Australasian Dentist Magazine March April 2021

Category Australasian Dentist 55 The greater the skeletal sagittal discrepancygives rise to the ideal treatment plan being a combined orthodontic and surgical approach if our aim is to correct the skeletal discrepancy and provide the patient with an ideal Class I occlusion and optimum overbite and overjet. One must also consider the vertical component as many of these severe Class 2 discrepancies also present with a very deep overbite. In these types of cases, surgery can also be advantageous in rotating the mandible downwards and hence aiding in correction of the dental deep overbite. – and hence he coined the term “Steiner Sticks”. This is a very important concept to understand, as traditional cephalometric norms are no longer valid in cases of skeletal discrepancies that require dental compensation. To provide an understanding of how we assess the position of teeth cephalometrically, the following measure­ ments are very useful – but as you will notice the norms associated with all those measurements are norms that relate to a perfect Class I skeletal relationship and are invalid for any patient with an underlying skeletal discrepancy . I relationship. The first caveat being that we have provided the patient ideal torque of the upper incisors to maintain lip position and the most important caveat is to ensure that we do not retract the lower teeth. If we do then further retraction of the upper teeth will be required which one would like to avoid. Hence a good rule of thumb is to avoid extractions in the lower arch of a Class 2 patient, as we need as much tooth structure in the lower arch as possible to minimise the amount of retraction of the upper arch. In a Class 2 Division 2 patient where the upper incisors are already in a very upright position, extraction of the upper first premolars can alleviate the upper crowding, providing the patient with an ideal Class I canine relationship, a good mutually protected occlusion with ideal overbite and overjet, and provided there are no extractions in the lower arch – there will be absolutely no adverse effects in the patient’s profile/lip position as the position of the upper incisors will not be altered detrimentally. In fact, with some improved torque the facial profile and upper lip position will actually be improved! clinical Figure 5 Diagrammatic representation of Class 2 correction with surgery. Figure 6 Case treated with combined orthodontic and surgical approach to correct both the sagittal discrepancy and deep overbite. However, if the skeletal sagittal discrepancy is mild in nature, with an ANB of 3 degrees to 5 degrees, then the option of dental compensation becomes far more viable. 2. To dentally compensate the dentition for the underlying skeletal discrepancy. Many Class 2 malocclusions have some existing dental compensations. By that I mean, the lower incisor teeth are usually somewhat proclined and it is not uncommon for the upper incisors to be slightly upright in attempt to compensate for the skeletal discrepancy. In fact, Dr Steiner realised that in these cases of skeletal discrepancy, in order to obtain anterior coupling of the teeth, a greater amount of dental compensation will be requiredwithgreater skeletal discrepancies Figure 7 Cephalometric measurements used to assess the position of the upper and lower incisors As discussed previously, to achieve an ideal overjet, the patient requires a Class I canine relationship. Hence, to extract a dental unit in the upper posterior segment, (and most commonly this would be the first premolar tooth) would allow retraction of the upper anterior segment to obtain a Class I canine relationship, and leave the patient with a Class II molar relationship. This result will still provide your patient with an ideal overjet and meet all of our functional goals of canine guidance and a mutually protected occlusion. This concept of dental extractions and imparticular upper extractions to reduce the overjet and/or obtain a Class 1 canine relationship in an existing Class II malocclusion is termed dental compensation. i.e. moving the teeth into a position to compensate for the underlying skeletal discrepancy. There is much debate as to whether the extraction of upper premolar teeth to provide a dental compensation for the Class II relationship will adversely affect the facial profile. It’s now time to discuss in more detail the myths associated with extractions causing a flattening of the profile, and how to avoid this common concern. It’s important to understand that we can only move the upper anterior teeth back to a position where the upper canines meet the lower canines in a Class Figure 8 Diagram showing extraction of upper first premolars to achieve a Class 1 canine relationship Figure 9 Case before and after with extractions of upper premolars. Figure 10 Patient with a Class 2 Division 2 malocclusion before Figure 11 Patient with a Class 2 Division 2 malocclusion after extraction 14 24