Staining from coffee is very superficial, effecting just the biofilm, a thin layer of bacteria which covers the teeth and gums, and doesn't penetrate through the enamel itself.
咖啡的着色是浅表性的，仅仅影响菌膜——覆盖牙齿和牙龈的一个很薄的细菌层，并不能穿透牙釉质。
There were thin gaps or voids in the hybrid layer between the flowable composite resin and the enamel probably leading to marginal leakage and the adsorption of the germs.
封闭剂与牙釉质的粘接面内存在微小孔隙，不排除边缘微渗漏及致龋菌吸附的可能。
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