Center v-toolbar-title

Add a v-spacer before the title

<v-spacer></v-spacer>
<v-toolbar-title class="white--text">{{title}}</v-toolbar-title>

A more complex alternative would be to use the grid layout with flex spacing

<v-toolbar dense dark color="teal" class="pa-0">
  <v-row>
    <v-col cols="2">
      ...
    </v-col>
    <v-col class="d-flex justify-space-around">
      <v-toolbar-title class="white--text">{{title}}</v-toolbar-title>
    </v-col>
    <v-col cols="2" class="d-flex justify-end">
      ...
    </v-col>
</v-toolbar>

In my case, I had only <v-toolbar-title>, so I had to put <v-spacer /> both on the right and left of it:

<v-toolbar>
  <v-spacer />
  <v-toolbar-title>
    Some title text
  </v-toolbar-title>
  <v-spacer />
</v-toolbar>