Search for: [Abstract = "Orthodontic extrusion allows for the reconstruction of the damaged tooth and preservation of its periodontium with all the benefits. While orthodontic crown lengthening is taking place, the clinical crown is improved, but a decrease in the crown to root ratio is observed.The aim of the study was to evaluate resistance of extruded andsubsequently prosthetically reconstructed teeth in a laboratory experimental model. Additional aim was to construct a diagnostic and therapeutic protocol for the orthodontic crown lengthening followed by prosthetic reconstruction.Study material consisted of 60 incisors divided into groups showing the most common clinical situations in which extrusion is needed before prosthetic reconstruction, and a diverse range of extrusion. The tested range of extrusion in groups was 0, 2, 4 and 6 mm. The control group was a group of healthy teeth. Specially designed for the purpose of research model consisted of laboratory samples which underwent endurance tests. The result of these tests was the force at which the destruction of the sample occurred \[kN\], displacement \[mm\] and the energy of destruction \[J\]. Comparisons in groups were made using analysis of variance \(ANOVA\) and differences in individual pairs of groups was assessed using a post hoc test Student\-Newman\-Keuls'a.Reduction of mean values of destructive forces in the control study groups was successively\: 31.5%, 45.5%, 55.3% and 66%. Reduction of mean values of destruction energy, in study groups relative to control was successively\: 23.3%, 41.2%, 48.5% and 66.8%. Regression analysis found the relationship of the rectilinear character between decreasing dimension cervical part of the tooth and destructive force, as well as between these measurements in extruded groups and destruction energy.The gradual decrease in the resistance parameters refers to a group of teeth reconstructed prosthetically and groups extruded 2 mm and 4 mm. In the fourth study group rapid decrease of resistance parameters, and an increasing number of cumulative internal stress of the sample before the moment when the resistance is exceeded was observed. The degree of taper shape of the root affects the loss of mechanical parameters in course of extrusion.In conclusion, the study has showed an inverse relationship between the degree of the achieved tooth’s extrusion and the relative change of its mechanical strength. Parameters determining strength of extruded and prosthetically restored teeth are the remaining length of the tooth’s root and expected after treatment crown to root ratio. An equation allowing the prediction of success of extrusion for prosthetic reconstruction has been developed\: , where A is the length of future prosthetic crown, B is the length of the remaining root and C is the size of the subgingival loss of hard tissues. The result of the equation \(x\) greater than 1 indicates\: the loss of the two thirds of the tooth’s mechanical strength and the unfavorable prognosis for prosthetic reconstruction."]

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