I ll give my point of view on this topic. Its gonna be long, but it might clear some doubts for you and others. Regarding that doubt , should you be repeating the info or not, i ll tell you something , and then its on you to decide whether you wanna repeat or not...
Firstly , SOP is also called PERSONAL statement.. So there are two words among both these abbreviations that would exactly tell you what you need to write... PURPOSE, and PERSONAL .. So this statement, is all about you, and your purpose.. This essay is like you written interview.. They gonna gauge you from what you write, and how you present yourself.. In one to one interview, there are chances that you might not be able to bring out your A GAME, and end up not expressing yourself completely .. And then you might regret that you couldnt tell this, or that interviewer never gave you the chance to discuss this blah blah aspect of you personality ...
So, in nutshell, you need to write all that you think is relevant about you, present yourself in an AWESOME manner, sell yourself... Make them feel that this person has all the qualities you need in a person...
Style of writing, this you can search on google.. Loads of info there, about its presentation, that it should be in a flow , and should be like a story and all that...
Alright, now let me tell you few things about WHAT TO WRITE , stating my examples .. Thing is, everyone has all the three stats with them, nbde,toefl ,and Gpa.. And thats written in you resume as well, and you are sending them the reports..So you dont need to write these again and waste precious words..
So what you need to write is .. Your dedication, your love for dentistry, why did you choose it, the things you did in your life, how do they make you a better dentist , Why should they choose you ... things like that.. For instance.. I am a chess player, and i have won awards... So if i write.. I play chess, and i have won awards.. That is just lame.. If i write " The game of chess, taught me how to analyse, how to work in high pressure situation.This in turn helped me in making decisions and work under pressure in my professional life too" .. Thats just the way of putting the same thing, in a good presentation.... So same thing goes with your professional experience...If you keep on writing i worked there, and then there... here and there... LAME !! Write.. I worked in a private dental clinic after college, that gave me knowledge about how the things are different in private setup ... Then i did observership in Usa , that gave me insight how dentistry is in other part of the world... So same thing, but you have linked WHAT YOU LEARNT FROM IT !!! So make sure whatever you write, you also tell them how it helps you in being a better dentist, how it added onto your personality ..Write your goals, what you wanna achieve, whats in you that makes you better and if possible give a proof of that with a small example or a story or a laurel that you have won !!
.Hope this helped... And make sure, you neva copy a single word from someone else... They are experts, and they have read all ...Dont just risk everything you have done till now, just by copying few lines from someone else and ending your career in a dump !!!

Good luck!!!
thank you goldendoc ..that was indeed helpful . Its quite a task to write a general sop especially when all the details are anyway entered in the other sections of caaipd. Like some suggest that you dont repeat all that info in the sop and some say that its better to.. confusing!