Autorotation of the Mandible as Sequelae to Maxillary Intrusion: A Systematic Review.

BACKGROUND: Autorotation of the mandible is a normally anticipated phenomenon following a surgical superior repositioning of the maxilla in clinical situations where patients have an excessive gummy smile. Prediction of the surgical treatment outcome following a presurgical orthodontic treatment is a critical element in the surgical treatment planning.
MATERIALS AND METHODS: The relevant articles were selected by hand search and electronic media (Google Scholar, PubMed, Science Direct, Medline, Embase, and Cochrane) from 1982 to 2020. All the relevant articles were properly screened, and findings were extracted from the articles.
RESULTS: It was observed that, following maxillary intrusion, mandible would eventually autorotate to take a new occlusion. Mandibular autorotation as a result of maxillary intrusion would lead to minimal shortening of the lower lip in the vertical plane. It was observed that the amount of mandibular autorotation correlates with the extent of maxillary impaction. Studies have shown that there is a passive soft-tissue response which may be attributed to the fact that no muscular detachment had been affected in the lower lip and soft-tissue chin region during the maxillary surgery.
CONCLUSION: It is observed that there is a definite influence on the mandibular and chin positions as a result of maxillary intrusion and autorotation of the mandible. Every 1 mm of maxillary superior impaction, the chin moved 0.6 mm vertically and 0.2 mm horizontally. There is an appreciable shortening of the lower lip length. Copyright:

INTRODUCTION

Facial esthetics is considered to be a critical factor in human interactions.[1] Vertical maxillary excess (VME) is a clinical scenario that results due to overgrowth of the maxilla. It manifests clinically with excess exposure of the upper incisors even at rest coupled with a gummy smile.[2] The vertical excess growth of the maxilla results in a consequent rotation of the mandible in a clockwise manner. This subsequently results in the mandible being positioned retrognathically.[2] The surgical correction of the VME is usually done by the superior repositioning of the maxilla through a LeFort 1 osteotomy. This subsequently results in the rotation of the mandible anteriorly and superiorly thereby enhancing the facial profile still further.[2]

Literature reveals that surgical impaction of the maxilla aids in the correction of long-face syndrome, anterior open bite, and in obtaining a competent lip seal in addition to the correction of VME.[34] The autorotation of the mandible associated with the maxillary impaction was initially advocated by Schendel et al., Bell et al., and Fish et al.[567] It is advocated that mandibular autorotation following a maxillary intrusion is associated with the projection of skeletal and soft tissues in the profile view and vertical shortening of the lower face in the frontal view.[3]

MATERIALS AND METHODS

Literature search

The systematic literature search (displayed as a flow diagram in Figure 1) was initiated with Google Search the references of the DOI used in Sci-Hub. This service allowed the authors to use PubMed Central, ProQuest Dissertations and Theses, Science Citation Index Elsevier Science Direct Complete, Highwire Press, Springer Standard Collection, DOAJ Directory of Open Access Journals, Free E-Journals, Ovid Lippincott Williams and Wilkins Total Access Collection, Wiley Online Library Journals, and Cochrane Plus databases.

Figure 1

Search criteria

The heading sequence ([”Maxillary” OR “Le Fort I”] AND [”mandibular autorotation”] AND [”Advancement” OR “Retrusion” OR “Setback” OR “Impaction” OR “Intrusion” OR “Superior Repositioning” OR “Down grafting” OR “Inferior Repositioning” OR “Expansion” OR “Widening”]) was selected. Our initial search showed 2418 published articles. Since our inclusion criteria delegated only academic publications and the number of articles selected was decreased to 852. No articles were excluded by means of their language. Articles discussing nonhuman research were excluded, and 163 potential articles were found. Articles pertaining to syndromic cases, osteodistraction, or bimaxillary surgery were excluded such that only 51 articles remained. Among them, only 11 fulfilled inclusion criteria and exclusion criteria (see selection criteria). To finish the search, the authors also reviewed the references for each selected publication. Due to this, an additional 15 articles were found. However, only four of these could fulfill the inclusion and exclusion criteria. Eventually, this systematic review included a total of 15 articles.

Selection criteria

This study comprised the following inclusion criteria to hand-pick the probable articles from the existing literature. These include: (1) Only human patients; (2) a set of patients in whom only single jaw surgery was undertaken and that was maxillary intrusion; (3) the number of patients was mentioned; and (4) at least one parameter of soft-to-hard tissue ratio was measured from the data included in that paper. This study comprised the following inclusion criteria to hand-pick the probable articles from the existing literature. These include (1) nonsyndromic patients in the form of cleft lip and palate, Pierre Robin syndrome; (2) unrelated disease (i.e., oncologic or traumatic cases); (3) systematic reviews or meta-analyses; and (4) the use of distraction.

Data extraction

The following data were taken out from the full-text articles: (a) demographic data (i.e., the number of patients, age, gender, and race); (b) type of the study (i.e., follow-up period [months/years], course of analysis [prospective vs. retrospective], randomization, level of evidence, and method of analysis [i.e., lateral radiographs, cone beam]); and (c) type of surgical intervention (i.e., the type of surgery used for a certain bony movement, added orthognathic and/or facial procedures, use of bone graft, use of implants, amount of movement in mm [mm], removal of anterior nasal spine, use of an alar cinch suture, the use of VeY lip closure, subspinal osteotomy, and type of osteosynthesis).

RESULTS

The results of the literature search reveal that maxillary intrusion which is generally known as maxillary impaction or superior repositioning of the maxilla was performed initially by Converse (1952) by posterior intrusion for the management of patients with open bite. However, it can also be performed anteriorly in clinical situations such as the long face syndrome with excessive prominence of the maxilla presenting with a gummy smile. All studies we found were mainly retrospective.

It was observed that, if an isolated maxillary intrusion was performed, the mandible would eventually autorotate to take a new occlusion. This ultimately would lead to the soft tissues to follow the hard tissues according to certain ratios. Previous studies have revealed that mandibular autorotation as a result of maxillary intrusion would lead to minimal shortening of the lower lip in the vertical plane.[8] However, few studies revealed that the lower lip actually lengthens following a mandibular autorotation as a result of maxillary intrusion.[9] Few studies have demonstrated that the amount of mandibular autorotation correlates with the extent of maxillary impaction.[10] Studies have shown that there is a passive soft-tissue response which may be attributed to the fact that no muscular detachment had been effected in the lower lip and soft-tissue chin region during the maxillary surgery [Table 1].

Table 1

Systematic review of published literature

Author (year)	Sample size	Follow-up period (months)	Course of analysis	Technique	Type of fixation	Magnitude of movement	Method for measurement
Schendel et al. (1976)	24	29	Retrospective	LeFort I impaction	Rigid internal fixation	6 mm	Cephalogram Computerized model
Radney and Jacobs (1981)	10	6	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Wessberg et al. (1982)	25	24	Prospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Mansour et al. (1983)	14	6	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Sakima and Sachdeva 1987	20	12	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Nattestad A and Vedtofte P 1992	10	5	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Nadjmi N et al. (1998)	20	Not clear	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Rosen 1988	23	9.8	Retrospective	LeFort I impaction	Rigid internal fixation	6 mm	Cephalogram
Rosenberg et al. (2002)	11	12	Retrospective	LeFort I impaction	Rigid internal fixation	6 mm	Cephalogram
Steinhauser et al. (2008)	42	Not clear	Retrospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Wang YC et al. (2008)	10	3	Prospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Ksiezycki Ostoya et al. (2009)	22	15	Retrospective	LeFort I impaction	Rigid internal fixation	6 mm	Cephalogram
Abhuzinada S et al. (2013)	10	Not clear	Prospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Jayakumar J et al. (2019)	45	3	Prospective	LeFort I impaction	Rigid internal fixation	Not clear	Cephalogram
Peleg O et al. (2019)	20	6	Prospective	LeFort I impaction	Rigid internal fixation	6 mm	Cephalogram

DISCUSSION

Literature search reveals that a clinician evaluating the esthetics particularly on a profile photograph of an individual who underwent an orthognathic surgery emphasizes more on the lips and chin, followed by the nose.[11] This implies that an ideal anatomical positioning of lips and chin is of boundless importance.

Influence of maxillary intrusion on mandible

It is noteworthy that, in patients who have a mandibular deficiency in addition to a gummy smile, the sagittal advancement accomplished by the mandibular autorotation following a maxillary intrusion is more appreciable as it will eventually result in enhanced sagittal relationship of both the jaws.[12] A previous study revealed that an average of 5 mm maxillary impaction would lead to a 2 mm horizontal advancement and 1.2 mm vertical shortening of the chin in the postoperative phase when using the radiographic condylar center of the mandible as the rotation center of mandibular autorotation in the presurgical predictions.[13]

It is a well-known fact that the vertical dimensions of the lower face would change when the maxilla is impacted and the mandible autorotates. There exist numerous reports in the literature on the degree of decrease in lower facial height following a maxillary impaction. Numerous researchers have dealt with the query of the impact of maxillary impaction on mandibular autorotation a long way back and suggested a replication of the esthetic outcome on the lateral cephalogram. They advocated a 1:1 ratio between lower-face shortening following maxillary impaction and mandibular autorotation.[1314]

Maxillary impaction is generally performed to reduce the lower anterior facial height with concomitant advantages of mandibular autorotation to get the chin movement. A previous study found that the rotation center of the mandible revealed huge variations. The rotation center in this study was found lower than the radiographic condylar center.[15] It was concluded from the result of few studies that the mandible will eventually follow any changes in occlusion that arises as a result of maxillary impaction. It can be advocated that the esthetic changes in the mandibular and chin position would be little inconsistent and little predictable following maxillary intrusion.[16]

Influence of maxillary intrusion on temporomandibular joint

Literature reveals that clicks in the temporomandibular joint are more likely to be resolved following a prognathic reduction and maxillary impaction surgery than after mandibular advancement or combination maxillary and mandibular surgery.[12] It was observed that movements that would force the condylar head in a posterior or superior direction would eventually lead to an internal derangement of the joint. A previous study of condylar pathway tracing advocated a higher incidence of hypomobility following a mandibular advancement surgery but an enhanced function following a LeFort I osteotomy and mandibular reduction osteotomy.[1718]

It was noted that the soft-tissue changes associated with a maxillary intrusion were prominent on the nasal tip with an increase in alar base width, shortening of lip length, and concurrent with horizontal movements of the maxilla.[8] Previous studies have revealed that autorotation of the mandible results in shortening of the elevator muscles. As a result of this, neither an active or passive distracting forces can be exerted on the intruded maxilla by the mandibular musculature. Hence, it is considered that superior repositioning of the maxilla with the aid of a LeFort osteotomy is perhaps the utmost stable orthognathic surgical intervention.[19] In addition to this, the biomechanics of the jaw can be changed due to the autorotation of the mandible.

There exists a controversy pertaining to the site for center of rotation of the mandible, following superior repositioning of the maxilla. Few authors advocated the condyle to be the center for the autorotation of the mandible, while few authors advocated that mastoid process as the center of rotation.[513] Wang et al. demonstrated that this center is located 2.5 mm behind and 19.6 mm below the radiographic condylar center of the mandible.[15] Another study proposed that the mandibular autorotation occurs at a point following maxillary intrusion that was similar to that occurred at preoperative mouth opening.[20]

A recent study observed that the occlusal plane angle in the mandibular autorotation group was steeper when compared to the nonautorotation group.[2] Another study advocated that the movement of maxilla in the superior direction has an effect on the repositioning of the chin in the anterior and cranial directions.[21]

CONCLUSION

The results of this study reveal that there is a definite influence on the mandibular and chin positions as a result of maxillary intrusion and autorotation of the mandible. It is noteworthy that every 1 mm of maxillary superior impaction, the chin moved 0.6 mm vertically and 0.2 mm horizontally. There is an appreciable shortening of the lower lip length.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.