The operative management of primary and secondary caries assumes that
all discoloured tissue at the enamel-dentine junction (EDJ) represents
active disease and this is removed to arrest the carious process. Thi
s study aims to establish clinical criteria to differentiate between a
ctive and arrested caries at the EDJ using microbiological assessment
of dentine samples to verify its clinical status. Radiographs were ava
ilable for posterior teeth. Cavities (n = 205) were prepared under rub
ber dam. After gaining access, areas of the EDJ were chosen and assess
ments made of consistency (soft, medium, hard), colour (dark brown, mi
d-brown, pale) and moisture content (wet, dry). Dentine was removed by
using a No. 3 round burr and placed in 1 ml of bacteriological cultur
e broth. This sampling procedure was repeated at the same site once du
ring cavity preparation and again when the cavity was judged as fully
prepared. Samples were vortexed, diluted and cultured to give viable c
ounts of the total anaerobic microflora, mutans streptococci and lacto
bacilli; viable counts were expressed as log10 (CFU per sample +1). Re
sults showed no significant differences between the microflora of prim
ary and secondary caries. The number of bacteria recovered diminished
significantly as cavities were completed. Initial samples from soft an
d wet lesions harboured significantly more bacteria, lactobacilli and
mutans streptococci than samples from medium, hard or dry lesions. Les
ions visible on radiographs harboured more bacteria, including lactoba
cilli and mutans streptococci, while dentine colour was not discrimina
tory. In conclusion, the relevant clinical criteria for the diagnosis
of infected dentine at the EDJ were visibility on radiographs, soft le
sions and wet lesions.