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ETIOLOGY OF DENTAL IRREGULARITIES. 695

laterals. Examination gave no indication of delayed teeth, but the
result of the .r-rav (Fig. 613) showed the laterals high up in the
process still only partly developed. It was several months later
before there were any indications of the laterals making their appear-
ance. Fig. 614 shows the same case eight months after the a:-ray was
taken."
Oftentimes the occlusion is sadly impaired by the non-eruption of
a bicuspid impacted between contiguous teeth. The skiagraph Fig.
615 reveals the exact position of the delayed tooth and shows the im-
portance of making room for its eruption. Fig. 616 shows a second
bicuspid caught under the shoulder of a first bicuspid, and suggests that
it can be released by forcing the latter into an upright position.
The exact position of a delayed canine may be revealed, and the
question settled whether it be possible for it to erupt without assistance,
or whether it can even be forcibly erupted.

Fig. 615. Fig. 616.

In some cases a deciduous tooth remains in place long after the time
when it should have fallen out. It may be so firm as to cause serious
doubts about the advisability of extracting it, even though there is mal-
occlusion while it is in place.
The skiagraph will reveal the presence
or absence of the bicuspid, and show whether extraction should be
resorted to or not.
The method of making the skiagraph is thus described^ bv C.
Edmund Kells, D. D. S., of New Orleans
:
"One of the requirements in o])taining a skiagraph is that the object
to be pictured and the plate or film must be held perfectly still during
the process. It is frequently possible to cut tlie film the proper shape,
inclose it in a black Hight-proof ) envelope, and allow the patient to
hold it in the moutli in the desired position
; but on general principles
this is not satisfactory, more especially with children, as it is liable to be
moved during the exposure.
' Dental Cosmos, October 1899, vol. xli. p. 1014.