Tufts OpenCourseware
Authors: John Morgan, Bonnie F. Zimble

Autism Spectrum Disorders:


Special Care in Dentistry
John Morgan, DDS
Tufts University School of Dental Medicine, 2008

Study Questions     

  1. What are the five types of Autism Spectrum Disorders (also known as Pervasive Developmental Disorders)?

  2. What is the current prevalence range for ASDs?

  3. List and describe the five behavioral categories that characterize ASDs.

  4. By what age is the diagnosis of ASD typically made?

What are the Autism Spectrum Disorders? 

Autism Spectrum Disorders (ASD), also known as Pervasive Developmental Disorders (PDD), are comprised of the following five neurobiological conditions:  

  • Autistic Disorder

  • Asperger’s Syndrome

  • Pervasive Developmental Disorder: Not Otherwise Specified (PDD:NOS)

  • Childhood Disintegrative Disorder

  • Rett Syndrome

Current prevalence rates suggest that ASDs affect between 1 in 166 and 1 in 500 children. The first three conditions - Autistic Disorder (also referred to as “classic autism”), Asperger’s Syndrome, and PDD:NOS (a diagnosis often given in a child’s second year of life, when a more specific diagnosis on the spectrum is not yet possible) account for most cases of ASDs. These three conditions share many of the same symptoms, but they differ in terms of the time and speed of onset, severity and other specific characteristics. Two other conditions - Rett Syndrome and Childhood Disintegrative Disorder – are relatively rare. Rett Syndrome affects 1 in 10,000 to 15,000 individuals, and occurs almost exclusively in females. Childhood Disintegrative Disorder occurs in approximately 1 in 50,000 individuals, and is almost exclusively found in males.

Common symptoms of Autistic Disorder, Asperger’s Sydrome and PDD:NOS, appear across five behavioral categories. They are:

  • Communication. Communication skills may be very slow to develop, or fail to develop at all. Children often resort to gestures and other behaviors to communicate needs.

  • Social interactions: Children prefer to spend time alone, and may avoid or be indifferent to social interactions with parents, siblings and peers. They respond poorly to social cues such as eye contact and smiles.

  • Sensory responses: Persons with ASD are often overly sensitive to touch. Other senses may also be affected.

  • Play skills: Play lacks spontaneity and imagination. Children tend not to imitate and learn from others, and they rarely engage in pretend play.

  • Behavioral abnormalities: Individuals with ASD often fixate on a single item, idea or person. They may throw tantrums or engage in self-injury, frequently in response to even minor changes in routines.

Children with ASD are typically diagnosed before the age of three. As suggested by the characteristics above, ASD profoundly affects the child’s ability to communicate, develop language, form social relationships and respond appropriately to the environment. Systematic behavioral intervention, begun as early as possible, is considered crucial for teaching new skills and managing problematic behaviors.

For more information on the prevalence, causes and characteristics of ASD, click here to go to the Centers for Disease Control and Prevention’s web site on “Autism:”