Journal of Dentistry, 3, 161-l 62
External forces causing tooth movement: a case report M. A. Foster, BDS A. V. Newton, BDS, MDS Department of Operative Ukversity of Liv&pool
Surgery, School - .
ABSTRACT A case is reported in which a cobalt-chromium casting fitted at the try-in stage did not fit 3 weeks later. It was therefore thought that there may have been some movement of the teeth. Measurements were taken to verify this and a possible cause suggested.
CASE
REPORT
AN l&year-old
girl required replacement of her immediate mucosal-borne partial upper denture. The denture replaced 2111 and it was intended that a new cobalt-chromium denture should be made. It was noticed at the time that there was some asymmetry of the arch but the significance of this was not appreciated immediately. The second impressions were taken on 29 April 1974 and the cast framework was successfully tried in on 13 May 1974. The try-in of the denture was on 3 June 1974, and at this visit it was found that the denture did not fit even when it was stripped down to the framework. New second impressions were taken at this appointment and a new casting made. This was tried in on 17 June 1974 and the completed denture satisfactorily fitted on 24 June 1974. It was suspected that the arch width had been reduced between the try-in of the casting and that of the denture. Although there are small long term movements in the adult dentition which might cause a denture to be ill fitting, the time intervals in this case were surprisingly short. Only 3 weeks had elapsed between the try-in of the casting and the try-in of the denture and in that short time it was so badly misaligned that it would not fit at all. In such instances it is always possible, and indeed likely, that the metal skeleton has suffered damage
of Dental Surgery,
during handling, but comparison with the original model, which was still available, showed that the first casting still fitted perfectly. On questioning the patient she revealed that she was preparing for her final examination and studying for prolonged periods lying on her bed resting her head on her right hand. On the middle finger of this hand was a large silver ring which was placed under the zygomatic arch opposite $1. It was thought that this continual pressure may have moved the teeth in the upper arch and this may also explain the original asymmetry (but this is supposition as no past records were available). It was decided to measure the distance between the 61 and 16 in the original and working models. Thiswas done with the aid of a travelling microscope. Thin cotton was stretched between the 61 and 16and also between the 51 and 12 in exactly the same place on the two models. This cotton was then aligned with the crosswire on the travelling microscope and measurements were taken between the points of maximum convexity of the two teeth. Tab/e /.-Mean 21and 1:
difference
between
61 and 12 and
Distance measured
First model
Second model
Mean difference
!I and I! 51 and 15
3.205 3.025
3.165 3.039
--0.040 1~0.014
The results are given in cm.
The distance between the 61 and 16 was measured tirst and compared with the new model. The results are shown in Table 1. The same measurements were taken between 21 and 12. Thus it appeared that the $1 had been pushed palatally, squeezing the 21 between the 61 and 41
162
and causing the 51 to move buccally. It was felt, however, that this conclusion should be tested by determining how much difference there would be between impressions taken of the same patient. Four impressions were taken of one patient and the mean distance between 61 and 16 was 3.356 cm with a standard deviation of ~0904cm. The
Journal of Dentistry, Vol. ~/NO. 4
difference between the measurements obtained in this control study and the tooth movements shown in Table Zwere statistically significant. Finally, it was decided to test the accuracy of the measuring technique and 10 measurements were taken blind by the same operator on one model. The readings varied from 3.042 to 3.040 cm.
External forces causing tooth movement: a case report M. A. Foster, BDS A. V. Newton, BDS, MDS Department of Operative Ukversity of Liv&pool
Surgery, School - .
ABSTRACT A case is reported in which a cobalt-chromium casting fitted at the try-in stage did not fit 3 weeks later. It was therefore thought that there may have been some movement of the teeth. Measurements were taken to verify this and a possible cause suggested.
CASE
REPORT
AN l&year-old
girl required replacement of her immediate mucosal-borne partial upper denture. The denture replaced 2111 and it was intended that a new cobalt-chromium denture should be made. It was noticed at the time that there was some asymmetry of the arch but the significance of this was not appreciated immediately. The second impressions were taken on 29 April 1974 and the cast framework was successfully tried in on 13 May 1974. The try-in of the denture was on 3 June 1974, and at this visit it was found that the denture did not fit even when it was stripped down to the framework. New second impressions were taken at this appointment and a new casting made. This was tried in on 17 June 1974 and the completed denture satisfactorily fitted on 24 June 1974. It was suspected that the arch width had been reduced between the try-in of the casting and that of the denture. Although there are small long term movements in the adult dentition which might cause a denture to be ill fitting, the time intervals in this case were surprisingly short. Only 3 weeks had elapsed between the try-in of the casting and the try-in of the denture and in that short time it was so badly misaligned that it would not fit at all. In such instances it is always possible, and indeed likely, that the metal skeleton has suffered damage
of Dental Surgery,
during handling, but comparison with the original model, which was still available, showed that the first casting still fitted perfectly. On questioning the patient she revealed that she was preparing for her final examination and studying for prolonged periods lying on her bed resting her head on her right hand. On the middle finger of this hand was a large silver ring which was placed under the zygomatic arch opposite $1. It was thought that this continual pressure may have moved the teeth in the upper arch and this may also explain the original asymmetry (but this is supposition as no past records were available). It was decided to measure the distance between the 61 and 16 in the original and working models. Thiswas done with the aid of a travelling microscope. Thin cotton was stretched between the 61 and 16and also between the 51 and 12 in exactly the same place on the two models. This cotton was then aligned with the crosswire on the travelling microscope and measurements were taken between the points of maximum convexity of the two teeth. Tab/e /.-Mean 21and 1:
difference
between
61 and 12 and
Distance measured
First model
Second model
Mean difference
!I and I! 51 and 15
3.205 3.025
3.165 3.039
--0.040 1~0.014
The results are given in cm.
The distance between the 61 and 16 was measured tirst and compared with the new model. The results are shown in Table 1. The same measurements were taken between 21 and 12. Thus it appeared that the $1 had been pushed palatally, squeezing the 21 between the 61 and 41
162
and causing the 51 to move buccally. It was felt, however, that this conclusion should be tested by determining how much difference there would be between impressions taken of the same patient. Four impressions were taken of one patient and the mean distance between 61 and 16 was 3.356 cm with a standard deviation of ~0904cm. The
Journal of Dentistry, Vol. ~/NO. 4
difference between the measurements obtained in this control study and the tooth movements shown in Table Zwere statistically significant. Finally, it was decided to test the accuracy of the measuring technique and 10 measurements were taken blind by the same operator on one model. The readings varied from 3.042 to 3.040 cm.
