中央牙阜在咬合過程中易發生斷裂或磨耗，造成齒髓組織提早壞死，於是根尖形成不全及明顯的根尖病變陸續產生。故臨床上我們應小心診視，若及早發現，可做預防性治療。若發現時齒髓已壞死，根尖形成不全，甚至有明顯的根尖病變產生時，則須以根尖成形術(Apexification)，建立起根尖的鈣化屏障，以利緻密充填。早期根管的用藥還不進步，對於根尖\"open"的病例，因無法達緻密的充填，只好借助根尖手術，以銀粉做逆充填來解決。近二、三十年來因為氫氧化鈣在臨床上的進一步使用，發現其對根尖成形有很大貢獻，不僅可建立起根尖的鈣化屏障，以利緻密的充填，同時患牙的牙根長度也有增長，且牙本質亦有增厚，以抗咬合力量。故以氫氧化鈣來完成根尖成形術不失為是一很紮實且按步就班的方法。現今因為材料的進步，MTA逐漸取代氫氧化鈣在根尖成形術的角色，但筆者二十幾年來以氫氧化鈣來完成根尖成形術的病例報告，可發現氫氧化鈣在根尖成形術的角色仍不可被忽視。

During mastication, central cusps are very easily fractured or worn out. This usually causes pulp necrosis in the early life. And the apical constriction will not form completely even causing pulpal pathosis. If we can diagnose early in the clinical situation, a preventive treatment can be done with good prognosis. But, when the pulp had become necrotic and the apical constriction was incomplete formed, even with periapical pathosis, using apexification, to build a hard tissue barrier was indicated. In early days, due to lack of proper medicarnent, tor the open-apex cases, periapical surgery with amalgam retrograde filling was the only treatment. During the last twenty to thirty years, Calcium hydroxide was indicated for this treatment due to its ability to build the periapical had tissue barrier hut also its ability to induce root formation and increase the thickness of dentin to resist occlusal force. Now a day, because of the improvement of material science, MTA gradually replaced calcium hydroxide in this aspect and become the most popular treatment in this case. In this case report, the author, with thirty years clinical experience, found that calcium hydroxide still can play an important role in apexificaton that can not he ignorant.