各種牙冠金屬與鈦合金在不同酸鹼度的電化學特性

研究背景：隨著科技技術與材料發展的進步，牙科領域中所使用的金屬材料種類繁多。此外，醫療環境的改善使得國人愈來愈長壽，口腔中的環境也相對的複雜，因此，口中可能出現各種不同時期製作的金屬填補物、牙冠或是植牙補綴物等。在臨床的經驗中，部分病患在各種不同合金與複雜的口腔環境中，口腔黏膜會出現不適的狀況，可能是金屬間之電位不同產生的電位差及口中富含唾液（電解質）而發生的伽凡尼腐蝕現象，因此，金屬間的電化學特性是值得探討的議題。研究目的：除了因各種金屬合金材質而產生的伽凡尼腐蝕外，飲食習慣的不同，口腔中的環境十分複雜，在口腔中的金屬會受到溫度、酸鹼度以及其他因素影響。因此，金屬材料的腐蝕是一個重要的議題，本研究欲探討牙科金屬其材料結構與在不同酸鹼度下的電化學特性，希望能夠提供牙醫師與病患在選擇金屬合金材料的參考依據。研究方法：本研究主要分析四種不同的牙冠合金，高金（金-8.5%鉑-2.6%鈀）、低金（金-24.9%鈀-19.0%銀）、鈀銀（鈀-37.7%銀-8.5%錫）與鎳鉻（鎳-25%鉻-11.5%鉬）合金。利用掃描式電子顯微鏡以及X光繞射觀察合金顯微結構與晶體結構，使用電化學儀器分析在不同酸鹼度下腐蝕特徵，以及利用電位差探討與鈦合金（鈦-5.6%鋁-3.5%釩）間的伽凡尼腐蝕電位。此外，各種金屬材料進行浸泡三個月，模擬分析材料在口腔中置放一段時間後，測試材料硬度變化的差異性。研究結果：經由顯微結構與X光繞射分析顯示，合金均顯示為面心立方結構（FCC），且除了高金合金與鈀銀合金外，其他合金為單相的顯微結構特徵，同時，在所有合金中均發現有鑄造偏析與缺陷的問題。經過浸泡實驗後，高金與鎳鉻合金的硬度有稍微變化的趨勢，而低金與鈀銀合金的硬度則較無變化。在pH= 3~7的環境下，腐蝕電位的結果顯示：高金合金為-0.106~-0.048V、低金合金為-0.177~0.029V、鈀銀合金為-0.046~0.112V與鎳鉻合金為-0.378~-0.150 V，而鈦合金在pH= 7的環境中其腐蝕電位為-0.443V。分析伽凡尼腐蝕電位後，鎳鉻合金在不同酸鹼度的環境下，與鈦合金的電位值均比其他合金小，顯示伽凡尼腐蝕發生的機率較小。研究結論：貴金屬合金在不同的酸性環境中（pH= 3-7）腐蝕電位較基底金屬良好，尤其是合金中鈀元素的比例對於合金在酸性環境下的腐蝕電位有正向的影響性。因此，在口腔環境中，貴金屬合金較適合。若考慮異種金屬伽凡尼腐蝕電位，鎳鉻合金與鈦合金的電位差小，因此發生伽凡尼腐蝕的傾向低，所以鎳鉻合金與鈦合金組合較好。

關鍵字

貴金屬；基底金屬；電化學腐蝕；伽凡尼腐蝕

並列摘要

Background: As technology and material advances, there are many different kinds of dental materials that we can choose. Nowadays, the environment of oral will become more complex as people live more long. Because there will different metal fillings in the mouth at various times. For example, dental crowns or implants. In the clinical, some patients will feel uncomfortable in their oral mucosa under various dental alloys and complex oral environments. The possible reason is not only the potential difference between dental alloys but also the oral is full of saliva (electrolyte) so that cause the galvanic corrosion. Therefore, the issue of electrochemical properties between dental alloys are important. Study objective: Except the potential difference between dental alloys. Dental alloys will be affected by temperature, pH value, and other factors in our mouth. Wherefore, the corrosion problem of dental alloys is very important. In this study is focus on the structures of dental alloys and electrochemical properties of dental alloys under different pH values. Methods: In present study, four different dental alloys: high gold alloy (Au-8.5% Pt-2.6% Pd), low gold alloy (Au-24.9% Pd-19.0% Ag), Pd-Ag alloy (Pd-37.7% Ag-8.5% Sn) and Ni-Cr alloy (Ni-25% Cr-11.5% Mo)are selected. The microstructure and crystal structure of the alloy were observed by scanning electron microscopy and X-ray diffraction. Use electrochemical instruments to analyze the corrosion characteristics under different pH values and the galvanic corrosion potential between titanium alloys (Ti-5.6%Al-3.5%V) by potential difference. Moreover, immersion experiments for analyze hardness changes of alloys, the immersed time is three month. Results: The result of microstructure and X-ray are shown: all alloys are face-centered cubic structure (FCC), and in addition to high gold alloys and palladium-silver alloys, other alloys are single-phase, In the otherh and, there are casting segregation and defects in the all alloys. After immersion experiments, the hardness of high gold and Ni-Cr alloys are slightly changed, but low gold and Pd-Ag alloys does not change. The results of the corrosion potential under different pH values show, high gold alloy is -0.106 to -0.048V, the low gold alloy is -0.177 to 0.029V, the Pd-Ag alloy is -0.046 to 0.112V and the Ni-Cr alloy is -0.378 to -0.150V, and titanium alloy is -0.443 V in a pH 7.The corrosion potential of galvanic, the potential difference of the Ni-Cr alloy and the titanium alloy is smaller than that of other alloys under different pH values, indicating that the potential of cause the galvanic corrosion is small. Conclusions: The corrosion potential of noble alloys are better than base metal alloy under different pH values. Moreover the content of the palladium in the alloy has a positive influence on the corrosion potential under the acidic environment. Therefore, in the oral environment, noble alloys are more suitable to apply in dental alloys. In the other hand, considering the galvanic corrosion, because the potential difference between the Ni-Cr alloy and the titanium alloy is the smallest, the potential of cause the galvanic corrosion is small. Therefore, Ni-Cr alloy is a better alloy with titanium alloy.