By:  Jeffrey W. Horowitz, DMD, FAGD

Originally printed in the Sleep Magazine

The role of vertical dimension increase with regard to airway improvement for edentulous patients has been well documented in the scientific literature.

Why then, is there any debate with regard to vertical dimension as it affects Oral Appliance Therapy (OAT) for Obstructive Sleep Apnea (OSA)? In this, the first installment
of a two part article, a position as
to the importance of understanding vertical dimension as an integral part of O.A.T. will be given. In part two, case studies will be explored, validating the testimony given below.

The controversy over vertical dimension can be traced back to several studies, though few are cited more often than the 2002 study which concluded that “bite opening induced by M.A.S. does not have a significant impact on treatment efficacy.”2 While this author firmly believes in evidence based practice, attention must be given to not just the conclusions, but to the methods and data. In this particular study, patients randomly received a mandibular advancement splint (MAS) with either 4mm or 14mm of inter-incisal opening and the results compared. There is an immediate concern with the methods of this study, as it compares only the extremes of minimum space needed to fabricate most appliances to excessive vertical dimension that has never been necessary in any dental case this author has been involved with. The other concern with this study is that no consideration as to the location of the obstruction is discussed, nor is the skeletal pattern of the subjects.

It has become apparent that an understanding of the therapeutic applicability of reasonable vertical dimensional changes must be explored.  In practice, we quite often refer to the part of the airway that we concern ourselves with as the pharyngeal airway, however to understand the role of vertical we must first
agree that airway compromise can occur within any of the anatomic components. Nasal breathing may be affected by congestion, polyps, septal anomalies, and high palatal vaults. The nasopharyngeal airway or velopharynx can be affected by mid-facial skeletal pattern, airway curvature and adenoidal hypertrophy.
As a common cause of both CPAP and OAT failures, nasal breathing inadequacies can result in obligate mouth breathing. In these patients, patency of both the oral cavity as well as the oro-pharyngeal airway is critical. Regarding the oral cavity, a large tongue, deep bite or constricted arch form can inhibit airflow before it reaches the oro-pharyngeal junction (OPJ). At the OPJ, tongue size, neuromuscular tone, redundant soft tissues, and retrognathia can have
a negative impact on the airway. Beyond the OPJ, the skeletal pattern, tonsilar tissues, fat deposition and neuro-muscular tone are all major contributors to compromise, with skeletal pattern and tongue size having less of an affect downward toward the hypopharynx. 3

While open bites and high mandibular plane angles have traditionally been associated with airway compromise at the velopharynx and upper oropharyngeal airway 4, deep bites or low mandibular plane angles can adversely affect oral cavity patency back to the OPJ.