Journal of Dental Medicine

Background and Aim: Stainless steel crown (SSC) is the most durable and reliable restoration for primary teeth with extensive caries but its metalic appearance has always been a matter of concern. With advances in restorative materials and metal bonding processes, composite veneer has enhanced esthetics of these crowns in clinic. The aim of this study was to evaluate the shear bond strength of SSC to composite resin using different surface treatments and adhesives.

Materials and Methods: In this experimental study, 90 stainless steel crowns were selected. They were mounted in molds and divided into 3 groups of 30 each (S, E and F). In group S (sandblast), buccal surfaces were sandblasted for 5 seconds. In group E (etch) acidic gel was applied for 5 minutes and in group F (fissure bur) surface roughness was created by fissure diamond bur. Each group was divided into 3 subgroups (SB, AB, P) based on different adhesives: Single Bond, All Bond2 and Panavia F. Composite was then bonded to specimens. Cases were incubated in 100% humidity at 37°C for 24 hours. Shear bond strength was measured by Zwick machine with crosshead speed of 0.5 mm/min. Data were analyzed by ANOVA test with p<0.05 as the limit of significance.

Results: There was no statistical interaction between surface treatment and adhesive type (P>0.05) so the two variables were studied separately. No significant difference was observed in mean shear bond strength of composite among the three kinds of adhesives (P>0.05). Similar results were obtained regarding surface treatments (P>0.05).

Conclusion: Based on the results of this study, treating the SSC surface with bur and using single bond adhesive and composite can be used successfully to obtain esthetic results in pediatric restorative treatments.

Background and Aim: Because of stable aesthetic and minimum destructive technique, Porcelain laminate veneer has an important role in aesthetic dentistry. But main reason of failure in this treatment is restoration fracture. Therefore tooth preparation have an important role in fracture resistance of porcelain laminate veneer. The aim of this in vitro study was to evaluate the fracture resistance of porcelain laminate veneer dependent on tooth preparation after exposure to dynamic loading.

Materials and Methods: In this study, 30 caries free mandibular incisors were devided into 3 groups. First group (Control group) remained unprepared. In second group (Window preparation) facial surface was prepared with 0.3, 0.5, 0.7 mm in cervical, middle and incisal, respectively. In third group (Incisal lap preparation) the preparation was like second group and included 2 mm of incisal edge. 20 feldespatic ceramic veneer were bonded adhesively with dual-cure luting cement (Rely X). All specimens were subjected to cyclic mechanical loading (720000 cycles, 1.3Hz, 30N) and thermal cycling (5-55 C, dwell time 60seconds, 500 cycles). The specimens were exposed to Universal testing machine until failure occurred with a constant crosshead speed of 1mm/min.

Results: Five specimens of first group, one specimen of second group and two specimens of third group fractured during cyclic loading. The mean failure loads(MPa) after exposure to continues load were as follows: First group: 168/96 (561.01-1115.08), second group: 394.10 (248.92- 641.33) and third group: 273.47 (135.45 - 479.80). Data analysis was performed by ANOVA, LSD and chi Square test.

Conclusion: Significant difference between 3 groups were found. Fracture resistance of control group was significantly higher than other groups and window group preparation was significantly higher than incisal lap group. The samples were under the cyclic loads before they put under the continuous pressures of universal testing machine. It was clear that incisal lap preparation is more resistance against fatigue failure compared to window preparation.

  Background and Aims: Marginal fit is one of the key factors in the success of fixed restoration. The aim of this study was to evaluate the fitness of feldespatic crowns made from additional silicon impression and gypsum cast by CAD/CAM.

  Materials and Methods: 10 intact extracted upper premolar teeth were used for this experimental study. After preparation of the mounted teeth with radial shoulder finish line, 2 Vita Mark II feldespatic CAD/CAM machined crowns were fabricated for each tooth (one from scanning the additional silicone impression of the prepared tooth and the other one from the plaster model). Marginal gap of each crown was measured using SEM in two points on the mesial and 2 points on the buccal surface. Data were analyzed using Paired t-test with SPSS version 17 software (P<0.05).

  Results: The mean of marginal gaps in crowns fabricated from additional silicone and model plaster were (155.13±37.11) and (130.18±12.35), respectively. However, no significant difference emerged between marginal gaps of the two methods (P=0.055). Also, the mean of marginal gaps in crowns fabricated from additional silicone and model plaster was higher in mesial (157.82±44.41) compared to buccal (127.50±24.26) region (P=0.003).

  Conclusion: Marginal fit was not significantly differen ce between crown s made of the plaster casts and silicone molds and both methods showed the same results .