Effect of mandibular setback surgery on occlusal force

Evaluation of occlusal force changes in orthognathic surgery using force-sensing sensors in 3 years of follow-up

Purpose

The aim of this study was to test a prototype device called occlusal force diagnostic system in relation to occlusal force adaptation following orthognathic surgery.

Methods

Retrospective study of 10 patients scheduled for a bimaxillary osteotomy involving a combination of maxillary Le Fort I impaction procedure coupled with a sagittal split advancement of the mandible; in a 3 years follow-up period.

Results

The selection of examiner is not a variable that affects the occlusal force (N) measured by FSS sensors in any of the experimental conditions tested. The sensor position and the surgery recovery time affect the occlusal force irrespective of the examiner selection and/or the surgery recovery time.

Conclusion

The piezoelectric sensors used in the present study have shown high reliability and validity of measurement. The surgery recovery time impacts the occlusal force (N), with a 50% increase in occlusal force (N) measured after 6 months post-surgery, with the value keeping stable at 36 months. This suggests that the patient is only fully recovered from the functional point-of-view at 6 months, having from that point on an improved and stable masticatory function.

Changes in occlusion after orthognathic surgery: a systematic review and meta-analysis

PURPOSE

This study aims to systematically review and identify the changes of occlusion in patients after orthognathic surgery.

METHODS

The protocol was developed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis Protocols (PRISMA-P) and was registered to the International Prospective Register of Systematic Reviews (PROSPERO) under the registration number CRD42021253129. Studies included were Original articles only, Additionally, studies were included if the outcome of occlusal force was measured pre- and postoperatively and if occlusal forces resulted from a long follow-up of a minimum of 1 year following orthognathic surgery using adequate measurement tools. Non-English articles, case reports, case series, and non-original articles, including systematic reviews and literature reviews, were excluded.

RESULTS

The search strategy yielded a total of 978 articles. Of the 978 articles, 285 were duplicates. After reading the titles and abstracts, 649 articles were excluded, and full-text articles of the remaining 47 studies were reviewed independently by two authors for eligibility wherein 33 articles were excluded, because they did not meet the inclusion criteria. Finally, a total of 14 studies were processed for critical review.

CONCLUSION

The occlusal force increased after orthognathic surgery, although not to the level of the control group; however, the maximal bite force remained unchanged. Immediately after orthognathic surgery, chewing and swallowing forces increased. Significant reductions in the postoperative occlusal contact pressure areas was also observed.

The biomechanical stability of miniplate osteosynthesis configurations in bilateral mandibular angle fractures

PURPOSE

The present study investigated the biomechanical stability of three miniplate osteosynthesis configurations used for internal fixation of bilateral mandibular angle fracture (BMAF).

METHODS

Standard fracture lines were created in 72 polyurethane mandibles and stabilized with 2.0-mm, 4-hole standard titanium miniplates and monocortical screws. The group descriptions and miniplate configurations were: 2Plates (1-1), 3Plates (1-2) and 4Plates (2-2). The mandibles were subjected to either incisal or molar loads (from both sides in the 3Plates group) up to a force of 120 N. The displacements of the constructs were recorded at each force increment of 10 N. ANOVA and Tukey's post-hoc tests were used for statistical analysis.

RESULTS

The 2Plates group showed higher displacement under both loading conditions (P < 0.05 for each). The same group reached displacement levels of 1 mm and 3 mm during molar loading and 1 mm, 3 mm, and 5 mm during incisal loading at lower force magnitudes relative to others (P < 0.05 for each).

CONCLUSION

Bone-plate constructs for BMAFs stabilized with three or four standard miniplates are more likely to provide similar resistance when subjected to incisal or molar loads, in contrast to the two-miniplate configuration, which is relatively more prone to displacement.

Comparison of the bite force and occlusal contact area of the deviated and non-deviated sides after intraoral vertical ramus osteotomy in skeletal Class III patients with mandibular asymmetry: Two-year follow-up

Objective

The objectives of this study were to compare the time-dependent changes in occlusal contact area (OCA) and bite force (BF) of the deviated and non-deviated sides in mandibular prognathic patients with mandibular asymmetry before and after orthognathic surgery and investigate the factors associated with the changes in OCA and BF on each side.

Methods

The sample consisted of 67 patients (33 men and 34 women; age range 15-36 years) with facial asymmetry who underwent 2-jaw orthognathic surgery. OCA and BF were taken before presurgical orthodontic treatment, within 1 month before surgery, and 1 month, 3 months, 6 months, 1 year, and 2 years after surgery. OCA and BF were measured using the Dental Prescale System.

Results

The OCA and BF decreased gradually before surgery and increased after surgery on both sides. The OCA and BF were significantly greater on the deviated side than on the non-deviated side before surgery, and there was no difference after surgery. According to the linear mixed-effect model, only the changes in the mandibular plane angle had a significant effect on BF (p < 0.05).

Conclusions

There was a difference in the amount of the OCA and BF between the deviated and non-deviated sides before surgery. The change in mandibular plane angle affects the change, especially on the non-deviated side, during the observation period.

Bite force changes after surgical correction of mandibular prognathism in subjects with increased vertical dimension : A prospective clinical trial

PURPOSE

Occlusal bite force (OBF) is the most important parameter in assessing biting efficiency. The aim of this study was to record OBF changes after surgical correction of high angle maxillary/mandibular (Max/Mand) class III patients and to compare these with that recorded in class III patients with average Max/Mand angle.

MATERIALS AND METHODS

Initially included were 42 patients with severe class III skeletal malocclusion who were scheduled for orthodontic surgery: group 1-22 patients with increased vertical relationship scheduled for bimaxillary surgery; group 2-20 patients with average vertical relationship scheduled for mandibular setback only. OBF measurements before surgery (T0), at debonding (T1) and at least 3 months after debonding (T2) were recorded using a portable occlusal force gauge. The following were also measured: maximum OBF (MOBF) achieved by the subject on each side, averaged OBF on each side (AOBF) and maximum OBF at the incisal region (MIOBF). At T2, only 33 patients (group 1: 17 and group 2: 16) were included in the analysis due to loss to follow-up.

RESULTS

MOBF increased significantly in group 1, while no significant changes were detected in group 2. MIOBF increased after surgical correction in both groups. Significant increase in MIOBF was observed at T1 (P < 0.001) followed by an insignificant decrease during the observation period (3-6 months after treatment; P > 0.05). The two groups differed significantly in MOBF at T1 and T2, while no statistically significant differences were detected between the groups for MIOBF changes at the various time intervals (P > 0.05). The number of posterior teeth with occlusal contacts increased in both groups. Relapse was detected in group 1 where the number of posterior teeth in contact decreased during the observation period (T1-T2).

CONCLUSION

OBF greatly improved after surgical correction of the vertical morphology. Correction of high angle mandibular prognathism improves oral function in addition to esthetics.

Effect of Bone Buttressing at the Vertical Osteotomy Site on Postoperative Stability After Mandibular Setback Surgery

ABSTRACT

This study aimed to assess the effect of bone buttressing at the vertical osteotomy site on postoperative stability after mandibular setback surgery and determine factors contributing to postoperative relapse. This retrospective study was conducted on patients who received mandibular setback surgery using bilateral sagittal split ramus osteotomy. Patients were divided into two groups: group I, intimate bony contact, and group II, bony gap of 2 mm or more. Using lateral cephalograms taken before surgery, 1 week after surgery, and 6 months after surgery, surgical changes, and postoperative relapse were compared between 2 groups. To assess associations between postoperative relapse and other variables, Pearson correlation analysis and multiple linear regression analysis were performed. Twenty-eight patients were evaluated (17 in group I and 11 in group II). Mean relapse was greater in group II (1.8 mm) than in group I (1.2 mm), although there were no significant differences between 2 groups (P = 0.203). Postoperative relapse was significantly associated with intraoperative clockwise rotation of the proximal segment (P < 0.001) and the amount of mandibular setback (P = 0.038). Bony gap was only correlated with postoperative counterclockwise rotation of the proximal segment (P = 0.014). In the regression analysis, intraoperative clockwise rotation of the proximal segment significantly predicted postoperative relapse (P < 0.001, R2 = 0.388). The absence of bone buttressing at the vertical osteotomy site may not significantly affect postoperative stability after mandibular setback surgery, and it is important to minimize intraoperative clockwise rotation of the proximal segment for better postoperative stability.

The Effect of Patient Specific Factors on Occlusal Forces Generated: Best Evidence Consensus Statement

PURPOSE

The purpose of this Best Evidence Consensus Statement was to search the literature to determine if there is a relationship between patient specific factors and occlusal force.

MATERIALS AND METHODS

A literature review was conducted in the following databases: Evidence-Based Medicine Reviews (EBMR), Cochrane Database of Systematic Reviews, Embase, and Ovid MEDLINE(R) and Epub Ahead of Print. Articles on patient factors and occlusal force were compiled by using a combination of the key words: "bite force," "occlusal force," "partial and complete edentulism," "bruxism," and "orthognathic class." Inclusion criteria included meta-analyses, systematic reviews, randomized controlled trials, case series, and journal articles. Exclusion criteria were case reports, studies in children, animals, and bench studies.

RESULTS

Of the 1502 articles that met the initial search criteria, 97 related to patient-specific factors affecting occlusal forces. These articles were evaluated, rated, and organized into appropriate categories addressing questions of foci.

CONCLUSIONS

The range of occlusal force is highly variable among subjects correlated to patient specific factors such as age, gender, partial and complete edentulism, the presence of a maxillofacial defect, location of edentulous area, orthognathic profile, and magnitude of occlusal vertical dimension. Tooth replacement therapies targeted at increasing occlusal contact seem to have a positive effect on increasing occlusal force. Bruxism does not necessarily demonstrate higher occlusal powering but may have greater tooth contact time. Occlusal force is not clearly affected by the type of dental restoration or restorative material used. The clinical significance of the changes in occlusal forces is yet to be determined.

Validity of Medical Insurance Guidelines for Orthognathic Surgery

PURPOSE

The purpose of this study was to assess the validity of the medical insurance guidelines for orthognathic surgery used by the major American medical insurance companies.

MATERIALS AND METHODS

This study assessed the validity of the medical insurance guidelines for orthognathic surgery used by Aetna, Anthem Blue Cross Blue Shield (BCBS), Cigna, Humana, and UnitedHealthcare (UHC). To evaluate the validity, we calculated the approval and denial rates of the 5 guidelines when we used them to assess the medical necessity for a control group of carefully selected patients. Patients were included in the control group if they met the criteria of a "prudent provider," crafted for this study. All rejected cases were analyzed to determine the root cause of the denials. The validity of the guidelines was also ascertained by determining their completeness and correctness.

RESULTS

The current study proves that no insurance guideline is in agreement with the criteria of a "prudent provider." When applied to carefully chosen patients, the requirements of BCBS, Aetna, Humana, and Cigna produce modest rejection rates of 6 to 12%. UHC is an outlier. Its guideline rejects 86% of patients, a rate about 7 times higher than its peers. Insurance guidelines disqualified patients for 3 different reasons: 1) no significant jaw deformity, 2) no demonstrable health impairment, and 3) the etiology of the condition is not a covered benefit. Additional evaluations demonstrate that the private insurance guidelines are incomplete, and at times, incorrect.

CONCLUSIONS

This study shows that the medical insurance guidelines for orthognathic surgery used by the major American medical insurance plans need revision. The most consequential flaw was considering etiology in judging medical necessity. Fortunately, only one company adopted this policy. Moreover, all guidelines have omissions and errors in the way jaw deformity is determined and how health impairment is determined.

Evaluation of border movement of the mandible before and after orthognathic surgery using a kinesiograph

PURPOSE

The purpose of this study was to examine the changes in the mandibular border movement between class II and class III jaw deformity patients before and after orthognathic surgery, by using the same device.

SUBJECTS

and Methods: Eighty one patients (28 in class II and 53 in class III) who underwent sagittal split ramus osteotomy (SSRO) with Le Fort I osteotomy using absorbable plate fixation and 27 controls with normal occlusion were enrolled. Mandibular border movement (observed using a kinesiograph) was recorded with a mandibular movement measure system (K7) before surgery, and at 6 months and 1 year after surgery. Time-course changes of 5 components of the mandibular border movement (MVO: Maximum vertical opening, CO to MAP: Maximum antero-posterior movement from centric occlusion, MLDL: maximum lateral deviation left, MLDR: maximum lateral deviation right, CO to MO: centric occlusion to maximum opening) were compared between classes II, III and controls statistically. The relationship between lateral cephalometric measurements and the components of mandibular border movement was also examined.

RESULTS

There was a significant difference in CO to MAP (P = 0.0025) and CO to MO (P < 0.0001) between class II and class III in the time-course change. In class III, mean and standard deviation of MVO were 44.5 ± 6.7 mm before surgery and 39.8 ± 6.8 mm after 1 year. Mean and standard deviation of CO to MAP were 25.2 ± 6.8 mm before surgery and 21.5 ± 7.9 mm after 1 year. Mean and standard deviation of CO to MO were 53.4 ± 9.0 mm before surgery and 47.3 ± 8.4 mm after 1 year. In class II, mean and standard deviation of MVO were 38.8 ± 5.8 mm before surgery and 36.2 ± 7.4 mm after 1 year. Mean and standard deviation of CO to MAP were 18.0 ± 6.3 mm before surgery and 17.8 ± 7.4 mm after 1 year. Mean and standard deviation of CO to MO were 43.1 ± 7.5 mm before surgery and 39.6 ± 10.5 mm after 1 year. In MVO, CO to MAP and CO to MO, the values after 1 year did not significantly reach the pre-operative values in class III (P = 0.0001, P = 0.0007 and P < 0.0001), although there was no significant difference between pre-operation and after 1 year in class II. In CO to MO, class II (mean and standard deviation 39.6 ± 10.5 mm) and class III (mean and standard deviation 47.3 ± 8.4 mm) still remained smaller values than control (mean and standard deviation 52.7 ± 9.2 mm) after 1 year (P < 0.0001 and P = 0.0095).

CONCLUSION

This study suggests that bi-maxillary surgery can have more influence on the reduction in the range of mandibular border movement including vertical or antero-posterior motion than lateral deviation motion, in both groups. The difference in the time-course change in the mandibular border movement between the groups might depend more on the mandibular length than on the movement direction of the mandible by surgery such as advancement or setback.

Impact of orthognathic surgery on the body posture

BACKGROUND

Postural control is classically described as being based on the visual, vestibular, and proprioceptive musculo-articular sensory systems. The influence of mandibular proprioception on postural stabilization remains controversial. Most previous studies analyzed how postural stability is influenced by partial changes in mandibular proprioception (dental occlusion and jaw position).

RESEARCH QUESTION

In the present experiment, we asked whether drastic mandibular changes, resulting from orthognathic surgery (including dental, joint and muscular efferents), modify postural control.

METHODS

The analyzes were performed in 22 patients tested before, and 2.5 months, after orthognathic surgery for treatment of dysmorphic jaws. Experiments were performed under 4 experimental conditions: 2 visual conditions: Eyes Open (EO) and Eyes Closed (EC), and 2 occlusal conditions: Occlusion (OC: mandible positioned by the contact of the teeth), and Rest Position (RP: mandible positioned by the muscles without tooth contact). The analyses focused on head orientation in the frontal plane and on postural stabilization in a static task, consisting of standing upright.

RESULTS

The results show that, 2.5 months after orthognathic surgery, head orientation in the frontal plane was improved, since patient's external intercanthal lines became closer to the true horizontal line when they were tested EC and in OC condition. Postural responses, based on the wavelet transformation data, highlight an improvement in maintaining an upright stance for all the tested sensory conditions. However, such improvement was greater in the EC and RP conditions.

SIGNIFICANCE

These results show, for the first time, that after drastic mandibular changes, the weight of proprioceptive cues linked to the mandibular system may be so enhanced that it may constitute a new reference frame to orient the head in space, in darkness, and improve static postural stabilization, even in the presence of visual cues.

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

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.

The amount of mandibular setback influence on occlusal force following sagittal split ramus osteotomy

PURPOSE

The purpose of this study was to examine the influence between the magnitude of setback in sagittal split ramus osteotomy (SSRO) and occlusal contact area and bite force without relapse after surgery.

PATIENTS AND METHODS

Sixty female patients with a diagnosis of mandibular prognathism were divided into 3 groups according to the magnitude of setback: group 1 (≤5 mm), group 2 (>5 mm but <10 mm), and group 3 (≥10 mm). All patients underwent skeletal analysis by lateral and frontal cephalogrammetry and measured the occlusal contact area and bite force by the pressure-sensitive system (Dental Prescale, Dental Occlusion Pressuregraph FDP-705; Fuji Photo Film Co., Tokyo, Japan) preoperatively and postoperatively at 1 month, 3 months, 6 months, and 1 year.

RESULTS

There were no significant differences in occlusal contact area and bite force between the 3 groups. Only group 3 showed a significant difference in occlusal contact area and bite force between the preoperative and 1-year measurements.

CONCLUSION

The results indicate that the magnitude of setback did not influence the bite force or occlusal contact area in SSRO.

Changes in occlusal function after orthognathic surgery in mandibular prognathism with and without asymmetry

This study aimed to evaluate the postoperative changes in masticatory function in patients with jaw deformities with or without asymmetry treated by orthognathic surgery. Thirty female patients who underwent a Le Fort I osteotomy with sagittal split ramus osteotomy (SSRO) were enrolled. The patients were divided into symmetry and asymmetry groups. The bite force, occlusal contact area, and bite force balance were measured before and at 1, 3, and 6 months and 1 year after surgery; these measurements were compared statistically within and between the two groups. In the symmetry group, there was a significant difference in the preoperative bite force and the 1 month postoperative bite force (P=0.0033). In the asymmetry group, the bite force before surgery was significantly different from that at 1 month (P=0.0375) and at 1 year (P=0.0353) after surgery. Significant differences in the bite force were also observed between the following time points: 1 month and 1 year (P=0.0003), 3 months and 1 year (P=0.0034), and 1 month and 6 months (P=0.0486). The occlusal contact area, bite force, and occlusal balance tended to change after Le Fort I osteotomy with SSRO, with a significantly improved bite force in patients with asymmetry before surgery.

Changes in electric activity of masseter and anterior temporalis muscles before and after orthognathic surgery in skeletal class III patients

OBJECTIVE

The purpose of this study was to evaluate, through clinical and electromyographic (EMG) assessments, the electric activity of masseter muscle and anterior temporalis muscles during clenching, before and after orthodontic treatment and mandibular setback, with or without LeFort I osteotomy, for correction of mandibular excess.

STUDY DESIGN

Seventeen adult patients (10 males, 7 females, mean age: 22.5 ± 2.4 years) were recruited for this study. All patients received orthodontic treatment and surgical corrections. EMG recordings were obtained from 4 channels of the 8-channel electromyograph FREELY (DeGoetzen spa, Olgiate Olona, VA, Italy).

RESULTS

A significant difference was found in the value of activity index at T0-T1 (33% T0, 1% T1) (P < .05), of asymmetry index at T0-T1 (21% T0, 4% T1) (P < .05), and of torque index at T0-T1 (24% T0, 5% T1) (P < .05).

CONCLUSIONS

The evaluation of EMG activity after surgery may be considered a sign of good adaptation of the neuromuscular system to the new occlusal condition and a good method for detecting nonresponding patients who might require further treatment.

Evaluation of recovery in lip closing pressure and occlusal force and contact area after orthognathic surgery

PURPOSE

The purpose of this study was to evaluate the relationship between lip closing force, occlusal contact area and occlusal force after orthognathic surgery in skeletal Class III patients.

SUBJECTS AND METHODS

The subjects consisted of 54 patients (28 female and 26 male) diagnosed with mandibular prognathism who underwent sagittal split ramus osteotomy with and without Le Fort I osteotomy. Maximum and minimum lip closing forces, occlusal contact area and occlusal force were measured pre-operatively, 6 months and 1 year post-operative.

RESULTS

Maximum and minimum lip closing forces, occlusal contact area and occlusal force increased with time after surgery, however a significant increase was not found in the occlusal contact area in women. In increased ratio (6 months/pre-operative and 1 year/pre-operative), the maximum lip closing force was significantly correlated with the occlusal contact area (P < 0.0001).

CONCLUSIONS

This study suggested that orthognathic surgery could improve the occlusal force, contact area and lip closing force, and an increase ratio in maximum lip closing force was associated with an increased ratio in occlusal contact area.

Improvement of asymmetric stomatognathic functions, unilateral crossbite, and facial esthetics in a patient with skeletal Class III malocclusion and mandibular asymmetry, treated with orthognathic surgery

Patients with a dentofacial skeletal deformity have not only esthetic and morphologic problems related to facial proportions and dentition, but also problems of stomatognathic functions. Therefore, in addition to morphologic analysis, functional analysis is important for the diagnosis and evaluation of treatment in these patients. However, no reports have described longitudinal simultaneous evaluations of stomatognathic functions, and the comprehensive effects of surgical orthodontics on the stomatognathic functions are unclear. A patient was diagnosed as having a skeletal Class III jaw-base relationship, mandibular asymmetry, unilateral crossbite, asymmetric stomatognathic functions, and a temporomandibular disorder. She was treated with a combination of surgery and orthodontic therapy. As a result, facial proportions and occlusion improved; in particular, asymmetric stomatognathic functions, including masticatory muscle activity, condylar movement, and occlusal force, became symmetric between the left and right sides. Moreover, after 2 years of retention, the activity of the masticatory muscles and the values of occlusal force and occlusal contact area exceeded those at pretreatment. These results suggest that improvement of asymmetric stomatognathic functions can be achieved by correction of dentofacial morphology by surgical orthodontic treatment in patients with mandibular asymmetry.

Postsurgical stability after mandibular setback surgery with minimal orthodontic preparation following upper premolar extraction

PURPOSE

To compare patterns of surgical change and postsurgical relapse between patients with mandibular setback surgery with minimal orthodontic preparation (MS-MO) and those with sufficient orthodontic preparation (MS-SO) after upper premolar extraction (UPE).

MATERIALS AND METHODS

Twenty-six patients were allocated to 2 groups based on the duration of presurgical orthodontic preparation: MS-MO/UPE (n = 15; 5.53 ± 3.14 months) and MS-SO/UPE (n = 11; 13.00 ± 5.33 months). Lateral cephalograms were taken during the initial examination (T0), at splint removal (4 weeks after surgery; T1), and immediately after debonding (T2). To evaluate the surgical changes (T1 vs. T0) and relapse (T2 vs. T1), linear, angular, and dental measurements were used and analyzed using paired t test and independent t test.

RESULTS

Although there was no significant difference in skeletodental patterns at T0 between the 2 groups, the MS-MO/UPE group showed a significantly larger amount of mandibular setback than the MS-SO/UPE group from T0 to T1. The 2 groups exhibited significant anterior and superior movement of the mandible from T1 to T2. However, the MS-MO/UPE group manifested greater counterclockwise rotation and forward movement of the mandible than the MS-SO/UPE group. Owing to such relapse of the mandible, the MS-MO/UPE group exhibited limited retraction of the upper incisors, whereas the MS-SO/UPE group showed slight labioversion of the upper incisors.

CONCLUSION

Compared with the MS-SO/UPE group, the MS-MO/UPE group showed a larger amount of surgical setback and greater postsurgical counterclockwise rotation and forward movement of the mandible.

Masticatory performance and taste perception in patients submitted to cancer treatment

The aim of this study was to analyse mastication and the sense of taste in 39 patients submitted to cancer treatment in different areas of the body and to compare these variables with those of 44 control individuals within the same age range. The following aspects were assessed: dental status (DMFT); stimulated and non-stimulated salivary flow; sense of taste (salty, sweet, bitter and sour); and masticatory performance (MP), through the calculation of X(50). Logistic regression models were established to test the association between the independent variables and cancer treatment. Cancer patients had lesser stimulated salivary flow, a smaller number of teeth and occlusal units, worse MP, higher salty, sweet and sour taste scores and a lower bitter taste score (P < 0·05). A significant positive correlation was found between MP and the DMFT index in both groups (P < 0·05), meaning that a lower DMFT index value denoted a smaller X(50) value (better masticatory performance). The logistic regression model revealed that patients who had undergone cancer treatment had a greater probability of exhibiting a smaller number of teeth, higher salty and smaller bitter taste scores (P < 0·05). It was concluded that patients who were submitted to cancer treatment presented oral physiology alterations when compared with control subjects at the same age range.

An in vitro evaluation of rigid internal fixation techniques for sagittal split ramus osteotomies: setback surgery

PURPOSE

The aim of this study was to evaluate the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomy for mandibular setback in vitro.

MATERIALS AND METHODS

Sixty polyurethane replicas of human hemimandibles were used as substrates, simulating a 5-mm setback surgery by sagittal split ramus osteotomy. These replicas served to reproduce 3 different techniques of fixation, including 1) a 4-hole plate and 4 monocortical screws (miniplate group), 2) a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3) 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). After fixation, hemimandibles were adapted to a test support and subjected to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge with an Instron 4411 mechanical testing unit. Peak loadings at 1, 3, 5, and 10 mm of displacement were recorded. Means and standard deviation were analyzed using analysis of variance and Tukey test with a 5% level of significance, and failures during tests were recorded.

RESULTS

Regardless of the amount of displacement and direction of force, the miniplate group always showed the lowest load peak scores (P < .01) compared with the other fixation techniques. The hybrid group demonstrated behavior similar to the inverted-L group in lateral and vertical forces at any loading displacement (P > .05). Molar load tests required more force than incisal load tests to promote the same displacement in the mandibular setback model (P < .05).

CONCLUSION

For mandibular setback surgery of 5 mm, this study concluded that the fixation technique based on the miniplate group was significantly less rigid than the fixation observed in the hybrid and inverted-L groups. Mechanically, adding 1 bicortical positional screw in the retromolar region in the miniplate technique may achieve the same stabilization offered by inverted-L fixation for mandibular sagittal split ramus osteotomy setback surgery in vitro.

Place of sagittal split osteotomy in mandibular surgery

With the development of craniofacial surgery, today sagittal split mandibular osteotomies are frequently used for the treatment of mandibular deformities with modifications and different fixation techniques. In clinics, 57 patients are evaluated in this study. Of these patients, 35 were male, 22 were female, and their ages were between 17 and 47 years (on average, it was 23 years). Thirty-seven of these patients were treated with bilateral sagittal split mandibular osteotomy (SSMO), 12 of them with unilateral SSMO, 6 of them with bilateral SSMO + Le Fort I osteotomy, and 2 of them with bilateral SSMO + Le Fort II osteotomy. Orthodontic treatment modalities were performed for 8 patients preoperatively and to all of the patients postoperatively. All patients were examined with cephalometric analysis preoperatively and postoperatively. Internal and external distractors were applied for 14 patients. Rigid fixation with plates and screws was done for 21 patients. Fixation with screws for 5 patients, fixation with wires for 3 patients, and intermaxillary fixation for 8 patients were performed. Patients were followed up on average 13 months (6-22 months). In 1 patient, infection on the osteotomy line and recurrency developed. Sensory area of the alveolar nerve became normal in 10 to 16 weeks usually, but in 3 patients, sensory loss developed at this region. Complaints of temporomandibular joint dysfunction developed in 1 patient at the third postoperative month. When the clinical use was determined, we observed that SSMO could give satisfactory results in selected patients with mandibular deformities. Dental structures are important in relation to the postoperative occlusion and masticatory functions, for this reason, we think that postoperative orthodontic treatment will be useful for these patients.

Functional assessment of the stomatognathic system

Clinically objective assessment of the occlusal function remains largely, even today, in the research laboratory instead of in the clinical setting, as part of the routine assessment along with the morphologic documentation. Functional outcomes of the stomatognathic system can be measured in terms of occlusal contact area, maximal voluntary bite force, maximal voluntary excursions, masticatory force, masticatory cycle pattern and masticatory performance. It should be emphasized, however, that many of these measures remain to be standardized and validated as tools relevant for assessment of patients who have dentofacial skeletal deformities. This remains a promising area of active research.

Changes in occlusal force after mandibular ramus osteotomy with and without Le Fort I osteotomy

The purpose of this study was to evaluate the differences in bite force changes and occlusal contacts after sagittal split ramus osteotomy (SSRO) and intraoral vertical ramus osteotomy (IVRO) with and without Le Fort I osteotomy. Sixty female patients with diagnosed mandibular prognathism with or without asymmetry were divided into four groups (SSRO, IVRO, SSRO with Le Fort I osteotomy and IVRO with Le Fort I osteotomy). Bite force and occlusal contacts were measured preoperatively and at 1, 3, 6 and 12 months after surgery with pressure-sensitive sheets. The differences among surgical procedures were examined statistically. Maximum bite force and occlusal contacts returned to preoperative levels after between 3 and 6 months. Regarding time-dependent changes in bite force and occlusal contact area, there were no significant differences among the groups. In conclusion, this study suggests that the combination of IVRO or SSRO and Le Fort I osteotomy does not affect postoperative time-dependent changes.

Changes in Stomatognathic Function Induced by Orthognathic Surgery in Patients With Mandibular Prognathism

PURPOSE

This study was designed to investigate the changes in stomatognathic function through orthognathic treatment in patients with mandibular prognathism.

PATIENTS AND METHODS

Thirty-six patients with mandibular prognathism were tested and compared with 30 healthy controls with normal occlusion. For each subject, the occlusal contact area and occlusal force were measured during maximum voluntary clenching (MVC). Activities of the masseter and temporalis muscles were recorded during MVC and voluntary gum chewing. Jaw movement was analyzed during chewing on the left and right sides. For the analyses, 2 parameters, asymmetry index (AI) and error index (EI), were established to further investigate the nature of masticatory function. AI was used to evaluate the bilateral balance of masticatory muscle activity, and EI indicates the rate of abnormal jaw movement pattern.

RESULTS

In patients with mandibular prognathism, the occlusal contact area and maximum bite force decreased before surgery, and increased after surgery. The masseter and temporal muscle activities also decreased before surgery, but showed no substantial increase even after surgery. The occlusal and muscle efficiency exhibited significantly smaller values in the patient group than in the controls, irrespective of treatment stages. The AI decreased after surgery. The EI decreased significantly after surgery, but was still significantly greater in the patient group than in the controls.

CONCLUSIONS

It is suggested that masticatory muscles in the patients with mandibular prognathism may adapt to the new environment achieved with surgically corrected dentofacial structure, although the activities remain at lower levels as compared with the controls.

Masticatory function and neurosensory disturbance after mandibular correction by bilateral sagittal split ramus osteotomy: a comparison between miniplate and bicortical screw rigid internal fixation

Bilateral sagittal split osteotomy is commonly used to treat mandibular prognathism. Several fixation methods for bony segments have been described. The present study compared masticatory function and neurosensory recovery patterns after mandibular correction between two methods of rigid fixation, bicortical screw (n = 38) and monocortical miniplate (n = 32). Patients who had undergone bilateral sagittal split osteotomy for Class III malocclusion were reviewed, and masticatory function and neurosensory recovery were studied with the appropriate indicators at 1, 3, 6 and 12 months postoperatively. Minimal differences were seen between groups at 1-year postoperatively, and although patients treated with miniplate fixation tended to recover faster, with regard to masticatory function and neurosensory disturbance, than those treated with screw fixation, no significant differences were identified. As the two methods seem to provide equal comfort and reliability, the choice should be made by the individual surgeon.

The Influence of Mandibular Advancement Surgery on Oral Function in Retrognathic Patients: A 5-Year Follow-Up Study

PURPOSE

Previous studies have shown that patients with mandibular retrognathism who were scheduled for orthognathic surgery have a lower maximum bite force and an impaired chewing performance. Surgical correction of this deformity is supposed to lead to an improvement of these oral functions. One year after surgery, no significant changes could be shown in these patients. However, a longer follow-up might demonstrate an improvement after all.

PATIENTS AND METHODS

Maximum bite force and chewing performance were determined in 12 patients with a mandibular retrognathism before mandibular advancement surgery and at least 5 years after surgery. Chewing performance (median particle size) was determined with a sieving method after chewing 15 strokes on an artificial test food. Maximum bite force was recorded bilaterally at the level of the first molars.

RESULTS

Five years after surgery, chewing performance was improved, especially in patients with a poor performance before treatment. An increase of the maximum bite force could not be shown.

CONCLUSION

Surgical correction of mandibular retrognathism had a positive effect on oral function 5 years after surgery, although it could not be detected 1 year after surgery. However, the function of the masticatory system was still impaired when compared with controls.

Bite force and occlusal contact area changes following mandibular widening using distraction osteogenesis

OBJECTIVE

To examine changes in bite force and occlusal contact area after mandibular widening by distraction osteogenesis using pressure-sensitive sheet (Dental-Prescale; Fuji Photo Film, Tokyo, Japan).

STUDY DESIGN

Fifteen patients with transverse mandibular deficiency (6 to 9 mm, mean distraction interval: 8 mm) were examined. They were measured just before the operation and at 1 week, 1 month, 3 months, 6 months, and 1 year after the operation. Ten control subjects with normal occlusion were also measured.

RESULTS

Both bite force and occlusal contact area were lowest at 1 month postoperatively. The values of bite force and occlusal contact area steadily increased thereafter. The bite force and occlusal contact area reached to the preoperative levels at 6 months after operation and slightly above the preoperative level at 12 months after operation. There were no statistically significant differences between 12 months and the control values for bite force measurements (P > .05).

CONCLUSION

Although statistically not significant, this study suggests that mandibular symphyseal distraction osteogenesis increases the bite force and occlusal contact area in patients with transverse mandibular deficiency.

Bite force determination in adolescents with and without temporomandibular dysfunction

The aims of this study were to compare bite force in adolescents with and without temporomandibular dysfunction (TMD), and to investigate the influence of gender, age, height and weight on bite force magnitude. The TMD was evaluated using a self-report questionnaire and the Craniomandibular Index, which has two subscales, the Dysfunction Index and the Palpation Index. Subjects with lower and upper extremity values were used to integrate the control (Group I -n = 20) and TMD (Group II -n = 20) groups, respectively. In addition, the TMD group should have at least one subjective symptom. Bite force was determined with a transducer, which consisted of a pressurized rubber tube connected to a sensor element (MPX 5700 - Motorola SPS, Austin, TX, USA). Analysis of covariance, Pearson's coefficient, Mann-Whitney and t-tests were applied to analyse the data. The results showed that Group II presented smaller values for bite force than Group I and boys had greater values than girls in Group II (P < 0.05). Bite force values were significantly smaller for girls between groups (P < 0.05), whereas for boys there was no statistical difference. Weak positive correlation between bite force and weight, height and age (P > 0.05) and significant negative correlation between bite force and Palpation and Craniomandibular Indexes (P < 0.05) were found. It was concluded that decreased bite force was correlated with TMD in girls, primarily with muscle tenderness.

The evaluation of jaw function subsequent to bilateral sagittal split osteotomy

OBJECTIVE

The objective of the present study was to evaluate the jaw function and anatomical changes subsequent to orthodontic treatment combined with mandibular advancement or set-back surgery.

STUDY DESIGN

The sample consisted of 67 combined skeletal and dental malocclusion patients, who had received orthodontic and surgical treatment previously. Three and 6 months following jaw surgery, the following jaw functions were evaluated: the level of occlusal force developed, the efficiency of masticatory function, the size in the temporomandibular joint (TMJ), the relationship between occlusal force and maxillo-mandibular skeletal change, and the range of mandibular movement.

RESULTS

The results revealed that after surgery the occlusal force, masticatory function, TMJ positioning, and mandibular movement distance were all different from presurgery values. The surgical set-back group jaw function recovery proved to be more rapid than that for the mandibular-advancement group.

CONCLUSION

Surgical mandibular advancement and set-back by sagittal-split osteotomy influence subsequent mandibular function.

Changes in the chewing path of patients in skeletal class III with and without asymmetry before and after orthognathic surgery

PURPOSE

The purpose of this study was to examine the relation between changes in the condylar long axis and the chewing path before and after mandibular ramus osteotomy for patients with prognathism with and without asymmetry.

PATIENTS AND METHODS

Eleven men and 16 women with mandibular prognathism were divided into groups on the basis of symmetry and osteotomy procedure. Preoperative and postoperative frontal chewing paths were recorded. The chewing path consisted of 4 components: deviated side range, undeviated side range, vertical range, and incisal path angle. The angle of the condylar long axis and the 4 components of the chewing path were compared between groups and the differences were analyzed statistically.

RESULTS

No significant differences in each of the 4 chewing path components were found between groups on the basis of symmetry or osteotomy procedure. A positive correlation was found between the changes in incisal path angle when chewing on the undeviated side and condylar long axis angle on the undeviated side (P < .05). A positive correlation was also found between the changes in undeviated side range when chewing on the deviated side and condylar long axis angle on the deviated side (P < .05).

CONCLUSION

This study suggests that surgically induced increase in the condylar long axis is correlated with increase in side range and incisor path angle, although surgical orthodontic treatment does not significantly change the chewing pattern.

Masticatory function in retrognathic patients, before and after mandibular advancement surgery

PURPOSE

Mandibular retrognathia is a dentofacial deformity that can be surgically corrected. The purpose of this study was to evaluate the influence of orthognathic surgery on masticatory function in a sample of retrognathic patients and to compare these findings with those of controls.

PATIENTS AND METHODS

Eleven retrognathic patients were tested before and 1 to 1.5 years after mandibular advancement surgery and compared with 12 controls. The median particle size after chewing a silicon rubber test food, the maximum bite force, and the electromyographic activity (EMG) of the anterior temporalis and the masseter muscles during isometric clenching and during chewing were determined. Patients, before and after treatment, and controls were statistically compared by analysis of variance.

RESULTS

Surgical correction of mandibular retrognathia did not change chewing efficiency, maximum bite force, EMG during maximal clenching, EMG during chewing, or the EMG/bite-force relationship. Compared with controls, the chewing efficiency, maximum bite force, EMG during maximal clenching, and EMG during chewing values were lower. No difference for the EMG/bite-force ratio at maximal clenching was found, indicating similar muscle efficiency for patients and controls. However, in the range of 10% to 40% of the maximum bite force, the slope of the EMG/bite-force regression line was steeper for the patients than for the controls, indicating decreased muscle efficiency for patients.

CONCLUSIONS

The results of this study suggest that in retrognathic patients, function of the masticatory system is impaired. Oral function was not influenced by mandibular advancement surgery.

Changes in bite force and dentoskeletal morphology in prognathic patients after orthognathic surgery

OBJECTIVE

We sought to evaluate the changes in bite force and dentoskeletal morphology in prognathic patients after orthognathic surgery.

STUDY DESIGN

Twenty-four patients underwent orthognathic surgery to correct Class III skeletal and dental malocclusions. Ten patients who underwent Le Fort I and bilateral sagittal split ramus osteotomy of the mandible (ie, surgical correction of 2 jaws) and 14 patients who underwent only bilateral sagittal split ramus osteotomy (ie, surgical correction of 1 jaw) were compared. Bite force was measured preoperatively and at 3, 6, and 12 months postoperatively. The dentoskeletal morphology was assessed through lateral cephalograms obtained preoperatively and 12 months postoperatively.

RESULTS

Twelve months postoperatively, the bite force was significantly greater in the patients who underwent surgery on 1 jaw than in the patients who underwent surgery on 2 jaws. Significant decreases in the gonial angle, occlusal plane angle, and anterior facial height were observed postoperatively in the patients with 1 surgically corrected jaw, but not in the patients with 2 surgically corrected jaws. Patients with 2 surgically corrected jaws experienced a greater increase in the Frankfort mandibular plane angle and a greater decrease in the posterior facial height than did those with 1 surgically corrected jaw.

CONCLUSION

The difference in the preoperative-to-postoperative change in dentoskeletal morphology between the 2 groups is one of the factors responsible for the significant difference in postoperative bite force between the 2 groups.

Changes in occlusal state of patients with mandibular prognathism after orthognathic surgery: a pilot study

This study examined the occlusal state of patients with mandibular prognathism and compared it with that of adults with normal occlusion (controls). It also examined changes in occlusal state after orthognathic operations in these patients. The values of occlusal contact area and bite force in patients before operation were significantly lower than in controls, and occlusal pressure in patients was higher than in controls. The occlusal contact area and bite force of the patients 1 month after the operation had decreased to below preoperative values. These values 12 months after the operation had increased by 2.0 and 1.8 times in women and 1.4 and 1.4 times in men, respectively, compared with preoperative values. However, absolute values remained extremely low compared with those of controls. In contrast to the above, occlusal pressure reached its maximum value 1 month after the operation and at 12 months it was close to the value for controls.

Changes in masticatory function after orthognathic treatment in patients with mandibular prognathism

Changes in masticatory function were measured in 27 patients in whom mandibular prognathism was corrected surgically. The mean value of masticatory efficiency before treatment was 46% of that of control subjects with normal occlusion. It improved, but remained at 60% of the control value postoperatively. Similar changes were seen in the number and area of occlusal contacts and the integrated muscle activities of the masseter and temporalis on the chewing side, but the postoperative improvement in masticatory efficiency was mainly the result of improvement in masseter activity. The mean values of masticatory cycle variables in the patient group did not differ significantly from those of the controls. Their preoperative mean coefficients of variation, which were significantly higher than those of the controls, decreased significantly postoperatively. These results suggest that the stability of masticatory rhythm was improved by orthognathic surgery.

The relationship between surgical changes in dentofacial morphology and changes in maximum bite force

PURPOSE

This study determined whether patients with greater surgical changes, and presumably greater normalization of their skeletal morphology, showed greater increases in their maximum voluntary bite forces after orthognathic surgery.

PATIENTS AND METHODS

A total of 104 adult patients (32 males and 72 females) treated with 1 of 8 different orthognathic surgical procedures were examined. Patients' presurgical and postsurgical morphologic and biomechanical measurements were taken from lateral cephalograms. Measurements known to be related to maximum bite force were used in the analysis. Patients' presurgical and postsurgical maximum bite forces were measured at 8 tooth positions (ie, right and left incisors, canines, premolars and molars).

RESULTS

Presurgical and postsurgical morphology and biomechanics variables were strongly correlated with each other, suggesting that orthognathic surgery produced relatively little change in patients' overall craniofacial form. Maximum voluntary bite forces were primarily correlated with variables relating to jaw size-both before and after surgery. No correlations were noted between the increases in maximum voluntary bite forces and surgically produced changes in skeletal morphology and the biomechanics variables.

CONCLUSIONS

Factors other than surgically produced changes in skeletal morphology are responsible for increases in maximum voluntary bite force after orthognathic surgery.

Changes in bite force and occlusal contact area after orthognathic surgery for correction of mandibular prognathism

OBJECTIVE

This study examined the long-term changes of bite force and occlusal contact area in patients with prognathous after orthognathic surgery with a newly developed pressure-sensitive sheet (Dental-Prescale; Fuji Photo Film Co).

STUDY DESIGN

Fifty-seven patients with prognathous were examined. Bite force and occlusal contact area were measured just before operation and at 2 weeks, 1 month, 3 months, 6 months, 1 year, 2 years, and 3 years after operation. Forty control subjects with normal occlusion were also measured.

RESULTS

The bite force and occlusal contact area of the patients were significantly greater than the preoperative level at 1 year, 2 years, and 3 years after operation. However, they were still significantly lower than the control subject level even at 3 years after operation.

CONCLUSIONS

This study suggests that orthognathic surgery improves the bite force and occlusal contact area of patients with prognathous. However, at 3 years from the time of operation, patients had not reached control subject levels.