A comparative study of smart lock hybrid arch bar with IMF (Intermaxillary fixation) screws in maxillomandibular fixation

Abstract

Background and Objective:

The “Universal Smart lock Hybrid IMF” system was designed to combine the mechanical strength and benefits of Erich arch bar (EAB) fixation with the speed and safety of intermaxillary fixation (IMF) screws. This study was done to compare the stability and efficacy of the “Smart lock Hybrid IMF System” with that of “IMF Screws” for the management of maxillomandibular trauma.

Materials and Methods:

This comparative prospective study involved 20 randomly selected patients, of which 10 patients had received IMF with Hybrid Arch bars (group A) and 10 patients had received IMF with IMF screws (group B) along with open reduction if required. The outcome variables were IMF stability, tooth root impingement, surgical time taken, soft tissue overgrowth, post-op pain, and postop occlusion. The groups were compared using independent test, chi-square test. The differences were considered significant at P < 0.05.

Results:

The mean percentage of screws loosened in group A was less than group B. The mean application time was significantly longer in group A than in group B. The number of roots impinged with Hybrid group having higher as compared to IMF screw group. The intergroup comparison of soft tissue overgrowth was higher in group B than in group A. The results of the chi-square test revealed non-significant difference in terms of occlusion between the two groups with a P value of 0.998.

Conclusion:

Hybrid arch bars are the best option in comparison with IMF screws on the basis of stability, soft tissue overgrowth and also it has versatility in application.

INTRODUCTION

Maxillomandibular fixation is a fundamental component in the management of facial trauma, reconstruction, maxillofacial surgery and orthognathic surgery.[1] It serves as a key factor for reduction and immobilization in maxillofacial reconstruction. Intermaxillary fixation (IMF) provides a steady framework by which normal facial appearance and function can be restored. Historically, the most widely applied technique for IMF is the use of “Erich arch bar” (EABs), although considered by many as the “gold standard” in the treatment of facial trauma.[1] Since World War I, arch bars have been the standard treatment for maxilla-mandibular bone injuries. To better fit the teeth and offer more stability, Blair and Ivy’s alteration was a flattening on one side that was roughly 2 mm in width.[2,3] Several techniques have been utilized for intermaxillary fixation, including Schuchardt’s arch-shaped splint consisting of metal and acrylic (Schuchardt and Metz, 1966), custom-made arch bars, Winter, German silver, Jelenko, and Krupps (Wipla pattern).[4] Baurmash et al.[3] 1988 applied direct bonding techniques more applicable to orthodontists and is achieved by modification of existing preformed metallic arch bar or application of specific polycarbonate splints (Wall 1986).

Currently, IMF screws are a popular substitute for IMF. Despite the fact that this approach has some advantages including speed, safety, and adaptability. Arthur and Berardo invented the self-tapping inter maxillary screws in 1989. They used 2 mm diameter self-tapping bone screws.[2] In 1999, Jones used capstan-head threaded titanium screws of 2 mm diameter and 10- or 16-mm length.[4] A high rate of screw loosening or displacement over time, which can affect the stability of maxillomandibular therapy, harm to the tooth roots, and soft tissue overgrowth on the screw heads, are some common problems associated with IMF screws.[5]

In order to combine the mechanical strength and advantages of EAB fixation with the speed and safety of IMF, the “Universal Smart Lock Hybrid IMF” system was created. Although this method provides some benefits such as the speed of placement, safety (from wire stick injury), versatility, and also reduces soft tissue overgrowth,[5] this technique can also be applied in some complicated cases where EABs and IMF screw cannot be placed like complete edentulous patients, partially edentulous patients, and malocclused patients (mandibular prognathism, maxillary prognathism, mandibular retrognathism).

This study will compare the safety and efficacy of the “SMARTLOCK HYBRID IMF SYSTEM” with that of “IMF SREWS” for the management of maxillomandibular trauma.

MATERIALS AND METHODS

This randomized prospective clinical study was conducted in the Department of Oral and Maxillofacial Surgery reporting with patients reporting with maxillomandibular trauma with the treatment indicative of closed reduction, initially between 2020 and 2022. This study involved 20 randomly selected patients, of which 10 patients had received IMF with hybrid arch bars (group A) and 10 patients had received IMF with IMF screws (group B) along with open reduction if required. The inclusion criteria were patients with a confirmed diagnosis of fracture with maxilla, mandible (favorable and unfavorable), with altered bite and fully/partially edentulous jaw. Medically compromised patients, younger than 18 years with pathological fracture, were excluded from this study. Ethical Clearance was obtained from DJ IEC (Institutional Ethical Committee) with Ref No: DJC/Ltr. /2023/285.

The parameters collected include surgical time, IMF stability, tooth root impingement, soft tissue overgrowth, postoperative occlusion, and pain assessment. IMF stability was evaluated clinically by loosening of screws with periodontal probe postoperatively 1^st week and 2^nd week. Tooth root impingement was checked by taking X-ray of that particular tooth region or OPG, and soft tissue overgrowth and postoperative occlusion was recorded by taking clinical photography.

Surgical procedure

When placing IMF screws, Measurement was taken using Orthopantomogram from cuspal tip or incisal edge to 2 mm distance above the apex of root. Bone was drilled using 2 mm drill bit between canine and premolar. Maxillomandibular fixation was achieved using 26-gauge stainless steel wire passing through these screws and patient was guided for occlusion and fixation was done in X or H cerclage pattern [Figure 1].

Figure 1.

a: Placement of mf screw and fixation with hexagon pattern, b: Soft tissue overgrowth on screw head on 1^st week follow up

While placing hybrid arch bar the arch bar fitted with eyelets is cut extending from first molar to first molar. The length of the arch bar is adjusted according to the individual situation. Arch bars were generally fixated using at least five, 2.0 mm diameter and 6 mm long self-tapping screws in the maxilla and five, 2.0 mm diameter and 8 mm long screws in the mandible at the junction of attached gingiva and alveolar mucosa. A hole is drilled into the bone through the gingiva at approximately 90 degrees to long axis of the adjacent teeth, taking care to pass the drill between the roots of the teeth without penetrating palatal or lingual mucosa. The number of screws placed was based on ensuring there were at least 5 screws on each jaw, upper jaw and lower jaw. In both groups 25-gauge surgical round stainless-steel wires were utilized to achieve IMF. The wire loop is placed over the maxillary and mandibular lugs of the arch bar and the wire loop is tightened [Figure 2]. IMF was maintained for approximately 4 weeks. Post-operative instructions were given. The patients were followed up clinically after 24 hrs, and then at weekly intervals for 6 weeks. They were followed up radio graphically with Orthopantomography [Figure 3].

Figure 2.

a: Soft tissue growth over screw head but healthy periodontal tissue b: OPG of the patient with proper position of the screws between the roots

Figure 3.

a: OPG of the patient in 4^th week follow up after removal of hybrid arch bar b: Gingival and periodontal tissue health after removal of hybrid arch bar at 4^th week

RESULT

Hospital database of 20 patients were prospectively reviewed and all the postoperative parameters are analysed. The stability (measured in terms if percentage of screws loosened) between the Hybrid and IMF screws were compared at 6^th week post operatively [Table 1 and Graph 1]. The mean percentage of screws loosened in Hybrid group was 6.66% and, in the IMF, group was 22.50%. The intergroup comparison of stability between the two groups was statistically significant (P = 0.020). The mean time taken for the surgery using the Hybrid screw system was 80.10 minutes with standard deviation of 40.23. The mean number of roots impinged in the Hybrid screw system were 0.50 with standard deviation of 0.70. The mean number of roots impinged in the IMF screw system was 0.00 with the Standard deviation of 0.00 [Graph 2]. The soft tissue overgrowth (measured in terms of percentage of screws involved) between the Hybrid and IMF screws were compared at 6^th week post operatively [Graph 3]. The mean percentage of screws involved in the Hybrid system were 30.00% and, in the IMF, system was 77.50% The intergroup comparison of soft tissue overgrowth between the two groups was statistically significant (P = 0.001) with higher tissue overgrowth in the IMF system as compared to Hybrid system. In the Hybrid arch system 100% of the subjects were having Angles Class I occlusion at the 6-week post-operative level whereas in the IMF screw system 90% of the subjects had Angles Class I occlusion. The difference between the two groups for the percentage of subjects with Class I occlusion was analysed using the Chi square test with P value less than 0.05 considered to be statistically significant. The results of the chi square test revealed non-significant difference in terms of occlusion between the two groups with P value of 0.998.

Table 1.

Comparison of the stability (measured in terms if percentage of screws loosened) between the Hybrid and IMF screws at 6^th week post operatively

	Mean no of screw involved	t	P-value	Significance
Hybrid	0.80±0.78	6.66±6.57	0.020	Significant
IMF	0.90±0.73	22.50±18.44

Graph 1.

Comparison of the stability (measured in terms if percentage of screws loosened) between the Hybrid and IMF screws at 6^th week post operatively

Graph 2.

The mean number of roots impinged in the Hybrid screw system and IMF screw system

Graph 3.

Comparison of soft tissue overgrowth (measured in terms of percentage of screws involved) between the Hybrid and IMF screws at 6^th week post operatively

DISCUSSION

The management of maxillofacial injuries one of the most demanding and rewarding aspect of surgery because the patients with maxillofacial injuries not only suffer from physical agony but slight disfigurement can become emotional distress for his whole life. The main goals in successfully treating maxillofacial trauma includes: Reduction of fracture, stabilization of fracture, and achievement of proper dental occlusion. For maxillomandibular fixation, numerous techniques have been reported, including the Ivy eyelet, suspension wires, and arch bars. Numerous studies have examined these procedures using various systematic approaches.

The first generation of IMF screws was to imply modified mono cortical self-tapping screws. Because these are requirement of drilling a hole for placement of IMF screws, there are chances of root damage that occurred during placement. So, in our study we have placed IMF screws by measuring the length of the root on Orthopantomogram (OPG), 2-3 mm above the apex of the root in between canine and premolar to avoid damage to the root. IMF screw is a quick and easy method. Furthermore, there are reports of a high rate of loosening or displacement of screws (29%) over time, which can compromise the stability of the IMF and the eventual healing of the fracture. Stryker Corporation, Kalamazoo, Michigan, created the Universal SMART Lock 1 hybrid IMF (HIMF) system to combine the mechanical strength and advantages of EAB fixation with the speed and safety of IMF screws.[5] In this prospective study, we evaluated the stability, pain perception, soft tissue overgrowth, root impingement, occlusion and surgical time taken between Conventional IMF and Hybrid System in 20 patients (10 in each group). On intergroup comparison of stability between the hybrid and IMF screws at 24 Hours post operatively showed no statistical significance between both the groups (P = 1.00) whereas Hybrid group proved to be significantly stable than IMF group at 1^st week as the mean percentage of screws loosened in Hybrid group was 5.83% and, in the IMF, group was 15.83%.). Nawaf Aslam-Pervez et al. (2020)[5] evaluated the stability of IMF and Hybrid screws and found that IMF group had the highest number of loosened screws (66.7%) these results were in accordance with the results of current study hence proving that Hybrid screw systems were more stable that the IMF system.

In a study conducted by Kendrick E et al. (2015)[6] radiographic analysis of tooth root damage showed that 7.5 percent of screws caused dentin injury, pulp injury, or root fracture. A majority of the screws (92.5 percent) either were completely in bone or encroached on the periodontal ligament but did not cause root damage. All screws placed were 6-mm screws, and it would be reasonable to think that placing 8-mm screws would increase the probability of root damage. The low incidence of clinically significant root damage supports the use of the SMART Lock system.[7] It appears the previous studies using maxillomandibular fixation screws showed high rates of root damage. By following these guidelines in the current study OPG was used for assessing the screw placement and 6 mm screws were preferred over 8 mm. the average number of roots impinging on the hybrid screw system was 0.50, with a standard deviation of 0.70, according to the results. The mean number of roots impinged in the IMF screw system was 0.00 with the Standard deviation of 0.00 The results of independent t test reveal significant difference between two groups (P = 0.038) in terms of mean number of roots impinged with Hybrid group having higher mean value as compared to IMF group.

Gingival overgrowth occurred more frequently surrounding the HIMF device compared to IMF screw fixation (n = 7 and 1, respectively) according to a study by Nawaf Aslam-Pervez et al. (2020).[5] The statistical significance of this was.004 (P = .004). He came to the conclusion that the HIMF device›s positioning and placement are crucial and do affect the chance of soft tissue overgrowth. Tissue overgrowth occurs when an implant is positioned in the non-attached mucosa beyond the mucogingival junction, either too superiorly in the maxilla or too inferiorly in the mandible. In order to prevent soft tissue compression while the screw is tightened and to keep space between the mucosa’s underside and the screw hole of the bar, the HIMF arch bar is attached using locking screws.[8] This reduces the likelihood of increased soft tissue irritation and overgrowth. As a result, the results for soft tissue are greatly influenced by placement position and technique.[3,9]

Surgical time taken for both group was almost same whereas IMF screw taken less time than hybrid group with P value of 0. 022 compared to the other techniques such as Erich arch bar, ivy loop it takes much less time.[10,11] Kumar P et al. (2018)[12] stated that the average duration of time to achieve IMF in group A (Erich arch bar) was 81 min, whereas it was 21.20 min in group B (hanger plate technique) and P value is 0.0001 which was found to be statistically significant.

CONCLUSION

Hybrid arch bars are best option for operator in comparison with IMF screws. IMF screws are quick to perform compared to Hybrid arch bar. Whereas on the basis of stability, soft tissue over growth hybrid arch bars have proved to be more reliable than IMF screw. On comparison of post-operative pain, occlusion and root impingement both the techniques proved to be relative good. Whereas surgical time take in hybrid arch bar is high than the IMF which is primarily due to increased numbers of screw (3 times more than IMF)

It also has the advantage of usage in partially edentulous patients, completely edentulous patients, periodontally compromised patients, in case of severe crowding (Orthodontic malocclusion) or patients with strong tooth contacts between the teeth. But it should be avoided in paediatric patients as its hinder the eruption of budding permanent teeth. Other disadvantages experienced during the course of surgery was difficulty in placing hybrid arch bar in displaced bilateral para symphysis fracture of mandible because of lingual displacement of inferior border of mandible. Apart from these disadvantages Hybrid arch bar proved to be excellent choice of IMF after cranio facial trauma.

Conflicts of interest

There are no conflicts of interest.

Funding Statement

Nil.