Crown-root ratio after orthodontic extrusion and surgical crown lengthening procedures – an ex-vivo study

Abstract

Abstract Introduction For restoration of extensively damaged teeth preprosthetic treatment measures are necessary. Surgical crown lengthening and orthodontic extrusion affect the prospective crown-root ratio (CRR). Evidence on true values of CRR is scarce. The subject of this in-vitro study was to compute CRRs for both treatment approaches. Methods 120 human maxillary central extracted incisors were measured. Measurements were calculated for five prospective treatment groups: C (control), OE-2mm (orthodontic extrusion of 2mm), OE-4mm (orthodontic extrusion of 4mm), SCL-2mm (surgical crown lengthening of 2mm), and SCL-4mm (surgical crown lengthening of 4mm). Tooth (TL), root (RL), and crown lengths (CL) were measured from mesial (m) and facial (f) cemento-enamel junction (CEJ). Anatomic (CRR) and effective crown-root ratios (eCRR) were calculated. Results For control TL was 22.8 ± 1.6mm, CL-m 6.7 ± 1.1mm, CL-f 9.5 ± 1.0mm, RL-m 16.1 ± 1.4mm, and RL-f 13.3 ± 1.3mm. Following CRR values were computed for C: CRR-m = 0.4 ± 0.1, CRR-f = 0.7 ± 0.1. For orthodontic extrusion in comparison to surgical crown lengthening all crown-root-ratios were lower for orthodontic extrusion. Effective CCRs were higher than anatomic CCRs. CRR at mesial CEJ was significantly lower than CRR with facial CEJ as reference. Conclusions Prospective crown-root ratios are lower for orthodontic extrusion than for surgical crown lengthening procedures.