A casting defect is an undesired irregularity in a metal casting process. Some defects can be tolerated while others can be repaired, otherwise they must be eliminated. They are broken down into five main categories: gas porosity, shrinkage defects, mould material defects, pouring metal defects, and metallurgical defects. Terminology
The terms "defect" and "discontinuity" refer to two specific and separate things in castings. Defects are defined as conditions in a casting that must be corrected or removed, or the casting must be rejected. Discontinuities, also known as "imperfections", are defined as "interruptions in the physical continuity of the casting". Therefore, if the casting is less than perfect, but still useful and in tolerance, the imperfections should be deemed "discontinuities". Types
There are many types of defects which result from many different causes. Some of the solutions to certain defects can be the cause for another type of defect.The following defects can occur in sand castings. Most of these also occur in other casting processes. Shrinkage defects
Shrinkage defects 
can occur when standard feed metal is not available to compensate for shrinkage as the thick metal solidifies. Shrinkage defects will have jagged or linear appearance. Shrinkage defects usually occur in either the cope or drag portion of the casting. Shrinkage defects can be split into two different types: open shrinkage defects and closed shrinkage defects. Open shrinkage defects are open to the atmosphere, therefore as the shrinkage cavity forms, air compensates. There are two types of open air defects: pipes and caved surfaces.
If the reconstruction is ultimately successful, it is easy to remove the percutaneous BAHA abutment. If the surgery is unsuccessful, the abutment can be replaced and the implant re-activated to restore hearing. External ear
The age when outer ear surgery can be attempted depends upon the technique chosen. The earliest is 7 for Rib Cartilage Grafts. However, some surgeons recommend waiting until a later age, such as 8–10 when the ear is closer to adult size. External ear prostheses have been made for children as young as 5. For auricular reconstruction, there are several different options:

Rib Cartilage Graft Reconstruction: This surgery may be performed by specialists in the technique. It involves sculpting the patients own rib cartilage into the form of an ear. Because the cartilage is the patients own living tissue, the reconstructed ear continues to grow as the child does. In order to be sure that the rib cage is large enough to provide the necessary donor tissue, some surgeons wait until the patient is 8 years of age; however, some surgeons with more experience with this technique may begin the surgery on a child aged six. The major advantage of this surgery is that the patients own tissue is used for the reconstruction. This surgery varies from two to four stages depending on the surgeons preferred method. A novel one stage ear reconstruction technique is performed by a few select surgeons. One team is able to reconstruct the entire external ear and ear canal in one operation.