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Azerbaycan Saytlari

 »  Home  »  Endodontic Articles 4  »  Measurement of strain on tooth roots during post removal with the Eggler post remover
Measurement of strain on tooth roots during post removal with the Eggler post remover
Results.



All posts were removed in less than 2 min with the Eggler post remover. Strain measurements could not be recorded in two teeth in group 1 when removing the post at 10 to the long axis of the tooth because the repeller arms did not contact the root surface when attempting to remove the post.
Strain is the change in length divided by the original length of the object and it has no unit of measurement. In this study, the amount of deformation was reported as ‘ strain’ (where 10 000 strain = 0.01 strain = 1% deformation). A positive value indicated tension, whilst a negative value indicated compression. Tables 1 and 2 list the ranges, means and standard deviations for the greatest strains during post removal, as well as the character of the strain (tension or compression). The greatest strain on any surface for each tooth was identified and the strains on the other three surfaces were measured at that same point in time.

Root strain during post removal parallel to the long axis.
The magnitude of strains measured on the buccal and lingual root surfaces was lower than those measured on the mesial and distal surfaces where the repeller arms of the Eggler post remover contacted the tooth. When posts were removed along the long axis of the teeth, the strain measurements were similar on the mesial and distal surfaces for most teeth, although there were large discrepancies between strain measurements in three teeth from group 1 and four teeth from group 2. All strain measurements in group 1 indicated compressive stresses on the mesial and distal surfaces, whilst seven out of 10 teeth had tensile stresses on the buccal and lingual surfaces. Compressive stresses were present in nine out of the 10 teeth on the mesial and distal surfaces in group 2. It was noted that the post was difficult to remove from the tooth that had tensile stresses and there was some rotation of the Eggler post remover during use on this tooth. Tensile stresses were present on the buccal or lingual surfaces of two of the 10 teeth in group 2. The Mann–Whitney U -test indicated that the strain measurements of group 1 were not statistically different to those of group 2 (Table 3) at the 95% level of confidence.

Table 1. Strain measurements for group 1 (1 mm thickness of dentine).

Strain measurements for group 1
Strain measurements do not have a unit of measurement but are expressed as ' strain' where 1  strain represents a change in dimension of 1 part in 1 million. Positive values indicate tension, whilst negative values indicate compression.

Table 2. Strain measurements for group 2 (2 mm thickness of dentine).

Strain measurements for group 2
Strain measurements do not have a unit of measurement but are expressed as ' strain' where 1  strain represents a change in dimension of 1 part in 1 million. Positive values indicate tension, whilst negative values indicate compression.

Table 3. Statistical analysis: Comparisons between groups 1 and 2 using the Mann-Whitney U-test at the 95% level of confidence.

Statistical analysis: Comparisons between groups 1 and 2 using the Mann-Whitney U-test at the 95% level of confidence

Root strain during post removal at 10 to the long axis.
The magnitude of the strains measured on the buccal and lingual surfaces were lower than those measured on the mesial and distal surfaces and the highest strains were recorded on the mesial surface. These strains were higher in seven out of eight teeth in group 1 and in seven out of 10 teeth in group 2. All teeth in both groups had compressive stresses on the mesial and distal surfaces. The Mann–Whitney U -test indicated that there was no significant difference in the strain measurements between groups 1 and 2 (Table 3) at the 95% level of confidence.

Comparison of strains within each group.
Comparisons were made within the same group using the Wilcoxon Signed Rank test when removing the post parallel to the long axis and at 10 to the long axis of the root. There were no significant differences between the strain measurements on the buccal, lingual, mesial and distal surfaces in both groups (Table 4) with a 95% level of confidence.

Table 4. Statistical analysis: comparisons within group 1 and within group 2 between removal of the posts parallel to the long axis and at a 10° angle to the long axis using the Wilcoxon Signed Rank Test at the 95% level of confidence.

Statistical analysis

Table 5. Number of root fractures that occurred in each group during post removal.

Number of root fractures that occurred in each group during post removal

Figure 4. Buccal surface of a tooth with an oblique root fracture following removal of a cast post/core with the Eggler Post Remover applied at a 10  angle to the long axis of the root. This specimen was from group 1 with only 1 mm thickness of dentine remaining in the coronal portion of the tooth.

uccal surface of a tooth with an oblique root fracture following removal of a cast post/core with the Eggler Post Remover applied at a 10  angle to the long axis of the root

Root fractures during post removal.
Fractures of the root occurred in four teeth – three of these were from group 1 and one from group 2. All of these fractures occurred when the posts were being removed at an angle of 10 to the long axis of the root (Table 5). The fractures in three of these teeth (two from group 1; one from group 2) were small slivers of dentine which resulted in loss of 1–2 mm of dentine on the outer surface of the root and all of these fractures occurred at the point where the repeller arms of the Eggler post remover contacted the tooth. The other tooth from group 1 had an oblique root fracture on the buccal surface which extended at least 6 mm in a disto-apical direction (Fig. 4).