GAP Magazine Clear Idea Volume 5

16 www.acasociety.com | info@acasociety.com (Note – this refers to aligner treatment where bite opening is a significant part of the treatment plan to achieve the desired treatment goals, and specifically refers to the treatment of non- or minimally growing individuals.) B ite opening is commonly required in the following orthodontic conditions: 1. Existing deep anterior overbite causing pathology, including labial gingival stripping (lower arch) or palatal gingival trauma (upper arch) or potentially contributing to excessive anterior tooth wear. 2. Where the depth of overbite results in inadequate room to align the lower anterior teeth 3. Where the position of the lower incisors behind the upper incisors prevents effective retraction of the upper incisors into existing natural or extraction spaces, or prevents distal movement of the upper anterior teeth (such as in Class II distalization cases) Some biological realities: “In nongrowing patients, the segmented arch technique can produce 1.5 mm of incisor intrusion in the maxillary arch and 1.9 mm in the mandibular arch.” 1 “In children, often the growth acts as a major catalyst in taking care of extrusive side effects. In adults, adaption of the muscles, vertical dimension, and TMJ is difficult. The treatment option in adults should be limited to teeth whenever possible. Intrusion of teeth can be accomplished without any change in skeletal and muscular components of the face.” 2 Incisor intrusion is recommended to be carried out using extremely low orthodontic forces 3 , so too-rapid aligner change must be questioned in these cases. Bite opening and Fixed Appliances: We use several strategies with fixed appliances to deal with deep overbites. These include: 1. Reverse curve archwires/Segmental mechanics 2. Bite ramps 3. Bite plates 4. Posterior vertical elastics 5. TADs 6. Surgery 7. J Hook Headgear Scientific Rationale: 1. The fit of the dental arches to each other is a 3-dimensional geometric association, reliant upon ratios of tooth size (Bolton discrepancies, tooth size discrepancies) overjet and overbite. If ideal arch relations are desired (alignment, overbite, and overjet), failure to achieve any one of these will result in failures in the other parameters also. For example, a deep bite in the presence of normal tooth sizes and normal Class I occlusion will result in either (or both) lower arch crowding, upper arch spacing and increased overjet. 2. Possibly the most clearly understood consistent failure that aligner treatment displays, according to all the scientific literature, is the inability of aligners to open the bite as much as the digital treatment plan projects. 4-7 3. Shortfalls of bite opening when compared to the projected outcome in the order of 60% are routine. 4,5 Studies have thus far failed to show true intrusion of upper incisors of more than 0-0.6mm, while in the lower arches the limit for true intrusion has been reported to be approximately 2.5mm. 8-11 4. Relative intrusion may give some Second commandment for improved clinical outcomes with aligners: Bite opening is king, so avoid deep bites Dr Tony Weir By Dr Tony Weir Figure 1. Appliances used to treat deep bites. Figure 2. Intended final treatment outcome position (A) and clinically achieved outcome (B). Note the deep bite, retroclined incisors, failure to close spaces, loss of anchorage and loss of anchorage. C l i N i C a l additional bite opening, but here again the scientific literature, while sparse, offers little comfort. 5. The greater the need to open the bite, the more significant the impact of this failure to the treatment outcome becomes – eg Class II corrections, treatment of spaced cases and extraction cases. 6. While aligner companies offer strategies, it is clear to date that the success of such strategies is limited. Indeed Align ® ’s much hyped G5 ® protocol for deep bites is not being superseded by G9 ® , again with a similar lack of scientific proof of efficacy. Clinical rationale: Failure to open the bite may lead to the following clinical problems: 1. Loss of anchorage 2. Loss of torque 3. Tipping + intrusion of posterior teeth 4. Deepening overbite 5. Failure to close spaces 6. Long additional aligners 7. Complete treatment failure