
\documentclass[8pt]{extarticle}
  \usepackage[width=6cm]{geometry}
  \usepackage{titletoc}
  \usepackage[frenchb]{babel}
  \pagestyle{empty}

\newcommand*{\subsectionbreak}{\space}
\titlecontents*{subsubsection}[2.1cm]
    {$\bullet$\space \itshape\small}{}{}
    {,~\thecontentspage}[ --- ][]

\begin{document}
\tableofcontents

\section{s1}
  \subsection{s2}
    \subsubsection{s3}
    \subsubsection{s4}
    \subsubsection{s5}
    \subsubsection{s6}
  \subsection{s7}
    \subsubsection{s8}
    \subsubsection{s9}

\section{s10}
    \subsubsection{s11}
    \subsubsection{s12}

\end{document}
