Traction test of temporary dental cements

Comparison of marginal leakage and retentive strength of implant-supported milled zirconia and cobalt-chromium copings cemented with different temporary cements

Background

Few studies assessed the effect of coping material (particularly milled metal copings) on the retentive strength of cements and reported contradictory results. Thus, this study aims to assess the marginal leakage and retentive strength of implant-supported milled zirconia and cobalt-chromium (Co-Cr) copings cemented with different temporary cements.

Materials and Methods

In this in vitro study, Zirconia and Co-Cr copings were fabricated on 100 straight titanium abutments. Each group of copings was divided into five subgroups (n = 10) for the use of different cements: permanent zinc-phosphate (ZP) cement, temporary zinc oxide eugenol cement (temp bond [TB]), calcium hydroxide-based temporary cement (Dycal [DC]), polymer-based eugenol-free acrylic-urethane temporary cement (Dentotemp [DT]), and methacrylate-based temporary cement (Implantlink [IL]). The retentive strength and marginal leakage of restorations were assessed. Data were analyzed by one-way ANOVA, Tukey, and Fisher's exact tests (α = 0.05).

Results

In the Co-Cr group, the retentive strength values (in Newtons) were as follows: ZP (411.40 ± 5.19) >DC (248.80 ± 5.01) >IL (200.10 ± 5.06) >DT (157.90 ± 5.19) >TB (98.50 ± 6.88). This order was as follows in the zirconia group: ZP (388.70 ± 5.35) >DC (226.60 ± 5.08) >IL (179.00 ± 3.71) >DT (136.00 ± 4.88) >TB (78.60 ± 3.50). All pairwise comparisons were statistically significant (P < 0.001). The difference in marginal leakage was not significant among the groups (P = 0.480).

Conclusion

The type of coping material and cement type significantly affected retentive strength, but not marginal leakage, of implant restorations. Milled Co-Cr copings showed higher retentive strength than zirconia copings, and ZP cement followed by DC yielded the highest retention.

Comparison of Mechanical Properties of Chairside CAD/CAM Restorations Fabricated Using a Standardization Method

The aim of this in vitro study was to investigate the fracture resistance, fracture failure pattern, and fractography of four types of chairside computer-aided design/computer-aided manufacturing (CAD/CAM) restoration materials in teeth and titanium abutments fabricated using a standardization method. An artificial mandibular left first premolar prepared for all-ceramic crown restoration was scanned. Forty extracted mandibular molars and cylindrical titanium specimens were milled into a standardized shape. A total of eighty CAD/CAM restoration blocks were milled into a crown and twenty pieces of each lithium disilicate (LS), polymer-infiltrated-ceramic-network (PICN), resin nano ceramic (RNC), and zirconia-reinforced lithium silicate (ZLS) materials were used. Crowns were bonded to abutments, and all specimens underwent thermal cycling treatment for 10,000 cycles. Fracture resistance was measured using a universal testing machine and fracture failure patterns were analyzed using optical microscopy and scanning electron microscopy. Statistical differences were analyzed using appropriate ANOVA, Tukey HSD post hoc tests, and independent sample t-tests (α = 0.05). The results indicated that, in both teeth abutments and titanium abutments, the fracture resistances showed significantly the highest values in LS and the second highest in ZLS (p < 0.05). The fracture resistances based on teeth abutments and titanium abutments were significantly different in all the CAD/CAM restoration materials (p < 0.05). There are statistically significant correlations between the types of materials and the types of abutments (p < 0.05). Each of the different materials showed different fracture failure patterns, and there was no noticeable difference in fractographic analysis. Lithium disilicates and zirconia-reinforced lithium silicates exhibited statistically high fracture resistance, indicating their suitability as restoration materials for natural teeth or implant abutments. There were no distinct differences in the fracture pattern based on the restoration and abutment materials showed that the fracture initiated at the groove where the ball indenter was toughed and propagated toward the axial wall.

Methodology in specimen fabrication for in vitro dental studies: Standardization of extracted tooth preparation

Background

Specimen preparation for in vitro study suffers a general lack of methodological homogeneity, as well as a lack of uniformity in the materials selected for fabricating them. This situation prevents comparisons between studies. When a specimen is not of dental origin it is not possible to study adhesion or bonding techniques realistically. The objective is to design and implement a method of specimen preparation that permits universal standardization for use in in vitro studies.

Material and Methods

A metal stump of specified dimensions was designed and fabricated by hand. It was scanned, the data digitalized, perfecting and standardizing the dimensions. Ten human molars were adapted to the size and shape of a standard milling block. A Cerec 3D inLab Cerec milling unit was used to prepare the molars to match the digitalized model.

Results

Ten specimens with identical dimensions were obtained.

Conclusions

CAD-CAM technology allows the preparation of natural extracted teeth to be standardized and could be used to establish a reproducible method that would facilitate comparison between different in vitro studies, and reduce bias arising from variations in sample fabrication.

Key words:Test ceramic, dentin analog, dentin model, dentin samples, methodology.