Before Going To The Dentist

I had my teeth professionally cleaned today.
Before I went out to go to the dentist, I studied English by talking with someone on Skype. Since I focused exclusively on this for a while, I lost track of time. Then, all of a sudden, I realized that the clock is ticking and I needed to leave.

** This version sounds a bit more natural.

Before Going To the Dentist

I had my teeth professionally [Having it cleaned means professionally done.  Normally we brush or floss our teeth]cleaned today. Before thisI went out to go to the dentist, I studied English on Skype by chatting with a person with whom I can converse in English. Since I concentrated exclusively on it for a while, too much that I lost track of time.__Then, all of a sudden, I realized that the clock the time is ticking away and I have to leave my home.

今日、歯医者で歯のクリーニングをしてもらいました。
歯医者に行く前に、スカイプで英語の勉強をしました。話し相手は、英語で会話をしてくれる方です。話すことに集中し過ぎて時間を忘れてしまっていました。そして、家を出る時間が迫っていることに突然気が付きました。

Before I Go To the Dentist

I had my teeth professionally cleaned today.
Before I went out to go to the dentist, I studied English on Skype with a person with whom I can converse in English. Since I concentrated exclusively on it for a wile, I lost track of time.Then, all of a sudden I realized that the clock is ticking to leave my home.

今日、歯医者で歯のクリーニングをしてもらいました。
歯医者に行く前に、スカイプで英語の勉強をしました。話し相手は、英語で会話をしてくれる方です。話すことに集中し過ぎて時間を忘れてしまっていました。そして、家を出る時間が迫っていることに突然気が付きました。

<<practice2>>

Before Going to the Dentist

I had my teeth professionallly cleaned today. 
Before I went to the dentist, I studied English on Skype by talking with a person with whom I can converse in English. Since I concentrated exclusively on this for a while, I lost track of time. Then all of a sudden, I realized that the time is ticking away and I need to leave.

<<practive1>>

Before Going to the Dentist

I had my teeth cleaned today. Before this, I studied English by chatting with someone on Skype. Since I focused too much that I lost track of time. Then all of a sudden, I realized that the time is ticking away and I have to leave.