PULP SENSIBILITY AND MASSETER INHIBITORY REFLEX IN DIABETIC POLYNEUROPATHY

Accurate assessment of dental pulp health is fundamental for correct endodontic diagnosis and for preventing unnecessary or inappropriate treatment decisions. In routine dental practice, pulp sensibility is commonly evaluated using electric pulp testing (EPT) and thermal (cold) testing. These methods primarily assess neural response rather than true pulp vitality and rely on patient perception, which makes them inherently subjective.

Several factors may influence pulp sensibility test outcomes, including systemic diseases affecting peripheral nerves, such as diabetic polyneuropathy, as well as trauma, anxiety levels, medication use, and metabolic disease duration. Diabetic polyneuropathy is a frequent complication of diabetes mellitus and is characterized by progressive sensory nerve dysfunction. This condition may alter trigeminal nerve conduction and pain perception, potentially leading to altered or reduced responses in conventional pulp sensibility tests and increasing the risk of false-negative results.

The masseter inhibitory reflex (MIR) is a well-established neurophysiological reflex mediated by trigeminal afferent and efferent pathways and can be objectively recorded using electromyography. Unlike conventional pulp tests, MIR provides quantitative and objective information about orofacial sensory and motor nerve function. However, the relationship between diabetic polyneuropathy severity, dental pulp sensibility responses, and MIR parameters has not been sufficiently investigated.

The aim of this clinical study is to evaluate the effect of diabetic polyneuropathy severity on dental pulp sensibility responses and masseter inhibitory reflex parameters. Individuals diagnosed with diabetic polyneuropathy who presented to the Department of Neurology at Bezmialem Vakıf University will be included and categorized into mild and severe neuropathy groups based on neurological evaluation. A healthy control group without systemic or neurological disease will also be included for comparison.

A total of 108 participants aged between 25 and 65 years will be enrolled. Demographic and clinical data including age, sex, duration of diabetes, presence of comorbid systemic diseases other than diabetes, and medication use within the last 24 hours will be recorded for all participants.

Dental pulp sensibility tests will be performed on the maxillary central incisor. The selected tooth must be free of caries or present only with small, non-extensive restorations, must not have undergone root canal treatment, and must show no clinical or radiographic signs of periapical pathology or periodontal disease. Teeth with extensive caries, restorations, periodontal pathology, or previous endodontic treatment will be excluded.

Thermal sensibility will be assessed using a cold test, and both the time to initial sensation and the duration of sensation decay will be recorded.

Electric pulp testing will be performed using a standardized protocol, and the response threshold will be recorded as a numerical value on a scale ranging from 0 to 64. All pulp sensibility tests will be conducted under standardized conditions, and patient responses will be documented.

Masseter inhibitory reflex recordings will be obtained using electromyography. Electrical stimulation will be applied to the maxillary central incisor using a sterile needle electrode. Surface electrodes will be placed according to standardized neurophysiological protocols to record MIR responses. Participants may experience brief and mild transient sensations during stimulation. All procedures will be explained in detail prior to testing, and participants will be informed that they may request termination of the procedure at any time. If a participant expresses discomfort or wishes to stop, all procedures will be immediately discontinued.

The primary hypothesis of this study is that increasing severity of diabetic polyneuropathy is associated with decreased dental pulp sensibility responses and altered MIR parameters compared to healthy controls. It is further hypothesized that conventional pulp sensibility tests may yield false-negative responses in individuals with advanced neuropathy, whereas MIR measurements will provide objective evidence of altered orofacial nerve function.

Statistical analysis will be performed using appropriate statistical software. Descriptive statistics will be calculated for all variables. Normality of data distribution will be assessed using the Shapiro-Wilk test. Group comparisons will be conducted using one-way analysis of variance (ANOVA) or Kruskal-Wallis test, depending on data distribution. Post hoc analyses will be performed where appropriate. Associations between neuropathy severity, pulp sensibility parameters, and MIR measurements will be evaluated using correlation and regression analyses. A p-value of <0.05 will be considered statistically significant.

The results of this clinical study are expected to improve understanding of the impact of diabetic polyneuropathy on dental pulp sensibility testing and to support the use of neurophysiological assessment methods as complementary tools in endodontic diagnosis. By identifying limitations of conventional pulp tests in diabetic patients, this study aims to contribute to more accurate diagnostic decision-making and improved patient care.

Inclusion criteria

Ability to understand the study procedures and provide written informed consent.

For diabetic polyneuropathy groups:

• Diagnosis of diabetic polyneuropathy confirmed by a neurologist
• Neuropathy severity (mild or severe) determined by nerve conduction studies

For healthy control group:

• No history of diabetes mellitus
• No history of peripheral neuropathy or neurological disease

Presence of at least one maxillary central incisor suitable for testing, defined as:

• No previous root canal treatment
• No extensive caries
• No clinical or radiographic signs of periapical pathology
• No periodontal disease affecting the selected tooth

Exclusion criteria

• History of chemotherapy, head and neck radiotherapy, or systemic conditions known to affect peripheral nerve function (other than diabetic polyneuropathy in the patient groups)
• Presence of acute or chronic orofacial pain disorders
• Use of medications within the last 24 hours that may affect sensory perception or nerve conduction (e.g., analgesics, sedatives, neuroactive drugs)
• History of trauma to the maxillary central incisor or surrounding tissues
• Extensive restorations, fractures, caries, or periodontal pathology involving the selected tooth
• Pregnancy or breastfeeding
• Inability to tolerate study procedures or refusal to continue participation at any point