acidic condition, corrosion in the form of pitting was identified. Just as with Cl⁻ions, fluoride ions (F⁻) may penetrate into the metal/oxide film interface.²⁵ This evidence corresponds with our present results for the NaF group, in that defects and pitting corrosion also existed on the metal bracket surface (Figure 3). As it is known that stainless steel will release nickel ions after corrosion occurs, a disadvantage with stainless steel bracket corrosion concerns patients with allergies to nickel and other specific substances.

From the present results, we recommend that substances with acidic or fluoride contents should be used with caution in patients undergoing orthodontic treatment.

Titanium brackets were found to have reduced pitting and crevice corrosion.²⁵ Replacing stainless steel brackets with titanium ones should be considered.

Surface irregularities observed on the NiTi arch wires may arise from the

manufacturing process.²⁶Thus it was found in the normal salivary group that the NiTi wire surface showed irregularities or roughness in the SEM observations (Figure 4).

The present electrochemical studies indicated that pitting corrosion of NiTi wires occurred in a pH 4 solution. The mechanism of hydrogen penetrating the NiTi wire was proven.²⁷ Acid treatment causes the wire to become brittle, and under stress, the NiTi wire may fracture.²⁷Usually titanium forms several oxides (during passivation, it forms TiO₂, TiO, and Ti₂O₅). The NiTi wire shows increased corrosion resistance.

When Ti is exposed to water, TiO2is expected to form according to the reaction, Ti + 2H₂O → TiO2+ 2H₂. During this reaction, H+ ions are produced, increasing the pH.

The resulting OH^- anions are adsorbed onto the surface, where they create an electrical field for ion migration and subsequent oxide growth.²⁸ This mechanism can explain the present results of SEM morphological observations, as the surfaces of the NiTi wires in the pH 4 group showed defects (Figure 4). The improper acid corrosion of NiTi wires increases the risk of wire fracture under the stresses of orthodontic treatmetn.

Fluoride ions can cause the breakdown of the protective passivation layer that normally exists on titanium and its alloys, leading to pitting corrosion.²⁹In the present study, the NaF corrosion potential was lower than pH 4 or pH 6 on the potentiondynamic curves (Figure 2). This indicates that wires in the NaF medium still corroded, but the corrosion resistance was stronger than that of the NiTi wire in the pH 4 or pH 6 groups. But according to the SEM observations, the NiTi wire corrosion defects in the NaF group were more obvious than those in the pH 4 or pH 6 groups.

That is probably because titanium easily dissolves in hydrofluoric acid [HF] which creates surface defects.³⁰

The present results showed that the surface of the stainless steel wire groups exhibited scratches and pitting corrosion under pH 4 and NaF treatments. This is

similar to reports that 316 stainless steel in an acetic acid solution containing F^-ions showed pitting corrosion.³¹ The mechanism involves penetration of F^- ions into the metal/oxide film interface.²⁹ In the present study, the surfaces of the brackets or wires showed roughness or defects before testing, and the corrosive potentials of stainless steel and nickel titanium were similar. Thus after specimens were treated in the corrosive media, the surface defects became more severe and obvious. These results are the same as other reports.^32,33 The reason might be that metallic materials are not susceptible to corrosion as long as the surface oxide film is intact. But when the breakdown potential of an alloy is reached, the oxide layer dissolves, and surface corrosion and pitting begins.

It was reported that NiTi superelastic alloy exhibits good corrosion resistance in saliva and saline solutions.³⁴ The titanium alloy forms titanium oxide which resists corrosion. Certain nickel-titanium arch wires are manufactured using an ion implantation technique. Nitrogen ions are introduced into the near-surface region of the arch wires in an attempt to reduce the amount of friction occurring between brackets and arch wires. The coating probably also increases the corrosion resistance of the wire. ^35-37 But Yokoyama et al.'s study showed that when stress is applied to NiTi, corrosion can still occur.³⁴

The corrosion resistances of metal brackets and wire were analyzed by electrochemical methods in the present study. Most brands of metal bracket were easily corroded in the NaF and pH 4 environments. Potentiodynamic curves showed that NiTi and stainless steel wires were easily corroded in pH 4 artificial saliva. According to the SEM morphological observations, the bracket and wire surfaces showed defects or pitting corrosion in all tested media. The

extent of surface roughness might influence the friction. How the rough corroded surfaces of brackets and wires influence the orthodontic tooth sliding movement is the next step for further investigation. Care must be exercised when fluoride-containing prophylactic agents are used on orthodontic patients.

Dental materials used in the oral environment are subject to electrochemical and chemical reactions, mechanical forces of mastication, and wear. Since orthodontic metal brackets are typically located proximate to periodontal tissue in the oral environment, it is critical to determine the relative level of biocompatibility of the various metal brackets in such an environment. The previous our study found that metal brackets may corrode in such an oral environment and metal-ion leaching may occur.³⁵ The biologic reaction of the metal bracket extracts is needed to evaluate. The extraction assay described above would appear to be one of the most frequently used methods to investigate the mechanism of intra-oral cytotoxicity in regard to the study of dental materials and their oral environmental interaction³⁶The MTT assay is often used to evaluate the activity of mitochondrial succinic dehydrogenase by measuring the amount of formazan produced by this enzyme.^37,38In present study, we chose this method to evaluate the relative toxicity to tested cells of orthodontic metal-bracket extracts.

Various authors have shown that human primary gingival cells can provide a more-sensitive and discriminating cultured-cell model for the cytotoxic assessment of dental materials than various permanent cell lines originally derived from animal tissue.^39,40 In 1994, Andreotti et al. did note that the resistance to dental material toxicity of normal cells is likely to be greater than that for cell lines,⁴¹ it being suggested that this is due to the high growth-rate conditions in which cell lines are

cultured. In present study we chose the primary cultured gingival fibroblast cell and the U2OS cell line which we believe was a representation of the alveolar bone, in order to detect the biocompatibility of the four different orthodontic metal bracket extracts. Comparing the results for the Ormco HGF group with those for the Ormco U2OS group,thelatter’ssurvivalrate(83.44± 5.38 %) proved to be statistically greater than the corresponding result for the HGF group (p<0.05). Our findings have demonstrated that cells of different origins reveal a different cellular reaction to contact with foreign bodies. From this result, HGF would appear to be more sensitive to Ormco metal-bracket extracts, it revealing similarity to the 1994 findings of Andreotti et al..³⁹

Our previous study revealed that a greater number of metal ions were released into solution from the metal brackets placed in the pH = 4 extract than was the case for the pH = 7 extract.⁴² The present results revealed that HGFs treated with Ormco metal-bracket extract at a concentration of 1μl/ml and at a pH of four reflected the overall lowest cell survival rate (69.42 ± 4.77 %). Interestingly, form our previous study showed that the immersed Ormco metal bracket group was responsible for eliciting the most-substantial nickel concentration of all tested metal bracket groups.

(260.5 ± 17.9µg/ml).⁴² Viewing other studies, it has been revealed that nickel ions present in bracket extracts were able to enter test cells in a number of different ways.^38-40 Essentially, under such circumstances, the nickel ions would bind with several biological compounds, and thus decrease the extent of a number of cellular functions,^43,44 including succinic dehydrogenase activity and protein synthesis.⁴⁴ The higher nickel content of the Ormco metal bracket should be the cause of the detected lowest survival rate for HGF cells exposed to metal-bracket extracts.

The metal bracket fabrication may be welded or brazed together. Since the brazing alloys generally consist of silver and cooper and sometimes palladium. The research showed that brazing alloy is more cytotoxic than stainless steel on gingival fibroblast.⁴⁴ The present result has revealed that for the low concentrations of Tomy metal-bracket extract (0.01 and 0.1μl/ml), under either pH = 4 or pH = 7 conditions, the survival rate for HGF and U2OS cells was greater than 100%, such results suggesting that the Tomy metal bracket actually contributed to a minor exposure-related proliferative response to the test cells. Our previous study revealed that the Tomy metal bracket released lower concentrations of metal ions such as nickel, chromium and copper into the immersing solution than was the case for the Unitek, Ormco and Dentaurum metal bracket.³⁵ Such a result can explain why the Tomy metal bracket was relatively biocompatible with U2OS cells and HGFs.

The morphological changes revealed by the U2OS cells and by HGFs following treatment with the four different metal bracket extracts did not appear to include any obvious cellular alterations. From microscopic observation, there appeared to be no evidence of any apoptotic change or necrosis, neither cell membrane demonstrating any evidence of bulb formation or destruction in the treated cells. The result suggesting that these four types of metal bracket are biocompatible. Further, according to the results obtained from mitochondrial activity and morphology investigations, the four different types of orthodontic metal bracket demonstrated a good biocompatibility with the U2OS cells and HGF.

CONCLUSION

The metal bracket can release the different concentrations of metal ions. The biocompatibility of the four types of metal bracket tested was evaluated using two

kinds of cell. The study demonstrated that cells of different origins exhibit different cellular responses to exposure to metal bracket extracts, although the four kinds of brackets do appear to be biocompatible with HGF and U2OS cells.

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圖 1. 金屬矯正支架於電化學腐蝕試驗—極化曲線圖。

Figure 1.The electrochemical analysis. Polarization curves of metal brackets in pH4, pH6.75 , and pH 3.5 NaF artificial saliva.

Ormco Unitek

Dentaurum Tomy

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4 NaF

pH 6

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4 NaF

pH 6

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4 NaF

pH 6

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4

NaF pH 6

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

圖 2. 金屬矯正線於電化學腐蝕試驗。

Figure 2.The electrochemical analysis. Polarization curves of stainless steel wire and nickel titanium wires in pH4, pH6.75 , and pH 3.5 NaF artificial saliva.

0.016x0022’SSW 0.014’SSW 0.010’SSW

0.016’NiTi 0.016 x 0.022’NiTi

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4 pH 6 NaF

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

NaF pH 6

pH 4

Potentisl(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4 pH 6 NaF

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4

NaF

pH 6

Potential(V)

Current density (A/cm²) NaF

pH6 pH4

1E-9 1E-8 1E-7 1E-6 1E-5 1E-4 1E-3 0.01 0.1 1

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0

pH 4

NaF

Potential(V) pH 6

Current density (A/cm²) NaF

pH6 pH4

圖 3. 金屬矯正支架於電化學腐蝕試驗後經電子顯微鏡（SEM）觀察。

Figure 3. The scaner electron microscope surface morphologic observation of different brands bracket in different medium treatment. A. in normal artificial saliva. B. in pH6.75 artificial saliva. C. in pH 4 artificial saliva. D. in pH3.5 NaF artificial saliva.

B A

Unitek

C D

A B

Tomy

C D

Dentaurum Ormco

B B A

A

C D C D

圖 4. 金屬矯正線於電化學腐蝕試驗後經電子顯微鏡（SEM）觀察。

Figure4 . The scaner electron microscope surface morphologic observation of stainless steel wire and nickel titanium wire in different medium treatment. A. in normal artificial saliva. B. in pH6.75 artificial saliva. C. in pH 4 artificial saliva. D. in pH3.5 NaF artificial saliva.

C D

C D

C D

C D

0.014’SSW 0.010’SSW 0.016 x 0.022’SSW

0.016 x 0.022’NiTi 0.016’NiTi

A B

A B A B

A B A B

C D

Table I. Contents of the artificial saliva.

Company Sinphar Pharm, Taipei, Taiwan Content Sali Lube (Saliva substitute)

Sodium Chloride 0.844 mg Potassium Chloride 1.2 mg Calcium Chloride Anhydrous 0.146 mg Magnesium Chloride 6 H2O 0.052 mg Potassium Phosphate dibasic 0.34 mg Sorbitol Solution 70% 60 mg

Methyl Paraben 2 mg

Hydroxyethyl Cellulose 3.5 mg

表 2A. 矯正支架之原子吸收光譜分析 2A. pH 6.75 AS metalbracket(μg/L)

Ni Cr Fe Co Ti Cu

Dentaurum Mean 38.65 12.98 8.32 1.23 -- 14.34

SD 4.38 2.23 1.26 0.22 -- 2.98

Unitek Mean 56.83 13.13 7.99 0.57 -- 12.77

SD 3.71 1.45 1.12 0.12 -- 3.24

Tomy Mean 45.31 11.98 9.56 0.10 -- 13.13

SD 5.29 2.31 2.95 0.03 -- 2.96

Ormco Mean 86.73 13.86 12.28 0.55 -- 17.96

SD 8.34 2.32 1.37 0.18 -- 3.92

Control 0.28±0.15 0.24±0.13 0.73±0.65 0 -- 0.32±0.13

表 2B. 矯正支架之原子吸收光譜分析 2B. pH 4 AS metal bracket

Ni Cr Fe Co Ti Cu

Dentaurum Mean 82.98 22.78 12.38 3.45 -- 16.60

SD 7.26 4.12 2.93 0.83 -- 2.37

Unitek Mean 102.65 28.96 15.38 1.35 -- 20.32

SD 20.21 7.32 3.21 0.21 -- 2.98

Tomy Mean 129.65 17.89 16.28 1.73 -- 21.28

SD 10.22 8.44 2.98 0.27 -- 3.22

Ormco Mean 289.74 21.76 21.57 2.36 -- 41.27

SD 24.37 7.21 3.19 0.30 -- 6.35

Control 0.28±0.15 0.24±0.13 0.73±0.65 0 -- 0.32±0.13

表 2 C. 矯正支架之原子吸收光譜分析 2C. pH 3.5 APF metal bracket

Ni Cr Fe Co Ti Cu

Dentaurum Mean 201.26 24.32 21.29 2.18 -- 58.39

SD 24.82 0.74 7.28 0.32 -- 9.20

Unitek Mean 130.67 25.23 20.66 0.25 -- 67.35

SD 21.54 2.45 6.90 0.02 -- 14.93

Tomy Mean 153.92 19.65 25.28 1.13 -- 48.32

SD 9.78 1.68 3.76 0.18 -- 11.86

Ormco Mean 372.27 49.83 38.52 2.43 -- 94.37

SD 29.36 2.66 12.19 0.28 -- 13.28

Control 0.28±0.15 0.24±0.13 0.73±0.65 0 -- 0.32±0.13

表 3A. 矯正金屬線之原子吸收光譜分析 3A.pH 6.75 AS metalwire(μg/cm²)

Ni Cr Fe Co Ti Cu

0.016-in NiTi Mean 18.27 -- 0 -- 0 --

SD 3.28 -- 0 -- 0 --

0.016 x 0.022-in NiTi

Mean 20.73 -- 0 -- 0 --

SD 5.43 -- 0 -- 0 --

0.014-in SSW Mean 21.38 12.63 2.73 -- -- 0.92

SD 5.32 5.27 0.26 -- -- 0.01

0.016 x 0.022-in SSW

Mean 26.21 11.27 3.29 -- -- 0.89

SD 5.43 4.47 0.32 -- -- 0.01

0.010 in SSW 38.24 15.21 3.10 -- -- 0.97

8.35 5.48 0.29 -- -- 0.01

Control 0.28±0.15 0.24±0.13 0.73±0.65 -- -- --

表 3B. 矯正金屬線之原子吸收光譜分析 2B. pH 4 AS metal wire

Ni Cr Fe Co Ti Cu

0.016-in NiTi Mean 58.21 -- 0 -- 21.42 0

SD 4.37 -- 0 -- 8.32 0

0.016 x 0.022-in NiTi

Mean 69.27 -- 0 -- 26.73 0

SD 5.49 -- 0 -- 9.28 0

0.014-in SSW Mean 45.32 17.28 3.74 -- 0 2.10

SD 6.43 9.20 0.32 -- 0 0.53

0.016 x 0.022-in SSW

Mean 50.48 21.20 2.82 -- 0 1.18

SD 8.39 11.27 0.29 -- 0 0.47

0.010 in SSW 43.93 29.51 4.21 -- 0 1.92

5.68 10.63 0.10 -- 0 0.55

Control 0.28±0.15 0.24±0.13 0.73±0.65 -- -- --

表 2C. 矯正金屬線之原子吸收光譜分析 2C. pH 3.5 APF metal wire

Ni Cr Fe Co Ti Cu

0.016-in NiTi Mean 63.28 -- -- -- 53.39 --

SD 7.39 -- -- -- 4.56 --

0.016 x 0.022-in NiTi

Mean 73.90 -- -- -- 67.83 --

SD 8.37 -- -- -- 8.47 --

0.014-in SSW Mean 68.38 43.39 21.38 -- -- 2.12

SD 8.87 6.30 5.32 -- -- 0.39

0.016 x 0.022-in SSW

Mean 74.39 37.71 32.19 -- -- 1.95

SD 9.93 4.38 8.34 -- -- 0.27

0.010 in SSW 74.54 49.37 25.31 -- -- 2.38

8.38 6.49 6.38 -- -- 0.41

Control 0.28±0.15 0.24±0.13 0.73±0.65 -- -- --

Figure 5. MTT assay photographs under examining light microscope (200x magnified) showing U2OS cells treated with various concentrations of immersed metal brackets solutions. A. the Dentaurum group, pH4, 1 ul/ml. B. the Dentaurum group, pH7, 1 ul/ml. C. the Unitek group, pH4, 1 ul/ml. D. the Unitek group, pH7, 1 ul/ml. E. the Tomy group, pH4, 1 ul/ml. F. the Tomy group, pH7, 1 ul/ml. G. the Ormco group, pH4, 1 ul/ml. H. the Ormco group, pH7, 1 ul/ml. Cell membranes appeared to be intact and no obvious cell damage or apoptotic body appeared.

B

C

F

H D

A

E

G

Figure 6. MTT assay photographs under examining light microscope (200x magnified) showing HGF treated with various concentrations of immersed metal brackets solutions. A. the Dentaurum group, pH4, 1 ul/ml. B. the Dentaurum group, pH7, 1 ul/ml. C. the Unitek group, pH4, 1 ul/ml. D. the Unitek group, pH7, 1 ul/ml.

E. the Tomy group, pH4, 1 ul/ml. F. the Tomy group, pH7, 1 ul/ml. G. the Ormco group, pH4, 1 ul/ml. H. the Ormco group, pH7, 1 ul/ml. Cell membranes appeared to be intact and no obvious cell damage or apoptotic body appeared.

A B

C

E F

G H

D

Figure 7. The survival rate of the Dentaurum metal-bracket immersion media treated on U2OS and HGF cells. Survival rate (%)= (absorbance of experiment / absorbance of control) X 100%

The survival rate (%) of the Dentaurum brackets pH 4 immersion media tested on HGF.

75.00%

80.00%

85.00%

90.00%

95.00%

100.00%

105.00%

110.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Denaturum brackets pH7 immersion media tested on HGF.

80.00%

85.00%

90.00%

95.00%

100.00%

105.00%

110.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of the Dentaurum brackets pH 4 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Dentarurum brackets pH7 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

Figure 8. The survival rate of the Unitek metal-bracket immersion media treated on U2OS and HGF cells. Survival rate (%)= (absorbance of experiment / absorbance of control) X 100%.

The survival rate (%) of Unitek brackets pH7 immersion media tested on U2OS

cell.

0.00%

50.00%

100.00%

150.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Unitek brackets pH7 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Unitek brackets pH4 immersion media tested on U2OS

cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Unitek brackets pH4 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

0.01 0.1 1

Concentration (ul/ml)

Survivaltrate(%)

Figure 9. The survival rate of the Tomy metal-bracket immersion media treated on U2OS and HGF cells. Survival rate (%)= (absorbance of experiment / absorbance of control) X 100%.

The survival rate (%) of Tomy brackets pH4 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Tomy brackets pH4 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Tomy brackets pH7 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalratre(%)

The survival rate (%) of Tomy brackets pH7 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

Figure 10. The survival rate of the Ormco metal-bracket immersion media treated on U2OS and HGF cells. Survival rate (%)= (absorbance of experiment /

absorbance of control) X 100%.

The survival rate (%) of Ormco brackets pH4 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Ormco brackets pH4 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Ormco brackets pH7 immersion media tested on U2OS cell.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

The survival rate (%) of Ormco brackets pH7 immersion media tested on HGF.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0.01 0.1 1

Concentration (ul/ml)

Survivalrate(%)

(六)計畫成果自評部份，

請就研究內容與原計畫相符程度：內容與計劃大致上相符合 達成預期目標情況：有達到第一與第二年年計畫的 研究目的 研究成果之學術或應用價值：已投稿期刊接受刊登

European Journal of Orthodontics. 2007 29: 198 –203 Angle Orthodontics.2007, 77(2):349-354

綜合評估:

1. 口腔健康含氟預防用品對於矯正患者之裝置會有腐蝕現象出現，使 用時應審慎。

2. 腐蝕之釋出物就目前研究結果發現會對細胞具有毒性，目前尚無證 據顯示會造成人體傷害，值得進一步研究。

3. 如何再改質矯正支架，以減少不必要之物質釋出，仍為可進衣不發 展之方向。

出席國際學術會議心得報告

計畫編號 95-2314-B-040-004-

計畫名稱 口腔中氟離子對金屬矯正裝置之機械與生物學效應研究(2/2)

出國人員姓名

服務機關及職稱 高嘉澤、中山醫學大學口腔材料科學研究所教授

會議時間地點 美國 NewOrleans

會議名稱 第八十五屆國際牙醫學會學術研究大會(85^th General session and Exhibition of the International Association of Dental Research)

發表論文題目 The study of friction force on orthodontic appliance 一、參加會議經過

本屆國際牙醫學會學術研究大會於三月二十一日至三月二十四日於美 國路易斯安那州的紐奧爾良(NewOrleans)舉辦，隨者學校一起參加人員，經 過多次轉機終於到達此二年前才經過災患摧殘的都市，外觀感覺似乎已重建 恢復。此屆大會參與人數也許因為上述原因人數較少，海報展是約有 3000 篇，其中不乏撤回者。口頭報告與專題演講的主題仍是一樣，聆聽人數較往 年減少。另外單獨特別的節目也有人參加。個人挑選有興趣之主題去聆聽，

並與發表者討論。晚上結束時參加姐妹校(UAB)之招待茶會，認識一些新朋 友。

二、與會心得

每年的 IADR 大會是世界上許多國家的口腔醫學方面研究者都來聚會 的會議，主辦單位應已至少八十四次辦理之經驗，大會之秩序與流程順暢，

各項工作者僅然有序，讓參加者感受到尊重與舒適，此會議之辦理直得學 習，以作為日後舉辦國際會議時之重要參考。

大會中最讓人感覺得有趣的還是於海報論文方面展示，可以詳細的與報 告者討論，分享別人的經驗，甚至交個朋友，作為日後交流討論之對象。而口頭 報告則因時間較短，報告完的醫師，隨即消失，不易有太多的收穫。另外會場中 之廠商展示，可以看到新的材料和儀器設備，也可知道當今之發展潮流。隨行中，

有研究生之參與，也趁機給與教導，讓後輩看到世界的脈動，刺激他們的興趣。

此種大會是值得鼓勵有志於於研究的人員參加，除了學術上經驗之交流 外，人際之交流也是參加會議之最大收穫。