變異鏈球菌於牙齒表面產生牙菌斑生物膜是導致蛀牙的主因，蛀牙之症狀輕則感覺疼痛，重則引起齒髓發炎，甚至發生蜂窩性組織炎，危及生命，目前傳統口腔滅菌方式如：漱口水之使用，會產生異味、造成牙齒染色、刺激口腔黏膜等缺點。因此，本研究希冀探討微電漿系統應用於口腔滅菌之可行性，因其屬於安全且較少刺激性之替代處理方式。
本實驗以射頻電源供應器作為毛細管式微電漿系統的激發源，使用功率為23 W，氬氣為主要激發氣體，氣體流量為15 L/min。為了應用於口腔使用，調控參數使電漿溫度低於37℃，於電漿激發過程中，以光學放射光譜儀即時監控電漿激發物種變化，如：NO、OH、O、Ar。處理標的有游離變異鏈球菌及生物膜中變異鏈球菌，並探討改變工作距離及處理時間之滅菌效果。在處理後，於掃描式電子顯微鏡下觀察其細菌形貌的變化及利用螢光顯微鏡即時觀察細菌活性。
由OES光譜分析中，距電漿噴口處越近，如：3 mm，其電漿內的物種較多，實驗結果顯示對於游離變異鏈球菌經30 sec電漿處理可達成滅菌；對於24及48 hours之生物膜經300 sec電漿處理分別可減少3.89及3.7個log CFU/mL。當工作距離延長至9 mm時，電漿內物種減少，導致滅菌效果下降，對於游離變異鏈球菌達滅菌時間須延長至120 sec；對於24及48 hours生物膜經300 sec電漿處理可減少菌落數降為2.88及2.89個log CFU/mL。電漿處理後之試片，經由SEM觀測，可看出細菌表面產生凹洞、甚至破碎之趨勢；螢光顯現紅色也代表細菌死亡。此結果顯示，本實驗裝置可以有效破壞細菌，使其呈現破碎狀態。
在本研究中，生物膜由於具有胞外基質可保護細菌及分散電漿物種，使滅菌成效下降。即使延長十倍處理時間至300 sec仍未達到滅菌，但藉由縮短工作距離及延長處理時間，可有效提升滅菌效率。本實驗證實電漿中反應性物種對於生物模是滅菌的主要因子，而電漿產生之UV光照射只能殺死表層細菌，因此，UV光並非主要滅菌因子。

Sreptococcus mutans is a significant cariogenic bacteria which would produce dental plaque on dental surface. The symptons of dental caries may lead to toothache, tooth pulp inflammation, even fatal cellulitis. The disadvantages of conventional methods for oral sterilization (eg., Chlorhexidine or Listerine mouthwashes) included producing peculiar smell, tooth staining, or oral mucosa irritation. Therefore, we wanted to discuss the possibility of micro-plasma systems for oral sterilization, because plasma was a safe and less aggressive alternative treatment way.
In this study, we used radio frequency power supply (23 W) to generate atmospheric pressure argon micro-plasma, the gas flow rate was 15 L/min. For oral usage, the plasma temperature was controlled to smaller than 37℃. In addition, we also used optical emission spectroscopy (OES) to detect the excited species (eg., NO, OH, O, and Ar) during plasma excitation process. The planktonic bacteria and biofilms containing specimens were exposed to micro-plasma for different exposure time and various working distances. After treatment, we evaluated the sterilization efficiency and observed the morphological change of the bacteria by a scanning electron microscopy (SEM). In addition, we also used fluorescence microscopy to observe bacterial viability immediately after the sterilization.
From OES spectroscopy, as working distance decreased to 3 mm, the excited species in micro-plasma increased. For this reason, it just took 30 sec to achieve sterilization for planktonic bacteria；for biofilms of 24 and 48 hours, it could reduce 3.89 and 3.7 log CFU/mL after 300 sec plasma treatment. As working distance increased to 9 mm, the micro-plasma excited species decreased, so the sterilization efficiency decreased. For planktonic bacteria, the sterilization time must extended to 120 sec；for 24 and 48 hours biofilms, it could only reduced 2.88 and 2.89 log CFU/mL. Based on SEM images, the bacteria appeared concaves or broken into debris after micro-plasma treatment；the red fluorescence also showed bacteria dead. These results showed our micro-plasma could destroy bacteria effectively.
In this study, biofilms had extracellular polymeric substances that could protect bacteria and disperse plasma excited species, so the sterilization efficiency decreased. Even we extended tenfold treatment time to 300 sec, it still could not achieve sterilization. If we decreased working distance and extended treatment time, it could promote sterilization efficiency. This study confirmed that plasma reactive species was main sterilization factors for biofilms. Plasma induced UV radiation could only kill surface bacteria, so plasma induced UV was not main sterilization factors for biofilms.

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