Reliable phonetic tests are preferred and carried out with an emphasis on “ch”, "s" and “j” sounds - indicators of an average speaking space - enunciated accurately and repeatedly. If the distance between the teeth during sibilant sounds is too large, a shorter VDO is present; while contacting anterior teeth or clicking suggests a VDO that is probably too big. Phonetic tests are particularly effective when old dentures are modified with treatment liners in order to recover/establish an optimal VDO.