How to convert string to SentenceCase

public static string SentenceCase(string text)

{

     string temporary = text.ToLower();

     string result = "";

     while (temporary.Length > 0)

     {

        string[] splitTemporary = SplitAtFirstSentence(temporary);

        temporary = splitTemporary[1];

        if (splitTemporary[0].Length > 0)

        {

           result += CapitaliseSentence(splitTemporary[0]);

        }

        else

        {

           result += CapitaliseSentence(splitTemporary[1]);

           temporary = "";

        }

     }

  return result;

}

private static string CapitaliseSentence(string sentence)

{

    string result = "";

    while (sentence[0] == ' ')

    {

     sentence = sentence.Remove(0, 1);

     result += " ";

    }

    if (sentence.Length > 0)

    {

     result += sentence.TrimStart().Substring(0, 1).ToUpper();

     result += sentence.TrimStart().Substring(1,sentence.TrimStart().Length - 1);

    }

   return result;

}

private static string[] SplitAtFirstSentence(string text)

{

  int lastChar = text.IndexOfAny(new char[] { '.', ':', '\n', '\r', '!', '?' }) + 1;

  if (lastChar == 1)

  {

    lastChar = 0;

  }

   return new string[] { text.Substring(0, lastChar),text.Substring(lastChar,   text.Length - lastChar) };

}