I have not read convincing evidence that eating bread helps prevent problems from bones and other sharp objects. The object is to add bulk and most bread will be digested adding little bulk. Whole grain bread might be more useful and undigestible fiber (bran, psyllium, etc.with water) are commonly used as bulk laxatives in humans, horses, dogs and cats. The bulk laxatives need to be given with reasonably large amounts of water. I have read about cotton (not synthetics) balls can help, but again have not read convincing evidence that they really help.
We all worry about chicken bones perforating the intestinal tract, but many dogs eat them and rarely have problems. Dogs usually chew them before swallowing reducing the size of the pieces, which allows them to pass through the intestines.
Apple seeds contain cyanide glycosides. Cyanide is toxic and dose related. Clinical signs are seen rapidly after exposure. A few seeds are not likely to contain enough cyanide to produce toxic effects in an 18 pound dog.
Waiting and watching is an option. Vomiting, lack of appetite, fever and abdominal pain are signs. These signs appear after perforation and are not sensitive early indicators of problems.
X-rays can indicate size and quantity of bones in the GI tract. Taken several times they indicate if the bone fragments are moving through the intestines without incident.
Let me know if you have follow up questions.