Classification of Dentin Caries based on pH and Acid Profile of Carious Dentin and its Clinical Application

本研究采用高效液相色谱法对龋牙本质和牙菌斑中的有机酸进行了分析。在龋齿本质中，乳酸（平均占总酸的30.7%）和醋酸（平均占36.7%）是我们之前报道的主要酸。而在阻滞型牙本质中检测到大量甲酸盐（平均13.4%）和琥珀酸盐（平均11.2%），而在活跃型牙本质中仅检测到少量甲酸盐和琥珀酸盐。羧酸分析仪和酶法测定了牙本质中甲酸和琥珀酸的含量。龋齿本质中存在大量甲酸，表明具有丙酮酸甲酸裂解酶的细菌生活在被抑制的龋齿病灶中，且病灶内的条件严格为厌氧。在龋齿本质中检测到大量琥珀酸盐，表明产生琥珀酸盐的细菌，如放线菌、拟杆菌、丙酸杆菌和蜘蛛菌，窝藏在被抑制的龋齿病变中。此外，我们比较了龋齿牙本质、覆盖在龋齿病灶上的牙菌斑和同一口腔健康牙齿上的牙菌斑之间的有机酸。长期饥饿后，活跃的龋牙本质和龋损处的牙菌斑都含有大量的乳酸，而正常牙表面的牙菌斑在不摄入糖的情况下几乎没有乳酸。这种差异意味着牙本质龋齿建立了一个稳定的环境，在这个环境中产生的酸不容易被唾液冲走。

In this study, we analyzed organic acids in carious dentin and dental plaque by HPLC. In carious dentin, lactate (mean: 30.7% of total acids) and acetate (mean: 36.7%) were the major acids as we reported previously. However, a high amount of formate (mean: 13.4%) and succinate (mean: 11.2%) were detected in the arrested type carious dentin, although only a little amount of formate and succinate were detected in the active type carious dentin. Formate and succinate in carious dentin were confirmed by Carboxylic Acid Analyzer and enzymatic assay. Existence of high amount of formate in carious dentin implies that bacteria having pyruvate formate-lyase are living in the arrested caries lesions and that the conditions in the lesions are strictly anaerobic. Detection of plenty of succinate in carious dentin indicates that succinate-producing bacteria, such as Actinomyces, Bacteroides, Propionibacterium, and Arachnia, are harboring in the arrested caries lesions. Furthermore, we compared organic acids among carious dentin, dental plaque covered on the caries lesion, and dental plaque on the sound teeth in the same mouth. Both active carious dentin and dental plaque on the caries lesion contained high amount of lactate over after being starved for long time, whereas dental plaque on the sound tooth surface had little lactate without sugar-intake. This difference implies that dentin caries establish a stable environment in which acids were produced are not easily washed away by saliva.