Bite Force in Teeth with and Without Root Canal Treatment: A Cross-Sectional Study

Abstract

Introduction: Bite force is a key indicator of masticatory system function and is influenced by various biological and dental factors. Alterations in pulpal innervation and periodontal sensory feedback following root canal treatment (RCT) may affect force regulation during mastication. The aim of this study was to compare pain/discomfort-limited bite force threshold values between root canal-treated and untreated teeth using a digital bite force transducer (GM10). Methods: A total of 131 patients (48 males and 83 females) participated in the study. Bite force measurements were obtained from 447 teeth (248 with RCT and 199 without RCT). Participants were instructed to bite on a digital bite fork until discomfort or pain was experienced. Therefore, the recorded values represent a pain/discomfort-limited bite force threshold rather than true maximal voluntary bite force. Peak force was recorded in Newtons (N). The device was modified with a rubber tip and a protective cover to improve safety and patient comfort. Results: Teeth without RCT demonstrated significantly higher bite force values than root canal-treated teeth (245.39 N vs. 197.06 N, adjusted p = 0.0347). Male participants exhibited significantly higher bite force values than female participants (277.62 N vs. 186.96 N, adjusted p = 0.0016). In addition, molars demonstrated significantly higher bite force values than premolars (227.83 N vs. 202.75 N, adjusted p = 0.0347). Conclusions: Root canal-treated teeth demonstrated lower bite force values than untreated teeth. However, these findings should be interpreted cautiously because of potential confounding factors.

1. Introduction

Bite force serves as an indicator of the functional status of the masticatory system. It is generated by the activity of the jaw elevator muscles and is influenced by the central nervous system, as well as by feedback mechanisms involving muscle spindles, mechanoreceptors, and nociceptors, all of which are modulated by craniomandibular biomechanics [1].

Mastication is a primary function of the dentition, during which the jaw muscles generate substantial forces over short distances and transmit them through the teeth. However, if these forces are not accurately regulated, they may damage the teeth and surrounding tissues, including the tongue and cheeks. Such damage may subsequently influence individuals’ food preferences and dietary choices, thereby affecting their general health, nutritional status, and quality of life [2,3].

Regulation of masticatory forces is mediated by periodontal mechanoreceptors (PMRs), which provide information regarding jaw position and the magnitude of forces exerted on the teeth, thereby contributing to the generation of efficient and effective masticatory forces. In addition, PMRs dynamically respond to jaw movements and chewing activity, helping to protect the teeth and supporting tissues [4,5].

Accurate clinical diagnosis of periradicular (PR) disease, characterized by inflammation of the periodontal ligament surrounding the tooth, requires assessment of the mechanical pain threshold. Mechanical allodynia (MA) refers to pain elicited by a normally non-painful stimulus, such as biting. Clinically, this may present as tenderness during biting or percussion despite these stimuli being non-noxious under physiological conditions. The subjective and non-quantitative nature of these responses has led to the development of methods for quantifying MA. One such method utilizes a modified digital bite force transducer that accurately measures the magnitude of force exerted during biting [6,7] and can detect changes in biting force associated with MA.

Khan and McCreary et al. [7] evaluated a digital bite force transducer (GM10 bite fork) positioned between the posterior teeth of healthy participants, who were instructed to bite until pain or discomfort was experienced. Because only individuals with normal periradicular tissues were included, the recorded bite force values were considered representative of the normal mechanical pain threshold. The authors suggested that the bite fork may serve as a quantitative diagnostic tool for assessing mechanical allodynia in patients with natural dentition [7].

Interestingly, a reduction in the mechanical pain threshold may provide a sensitive means of distinguishing periradicular from pulpal pain [8]. Previous studies [9,10] have suggested the presence of a protective feedback mechanism within the dental pulp that activates neural pathways and induces a jaw-opening reflex in response to mechanical stimulation. This protective mechanism may be impaired following endodontic treatment, which could explain why vertical root fractures (VRFs) are more frequently observed in endodontically treated teeth, although they may also occur in vital teeth [9].

Vertical root fractures represent one of the most challenging clinical conditions to diagnose and manage. Although advances in diagnostic techniques and the development of improved dental materials have expanded treatment options, extraction is often still required [11]. Teeth requiring root canal treatment frequently exhibit substantial loss of tooth structure because of caries, trauma, or previous restorative procedures. Furthermore, contemporary root canal treatment involves the additional removal of tooth structure during access cavity preparation and canal instrumentation [12,13].

Previous in vitro studies have demonstrated the influence of coronal tooth structure on the biomechanical behavior of endodontically treated teeth. Importantly, most of these investigations evaluated fracture resistance under continuous loading conditions [12]. Mechanical pain thresholds in periradicular tissues may be assessed by quantifying the magnitude of masticatory force required to induce pain.

Although bite force has been investigated in various dental conditions [7,8], limited clinical information is available regarding bite force in root canal-treated teeth compared with untreated teeth. This comparison is clinically relevant because root canal-treated teeth are not simply non-vital teeth. They often differ from untreated teeth in terms of previous disease, restorative history, access cavity preparation, and the amount of remaining tooth structure. These factors may influence the manner in which teeth respond to occlusal loading.

Another important consideration is sensory feedback. Following root canal treatment, pulpal sensory input is lost, whereas periodontal sensory feedback remains intact [9,10]. It is therefore unclear whether root canal-treated teeth can tolerate higher forces because of reduced pulpal sensation or lower forces because of structural alterations, previous symptoms, or protective biting behavior. This uncertainty provided the rationale for the present study.

The aim of the present study was to compare pain/discomfort-limited bite force threshold values between teeth with and without root canal treatment using a digital bite force transducer (GM10). The null hypothesis was that no significant difference would be observed between the two groups.

2. Materials and Methods

The study was conducted at the Department of Endodontics, Maurice and Gabriela Goldschleger School of Dental Medicine, Tel Aviv University, Tel Aviv, Israel. Ethical approval was obtained from the Institutional Ethics Committee (Approval No. 0000260-4). Written informed consent was obtained from all participants prior to their enrollment in the study.

Patients were recruited from individuals receiving routine dental treatment at the School of Dental Medicine. As part of their standard dental care, all patients underwent comprehensive clinical and radiographic examinations performed by undergraduate dental students under faculty supervision. These examinations routinely included bitewing radiographs and when indicated, periapical radiographs. All examinations were conducted independently of the present study and formed part of routine patient care.

Following completion of the routine examination, the investigator reviewed the clinical and radiographic findings and selected teeth that fulfilled the predefined inclusion and exclusion criteria. Eligible participants were at least 18 years of age. Selected teeth were premolars or molars with occlusal contact and a corresponding antagonist tooth in the opposing arch. Exclusion criteria included periodontal disease, caries, systemic disease, cracked teeth, extensive loss of tooth structure (large restorations), orofacial pain, and temporomandibular disorders.

The examined teeth were either untreated teeth with normal pulp status or root canal-treated teeth with satisfactory root canal fillings, adequate coronal restorations, and normal apical tissues. For root canal-treated teeth, radiographic examination was used to verify the quality of the root canal treatment and the absence of radiographic signs of apical pathology. In addition, all selected teeth were asymptomatic and exhibited no sensitivity to percussion. For teeth without root canal treatment, radiographic examination confirmed the absence of caries or other pathology, and participants reported no symptoms associated with the selected tooth. Teeth exhibiting pain, tenderness to percussion, suspected cracks, periodontal involvement, extensive loss of tooth structure, or radiographic signs of apical pathology were excluded.

Teeth were included only after completion of the routine clinical and radiographic examination and confirmation that all study inclusion and exclusion criteria had been satisfied. All bite force measurements were performed by the same investigator using a standardized measurement protocol. Participation in the study did not alter the routine treatment provided to the patients.

Participants who provided written informed consent were instructed to maintain an upright seated position with the Frankfort plane approximately parallel to the floor. Bite force was measured using a digital bite force transducer (GM10; Nagano Keiki Co., Ltd., Ueda, Nagano, Japan). The bite force device was positioned between the maxillary and mandibular teeth, ensuring that the conical portion of the bite fork was aligned with the tooth selected for examination (premolar or molar). Participants were then instructed to bite down until pain or discomfort was experienced. Importantly, participants were not instructed to bite with maximal voluntary force. Therefore, the recorded values should be interpreted as pain/discomfort-limited bite force threshold values rather than maximal voluntary bite force.

Two measurements were obtained for each tooth at 30-s intervals to minimize random variation between recordings, and the mean value was used for statistical analysis. The procedure was repeated for the contralateral tooth, adjacent teeth, and the opposing tooth when available and when these teeth fulfilled the study inclusion criteria.

The digital bite fork records force values of up to 1000 N; however, a cut-off value of 750 N was imposed to minimize the risk of tooth injury, as this force has previously been reported to represent maximal voluntary contraction without pain in healthy teeth. To further reduce the risk of tooth fracture or injury, a rubber covering was attached to the biting surface of the fork. In addition, the bite fork was covered with a thin nylon sheet before each use to reduce the risk of cross-contamination between participants.

Measured variables included age, gender, tooth type, and bite force. All collected data were entered into an Excel database and subsequently analyzed using RStudio (version 2024.04.2) with the lme4 and lmerTest packages. A linear mixed-effects model was fitted with patient included as a random effect and gender, root canal treatment status, and tooth type included as fixed effects. Model assumptions were evaluated by the inspection of residual Q–Q plots. Adjustment for multiple comparisons was performed using the false discovery rate (FDR) method. Statistical significance was set at p < 0.05.

3. Results

Out of the 150 patients screened, 131 (48 males and 83 females) met the inclusion criteria and were enrolled in the study. A total of 447 tooth-level evaluations were performed, including 308 molars and 139 premolars. Of the evaluated teeth, 248 had undergone root canal treatment (94 in males and 154 in females), whereas 199 had not undergone root canal treatment (72 in males and 127 in females). Patient demographic characteristics according to gender, tooth type, and treatment status are presented in

Table 1. Patient demographics.

Gender	Treatment Evaluation	Tooth Type	Numbers
Male	Teeth with RCT	Molars	63 (14.09%)
		Premolars	31 (6.9%)
	Teeth without RCT	Molars	61 (13.6%)
		Premolars	11 (2.46%)
Female	Teeth with RCT	Molars	95 (21.25%)
		Premolars	59 (13.19%)
	Teeth without RCT	Molars	89 (19.9%)
		Premolars	38 (8.5%)
Total			447 (100%)

.

A single tooth was evaluated in 100 participants, whereas 31 participants contributed data from multiple teeth, with or without root canal treatment. Because some participants contributed more than one tooth-level observation, linear mixed-effects models were used to account for within-patient clustering, with patient included as a random effect.

Figure 1, Figure 2 and Figure 3 present descriptive patient-level mean bite force values for visualization purposes. However, all statistical comparisons were performed using linear mixed-effects models based on tooth-level observations, with patient included as a random effect to account for clustering of multiple teeth within the same participant.

Significant differences in bite force were observed according to gender, root canal treatment status, and tooth type. Male participants demonstrated significantly higher bite force values than female participants (277.62 N vs. 186.96 N, respectively; adjusted p = 0.0016; Figure 1). Teeth without root canal treatment demonstrated significantly higher bite force values than root canal-treated teeth (245.39 N vs. 197.06 N, respectively; adjusted p = 0.0347; Figure 2). In addition, molars demonstrated significantly higher bite force values than premolars (227.83 N vs. 202.75 N, respectively; adjusted p = 0.0347; Figure 3).

4. Discussion

This study was designed to compare pain/discomfort-limited bite force threshold values between teeth with and without root canal treatment using a digital bite force transducer (GM10). Our results demonstrated that the root canal-treated teeth exhibited significantly lower bite force values than untreated teeth.

Bite force may play an important role in understanding the increased incidence of vertical root fractures (VRFs) in root canal-treated teeth [10]. Previous studies have shown that the bite fork used in the present study provides highly reliable and reproducible measurements [7], although minor variability between examiners has been reported, making the use of a single examiner preferable for the assessment of mechanical pain thresholds [14]. Because bite force measurements may be influenced by the positioning of the device, we modified the bite fork by adding a rubber cover that acted as an occlusal guide, as previously described [15], thereby ensuring standardized placement during all measurements.

Root canal-treated teeth demonstrated lower bite force values than the untreated teeth. This finding was unexpected and does not support the assumption that loss of pulpal innervation necessarily results in increased loading of root canal-treated teeth. Several explanations may account for these findings; however, they remain speculative because the present study was not designed to directly investigate the biological mechanisms underlying the observed differences.

It is important to recognize that multiple factors may influence bite force measurements, including facial morphology, oral health status, functional disturbances of the masticatory system (such as pain or temporomandibular disorders), as well as gender, age, craniofacial characteristics, and occlusal features [16]. Although strict inclusion and exclusion criteria were applied to minimize the influence of these variables, residual confounding cannot be completely excluded.

Moreover, the present findings should not be interpreted as evidence that root canal treatment itself directly reduces bite force. Root canal-treated teeth often differ from untreated teeth in several respects, including previous disease, restorative history, access cavity preparation, and the amount of remaining tooth structure. Any of these factors may have contributed to the observed differences.

A behavioral explanation is also possible. Some patients may consciously or subconsciously avoid applying excessive force to teeth that have undergone root canal treatment, even when those teeth are asymptomatic. This behavior may reflect previous painful experiences or a learned protective response. However, patient behavior was not directly evaluated in the present study, and therefore this explanation cannot be confirmed.

Therefore, the lower bite force observed in root canal-treated teeth should be interpreted as an association rather than evidence of a specific underlying mechanism. Further studies are required to clarify the biological, structural, and behavioral factors that may contribute to this finding.

Notably, the bite force observed in the present study (50–723 N) was lower than previously reported values for healthy adults (244–859 N) [17,18]. This difference may be attributable to methodological differences, including the instruction given to participants to stop biting when discomfort or pain was experienced. Furthermore, discrepancies among studies may result from differences in measurement devices and biting interfaces, including the use of uncovered bite fork transducers [9], modified acrylic coverings [15], or entirely different force-measurement systems [19].

Differences in bite force values may also be influenced by muscle fatigue, psychological factors such as anxiety, and external factors including diet, habits, and occupation, all of which may affect the measured values [20,21]. In the present study, the biting surface of the bite fork was covered with rubber to reduce the risk of tooth fracture and injury. This modification created a smaller contact area between the transducer and the tooth than that used in some previous studies, which may have also influenced the recorded values [15].

Previous studies [9,10,22] have suggested that root canal-treated teeth may exhibit higher bite force values because of alterations in periodontal ligament innervation and proprioception. Such changes have been proposed as a possible contributing factor to the development of VRFs. In contrast, our findings indicate that root canal-treated teeth demonstrated lower bite force values than the untreated teeth [9,10].

Another possible explanation relates to the method used to assess periapical status. Because our study relied exclusively on periapical radiographs, an undetected apical pathology may have been present and could have influenced the pain thresholds. Although assessment based on periapical radiographs reflects routine clinical practice, some lesions or structural defects may only be detected using cone-beam computed tomography (CBCT). Undetected pathology, cracks, or restoration-related complications may therefore have influenced the measured force values. However, because these variables were not directly assessed, their contribution remains uncertain. More advanced imaging techniques, such as CBCT, may provide more accurate diagnostic information and potentially yield different findings [23,24]. Nevertheless, routine CBCT examination of asymptomatic teeth solely for research screening purposes would not be justified because of the radiation exposure considerations.

We caution that root canal treatment may not be the sole factor influencing bite force and the risk of vertical root fracture. An additional limitation of the present study is that restoration status, remaining coronal tooth structure, and previous structural damage were not systematically quantified. Although strict inclusion criteria were applied, these factors may independently influence bite force and therefore represent potential confounders. Future studies should incorporate restoration type and remaining tooth structure into adjusted analyses.

The cross-sectional design represents another limitation of the study. Because bite force was not measured before root canal treatment, it is impossible to determine whether the lower values observed were present before treatment or developed afterward. Consequently, the findings should be interpreted as an association between root canal treatment status and bite force rather than as evidence of a causal relationship.

Our results also demonstrated a significant influence of gender on bite force, with higher values observed in males across all study groups. This finding is consistent with previous reports showing that males generally exert greater bite forces than females [19,20,25].

This difference is likely attributable to anatomical and physiological characteristics associated with greater muscular strength, including larger masseter muscle fibers and greater muscle cross-sectional area in males [26]. This observation may have clinical relevance because it could influence treatment planning and restorative material selection.

Tooth type was another factor that significantly influenced bite force. Molars demonstrated higher bite force values than premolars, which may be explained by their larger size, greater occlusal surface area, and primary role in food grinding [27,28]. Although premolars are capable of generating substantial force, they are generally less suited than molars for withstanding the high forces involved in mastication [28].

5. Clinical Implications

The findings of the present study may have implications for clinicians involved in restorative and endodontic treatment planning. In the present sample, root canal-treated teeth demonstrated lower bite force values than teeth without root canal treatment.

Clinically, these findings suggest that root canal-treated posterior teeth should not automatically be considered functionally equivalent to intact, untreated teeth. Even when asymptomatic and radiographically acceptable, their bite force response may differ from that of untreated teeth.

Although these findings should be interpreted cautiously because of the potential influence of restoration status, remaining tooth structure, and other confounding factors, they may contribute to a better understanding of the functional performance of endodontically treated teeth and provide additional insight into factors affecting occlusal loading during function.

These observations may be relevant when planning the restoration of root canal-treated posterior teeth, particularly in cases with reduced remaining coronal tooth structure. However, the results should not be interpreted as justification for routine occlusal reduction or systematic modification of occlusal contacts in root canal-treated teeth. Rather, such teeth should be assessed individually, with careful consideration of structural integrity, occlusion, and restorative design.

6. Future Research

Future studies should include a more detailed evaluation of restoration type, remaining tooth structure, occlusal contacts, and periapical status. Such factors may help determine whether the lower bite force observed in root canal-treated teeth is primarily related to endodontic treatment, structural loss, restoration-related variables, or patient-related biting behavior.

Prospective longitudinal studies may help clarify whether the observed differences are attributable to root canal treatment itself or to associated structural and restorative factors.

Measurement of bite force before treatment, after root canal treatment, and following definitive restoration may help determine whether bite force changes over time and identify the stage of treatment that has the greatest influence on functional loading.

In addition, studies involving larger patient populations may further improve our understanding of the relationship between endodontic treatment and functional bite force.

7. Conclusions

Root canal-treated teeth demonstrated lower pain/discomfort-limited bite force threshold values than untreated teeth. Gender and tooth type were also significantly associated with bite force measurements. Statistical analyses accounted for within-patient clustering using linear mixed-effects models; however, potential confounding factors, including restoration status and remaining tooth structure, should be considered when interpreting these findings. Further research is warranted to clarify the relationship between root canal treatment and bite force and to evaluate its potential clinical implications.