Evaluation of the Effectiveness of Fracture Repairing of the Ceramic- Metal and Zirconia Prostheses by the Direct Method ( In Vitro Study)

Abstract

Introduction: Metal-ceramic and zirconia restorations are among the most common and widely used in dentistry due to their durability, aesthetics, and other advantages. However, a recurring issue has emerged: the feldspathic porcelain covering these restorations is prone to fracture at very similar rates, as shown in previous research Therefore, it became necessary to seek a solution to this common problem and to develop an effective method that can be relied upon and followed as a standardized protocol for both types of restorations when facing such fractures in dental clinics. Especially since these fracture cases are often urgent and require a quick and direct solution. This is where the idea for the research originated.

Objectives: to compare the effectiveness of the direct method in repairing fractures of porcelain fused to metal (PFM) and  porcelain fused to zirconia (PFZ) restorations using nanohybrid composite and universal ceramic primer by studying shear bond strength.

Materials and methods:The research sample consisted of  40  samples in the form of parallelepipeds with dimensions (10x10x3mm). 20 of them were made of metal with a thickness of 1mm, and the other 20 were made of zirconia with a thickness of 1mm. Feldspathic porcelain was applied over all samples  with a thickness of 2mm They were then divided into four groups: Group A:  10 fractured metal-ceramic samples with mixed fracture,Group B:10 intact metal-ceramic samples (control group),Group C:  10  fractured zirconia-ceramic samples with mixed fracture, Group D:  10  intact zirconia-ceramic samples (control group) .  A standardized method  was used for surface treatment of both types of prostheses mentioned above, which is a (mechanical-chemical) method ,then nanohybrid composite resin applied. The samples were then placed in an incubator at 37°C for 48 hours. shear strength  test was performed using a Universal Testing Machine.

Results: There were no statistically significant differences between the fractured metal-ceramic samples that were repaired using the direct method group(A) and the fractured  zirconia-ceramic samples that were repaired using the direct method group (C), the average shear bond strength for the first group was 36.17MPa, while it was 40.04MPa for the second group .The most common failure pattern in group (A) was cohesive failure, while in group (C) it was adhesive failure.

 Conclusions:The direct method of repairing fractured metal-ceramic and zirconia-ceramic prostheses can be considered effective  for both types of prostheses.in addition, the technique of mechanical-chemical dual surface conditioning  is an ideal method that has achieved a high shear bond strength results in the contex of direct repair , A unified and effective repair strategy or protocol has been developed that can be adopted for both types of restorations , and this is a good thing that saves time, effort, and money.