Effectiveness of dental guards in reducing incisor injuries during direct laryngoscopy: A retrospective comparative clinical study

Abstract

Objective

To evaluate the effectiveness of dental guards in preventing incisor injuries during direct laryngoscopy in microlaryngeal surgery (MLS).

Study design

Nonrandomized retrospective comparative study.

Methods

Between 2022 and 2024, 50 patients who underwent elective MLS using a dental guard were consecutively selected as the dental guard group, and another 50 patients who underwent surgery without a dental guard were selected as the control group. A standardized silicone dental guard was applied to the maxillary incisors of the experimental group. An independent dentist conducted postoperative dental evaluations to assess incisor mobility and enamel damage.

Results

The experimental group demonstrated significantly lower rates of dental injury (2% vs. 20%) compared with those of the control group. No adverse events related to dental guard use were reported.

Conclusion

Dental guards effectively reduced the incidence of incisor injuries during direct laryngoscopy. Routine use is recommended to minimize perioperative dental complications.

Introduction

Direct laryngoscopy during microlaryngeal surgery (MLS) is essential for laryngeal visualization but poses a significant risk of traumatic injury to the maxillary incisors, which are the most vulnerable dental structures during instrumentation. Studies have reported an incidence of dental injury ranging from 0.02% to 12.1%, depending on the procedural context,^1–3 with incisor loosening, enamel fractures, and prosthetic damage being the most common complications.^4–6

These injuries arise from the mechanical forces exerted by the laryngoscope during vocal cord manipulation, particularly in procedures requiring prolonged suspension or aggressive tissue retraction. Patient-specific risk factors that increase this risk include poor dentition (such as periodontitis, caries, or prior root canal therapy), the presence of ceramic prostheses or implants, and anatomical challenges, such as limited mouth opening or micrognathia. ⁶ Additionally, operator-dependent variables, such as laryngoscope design (including sharp-edged Macintosh blades), inadequate dental protection, and prolonged suspension time, further exacerbate trauma. ⁷ Despite advancements in surgical techniques, debates persist regarding the efficacy of preventive measures, such as dental guards, with some studies highlighting their protective role in force distribution, ⁸ whereas others cite concerns about airway obstruction or inconsistent utilization. This underscores the need for standardized protocols to mitigate preventable morbidity and the medicolegal consequences associated with perioperative dental trauma.

In this study, we investigated whether dental guards reduce incisor injuries during direct laryngoscopy. We hypothesized that patients using dental guards would experience fewer postoperative dental complications than those without protection.

Patients and method

Participants and study design

Data for the dental guard group were collected consecutively from 50 patients at the Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University who underwent MLS and agreed to use dental guards during surgery between January 2022 and December 2024 (see Supplemental material). In the dental guard group, a preformed silicone dental guard (Under Armour^®, R-1-1105-A) was placed over the maxillary incisors before laryngoscopy. The dental guard is reusable and one-size-fits-all, covering the teeth from the left maxillary first premolar to the right maxillary first premolar (Figure 1). The thickness was 1 mm. Before use, the guard was softened in water heated to 70°C, then cooled at room temperature for 30 s to allow adjustment to the patient's mouth shape.

To evaluate the effectiveness of the dental guard, 50 patients who underwent MLS during the same period at the same hospital without a dental guard but with simple gauze covering the incisors were selected as the control group.

Before surgery, a dentist performed a simplified physical examination of each patient's teeth and obtained a relevant dental history. Periodontitis was evaluated on the basis of a previous consensus report, and patients diagnosed with stage 1 or 2 periodontitis were classified as having periodontitis. ⁹ The baseline characteristics of each group are presented in Table 1.

Table 1.

Groups’ basic information.

Group	Gender (male: female)	Periodontal disease ratio	Smoking history ratio	Age
Exp	56%	14%	10%	48.69 + 11.75
Control	60%	10%	34%	41.25 + 9.27

Each surgical procedure was performed by one experienced ENT surgeon, and the duration of surgery for both the dental guard and control groups was less than 30 min. No issues related to airway obstruction or operative accessibility were encountered in any of the 100 patients.

The Medical Ethics Committee of the Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University approved this study (Approval Number: 2023-K-102-01, https://www.wzhealth.com/news/1053-1.html, 12 June 2023), and written informed consent was obtained from all participants. Inclusion criteria were age ≥ 18 years, elective MLS, and intact maxillary incisors. Exclusion criteria were preexisting dental trauma, esthetic prostheses, implants, edentulous status, stage > 2 periodontitis, or refusal to participate. All procedures were conducted in accordance with the 1975 Declaration of Helsinki (2024 revision). The reporting of this study conforms to the STROBE guidelines. ¹⁰ All 100 patients completed the follow-up.

Outcome measures

The primary outcomes were postoperative incisor loosening (graded using the Miller mobility index) and enamel fractures. A blinded dentist evaluated the patients 24 h after surgery using clinical examinations and periapical radiographs. The Andreasen classification, focusing on dental hard tissue, periodontal tissue, and mucosal tissue, was used to evaluate dental injury. The details are provided in a previous work. ¹¹

Statistical analysis

Data were analyzed using SPSS software (IBM SPSS Statistics 26, IBM, USA) with binary logistic regression models to identify the risk factors associated with postoperative dental complications. Dichotomous complications (zero = no, one = yes) were set as dependent variables, and group assignment (binary), age (continuous), and periodontitis status (binary) were set as predictors. To improve the performance of the logistic regression model, smoking status and sex were excluded from the analysis.

Continuous variables were assessed for linearity of the log odds using restricted cubic splines.

The full model was specified as follows: logit[P(complication)] = β₀ + β₁(group) + β₂(age) + β₃(periodontitis).

The discriminatory ability of the model was evaluated using the area under the receiver operating characteristic curve.

Odds ratios (ORs) with 95% confidence intervals were reported for all predictors. Statistical significance was set at p ≤ 0.05.

Results

Overall, the incidence of dental injury was greatly reduced in the dental guard group (one patient [2%] in the experimental group experienced dental injury compared with 10 patients [20%] in the control group; t-test, p < 0.05).

Applying Andreasen's classification to evaluate dental injury (World Health Organization Andreasen classification, 1994, based on anatomic, therapeutic, and prognostic considerations), there was one patient in the intervention group and five in the control group with enamel infarction. In the control group, three additional patients reported contusion of the gingiva or oral mucosa, and two were diagnosed with periodontal tissue concussion, having reported vibration of the incisor.

Logistic regression analysis included 100 patients, with complications modeled as a function of group assignment, age, and periodontitis status. The model demonstrated excellent discriminative ability, with an area under the curve of 0.812 (Figure 2, receiver operating characteristic curve) and explained approximately 51.2% of the variance in complications (pseudo-R² = 0.512). The likelihood ratio test confirmed the overall significance of the model (LLR p = 0.0015).

Figure 1.

Application of dental guard during surgery.

Figure 2.

ROC curve of logistic regression model.

The strong association between group assignment and complications (OR = 19.29; Table 2) highlighted the critical risk disparity between the cohorts. Patients in the control group had 19.29 times higher odds of complications than those in the intervention group (OR = 19.29; 95% confidence interval, 1.83–203.61; p = 0.014). A history of periodontitis was significantly and positively associated with the risk of complications, which should not be overlooked. This finding likely reflects the increased vulnerability of patients with a history of periodontitis to postoperative complications caused by tooth root instability. Although age did not reach statistical significance, its effect size suggests clinical relevance, warranting validation in larger studies.

Table 2.

Generalized linear model with logistic regression for variables associated with dental injury.

Variables	Odds ratio	95% coefficient CI	P-value
Group	19.29	1.83–203.61	0.014
Age	1.07	0.96–1.18	0.206
Periodontitis	12.58	1.90–83.08	0.009

The wide 95% confidence intervals for group (1.83–203.61) and periodontitis (1.90–83.08) indicate imprecision in effect estimates, likely because of the small sample size (n = 100) and low incidence of dental injury. Sensitivity analyses addressing missing data have not yet been conducted. No adverse events related to the trial were reported.

Discussion

Dental injury remains a critical yet often underappreciated complication of otolaryngologic procedures, particularly during MLS, where prolonged laryngeal manipulation and endotracheal intubation impose mechanical stress on the dentition. Iatrogenic dental trauma, including enamel fractures, tooth avulsion, and subluxation, occurs in 0.02%–12%^{1–3,12–14} of cases involving airway instrumentation, with the anterior teeth being the most vulnerable because of direct contact with rigid laryngoscopes or inadvertent leverage forces. In the present study, we addressed this challenge by introducing a customized, sports-type dental guard as a protective intervention. In our retrospective comparative study, we demonstrated a significant reduction in postoperative dental complications, likely because of the guard's ability to redistribute pressure across the dental arch, minimize direct instrument-tooth contact, and stabilize mobile teeth during dynamic surgical maneuvers. These results align with emerging evidence advocating proactive dental protection in high-risk procedures, suggesting that such interventions can mitigate medicolegal disputes and enhance patient safety without compromising surgical access. Although dental damage in this cohort was minimal—primarily enamel infarction or gingival lesions—we still recommend the use of a dental guard to prevent such minor injuries. The number of outcome events was small, particularly in the dental guard group, making the results of the binary logistic regression less reliable. Future studies should explore long-term outcomes and cost-effectiveness across diverse patient populations.

Biomechanical analysis of the anterior dentition during MLS procedures^8,15 has revealed that the maxillary incisors are subjected to significant localized stress, particularly during laryngoscope insertion and manipulation. Force mapping data indicated peak pressures of 15 to 32 N/cm² at the central incisors, predominantly caused by direct instrument contact, leveraging forces during glottic exposure, or inadvertent lateral torque. These values exceed the reported enamel fracture threshold (8–20 N/cm²), highlighting the vulnerability of the anterior teeth during such procedures. However, the application of a customized silicone-based dental guard resulted in a marked reduction in stress concentration. A study involving 12 patients who underwent direct laryngoscopy with dental guards reported no dental injuries, validating the effectiveness of dental guard use. ¹⁶ This protective effect, further supported by our retrospective study with a larger sample size, was estimated to arise from three mechanisms: (1) force redistribution through the guard's viscoelastic material, dissipating stress across the dental arch rather than at focal points; (2) a physical barrier function that prevents direct metal-tooth contact and minimizes abrasive microtrauma; and (3) stabilization of mobile teeth through anatomic molding, reducing mechanical loosening during dynamic maneuvers. These findings align with the biomechanical principles of dental trauma prevention and underscore the importance of integrating tailored protective strategies into high-risk airway surgeries to mitigate both overt and subacute dental injuries.

Although the use of dental guards in MLS demonstrates significant potential for reducing dental trauma, several limitations warrant careful consideration. First, the bulk of conventional dental guards may restrict intraoral space, partially obscure the surgical field, or interfere with laryngoscope manipulation, particularly during delicate maneuvers requiring precise glottic visualization. This trade-off between dental protection and operative accessibility necessitates further optimization of guard thickness and transparency. Second, in patients with restricted mouth opening (such as because of trismus, temporomandibular joint disorders, or radiation-induced fibrosis), inserting a premolded dental guard becomes technically challenging, potentially exacerbating soft tissue trauma or delaying airway management. These anatomical constraints highlight the need for adaptable, low-profile designs that can accommodate varying oral apertures without compromising stability. Recently, a transoral robotic surgery team adopted an Aquaplast nasal splint (WFR/Aquaplast Corp., Avondale, PA) to protect teeth and achieved satisfactory outcomes. ¹⁷ However, the cost of the Aquaplast sheet is substantially high. Third, standardized one-size-fits-all guards often fail to conform to individual dental arch morphology, resulting in uneven force distribution and suboptimal protection for structurally compromised teeth. Future innovations should focus on integrating thermoformable materials or smart polymers that balance rigidity for stabilization and flexibility for anatomical conformity, thereby addressing challenges of both visibility and fit. In addition, interdisciplinary collaboration between otolaryngologists and dental engineers could yield hybrid devices that enhance protection while preserving critical surgical ergonomics.

Conclusion

This study suggests that customized dental guards may mitigate intraoperative dental injuries during MLS. After further confirmation in randomized controlled trials, institutional guidelines and training programs should be established to standardize preoperative dental risk assessments and dental guard application protocols. By embedding these innovations into routine practice, the medical community can minimize iatrogenic injuries and reduce medicolegal liabilities, thereby advancing the dual goals of patient safety and surgical precision in MLS.

Supplemental Material

sj-xlsx-2-sci-10.1177_00368504251400808 - Supplemental material for Effectiveness of dental guards in reducing incisor injuries during direct laryngoscopy: A retrospective comparative clinical study

Supplemental material, sj-xlsx-2-sci-10.1177_00368504251400808 for Effectiveness of dental guards in reducing incisor injuries during direct laryngoscopy: A retrospective comparative clinical study by Ziyue Li, Haolai Pan, Xinlong Huang, Shaoxiao Li, Siwen Xia and Huixia Huang in Science Progress