Abstract The aim of this systematic review was to compare the clinical performance and failure modes of teeth restored with intra-radicular retainers. A search was performed on PubMed/Medline, Central and ClinicalTrials databases for randomized clinical trials comparing clinical behavior and failures of at least two types of retainers. From 341 detected papers, 16 were selected for full-text analysis, of which 9 met the eligibility criteria. A manual search added 2 more studies, totalizing 11 studies that were included in this review. Evaluated retainers were fiber (prefabricated and customized) and metal (prefabricated and cast) posts, and follow-up ranged from 6 months to 10 years. Most studies showed good clinical behavior for evaluated intra-radicular retainers. Reported survival rates varied from 71 to 100% for fiber posts and 50 to 97.1% for metal posts. Studies found no difference in the survival among different metal posts and most studies found no difference between fiber and metal posts. Two studies also showed that remaining dentine height, number of walls and ferrule increased the longevity of the restored teeth. Failures of fiber posts were mainly due to post loss of retention, while metal post failures were mostly related to root fracture, post fracture and crown and/or post loss of retention. In conclusion, metal and fiber posts present similar clinical behavior at short to medium term follow-up. Remaining dental structure and ferrule increase the survival of restored pulpless teeth. Studies with longer follow-up are needed.

Abstract This study aimed to characterize and compare the effect of different aging regimens on surface characteristic (topography and roughness), structural stability (phase transformation) and mechanical performance (Weibull analysis) of a Y-TZP ceramic. Discs (15 × 1.2 mm; VITA In-Ceram YZ) were prepared according to ISO 6872-2015 for biaxial flexural strength testing and randomly assigned into five groups (n = 30): as-sintered, no aging treatment (CTRL); 20 h in autoclave at 134°C, 2 bar pressure (AUT); intermittent mechanical loading at 20 Hz/106 load pulses (MechLoad); AUT followed by MechLoad (AUT+MechLoad); and storage in distilled water at 37°C, for 1 year (STO). The following analyses were performed: roughness (n = 30), surface topography (n = 2), phase transformation (n = 2) and biaxial flexure strength (n = 30). Phase transformation (increase of m-phase content) was shown to be a spontaneous, unavoidable and time-dependent process, occurring even under ambient conditions (dry storage after 1 year = 6.0% increase), and is considerably accelerated in the presence of moisture (STO = 17.6%; AUT= 63.1%; and AUT+MechLoad = 59.9%). For roughness parameters, only Ra was affected by aging, and the highest values were observed for AUT+MechLoad (0.25 ± 0.07 µm). For Weibull analysis, structural reliability (Weibull moduli) and characteristic strength were not impaired after aging, and some aging conditions led to increased values (highest weibull moduli in AUT, and highest characteristic strength in STO). Phase transformation proves to be a time-dependent spontaneous mechanism that is accelerated in the presence of different stimuli. However, none of the aging regimens had a negative effect on the characteristic strength and structural reliability of Y-TZP ceramic.

Objective: To evaluate the impact of the type of root canal preparation, intraradicular post and mechanical cycling on the fracture strength of roots. Material and Methods: eighty human single rooted teeth were divided into 8 groups according to the instruments used for root canal preparation (manual or rotary instruments), the type of intraradicular post (fiber posts- FRC and cast post and core- CPC) and the use of mechanical cycling (MC) as follows: Manual and FRC; Manual, FRC and MC; Manual and CPC; Manual, CPC and MC; Rotary and FRC; Rotary, FRC and MC; Rotary and CPC; Rotary, CPC and MC. The filling was performed by lateral compactation. All root canals were prepared for a post with a 10 mm length, using the custom #2 bur of the glass fiber post system. For mechanical cycling, the protocol was applied as follows: an angle of incidence of 45°, 37°C, 88 N, 4 Hz, 2 million pulses. All groups were submitted to fracture strength test in a 45° device with 1 mm/ min cross-head speed until failure occurred. Results: The 3-way ANOVA showed that the root canal preparation strategy (p<0.03) and post type (p<0.0001) affected the fracture strength results, while mechanical cycling (p=0.29) did not. Conclusion: The root canal preparation strategy only influenced the root fracture strength when restoring with a fiber post and mechanical cycling, so it does not seem to be an important factor in this scenario.

O objetivo deste estudo foi avaliar a resistência à fratura de dentes amplamente destruídos após duas técnicas de preparo (limas manual e rotatória) e após duas técnicas obturadoras (compactação ativa e passiva). Sessenta e oito raízes de caninos superiores com diâmetro apical igual a uma lima K #25 foram embutidas em resina acrílica e o ligamento periodontal foi simulado utilizando um material de moldagem à base de poliéter. As raízes foram distribuídas aleatoriamente em quatro grupos (n=17): preparo manual e compactação ativa (MA), preparo manual e compactação passiva (MP), preparo rotatório e compactação ativa (RA) e preparo rotatório e compactação passiva (RP). Todas as raízes foram restauradas com pino de fibra de vidro e coroa metálica. Os espécimes foram ciclados mecanicamente (500.000 ciclos, 45°, 37°C, 133 N, 2 Hz) e depois submetidos ao teste de resistência à fratura. Um único examinador cego analisou a superfície externa das raízes e classificou o padrão de falha em favorável ou desfavorável. Os valores de resistência à fratura variaram entre 621,15 N (MP) e 785,71 N (MA). Entretanto, o teste de Kruskal-Wallis não revelou diferença nos valores de resistência à fratura entre os quatro grupos (p=0,247). Diante das condições testadas, as técnicas de preparo e de obturação do canal radicular não influenciam na resistência à fratura de dentes amplamente destruídos restaurados com pino de fibra de vidro e coroa metálica.

The purpose of this study was to assess the fracture resistance of extensively damaged teeth after two root canal preparation techniques (hand and rotary files) and after two filling techniques (active and passive compaction). Sixty-eight maxillary canines roots with an apical diameter equal to that of a #25 K-file were embedded in acrylic resin and the periodontal ligament was simulated by using a polyether impression material. The roots were randomly distributed into four groups (n=17): hand preparation and active compaction (HA), hand preparation and passive compaction (HP), rotary preparation and active compaction (RA), and rotary preparation and passive compaction (RP). All roots were restored with glass fiber post and metallic crown. The specimens were mechanically cycled (500,000 cycles, 45°, 37°C, 133 N, 2 Hz) and then subjected to a fracture resistance test. A single blinded examiner analyzed the external root surface and classified the failure pattern as favorable or unfavorable. The fracture resistance values ranged between 621.15 N (HP) and 785.71 N (HA). However, the Kruskal-Wallis test did not reveal differences in the fracture resistance values among the four groups (p =0.247). Under the tested conditions, root canal preparation and filling techniques had no influence on the fracture resistance of extensively damaged teeth restored with fiber post and metallic crown.