Increase of bigonial distance after BSSO

[Sergio-OMS]

So MSDO can’t increase bigonial width and masculinize the lower jaw?

https://looksmax.org/threads/how-to-increase-bigonial-angle-mandible-width.87258/post-1507583

What about this vid? Does the lower jaw not increase laterally?

In that animation (not actual simulation) the mandibular condyles are displaced laterally and “pushed out” of the glenoid fossae. I don’t think actually happens, it would actually cause TMJ problems but it’s also difficult from a biomechanical point of view (I can’t prove it to you though, but it look like you should first prove what you say).

To me, condyles act as a pivot point. So, can you imagine the actual widening at the back part of the mandible if the condyles are the pivot point?

 

[GetThatBread]

In that animation (not actual simulation) the mandibular condyles are displaced laterally and “pushed out” of the glenoid fossae. I don’t think actually happens, it would actually cause TMJ problems but it’s also difficult from a biomechanical point of view (I can’t prove it to you though, but it look like you should first prove what you say).

To me, condyles act as a pivot point. So, can you imagine the actual widening at the back part of the mandible if the condyles are the pivot point?

I see then what does MSDO do? Just widens the chin? Is The actual widening of the mandible possible? Wouldn’t it cause TMJ if the maxilla isn’t matching the condyles? My ortho told me to get MSE and MSDO at the same time so TMJ issues doesn’t occur. The arrows pointing are MSE and MSDO in conjunction expanding the face laterally.

 

[Sergio-OMS]

MSDO can be useful to the orthodontist (and the patient, of course) to get a proper bite, specially at the front part (canines). Not really more than that. Actual posterior widening is, in my opinion, negligible.

Can you perform MSE for aesthetics ?

sorry I didn’t see this one.

can you explain a bit more? Most orthodontic treatments are done with an aesthetic motivation or achieve a better aesthetic result.

 

[Gonion]

In that animation (not actual simulation) the mandibular condyles are displaced laterally and “pushed out” of the glenoid fossae. I don’t think actually happens, it would actually cause TMJ problems but it’s also difficult from a biomechanical point of view (I can’t prove it to you though, but it look like you should first prove what you say).

To me, condyles act as a pivot point. So, can you imagine the actual widening at the back part of the mandible if the condyles are the pivot point?

Considering that condyles are the pivot point and the chin gets widened, then aren't the gonion pushed inward with a resulting decrease of the bigonial distance after MSDO?

 

[Sergio-OMS]

Considering that condyles are the pivot point and the chin gets widened, then aren't the gonion pushed inward with a resulting decrease of the bigonial distance after MSDO?

Mandibular angles are frontal to the condyles. they separate from each other a little bit in MSDO, but just a very little bit.

 

[everythingmatters]

As a matter of fact, as the mandibular intermolar distance increases, a larger amount of maxillary expansion is needed.

Dr, how many mm could the IMW of the lower jaw be expanded with IMDO?

 

[Sergio-OMS]

It really depends on the shape of the mandible and the amount of distraction. Maybe 5 mm widening for 8 mm overjet?

 

[Deleted member 2729]

By what mechanisms does it widen the Bigonial width tho?

 

[Deleted member 2729]

.

 

[normie_joe]

Posterior mandibular widening secondary to advancement sagittal split osteotomy: A retrospective study

Patients sometimes spontaneously report a modification of the width of their lower face after an advancement bilateral sagittal split osteotomy (ABSSO…

www.sciencedirect.com

The first goal of the study was to assess the impact of ABSSO (advancement bilateral sagittal split osteotomy) on the BGD (bigonial distance), one day and one year after surgery. The second objective was to look for a possible relation between the increase of BGD and the amount of mandibular advancement.



The technique used in the study was the Obwegeser-Dal Pont II technique.


Measurement methods
The amount of mandibular advancement was measured by comparison between pre- and postoperative lateral teleradiographies made in centric occlusal positionand taken one day and one year postoperatively. In order to be reproducible, measures were made between the anterior face of incisors or orthodontic brackets and projected on a horizontal axis (fig. 2).

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The amount of posterior mandibular widening was assessed by measuring the variations of the BGD on frontal teleradio-graphies using the same chronology. Gonions were spotted as the most lateral points located on each mandibular angle (fig. 3).
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Intrinsic reliability was evaluated by measuring the medial intercanthal distance (ICD), considered as constant, on pre-operative and one day postoperative frontal teleradiographies (fig. 3).

Results
One day after surgery, BGD increased in all patients. Statistical analysis reported a significant mean increase of 9.8 mm(P<103). One year after surgery, mean BGD increase was 4 mm and remained significant compared with preoperative value(P<103). BGD decreased at one year postoperative in 9 patients (18%) comparatively to the preoperative measure. Schematic representation of all the BGD measures made by both evaluators shoved an ‘‘increase-decrease’’ profile (fig. 5).

View attachment 232506


Not significant relation was found between the amount of mandibular advancement and the postoperative variation of the BGD as shown by the absence of any specific pattern in the relation between these two variables (fig. 6).

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Discussion
BGD increase after ABSSO can first be explained by the anatomy. Because of the V-shape of the mandible, there will be an interference inside the osteotomy line during advancement of the dental arch, responsible for lateral displacement of the lateral valve on each side (fig. 7).

View attachment 232528



The osteotomy technique may be of great importance in this phenomenon. In the technique described by Epker, residual lingual cortical bone on the lateral valve may interfere with the medial valve, responsible for a lateral flaring of the mandibular angles. The use of the Obwegeser-Dalpont II technique, may reduce these bony interferences, as the osteotomy is extended down to the basilar edge. The kind of fixation must also be considered. Semi-rigid fixation, might facilitate lateral flaring of mandibular angles. It would therefore be relevant to compare semi-rigid and rigid fixation. However, temporo-mandibular joint disorders seem to be more frequent when using rigid fixation techniques because of more severe modifications in condylar position induced by these devices.

Posterior mandibular widening seems to reduce one year aftersurgery, even if it remains significant. 9 patients(18%) showed a decrease in their posterior mandibular width at the one-year control. This was significantly observed in the youngest patients.

The hypothesis proposed in the study is that mandibular bone remodeling induced modifications in muscular strains is more important in young patients than in older ones.

Modifications induced by mandibular advancement on mus-cular strains and their effect on bone remodeling process mayexplain the decrease of posterior mandibular width one yearafter surgery in young patients.


TL;DR:

• Bigonial distance mean increase was 4mm after BSSO using the Obwegeser-Dal Pont II technique
• The bigonial distance decreased in some patients, especially on the younger ones.
• There was no relation between the amount of mandibular advancement and the increase of BGD.

Life fuel.