Keywords mandibula - residual ridge resorption - bone density - complete dentures
Introduction
Residual ridge resorption (RRR) is a chronic, progressive, irreversible, and highly
complex process with a multifactorial etiology. Bone loss varies from person to person,
with its intensity being highest during the first 6 months after tooth extraction.[1 ]
The factors influencing RRR, as categorized by Atwood, include anatomical factors
(mass, shape, density of the alveolar ridge), metabolic factors (nutrition, hormonal
factors), functional factors (intensity, duration, and direction of masticatory forces),
and prosthetic factors (denture fabrication techniques, prosthetic design and principles).[1 ]
[2 ]
It is believed that RRR is exacerbated by imbalances in cellular activity, specifically
between bone-forming cells (osteoblasts) and bone-resorbing cells (osteoclasts) Systemic
factors are thought to play a role in the rate and intensity of RRR, including osteoporosis.[3 ]
[4 ] Anatomical changes affect the alveolar ridge in horizontal and vertical directions.
Trabecular bone is more affected by metabolic changes and consequently, resorptive
processes are significantly greater in trabecular regions than in cortical areas.[5 ]
[6 ]
Osteoporosis is a metabolic bone disease characterized by microarchitectural disruption
of bone structure and loss of bone mass density. The disease affects women three times
more than men.[7 ]
[8 ] Systemic bone density loss is considered a risk factor for oral bone loss, including
alveolar ridge resorption.[9 ] The highest rate of RRR has been reported in women especially after the menopause
due to drastic decrease in the level of the hormone estrogen as a promoter of bone
formation processes.[10 ]
Continued ridge reduction is evident in both denture wearers and nondenture wearers,
but mandibular resorption is directly related to the period of denture wearing/duration
of edentulism.[11 ]
[12 ]
It is crucial to assess the degree of RRR before planning prosthetic rehabilitation
to ensure proper prosthetic treatment planning, stability, and retention. The multifactorial
nature makes predicting the extent of RRR very challenging.[13 ]
One of the methods for measuring the degree of alveolar ridge resorption is the method
described by Wical and Swoope, modified by Ortman et al. Using this method, the ratio
between the two distances (distance Ia: from the upper edge of the alveolar ridge
to the lower edge of the mandible, and distance Ib: from the lower edge of the mental
foramen to the lower edge of the mandible) represents the degree of alveolar ridge
resorption, which is categorized in to three categories: class I (mild) ≥2.34; class
II (moderate) 1.67–2.33; class III (severe) ≤1.66.[14 ]
The objective of the study is to investigate the correlation between general bone
density and RRR, analyze the impact of duration of complete edentulism on RRR, and
determine the impact of wearing a complete denture on RRR.
Materials and Methods
The research was conducted at the Specialized Dental Polyclinic, Department of Mobile
Prosthodontic in Pristina. The study was approved by the Ethics Committee of the Kosovo
Dental Chamber (Prot No:15/10.06.2021). An information letter regarding the research
was provided to all patients for consent, and they all signed the written consent
agreeing to participate in the study.
Inclusion Criteria
Women aged 50 to 80 years.
Women who were examined to assess general bone density.
Women with complete edentulism in both jaws.
Exclusion Criteria
Patients who have undergone oral surgical procedures (sulcus deepening, alveolar ridge
leveling, etc.).
Patients suffering from systemic diseases that affect bone metabolism: hyperparathyroidism,
metastatic carcinoma, diabetes, renal insufficiency, and liver diseases.
Patients with partial edentulism and other forms of prosthetic treatment.
Structure of the Research Sample
The participants of the study were 60 postmenopausal women with complete edentulism
in both jaws, aged 50 to 80 years. Patients were allocated into two groups based on
the body's bone mineral density (BMD) measured by the dual-energy X-ray absorptiometry
(DXA) test.: 30 women in study group with low BMD osteopenia/osteoporosis (N1) and
30 women in control group with normal BMD (N2).
Research Methodology
The patients were examined using the DXA test by a nuclear medicine specialist from
the University Clinical Center in Pristina. The overall bone density examination -
DXA was performed using the MEDILINNK device, model: MEDIX DR 2020. Allocation of
patients was done according to the World Health Organization T-score scale, which
indicates the number of standard deviations above or below the mean for a healthy
30-year-old adult patient of the same sex and ethnicity, where normal BMD has ≥ − 1.0,
osteopenia has −1.0 to −2.5, osteoporosis has ≤ − 2.5 standard deviations ([Fig. 1 ]).
Fig. 1 Bone density assessment using the DXA test (medical reports presented with patient
consent). DXA, dual-energy X-ray absorptiometry.
To determine RRR, radiological assessment was performed using panoramic radiography
(orthopantomogram [OPG]) with a Sirona Ortho Phos E2D, conducted by a single radiology
technician to ensure consistent reference points. The mandibular ratio index (MRI)
was measured using the Sidexis SG Software system. Measurements were taken twice,
with a three-week interval between assessments.
The duration of edentulism was categorized into three groups: 0 to 5, 5 to 10, >10
years. All participants received complete dentures. Measurements for MRI were performed
before treatment and 1 year after wearing complete dentures.
Examining and Assessment Technique Using Panoramic Radiography
In the OPG, assessment of the MRI was conducted. Initially, the mental foramen was
identified as the recommended reference point. Using the Sidexis SG Software system,
two measurement lines were drawn: Ia: this is the distance from the lower edge of
the mandibular body to the upper edge of the mandibular ridge. This measurement is
taken near the mental foramen. Ib: this line measures the distance between the lower
edge of the mandibular body and the lower margin of the mental foramen. According
to the values obtained from the Ia/Ib ratio (right) + Ia/Ib ratio (left)/2, we obtained
the MRI values ([Fig. 2 ]).
Fig. 2 The identification of reference points and radiomorphometric measurements using the
software program.
Statistical Analysis
SPSS software package, version 23.0 and statistical software Statistica 7.1 for Windows
were used to process research data. Descriptive statistics included mean, standard
deviation range, and maximum and minimum for numerical variables. Independent samples
t -test was used to check the differences between sample groups. Difference and relation
were analyzed using Fisher's exact test and Pearson chi-square (p ) test. The Mann–Whitney U-test was used to analyze the difference between two research
groups. The multiple regression statistical analysis was used to analyze the relationship
between the dependent variable and the independent variables. Values of p <0.05 were considered statistically significant.
Results
The study included a total of 60 female subjects. The average age of patients in the
study group varied at 63.37 ± 6.32, in the control group, and 62.90 ± 7.07 with nonsignificant
difference ([Table 1 ]). The mean ± standard deviation values of the DXA test for the study group N1 range
at −2.98 ± 0.76, and for the control group N2, −1.16 ± 0.40. From 60 examined women
in our study, 30% (n = 30) had osteoporosis, 70% (n = 21) osteopenia, and 30% (n = 9) resulted with normal bone density ([Table 1 ]).
Table 1
Demographic and clinical characteristics of the patients
Characteristics
N1: group with low bone density
N2: group with normal bone density
p- Value
Z - adjusted
t -value
(T-score −1.0 to −2.5 < − 2.5)
(T-score > 2.5)
Number of patients
30
30
Sex
F (female)
F (female)
Mean, age, years (SD)
Mean ± SD
63.37 ± 6.32
62.90 ± 7.07
p > 0.0005
p = 0.73
Z = 0.33
Min/max
52/76
51/77
Median (IQR)
61
61
DXA test
Mean ± SD
−2.98 ± 0.76
−1.16 ± 0.40
p < 0.001
p = (0.000)
Z = −6.68
Min/max
1.90/− 2.5
−2.10/− 0.40
Median (IQR)
−2.70
−1.10
Bone status, T-score values
Cumulative count (percent)
Cumulative count (percent)
T score < − 2.5
30 (100%)
0 (0.00%)
p < 0.001
(p = 0.000)
Z = − 6.68
T score −1.0 to −2.5
0 (0.00%)
21 (70%)
T score > − 1
0 (0.00%)
9 (30%)
Length of period of edentulism
Cumulative count (percent)
Cumulative count (percent)
0–5 years
3 (10.00%)
0 (0.00%)
p > 0.05
(p = 0.347)
5–10 years
2 (6.67%)
8 (26.67%)
>10 years
22 (73.33%)
22 (73.33%)
Missing
0 (0.00%)
30
Abbreviations: DXA, dual-energy X-ray absorptiometry; IQR, interquartile range; SD,
standard deviation.
Note: Z = Mann–Whitney U-test. P = Pearson chi-square (significant for p < 0.05). T-test: grouping t/p.
The values of MRI in the study group vary within the range of 1.93 ± 0.34 mm. In the
control group, the values vary in the range of 1.96 ± 0.28 mm. One year after wearing
complete dentures, the values of MRI vary within the range 1.98 ± 0.33 for the study
group ([Table 2 ]).
Table 2
Mandibular resorption index—descriptive data for the two study groups
Variable
Valid N
Mean
Confidence—95.00%
Median
Minimum
Maximum
Std. Dev.
MRI—before prosthetic rehabilitation
MRI—study group
30
1.93
1.80
2.05
1.10
2.90
0.34
MRI—control group
30
1.96
2.07
1.90
1.60
2.80
0.28
Variable
Valid
N
Mean
Confidence—95.00%
Median
Minimum
Maximum
Std. Dev
MRI-1 year after wearing complete dentures
MRI—study group
30
1.98
1.85
2.10
1.10
2.90
0.33
MRI—control group
30
1.96
2.07
1.90
1.60
2.80
0.30
Abbreviation: MRI, mandibular ratio index.
A moderately strong positive insignificant correlation was determined between DXA
test values and MRI values, R = 0.32 (p > 0.05). With the increase in DXA test values, the values of MRI increase insignificantly
([Table 3 ] and [Fig. 3 ]).
Table 3
Cross-analysis between T-score values and MRI
DXA test
MRI index
Total
Class I > 2.34 mm
Class II 1.7–2.33 mm
Class III < 1.66 mm
T-score < − 2.5 Count %
3
10.0%
21
70.0%
6
20.0%
30
100%
T- score −1 to −2.5 Count %
1
4.8%
18
85.7%
2
9.5%
21
100.0%
T- score > − 1
Count %
1
11.1%
7
77.8%
1
11.1%
9
100.0%
Total
Count %
5
8.3%
46
76.7%
9
15.0%
60
100.0%
Abbreviations: DXA, dual-energy X-ray absorptiometry; MRI, mandibular ratio index.
Fig. 3 Correlation between DXA test values and MRI values. DXA, dual-energy X-ray absorptiometry;
MRI, mandibular ratio index.
One year after wearing the complete prosthesis the statistical data show an increase
in alveolar ridge resorption. The ratio of patients classified as Class III on MRI
(ridge height < 1.66 mm) increased from 20% (n = 6) prior to prosthetic rehabilitation to 30% (n = 9) at the one-year follow-up. ([Tables 4 ] and [5 ]).
Table 4
Distribution of the MRI values before prosthodontic rehabilitation and 1 year after
wearing complete dentures
MRI—before prosthetic rehabilitation
N1: study group
(low bone mass)
N2: control group (normal bone mass)
p -Level
Z -adjusted
Frequency
Percent %
Frequency
Percent %
Class I: >2.34 mm
3
10.00
2
6.67
0.79
0.27
Class II: 1.67–2.33 mm
21
70.00
25
83.33
Class III: <1.66 mm
6
20.00
3
10.00
Missing
0
0.00
0
0.00
MRI—1 year after wearing complete dentures
N1: study group
N2: control group
p
-Level
Z
-adjusted
Frequency
Percent %
Frequency
Percent %
Class I: >2.34 mm
1
3.33
2
6.66
0.85
−0.19
Class II: 1.67–2.33 mm
20
66.66
25
83.33
Class III: <1.66 mm
9
30.00
3
10.00
Abbreviations: MRI, mandibular ratio index.
Note: Z = Mann–Whitney U-test (significant for p < 0.05). P = Pearson chi-square.
Table 5
Comparative analysis of the MRI values before prosthodontic rehabilitation and 1 year
after wearing complete dentures
Pair of variables
Valid N
T
Z
p -Level
MRI and MRI/1 year after wearing complete denture
MRI—study group
30
9.50
2.31
0.02
MRI—control group
30
0.00
2.05
0.01
Abbreviations: MRI, mandibular ratio index.
The data from the multiple regression analysis between the values of MRI as a dependent
variable and age, DXA test, and length of edentulism period in the study group are
presented in [Table 6 ]. For each unit increase in T-score value, MRI (mean) increases by 0.04 (B = 0.04), a nonsignificant difference at p >0.05 with unchanged values for other parameters. Patients with edentulous period
>10 years have an average of 0.01 mm (B = 0.01) resorption compared with patients with edentulous period of 1 to 10 years,
nonsignificant at p >0.05 (p = 0.97). For each year of increasing age, the mandibular resorption index decreases
by 0.0004 mm (B = 0.0004) and is not significant at p >0.05 (p = 0.97; [Table 6 ]).
Table 6
Multiple regression analysis between MRI values, age, DXA test, and duration of edentulism
Regression summary for dependent variable: МRI/average
R = 0.33; F (6.23) = 0.48; p > 0.05
N = 30
Beta
Std. Err. of B
B
Std. Err. of B
t (23)
p -Level
Intercept
1.62
1.62
0.93
0.09
Age
−0.01
0.21
−0.0004
−0.0004
0.01
0.97
DXA test
0.09
0.22
0.04
0.04
0.10
0.70
Length of period of edentulism (1)
−0.01
0.21
−0.01
−0.01
0.19
0.97
Abbreviation: DXA, dual-energy X-ray absorptiometry.
Discussion
The critical issue in the treatment of complete edentulism is bone resorption, especially
in the mandible where the rate of resorption is twice more pronounced than in the
maxilla and where anatomical support is very limited, particularly in cases of rehabilitation
with complete dentures.[3 ]
[4 ]
Osteoporosis is a severe disease that garners special attention due to its progressive
yet latent development. Bone mass loss begins around age 35 and peaks upon entering
menopause.[7 ]
[8 ]
The relationship between osteoporosis and changes in oral bones has been recognized
since the 1960s.[4 ] Given that RRR is a very complex and multifactorial process, many authors do not
attribute the impact solely to osteoporosis.[3 ]
[6 ]
Many studies have been conducted on the relationship between RRR and skeletal BMD,
resulting in conflicting results. However, only a few studies used multiple analyses
such as and BMD, age, duration of edentulism, and influence of dentures to analyze
the effect of each as analyzed in our study.[12 ]
[13 ]
[14 ]
The method used to evaluate RRR in our study has several advantages, such as simplicity
due to the relevant anatomical structures used as reference points, optimal degree
of accuracy, and possibilities of comparison of radiographs at different intervals
enabling evaluation at different time periods.[14 ]
[15 ]
Difficulties in identifying the mental foramen with clear visibility of upper and
lower boundaries as a reference point are very common, especially when resorptive
processes are pronounced.[15 ]
[16 ] In our research, we also encountered these difficulties. Even after a second examination,
full consensus was not reached on the effective visibility of the reference point.
Ultimately, we include in our research only OPGs from patients with clearly visible
anatomical structures that meet the guidelines and criteria for performing radio-morphometric
measurements.
Many authors, who have analyzed the most appropriate measurement methodology for evaluation
of MRI, have given priority to measurements made with digital methods due to their
advantages in technical aspects, reliability, and accuracy. Arifin et al developed
a computer-aided system for measuring radio-morphometric indices on dental panoramic
radiographs and clarify the diagnostic efficacy of the digital system.[16 ]
[17 ] To achieve the most accurate assessment, we have also used the digital method.
In our study, a moderately strong positive insignificant correlation was determined
between DXA test values and MRI values. With the increase in DXA test values, the
values of MRI increase insignificantly. Our study data show that 20% of patients with
T-score < − 2.5 have MRI class III, which represents the highest degree of RRR, while
70% have MRI class II. Our data are consistent with the findings of von Wowern and
Kollerup, who caried out a study with an aim to determine whether symptomatic osteoporosis
was associated with greater reduction in residual bone in edentulous patients. They
reported that osteoporosis in women is not associated with mandibular atrophy.[18 ] Klemetti and Vainio investigated the relationship between bone density and the rate
of alveolar ridge resorption in 77 women by measuring several reference points on
the lower jaw. The study reported that RRR in some regions of the mandible was influenced
by the overall loss of bone density.[19 ] Moreover, Ortman et al conducted a study of 459 edentulous patients using the Wical
and Swoope method. The data demonstrated a significantly larger percentage of women
with class III RRR (p less than 0.01), but this difference could not be related only to systemic bone loss
and menopause.[20 ] Another prospective, cross-sectional study by Springe et al in 45 edentulous postmenopausal
women found no statistically significant relationship between BMD and mandibular bone
high at the midline and both mental foramina regions.[21 ]
No significant association between the subject's age, duration of edentulism, and
RRR was found in the present study. 0.01 mm (B = 0.01) is the difference in mean values of RRR between the length of period of edentulism
>10 years and the period 1 to 10 years. Our data are in line with a study conducted
by Xie at al, who investigated the influence of local factors in 177 elderly patients,
including duration of edentulism, the time of wearing the prosthesis, the condition
of the prosthesis, and oral hygiene habits. No significant association was found between
degree of resorption and duration of edentulism in either the mandible or the maxilla.
RRR was related to denture quality (p < 0.05).[22 ]
In the complex multifactorial mechanism of RRR, the pressure developed under the removable
prosthesis plays an important role, being an additional factor of an intensive process
of resorption of the edentulous arch. These data have been verified by a study conducted
by Campbell.[11 ] According to our data, wearing dentures can affect RRR in women with osteoporosis.
The data we obtained from the comparative analysis show significantly increased values
of alveolar resorption compared with the values 1 year ago (Z = 2.31). Statistically significant results were reported also from a prospective
5-year case–control study by Alsaggaf and Fenlon, who investigated the effects of
denture on RRR in edentulous patients from two study groups. The residual alveolar
ridges of those wearing dentures were resorbed significantly more over a 5-year period
of denture wear than those not wearing dentures.[23 ] According to Al-Jabrah and Al-Shumailan, 44.3% of the mandibular ridges had resorbed
in patients who had been wearing conventional dentures for 20 years or more.[24 ] Moreover, some studies reported different results. From their 5-year prospective
study with five reference points in maxilla and mandibula, Kovačić et al reported
low rate of resorption (8%) in patients wearing dentures. However, they reported a
significant relationship with the duration of edentulism, while Zmysłowska et al reported
a high rate of RRR (45%).[25 ]
[26 ]
Women have a higher risk for a higher degree of resorption according to Kordatzis
at al. However, their data did not find any association with factors such as the period
of edentulism and the number of dentures used.[23 ]
[27 ] In the literature, there are numerous experimental data that have produced clear
conclusions about the correlation of estrogen deficiency in postmenopausal women,
which can accelerate RRR, which affects a significant loss of bone mass in the edentulous
jaw.[7 ]
[8 ] However, more research is required to confirm the mechanism of this relation.[28 ]
[29 ]
[30 ]
[31 ]
[32 ]
[33 ]
[34 ]
[35 ]
[36 ]
One of the limitations of this study was the method used to measure RRR. Although
it is a reliable method, it provides data about RRR in the region of mental foramen.
RRR in other areas is not assessed. The small sample size was another limitation.
Being a complex multifactorial process, a prospective study design that includes a
wider range of local and systemic factors would be even more useful in assessing their
impact on the rate of RRR.
Conclusion
Assessing bone quality before prosthetic rehabilitation is highly beneficial for patients
with osteoporosis.
Residual alveolar ridge resorption is not significantly correlated with DXA measurements.
Age and duration of edentulism do not have a significant impact on residual alveolar
ridge resorption. Wearing dentures can affect RRR.
Recommendations should be followed during the fabrication of removable dentures, focusing
on protecting the jawbone from excessive masticatory force loads. A pressure-free
impression (the open-mouth technique) should be applied to minimize pressure on the
alveolar ridge. Acrylic teeth with semi-anatomical cusps (25°–33°) should be used
to reduce stress on the remaining bone and reduce unwanted horizontal force.
