In this article by Gerassimos Angelopoulos, an orthodontist in Greece, the issue of missing second premolars and the management of the retained deciduous molar is discussed and the relative advantages and disadvantages of each are outlined but not entirely addressed. In my experience retention of the primary molar is a realistic option which obviously depends on the tooth's restorative status and how it relates to the occlusal plane. Where infraocclusion is significant enough to result in an increased chance of caries then extraction may need to be seriously considered. Where the tooth is at an acceptable level in the absence of ankylosis the occlusal surface can be restored to maintain contact with the opposing unit. If the deciduous tooth is extracted resin bonded bridges or implants may be an option if space closure is not possible. Alternatively the patient may just be happy with having a space there with no further elective treatment ! Much a dentists head has been scratched on hypodontia clinics thinking about what the best option may be.
Have a read of an orthodontists view.
Angelopouos on the missing second mandibular premolar
Have a read of an orthodontists view.
Angelopouos on the missing second mandibular premolar