Changes in bite force after orthognathic surgical correction of mandibular prognathism: a systematic review

Abstract

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.

Methods

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 ).

Table 1
Search strategy.
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
Total 129 22

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.

Results

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 ).

Fig. 1
PRISMA flow diagram of the selection and screening process ( a Two additional studies were identified from a manual search of the references in the 22 full-text articles).

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.

Table 2
Overview of the articles included and patient demographic data.
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
TMJ, temporomandibular joint; 3D CT, three-dimensional computed tomography; EMG, electromyography; NR, not reported.

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.

Table 3
Methodology of the studies included, length of follow-up, and mean bite force and occlusal contact area before surgery, at 6 months after surgery, and at last measurement. All studies had pre-surgical and post-surgical orthodontics except for Nagai et al. (not reported) and Ellis et al. (one patient had no pre-surgical orthodontics and post-surgical not reported). The 6-month interim postoperative reading was chosen, as it was a common time period selected for measurement.
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)
200 (F)
6 (M and F) 700 (M)
400 (F)
17 (M)
16 (F)
800 (M)
600 (F)
21 (M)
18 (F)
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)
Not measured
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)
26 (F)
30 (number of occlusal contacts) 12 13 (M)
9 (F)
8 (number of occlusal contacts) 25 (M)
18 (F)
20 (number of occlusal contacts) 27 (M)
20 (F)
20 (M)
21 (F)
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
BF, bite force; OCA, occlusal contact area; NA, not applicable; M, male; F, female.

a Values extrapolated from graphs.

b Bite force measured with a T-Scan System, expressed as a relative value not in Newtons.

Table 4
Surgical procedures and method of bite force measurement.
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
IVRO 30 24.2
Kato et al. BSSO NR NR NR Used (chewing gum) 34 23 DPS
BSSO Not used 13 23
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
BSSO; LFI 4
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
BSSO; LFI 15
IVRO Not used 2–3 weeks, then sequential elastic traction 15
IVRO; LFI 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
BSSO 14
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
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Dec 14, 2017 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Changes in bite force after orthognathic surgical correction of mandibular prognathism: a systematic review
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