Preserving dentine in minimally invasive access cavities does not strengthen the fracture resistance of restored mandibular molars

Abstract

Aim To evaluate the correlation between the volume of dental hard tissues removed and the fracture resistance of mandibular molar teeth with ultraconservative (UltraAC) or traditional (TradAC) access cavity preparations. Methodology Sixty recently extracted and intact mandibular first molars were scanned in a microcomputed tomographic (micro‐CT) device, anatomically matched and assigned at random to 2 groups (n = 30), according to the access cavity type: UltraAC or TradAC. After access preparation, mesial and distal canals were prepared using Reciproc instruments and a new scan was taken. The volumes of pulp chamber and dental hard tissues in each specimen were measured before and after the experimental procedures, and the percentage volume reduction of hard tissues calculated for the entire tooth and for the crown separately. Teeth were then root filled, restored and subjected to fracture resistance tests in an universal testing machine. The force required to fracture was recorded in Newtons (N). The adherence of the variables to a Gaussian curve was verified using a Shapiro–Wilk test. Skewed data were analysed with nonparametric Wilcoxon signed rank or Spearman correlation tests, whilst the normally distributed data were analysed with a dependent samples Student t‐test. Level of significance was set at 5%. Results Pre‐operatively, no difference was observed between groups regarding the volume of pulp canal space or dental hard tissues (P > 0.05). After access preparation, volumes of the removed hard tissues from the entire tooth and from the crown were significantly greater in teeth prepared with TradAC than with UltraAC (P < 0.05). No significant difference was observed in the fracture resistance values between TradAC (902.9 ± 347.8 N) and UltraAC (948.7 ± 405.7 N) groups (P = 0.975). The Spearman test was unable to identify a correlation between fracture resistance and percentage volume of removed dental hard tissues in the entire root (P = 0.525, r = −0.084) or only in the crown (P = 0.152, r = −0.187). Conclusion The volume of hard dental tissues removed, although greater in teeth with TradAC compared to UltraAC, did not correlate with the fracture resistance results, indicating that a minimally invasive access cavity did not increase the resistance of restored mandibular first molars to fracture.

Present status and future directions – Minimal endodontic access cavities

“…Micro‐CT allows several morphometric parameters of the dental hard tissues and the root canal system (volume, surface area, aspect ratio, etc.) to be calculated, thus minimizing the intrinsic anatomical heterogeneity of teeth and improving the internal validity of the study (De‐Deus et al, 2020; Silva et al, 2021b). In the context of minimally invasive endodontics, nine studies used the micro‐CT approach for sample selection and distribution, assuring the creation of a reliable baseline for comparison.…”

“…While Rover et al (2020) reported no difference in mandibular incisors prepared with ConsAC and TradAC, other studies in posterior teeth (Barbosa et al, 2020; Lima et al, 2021; Pereira et al, 2021) reported larger amounts of remaining filling materials in the pulp chamber of teeth prepared with contracted cavities than that of TradAC, even using microscope magnification. In another study, the operator was unable to remove the remnants of filling materials from the pulp chamber prior to restoration of teeth prepared with UltraAC, even with the aid of ultrasonic tips, magnification under microscope, and extra time to complete the treatment (Silva et al, 2021b) (Figure 22). This extended operative period might contribute to the fatigue of both the patient and dentist, while the filling remnants can compromise aesthetics by causing tooth crown discoloration over time (Lenherr et al, 2012; Marchesan et al, 2018).…”

“…It is possible that the volume of the pulp chamber as well as the thickness, height, and volume of the remaining dental hard tissues may directly affect the fracture resistance of teeth, parameters that can be exactly quantified by means of micro‐CT technology in order to create a reliable baseline. Strict sample selection criteria based on the external and internal morphologies of teeth using micro‐CT imaging was done in nine studies and, in all of them, no difference on the fracture resistance was found amongst teeth prepared with different types of access cavities (Augusto et al, 2020; Barbosa et al, 2020; Lima et al, 2021; Pereira et al, 2021; Rover et al, 2017, 2020; Silva et al, 2020a, 2021b; Xia et al, 2020).…”

Present status and future directions: vertical root fractures in root filled teeth

“…A renewed interest in minimally invasive endodontic techniques has emerged (Marinescu et al, 2020; Saberi et al, 2020; Santosh et al, 2021). However, despite several studies being published on the impact of conservative access cavity preparation on the fracture resistance of root filled teeth, the results are conflicting and do not permit tangible conclusions to be drawn (Plotino et al, 2017; Silva, Lima, et al, 2021). In a recent narrative review (Silva et al, 2022), the inconsistent findings of ex vivo and in vitro studies assessing the effect of access cavity modification on fracture resistance were attributed to study heterogeneity, and also, flaws in experimental design and methodology.…”

Influence of conservative endodontic access cavities on instrumentation of oval‐shaped straight root canals

“…The preservation of tooth structure with the use of minimal access cavities has been shown to increase fracture resistance by 20% in premolars and 12.3% in molars, compared with traditional access (TradAC) cavities (Plotino et al, 2017;Silva et al, 2021aSilva et al, , 2021b. Whilst a prior study comparing ultraconservative access (UltraAC), TradAC and extended access cavities reported similar stress values on the occlusal surfaces of maxillary molars, a greater loss of tooth structure during access cavity preparation was associated with a higher concentration of stress at the cervical region, thus resulting in an increased risk of fracture (Jiang et al, 2018).…”