Patients requesting treatment for mandibular prognathism seek functional and aesthetic improvements. Improvements in bite force and efficiency are generally used as measures of better function. It is unclear what effect the surgical correction of mandibular prognathism will have on the patient’s occlusal forces. The literature was searched using medical subject heading (MeSH) and key word terms ‘bite force’, ‘osteotomy’, ‘orthognathic surgery’, and ‘prognathism’. A total of 17 articles were included in this review. These included a total of 697 patients, who ranged in age from 15 to 44 years. Male patients outnumbered female patients in only one study. Five hundred and thirty-two patients underwent bilateral sagittal split osteotomy, 108 patients underwent intraoral vertical ramus osteotomy, and 24 patients underwent extraoral vertical ramus osteotomy (approach unspecified). In general, masticatory efficiency at 3 months after surgery was greater than that found pre-surgically; the increase was significant at 6 months after surgery. The occlusal contact area and points tended to increase from 3 months after surgery, and there was a significant increase at 12 months after surgery. Occlusal forces, although improved, will be lower in corrected prognathic patients than in normognathic patients even at 2 years after surgery.
Orthognathic surgery in combination with pre-surgical and post-surgical orthodontic treatment is performed when the severity of malocclusion precludes orthodontic camouflage alone. In the East Asia region, the most common deformity is that of mandibular prognathism. The most frequent procedures for mandibular setback are the bilateral sagittal split ramus osteotomy (BSSO) and intraoral vertical ramus osteotomy (IVRO). The extraoral vertical ramus osteotomy (EVRO) is less often utilized. The area of bony contact between the proximal and distal mandibular segments is larger in BSSO than IVRO or EVRO. Rigid internal fixation is almost always used with BSSO, whereas in IVRO and EVRO the overlapping segments are not rigidly stabilized. Intermaxillary fixation (IMF) is consequently of a shorter duration or is not required with BSSO, whereas with IVRO and EVRO, patients are typically placed in IMF for 6–8 weeks. A concomitant Le Fort I osteotomy (LFI) is commonly employed in the treatment of prognathic patients, who may also exhibit maxillary deformities such as maxillary retrognathia or vertical maxillary excess.
Patients requesting treatment for mandibular prognathism seek functional rehabilitation along with improvement in aesthetics. These patients tend to have poorer masticatory function than normal individuals. A major contributing factor is poor occlusion, with anterior and posterior cross-bite and poor intercuspation. Another reason could be the weaker capacity of the jaw musculature, which has been shown to be smaller in dimension and lower in electromyographic activity.
The post-surgical recovery of masticatory function is difficult to assess and quantify objectively. Measurements of maximum bite force, occlusal contacts, masticatory efficiency, electromyographic activity and dimensions of masticatory muscles, mandibular range of motion, and the shape and timing of the chewing cycle have been used. Of the many varied methods, maximum bite force is widely recognized as an effective indicator of both the state of the dentition and capacity of the masticatory muscles.
Improved outcomes are a measure of the success of a procedure. As such, the following questions arise for orthognathic surgery in terms of functional rehabilitation: (1) Is there an improvement in the bite force or masticatory efficiency? (2) In the many studies published, what were the overall improvements and how were the outcomes (bite force and masticatory efficiency) measured? The aim of this study was to answer these questions by performing a systematic review of the literature.
This systematic review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement for systematic reviews. Electronic searches of the MEDLINE/PubMed database were performed to identify relevant human studies published in the English-language literature from 1966 to the present. Initial searches were performed to identify seed articles to suggest appropriate free-text terms and medical subject heading (MeSH) terms. The key words derived were the free-text terms ‘bite force’, ‘masticatory efficiency’, ‘osteotomy’, ‘orthognathic surgery’, and ‘prognathism’, and the MeSH term ‘prognathism/surgery’. These were used in combinations for the final search strategy ( Table 1 ).
|Search entry||Articles displayed||After elimination of duplicates||Potentially relevant articles|
|Bite force AND osteotomy||86||86||18|
|Bite force AND orthognathic surgery||55||29||3|
|Bite force AND prognathism||36||12||1|
|Bite force AND (prognathism/surgery [MeSH Terms])||23||0||0|
|Masticatory efficiency AND osteotomy||10||0||0|
|Masticatory efficiency AND orthognathic surgery||13||0||0|
|Masticatory efficiency AND prognathism||14||2||0|
|Masticatory efficiency AND (prognathism/surgery [MeSH Terms])||0||0||0|
The inclusion criteria for the search were as follows: (1) clinical studies measuring bite force, (2) adult patients with mandibular prognathism (skeletal class III malocclusion) who were treated by orthognathic surgical procedures such as LFI, BSSO, IVRO, and EVRO.
Studies were excluded if they involved patients with craniofacial syndromes and if the time interval between surgery and post-surgical bite force measurement was not specified. Case reports and review articles were also excluded.
This initial screening yielded 127 articles concerning (1) bite force, (2) masticatory efficiency, (3) orthognathic surgery, and (4) mandibular prognathism. There was overlap of articles between the bite force and masticatory efficiency search terms; after the elimination of duplicates as well as the assessment of relevance, no new articles were selected. After the initial screening, 22 articles were identified as potentially relevant. Subsequently, the full texts of these articles were obtained and their references were searched manually. This manual search added two potentially relevant articles. The authors read the 24 articles, and agreement on inclusion was reached by discussion ( Fig. 1 ).
After this screening, seven more articles were excluded. Data were extracted from the 17 articles that remained eligible for inclusion in this literature review ( Table 2 ). The articles were published between 1994 and 2014. Of the 17 articles, 16 reported longitudinal studies and one reported a cross-sectional study.
|Author, Ref.||Year||Country||Areas of study||Dentofacial deformity||Patients ( n )||Male ( n )||Female ( n )||Age range (years)|
|Choi et al.||2014||South Korea||Bite force and contact area||Class III malocclusion; mandibular prognathism||78||39||39||18.5–44.1|
|Kato et al.||2012||Japan||Bite force and contact area; masticatory efficiency; masticatory exercise||Mandibular prognathism; mandibular prognathism with mandibular asymmetry; mandibular prognathism with open bite; mandibular prognathism with mandibular asymmetry and open bite||47||12||35||16–39|
|Yamashita et al.||2011||Japan||Bite force and contact area; TMJ function; labiomental sensory disturbance; method of rigid fixation||Class III malocclusion||77||–||77||16–40|
|Ueki et al.||2009||Japan||Bite force and contact area; 3D CT morphologies of masseter, ramus, and condyle||Mandibular prognathism; mandibular prognathism with maxillary retrognathia||26||–||26||16–42|
|Yamashita et al.||2007||Japan||Bite force and contact area; maximum mouth opening, masticatory performance, TMJ function; labiomental sensory disturbance; method of rigid fixation||Class III malocclusion||70||19||51||16–35|
|Ueki et al.||2007||Japan||Bite force and contact area||Mandibular prognathism; mandibular prognathism with mandibular asymmetry; mandibular prognathism with bimaxillary asymmetry||60||–||60||15–36|
|Nakata et al.||2007||Japan||Bite force and contact area; jaw movements; EMG of masseter and temporalis||Mandibular prognathism||36||12||24||NR|
|Iwase et al.||2006||Japan||Bite force and contact area; masticatory efficiency||Class III malocclusion; mandibular prognathism||27||10||17||17–29|
|Harada et al.||2003||Japan||Bite force and contact area; cephalometrics||Class III malocclusion||24||13||11||18–38|
|Ohkura et al.||2001||Japan||Bite force and contact area||Mandibular prognathism||57||26||31||18–37|
|Nagai et al.||2001||Japan||Bite force, contact area, and pressure||Class III malocclusion; mandibular prognathism||43||21||22||20–26|
|Harada et al.||2000||Japan||Bite force and contact area||Mandibular prognathism||25||10||15||18–39|
|Iwase et al.||1998||Japan||Bite force and contact area||Class III malocclusion; mandibular prognathism||23||7||16||NR|
|Ellis et al.||1996||USA||Bite force; cephalometrics; mechanical advantages of masseter and temporalis muscles||Mandibular prognathism||24||8||16||16.0–41.2|
|Athanasiou||1992||Denmark||Bite force and contacts||Mandibular prognathism||33||11||22||17–39|
|Shiratsuchi et al.||1991||Japan||Bite force and contact area; masticatory efficiency||Mandibular prognathism||17||NR||NR||NR|
|Kikuta et al.||1994||Japan||Bite force and contacts; masticatory performance||Mandibular prognathism||30||NR||NR||NR|
The total number of patients included in the studies was 697, and they ranged in age from 15 to 44 years. Male patients outnumbered female patients in only one study. The number of male patients ( n = 188) ranged from 7 to 39, and the number of female patients ( n = 462) ranged from 11 to 77.
All studies addressed mandibular prognathism or skeletal class III malocclusion. BSSO alone was performed in 12 studies and in combination with LFI in four studies. Two studies reported that BSSO was performed and no specific maxillary procedures were consistently performed in combination. IVRO alone was performed in two studies, and in combination with LFI in two studies. One study reported that VRO was performed, although there was nothing mentioned on the surgical approach used (extraoral or intraoral); VRO alone and in combination with LFI were performed.
Amongst the different surgical groups, the mean age of the patients ranged from 19 to 25.5 years. Five hundred and thirty-two patients underwent BSSO, 108 patients underwent IVRO, and 24 patients underwent EVRO (approach unspecified). The amount of movement of bony segments was reported in seven studies and not reported in 10 studies. Rigid fixation of the segments with no IMF was used in four studies. Rigid fixation followed by post-surgical IMF was used in five studies. Non-rigid fixation of the segments followed by IMF was used in four studies. Rigid fixation and non-rigid fixation, both with IMF, were used in two studies. The method of fixation was not reported in three studies.
With regards to the sets of records, two studies took two sets, one study took three sets, two studies took four sets, five studies took five sets, three studies took six sets, one study took seven sets, two studies took eight sets, and one study took nine sets of records at six points in time. The duration of follow-up ranged from 6 to 60 months.
Pressure-sensitive sheets (Dental Prescale System) were used in 12 studies, tactile pressure sensor arrays (T-Scan System) were used in one study, force transducers were used in three studies, and a photocclusion technique was used in one study.
Patients with temporomandibular joint (TMJ) dysfunction were excluded in one study, patients with no severe TMJ dysfunction were included in one study, and the TMJ status of patients was not reported in 15 studies.
Patients had pre- and post-surgical orthodontic treatment in 15 studies; some patients had pre-surgical orthodontic treatment but no recorded post-surgical orthodontic treatment in two studies.
Two studies reported using post-surgical functional rehabilitation, three others reported not using it, one compared the use of rehabilitation in one group to no rehabilitation in another group, and there was no report of any usage in 11 studies.
Table 3 provides an overview of the included articles, summarizes the methodology, reports the follow-up period, and shows the mean bite force and occlusal contact before surgery, at 6 months post-surgery, and at last measurement. Table 4 summarizes the surgical procedures and methods of measurement. Statistics other than the mean and standard deviation were not reported in three studies; multiple tests were used in the remaining studies, including the χ 2 test, Student t -test, Mann–Whitney U -test, and one-way analysis of variance.
|Author, Ref.||Study type||Control group||Control group||Follow-up, months||Preoperative||6 months postoperative||Last measurement|
|Mean BF (N)||Mean OCA (mm 2 )||Mean BF (N)||Mean OCA (mm 2 )||Mean BF (N)||Mean OCA (mm 2 )||Mean BF (N)||Mean OCA (mm 2 )|
|Choi et al.||Longitudinal (prospective)||Internal control||655.7 ± 229.5||18.4 ± 7.4||24||452.6 ± 92.5||10.6 ± 2.4||257 ± 43.8||5.3 ± 0.9||516.8 ± 72.8||11 ± 1.7|
|Kato et al.||Longitudinal||Internal control||816 ± 248||15.9 ± 8.1||12||249 ± 114 (masticatory exercise group)
239 ± 121 (1 jaw)
256 ± 112 (2 jaw)
|5.3 ± 3.1 (masticatory exercise group)
4.7 ± 2.8 (1 jaw)
5.7 ± 3.2 (2 jaw)
|272 ± 106 (masticatory exercise group)
270 ± 74 (1 jaw)
273 ± 124 (2 jaw)
|6.4 ± 2.9 (masticatory exercise group)
6.9 ± 3.0 (1 jaw)
6.1 ± 2.9 (2 jaw)
|488 ± 196 (masticatory exercise group)
462 ± 215 (1 jaw)
504 ± 108 (2 jaw)
|9.8 ± 5.6 (masticatory exercise group)
9.4 ± 6.7 (1 jaw)
10.1 ± 4.9 (2 jaw)
|Yamashita et al. , a||Longitudinal (retrospective)||Internal control||700 ± 250||19 ± 6||60||280||6||270||7.5||600||18|
|Ueki et al.||Longitudinal||Normative literature value||NA||NA||12||402.9 ± 150||8.4 ± 3.5||Not measured||Not measured||503.9 ± 158||10.2 ± 3.7|
|Yamashita et al. , a||Longitudinal (retrospective)||Normative literature value||NA||NA||12||270||5||320||6.5||390||7.8|
|Ueki et al. , a||Longitudinal (retrospective)||Normative literature value||NA||NA||12||353.6||7.13||393||7.7||441.9||8.8|
|Nakata et al. , a||Longitudinal (prospective)||Internal control||1000||25||31||200||5||400||8||400||10|
|Iwase et al. , a||Longitudinal (prospective)||Internal control||No detail given||No detail given||24||300 (M)
|6 (M and F)||700 (M)
|Harada et al. , a||Longitudinal||Normative literature values||NA||NA||12||240||Not measured||240 (2 jaw)
350 (1 jaw)
|Not measured||280 (2 jaw)
380 (1 jaw)
|Ohkura et al.||Cross-sectional||Internal control||773.4 ± 208.5 (M)
649.9 ± 325.0 (F)
|18.0 ± 5.7 (M)
15.0 ± 8.6 (F)
|36||264.6 ± 136.5 (M)
189.8 ± 96.5 (F)
|5.0 ± 2.5 (M)
3.6 ± 1.8 (F)
|340.0 ± 169.0 (M)
258.7 ± 108.7 (F)
|6.4 ± 3.2 (M)
4.7 ± 2.1 (F)
|599.1 ± 202.8 (M)
455.1 ± 132.0 (F)
|12.4 ± 4.4 (M)
9.5 ± 2.4 (F)
|Nagai et al.||Longitudinal||Internal control||677.5 ± 163.1 (M)
625.2 ± 200.4 (F)
|110.3 ± 24.5 (M)
101.4 ± 32.6 (F)
|12||183.7 ± 99.9 (M)
120.3 ± 64.0 (F)
|28.4 ± 16.1 (M)
18.1 ± 10.9 (F)
|195.6 ± 62.5 (M)
151.3 ± 64.6 (F)
|30.6 ± 10.3 (M)
23.2 ± 10.3 (F)
|255.4 ± 98.7 (M)
220.2 ± 85.0 (F)
|40 ± 15.6 (M)
35.7 ± 9.4 (F)
|Harada et al.||Longitudinal||Internal control||625.9 ± 387.9||14.1 ± 10||6||242.4 ± 131.6||4.7 ± 2.5||301.5 ± 181.5||5.4 ± 3.5||301.5 ± 181.5||5.4 ± 3.5|
|Iwase et al. , a , b||Longitudinal||Internal control||39 (M)
|30 (number of occlusal contacts)||12||13 (M)
|8 (number of occlusal contacts)||25 (M)
|20 (number of occlusal contacts)||27 (M)
number of occlusal contacts
|Ellis et al. (only molar BF values used for comparison)||Longitudinal (retrospective)||Internal control||396 ± 129||Not measured||36||215 ± 86||Not measured||247 ± 126.5||Not measured||373.6 ± 221.6||Not measured|
|Athanasiou||Longitudinal (retrospective)||Normative literature values||NA||NA||6||359 ± 263.5||9.36 ± 6.5 (expressed as number of contacts)||519.2 ± 199||13.9 ± 5.5 (expressed as number of contacts)||Not measured||Not measured|
|Shiratsuchi et al.||Longitudinal||Normative literature values||NA||NA||24||760 ± 322||65.2 ± 27||1220 ± 422||97.2 ± 24.1||1500 ± 713||105.4 ± 31.1|
|Kikuta et al. (molar BFs)||Longitudinal||Normative literature values||NA||NA||12||230.5||No detail||274.6||No detail||308.9||No detail|
|Author, Ref.||Surgical procedures||Mean setback (mm) (SD)||Segment fixation||Duration of IMF||Post-surgical rehabilitation||Patients ( n )||Mean age (years)||Method of bite force measurement|
|Choi et al.||IVRO; LFI||NR||Not used||2 weeks, then sequential elastic traction||Used||48||23.1||DPS|
|Kato et al.||BSSO||NR||NR||NR||Used (chewing gum)||34||23||DPS|
|Yamashita et al.||BSSO||Right 7.3 (3.0)
Left 6.1 (3.6)
|Rigid, miniplates, monocortical screws||7–20 days||NR||36||23.1||DPS|
|Right 7.0 (2.8)
Left 7.0 (3.1)
|Rigid, bicortical screws||41||21.3|
|Ueki et al.||BSSO||Right 6.2 (3.0)
Left 6.6 (3.2)
|Rigid, miniplates, monocortical screws||Not used; elastics only||Not used||22||25.5||DPS|
|Yamashita et al. ,a||BSSO||Right 7.6 (3.0)
Left 7.1 (3.7)
|Rigid, miniplates, monocortical screws||10–20 days||NR||32||22||DPS|
|Right 8.5 (3.8)
Left 7.7 (3.4)
|Rigid, bicortical screws||38||22.7|
|Ueki et al. ,a||BSSO||NR||Rigid, miniplates, monocortical screws||1 week, then sequential elastic traction||NR||15||23.2||DPS|
|IVRO||Not used||2–3 weeks, then sequential elastic traction||15|
|Nakata et al. ,a||BSSO||NR||NR||NR||NR||36||19||DPS|
|Iwase et al. ,a||BSSO; maxillary procedures not consistently performed||NR||Rigid, miniplates, monocortical screws||5 days||Not used||27||23||DPS|
|Harada et al. ,a||BSSO; LFI maxillary advancement||NR||Mandibular rigid, bicortical screws; maxillary rigid, miniplates||Not used; elastics only, removed at 2 months||NR||10||23.2||DPS|
|Ohkura et al.||BSSO||8.0 (range 1.0–16.0)||Rigid, bicortical screws||Not used; elastics only, removed at 2 months||NR||57||23.7||DPS|
|Nagai et al.||BSSO||Right 4.9 (range 3.5–11)
Left 5.0 (range 3.0–11)
|Rigid, miniplates||7 days||NR||43||22||DPS|
|Harada et al.||BSSO||8.0 mm (range 1–13.5 mm)||Rigid, bicortical screws||Not used; elastics only, removed at 2 months||NR||25||24.4||DPS|
|Iwase et al. ,a,b||BSSO; maxillary procedures not consistently performed||NR||Rigid, bicortical screws||5 days||Not used||23||24.3||T-Scan System|
|Ellis et al.||VRO||4.1 mm||Mandibular non-rigid; maxillary rigid||2–3 weeks||Used||7||24.6||Transducer|
|VRO; maxillary advancement/inferior repositioning||12|
|VRO; maxillary intrusion||5|
|Athanasiou||EVRO||NR||Non-rigid, stainless steel wiring in about one half of cases; not used in the rest||6 weeks||NR||33||NR||Photocclusion technique|
|Shiratsuchi et al.||BSSO||NR||Non-rigid, circumferential wiring||6 weeks||NR||17||NR||Transducer|
|Kikuta et al.||BSSO||NR||NR||NR||NR||30||NR||Transducer|