ORIGINAL RESEARCH

https://doi.org/10.5005/jp-journals-10019-1400
International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 2 | Year 2023

Categorization of Extremely Resorbed Mandibular Edentulous Ridges and Formulation of Edentulous Stock Trays Conforming to Different Resorbed Ridge Forms: An Observational Study

Neha Verma¹ https://orcid.org/0000-0002-3174-1026, Shefali Singla² https://orcid.org/0000-0002-1443-6054, Komal Sehgal³, Puneet Sahore⁴ https://orcid.org/0000-0003-0051-0695, Lalit Kumar⁵, Manisha Khanna⁶ https://orcid.org/0000-0001-6837-885X

^1-6Department of Prosthodontics, Dr Harvansh Singh Judge Institute of Dental Sciences & Hospital, Panjab University, Chandigarh, Punjab, India

Corresponding Author: Shefali Singla, Department of Prosthodontics, Dr Harvansh Singh Judge Institute of Dental Sciences & Hospital, Panjab University, Chandigarh, Punjab, India, Phone: +91 9417194185, e-mail: shefali_singla@yahoo.com

Received on: 27 April 2023; Accepted on: 20 May 2023; Published on: 28 June 2023

ABSTRACT

Purpose: Commercially available stock trays do not usually fit the arch form and are relatively flat in dimensions, leading to a compromised impression and prosthesis. So, the purpose of this study was to categorize resorbed mandibular ridges according to arch width and sulcus depth and formulation of stock tray design conforming to different resorbed ridge forms.

Materials and methods: Measurements on master casts of completely edentulous resorbed ridges (n = 280) were done using a digital vernier caliper. Cluster analysis of means of anterior and posterior arch width and posterior alveololingual sulcus (ALS) depth was done to categorize the extremely resorbed residual ridges for the formulation of conforming stock trays. Cluster analysis formulated three categories. Category 1 had a mean anterior arch width of 23 mm, posterior arch width of 50 mm, and posterior ALS depth of 5.5 mm. Respective dimensions in category 2 were 31, 58, and 12 mm, and in category 3 were 27, 55, and 8.7 mm. Means of arch length, ridge width, sulcus depth, and retromolar pad (RMP) angle were used to modify tray flange dimensions. One-way analysis of variance (ANOVA) for K-means and multiple Tukey honestly significant difference (HSD) tests were applied for validation of clusters/categories.

Results: Significant p-values in one-way ANOVA for K-means cluster (p < 0.001) and multiple Tukey HSD test (p < 0.001) validated categorization of extremely resorbed mandibular residual ridges in the study. Mean values of other parameters were used to modify the tray flanges. The 135° angle of the RMP with residual resorbed ridge was suggested to be incorporated in trays to accommodate higher angles too.

Conclusion: Use of the formulated stock trays, will improve their adaptation to the resorbed mandibular edentulous ridges and hence the primary impression making, which will provide a strong foundation for a successful final complete denture in such patients.

How to cite this article: Verma N, Singla S, Sehgal K, et al. Categorization of Extremely Resorbed Mandibular Edentulous Ridges and Formulation of Edentulous Stock Trays Conforming to Different Resorbed Ridge Forms: An Observational Study. Int J Prosthodont Restor Dent 2023;13(2):70-75.

Source of support: Nil

Conflict of interest: None

Keywords: Angle of retromolar pad, Edentulous mandibular arch, Edentulous stock trays, Laboratory research, Lingual flange, Resorbed residual ridges

INTRODUCTION

After tooth extraction, the remaining alveolar process forms the residual ridge that resorbs unevenly, resulting in a gradual change in shape and height of the ridges often leading to diminished quantity and quality of the residual ridge.¹^-⁴ After resorption, the maxillary ridge is palatal to the original teeth position while the mandibular ridge flattens and widens and is buccal to the natural teeth position.⁵

Tallgren⁶ reported that maximum bone loss is seen in the 1st year of extraction. The mandibular resorption rate is four times more than the maxilla, further compromising the already smaller mandibular denture-bearing area. This resorption is further accentuated with age and various anatomic, functional, prosthetic, and metabolic factors.⁷^,⁸ Due to extreme residual ridge resorption, there is significantly reduced surface area, transformed facial esthetics, the altered vertical dimension of occlusion, and an interarch relationship. Compromised retention, stability, and support in such ridges make it difficult to deliver good functional, and stable dental prostheses.⁹^,¹⁰

According to Levin,¹¹ the first step in complete denture fabrication is diagnostic impression with an appropriately fitting stock tray, to form a primary cast that records the correct borders, and anatomic landmarks so as to record maximum basal seat area within the functional limits. Digital intraoral scans have the limitation of high equipment cost and unavailability.¹²^,¹⁵ Impression making and fabrication of successful dentures over flat ridges is a challenging task, especially with the commercially available stock trays which rarely fit all ridges without tissue distortion. The available stock trays are very shallow, have negligible flange depth, and have the same plane throughout, which doesn’t conform to the arch form and anatomy of the residual resorbed mandibular ridges which become wider with a shallow sulcus after resorption of lingual plates.¹¹^,¹⁶ This necessitates the formulation of special stock trays conforming to the extremely resorbed ridges.

This study was conducted to identify the flat mandibular ridge cases amongst the edentulous population and to assess the size of edentulous ridges in terms of length, width, depth, and angle that the RMP makes with the crest of the ridge. The purpose of this study was to categorize flat ridge cases according to their arch width and sulcus depth so as to formulate stock tray designs conforming to different flat ridge forms. The null hypothesis was that arch width and sulcus depth of extremely resorbed ridges do not differ significantly.

MATERIALS AND METHODS

This observational study was conducted in the Department of Prosthodontics, Dr. Harvansh Singh Judge Institute of Dental Sciences & Hospital, Panjab University, Chandigarh, India. The study protocol was approved by Institutional Ethics Committee (No. PUIEC201210 - 1 - 002).

A sample size of 280 was calculated based on the formula, sample size (n) = [(z1–α/2) 2 *p*(1 - p)]/δ 2, where the prevalence of target population p = 0.763, δ (precision) = 0.05 (5%), type I error (α) = 5% and z1–α/2 = 1.96. Using the measured values, the sample size required is 280. Participants included 173 males and 107 females, in the age range of 41–91 years to eliminate gender and age bias. Further, only edentulous patients falling under Atwood’s orders IV, V, and VI were included. Patients with unhealed extraction sockets or recent extractions, neuromuscular disorder patients, patients with partially edentulous mandible, and patients with a history of maxillofacial trauma and mandibular fracture were excluded. Informed consent of all patients was taken before the study.

A standard protocol of recording the initial impression using impression compound (Maarc impression composition, Maarc dental, Palghar, India) and the final impression using zinc-oxide eugenol impression material (DPI Impression Paste, DPI, Mumbai, India) in a custom tray modified with green stick compound, was followed and working master casts were poured in type III dental stone (Kalstone, Kalabhai, Mumbai, India) and used for the measurements.

The following measurements were made on the master casts by the same operator using a digital vernier caliper for standardization.

Posterior arch width (arch width RMP) is the distance between the anterior-most point of RMP bilaterally (Fig. 1A).¹⁷
Anterior arch width (arch width CE) is the distance between the distal end of canines bilaterally (Fig. 1B).
Depth of the sulcus in the posterior region is the depth of the lingual (ALS M) and buccal vestibule molar (BVM) in the molar regions on both sides (Fig. 1C).
The arch length was measured from the midpoint in the incisor region of the edentulous ridge to the center point of intersection on the line joining the anterior-most points of the RMPs on both sides (Fig. 1D).¹⁷
The angle that RMP makes to the residual ridge (RMP Angle)—the blue line was marked over the RMP and the red line on the crest of the distal ridge joined with the RMP (Fig. 1E). The angle formed by these colored lines was measured using protractor, keeping it at the eye level (Fig. 1E).
Depth of the sulcus in the anterior region as deepest points in the canine region on both sides in the BV canine eminence (CE) and ALS CE using a UNC-15 Probe (Fig. 1F).
The anterior width of the ridge was measured from the labial to lingual sulcus depth in the canine region (Fig. 1G).
The posterior width of the ridge was measured from labial to lingual sulcus depth in the molar region (Fig. 1H).
The anterior and posterior arch width and the posterior ALS depth were taken as the three primary parameters to categorize the stock trays.

Figs 1A to H: (A) Posterior arch width; (B) Anterior arch width; (C) Depth of posterior ALS; (D) Arch length; (E) Angle that RMP makes to the residual ridge; (F) Depth of sulcus in the anterior region; (G) Anterior ridge width; (H) Posterior ridge width

The excessive residual ridge resorption causes the widening of the edentulous arches, which need to be recorded and accommodated in the tray dimensions. Also, the posterior ALS depth is variable in cases with extreme ridge resorption. The currently available metal stock trays have shallow, almost nonexistent flanges, especially in the posterior lingual region. So, recording of this entity should be done from the primary impression itself, which needs a suitable stock tray. The data was collected and analyzed using Statistical Package for the Social Sciences (SPSS) software (IBM Corp. Released 2015. IBM SPSS Statistics for Windows, version 23.0. Armonk, New York: IBM Corp). Cluster analysis was done for the formation of clusters/categories. One-way ANOVA for K-means and multiple Tukey HSD tests was applied for the validation of clusters/categories.

RESULTS

The present study reported a mean anterior arch width of 26.31 ± 3.44 mm, posterior arch width of 53.68 ± 3.68 mm, and posterior lingual sulcus depth of 8.00 ± 2.78 mm. The cluster analysis sorted the data into three categories (Table 1).

**Table 1:** Overall range and mean values of each category that formed the clusters
Variable	Overall range (280 subjects) (mm)	Category 1 (118 subjects)		Category 2 (46 subjects)		Category 3 (116 subjects)
Variable	Overall range (280 subjects) (mm)	Range (mm)	Mean ± standard deviation (mm)	Range (mm)	Mean ± standard deviation (mm)	Range (mm)	Mean ± standard deviation (mm)
Anterior arch width (mm)	18.00–39.00	18.00–25.00	23.13 ± 1.68	29.50– 39.00	31.46 ± 2.22	25.50–29.50	27.50 ± 1.2
Posterior arch width (mm)	36.00–65.00	36.0–53.00	50.4 ± 2.71	57.00–65.00	58.8 ± 1.62	53.00–57.00	55.0 ± 1.02
Sulcus depth—ALS molar (mm)	1.00–20.00	1.00–7.00	5.51 ± 1.26	11.00–20.00	12.55 ± 1.67	7.00–10.50	8.72 ± 0.95

One-way ANOVA for K-means clustering applied for the comparison of clusters gave statistically significant differences (p < 0.001) in the three categories of resorbed ridges formed in the present study. Figure 2 represents significantly different Z-scores of the three clusters formed.

Fig. 2: Graphical representation of Z-scores of the three clusters

On multiple comparisons of the individual variables within the three categories using the Tukey HSD test (Table 2), three clusters/categories were found significantly different from each other in terms of all three variables.

**Table 2:** Multiple comparisons by Tukey HSD test for intervariable comparison between three clusters at 95% confidence interval
Cluster		Posterior arch width (mm)		Anterior arch width (mm)		Sulcus depth—ALS molar (mm)
Cluster		Mean difference	p-value	Mean difference	p-value	Mean difference	p-value
1	2	−8.40604	0.001*	−8.32940	0.001*	−7.04587	0.001*
1	3	−4.59738	0.001*	−4.36857	0.001*	−3.21566	0.001*
2	1	8.40604	0.001*	8.32940	0.001*	7.04587	0.001*
2	3	3.80866	0.001*	3.96083	0.001*	3.83021	0.001*
3	1	4.59738	0.001*	4.36857	0.001*	3.21566	0.001*
3	2	−3.80866	0.001*	3.96083	0.001*	−3.83021	0.001*

Level of significance at p < 0.05, *indicates statistically significant

Further application of Kolmogorov–Smirnov and Shapiro–Wilk tests gave significant p-values (p < 0.001) showing that the data in each cluster was normally distributed (Figs 3A to C).

Figs 3A to C: (A) Normal Q–Q plot for posterior arch width for the three categories; (B) Normal Q–Q plot for anterior arch width for the three categories; (C) Normal Q–Q plot for anterior arch width for the three categories

To standardize the rest of the variables for the fabrication of trays, the range, and means of all other study variables, were tabulated after the removal of the outlier values (Table 3).

**Table 3:** Mean values of each category that formed stock trays
Variable	Range (mm)	Mean (mm)
Arch length	24–51	34.6 ± 4.9
Sulcus depth ALS CE*	1.5–11.5	6.3 ± 0.8
Sulcus depth BV M**	0–6.5	3.14 ± 1.5
Sulcus depth BV CE***	0–8	4.4 ± 1.8
Ridge width anterior	6.5–15	10.76 ± 2
Ridge width posterior	7.5–17.5	12.7 ± 2.4
Angle (degrees)	135–175^°	154^° ± 9.4

*ALS CE, alveololingual sulcus canine eminence; **BV M, buccal vestibule molar; ***BV CE, buccal vestibule canine eminence

The mean values of these parameters can be used for the tray flange dimensions. The mean value of the angle that the RMP makes with the crest of the ridge was 154° with a range of 135–175°. The study suggests the use of a 135° angle in clinical trays so as to accommodate all the higher angle values too.

The mean values of the three main study parameters of posterior arch width, anterior arch width, and depth of the ALS in the posterior region were found to be significantly different for the three clusters/categories of the resorbed mandibular arch, established in this study. The three categories formed were utilized for designing mandibular stock trays for more accurate and easy recording of mandibular resorbed residual ridges (Fig. 4).

Fig. 4: Formulated trays in categories 1, 2, and 3

DISCUSSION

The resorbed ridges compromise complete denture adaptation and stability and consequently may lead to more alveolar bone loss. But with proper prosthetic measures, instability of the mandibular dentures can be prevented. A correctly made preliminary impression is the keyway to the success of the final complete denture, which requires stock trays with adequate coverage and form.⁶

Commercially available stock trays don’t usually fit the mandibular arch form and do not cover the arch length and sulcus depth properly, leading to a compromised impression, especially in the extremely resorbed mandibular edentulous ridges, which jeopardizes the final prognosis. The need for stock trays conforming to flat ridges is all the more important because of their already compromised prognosis.¹⁸^-²⁰ The present study assessed 280 extremely resorbed mandibular edentulous ridges based on the parameters like anterior and posterior arch width and sulcus depth in the posterior ALS. Wide range of these parameters mandated cluster analysis so as to formulate stock trays. Significant p-values in one-way ANOVA for K-means clustering and the multiple Tukey HSD test validated the three clusters as significantly different. Anterior arch width, posterior arch width, and posterior ALS were found to be significantly different in patients, thus, the null hypothesis was rejected.

Other parameters evaluated bilaterally were anterior and posterior ridge width, anterior buccal as well as lingual sulcus depth, and angle that RMP makes with a residual alveolar ridge to modify tray flange dimensions as well. Measurement points used to measure arch width, length, and sulcus depth in the present study are similar to previous studies.⁵^,¹⁷^-²² Ryu et al.²³ used the posterior end of RMP for measuring the arch length and reported a mean arch length of 56.03 ± 4.04 mm, whereas the mean arch length reported in the present study was 34.6 ± 4.9 mm. This can be attributed to the use of the anterior end of the RMP for measuring arch length.¹⁷

Pietrokovski et al.,¹⁷ reported mandibular arch length ranging from 45–48 mm and posterior arch width from 39–60 mm. The arch length (24–51 mm) and posterior arch width (36–65 mm). The present study is similar to that reported by Pietrokovski et al.¹⁷ but with a lesser lower limit. This may be because only extremely resorbed ridges covered under Atwood’s orders IV, V, and VI were evaluated in the present study and hence had lesser dimensions. Pietrokovski et al.¹⁷ categorized both the arches into small, medium, and large based on the arch length and posterior arch width using the formula size = posterior arch width × 100 ÷ arch length. This size categorization did not include ridge height, anterior arch width, and critical depth of the ALS in the posterior region, which was included in the present study for the formulation of tray dimensions.

Ahmed²¹ reported mandibular arch length in the range of 25.60–39.81 mm and posterior arch width as 43.76–56.00 mm, measured in dentulous subjects. The narrow width range reported by the authors can be explained on account of dentulous subjects. Since the mandibular arch widens with resorption, the arch width range in the present study was found wider than in dentulous subjects and this fact needs to be taken into consideration while designing trays for resorbed ridges.

Ryu et al.²³ studied the size of edentulous ridges to modify stock trays for elderly edentulous Japanese patients. They reported mean mandibular posterior width of 57.33 ± 3.2 mm and an arch length of 56.03 ± 4.04 mm. The arch length was measured from the center of the anterior ridge crest to the center of RMP on either side and hence was higher than observed in the present study. Posterior arch width was measured between centers of two RMPs of each patient and was similar to that reported in the present study 53.68 ± 3.68 mm. Ryu et al.²³ also proposed that modification of trays according to sulcus depth in the anterior region was required regardless of arch length and width. This limitation was addressed in the present study by including the sulcus depth dimensions.

The present study observed anterior ridge width to be in the range of 4.00–16.50 mm and posterior in 4.75–19.50 mm. Pietrokovski et al.¹⁷ reported ridge width in the range of 2–11 mm in the premolar region. They also reported buccal ridge height in the premolar region in a range of 0.5–12.00 mm. Mean buccal sulcus depth of 4.62 ± 2.09 mm in the anterior region was similar to 5.63 ± 3.5 mm reported by Ryu et al.²³ According to Edwards and Boucher,¹⁰ the floor of the mouth in the sublingual crescent region is shorter as compared to the distolingual region due to the presence of lingual frenum and tongue elevation, which causes further reduced height of anterior lingual sulcus. So, the stock metal tray should be shorter so as to accommodate the anatomy of the mobile tissue here. The present study assessed buccal as well as lingual sulcus depths in the anterior and posterior regions and suggests modifying the stock tray flanges as per the reported mean dimensions.

The RMPs are considered to be a relatively stable landmark in the mandibular arch even in the cases with extreme ridge resorption.⁹ So, there is a change in the level of the residual ridge and the RMP as the ridges resorb, which creates an angle between the two. None of the previous studies²⁴^-²⁶ in the literature so far, has studied this angle. This study has reported RMP angle with a wide range of 135–175^°. Rather than the reported mean angle of 154^°, a lower limit value of 135 is suggested for modification of the tray so as to accommodate ridges with higher angles too. None of the previous studies¹⁸^,²³^,²⁷^-²⁹ have been able to successfully classify extremely resorbed mandibular completely edentulous ridges. According to the observations in the present study, a classification has been formulated for the tray design conforming to different resorbed ridge forms.

The trays formulated in accordance with the study clusters will better adapt the extremely resorbed completely edentulous ridges and thus make a better impression so that the final denture base is well adapted to the ridges and thus be more comfortable to the patient. The study included patients from a part of north India. Further studies are needed, with a larger sample size from different regions for the generalization of these results. Also, the trays formulated as per the findings of this study need to be validated in a planned clinical study.

CONCLUSION

This study formed three categories of extremely resorbed mandibular completely edentulous ridges on the basis of anterior-posterior arch width and posterior lingual sulcus. Modification in mandibular edentulous tray buccal and lingual flange depths was suggested. The study suggests modification of the mandibular impression tray in the RMP region to an angle of 135^°. Trays thus formulated will help in creating a strong foundation for good complete denture prosthesis in patients with extremely resorbed mandibular edentulous ridges.

ORCID

Neha Verma https://orcid.org/0000-0002-3174-1026

Shefali Singla https://orcid.org/0000-0002-1443-6054

Puneet Sahore https://orcid.org/0000-0003-0051-0695

Manisha Khanna https://orcid.org/0000-0001-6837-885X

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