Correlation between Body Mass Index and the Occurrence of Postoperative Complications after Surgical Removal of the Lower Third Molar.

Objectives: Swelling, pain and trismus after the surgical removal of the mandibular third molars are the most common and expected postoperative complications. The aim of this cross-sectional study was to assess the association of those postoperative complications and BMI after surgical removal of the mandibular third molars. Material and methods: 84 patients who required the surgical removal of their lower third molar were enrolled in this study and were divided into 4 groups dependent on their BMI. Data were tested by one-way analysis of variance (Welch's ANOVA). The differences were tested by the intragroup using the Games-Howell test.
Results: The effect of BMI on pain had a statistically significant difference within the first 24 postoperative hours: 4 hours (p=0.014), 6 hours (p=0.034, p=0.049), 12 hours (p= 0.00.P=0.023), and 24 hours (p=0.010). For swelling and trismus in the exception on first postoperative day between underweight and normal weight groups (p=0.026), and underweight and overweight groups (p=0.014) no statistically significant correlation was found.
Conclusion: BMI has an impact on a patient's early postoperative recovery.

Introduction

The mandibular third molar is the most common impacted tooth with a prevalence between 16.7% and 68.6%, and its surgical extraction, taking into account indications and contraindications, is one of the most performed procedures in oral and maxillofacial surgery (-). This surgical procedure includes various surgical procedures (incision, mucoperiosteal flap elevation, targeted removal of the part of the bone that interferes with the tooth extraction, tooth extraction, flap repositioning and suturing) that can lead to the most frequently expected postoperative complications in the form of trismus, pain and swelling (, ).

The release of histamine and bradykinin, due to surgical trauma, leads to vasodilatation, hyperemia and increased permeability followed by accumulation of fluid in the interstitium, and migration of monocytes and granulocytes. The above mentioned release leads to development of clinical visible swelling or edema. Histamine and bradykinin, along with the important role in development of edema, participate in development of pain by sensitizing nociceptors. Their effect is noticeable in the initial postoperative phase as a result of a very short half-life (). Although it is an expected physiological response to the tissue damage, pain is the most common complication that significantly affects the patient's quality of life (, ).

Trismus is a prolonged spasm of one or more masticatory muscles resulting in the formation of connective tissue contractures. It is most often caused by improper application of nervus alveolaris inferior anesthesia, needle penetration of the pterygoideus medialis or blood vessel resulting in mild bleeding and hematoma formation. In addition, it can be caused by a mild infection or a mucoperiosteal flap elevation above the external oblique ridge. The condition is characterized by difficulty in opening of the mouth and the diagnosis is made, clinically, by measuring the maximum interincisal distance (MID), the values of which in the case of trismus are less than 35 to 40 mm. (-).

There exist a large number of preoperative and postoperative factors that can influence postoperative complications such as age, gender, systemic diseases, oral hygiene level, cigarette smoking, surgeon's experience, duration of the surgical extraction, tooth angulation, depth of impaction, amount of removed bone, tooth separation, the shape and size of the mucoperiosteal flap, suturing techniques and BMI which is processed in this clinical trial etc. (-). Obesity has ceased to be just an aesthetic problem. As one of the listed factors influencing the development of complications, an overweight patient is a challenge for the surgeon when removing third molars due to potential clinical postoperative repercussions on the patient's recovery, restoration of vital functions and decisions on oral surgery in the future (, ).

The Body Mass Index (BMI), formerly known as the Quetelet index, is a measure indicating nutritional status in adults. It is considered to be the most accurate way to determine the relationship between body weight and health risk. It is defined as body weight in kilograms divided by height squared in meters (kg/m2) (, ).

According to WHO data from 2008, 57.7% of the population in Croatia was overweight or obese. Such a "negative trend" has affected not only Croatia, but also every region of the world apart from sub-Saharan Africa and Asia (, ).

When planning and performing the procedure on an obese patient, the surgeon must consider numerous health implications and anatomical aspects of obesity. Although white adipose tissue (WAT) has been considered an inert and energy storage site for a long period of time, current research has shown that it actively participates in the regulation of physiological and pathological processes and is associated with immune and inflammatory changes. Moreover, there is a characteristically elevated number of inflammatory cytokines (TNF-α, IL-1, IL-6) indicating that being overweight is associated with chronic low-grade systemic inflammation. The main source of tumor necrosis factor (TNF-α) and part of the produced IL-6 are macrophages found in white adipose tissue, and their number is associated with obesity and adipocyte size (, , ).

Due to the lack of scientific evidence on this issue and a relatively small number of studies that have yielded conflicting results, the aim of this study was to investigate whether there is a correlation between body mass index and the incidence of the most common expected postoperative complications such as trismus, pain and swelling. The null hypothesis of the study is that body mass index is not related to the development and severity of the most common postoperative complications: pain, trismus and swelling.

Material and methods

This cross sectional clinical trial, which was approved by the Committee of University Hospital Dubrava, was performed at the Department of Oral and Maxillofacial Surgery, University Hospital Dubrava, Zagreb, Croatia. The clinical trial was in full consent with the ethical principles defined in the World Medical Association's Declaration of Helsinki and written in accordance with the Consort recommendation. Participation in the clinical trial was voluntary. Each patient was informed of the purpose and design of the study and was asked to sign a consent form.

Participants

In the period from April 2017 to February 2020, 84 patients with detailed medical and dental histories, and with impacted lower third molars were included in this clinical study.

The sample size was calculated by the G Power software. With a 95% confidence interval, an 80% power, and an effect size of 80% (), a total sample size of 80 individuals was necessary.

The inclusion criteria were healthy adults of both genders (ASA I physical status), with no allergies to any of the medications administered during this clinical research. All participants needed to be pain free and without signs of inflammation in surgical field. They were not allowed to take any pharmacological agents that could have an impact on postoperative recovery 7 days prior to the surgical procedure. Exclusion criteria were pregnancy, breastfeeding, tobacco or cigarette smokers, and drug abuse.

Before the surgical removal of mandibular third molars, for each patient it was confirmed radiographically by orthopantomograph that all lower third molars were in the same bone position and angulation. All surgically removed mandibular third molars belonged to the Parant 3 scale (the scale for predicting the difficulty of removing third molars).

Surgical procedure

All participants rinsed their oral cavities for 1 minute with 15 ml 0.2% Chlorhexidine (Miradent, Mouth Rinse paragard chx, Hager Pharma GmbH, Duisburg, Germany) prior to local anesthesia administration. The surgery was performed under local anaesthesia of inferior alveolar nerve block with a 1ml injection suspension containing 40mg of articainchloridum and 0.005mg of adrenaline in the form of adrenalinchloridium (Ubistesin-articaine, 3M ESPE, Neuss, Germany). All treatments were performed by the same surgical team, with the same equipment and by taking the same surgical approach.

Triangular flap design was performed with scalpel blade No: 15 (Carl Martin GmbH, 42657 Solingen, Germany). The incision was performed from the mandibular ramus the distobuccal part of the first lower molar. Elevation of a full-thickness mucoperiosteal flap was performed by Willinger periosteal elevator (Carl Martin GmbH, 42657 Solingen, Germany). To provide a better visibility of the surgical field, Stenberg lip retractor (Carl Martin GmbH, 42657 Solingen, Germany) was used. Straight handpiece (Ti-Max X-SG65L, NSK Europe GmbH Eschborn, Germany) and steel bone cutters (REF: H141104023, H267104016, H141104010, Komet Dental, Bras seller Gmbh & Co, Lemgo, Germany) with maximum speed 40000 rpm and cooling aqueous irrigation were used for bone removal and tooth separation. Depending on the situation, extracting forceps, root elevators, and luxating instruments were used. Extraction wounds were closed with 3-0 silk simple interrupted sutures which were removed 7 days after the surgical procedure. Postoperative instructions were the same for all participants. The analgesics that they were allowed to take as needed in the postoperative period were only ibuprofen tablets (Neofen Forte 400 mg, Belupo, Koprivnica, Croatia). All participants who used other analgesics, other pharmacological agents than those allowed were excluded from this clinical study. Given that there are conflicting studies on the results of using ice packs (cryotherapy), and because there was a possibility that some subjects would use ice packs and other patients would not, a cryotherapy of the surgical area was not allowed.

Postoperative control, observation and all postoperative measurements of the study were done by the surgeon who performed surgical procedures.

Assessment of BMI, swelling, pain and trismus

Depending on BMI, which was calculated by the ratio between weight and height, participants were divided into 4 groups: 1-underweight ≤ 18,5, 2-normal weight- 18,6-24,9, 3-pre-obesity 30-34,9,4-obesity->30.

A four grade descriptive scale was used to measure the degree of swelling on the first, second and third postoperative day after the removal of the mandibular third molar: 0- none (no swelling), 1- light (intraoral, localized to the surgical field), 2- moderate (extraoral swelling localized to the surgical field), and 3- severe (extraoral swelling extending beyond the surgical field) ().

A pain assessment was performed by patients who were marking the pain level on the VAS scale (10-cm long line with marked “no pain” on the far-left side of the scale (0 cm) and “unbearable pain” on the far-right side of the scale (10 cm)), 2, 4, 6, 12, 24, 48 and 72 hours after the removal of the mandibular third molar.

Trismus was measured by the distance between the incisal surfaces of the mandibular and maxillar central incisor using TheraBite scale (Atos Medical UK, Nottingham, England) before the operative procedure on the first, second and third postoperative day ().

Statistical analysis

The SPSS software (Version 25.0. Armonk, NY: IBM Corp.Armonk, NY, USA) was used for statistical analysis. Data was tested by one-way analysis of variance (Welch's ANOVA). The assessment of data normality was conducted by the Kolmogorov-Smirnov test. The differences were tested intragroup using the Games-Howell test. The level of significance was set at 0.05.

Results

Eighty-four patients met the criteria and participated in the present study. Sociodemographic characteristics of participants are present in Table 1. Participants were divided into 4 groups according to the calculated body mass index. The group of underweight (BMI ≤ 18.5) consisted of seven, the group of normal body weight (BMI 18.6 – 24.9) fourty eight, the group of overweight (BMI 25.0 – 29.9) twenty four, and the group of obese (BMI ≥ 30.0) five respondents.

Table 1

Sociodemographic characteristics of the participants

BMI	Age (years)	Male	Female
≤ 18.5	24.71±3.65	4	3
18.6 – 24.9	23.56±3.09	25	23
25.0 – 29.9	24.63±3.39	14	10
≥ 30.0	27.80±2.64	2	3
		TOTAL: N=84

The level of postoperative pain measured by the VAS scale and the statistical differences between BMI groups are shown in Table 2. The results showed that there was a statistically significant difference in the level of postoperative pain within the first 24 postoperative hours: 4 hours (p = 0.014), 6 hours (p = 0.034, p = 0.049), 12 hours (p = 0.00. P = 0.023), and 24 hours (p = 0.010) after the surgery.

Table 2

Pain level (VAS scale) between BMI groups

PAIN (VAS scale)	BMI GROUPS
	≤ 18.5	18.6 – 24.9	25.0 – 29.9	≥ 30.0
2 h	2.43 ± 1.81	2.34 ± 1.91	3.58 ± 2.92	3.80 ± 2.68
4 h	3.57 ± 1.99	3.71 ± 2.2a	5.29 ± 1.9a	5.4 ± 3.36
6 h	2.86 ± 1.77b	3.56 ± 2.13c	4.75 ± 2.13	5.8 ± 1.30bc
12h	2.14 ± 1.07d	3.45 ± 2.26e	5.17 ± 2.33de	4.6 ± 1.67
24 h	2.43 ± 1.27f	3.58 ± 2.48	4.92 ± 2.54f	4.00 ± 1.87
48 h	3.00 ± 1.91	3.49 ± 2.36	4.21 ± 2.80	3.6 ± 0.55
72 h	2.57 ± 1.51	3.05 ± 2.42	3.9 ± 2.68	3.2 ± 0.45

a = 0.014; b = 0.034; c = 0.049; d = 0.000; e = 0.023; f = 0.010

The results of the level of postoperative swelling and the ability of mouth opening between BMI groups are shown in Table 3. According to Games-Howell post hoc test, there was no statistical difference for the level of postoperative swelling in all tested times. Also, the test showed there was no statistical difference for the mouth opening among the BMI groups with the exception of the first postoperative day when statistically significant differences between underweight and normal weight groups (p=0.026), also underweight and overweight groups (p=0.014) were found.

Table 3

Level of postoperative swelling. duration of operation, first and total analgetics consumation and the ability of mouth opening between BMI groups

	BMI GROUPS
	≤ 18.5	18.6 – 24.9	25.0 – 29.9	≥ 30.0
Duration of operation (min.)	23.0 ± 9.04	19.79 ± 6.30	20.17 ± 5.80	23.60 ± 8.96
Pain Caused by Anesthetic Application (VAS scale)	2.71 ± 0.95	2.62 ± 1.68	4.04 ± 2.65	4.20 ± 1.92
Personal Experience of the Operation	6.14 ± 3.76	7.63 ± 2.40	8.21 ± 1.35	6.60 ± 1.52
Duration of Anesthesia (min)	299.14 ± 140.98	264.29 ± 55.36	263.50 ± 53.21	233.00 ± 49.95
Swelling
1st day	2.71 ± 0.49	2.77 ± 0.81	2.75 ± 0.53	2.40 ± 0.89
2nd day	2.86 ± 0.69	2.88 ± 0.76	2.79 ± 0.83	3.00 ± 1.00
3rd day	2.71 ± 0.49	2.73 ± 0.92	2.71 ± 0.96	3.2 ± 0.84
Trismus
1st day	29.86 ± 5.01ab	37.60 ± 10.07a	38.96 ± 9.23b	40.8 ± 14.22
2nd day	31.00 ± 4.58	36.08 ± 9.52	36.38 ± 8.01	28.00 ± 11.51
3rd day	33.00 ± 6.40	38.13 ± 11.11	35.83 ± 12.00	34.00 ± 6.52
First analgetic (min. postoperative)	271.00 ± 98.46	374.4 ± 457.07	213.00 ± 84.56	157.60 ± 53.99
Analgetic consumption
1st day	2.14 ± 0.69	2.13 ± 1.32	2.17 ± 0.96	2.20 ± 0.45
2nd day	1.86 ± 1.07	2.08 ± 1.86	1.96 ± 1.65	2.4 ± 0.55
3rd day	1.14 ± 1.07	1.6 ± 1.74c	1.63 ± 1.56	1.6 ± 0.89c

a = 0.026; b = 0.014; c = 0.026

In addition to the above mentioned observations, a statistically significant difference was also found for the consumption of analgesics during the first postoperative day between normal weight and overweight groups (p=0.026).

Discussion

The purpose of this study is to evaluate the correlation between body mass index and the occurrence of the most common postoperative complications after surgical removal of the lower third molar: trismus, pain and swelling. To the best of our knowledge, the literature on this specific topic is very scarce and there are only a few papers about this correlation. Also, this is the first clinical trial which studies this correlation in patients who were statistically approximately of equal ages, had identical tooth position, degree of bone impaction and the same Parant class in the surgical removal of the lower third molars.

Previous research has shown that obesity significantly affects health and the occurrence of operative and postoperative complications (). However, the association between BMI and operational outcomes is still considered controversial. According to the available literature, the association between the body mass index and the occurrence of complications varies considerably among different, and even in the same, surgical procedures (). For instance, by reviewing the neurosurgical literature, it has been proven that there is an increased incidence, and prevalence, of postoperative complications such as infections in overweight patients undergoing spinal surgery due to degenerative diseases. On the other hand, obesity poses very little or no risk of adverse events in the field of general neurosurgery (-).

Although the incidence of complications following the surgical removal of the lower third molar is low and is mostly referred to minor complications, the approach to an obese person may pose particularly difficult challenges to the oral and maxillofacial surgeon (, ).

As previously mentioned, pain is the most common complication that the health workers encounter in oral surgery practice. According to the available literature, previous studies have not shown an association between BMI and postoperative pain levels, but neither BMI and trismus or swelling.

Moreover, Waisath et al. have studied the occurrence of postoperative infection, nerve damage, dry socket, oral antral (O / A) fistula, soft-tissue defect, temporomandibular joint dysfunction (TMD), during various dentoalveolar surgeries and obtained equal results, and found no associations between BMI and complications (). Also, Matijević et al. stated that BMI has no effect on the duration and intensity of pain in the first seven postoperative days (). Although in the present study the patients were not monitored for seven postoperative days, but for three (72 hours), conflicting results were obtained when compared to the aforementioned studies. The results showed that there was a statistically significant difference in the level of postoperative pain within the first 24 postoperative hours. Lower levels of postoperative pain intensity were observed in patients with the lowest BMI. After 4 hours, a significantly lower level of pain was observed in patients of normal body weight than the group of overweight patients (BMI 25.0 – 29.9) (p = 0.014). Furthermore, after 6 hours, a lower pain level was observed in underweight patients compared to normal-weight patients (p = 0.034) and in normal weight patients compared with obese patients (p = 0.049). After 12 hours, a higher pain level was observed in the overweight patients compared to those underweight (p ≤ 0.001) and normal weight (p = 0.023). Also, 24 hours after the surgery, the pain level was lower in underweight patients compared to overweight patients (p = 0.010) (Table 2.) It should be emphasized that a statistically significant difference has always been in favour of the group of overweight and obese patients. Unlike the previously mentioned studies, the advantage of this present study and the reliability of the results is that the surgery was performed by one surgical team, and each removed mandibular molar belonged to Parant scale 3. Therefore, the surgeon's experience, the position of the tooth and the approach to surgical procedure could not interfere with the results of this clinical study.

As in previous clinical studies to date, this trial has found no association between BMI and swelling (Table 3). The authors believe that this issue should be further investigated using more objective methods. For example, swelling can be evaluated by measuring reference points on the subject's face. Contrary to the reviewed literature, this study showed that there was a statistically significant difference in the ability of mouth opening on the first postoperative day between the group of underweight and the group of normal weight (p = 0.026) and underweight and overweight patients (p = 0.014). The difference was in favor of the normal weight group which had 7.747 and overweight group which had 9.101 higher score.

The concept of extended procedure duration due to slightly different anatomical characteristics of overweight people is frequently mentioned in the literature. More precisely, such individuals very often have more pronounced and fuller cheeks, and thus the visibility of the operative field is reduced, which makes the procedure more difficult, prolonged and more challenging (, , ). Gbotolorun et al. stated that the duration of the procedure was statistically significantly prolonged by an increase in BMI (). Similar results can also be found in the literature of other surgical fields. For example, Ri M et al. concluded that during cardiovascular and gastroenterological surgical procedures, the increase in BMI is associated with prolonged time of the procedure (). Contrary to these findings and the same as the study by Obimakinde et al. (), in this clinical trial, a statistically significant correlation between a patient’s BMI and duration of surgical procedure was not found.

Akadiri et al. have mentioned that body weight and the body surface area are the factors that can make it difficult for a surgeon to perform the surgical removal of the lower third molar. However, they have emphasized that althought BMI is a total body weight, it does not necessarily reflect the size of oral tissue, which could explain why there are such contradictory results on duration of surgical procedure due to BMI. ()

There are several limitations to the study that need to be considered. There is a small number of respondents in the group of underweight and obese patients, which can be justified by the fact that such groups generally include young and physically active individuals. Furthermore, BMI is a good indicator of a patient’s nutritional status, but not ideal. Increased BMI does not necessarily mean an increased amount of adipose tissue in the body. Namely, an increased BMI can be seen in people with large muscle mass, e.g. athletes. Besides, BMI doesn't give information about a person’s body constitution. For example, as we mentioned before, an increased BMI does not necessarily mean having a fuller cheek. Therefore, additional measurements such as waist-to-hip ratio, waist circumference, skinfold thickness and neck circumference should be used in further studies to make the results as accurate and reliable as possible ().

Conclusions

The null hypothesis of the study was rejected. The study showed that body weight above normal had an effect on pain levels within the first 24 hours of the procedure. On the first postoperative day, difficulty in opening the mouth is visible in normal and overweight patients compared with those malnourished.

In conclusion, pathophysiological changes that occur with weight gain reduce the quality of the postoperative period, make recovery more difficult for the patient, thus making the procedure far more complex for the oral surgeon to perform. All things considered, the authors of the present study believe that good planning and a more careful performance are needed, particularly if we take into account the growing increase in the number of obese people in the world.