I had a request to post about "safe" things for dogs to chew on. Generally speaking, there is no such thing. Sorry for the bad news. End of post.
Just kidding. It's true about the lack of truly safe toys, especially for aggressive chewers but I will elaborate on why and what is is better.
So what makes an object unsafe? Basically if an object of soft enough not to break teeth it's soft enough to be chewed into pieces and swallowed possibly causing a foreign body. It they can't chew it up then it's probably hard enough to break teeth.
Most commonly the tooth that breaks is the upper fourth premolar. This is one of the largest teeth in the mouth and is labeled Carnassial tooth in the diagram. When chewing on hard objects this tooth will frequently suffer a "slab" fracture where a slab of the tooth gets knocked off. Best case scenario this is a superficial fracture that does not penetrate into the pulp cavity (where the nerve and blood vessels are) and is not a painful injury.
Ok. So what does this all mean? Lets start with rawhides. I think rawhides are kind of medium hardness and get asked about them all the time. I advise people that while there is a risk of tooth fracture it is fairly small compared to other objects. I also tell them never to let the dogs have rawhide unattended as they can try to swallow a piece whole resulting in choking or foreign body. I give my own dogs rawhides but usually choose the rolled ones-they seem somewhat durable but not as hard as the big knotted bones. They also don't seem as prone to try swallowing the ends.
Up next, Nylabones. These are one the veterinary dentist "don't" list and are apparently one of the top causes of fractured teeth. Like rawhides though these come in varying hardnesses so in theory you could pick a softer one if you were worried. However, I also give these to my dogs. It has been some of the best money I have spent over the years! Zodiac and Holli are chewing them as I write this. I cringe a little when I see them really chomping down on the big one but I acknowledge the risk and am willing to pull the tooth or pay for the root canal. I check the teeth often and so far we have not had a chewing accident.
Other items on the doggie dentist no-no list are cow hooves and natural bones. Cow hooves are just plain hard. Bones have a whole host of problems associated with them including fractured teeth, foreign bodies, and GI upset depending on the type, size, and cooked or raw status of the bones.
Deer antlers are also on the list of things hard enough to break teeth but I have no personal experience with those.
Another reasonable choice for chewing are the product usually referred to as "bully sticks." These seem to be chewy enough to last awhile but not hard enough to break teeth. They also don't seem to chew chunks off and try to swallow them since they do get kind of stringy/chewy.
My favorite recommendation for a safe chew toy is the Kong. While there are some dogs that will chew up and ingest a Kong they are still great toys for the majority of dogs. Always choose one the right size and toughness for your dog and watch them at first to see if they are aggressive enough to destroy it. While there are other tough rubber toys that can be used for chewing the Kong is stuffable to make it enticing (dogs don't seem to like rubber much). I like peanut butter for a quick fix but if you need your dog entertained for a longer period of time or have an aggressive chewer you can stuff it full of canned food and freeze it into a Kongcicle! This is great because you can tailor it to your dog's dietary needs. Plus they don't stain carpet or leave crusty rawhide goo on your dog's feet.
So that's best rundown I can give on safe and not-safe chew toys. Basically use your best judgement for your dog and be prepared to handle a fracture or other issue if it arises. Also one of the veterinary dentists recommends the "knee-cap rule" if you are concerned about dental damage. Basically if you wouldn't want to bang it into your knee cap it's not something you should give your dog to chew on.