CLINICAL
The “therapeutic” Class II and Class III first molar relationship Drs. Donald J. Rinchuse, Dara L. Rinchuse, and Ethan Drake share perspective on first molar arch relationships
A
ngle1 and Andrews2 established criteria for “optimal” static occlusion. In addition, there have been classification systems for malocclusion,1,3,4,5 which help orthodontists glean and distinguish optimal from non-optimal occlusions. From a juxtaposition comparison of over 1,150 welltreated American Board of Orthodontics cases with 120 non-orthodontic treated ideal occlusions, Andrews2 developed his six keys to optimal occlusion. The six keys to optimal occlusion deal with: 1. molar relation, 2. angulation, 3. inclination, 4. no rotations, 5. no spacing, and 6. flat Curve of Spee. Andrews’ six key measurements were taken from the clinical crowns of the teeth and not from the long axes of the teeth (roots). The key characteristic of Angle’s “optimal/normal” occlusion (i.e., key # 1)
Donald J. Rinchuse, DMD, MS, MDS, PhD, graduated from the University of Pittsburgh School of Dental Medicine in 1974 with degrees in Dentistry (DMD) and Pharmacology/Physiology (MS). He received his certificate and MDS degree in orthodontics in 1976 and a PhD in Higher Education in 1985 from the University of Pittsburgh. He is a Diplomate of the American Board of Orthodontics. In addition, Dr. Rinchuse is on the editorial review board of many professional journals including the American Journal of Orthodontics and Dentofacial Orthopedics. He has published over 100 articles, several book chapters, a book, and has made many presentations. Dr. Rinchuse is presently Professor and Graduate Orthodontic Program Director at Seton Hill University, Center for Orthodontics, Greensburg, Pennsylvania. He can be reached at rinchuse@setonhill.edu. Dara L. Rinchuse, DMD, graduated from the University of Pittsburgh School of Dental Medicine (DMD) in 2008 and Jacksonville University School of Orthodontics (Certificate) in 2010. She is a Clinical Faculty, Graduate Orthodontic Program, Seton Hill University, Greensburg, Pennsylvania and is in private orthodontic practice in Belle Vernon, Pennsylvania. She has authored several papers, including several in the American Journal of Orthodontics and Dentofacial Orthopedics. She can be reached at dararinchuse13@gmail.com. Ethan Drake, DMD, MS, is a former orthodontic resident at Seton Hill University, Greensburg, Pennsylvania and is currently in orthodontic practice in Chambersburg, Pennsylvania.
14 Orthodontic practice
Figure 1: Andrews key #1- molar relation- note distal angulation (about +5% tip) of maxillary first molar so that this cusp occludes in the embrasure between the distal of the mandibular first molar and the mesial of the mandibular second molar
Figure 2: Case under orthodontic treatment in which there was single arch extractions of maxillary bicuspids to mitigate a Class II (1) malocclusion and final occlusion will end up with a Class II interarch (therapeutic) molar relationship, with the canines and incisors in a Class I/ normal occlusal relationship
was that the maxillary and mandibular molars should be in an interarch, saggital relatationship such that the mesiobuccal cusp of the upper molar occludes in the buccal groove of the lower molar (the mesiolingual cusp of the upper first molars occludes in the central fossa of the lower first molars).1 Andrews expanded on the thinking of Angle concerning the optimal first molar interarch relationship by discussing the proper distal angulation (“tip”) of the maxillary first molar and its interarch contact relationship with the mandibular second molar. He wrote: “The distobuccal cusp of the upper first permanent molar should make contact and occlude with the mesial surface of the mesiobuccal cusp of the lower second molar.”2 Based upon Andrews, the maxillary molars should have approximately +5 degrees distal angulation (Figure 1).6 It should be pointed out that there are many instances where a first molar interarch relationship can be judged ideal from Angle’s perspective but not from Andrews.2
set in a “therapeutic Class II” relationship; however, the incisors, canines, and most of the rest of the dentition is in a “normal”/Class I relationship (Figure 2).7 Or perhaps, lower bicuspids are extracted (no extractions in the upper arch) to address an Angle’s Class III malocclusion, and the final first molar occlusion results in a “therapeutic Class III relationship.”
Discussion There are instances in orthodontic treatment when single arch extractions are performed to address Class II or III malocclusions,7,8,9,10 and the final occlusions end up with Class II/III first molar occlusion, but the remaining occlusion is Class I/normal. That is, when upper first bicuspids are extracted (no lower teeth removed) to mitigate an Angle’s Class II malocclusion, the first molars will be
Therapeutic Class II and Class III molars – clinical implications An issue that can arise based on Andrews’ key #1, maxillary first molar angulation, is: should orthodontically treated cases with single arch extractions and treatment planned to end up in a therapeutic Class II or Class III relationship have maxillary first molars with approximately a +5 degree distal angulation, as discussed by Andrews for optimal Class I/normal, interarch molar relationships? There is some literature that has briefly addressed this issue and suggests that “therapeutic Class II molars” should have an upright angulation/slant; 0 degrees, not +5 degrees as for Class I/ normal molars (Figure 2). 7 For orthodontically treated cases with “therapeutic Class II molars” having the maxillary molars angulated +5 degrees as for Class I occlusions (i.e., distal aspect of the molar tipped down), could cause several possible adverse effects. That is, having “therapeutic Class II molars” with +5 degree angulations as in Class I/normal occlusions can produce a situation where Volume 4 Number 4