Dynamic Photoelastic Analysis of Stress Distribution in Simulated Canals Using Rotary Instruments with Varied Tip and Taper Sizes: A Quasi-3D Approach.

INTRODUCTION: To compare the stress produced on the walls of simulated canals by rotary instruments with varied tip and taper sizes. METHODS: Ninety isotropic transparent blocks, each containing a 60-degree curved canal, were distributed into 18 groups (n = 5) based on the instrument tip (sizes 10, 15, 20, 25, 30, and 35) and taper (sizes 0.02, 0.04, and 0.06). The blocks were fixed in a circular polariscope setup for dark field analysis. A digital camera was employed to capture the real-time birefringence patterns generated by each instrument. Digital image frames, corresponding to the instrument reaching the end of each canal third, were extracted and evaluated by 2 independent observers for the stress generation on canal walls. The data analysis employed a semi-quantitative scale ranging from 0 to 5. Cohen's Kappa coefficient test was used to determine the inter-observer agreement while the results were compared using Kruskal-Wallis test followed by an all-pairwise posthoc procedure (α = 5%). RESULTS: Inter-observer agreement was 0.95. A significant influence of the tip size on stress was observed across the coronal (P = .011), middle (P = .006), and apical (P = .026) thirds. In contrast, taper size did not affect the stress induced at the coronal (P = .509), middle (P = .958), or apical (P = .493) thirds. The variations in tip and taper sizes did not result in a significant stress differences among the thirds (P = .181). CONCLUSIONS: The stress significantly increased across all canal thirds with larger tip sizes of rotary instruments, whereas the taper sizes did not influence the stress when compared to the canal thirds.

Quasi-3D dynamic photoelastic analysis of stress distribution during preparation of simulated canals with 13 mechanical preparation systems.

AIM: The aim of this study is to compare the stress produced on the internal walls of simulated canals by nine rotary and four reciprocating systems. METHODOLOGY: Sixty-five isotropic transparent blocks containing a 60° curved and tapered simulated canal were selected and distributed into 13 groups (n = 5) according to the preparation system: BioRace, HyFlex EDM, iRaCe, Mtwo, One RECI, ProTaper Next, RaCe EVO, Reciproc, Reciproc Blue, R-Motion, VDW.ROTATE, XP-Endo Rise Shaper, and XP-Endo Shaper. Each resin block was mounted in a vice and a digital camera recorded the entire sequence of each preparation system through a circular polariscope set for dark field analysis. The video frames when each instrument reached the end of the coronal, middle, and apical thirds of the canal were extracted from the recordings and analysed by two independent observers regarding the stress generated on the canal walls using a semi-quantitative evaluation on a 0-5 scale. Intra- and inter-observer agreement were subjected to the Cohen's Kappa coefficient test, whilst the experimental results were compared using Kruskal-Wallis test post hoc pairwise comparisons with Bonferroni correction (α = 5%). RESULTS: The inter- and intra-observer agreement were 0.98 and 1, respectively. Most instruments demonstrated acceptable performance (scores ≤ 2) in all thirds. Other instruments, such as the HyFlex EDM 25.12 (coronal and middle thirds), Reciproc Blue R25 and Reciproc R25 (coronal and apical thirds), R-Motion 30.04 (apical third), and VDW.ROTATE 20.05 (apical third) showed scores higher than 3. Statistical analysis revealed a significant difference amongst the tested systems at the coronal, middle, and apical thirds (p < .05). CONCLUSION: None of the canal instrumentation protocols were stress-free, showing varying levels of stress concentrations. Various factors seemed to influence the magnitude of stress and its distribution pattern on the canal walls. Overall, instruments characterized by a larger taper, lower speed, reciprocating motion, and made of heat-treated NiTi alloy exhibited higher patterns of stress distribution.

Estudo do comportamento biomecânico de próteses parciais removíveis classe I de Kennedy associadas a quatro diferentes coroas fresadas: análise fotoelástica / Study of the biomechanical behavior of removable partial dentures Kennedy Class I associated with four different milled crowns: photoelastic analysis

Esta pesquisa realizou, através da análise fotoelástica, o estudo do comportamento biomecânico de próteses parciais removíveis classe I de Kennedy associadas a quatro diferentes coroas fresadas. Foram utilizados quatro modelos de resina epóxica, que simularam uma arcada mandibular parcialmente edêntula com presença do primeiro pré-molar do lado direito ao primeiro pré-molar do lado esquerdo. Foram realizadas próteses seguindo quatro diferentes planejamentos de coroas protéticas associadas à prótese parcial removível (PPR). A seguir foi aplicada uma sequência de cargas de cada lado dos corpos de prova, e as franjas resultantes foram observadas no lado de trabalho e no lado de não trabalho em um fotoelasticimetro. Após avaliação dos resultados concluiu-se que: a) o planejamento de PPR com coroas protéticas providas de descanso oclusal mesial em primeiros pré-molares e descanso em cíngulo de caninos proporcionou as menores tensões nas raízes dos dentes-suportes primários e secundários. As maiores tensões nas raízes do dente-suporte primário (primeiro pré-molar) e dente-suporte secundário (canino) ocorreram naqueles planejamentos de PPR nos quais foram confeccionadas coroas fresadas com degrau cervical nos respectivos dentes; b) todos os planejamentos de PPR associadas a coroas fresadas com degrau cervical resultaram em maiores tensões nas raízes dos dentes-suportes primário e secundário quando comparado ao planejamento que simulou a realização de planos-guias em esmalte de dentes hígidos; c) o procedimento de ferulização através da soldagem de duas coroas fresadas com degrau cervical não uniformizou a distribuição das tensões nos dentes-suportes, nem diminuiu a intensidade das mesmas; d) não foi possível observar tensões significativas no lado de não trabalho ao se aplicar cargas verticais do lado de trabalho em qualquer um dos quatro planejamentos avaliados

Photoelastic analysis was performed in this research to study the biomechanical behavior of bilateral distal extension removable partial dentures (Kennedy class I) assembled with four different surveyed crowns plannings. Tests were accomplished in four epoxy resin casts simulating a partially edentulous mandibular arch with the presence from the right first premolar until the left first premolar. Crowns and respective removable partial dentures were made following four different plannings. It was applied a load sequence in each side of the test specimen and resultant fringes were observed at the working and non-working side in a photoelasticimeter. After the evaluation of the results, it could be concluded: a) the planning of a removable partial denture (RPD) assembled with crowns provided with mesial oclusal rest in first premolars and cingulum rest in canines resulted in the lowest stresses in the roots of the primary and secondary abutment teeth. The highest stresses in the roots of the primary abutment tooth (first premolar) and the secondary abutment tooth (canine) occurred in those RPD plannings where surveyed crowns with lingual cervical ledges were made for these teeth; b) all RPD plannings assembled to surveyed crowns provided with lingual cervical ledge resulted in higher stresses in the roots of the primary and the secondary abutment teeth when compared to the planning that simulated the accomplishment of guide-planes in sound teeth enamel; c) the splint procedure through the soldering of two surveyed crowns with lingual cervical ledge did not homogenize the distribution of the stresses in the abutment teeth, nor decreased their intensity; d) it was not possible to observe significant stress in the non-working side when vertical load were applied to the working side in any of the four evaluated plannings