Evaluation of the effect of surface roughness and modification of implant abutment axial wall on the retention of zirconium oxide copings before and after thermocycling.

Background: The purpose of this study was to determine the effect of one-wall elimination of the abutment and also the surface treatment of the abutment on the retention of cement-retained, implant-supported zirconium oxide copings. Material and Methods: In this experimental study, four straight abutments were connected to four implant analogs (DIO, UF, Busan, Korea) with 35 Ncm torque. They are mounted vertically in resin blocks. Abutments were prepared as following groups: A) abutment was used in its intact standard form as a control group. B) 4 mm of the flat wall was removed to produce an abutment with 3 walls. C) The abutment surface was abraded with 50 µm AL2O3 powder. D) 4 mm of a flat wall of the abutment was removed, then the abutment surface was abraded with 50 µm AL2O3 airborne particle.10 zirconium oxide copings were made. Samples were cemented with temp bond NE to abutments. The retention of copings was measured before and after incubation using the universal testing machine. T-test, one-way ANOVA, and Post Hoc Tukey Test were used for statistical analysis of data. Results: In all groups, retention was decreased after thermocycling (P ≤0.001). 3 wall abutments had less retention than the control group before thermocycling. A significant difference was detected between 3 wall abutments and 4 walls of sandblasted abutments before thermocycling. After thermocycling, no difference in retention was seen between groups. Conclusions: Thermocycling significantly reduces the retention of implant-supported ceramic copings. Sandblasting abutments with 50 µm AL2O3 air-borne particles did not increase the retention of ziconium oxide copings which were cemented with temp bond NE. One wall elimination of abutment decreased the retention of zirconia copings. Key words:Retention, crown, abutment, zirconia coping, sandblasting.

Effect of Surfosept and Deconex® 53 Disinfectant Agents on the Accuracy and Dimensional Stability of Panasil Dental Impression Materials: An Experimental Study.

MATERIALS AND METHODS: This in vitro study was performed on 30 dental casts. The samples were divided into one control group and two experimental groups to be disinfected with Surfosept (1%) and Deconex® 53 (2%) using a sequential sampling method (10 per group). The impressions in the experimental groups (i.e., Surfosept and Deconex® 53) were rinsed and dried; then, the disinfectant was sprayed on the impressions and remained for 30 seconds before pouring with stone. In the control group, the impressions were only rinsed and dried and were poured in 10 minutes. Cast dimensions were measured by a profile projector device, and the mean values obtained from the experimental groups were compared with those of the control group. RESULTS: There were no significant differences among the groups regarding the height of the resulting dies without undercut (P=0.62). Moreover, there was no significant difference among the groups regarding the distance between the two dies (P=0.77). However, the diameter of the dies with undercut and without undercut was different significantly among the control and experimental groups (P < 0.005). CONCLUSION: In general, no significant difference was encountered between dimensional stability and accuracy of the dental impressions using Surfosept and Deconex® 53 in this study.

Effects of abutment diameter, luting agent type, and re-cementation on the retention of implant-supported CAD/CAM metal copings over short abutments.

PURPOSE: The aim of this study was to evaluate the effects of abutment diameter, cement type, and re-cementation on the retention of implant-supported CAD/CAM metal copings over short abutments. MATERIALS AND METHODS: Sixty abutments with two different diameters, the height of which was reduced to 3 mm, were vertically mounted in acrylic resin blocks with matching implant analogues. The specimens were divided into 2 diameter groups: 4.5 mm and 5.5 mm (n=30). For each abutment a CAD/CAM metal coping was manufactured, with an occlusal loop. Each group was sub-divided into 3 sub-groups (n=10). In each subgroup, a different cement type was used: resin-modified glass-ionomer, resin cement and zinc-oxide-eugenol. After incubation and thermocycling, the removal force was measured using a universal testing machine at a cross-head speed of 0.5 mm/min. In zinc-oxide-eugenol group, after removal of the coping, the cement remnants were completely cleaned and the copings were re-cemented with resin cement and re-tested. Two-way ANOVA, post hoc Tukey tests, and paired t-test were used to analyze data (α=.05). RESULTS: The highest pulling force was registered in the resin cement group (414.8 N), followed by the re-cementation group (380.5 N). Increasing the diameter improved the retention significantly (P=.006). The difference in retention between the cemented and recemented copings was not statistically significant (P=.40). CONCLUSION: Resin cement provided retention almost twice as strong as that of the RMGI. Increasing the abutment diameter improved retention significantly. Re-cementation with resin cement did not exhibit any difference from the initial cementation with resin cement.

The use of functionally graded dental crowns to improve biocompatibility: a finite element analysis.

In post-core crown restorations, the significant mismatch between stiffness of artificial crowns and dental tissues leads to stress concentration at the interfaces. The aim of the present study was to reduce the destructive stresses by using a class of inhomogeneous materials called functionally graded materials (FGMs). For the purpose of the study, a 3-dimentional computer model of a premolar tooth and its surrounding tissues were generated. A post-core crown restoration with various crown materials, homogenous and FGM materials, were simulated and analyzed by finite element method. Finite element and statistical analysis showed that, in case of oblique loading, a significant difference (p < 0.05) was found at the maximum von Mises stresses of the crown margin between FGM and homogeneous crowns. The maximum von Mises stresses of the crown margin generated by FGM crowns were lower than those generated by homogenous crowns (70.8 vs. 46.3 MPa) and alumina crown resulted in the highest von Mises stress at the crown margin (77.7 MPa). Crown materials of high modulus of elasticity produced high stresses at the cervical region. FGM crowns may reduce the stress concentration at the cervical margins and consequently reduce the possibility of fracture.

Influence of inhomogeneous dental posts on stress distribution in tooth root and interfaces: Three-dimensional finite element analysis.

STATEMENT OF PROBLEM: In post-and-core crown restorations, the use of flexible posts concentrates stresses at the dentin and the use of stiff posts concentrates stresses at the interfaces. A class of inhomogeneous materials (called functionally graded materials) has been proposed for posts to resolve the weaknesses of both flexible and rigid posts. PURPOSE: The purpose of this in vitro study was to design an inhomogeneous post and investigate its influence on the stress distribution of post-and-core crown restorations. MATERIAL AND METHODS: An extracted tooth was mounted, sectioned, and photographed to create a 3-dimensional model of the first premolar tooth. The post-and-core crown restoration was modeled with and without a ferrule. The surrounding tissues of the mandibular tooth, periodontal ligament, and cortical and trabecular bones were modeled. Fiber-reinforced composite (FRC), metallic, and inhomogeneous posts were investigated by finite element analysis and the stress distribution results compared. RESULTS: FRC posts resulted in the highest maximum tensile stress (MTS) at the remaining dentin (90.4 to 93.2 MPa), while inhomogeneous posts graded by index n=10 (FGM10) caused the lowest MTS, both with and without a ferrule (72.3 to 74.8 MPa). CONCLUSIONS: The use of FRC posts concentrated more MTS at the dentin and less MTS at the dentin-adhesive interface than metallic posts. Inhomogeneous posts (FGM10) resolved the weaknesses of both flexible and rigid posts by simultaneously reducing stresses at the dentin and interface. The ferrule effect resulted in fewer dentin and interface stresses.

Metal ion release from fixed orthodontic appliances--an in vivo study.

The aim of this study was to test the hypothesis that there is no difference in salivary metal ion content between subjects with fixed orthodontic appliances and their same-gender sister or brother without any orthodontic appliance. This retrospective study was carried out on 28 subjects (16 females and 12 males) who had undergone fixed orthodontic therapy for a duration of 12-18 months. In order to limit the effects of dietary and hygiene habits on salivary metal ion concentration, a same-gender brother or sister (total of 28 subjects) was selected as a control. Approximately 5 ml of saliva was collected from each subject, and the samples were analysed using an atomic absorption spectrophotometer. The detection limit of the method for sample solutions was 1 ng/ml. Since some variables were not normally distributed, non-parametric tests (Mann-Whitney U and Wilcoxon W) were used for statistical analysis. The mean salivary nickel (Ni) content in subjects with and without a fixed orthodontic appliance was 18.5 ± 13.1 and 11.9 ± 11.4 ng/ml, respectively. A statistically significant difference (P < 0.035) was found between the two groups. The mean salivary chromium (Cr) ion level recorded was 2.6 ± 1.6 ng/ml in the study group and 2.2 ± 1.6 ng/ml in the control group. The difference, however, was statistically insignificant. Within the limits of this in vivo study, it can be concluded that the presence of fixed orthodontic appliances leads to an increased concentration of metal ions in salivary secretions.

The importance of long time follow-up after vital pulp therapy: a case report.

This report describes a case of an eight years old girl who was treated for complicated crown fracture of right maxillary central incisor because of a sport accident. For the tooth total pulpotomy was performed in order to achieve apexogenesis and the tooth was restored with a composite resin. The patient was reviewed over 10 years. At first the tooth showed continued root development and complete apex formation following vital pulp therapy, however, after 10 years the tooth developed pulp necrosis and periapical radiolucency. Following root canal therapy, periapical radiolucency has been healed.