PubMed · 15215573
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Rosalia Leonardi, Ersilia Barbato. 2004. A late-developing supernumerary premolar.. https://pubmed.ncbi.nlm.nih.gov/15215573/
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OBJECTIVES: The aim of this study was to measure the cusp deflection by polymerization shrinkage during composite restoration for mesio-occluso-distal (MOD) cavities in premolars, and to examine the influence of cavity dimension, C-factor and restoration method on the cusp deflection. METHODS: Thirty extracted maxillary premolars of similar size were prepared with four different sizes of MOD cavity, and divided into six groups. The width and depth of the pulpal wall of the cavity were as follows: group 1: 1.5x1 mm, group 2: 1.5x2 mm, group 3: 3x1 mm, and groups 4-6: 3x2 mm. Groups 1-4 were restored using a bulk filling with a composite. Group 5 was restored incrementally, and group 6 was restored with an indirect composite inlay. Cusp deflections were measured using LVDT transducers. The cusp deflections were compared between groups using ANOVA and Scheffe tests, and a correlation analysis was done. RESULTS: The cusp deflections of groups 1-4 were 12.1 (2.2), 17.2 (1.9), 16.2 (0.8) and 26.4 (4.2) microm, respectively. There was a strong positive correlation between the length cubed divided by the thickness cubed of the remaining cusp (L3/T3) and cusp deflection. The C-factor was related to the % flexure (100xcusp deflection/cavity width). The cusp deflections of groups 5 and 6 were 17.4 (2.0) and 17.9 (1.4) microm, respectively, which were much lower values than those of group 4. SIGNIFICANCE: The cusp deflection increased with increasing cavity dimension and C-factor. Use of an incremental filling technique or an indirect composite inlay restoration could reduce the cuspal strain.
BACKGROUND: Canines or premolars must often be derotated during fixed appliance therapy. If such derotation is carried out on the continuous archwire during the leveling phase, it may lead to unwanted side effects on the neighboring teeth. MATERIAL AND METHODS: At the University of Ulm a .018" x .018" nickel-titanium segmental derotation archwire was developed to start derotation as early as possible. This wire can be inserted during leveling. This system consists of a vertical slot bracket, an elastic ligature, and the derotation archwire. We tested the derotation archwire under clinical application. The occurring forces and torquing moments were measured in vitro via a hexapode and a sensor working in three dimensions. RESULTS: In this investigation, a derotation moment of 12 Nmm occurred in the canine with a 140 degrees archwire rotation and a force in lingual direction. This archwire also made overcorrection possible, since it remains active after complete derotation. A complete derotation of the tooth was effected with no reactivation, due to the wire's superelasticity.
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