A comparative study of skeletal and dental stability between rigid and wire fixation for mandibular advancement

This study examined the skeletal and dental stability after mandibular advancement surgery with rigid or wire fixation for up to 2 years after the surgery. Subjects for this multisite, prospective, randomized, clinical trial were assigned to receive rigid (n = 64) or wire (n = 63) fixation. The rigid cases received three 2-mm bicortical position screws bilaterally and elastics; the wire fixation subjects received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Skeletal and dental changes were analyzed using the Johnston's analysis. Before surgery both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior advancement of the mandibular symphasis was 5.5 mm (SD, 3.2) in the rigid group and 5.6 mm (SD, 3.0) in the wire group. Two years after surgery, mandibular symphasis was unchanged in the rigid group, whereas the wire group had 26% of sagittal relapse. Dental compensation occurred to maintain the corrected occlusion, with the mandibular incisor moving forward in the wire group and posteriorly in the rigid group. However, at 2 years after surgery, when most subjects were without braces, the overjet and molar discrepancy had relapsed similarly in both groups.     

Skeletal stability after mandibular advancement with rigid versus wire fixation.

PURPOSE: This study examined the stability of skeletal changes after mandibular advancement surgery with rigid or wire fixation up to 2 years postoperatively. PATIENTS AND METHODS: Subjects for this multisite, prospective, clinical trial received rigid (n = 78) or wire (n = 49) fixation. The rigid cases were fixed with three 2-mm bicortical position screws and 1 to 2 weeks of skeletal maxillomandibular fixation with elastics, and the wire fixation subjects were fixed with inferior border wires and had 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric radiographs were obtained before orthodontics, immediately before surgery, and at 1 week, 8 weeks, 6 months, 1 year, and 2 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. RESULTS: Before surgery, both groups were balanced with respect to linear and angular measurements of craniofacial morphology. Mean anterior sagittal advancement of the mandibular symphysis was 4.92 +/3.01 mm in the rigid group and 5.11 +/- 3.09 mm in the wire group, and the inferior vertical displacement was 3.37 +/- 2.44 in the rigid group and 2.85 +/- 1.78 in the wire group. The vertical changes were similar in both groups. Two years postsurgery, the wire group had 30% sagittal relapse of the mandibular symphysis, whereas there was no change in the rigid group (P < .001). Both groups experienced changes in the orientation and configuration of the mandible. CONCLUSIONS: Rigid fixation is a more stable method than wire fixation for maintaining mandibular advancement after sagittal split ramus osteotomy.     

Rigid versus wire fixation for mandibular advancement: Skeletal and dental changes after 5 years

The bilateral sagittal split osteotomy (BSSO) is the most common surgical procedure for the correction of mandibular retrognathism. Commonly, the proximal and distal segments are fixated together with either wire or rigid screws or plates. The purpose of this study was to compare long-term (5 years) skeletal and dental changes between wire and rigid fixation after BSSO. In this multisite, prospective, randomized clinical trial, the rigid fixation group received three 2-mm bicortical position screws, and the wire fixation group received inferior border wires and 6 weeks of skeletal maxillomandibular fixation with 24-gauge wires. Cephalometric films were obtained 2 weeks before surgery and at 1 week, 8 weeks, 6 months, 1 year, 2 years, and 5 years after surgery. Linear cephalometric changes were referenced to a cranial base coordinate system. Before surgery, both groups were comparable with respect to linear and angular measurements of craniofacial morphology. Both groups underwent similar surgical changes. Skeletal and dental movements occurred in both groups throughout the study period. Five years after surgery, the wire group had 2.2 mm (42%) of sagittal skeletal relapse, while the rigid group remained unchanged from immediately postsurgery. Surprisingly, at 5 years, both groups had similar changes in overbite and overjet. This was attributed to dental changes in the maxillary and mandibular incisors. Although rigid fixation is more stable than wire fixation for maintaining the skeletal advancement after a BSSO, the incisor changes made the resultant occlusions of the 2 groups indistinguishable.     

Optimal placement of bicortical screws in sagittal split-ramus osteotomy of mandible

When a bicortical screw is used for the rigid fixation of sagittal split-ramus osteotomy, by definition the threads of the screw should engage in the buccal plates as well as in the lingual plates. In a study of six dry mandibles we found that when 2 and 2.7 mm screws are used in noncountersunk holes, it is almost certain that a thread will engage the buccal cortical plate. With countersinking 55% of the 2.7 mm and 27% of the 2.0 mm screws had no threads engaged in the buccal cortical plate. This changes these screws from bicortical to compression type. An anatomic study of bone thickness demonstrated that the thickest buccal and lingual cortical plates were in the superior border of the ramus, just distal to the last molar. In addition, a change in the intercondylar distance before and after surgery was observed in every mandible.     

Stability of osteosynthesis with bicortical screws placed in a triangular shape in mandibular sagittal split 5 mm advancement osteotomy: Biomechanical tests

Sagittal split ramus osteotomy (SSRO) is common in orthognathic surgery, and osteosynthesis with bicortical titanium screws placed in a triangular shape is used for stabilisation. We biomechanically tested the stability of this configuration in 5 mm advancement SSRO with condylar replacement in the initial position using six fresh frozen human mandibles raised subperiosteally for surgical simulation. Osteotomy was done after marking the initial positions of the condyles and the symphysis on graph paper. The condyle was set in its initial position and the symphysis advanced exactly 5 mm; this position was maintained during osteosynthesis using 2.7 mm bicortical screws placed in a triangular shape. The mandible was then placed horizontally on the testing machine and a continuous static force was applied perpendicularly at a displacement speed of 5 mm/min. A stainless steel plate was used to transmit the forces independently of the teeth.A mean force of 129.6 Newtons (N) was applied at the elastic/plastic limit on an effort/displacement curve, which is well beyond the maximal mean (SD) chewing forces of 21 N (14) measured after bilateral sagittal split ramus osteotomy (BSSRO). A linear equation relating force to displacement was worked out from this experiment.Osteosynthesis using three bicortical screws mounted triangularly after advancement SSRO of 5 mm is experimentally stable, and our results could be used experimentally to compare two osteosyntheses using the equation.     

A comparison of skeletal and dental changesbetween rigid and wire fixation for bilateral sagittal split osteotomy

For two years, this multisite prospective clinical trial examined longitudinalskeletal and dental changes after bilateral sagittal split osteotomy for mandibular advancement in which either rigid or wire fixation was used. Subjects in the rigid fixation group (n = 78) received 2-mm bicortical position screws, while the subjects in the wire fixation group (n = 49) received inferior border wires. Skeletal and dental changes were measured from cephalometric films taken immediately before surgery, one week after surgery, and at eight weeks, six months, one year, and two years after surgery. In both groups, the overbite and overjet increase with time, but were not different from each other. The B-point in the wire group progressively moved posteriorly, and at two years, it had relapsed 28%. In the rigid fixation group, there was a transient anterior movement of the B-point during the first six months and by two years after surgery, the B-point was unchanged from immediate post surgery. Dental changes occurred in both groups. These changes, however, were not able to accommodate the skeletal changes, resulting in similar increases in both overbite and overjet in both groups of patients. These results have implications for the orthodontists in management of the postmandibular advancement occlusion.     

In vitro strength analysis of sagittal split osteotomy fixation: noncompression monocortical plates versus bicortical position screws.

An in vitro study using bovine ribs was performed to compare the strength of monocortical plates with bicortical position screws. An osteotomy was created to simulate a sagittal split and a 5-mm bone gap was produced. Four study groups were created: screw nongap, screw with gap, plate nongap, and plate with gap. Parameters of strength were analyzed by elastic deformation, stiffness ratio, permanent deformation, and breaking load. The results showed that monocortical plate fixation in bovine ribs provides less rigidity and is more susceptible to deformation than is bicortical position screw fixation.     

Stability of the mandible following advancement: a comparison of three postsurgical fixation techniques

This study examines short-term stability of the mandible following mandibular advancement surgery by means of three standard techniques of postsurgical fixation. Twenty-two adult female rhesus monkeys (Macaca mulatta) underwent sagittal ramus advancement osteotomy of approximately 4 to 6 mm. Six animals had dental maxillomandibular fixation alone. Six animals had dental plus skeletal maxillomandibular fixation with circummandibular wires connected to pyriform aperture wires. Ten animals had rigid internal fixation with bicortical bone screws between the proximal and distal segments without maxillomandibular fixation. Radiographic cephalograms with the aid of tantalum bone markers and dental amalgams were analyzed during the first 6 postoperative weeks to evaluate skeletal and dental stability. Rigid internal fixation and the use of dental plus skeletal maxillomandibular fixation were both equally effective in the prevention of postsurgical relapse. However, in the animals in which only dental maxillomandibular fixation was used, statistically significant changes (relapse) occurred when compared with either of the other groups.     

下颌骨双侧升支矢状劈开双皮质螺钉内固定的生物力学分析

目的:对下颌骨升支矢状劈开不同方式双皮质固位螺钉内固定进行三维有限元分析,为临床提供理论指导。方法:建立下颌骨升支矢状劈开6种双皮质螺钉固定方式的三维有限元模型;计算不同固定方法在3种咬合情况下颌骨的应力、内固定系统的应力以及骨劈开处的位移,对比这些固定方式的固定效果以及不同咬合情况对固定稳定性的影响。结果:在相同咬合情况下,颌骨的应力、内固定系统的应力以及劈开处的位移的大小情况如下:单纯上缘固定大于倒"L"型固定;直径2.0mm大于直径2.7mm螺钉固定;倒"L"型60°大于倒"L"型90°和120°固定;间距2.0cm大于间距3.0cm固定。相同固定方式情况下,颌骨的应力、内固定系统的应力以及劈开处的位移从大到小排列顺序为:前牙咬合、前磨牙咬合、磨牙咬合。结论:双皮质固位螺钉内固定的排列方式,如:间距、角度、位置和内固定系统的规格均对固定稳定性有不同程度的影响;前牙咬合对固定的不良影响最大,应尽量避免。     

A comparative evaluation of osteosynthesis with lag screws, miniplates, or Kirschner wires for mandibular condylar process fractures.

PURPOSE: This study compared the clinical and radiologic outcomes of open treatment of mandibular condylar process fractures using lag screws, miniplates, or Kirschner wires. PATIENTS AND METHODS: Open reduction and internal fixation was performed for severely displaced or dislocated mandibular condylar process fractures in 23 patients (26 fractures) using Eckelt lag screws, in 10 patients (10 fractures) using Kirschner wires, and in 21 patients (22 fractures) using miniplates. Clinical and radiologic evaluations were made 6 months postoperatively and at final follow-up (mean, 18.4 months; range, 7 to 106 months). Radiologic evaluation included accuracy of reduction of the fractured condylar processes and changes in ramus height. RESULTS: Most fractured condylar processes (approximately 90%) were repositioned precisely in all groups. A shortening of the ramus of more than 5 mm was observed significantly more frequently (P <.05) in the miniplate group than in the lag screw group at 6 months. The condyles were severely resorbed in 2 or 3 patients in each group. All of these patients were associated with malunion, and partial bone resorption of the condyles was seen during the first 6 months. The relation between reduction or screw position and bone healing in patients treated with lag screws indicated that correct reduction and screw insertion allowed normal bone healing. The patients in all groups showed satisfactory clinical results. No significant intergroup differences were noted in maximum mouth opening and laterotrusion. However, deviation during mouth opening was significantly greater (P <.05) in cases treated with miniplates than with lag screws. CONCLUSION: Lag screw osteosynthesis may be more advantageous for restoration of ramus height than miniplates or Kirschner wires.     

A retrospective study of relapse in rigidly fixated sagittal split osteotomies: contributing factors

Fifty-one patients who underwent mandibular advancements with or without genioplasties were rigidly fixated with three, 2-mm bicortical screws per side. Radiographs were digitized preoperatively, immediately postoperatively, at 6 weeks, at 6 months, and at a subsequent long-term follow-up period. Location of the cephalometric landmarks, referenced to a vertical reference line (in millimeters), was used as the dependent variable. An overall inspection of the data shows that rigidly fixated mandibular advancements were very stable. The average case showed further advancement of pogonion from 6 weeks to the long-term follow-up period. However, relapse was noted in several cases. Factors that could be used as predictors of relapse were examined. Results indicated that magnitude of advancement was the only factor that successfully predicted relapse, accounting for 37.9% of the variance in the sample. Anatomic changes found to accompany such advancement are as follows: (1) when pogonion comes forward, anterior facial height and mandibular plane decrease while the proximal segment rotates forward, and (2) the maxillary central incisors flare and the mandibular incisors upright during this time period. A small degree of relapse as assessed at pogonion occurred during the first 6 weeks, followed by an advancement from 6 weeks to the longest time interval after the surgical procedure. However, these directional movements were not statistically significant.     

Immediate mechanical stability of sagittal split ramus osteotomy fixed with resorbable compared with titanium bicortical screws in mandibles of sheep

Ten fresh mandibles from adult sheep were stripped of all soft tissues and sectioned in the midline. We did sagittal split osteotomies and 5 mm advancement on all the 20 hemimandibles. Ten hemimandibles were fixed with three 2.0 mm x 13 mm titanium bicortical screws, and the other 10 were fixed with three 2.0 mm x 13 mm poly-l-lactic acid/polyglycolic acid (PLLA/PGA) bicortical screws in an inverted L pattern. All the hemimandibles were then mounted in a servohydraulic testing unit and tested to permanent deformation. Maximum forces that the mandibles resisted before breaking, maximum displacements, and the displacement values under 20, 60, 120, and 150 N were compared using the Mann-Whitney U-test. There were no significant differences in stability between the bones fixed with titanium and those fixed with resorbable screws.     

Comparative study of skeletal stability between bicortical resorbable and titanium screw fixation after sagittal split ramus osteotomy for mandibular prognathism

IntroductionResorbable screw fixation for orthognathic surgery is widely used in oral and maxillofacial surgery and has several advantages. However, surgeons are concerned about using resorbable screws in orthognathic surgery because of possible postoperative complications such as relapse, screw fracture, and infection. The purpose of this study was to evaluate the skeletal stability of bicortical resorbable screw fixation after sagittal split ramus osteotomies for mandibular prognathism.Materials and methodsThis study included 25 patients who underwent mandibular setback surgery fixed with resorbable screws after sagittal split osteotomy at the Department of Oral and Maxillofacial Surgery at Seoul National University Dental Hospital. Five resorbable screws (Inion CPS^®, Inion Ltd., Finland) were applied bicortically at each osteotomy site via a transbuccal approach. No rigid intermaxillary fixation was applied on the first postoperative day. Passive mouth opening exercises were allowed, using two light, rubber elastics for guidance. The control group was 25 patients fixed with four titanium screws. The follow-up period was 12–22 months (mean 17.8 months). Postoperative skeletal changes on lateral cephalometric radiographs were analyzed and compared between the two groups preoperatively, immediately postoperatively, and 6 months postoperatively.ResultsThe average setback was 6.9 mm and no major intraoperative complications occurred. One patient experienced infection immediately after surgery that was controlled uneventfully. The data did not demonstrate any significant difference in postoperative skeletal stability between the two groups. Differences between the immediate postoperative state and 6 months after surgery were not significant. In earlier cases, especially for patients with severe mandibular prognathism, immediate postoperative elastic traction was needed for stable occlusal guidance.ConclusionsThe results of this study indicate that bicortical resorbable screws offer a clinically stable outcome for the fixation of mandibular sagittal split osteotomies in mandibular prognathism. However the resorbable screws showed less stable results vertically than the titanium screws.     

The stability of facial osteotomies. 2. Mandibular advancement with bicortical screw fixation

Surgical repositioning of the dento-skeletal components of the lower third of face, combined with appropriate orthodontic treatment, can be used to improve function and aesthetics. However, the attainment of three-dimensional stability following corrective jaw surgery continues to be a major problem in the post-surgical period.
This paper examines the short-term (6 week postoperative) and long-term (12 months postoperative) horizontal skeletal stability of bilateral sagittal split mandibular advancement in 15 patients. The mean horizontal advancement of the mandible was 6.1 mm. Six weeks later, a mean continued forward movement of 0.16 mm was identified. The mean relapse at long-term follow-up was 0.46 mm (7.5%). Results indicate that rigid bicortical screw fixation of bilateral sagittal split osteotomies undertaken to correct horizontal lower dentofacial deficiency is both statistically and surgically predictable and stable when reviewed up to twelve months after surgery.     

In vitro comparison of fixation methods used in sagittal split osteotomy with a major advancement and counterclockwise rotation

The aim of this study was to compare the mechanical characteristics of five commonly used fixation methods for sagittal split osteotomy with a major advancement and counterclockwise rotation with a model that mimics the human mandible. Twenty-five virtually osteotomised and 3-dimensionally printed hemimandibles were fixed with an 8mm gap at the upper border and a 12mm gap at the lower border of the osteotomy. The following fixation methods were used: Group 1: a single miniplate, group 2: two miniplates, group 3: three bicortical screws in the upper border, group 4: three bicortical screws in an inverted L configuration, group 5: a single miniplate and a bicortical screw. A mechanical test using vertical linear loading at 1 mm/min velocity on a universal testing machine was carried out. The forces needed to displace the distal segment from 1-5 mm were recorded. The difference between groups was statistically significant for all displacement levels. Group 1 showed the minimum, group 5 showed the maximum resistance in almost all displacement values and there was a trend for higher to lower resistance values towards groups 5 to 1. Fixation methods that used one bicortical screw and a miniplate or three bicortical screws showed higher load resistance against displacement.     

Mandibular,sagittal split osteotomies fixed with biodegradable or titanium screws: a prospective,comparative study of postoperative stability

OBJECTIVE: Comparison of skeletal stability following bilateral sagittal split osteotomy (BSSO) advancement of the mandible fixed with titanium or biodegradable bicortical screws. STUDY DESIGN: Forty consecutive patients underwent mandibular advancement by means of BSSO performed with a standardized technique. In 20 patients rigid fixation was achieved by means of titanium bicortical screws; the other 20 patients were fixed with biodegradable copolymer screws made of poly-L-lactic acid (82%) and polyglycolic acid (18%). Lateral cephalograms were obtained 1 week preoperatively, 1 week postoperatively and after a minimum of 6 months postoperatively. Relevant skeletal points were traced and digitized to evaluate 2-dimensional skeletal change. Changes at each time point were analyzed and compared statistically. RESULTS: There was no statistically significant difference in long-term stability between the 2 groups. No clinical or radiographic evidence of wound healing problems were noted. CONCLUSION: Resorbable poly-L-lactic/polyglycolic acid copolymer bicortical screw fixation of a BSSO is a viable alternative to titanium screws for the fixation of advancement BSSO.     

Biodegradable self-reinforced poly-L/DL-lactide plates and screws in bimaxillary orthognathic surgery: short term skeletal stability and material related failures

Biodegradable self-reinforced poly-L/DL-lactide plates and screws were used for osteosynthesis in 10 consecutive cases of bimaxillary procedures with simultaneous genioplasties, without postoperative rigid intermaxillary fixation. During surgery, data were gathered concerning failure of the osteosynthesis material. Clinical examination was carried out weekly until the sixth postoperative week. Cephalometric analysis of standardized cephalograms was performed to evaluate the short-term skeletal stability pattern, which was compared with similar reports in the literature. Six weeks postoperatively, all jaws were clinically stable and there was no clinical evidence of foreign body reactions. For the whole group (n = 10), the mean maxillary advancement at point A was 2.9 mm with a mean postoperative relapse of 0.0 mm. The mean advancement at point B was 2.8 mm with a mean additional advancement postoperatively of 1.1 mm. The mean vertical surgical displacement at point A was directed inferiorly with a value of 1.8 mm and a relapse of -0.4 mm. At point B the corresponding values were 1.9 mm and -0.4 mm. In the Angle Class III group (n = 4), the mean advancement at A was 5.9 mm with an additional postoperative advancement of 0.3 mm. In the Angle Class II group (n = 6), mean advancement at point B was 4.0 mm, with an additional postoperative advancement of 1.1 mm. In the group with short face deformity (n = 3), the mean inferior movement in ANS was 6.6 mm with a relapse of -0.2 mm. At menton the vertical surgical movement was 13.0 mm with a relapse of -0.2 mm. None of the plates, which were bent at room temperature, broke. The screw heads broke or had an insufficient fit in the bone in 12 of 305 (3.9%) screws. It can be concluded that the tested system of biodegradable self-reinforced poly-L/DL-lactide screws and plates has a small material-related failure rate, and that their application in orthognathic surgery leads to a predictable short-term skeletal stability pattern which is comparable to the 'gold standard' of titanium plates and screws.     

Five-year outcome and predictability of soft tissue profiles when wire or rigid fixation is used in mandibular advancement surgery.

The purpose of this study was to follow the covariation of hard and soft tissue changes in Class II malocclusion subjects who received a bilateral sagittal split osteotomy. The subjects were randomized to receive wire or rigid fixation after the surgery. Subjects in the rigid group (n = 78) received 2-mm bicortical position screws, and those in the wire group (n = 49) received inferior border wires and 6 weeks of skeletal intermaxillary fixation with 24-gauge wires. Additionally, some subjects received genioplasty in both the rigid (n = 35) and the wire groups (n = 24). Soft and hard tissue profile changes were obtained from cephalometric films immediately before surgery and at various times up to 5 years postsurgery. Soft and hard tissue profile changes were referenced to a cranial-base X-Y coordinate system. Horizontal changes in mandibular incisor, lower lip, B-point, soft tissue B-point, pogonion, and soft tissue pogonion were calculated at each time. There was considerable skeletal relapse in the wire fixation group. Bivariate correlations and ratios between the hard and soft tissue changes were calculated for each time period. Hard to soft tissue correlations were the highest at the earlier times, although the ratios varied among the 4 groups. These results provide a solid basis for both short-term and long-term prediction.     

Stability of skeletal Class III malocclusion after combined maxillary and mandibular procedures: titanium versus resorbable plates and screws for maxillary fixation.

PURPOSE: The aim of this study was to evaluate skeletal stability after double jaw surgery for correction of skeletal Class III malocclusion to assess if there were any differences between resorbable plate and screws and titanium rigid fixation of the maxilla. PATIENTS AND METHODS: Twenty-two Class III patients had bilateral sagittal split osteotomy for mandibular setback stabilized with rigid internal fixation. Low level Le Fort I osteotomy for maxillary advancement was stabilized with conventional titanium plate and screws in 12 patients (group 1) and with resorbable plate and screws in 10 patients (group 2). Lateral cephalograms were taken before surgery, immediately postoperatively, 8 weeks after surgery, and 1 year postoperatively. RESULTS: Before surgery both groups were balanced with respect to linear and angular measurements of craniofacial morphology. One year after surgery, maxillary stability was excellent in both groups. In group 1 no significant correlations were found between maxillary advancement and relapse. In group 2, significant correlations were found between maxillary advancement and relapse at A point and posterior nasal spine. No significant differences in postoperative skeletal and dental stability between groups were observed. CONCLUSION: Surgical correction of Class III malocclusion after combined maxillary and mandibular procedures appears to be a fairly stable procedure for maxillary advancements up to 5 mm independently from the type of fixation used to stabilize the maxilla. Resorbable devices should be used with caution for bony movements of greater magnitude until their usefulness is evaluated in studies with large maxillary advancements.     

A comparison of the stability of miniplate with bicortical screw fixation after sagittal split setback

OBJECTIVE: The objective of this study was to decide whether use of bicortical screw fixation provides sufficient stability to dispense with intermaxillary fixation.Study Design: Thirty consecutive patients who had undergone surgical setback of the mandible by means of bilateral sagittal split ramus osteotomies were studied. Group 1 (15 patients) had miniplate fixation with intermaxillary fixation for 6 weeks, and group 2 (15 patients) had bicortical screw fixation and immediate postoperative function. The 2 groups were evaluated radiographically for postsurgical changes of pogonion in the early (6 weeks) phase. RESULTS: The results showed that there were no significant differences between the 2 groups. Overall, there was good stability in both groups. CONCLUSION: The use of bicortical screw fixation after sagittal split setback of the mandible provides sufficient stability to dispense with intermaxillary fixation.