This blog looks at the stability of orthognathic surgery, with a contemporary review of evidence and our update of the hierarchy of stability established by William Proffit 17 years ago. Ronald Roth once said "If we were clever enough to get the teeth into ideal position at the end of the treatment using the Straight Wire Appliance, would the teeth remain in those positions?". Similarly, in orthognathic surgery, the risk of relapse remains a significant concern.
In part 1 we described ‘what orthodontic preparation is required’ and in this part 2 we ask the question ‘Do the jaws remain in their post-surgical positions’? This blog is based on a recent and comprehensive meta-analysis by Haas Junior 2019, which contained a whopping total of 148 studies with 6278 patients involved in the analysis, the largest currently available research on orthognathic stability.
The scale of relapse has been astutely changed by Haas, to help understand stability relative to the amount of surgical movement. Stability is measured as a percentage of relapse, and not the quantitative amount of relapse as William Proffit did in his seminal paper. This helps the reader put into context the proportion of relapse expected from their planned movement.
Orthognathic Stability Scale
Anatomy, function and by association, the direction of surgical movements. Elongation of muscles can occur during surgery, notably the masseter and medial pterygoid (termed ‘pterygomandibular sling’) have been implicated in post orthognathic relapse. Post-surgery these muscles attempt to re-establish their pre-surgical length, and in doing so relocates the jaw towards its previous location. New functional habits and adaptation establish following orthognathic surgery, however established engrams of previous muscle function (muscle memory) can re-assert themselves if the patient does not physiologically adapt, resulting in relapse Gracco 2015. Transverse expansion is prone to relapse due to stretching of the palatal soft tissues and elastic recoil decreases the expansion post-surgically. Other factors such as growth, condylar changes, surgical error and orthodontic errors are also potential causes of relapse Matos 2023.
The stability of common surgical movements are listed below and relate to the use of rigid fixation with titanium plates, and varies depending on the direction of movement, from most stable to least, with their associated relapse from Haas Junior’s systematic review 2019.
The most stable movements are antero-posterior movements of either jaw 0-12% (except maxillary setback). Antero-posterior movements are considered the most stable, possibly due to the lack of rotational effects to the maxilla and / or mandible. The second most stable movements are vertical changes 18-20%, with the maxilla having greater stability than the mandible. Transverse movements are one of the least stable, however comparing a segmental Le-Fort I with Surgical Assisted Rapid Palatal Expansion (SARPE) it appears a segmental Le-Fort I is more stable over 2 years by 3-16% (overall 20-25% relapse) Marchetti 2009. The least stable movement is maxillary setback 55%, this is due to the surgical difficulty from both surgical access and anatomical obstruction of the pterygoid plates and maxillary tuberosity Wong 2021.
The innovation of bioresorbable fixation was designed to prevent surgical complications from fixation, however there is an increase in relapse in most movements when compared to Titanium plates, from an increase in 8% when used for mandibular advancement, to an increase in 30% when used for maxillary impaction. Semi-rigid fixation (elastic inter-maxillary fixation or mini plates) can also have a greater rate of relapse when compared to rigid fixation, from no difference to 27% for maxillary downset. Bicortical screws have a large variation on stability, from enhancing stability to a significant increase in relapse (8% less relapse for mandibular setback, to 71% greater relapse of clockwise rotation of mandible). This variation relates to the advantage of possible greater rigidity enhancing stability Kuik 2021, as well as the negative effect of the rigidity causing torquing forces of the condyle and promoting post-surgical change Can 2021. The quantity of surgical movement can impart instability, with small movements considered unstable due to the ease of re-adaptation to a new occlusal position with dental compensation. Surgical technique, with a vertical ramus osteotomy has a 21% greater relapse when compared to a bilateral sagittal split osteotomy for a mandibular setback. It is thought a vertical ramus osteotomy lacks accommodation of the condylar position and imparts instability as a result.
Valladares-Neto 2014
Changes of the maxilla and mandible can appear long-term following orthognathic surgery, and reflect adaptive bone remodelling, resumption of growth, or adaptive changes in the dentition.
Surgical relapse is a varying, and unfortunately, commonly occurring aspect of orthognathic surgery, however “Surgical relapse is not the same as failure” Kerolos points out, and through planning around relapse, more stable decisions can be made through direction of movement, materials, and techniques. Once more, long-term occlusal changes are fortunately minimal, whereas skeletal relapse may be evident, this is due to adaptive dental changes.
We have been selective in the reporting in this blog, focusing on common movements, we recommend reading Haas junior’s excellent systematic review for further details, and discussions of the nuances of orthognathic relapse:
Part 3 of our orthognathic blog series will look at surgery first, an approach which has gained popularity of recent years.
Contents: Kerolos AlHakeem 
Contents: James Andrews
Edited/contents: Farooq Ahmed
We hope you have enjoyed this blog, This blog started with a conversation between Kerolos AlHakeem, Farooq Ahmed and James Andrews, to follow more conversations, clinical tips and commentaries on orthodontics please check us out on Instagram / facebo
