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 »  Home  »  Endodontic Articles 6  »  Stainless steel bands in endodontics: effects on cuspal flexure and fracture resistance
Stainless steel bands in endodontics: effects on cuspal flexure and fracture resistance
Introduction - Materials and methods.



E. S. Pane, J. E. A. Palamara & H. H. Messer
School of Dental Science, University of Melbourne, Melbourne, Australia.

Introduction.
Most teeth requiring root canal treatment have typically lost substantial tooth structure as a result of caries or trauma, and often from repeated restorative procedures. The loss of tooth structure increases cuspal flexure under occlusal load and weakens the tooth. Both the amount of tooth tissue lost and the location of the loss have been found to decrease the stiffness of the tooth (Morin et al. 1988, Reeh et al. 1989, Panitvisai & Messer 1995). Hence, a temporary restoration should protect a tooth from fracture during endodontic treatment.
The use of preformed stainless steel bands (orthodontic bands) has been recommended as an aid for crown buildup of severely broken-down posterior teeth or to retain large temporary restorations (Ehrmann 1968, Ingle et al. 1994, Messer & Wilson 1996, Weine 1996, Pitt Ford 1997). Preformed stainless steel bands are ready-made for orthodontic purposes, and come in a sufficiently large number of sizes to fit most teeth with only occasional contouring. Stainless steel bands have also been recommended in the management of incomplete cusp fracture (cracked–tooth syndrome), as a diagnostic aid and as an immediate treatment option. The cemented band may serve as a splint to prevent further crack propagation (Ehrmann & Tyas 1990, Liu & Sidhu 1995).
It is widely assumed that the stainless steel band protects against cuspal flexure, both in temporary restoration during endodontic treatment and in the immediate treatment of cracked–tooth syndrome. However, this has not been proven, as there has been no experimental study to confirm the beneficial effect of stainless steel bands. Therefore, the aims of this study were to compare the cuspal flexure and fracture resistance of extracted teeth with mesio-occluso-distal (MOD) cavities and endodontic access, with and without stainless steel bands.

Materials and methods.

Cuspal flexure.
Twenty extracted intact non-carious human maxillary premolars (matched contralateral pairs from patients aged 12–16 years) were used in the study and were stored individually in buffered saline plus 0.5% thymol. All teeth had been extracted for orthodontic reasons. Institutional ethical approval was obtained for the study. Each tooth was cleaned and examined under fibreoptic light, and teeth with cracks or other visible defects were excluded. Each tooth was mounted vertically in a nylon ring with dental stone, using a mounting device to produce vertical orientation of the tooth. The tooth was mounted with the root covered to 2 mm below the cementoenamel junction, approximating the support of alveolar bone. A MOD cavity and endodontic access preparation were cut on each tooth using a diamond fissure bur. The isthmus width of the cavity was one-third of intercuspal distance, and the depth of the gingival floor was 1.5– 2 mm from the cemento-enamel junction, with no dentine remaining between endodontic access and proximal boxes. All measurements were made using a digital caliper. To provide adequate contact with the loading sphere during load testing, the inner occlusal enamel incline was prepared by cutting a shallow concavity to prevent lateral deflection of the sphere. A small notch was also prepared in both buccal and palatal enamel near the cusp tips to accommodate the extensometer probe tips. During preparation and testing all teeth were stored in 100% humidity to prevent dehydration.
Cuspal flexure measurements were made after cavity and endodontic access preparation in all teeth without a band present and again after a band had been cemented. Before the cementation, the stainless steel bands (Pre-Fit®. Universal Bicuspid Bands, TP Orthodontic, Inc., LaPorte, IN, USA) were fitted to all 20 teeth according to each size. The sizes of band were between 15 and 24. The band was cemented with glass ionomer luting cement (Ketac-Cem Aplicap, ESPE America, Inc., Norristown, PA, USA) and kept in 100% humidity for 24 h before testing. Excess cement was removed after the insertion of the band.
The loading tests were conducted with the nylon ring and mounted tooth fastened to the lower platen of an MTS servo-hydraulic testing machine (MTS Model 810, MTS Systems, Eden Prairie, MN, USA). A steel loading sphere with 4.75 mm radius of curvature was rigidly fastened to the load cell of the MTS machine. The sphere was brought into contact with the tooth and used to apply a ramped load of 100 N to the cusps. Cuspal deflection during loading was measured as a linear deflection by means of an extensometer (Extensometer Model 632, MTS Systems) via two pins attached to the buccal and palatal cusps. Data from the extensometer and load cell were recorded simultaneously on a microcomputer using Labview software (National Instruments Corp, Austin, TX, USA). Maximum cusp deflection of both cusps combined was calculated for 100 N of load, since this load is within physiological limits of normal chewing in the human dentition (DeLong & Douglas 1983). Each tooth was tested first without a band and again 24 h after a band was fitted and cemented.

Fracture resistance.
After the cuspal deflection tests, 10 teeth (one of each pair) had the band removed. All teeth were then loaded to fracture in the servo-hydraulic testing machine, at a cross head speed of 5 m s−1. Load at fracture was recorded in Newtons (N).

Statistical analysis.
Paired t-test analysis was used to identify statistically significant differences resulting from effects of banding on cuspal flexure and fracture. For cuspal flexure, each tooth served as its own control; for fracture resistance, contralateral teeth from the same subject were tested in pairs, one with and one without the band present. The null hypotheses for the study were: (i) banding did not influence cuspal deflection; and (ii) banding did not influence fracture resistance.