meet our team

A Team that Roots for You

Friendly Dental Experts

Our energetic, enthusiastic team is proud to provide the attentiveness and personalized dental care each child deserves. Every member of our team communicates in a way that children and parents understand and appreciate. Nothing makes us happier than to encourage healthy hygiene habits and educate our patients about how to care properly for their smiles!

Get to Know Dr. Nasem

Dr. Nasem specializes in dental care for children, young adults, and individuals with special needs. She truly believes that every child deserves personalized care and attentiveness at each visit because she understands the importance of positive dental experiences. As a mother of two herself, she truly cares for every child as if they were her own.

Dr. Nasem's education started at Indiana University, where she was a dual major gaining a bachelor of science in Biology and a bachelor of science in Psychology. She then went to Boston, Massachusetts to study at Tufts University School of Dentistry. Graduating at the top of her dental class, she was accepted at the University of Southern California Herman Ostrow School of Dentistry for her residency in pediatric dentistry. Upon graduating, she earned the Hugh M. Kopel resident of the year award. Dr. Nasem received the highest achievement possible in pediatric dentistry, she is a Board Certified Pediatric Dentist.

Dr. Nasem has been practicing in South Orange County for over 8 years. During her residency, she was placed at Children's Hospital Orange County (CHOC) to gain extensive knowledge of special needs children and hospital dentistry. She cherishes this special training and continues to work at CHOC treating children in their operating room facilities. She was formerly the residency director for the Orange County hospital USC residents and is currently on faculty at USC to help shape the pediatric dentists of the future.

  • Hugh M. Kopel Resident of the Year - USC
  • Board Certified Pediatric Dentist
  • Incisal Edge Top 40 Under 40 Dental Specialist 2019
  • University of Southern California (USC) Pediatric Dentistry Graduate
  • Tufts University of Dental Medicine Graduate
  • Children's Hospital of Orange County (CHOC) on staff Dentist
  • Member of the:
    -American Academy of Pediatric Dentistry (AAPD)
    -American Board of Pediatric Dentistry (ABPD)
    -California Dental Association (CDA)
    -California Society of Pediatric Dentistry (CSPD)
    -Orange County Dental Society (OCDS)
    -American Dental Association (ADA)

Get to Know Dr. Shivani

Dr. Shivani Keshav was born and raised in Diamond Bar, CA. She attended University of the Pacific where she received her Bachelors of Science in Dental Hygiene. She then earned her dental degree at USC School of Dentistry. She found her passion for pediatric dentistry while providing dental care to children in underserved communities, both locally and internationally, and was awarded the ICD Humanitarian Award. She went on to complete her Pediatric Dental Residency at USC and Long Beach Memorial/Miller Children’s Hospital. During residency she was actively involved in organized dentistry as a liaison and intern where she advocated for the wellbeing of pediatric dentists and their patients.

Dr. Shivani is passionate about providing quality care and oral health education through positive dental experiences for her patients!

In her free time, Dr. Shivani enjoys spending time with her family and friends, traveling, exploring cities by foot, and painting.

Get to Know Dr. Sun

Dr. Dien Sun grew up in San Diego, CA, and journeyed up the California coast to complete her education. She first completed her undergraduate degree at UCLA and then headed up to San Francisco, where she received her DDS degree from UCSF. Dr. Sun found her passion for working with children while in dental school, connecting to kids in all different parts of the Bay Area through community outreach and clinical care. She then journeyed back down to Southern California, completing her two-year residency in pediatric dentistry at USC. While in residency, she trained at Children’s Hospital Los Angeles, where she treated special needs children. Dr. Sun has now found her home back in SoCal, loving the beach, running, attending spin class, cooking, and spending time with her husband and their tabby cat, Peach.

Get to Know Dr. Andrea

Dr. Andrea was born and raised in Southern California. She attended California Baptist University, where she received her Bachelors of Science degree in Biology. Since college, she has spent most of her time at the University of Southern California where she received a Masters of Science in Global Medicine, Doctor of Dental Surgery, and completed her advanced pediatric dental residency- making her a Pediatric Dentist! During her pediatric residency, she trained at Healthy Smiles for Kids of OC and Children's Hospital of OC.

In her free time, she enjoys spending time with her family, friends, and her three furry pups, Dash, Lincoln and Royce. She loves food and enjoy finding new places to eat and different cuisines to try! If you have a great hidden gem, let her know! 

Get to Know Dr. Trishia

Dr. Trishia Johnson is a Board-Certified Pediatric Dentist native to Orange County. She is a triple USC Trojan having received her bachelor's degree, Doctor of Dental Surgery (DDS) degree, and Advanced Pediatric Dentistry Certificate from the Herman Ostrow School of Dentistry of USC. During her residency, she spent much of her time caring for medically compromised children at the Children's Hospital of Orange County (CHOC).

Dr.Trishia bases her practice around prevention and education. She enjoys sharing with parents how the mouth is foundational to many aspects of our lives from feeding, speech, breathing, overall health, and well-being. Her goal is to make each child's visit personable and engaging.

When she is not at the office, you will find Dr. Trishia cherishing the fun adventures of being a mom, going to spin class, and trying new restaurants.

Meet the Team

Viri Gutierrez

Front Office Coordinator

When you call the office, you’re most likely being greeted by Viri, our front office coordinator, also known as our front office guru of all things! She is also an Orange County native and has over ten years in the dental field (hence guru!). Her experience has made her a great resource to our patients and parents, equipping them with all the knowledge and help with their insurance, benefits and hospital scheduling needs.  Viri holds a bachelor’s degree in Human Services and has worked in several non-profit agencies alongside social workers and family case workers. She is passionate about being able to bring her educational background to the dental field and utilize these skills to provide our families the help they need.  In her spare time, Viri enjoys spending time with her son and catching up with family and friends. She also enjoys time outdoors- beach, hiking &camping! One of her favorite things to do is to travel, she tries to go on an adventure at least twice a year!

Haley Nelissen

Front Office Staff

Ms. Haley was Treehouse Pediatric Dentistry’s first employee, starting with Dr. Nasem in 2017 before the doors even opened! She grew up in Southern California and has lived here most of her life, only leaving California and the Treehouse team for a few years to live in England! She loved being able to live in another country, it gave her a new respect for the beauty and sunshine California holds. You’ll find Haley at the front desk with a huge smile and a cheerful Hello! She has always had a passion working with kids and has volunteered at Saddleback Church in the special needs or toddler class. She enjoys her role in our office- creating a positive impact in the community every day! When Haley isn’t greeting our patients, she enjoys being outdoors-horseback riding, working on her family farm, competing in Spartan races, hiking and doing CrossFit. She can’t wait to welcome your family to our office!

Andrea Ramos

Dental Assistant

Ms. Andrea, an aspiring dental hygienist, enjoys comforting kids and providing patience and care that each child deserves during their visits. Her calm, loving approach makes kids feel welcomed and safe during their visits. She loves to spend most of her free time outdoors gardening - you name it, she grows it! She also loves taking her dog, Oso, out for beautiful hikes!

Sadie Rivas

Dental Assistant

Sadie’s nickname could be the Giggler, when you walk in the office and hear someone giggling or laughing, it’s most likely Sadie. This South OC native started her dental career at a young age at a pediatric dental office where it started as a summer job then quickly turned into a career she wanted to pursue. Sadie graduated from Concorde Dental Assisting program in 2011 with honors. She can chit chat about Star Wars or sports with the best of them, making all our patients feel like her best friend. In her spare time, Sadie loves spending time with her two dogs, Lily and Rocky as well as her family. Some hobbies she enjoys on her free time are playing soccer with her cousins, going to sporting events with family, attending concerts, cooking and staying up to date with her favorite shows and movies.

Maria Medina

Dental Assistant

Maria is our kind, soft spoken dental assistant, making kids feel welcomed and cozy while getting their teeth cleaned. She always knew she wanted to work with children and went to pursue a career in a field where she would create unforgettable bonds with them. Her favorite part about working at Treehouse Pediatric Dentistry & Orthodontics is meeting new patients every day and helping them get over their fear of the dentist. She’s even become our official, unofficial hand holder in the treatment room! When she’s not at work, Maria enjoys going to baseball games (Go Angels!), spending time with friends and family and going on new adventures!

Marissa Labayen

Dental Assistant

Marissa, our dental assistant superstar, is an Orange County native. This American Career College Graduate is our little bundle of joy and you'll always see her smiling! Her favorite part of her job is making patients feel special and cared for. Her biggest goal is to defeat any of their dental fears. Dr. Nasem welcomed Marissa with open arms as she performed clinical hours during her time at school and then the rest is history as she became a full-time dental assistant at the office! When Marissa isn't singing and smiling around the office, she sings and smiles her way through spin class as a spin instructor!

Ready to Join Our Family?