Examination of chewing performance with extraction and non-extraction fixed orthodontic treatment – A prospective clinical 1-year study

INTRODUCTION

One of the most important goals of orthodontic treatment is to preserve the long-term stability of the occlusion and tooth alignment obtained as a result of the treatment. Dental occlusion is the static relationship of teeth.^[1] Prosthetic dental treatment is aimed to provide appropriate esthetics, phonation, function, and occlusion while replacing the lost tissues. All elements of the masticatory system are affected by changes in occlusion. In ideal occlusion, alanced force distribution is provided to all components with bilateral and simultaneous contacts on the teeth.^[2,3] If the proper occlusion is not achieved, adverse effects may be seen in teeth, periodontal tissues, masticatory muscles, and temporomandibular joint (TMJ). To avoid these, occlusal analysis and alignment must be done carefully. Many methods have been developed for occlusal analysis. Materials such as articulating paper, metal sheets (shim stock), and silk ribbon have been widely used for many years and studies have been carried out on these methods.^[4,5] With the advancement of technology, digital methods have been introduced and interest in these methods has increased rapidly. One of these methods is the T-Scan^® occlusal analysis system (Tekscan Inc., USA). CEREC Omnicam^™ (Sirona Dental Systems, Germany), a computer-aided design and manufacturing system, is primarily used for the design and manufacture of all-ceramic restorations.^[6,7] In addition to the design and production feature, the occlusal contact points on the teeth are also shown by referring to the images obtained. Studies evaluating the accuracy of these contact data are limited in the literature.^[8,9] With the T-scan system, it is stated that dynamic contact relations, occlusal force distributions, and disclusion and occlusion times can be evaluated both in maximum intercuspation and during lateral movements of the lower jaw.^[10-12] In addition, the estimated error rate, sensitivity, and reliability of the measurements obtained with this system are 1%, 98%, and 97.2%, respectively, and it provides more advanced and reliable information than conventional methods used in the evaluation of occlusion.^[13] However, none of the previous studies have adequately evaluated the occlusion using the T-scan III device during the active orthodontic treatment period. On the other hand, no study has been found in the literature in which occlusion was evaluated with T-scan III during the active orthodontic treatment period. It is reported in the literature that the effect of occlusion on TMJ disorders is 10–15%. While some studies investigating the role of TMJ disorders and occlusal factors found a positive relationship between signs and symptoms of TMJ diseases and Angle classification and occlusal guidance factors, no relationship was found in some studies. However, with the thought that malocclusion is the most important factor leading to TMJ disorders, irreversible occlusal adjustments are made by dentists today as in the past.^[14,15]

This study aims to determine the distribution of occlusal factors and whether there are changes in the joint due to this in individuals receiving fixed orthodontic treatment.

MATERIAL AND METHODS

Forty-three healthy individuals, aged between 16 and 30 years, who visited the Department of Orthodontics for fixed orthodontic treatment (with and without tooth extraction, 13 and 30 patients, respectively), were included in this study (treatment group).

The study included patients who were systemically and periodontally healthy; treated using fixed orthodontic appliances; underwent symmetrical extraction of premolars, if required, for orthodontic treatment; were not treated with orthognathic surgery; and who achieved optimum occlusion and treatment goals. The analyzes were applied to the patients in 3 different periods: Before starting the treatment (T0), the 6^th month of the treatment (T1), and the 12^th month (T2), the end of the treatment, and the results obtained were evaluated statistically. All patients in the treatment group received orthodontic treatment using fixed edgewise 0.18-inch Roth brackets.

The occlusal factors determined in our study were recorded as follows:

1. Sagittal tooth relationship Angle classifications were made according to the intermaxillary relationship of the right first molar teeth.

2. Occlusal guides; lateral anterior guidance was recorded by asking the patient to shift the mandible from the maximum intercuspal position to the right and left. During this movement, if only the canines were in contact, the canine was considered as protective occlusion, and if one or more molars were in contact with the canine, group function occlusion was considered. When the patient slides the lower jaw forward, if there is contact with the anterior teeth, it was recorded as “Anterior guidance available,” otherwise “No anterior guidance.”

3. The presence of balancing party conflict and contact; when the patient shifts his teeth to the right or left if there is a tooth contact on the balancing side, it is considered as “balancing party contact,” if the balancer side makes tooth contact to eliminate the contact on the working side, it is considered as “balancing party conflict.”

The subjects sat in an upright position. Their maximum unassisted opening and lateral deflections were recorded clinically and entered into the computer with the BioPak software program. The headset device was then placed on the subject’s head with the sensors positioned over the TMJs; the subjects were instructed to watch the monitor where they observed an animation illustrating opening and closing mouth movements, synchronized to a metronome. They were then instructed to open their mouth as wide as they could and close, tapping their teeth together following and matching the animation and the metronome, which they observed on the screen. As the subject performed the opening and closing with the joint vibration analysis (JVA), the characteristic vibrations produced by the condyles were detected by the accelerometers and recorded on the computer. After the first set of JVA tracings was recorded, the Research Diagnostic Criteria examination was performed, then the second set of JVA tracings was recorded [Figure 1a and b]. In our study, the T-scan III (Tekscan, Inc., South Boston, USA) system was used to analyze the number of contact points and occlusal force parameters associated with centric occlusion and eccentric movements. The T-scan III system consists of a foil/sensor, bite-fork (with small and large options), holding part, and software [Figures 2 and 3]. Each foil/ sensor is 0.06–1-mm thick; there are approximately 1300– 1500 sensors on the system that can detect even the smallest force. On connecting the device to the computer, the data received by the sensor can be evaluated during the recording and saved for subsequent analysis. This diagnostic device is compatible with Microsoft Windows (Microsoft Corp. USA) and requires a standard Intel processor computer and a minimum of 1 GB RAM. The G * Power (G * Power Ver.3.0.10, Kiel, Germany) package program was used to determine the number of individuals to be included in the study. In our study, for a power >80%, at least 15 patients were required in each group to achieve a significance level of α = 0.05. All statistical analyses were performed using the Statistical Package for the Social Sciences (SPSS) 22.00 (SPSS Inc., Chicago, IL, USA) for Windows. For each parameter, a normal value was determined using the arithmetic mean of all the values obtained. The Wilcoxon test was used to compare the qualitative data. The results were evaluated using a 95% confidence interval and a significance level of P < 0.05. The distribution of the data was evaluated using the Shapiro–Wilk test. Since the quantitative data did not show a normal distribution in the comparison between the periods, they were evaluated using the Friedman test.

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Figure 1:

(a and b) Joint vibration analysis record.

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Figure 2:

Tscan analysis record.

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Figure 3:

Screenshot of force/timeline, two-dimensional, and three-dimensional graph of maximum occlusal force recording taken.

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RESULTS

Descriptive statistics regarding the mean age and total duration of the treatment of the individuals included in the study are shown in [Table 1]. As shown in the table, the mean treatment period of 43 individuals included in the study was 13.08 ± 0.50 years (months), and their mean age was 16.22 ± 3.45 years [Table 1]. As a result of the comparison of the number of occlusal contact points at maximum intercuspidation between the beginning of treatment and the ^6th and 12^th months in individuals treated with and without extraction treatment: The increase in the number of posterior regions occlusal contact points is P < 0.001, the increase in the number of anterior regions occlusal contact points is P < 0.05, and the increase in the total number of occlusal contact points was statistically significant at the P < 0.001 level. As a result of the comparison between the 6^th and 12^th months, it was determined that there was no statistically significant difference in terms of the number of anterior occlusal contact points, the number of posterior occlusal contact points, and the total number of occlusal contact points [Table 2]. As a result of the comparison of the occlusal force distributions of the right anterior, right posterior, left anterior, and left posterior quadrant at maximum intercuspidation between the beginning of the treatment and the 6^th and 12^th months in fixed orthodontic treatment, it was observed that there was no statistically significant difference [Table 3]. As a result of the comparison of the occlusal force distributions of the right half-jaw and the left half jaw at maximum intercuspidation between the beginning of the treatment and the 6^th and 12^th months, it was observed that there was no statistically significant difference in the individuals who received treatment with and without extraction [Table 4]. As a result of the comparison of the force distributions of the right working and non-working side observed during lateral movements in individuals receiving treatment with and without extraction, there was no statistically significant difference between the beginning of the treatment and the 6^th and 12^th months. Likewise, when the force distributions of the left working and non-working sides were compared between the beginning of the treatment and the 6^th and 12^th months, it was seen that there was no statistically significant difference [Table 5]. As a result of the comparison of the occlusion time between the beginning of the treatment and the 6^th and 12^th months in individuals treated with and without extraction, it was seen that there was no statistically significant difference. In addition, as a result of the comparison of the disclusion time determined for the right and left sides between the beginning of the treatment and the 6^th and 12^th months, it was seen that there was no statistically significant difference [Table 6]. There was no significant difference between the left and right sides (total integral, integral 300 Hz, and Ratio) P > 0.05 [Figure 4].

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Figure 4:

Joint vibration analysis diagram.

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DISCUSSION

In orthodontic treatments, tooth extraction is a method frequently implemented by orthodontists to make space in cases with excessive space restriction in the jaw. Providing three-dimensional control during the retraction of canines in extraction treatments is of great importance for the stability of orthodontic treatment.^[16] Therefore, success in orthodontic treatments depends on the treatment mechanics as well as a good treatment plan. In our study, there was a significant increase in the number of posterior, anterior, and total contact points in the individuals who underwent fixed orthodontic treatment (with and without extraction) between T0, T1, and T2. There is a lack of studies in the literature regarding the changes in occlusion analysis values of the number of contact points before and after individuals’ orthognathic surgery, with and without fixed orthodontic treatment.^[17-19] In our study, the distribution of forces in the teeth varied between 0% and 40%, and the greatest force was concentrated on the first molars, followed by the second molars and first premolars, respectively. The lateral incisors were subjected to the least amount of force. Okeson^[20] has stated that occlusal forces are affected by several factors such as age, sex, skeletal morphology, and malocclusion and that the first molars are subjected to the greatest force during chewing. Qadeer et al.^[6] compared the occlusal strength parameters in 25 individuals with Angle class I relationship with and without orthodontic treatment using T-Scan III, and in both groups, the largest amount of force was concentrated on the second molars, followed by the first molars and second premolars, respectively. They reported the lateral incisors being subjected to lesser forces. They also stated that the distribution of forces on the teeth within the arch varied between 0% and 35%. These findings correspond to the results of our study. In our study, there was no significant change between T0 and T1 in terms of force per tooth. Moreover, the occlusal forces were distributed equally in the right and left jaws, and there was no significant change in the occlusal force distribution in the right and left jaws between T0 and T1. In another study, the occlusal forces observed in the right and left hemispheres demonstrated a balanced distribution not exceeding 50% for one side.^[21] The findings in these studies are consistent with the results of our research. In another study conducted by Giray and Sadry using T-Scan, JVA, and JT, the 6-month result of the study performed in 43 experimental groups did not find any findings that would raise the suspicion of temporomandibular disorder (TMD), and it was observed that the duration of disclusions was shortened. However, at the end of the study, it is recommended to check the JVA values with occlusion analysis at the beginning and the end of orthodontic treatments.^[8] They also recommend that these studies be conducted by researchers for a longer period and with more individuals. However, the higher number of cases in this study shows a difference from the results of the study conducted by Giray and Sadry.^[17] The study, which was conducted for 6 months or less, and this study, which covered 12 months, was conducted in the same clinic, but independently with different duration and individuals. Therefore, although the working environment and the test material used and the study results are very similar, the differences in the working process suggest that there may be changes in the quality of orthodontic treatment. However, the similarities in the results are quite striking. In the study conducted by Henrikson et al.,^[22] orthodontic treatments with and without extraction were considered important in terms of the prevalence of TMD, and it was stated that the changes in occlusion during orthodontic treatment may have an important role in terms of TMD. In our study, even though there was no significant difference between the duration of disclusion and occlusion, as Henrikson et al. have stated, group-based changes should be approached more protectively in terms of TMD.^[22] Considering the results of our study, it was determined that the occlusal force distributions observed in the right anterior, left anterior, right posterior, and left posterior quadrants, and right and left hemi-jaws in the treatment group at T0,T1, and T2 were similar to those of the individuals with Angle class I relationship (non-extraction group). Studies have reported that in healthy individuals, the incidence of group-function occlusion is higher than that of canine-sparing occlusion.^[23] Moreover, it has been stated that the non-working side contacts observed in individuals who have undergone orthodontic treatment are similar to those of healthy individuals who have not undergone treatment, with a higher incidence of group function occlusion pattern in the former, compared to canine-protected occlusion.^[24] There is no previous study in the literature investigating the change in the distribution of forces on the working and non-working sides during fixed orthodontic treatment in individuals with extraction cases.^[25] In our study, no statistically significant difference was observed in the non-extraction group between T0, T1, and T2 in terms of force distribution on the working and non-working sides. The time from the first tooth contact to maximum intercuspation during the closing movement is defined as the occlusion time.^[26] In our study, it was observed that the occlusion time was 0.33±0.35, 0.28±0.15 ve 0.32±0.20 0.18 s in the T2 time. In addition, no statistically significant difference was observed between the extraction group at T0, T1, and T2, and the non-extraction group, in terms of the occlusion times. A longer occlusion time (ideal occlusion time is desired to be <0.2 s) indicates the presence of premature contact during closure and negatively affects occlusal stability.^[11,15] In contrast, Qadeer et al.^[6] have stated that the average occlusion time was 0.38 s in individuals who underwent orthodontic treatment and 0.41 s in individuals who did not undergo orthodontic treatment. These results are consistent with the results of our research. In a study evaluating the relationship between the duration of disclusion and the maximum bite force, it was reported that greater bite forces were observed in individuals whose disclusion duration was reduced to <0.5 s.^[12] In our study, no statistically significant difference was observed in the treatment group between T0 (with and without extraction) and T1 in terms of disclusion times. Based on the results of our study, the period of disclusion was longer than normal in individuals who underwent orthodontic treatment. Kerstein and Radke^[27] have reported that the presence of group function contacts on the working side prolongs the disclusion time. Hence, the observation of group function occlusion pattern in the individuals included in our study was a factor of prolonged disclusion time. When evaluated together with the results of our study, this research shows that canine-sparing occlusion can protect the person from developing TMJ. Our result is supported by some studies. Some other studies have reported that occlusal guidance does not affect TMJ disorders. Butler et al.^[28] found no relationship between lateral occlusal guidance and joint sounds and muscle tenderness in their study with 56 patients. Roberts et al.^[29] compared individuals with disc displacement and normal disc position and found no difference in terms of occlusal guidance. Runge et al.^[30] evaluated the relationship between joint sounds and occlusion in their study on 226 pre-orthodontic individuals. They did not find any relationship between working or non-working side contacts and joint sounds. The most striking result obtained with T-Scan is Qadeer et al.^[6] and the fact that the number of cases studied in this study is much higher, and the inclusion of the control group in the timeline supports the robustness of this result. It was evaluated as what caused it. However, the high significance of the results obtained with JT in all comparisons (P < 0.001) indicates that the reason for the changes in the chewing pattern during orthodontic treatment may be orthodontic treatment and supports the study by Kerstein and Radke.^[31] Another factor that draws attention to all three methods is that the increase in the frequency values of the chewing pattern and TMJ sounds in the 6^th month of orthodontic treatment changes significantly and positively in the 12^th month of the treatment. This shows that orthodontic treatments are the most risky period in terms of deterioration in the joint around the 6^th month.

CONCLUSION

It was observed that the number of occlusal contact points increased in the first 12 months during extraction fixed orthodontics and in individuals who received non-extraction treatment, at the beginning of the treatment and the 6^th and 12^th months; occlusal force distribution for each tooth region, occlusal force distribution for the right anterior, right posterior, left anterior and left posterior quadrants, and occlusal force distribution for the right half jaw and left half jaw, force distribution for the working and non-working sides in lateral movements, occlusion, and disclusion. There was no significant change in the parameters of the occlusal time parameters, the occlusal force distributions in the right and left half jaws were symmetrical, the right and left disclusion times were longer than the normal values, the group function occlusion pattern was observed, and the force distributions formed on the working and non-working sides in these individuals were similar to individuals with natural dentition. It has been determined that the T-scan III system is a useful clinical tool in the evaluation of occlusion during orthodontic treatment.