数列\(\{a_{n}\}\)中，\(a_{1}= \dfrac {1}{2}\)，\((n+1)(na_{n}\cdot a_{n+1}+a_{n+1})-na_{n}=0(n∈N^{*})\)，设数列\(\{ \dfrac {a_{n}}{n+2}\}\)的前\(n\)项和为\(S_{n}\)，则\(S_{n}=\) ______ ．