Effect of luting agents and reconstruction techniques on the fracture resistance of pre-fabricated post systems

WOS: 000229172100007PubMed ID: 15899022Fracture resistance and fracture modes of endodontically treated maxillary central incisors restored with different post-and-core systems covered with all-ceramic copings were evaluated. Ten samples were prepared for each group. Groups 1, 2 and 3 consisted of tooth-coloured post-and-core, zirconia post (Cosmopost) with a composite core (Tetric Ceram), zirconia post (Cosmopost) with a custom made ceramic core (Cosmo Ingot), glass fibre-reinforced post (FRC Postec) with a composite core (Tetric Ceram), respectively. Group 4 consisted of a titanium post (ERpost) with a composite core (Tetric Ceram). The control group (group 5) consisted of root-filled incisors without posts. Tooth-coloured posts were cemented in the roots using Variolink-2, while titanium posts were cemented in the roots using Harvard cement. The all-ceramic copings were cemented using Variolink-2. Static load was applied to 2 mm below the incisal edge on the palatinal surface of each sample until they were fractured. Fracture data were obtained and statistically analysed with One-way ANOVA and a Tukey's test. The results of the means and standard deviations of the fracture resistance during static loading were: 497.5 +/- 61.94 (1), 474.61 +/- 96.84 (2), 494.61 +/- 104.67 (3), 581.34 +/- 105.36 (4), 420.42 +/- 127.48 (5). There were statistically significant differences between groups 4 and 5. Glass fibre-reinforced posts and composite cores (group 3) showed the most catastrophic failure. Consequently, zirconia ceramic posts can be used in clinical practice

Resistance to compression of weakened roots subjected to different root reconstruction protocols

OBJECTIVE: This study evaluated, in vitro, the fracture resistance of human non-vital teeth restored with different reconstruction protocols. MATERIAL AND METHODS: Forty human anterior roots of similar shape and dimensions were assigned to four groups (n=10), according to the root reconstruction protocol: Group I (control): non-weakened roots with glass fiber post; Group II: roots with composite resin by incremental technique and glass fiber post; Group III: roots with accessory glass fiber posts and glass fiber post; and Group IV: roots with anatomic glass fiber post technique. Following post cementation and core reconstruction, the roots were embedded in chemically activated acrylic resin and submitted to fracture resistance testing, with a compressive load at an angle of 45º in relation to the long axis of the root at a speed of 0.5 mm/min until fracture. All data were statistically analyzed with bilateral Dunnett's test (α=0.05). RESULTS: Group I presented higher mean values of fracture resistance when compared with the three experimental groups, which, in turn, presented similar resistance to fracture among each other. None of the techniques of root reconstruction with intraradicular posts improved root strength, and the incremental technique was suggested as being the most recommendable, since the type of fracture that occurred allowed the remaining dental structure to be repaired. CONCLUSION: The results of this in vitro study suggest that the healthy remaining radicular dentin is more important to increase fracture resistance than the root reconstruction protocol

Determining Mhc-DRB profiles in wild populations of three congeneric true lemur species by noninvasive methods

The major histocompatibility complex (MHC) is a highly polymorphic and polygenic genomic region that plays a crucial role in immune-related diseases. Given the need for comparative studies on the variability of immunologically important genes among wild populations and species, we investigated the allelic variation of MHC class II DRB among three congeneric true lemur species: the red-fronted lemur (Eulemur rufifrons), red-bellied lemur (Eulemur rubriventer), and black lemur (Eulemur macaco). We noninvasively collected hair and faecal samples from these species across different regions in Madagascar. We assessed DRB exon 2 polymorphism with a newly developed primer set, amplifying nearly all non-synonymous codons of the antigen-binding sites. We defined 26 DRB alleles from 45 individuals (17 alleles from E. rufifrons (N = 18); 5 from E. rubriventer (N = 7); and 4 from E. macaco (N = 20). All detected alleles are novel and show high levels of nucleotide (26.8%) and non-synonymous codon polymorphism (39.4%). In these lemur species, we found neither evidence of a duplication of DRB genes nor a sharing of alleles among sympatric groups or allopatric populations of the same species. The non-sharing of alleles may be the result of a geographical separation over a long time span and/or different pathogen selection pressures. We found dN/dS rates > 1 in the functionally important antigen recognition sites, providing evidence for balancing selection. Especially for small and isolated populations, quantifying and monitoring DRB variation are recommended to establish successful conservation plans that mitigate the possible loss of immunogenetic diversity in lemurs