Influence of ultraconservative access cavities on instrumentation efficacy with XP-endo Shaper and Reciproc, filling ability and load capacity of mandibular molars subjected to thermomechanical cycling.

AIM To evaluate the influence of ultraconservative access cavities (UltraAC) on canal shaping and filling ability and load capacity of mandibular molars after root canal preparation with XP-endo Shaper (XP) or Reciproc (RC), under simulated clinical conditions. Traditional access cavities (TradAC) were used for comparison. METHODOLOGY Forty mandibular molars were scanned by micro-computed tomographic and, based on similar anatomical features, were divided into four groups (n=10), according to the type of access cavity and canal instrumentation protocol: TradAC/RC, TradAC/XP, UltraAC/RC and UltraAC/XP. All root canal procedures were performed on a dental mannequin. Teeth were scanned after root canal instrumentation and filling. Unprepared area, dentine removed, accumulated hard tissue debris (AHTD), canal transportation, presence of voids and filling material remnants within the pulp chamber were analyzed. After restorative procedures, the teeth were subjected to thermomechanical cycling and to a load capacity test. Statistical analyses were performed using two-way ANOVA test, considering the randomized blocks design (P<0.05). RESULTS The percentage of unprepared canal area was significantly lower in TradAC groups when compared to UltraAC groups (P<0.05), regardless of the instrument used. The UltraAC/XP group had significantly lower percentage of radicular dentine removed when compared to other groups (P<0.05). UltraAC/XP and TradAC/XP groups had significantly lower percentage of AHTD than UltraAC/RC and TradAC/RC groups (P<0.05). Regarding canal transportation, in the MB root canals, the TradAC/XP group had significantly lower values than other groups (P<0.05). In general, in ML and distal root canals, TradAC/XP and UltraAC/XP groups had significantly lower values of canal transportation when compared to other groups (P<0.05). Moreover, the UltraAC/RC had the highest canal transportation values in MB and distal canals. The UltraAC groups had significantly greater percentage of voids and volume of remaining root filling material within the pulp chamber after cleaning procedures than TradAC groups (P<0.05). There was no difference in the load capacity among groups (P<0.05). CONCLUSION The UltraAC/XP and UltraAC/RC groups had significantly more unprepared canal area, significantly more voids and volume of root filling material remnants within the pulp chamber after canal filling. UltraAC/XP had been associated with a significantly less amount of dentine removal and a significantly AHTD while TradAC/XP had overall significantly less canal transportation. No differences were observed in the load capacity among groups.