Faculty & Staff

Faculty and Staff

Mitchell Ryan Davis, M.D
Program Director

Ryan Davis is a family medicine physician, board-certified in that specialty since 1998. He graduated with his M.D. from the Boston University, School of Medicine in 1995. Dr. Davis completed his residency in family medicine in 1999 at Franciscan Medical Center in Dayton, Ohio, formerly St. Elizabeth Medical Center. In 1998, Dr. Davis accepted full-time employment with The Chickasaw Nation at Carl Albert Indian Hospital, now known as the Chickasaw Nation Medical Center, where he currently serves as the Program Director for the Family Medicine Residency. Dr. Davis has held a number of clinical appointments in his career. He has served as chief of staff, chairman of morbidity and mortality committee, member of credentials committee, chairman of pharmacy and therapeutics committee, and currently serves as chairman of Medisaw Committee/Contract Health. Dr. Davis loves spending time with his wife of 27 years, Marcy. They have two children: a son, Taylor who is currently attending Oklahoma State University; and a daughter Madison, who is attending the University of Oklahoma. Dr. Davis enjoys collecting comic books and is a huge Thunder basketball fan. He enjoys exercise and the outdoors, loves to travel and spend time with his family and friends. He also is a world-known judge of Pokémon, judging tournaments around the world.


Steven Fillmore, M.D, FACP, MBA
Core Faculty

Steven Fillmore is an internal medicine physician, board-certified in that specialty since 1985. He graduated with an M.D. from the University of Oklahoma in 1982 and completed residency in Oklahoma City, Oklahoma, at the University of Oklahoma Tulsa Medical College. In 2012, Dr. Filmore accepted full-time employment with the Chickasaw Nation Department of Health, where he serves as Chief of Inpatient Medicine, Chief of Staff Elect, Chair of the P&T Committee and Chair of the HIM Committee. Dr. Fillmore has been married to his wife and best friend, Lisa, since 1979. They have three sons and one daughter-in-law. He enjoys working on his ranch and strives to learn something new each day.


Tessa Ray
Program Coordinator

In 2011, Ray accepted a full-time position with the Chickasaw Nation Department of Health, where she currently serves as the Program Coordinator for the Family Medicine Residency. Prior to the residency program, she was the Medical Support Services Coordinator. Ray lives in Ada, Oklahoma. She has two sons and a cat. She enjoys Thunder basketball, OSU football, loves to travel, and spend quality time with her family.

Denise Nguyen, D.O.

Denise Nguyen was born in Oklahoma City, Oklahoma. Nguyen attended the University of Oklahoma for undergraduate studies and attended medical school at A.T. Still University. Her hobbies include group fitness, barre and spin class, traveling, swimming and reading. Nguyen’s career goal is to become a hospitalist.

Jacob Hollenbeck, D.O.

Jacob Hollenbeck was born and raised in south central Oklahoma. He graduated from Dickson High School. Hollenbeck earned his Bachelor of Science in biology from the University of Science and Arts of Oklahoma, in Chickasha. While in Chickasha, he married his high school sweetheart Kendra, who to this day, still endures him.

Hollenbeck attended medical school at Oklahoma State University, where he was part of the rural medical track. He decided on family medicine because of the versatility it offers in serving patients in rural Oklahoma.

As a Chickasaw citizen, he experienced firsthand the dedication of the Chickasaw Nation, in enhancing the overall quality of life of the Chickasaw people, leading him to pursue his residency training at the Chickasaw Nation Medical Center.

Hollenbeck is proud to be part of the Family Medicine Residency Program and is excited to see it grow. In his free time, he enjoys spending time with his wife and son, Johnny. He also loves hiking with his dog Lilly, playing board games and listening to history lectures while finishing his “honey do” list.

Pamela Kelli Grafton, D.O.

Pamela Grafton was born and raised in Oklahoma. Grafton spent most of her life in Sand Springs, Oklahoma, with her family. She married her best friend in 2012. They were married by Elvis in Las Vegas, on leap day. Together, they have a 14-year-old pug and two Manx kittens. In her free time, Grafton’s hobbies include weaponry, cooking and traveling. Her favorite areas of medicine are emergency, addiction and psychiatry.