"Opaque and transparent dentin in connection with caries" by Bernhard Gottlieb (1947)

Berhard Gottlieb (former professor of Oral Pathology, Baylor University College of Dentistry, Dallas, USA), on his book "Dental Caries: its etiology, pathology, clinical aspects and prophylaxis" (Lea & Febiger: Philadelphia, 1947), one of the founders of oral histology, wrote some notes (on page 158) on translucent (called transparent) dentin related to caries:

Reference 7 cited is Applebaum E, Hollander F, Bodecker C (1933). Normal and Pathological Variations in Calcification of Teeth as Shown by the Use of Soft X-rays. Dent Cosmos 75: 1097–1105. Grenz rays is the early term used to describe micro-radiography of teeth (first performed at Columbia University, NY, USA) at that time.

   Gottlieb also provides in his book some images of transparent dentin under transmitted light microscopy and micro-radiography.