Article, Dentistry

Dental fracture risk of metal vs plastic laryngoscope blades in dental models

Dental fracture risk of metal vs plastic Laryngoscope blades in dental modelsB

Erick M. Itoman, Eric H. Kajioka, Loren G. Yamamoto MD, MPH, MBA*

Department of Pediatrics, University of Hawaii John A. Burns School of Medicine

Emergency Department, Kapiolani Medical Center For Women and Children, Honolulu, HI 96826, USA

Received 29 March 2004; accepted 29 March 2004

Abstract

Background: Dental fracture is a complication of laryngoscopy and endotracheal intubation. Purpose: The purpose of this study is to compare the potential fracture rates in dental models using metal laryngoscope blades with those using plastic laryngoscope blades.

Methods: Size 3 Macintosh plastic and metal laryngoscope blades were applied against 4 different dental model materials at varying torques to determine when the dental model material would fracture. Results: The plastic blade did not fracture any of the dental model materials. The metal blade fractured the glass dental model material even at the lowest torque setting. At a moderate torque setting, the plastic blade showed evidence of structural failure, whereas the metal blade did not fail at any torque setting. Fracture of wooden dowel and ceramic teeth model materials occurred with the metal blade but only at torque settings higher than what the plastic blade could achieve.

Conclusion: Based on the dental fracture models studied, plastic laryngoscope blades have a lower potential for dental fracture compared with metal blades. Plastic laryngoscope blades would be best suited for trainees performing routine intubations under direct supervision. Metal blades would be more advantageous in difficult intubations preferably done by Experienced intubators.

D 2005

Introduction

Dental fracture is a common complication of tracheal intubation [1]. In a study of 366 patients by McGovern et al [1], dental fracture was the most common complication. A

B The Chun Foundation, Honolulu, HI, provided financial support to purchase materials used in this study.

* Corresponding author. Tel.: +1 808 983 8387; fax: +1 808 945 1570.

E-mail address: [email protected] (L.G. Yamamoto).

retrospective study of 598904 consecutive patients requir- ing anesthesia over an 11-year period found the dental injury rate to be as high as 1 in 4 patients [2]. These injuries not only have a direct comfort and cosmetic effect but may also increase the risk of aspiration. Repair of dental injuries is significant and can amount to US$782 per incident [2]. Despite their availability, plastic laryngoscope blades are not routinely used in residency programs for intubations by physicians in training.

Although plastic blades may reduce the risk of dental fractures, no study has compared plastic laryngoscope

0735-6757/$ – see front matter D 2005 doi:10.1016/j.ajem.2004.03.007

Laryngoscope blades 187

blades with metal blades. The purpose of this study is to compare the potential fracture rates in dental models using metal laryngoscope blades and those using plastic laryngo- scope blades.

Methods

A standard #3 Macintosh stainless steel laryngoscope blade was attached to a standard laryngoscope handle. Plastic #3 curved Macintosh laryngoscope blades were obtained in 3 variants and from 3 sources: (1) Rusch Lite blade kit (Rusch, Duluth, Ga, purchased from Moore Medical, New Britain, Conn), (2) PMX Medical disposable laryngoscope blades (PMX Medical, Salt Lake City, Utah), and (3) Vital View laryngoscope blades (Vital Signs Inc, Totowa, NJ).

Fig. 1 describes the study model. Various dental model materials were placed in a vise and oriented 4 cm from the base of the blade. The dental model materials were oriented perpendicular and tangent to the side adjacent the palate- facing surface of the laryngoscope blade (at the bfulcrumQ position). The tip of the laryngoscope blade was held in a fixed position. A preset torque was set on a torque wrench (Mac Tools TWX80, Columbus, Ohio) at 5, 10, 15, 20, 25, and 30 ft-lb (1 ft-lb = 1.355 Nm). A rotational force was applied to the handle of the laryngoscope apparatus via a torque wrench. Rotation was ceased if (1) the preset torque was met, (2) the dental model was compromised, or (3) the laryngoscope blade was compromised. Compromise of the dental model was defined as any visible/audible break, chip, or crack in the dental model. Compromise of the laryngo- scope blade was defined as any visible/audible break, crack, chip, or deformation of the blade.

Various dental model materials were placed in the vise holding the bdental model.Q These included ceramic teeth (A20A-200 ceramic composite crown with epoxy dentin upper anterior incisors, Kilgore International, Coldwater, Mich), a 3.2 mm diameter by 2.5 cm long hardwood dowel, a 2.5 x 0.32 cm ceramic tile (#D31411MFIP, Daltile Corp, Dallas, Tex), and a 1.3 x 1.3 x 0.16 cm glass piece (#1613- 49, Darice Inc, Strongville, Ohio). The ceramic tile and the glass dental models were oriented in a vise so that their planes were perpendicular to the plane of the laryngoscope blades. The ceramic tile protruded 1.2 cm above the vise with the remaining 1.3 cm within the vise. The glass piece protruded 0.6 cm above the vise with the remaining 0.7 cm within the vise. The ceramic tooth was held in an approximate anatomic position. The base of the tooth was

1.3 cm within the vise and protruded 1.2 cm in above the vise. The 3.2 mm wooden dowel was 1.4 cm within the vise and protruded 1.2 cm outside the vise.

Five trials with each dental model material type with both laryngoscope blade types were run at multiple torque wrench settings. The torque wrench was initially set at a torque of 5 ft-lb (6.8 Nm). The torque was increased by an interval of 5 ft-lb until a maximum of 40 ft-lb was achieved. The respective preset torque intervals at which either the blades or the dental models were compromised were recorded and compared.

Results

The results are summarized in Table 1. Plastic laryngo- scope blades failed to fracture any of the dental model materials in all torque ranges. The plastic blade integrity was compromised at the 11 to 15 ft-lb range. Thus, higher torque

Fig. 1 Setup of a laryngoscope blade with handle, dental model material, and vise.

188 E.M. Itoman et al.

Table 1 Dental model fracture results with increasing torque

Model material

Torque range (in ft-lb)

0-5

6-10

11-15

16-20

21-25

26-30

31-35

36-40

Wooden dowel

Metal blades

0

0

20

80

100

100

100

100

Plastic blades

0

0

n/a

n/a

n/a

n/a

n/a

n/a

Ceramic tile

Metal blades

0

0

0

0

0

0

0

0

Plastic blades

0

0

n/a

n/a

n/a

n/a

n/a

n/a

Glass

Metal blades

Plastic blades

100a

0a

100a

0a

100

n/a

100

n/a

100

n/a

100

n/a

100

n/a

100

n/a

Ceramic teeth

Metal blades

0

0

0

100

100

100

100

100

Plastic blades

0

0

n/a

n/a

n/a

n/a

n/a

n/a

Percent of 5 trials in which model material compromise was sustained. n/a indicates that the plastic laryngoscope blade was compromised before any dental model material was compromised.

a Represents statistical significance where dental models in the plastic blade trial broke whereas models in the metal blade trial did not break at given torque

intervals, P b .05.

ranges could not be attempted. This essentially functions as a bstop level,Q such that the application of forces above this level is not possible (similar to a bpop-off valveQ during handbag ventilation).

The metal blade fractured all the glass model materials even at the lowest torque range compared with no fractures with the plastic blade ( P b .05). The metal blade began to fracture the wooden dowel at the 11 to 15 ft-lb range, and by the 21 to 25 ft-lb range, 100% were fractured. The metal blade fractured all the ceramic teeth at the 16 to 20 ft-lb range. None of the metal Macintosh blades experienced structural compromise.

In earlier preliminary trials with straight blades, a metal #2 straight blade experienced structural compromise at a high torque level with the ceramic tile. The blade was too expensive to be repeatedly replaced, so the study was carried out using only curved Macintosh blades. Similarly, the plastic straight blades that were used for the straight blade comparisons would bend at lower torques compared with the curved plastic blades. Metal laryngoscope blades did not suffer any damage at any torque interval.

Discussion

There are no present studies that compare Dental injury outcomes of metal vs plastic laryngoscope blades used in intubation. This study demonstrates that plastic laryngoscope blades consistently break at a torque interval of 11 to 15 ft-lb whereas metal blades do not, regardless of the dental model used (ie, ceramic tile, wood, glass, ceramic teeth) ( P b .05). The glass model suggests that the plastic blade has a lower risk of dental fracture because the metal blade fractured the glass in all the trials even at the lowest torque setting whereas the plastic blade was not able to fracture the

glass even at a higher torque setting.

In addition, the maximum torque that the plastic blade can apply is limited by its own structural composition. Because the metal blade is much stronger, the maximum torque of the metal blade is essentially unlimited within the range of normal human strength.

The torque required for normal intubation ranges between

2.7 and 10.8 ft-lb (2-8 Nm) [3]. The plastic blade is strong enough to achieve this torque through most of this torque range, but at the upper limit of this range, the plastic blade integrity might be compromised. It is difficult to be certain of this because the concept of btorqueQ in this study might not be exactly identical to the torque measurements obtained in our study.

The validity of these dental fracture models has not been proven. Different model materials were used to simulate a variety and range of dental strength characteristics that might be encountered. Human dentition strength is variable, ranging from weak to very strong. Using extracted human teeth would have introduced structural strength variation between the different trials. It would have been potentially misleading to use a small number of teeth of variable structural strength. Such bvarianceQ within the sample itself could only be overcome to reveal the true difference only if a large number of human teeth were to be used (not easily obtained and not feasible). Thus, the only practical and ethical alternative to study this problem is to use models of different types that have some structural resemblance to human teeth.

During the process of endotracheal intubation, laryngos- copy places the distal end of the laryngoscope blade in the vallecula. Although the term btorqueQ is used in our study and by others, there should ideally be no torque applied to the teeth. Using the teeth as a fulcrum is a common mechanism of dental fracture. The laryngoscope blade has a distal side opposite the laryngoscope blade (facing the

Laryngoscope blades 189

palate), which has the potential of fulcrum against the upper teeth, and has a proximal side closer to the laryngoscope handle (facing the tongue), which has the potential (but less likely) to fulcrum against the lower teeth. Our model only tested the dental fracture risk associated with the distal side (palate side) of the laryngoscope blade, where it potentially impacts on the upper teeth.

Although experienced emergency physicians are com- fortable with most intubations using the standard metal blades, many emergency physicians must also supervise endotracheal intubation done by physicians in training. The difficulties of supervising this procedure include the critical nature of a patient’s condition and the inability to see what the intubator sees. At an angle, the supervising attending physician cannot see the vocal cords. In addition, if a trainee decides to descend the laryngoscope blade against a patient’s upper teeth and torque the blade, this could happen too fast for the supervising attending physician to prevent.

Our study suggests that plastic laryngoscope blades have a lower dental fracture potential. This would be very useful in the supervision of endotracheal intubation by less- experienced trainees. If a trainee were to torque the blade against a patient’s teeth as a fulcrum, it would be less likely to cause a dental fracture. This would give the supervising physician the opportunity to correct the trainee’s technique without letting the patient sustain any dental fracture. This would permit the supervising physician to focus more attention on securing the airway.

During these trials, the plastic blades were noted to have an audible click, without gross permanent deformation of the blade. The audible click could serve as a warning for a trainee intubator. Thus, a trainee using the plastic blade could potentially hear an audible click as a warning that a high torque has been applied and that the blade has sustained a crack somewhere within it. The blade could

potentially break, resulting in an intraoral injury. Thus, the blade should be removed as soon as any sign (audible, visual, or by feel) that the structural limit of the plastic blade has been reached is obtained.

Difficult intubations require more force applied to the laryngoscope blade [3], in which case, a plastic laryngoscope blade might not be strong enough. Although our study was not designed to demonstrate the maximum torque required for a difficult intubation, our study did demonstrate that metal laryngoscope blades are stronger than plastic blades. Thus, it makes sense to use a metal blade for a potentially difficult intubation. For such difficult intubations, it would be best to have the intubation performed by the most skilled intubator in the room. It would be unwise for a junior-level trainee to attempt such an intubation until a greater Experience level is achieved with routine intubations. Thus, plastic laryngoscope blades are more suitable for trainees performing routine intubations under direct supervision.

In summary, based on the dental fracture models studied, plastic laryngoscope blades have a lower potential for dental fracture compared with metal blades. Plastic laryngoscope blades would be best suited for trainees performing routine intubations under direct supervision. Metal blades would be more advantageous in difficult intubations preferably done by experienced intubators.

References

  1. McGovern FH, Fitz-Hugh GS, Edzeman LJ. The hazards of endotra- cheal intubation. Ann Otol Rhinol Laryngol 1971;80:556.
  2. Warner ME, Benenfeld SM, Warner MA, et al. Perianesthetic dental injuries: frequency, outcomes, and risk factors. Anesthesiology 1999;90(5):1302 – 5.
  3. Hastings RH, Hon ED, Nghiem C, et al. Force, torque, and stress relaxation with direct laryngoscopy. Anesth Analg 1996;82:456 – 61.