Avoiding extraction of severely damaged teeth: Impact of crown-root ratio altering apical root resection, orthodontic extrusion, and surgical crown lengthening on load capability

Abstract

Abstract Objectives to investigate the biomechanical impact of procedures changing crown-to-root ratio (RCRR) aimed to restore severely damaged upper central incisors to avoid tooth extraction compared to implant placement. There is no evidence on load capability after apical root resection (AS), orthodontic extrusion (OE), and surgical crown lengthening (SCL) in respect to RCRR, respectively. Material and Methods Human maxillary central incisors were endodontically treated, decoronated and divided into 4 groups (n = 48). Following specimen preparation was performed: (I) adhesive core-and-post build-up (control), (II) as (I) and 2mm apical root resection (AS), (III) before adhesive core-and-post build-up teeth were shortened 2mm coronally (OE) (IV) as (I), but specimens were embedded 4mm instead of 2mm below the CEJ (SCL), group (V) implant-borne restoration with individual all-ceramic abutments (n = 12; ∅4.1/l = 12mm) (IBR). All specimens received all-ceramic crowns, thermo-mechanical (TML), and subsequent linear loading (LL) until failure. RCRR were calculated and Log-rank, Kruskal-Wallis, Mann-Whitney-U, ANOVA, and Chi-Square tests applied (p = 0.05). Results Fracture loads after subsequent LL differed significantly (p = 0.001) between groups, while implants showed highest values. Fmax median (min/max): (I) 252 (204/542), (II) 293 (243/443), (III) 253 (183/371), (IV) 195 (140/274), (V) 446 (370/539). Pair-wise comparison showed significant differences (p = 0.001) between group I / IV and group V, I and IV (p = 0.045), II and IV (p = 0.001), and III compared to IV (p = 0.033), respectively. RCRR below 1 significantly increased load capability compared to RCRR =1. Conclusions OE appears to preferable to ensure biomechanical stability of severely damaged teeth compared to SCL. AR has no adverse biomechanical impact. RCRR < 1 is biomechanically beneficial. Clinical Relevance: In case of a severely damaged maxillary incisor orthodontic extrusion should be preferred compared to surgical crown lengthening prior single-crown restoration. As orthodontic extrusion apical root resection has no adverse effect on load capability. Single-crown implant-borne restoration are most load capable.