Back to basics: Maxillary expansion.
In this latest “Back to Basics” post, we will continue with the orthopaedic theme that began last year when we talked about growth and growth modification and discussed the subject of maxillary expansion. There seems to be much maxillary development being done out there judging by the content of some orthodontic Facebook groups. This is possibly partly due to the continuing technical advances that we have seen in methods available to effect orthopaedic expansion of the maxilla – particularly bone-anchored devices.
We decided to look at the literature on maxillary expansion over the following few blogs. We will discuss conventional methods first. There are a LOT of systematic reviews on this subject; all hampered to varying degrees by a lack of high-quality investigations and significant heterogeneity between studies. In essence, there are too many case series, too many different appliances and too many ways of measuring expansion. And, of course, most studies only follow patients up over the relatively short term. We have tried synthesising what we think is the salient evidence (apologies for only including a few).
Maxillary transverse skeletal deficiency is a common clinical finding often associated with unilateral or bilateral posterior crossbites and crowding. It can be managed with orthopaedic expansion of the maxilla. This is readily achievable using a variety of appliances and techniques. The anatomy of the tooth-bearing and bony maxilla lends itself nicely to transverse force application. It is mechanistically relatively straightforward to accomplish separation of the intermaxillary suture using fixed expansion appliances, depending upon the child’s age.
A fundamental principle that sometimes gets lost when talking about maxillary expansion:
- Maxillary orthopaedic expansion aims to achieve skeletal development of a narrow maxilla. However, when prescribing this treatment, we should consider mandibular dental archform and buccal occlusal relationships. Significant expansion of the maxillary arch (either skeletal and/or dental) in the absence of posterior crossbites will inevitably require compensatory expansion of the mandibular dentition. This is likely to be unstable;
- Another thing to remember is that whilst there is a poor correlation between the maturational stage of the intermaxillary suture and chronological age, the suture does become increasingly interdigitated and complex with age. However, it is not thought to completely fuse until the late teenage years. Therefore, the older the patient, the more difficult it becomes to split the suture.
Rapid Maxillary Expansion
Increasing age and suture complexity in the late mixed and early permanent dentitions means that a robust and intensive high-force approach is required for effective suture separation. This is conventionally achieved using Rapid Maxillary Expansion (RME). This aims to maximise skeletal expansion by separating the suture and minimising buccal tipping of the maxillary molar dentition. Conventional RME is generally applied via the maxillary dentition using an appliance incorporating bands cemented to the first molar and first premolar teeth or via an acrylic plate cemented directly onto the maxillary dentition.
- Conventional RME can produce significant differences in post-expansion skeletal and dental dimensions over the short-term (+2.46 mm maxillary basal bone width; +3.09 mm alveolar palatal crest width; +5.69 mm intermolar width; +2.85 mm inter-molar root apex width; accompanied by +3.75 degrees dental tipping). However, at 4-8 months post-retention, around 10 per cent of this skeletal change can be expected to have relapsed in addition to some uprighting of the dentition.
- Over the longer term (2-14 years), it has been suggested that the skeletal effects of both rapid and slow conventional maxillary expansion are reasonably stable Nevertheless, more skeletal maxillary width seems lost when expansion is carried out in post-pubertal patients.
So conventional RME will provide significant skeletal and (greater) dental expansion, but some tipping of the posterior dentition will accompany this. Both will relapse to some extent, particularly over the short term. In the next blog, we will discuss the evidence relating to bone-anchored maxillary expansion as a stand-alone procedure and, in comparison, to conventional methods.
A version of this post appeared first on Martyn Cobourne’s and Andrew DiBiase’s Evidence-Based Orthodontic Facebook Group.
Professor of Orthodontics, Kings College, London.