Many people do not know the difference between surface piercings and dermal anchors, in fact, they may even come in and ask for the wrong one. Normally piercings go through parts of the body which have a front and a back or an inside and an outside. These piercings, however, go through parts of the body which are flat.
Surface piercings have a higher chance of rejection and most will end up coming out. The exception to this is the back of the neck and the nape as these areas do not get a lot of the type of skin movement which can cause the piercing to migrate or tear. Originally, surface piercings were supposed to be temporary but many people didn't understand that and were left with unsightly scars. Most professional piercers will no longer offer surface bars because of the problems and will advise clients to go with dermal anchors instead.
Surface jewelry looks like a flat steel bar that is C shaped because of a post on either end. The posts can have balls or other attachments on the end. The jewelry comes in a variety of lengths depending on the piercing but is usually between 5/8" of an inch to 1.5 inches long. When surface piercings first became popular many piercers would use ordinary piercing jewelry such as curved barbells which increased the chances of rejection simply because no other jewelry had been designed yet.
Dermal or subdermal anchors were invented after surface piercings and they have generally made surface piercings obsolete because they offer the same looking piercing with a much lower chance of rejection. These are a small t-shaped bar with a screw hole or post which is inserted into a punched hole through the skin. It is a single point piercing and does not come back out through a second part of the skin. As the piercing heals the skin grows around the anchor and holds it in place. Two dermal anchors can be used in place of a surface bar and will give the exact same look without the healing complications that the bar causes. The skin can move freely between the piercings which it cannot when held by a solid bar piece of jewelry. There is very little healing involved because it is only a single hole in the skin.
Dermal anchor jewelry can be vary varied. The small screw post on the jewelry can be used to attach rings, gems, balls, spikes and more which makes it a very versatile piercing. The rings can also be used with multiple dermal piercings to create a corset design using ribbons. Most people that have dermal anchors in areas which are likely to get caught on clothing choose to keep flat disks that stay flush with the skin unless they are being shown off. This reduces the risk that the piercing will get caught and ripped out significantly.
When piercing a dermal anchor a dermal punch is used to take out a small piece of skin, there is no exit hole and nothing else is needed. With a surface bar a channel has to be created between the entry and exit holes underneath the skin. It requires more healing because there is an inch or so of damage where the bar sits. Comparatively it is a lot of tissue to heal, there are no other piercings which require that level of damage. The other issue with surface piercings is that because the bar is a solid construct it cannot stretch with the tissue around it. Skin moves and stretches so while the are may have been pierced at the correct distance for the bar as it is stretched it can cause tearing and discomfort just by normal movement if it's in an area like the hips. This eventually causes scarring and rejection. As there is nothing connecting dermal anchors the skin can move and stretch normally without this problem.
The risk with a dermal piercing and a surface bar is that it can become snagged and get ripped out or partially ripped out. However, while a surface bar will have to be removed and may not be able to be replaced because of scarring the dermal anchor can be replaced as soon as the skin around has healed from the tear. It will also leave only a small dot or scar if you decide not to replace it.