ABSTRACT
@#An id eal balance between the post length within root and the coronal extension should exist. Some theories advocated the use of the longest post as possible as the apical seal is not disturbed. Others advocated that the post should be longer than the crown or that the post should be a certain fraction of the length of the root. The conventional post length has been equal to 2/3-3/4 of the root length from half a century ago. Most of these theories have emphasized the post length in order to achieve sufficient retention and rigidity for coronal restoration. However, dental materials are evolving.With the use of fiber post and resin cement, stress distribution and post retention are improved over conventional metal post and zinc phosphate or glass-ionomer cement. Therefore, with improved bonding strength of fiber post, the post length within root should be minimized to maintain sufficient coronal rigidity. Factors affecting fracture resistance balance of a post-and-core system include the amount of Ferrule height (FH), Post length in root (PLIR), Post length in bone (PLIB), Abutment height (AH), Core length (CL) and Post length out of bone (PLOB). In view of the factors mentioned above, this paper investigated the mechanical factorsin a post-and-core system with literature review.
ABSTRACT
Objective To explore the influence of different lengths and contents of glass-fiber post on the fracture resistance of teeth, and to investigate the optimal length and content of glass-fiber post used for restorative treatment. Meth-ods Forty-two intact single canal mandibular premolars were collected from orthodontic patients and were divided into three experimental groups (A, B and C). All the teeth were endodontically treated after cut off the crowns from the 2 mm above cemento-enamel junction. The post lengths were10 mm in A group, 8 mm in B group, and 6 mm in C group.There were two subgroups for each experimental group (A1, A2, B1, B2, C1, C2 ), 7 teeth for each subgroup.The 42%glass fiber post was used in A1, B1 and C1 groups. The 75%glass fiber post was used in A2, B2 and C2 groups. All of groups were restored with resin cores and metal crowns. The fracture resistance was measured with universal testing machine and recorded the root frac-ture pressure data and the mode of all the teeth. Results The fracture resistance was significantly higher in group A than that of group B and group C (P<0.05), and the fracture resistance was significantly higher in group B than that of group C (P<0.05). The fracture resistance was significantly higher for 75%glass fiber post than that of 42%glass fiber post (P<0.05). Conclusion Within a certain range, the longer the length of glass fiber post, the greater the tooth fracture resistance. The fracture resistance of fiber content is better for 75%glass fiber post than that of 42%glass fiber post.
ABSTRACT
Aims and Objectives: to evaluate the resistance to displacement of metal intraradicular retainers of different lengths by means of the shear test. Material and Methods: Thirty-six maxillary central incisors were cross-sectioned at 16 mm from the root apex, endodontically treated and randomly divided into three groups that were treated as follows: G1 (control) preparation of 2/3 (10.6 mm) of the total root length; G2: preparation of 1/2 (8 mm) of the total root length and G3: preparation of 1/3 (5.3 mm) of the total root length. After canal preparation, a matrix was made of the coronal and radicular portions using Duralay to obtain metal intraradicular retainers. These retainers were cemented with zinc phosphate cement and subjected to the compression shear test in a Universal Test Machine (EMIC DL 2000) at a crosshead speed of 0.5 mm/minute. The results were subjected to statistical analysis by analysis of variance (ANOVA) and Newman- Keuls, which showed statistically significant difference (P < 0.01). Results: The means in Newtons and their respective standard deviations were: G1 = 972.05 (±81.36); G2 = 921.15 (±112.25); G3 = 686.66 (±113.02). Conclusion: It could be concluded that metal retainers of 2/3 and 1/2 the length of the root portion showed higher resistance to displacement values when compared with the group that had been prepared for 1/3 of the root length.