Dental Department, Dr. KNS Memorial Institute of Medical Sciences, Barabanki, Uttar Pradesh, India
Address for correspondence: Dr. Isha Rastogi, Dental Department, Dr. KNS Memorial Institute of Medical Sciences, Barabanki, Uttar Pradesh, India E-mail: excellent123@gmail.com
Submitted: 11-Jan-2023
Accepted in Revised Form: 27-Nov-2023
Published: 03-Apr-2024
DOI: 10.4103/sidj.sidj_4_23
Saint Int Dent J 2023;7:47-50.
Copyright: © 2024 The Saint's International Dental Journal
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This article was originally published by Wolters Kluwer Medknow Publications & Media Pvt Ltd and has now been officially transferred to Society of Dental Research & Education due to a change in publishing entity.
Background: Successful denture fitting depends on three key factors: retention, stability, and support. While creating a denture for the upper jaw is relatively easy, the lower jaw presents more challenges due to greater issues with retention and stability. This is because dentures tend to move around relative to the underlying bone during use. To address this problem, a customized tool (an impression and cast) was used in a study to measure the depth of the retromylohyoid fossa.
Purpose: The purpose of this study was to analyze the type of tongue and depth of the retromylohyoid fossa using an impression and cast.
Materials and Methods: This study was conducted in the department of prosthodontics, where all patients received regular check-ups and dental treatments. The retromylohyoid fossa(extension) and tongue were examined in a sample of 500 patients aged between 20 and 50 years, and impressions were taken.
Results: The measurements were recorded, and the depth of the retromylohyoid fossa was assessed. The tongue was also studied.
Conclusion: This retromylohyoid fossa and tongue are a suspense itself, and our method is just a suggestion for the mandibular denture prosthesis success.
Keywords: Denture, mandible, retromylohyoid fossa, tongue
Although the process of creating dentures and prostheses may seem simple, it is actually a complex task. This is especially true when a dentist is making mandible dentures, where the tongue plays a critical role. In such cases, various factors such as retention, stability, and support based on based on Devan’s principles of preservation become crucial. Additionally, the distolingual flange must be positioned correctly in the retro mylohyoid fossa, with the appropriate thickness and length to achieve an adequate peripheral and border seal.[1,2] The retromylohyoid fossa, also known as the lateral throat form, is located at the most distal point of the alveololingual sulcus.[3] Muscular forces and the tongue can hinder swallowing, chewing, talking, retention, and stability, making it essential for dentists to consider intraoral anatomy before complete denture fabrication.[4,5] Although complete dentures have been used for centuries, mandibular dentures can still pose challenges for both dentists and patients.[6] This is due to the comparatively small 14 cm2 mandibular denture bearing area, which is <24 cm2 maxillary denture bearing area and affects the stability and retention.[7,8] Over-trimming the lingual borders can cause discomfort for patients, and it is important to prepare the proper length of the lateral throat form in the preimpression stage.[9,10]
The study was conducted in a dental hospital and evaluated 500 dentulous patients aged 20-50. The inclusion criteria were based on visible, easily recognized retromolar pads, second permanent molars, and adequate mouth opening without inflammation or surgical defects/abnormalities. Only patients who were willing to cooperate were considered for the study. Initially, the mirror method, according to Neil’s classification, was used to determine the movement of the tongue. The maximum tongue protrusion length was measured, and subsequently, the mandible was imaged using alginate in the mandibular tray with Rim-Lok. An impression made using dental stone was then used to obtain a cast. The dimensions of the cast were evaluated in the vertical and horizontal planes using a scale and divider, respectively, from the distal end of the last permanent tooth to the greatest depth of the distolingual vestibule and from the middlemost point to the end of the retromolar pad.
To obtain accurate impressions for mandibular dentures, it’s crucial to select the right stock tray based on the exact depth and shape of the lateral throat.[11] This will result in a custom tray that is well-fitted, providing proper extensions, which in turn offers better stability and retention for the final denture. It’s worth noting that the mylohyoid muscle extends approximately 1 cm distally at the mylohyoid ridge, which can prevent the denture from locking against the bone in the retro mylohyoid region.
The tongue can be categorized based on its degree of activity. According to Barnett Kessler, there are four types of tongues: occupational, still, normal, and habitual. An occupational tongue is present in individuals such as teachers, lecturers, and musicians, while a still or passive tongue is present in individuals with limited tongue activity due to injury or ankyloglossia. The best tongue for prosthodontists is considered normal, with regular movement and function. A habitual tongue is caused by habits that lead to powerful movements that can dislodge dentures.[12-15] During clinical examinations, the tongue is inspected by asking patients to open their mouths wide for small portions of food. The tongue is considered the fastest-acting and most accurate muscular organ in the body.
By the mirror method, Class I was the maximum, then Class II. Of the tongue, normal and occupational were the most, followed by habitual tongue.
The patients in the study were divided into two groups based on their gender: male (M) and female (F), as shown in Tables 1 and 2. Among the male group, there were 115 patients aged between 20 and 35 years and 121 patients aged between 36 and 50 years. Similarly, among the female group, there were 160 patients aged between 20 and 35 years and 104 patients aged between 36 and 50 years.
Table 1. Age and frequency
| Age (years) | Frequency |
|---|---|
| 20-35 | 275 |
| 36-50 | 225 |
| Total | 500 |
Table 2. Variables showing gender and age
| Age (years) | Male | Female | Total |
|---|---|---|---|
| 20-35 | 115 | 160 | 275 |
| 36-50 | 121 | 104 | 225 |
| Total | 236 | 264 | 500 |
According to Table 3, there were a total of 262 cases of Class I, 158 cases of Class II, and 80 cases of Class III on the left side of the mouth. This translates to 52.4%, 31.6%, and 16%, respectively, for each class. On the right side, there were 271 cases of Class I, 162 cases of Class II, and 67 cases of Class III. This translates to 54.4%, 35.6%, and 10%, respectively, for each class.
Table 3. Vertical dimension-on cast
| Clinical type (mm) | Cast vertical dimensions extraoral | |
|---|---|---|
| Left | Right | |
| 15-20 | 262 | 271 |
| 10-14 | 158 | 162 |
| 5-9 | 80 | 67 |
According to Tables 2 and 3, there were 262 cases in Class I, 158 cases in Class II, and 80 cases in Class III, which represent 52.4%, 31.6%, and 16% respectively. The average vertical dimension on the left side was 12.86 mm, 8.45 mm, and 6.50 mm for Class I, Class II, and Class III, respectively. The standard deviations for the three classes were 2.349, 0.497, and 0.577, respectively. On the left side, the average horizontal dimensions were 290.55 mm, 192.15 mm, and 61.88 mm for Class I, Class II, and Class III, respectively. The standard deviations were 16.87 for Class I, 17.80 for Class II, and 5.32 for Class III.
In Tables 4 and 5, it was observed that there were 262 cases in Class I, 158 cases in Class II, and 80 cases in Class III, accounting for 52.4%, 31.6%, and 16%, respectively. On the left side, the mean vertical dimension was 12.86 mm in Class I, 8.45 mm in Class II, and 6.50 mm in Class III. The standard deviation for these dimensions was 2.349, 0.497, and 0.577 respectively. Similarly, the mean horizontal dimension on the left side was 201.00 mm in Class I, 170.83 mm in Class II, and 59.12 mm in Class III. The standard deviation for these dimensions was 13.87, 8.93, and 4.93 respectively for the three classes.
Table 4. Association between clinical type and vertical dimension-on cast (left side) (n=500)
| Clinical type (mm) | Number of cases | Percentage of total | Mean | SD |
|---|---|---|---|---|
| I (15-20) | 262 | 52.4 | 290.55 | 16.87 |
| II (10-14) | 158 | 31.6 | 192.15 | 7.80 |
| III (5-9) | 80 | 16 | 61.88 | 5.32 |
Table 5. Association between clinical type and vertical dimension-on cast (right side) (n=500)
| Clinical type (mm) | Number of cases | Percentage of total | Mean | SD |
|---|---|---|---|---|
| I (15-20) | 272 | 54.4 | 287.47 | 13.87 |
| II (10-14) | 178 | 35.6 | 190.82 | 4.58 |
| III (5-9) | 50 | 10 | 59.12 | 7.17 |
The area behind the lower back teeth, known as the retromylohyoid fossa, has a long and thick flange due to the adjacent structures and their activity.[16] However, this region is often neglected in the construction of lower complete dentures. Extending the denture into this area can prevent the tongue from moving back to the polished surface of the denture and improve neuromuscular control. The retromylohyoid fossa is located behind the retromolar pad, and its depth can be classified by Neil as Class I deep, Class II moderate, or Class III shallow.[17-19] The most posterior part of the alveololingual sulcus is called the retromylohyoid fossa. For proper retention, it is important that the border molding allows for proper muscular function in the inferior portion of the fossa. Moreover, W.R. Laney expanded on Neil’s lateral throat form. The tongue is a multifunctional muscle that is involved in speech, swallowing, and chewing. Loss of occlusal support can cause complex tongue-tip motion, leading to tongue movement complexity.
Our study revealed that 275 individuals aged between 20 and 35 years (115 males and 160 females) and 225 individuals aged between 36 and 50 years (121 males and 104 females) were present. The vertical dimension on the cast’s left side had a maximum range of 262, a medium range of 158, and a minimum range of 80. On the right side, the maximum dimension was 271, the medium was 162, and the minimum was 67. The maximum horizontal dimension on the cast’s left side was 272, the medium was 178, and the minimum was 100 [Tables 6–8]. The value of Class 1 was maximum, followed by Class II and Class III, as the patient is in the younger age group 1, 22. We observed that the lateral throat form in the patient’s mouth was more than in their dentures, with a count of 17. We also found that the mandibular complete denture border extensions in the lateral throat form were shorter than the space available, with a count of 18. We consistently observed that Class I had more results, and the horizontal dimensions were proportional to the vertical dimensions. It was observed that there were more differences between the right and left sides in Classes I and II, as it was more common. However, there were fewer differences between the left and right sides in Class III, as it is rare and least common. Edentulism is a condition in which a person has no teeth, which may occur due to various factors such as dental attendance, educational levels, income, oral hygiene, biological and patient-related factors. Although complete edentulism has decreased in developed countries, a significant proportion of the elderly population still suffer from this condition. The percentage of the senior population suffering from complete edentulism ranges from 15% to 54%.
Table 6. Horizontal dimension-on cast
| Clinical type (mm) | Cost horizontal dimensions extraoral | |
|---|---|---|
| Left | Right | |
| 15-20 | 218 | 272 |
| 10-14 | 169 | 178 |
| 5-9 | 113 | 100 |
Table 7. Association between clinical type and horizontal dimension-on cast (left side) (n=500)
| Clinical type (mm) | Number of cases | Percentage of total | Mean | SD |
|---|---|---|---|---|
| I (15-20) | 218 | 43.6 | 201.00 | 13.87 |
| II (10-14) | 169 | 33.8 | 170.83 | 8.93 |
| III (5-9) | 113 | 22.6 | 59.12 | 4.93 |
Table 8. Association between clinical type and horizontal dimension-on cast (right side) (n=500)
| Clinical type (mm) | Number of cases | Percentage of total | Mean | SD |
|---|---|---|---|---|
| I (15-20) | 272 | 54.4 | 184.61 | 84.68 |
| II (10-14) | 178 | 35.6 | 169.16 | 5.87 |
| III (5-9) | 50 | 10 | 83.17 | 3.28 |
For a prosthodontist, the region responsible for the peripheral seal and success of mandibular complete denture is important due to the following:
The extension of denture borders, both horizontally and vertically, is more in Class I and II rather than Class III
The dimensions in the vertical and horizontal planes correspond to each other. It was observed that the normal occupational tongue was more prevalent than the habitual one
When the tongue is normal, occupational, and has a lateral throat form of type 1 or 2, the cast dimensions are all interconnected.
Patients with oral submucous fibrosis and trismus
Temporomandibular disorders and degenerative conditions of the patients
A more reliable technique to be developed
Tongue movement and function sometimes need more precision while recording
Requiring multiple visits and high laboratory expenses.
Nil.
There are no conflicts of interest.
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