Residual Ridge Resorption Classification and Pathophysiology

RESIDUAL
RIDGE
RESORPTION
INDIAN DENTAL ACADEMY
Leader in continuing Dental Education
www.indiandentalacademy.com

INTRODUCTION
Residual Ridge resorption (RRR) is a complex
biophysical process. According to Mosby the following terms
are defined:
Residual: Pertaining to the position of something that
remains after an activity that removes the bulk of the
substance.
Ridge: A projection or projecting structure.
Resorption: A loss of substance or bone by physiologic or
pathologic means, such as the reduction of the volume and
size of the residual ridge of the mandible or maxilla.www.indiandentalacademy.com

Residual Ridge: The portion of the dental ridge that
remains after the alveolar process has disappeared after
extraction of the teeth.
Residual ridge resorption (GPT 7): A term used for the
diminishing quantity and quality of the residual ridge after
teeth are removed.

CLASSIFICATIONS OF RESIDUAL RIDGE
RESORPTION
According to Brånemark et al in 1985, ridges were classified
on the basis of bone quantity and bone quality by
radiographic means.
BONE QUANTITY: (Brånemark)
Class A: Most of the alveolar bone is present
Class B: Moderate Residual Ridge Resorption occurs
Class C: Advance residual ridge resorption occurs
Class D: Moderate resorption of the basal bone is present
Class E: Extreme resorption of the basal bone

ATWOOD’S CLASSIFICATION:
Order I - Pre-extraction
Order II - Post – extraction
Order III - High, well rounded
Order IV - Knife edge
Order V - Low, well rounded
Order VI - Depressed

PATHOLOGY OF RRR
A frequent lay expression for RRR is “my gums have
shrunk”. Actually, the basic structural change in RRR is a
reduction in the size of the bony ridge under the
mucoperiosteum. It is primarily a localized loss of bone
structure. In some situations, this loss of bone may leave the
overlying mucooperiosteum excessive and redundant.
However, sometimes there is no redundant soft tissue in
areas where severe bone loss has occurred.

Gross anatomic studies of dried jawbones have shown
a wide variety of shapes and sizes of residual ridges. In order
to provide a simplified method for categorizing the most
common residual ridge configurations, a system of six orders
of residual ridge forms have been described earlier. This self
descriptive system is useful clinically as well as for research
purposes and helps one to differentiate the various stages of
RRR in the individual patient.

 Another gross finding seen on dry specimens is that while
external cortical surfaces of the maxilla and mandible are
uniformly smooth, the crestal areas of residual ridge have a
different appearances and show many more porosities and
imperfections no matter at what stage of residual ridge
configuration.
 Bones with the most severe RRR (Order V and VI) may
display the gross porosity of medullary bone on the crest of
the ridge and eventually may even display the uncovering of
the inferior alveolar canal on the mandible.
 RRR does not stop with the residual ridge; but may go well
below where the apices of the teeth were, sometimes leaving
only a thin cortical plate on the inferior border of the mandible
or virtually no maxillary alveolar process on the upper jaw.

 However, a knife-edge may be masked by redundant or
inflamed soft tissues.
 One can more accurately determine the amount of
underlying bone by palpation in the mouth rather than by
attempting to take measurements on stone casts.
 Lateral cephalometric radiography provides the most
accurate method for determining the amount of residual ridge
and the rate of RRR over a period of time.
 The panoramic radiographic technique described by Wical
and Swoope is a simple, useful method for arriving at a gross
estimate of the amount of RRR to date in a given patient.
 Clinically, the soft tissues, overlying residual ridges that
have undergone RRR may range from normal to inflamed,
edematous, ulcerated, indented or otherwise abused tissue.

PATHOPHYSIOLOGY OF RRR
 It is a normal function of bone to undergo constant
remodeling throughout life through the processes of bone
resorption and bone formation. Except during growth, when
bone formation exceeds bone resorption, bone resorption and
bone formation are normally in equilibrium.
 Osteoporosis is a generalized disease of bone in which bone is
in negative balance, because bone resorption exceeds bone
formation.
 In periodontal disease, there is a localized destruction of the
bone around teeth, perhaps due to certain local pathologic
processes. In both generalized osteoporosis and localized
periodontal disease, when bone matrix is lost it does not

 RRR is a localized pathologic loss of bone that is not built
back by simply removing the causative factors.
 To date, the process of RRR has not been reversed such
that the residual ridge has increased in size. Yet the
physiologic process of internal bone remodeling goes on even
in the presence of this pathologic external osteoclastic activity
that is responsible for the loss of so much bone substance.
 New bone is laid down inside the residual ridge in advance of
the external osteoclastic removal of bone.
 RRR is not inevitable, and the rate of RRR varies, and that
RRR can proceed far beyond the “alveolar bone, and that the
rate of resorption in some patients is not much greater than the
rate of formation that the patient ends up with no cortical bone
on the crest of the ridge. From a practical point of view, RRR
should be considered a pathologic process.www.indiandentalacademy.com

ETIOLOGY OF RRR
It is postulated that RRR is a multifactorial
biomechanical disease that results from a combination of
anatomic, metabolic, and mechanical determinants. Each of
the major co-variables will be discussed separately and then
will be brought together in a combined major variable
formula.
ANATOMIC FACTORS
It is postulated that RRR varies with the quantity of
the bone of the residual ridges.
RRR ∝ Anatomic factors

 However, this must be interpreted carefully. It is to state
that the more bone there is, the more RRR there will
ultimately be, sometimes large ridges resorb rapidly and some
knife-edge ridges may remain with little change for long
periods of time. If a low depressed ridge has existed thus for
many years, future RRR will probably be at a low rate.
 Another way to evaluate the anatomic factors is to consider
the mechanical factors that would be favorable to stability and
retention of a denture. Thus, large well – rounded ridges and
broad palates would seem to be favorable anatomic factors.
 Still another anatomic factor to consider is the density of the
ridge. However, here again one must interpret carefully, for the
density at any given moment does not signify the current
metabolic activity of the bone, and bone can be resorbed by
osteoclastic activity regardless of its degree of calcification.www.indiandentalacademy.com

METABOLIC FACTORS
It is further postulated that RRR varies directly with
certain systemic or localized bone resorptive factors and
inversely with certain bone formation factors:
RRR α Bone resorption factors
Bone formation factors

 RRR is a localized loss of bone on the crest of the residual
ridge. It is quite possible that some of the local biochemical
factors that have been studied in relation to periodontal
disease could play an important role in RRR.
 These factors include endotoxins from dental plaque
(plaque can occur in edentulous mouths, especially in patients
who do not properly clean their dentures), osteoclast
activating factor (OAF), prostaglandins human gingival bone-
resorption stimulating factor, and others.
 Heparin, which has been shown to be a cofactor in bone
resorption, has been associated with mast cells that have been
observed in microscopic sections of residual ridges close to
the bone margins.

Other possible local bone resorption factors could be
related to trauma (especially under ill-fitting dentures), which
leads to increased or decreased vascularity and changes in
oxygen tension.
Whatever the local bone resorbing factors may be, they
must be considered in the environment of the systemic
factors that influence the balance between normal bone
formation and bone resorption. There are some patients who
seem to have a natural resistance to unfavorable local factors
whether it be calculus or bacteria; occlusal force in patients
with natural teeth; or vertical dimension, cusp form, or other
prosthetic factors in denture wearers.

Perhaps such individuals have the correct amounts of
circulating estrogen, thyroxine, growth hormone, androgens,
calcium, phosphorus, vitamin D, protein, fluoride, and so on to
compensate for poor local factors, while others may be already
in a negative bone balance owing to some form of osteoporosis
and may therefore be more vulnerable to unfavorable local
factors.

MECHANICAL FACTORS
Though mechanisms are not yet clearly
understood, the remodeling of bone is influenced by force
factors. Bone that is used, as by regular physical activity, will
tend to strengthen within certain limits, while bone that is in
“disuse” will tend to atrophy. Once the teeth are removed, the
residual alveolar ridge is subjected to entirely different types of
forces. Some postulate that RRR is an “abuse” bone resorption
due to excessive forces transmitted through dentures. Perhaps
there is truth in both hypotheses. The fact is that with or
without dentures some patients have little or no RRR and
some have severe RRR.

In considering force, one must concern oneself not only
with the amount of force, but also with the frequency of force,
the duration of force, the direction of force, the area over which
force is distributed (force per unit area), and the damping effect
of the underlying tissue.
Abnormal parafunctional forces from clenching and
grinding of teeth may last may up to several hours per day. In
some patients it is quite likely that this can place pathologic
loads on the residual ridges.
In summary, it is likely that force is a cofactor in RRR that can
be expressed as:
RRR α force

A force applied to the bone may be affected inversely
by the “damping effect” or energy absorption. This cofactor
may be expressed as follows:
RRR α 1
Damping effect
The “damping effect” may take place in the
mucoperiosteum, which can be considered a visco-elastic
material. Since the overlying mucoperiosteum varies in its
visco-elastic properties among patients and from maxilla to
mandible, its energy absorption qualities may influence the
rate of RRR.

The fact that the maxillary residual ridge is frequently
broader, flatter, and more cancellous than its mandibular
counterpart is of interest and may be a factor in the frequently
observed differences in the RRR of the two jaws.
Frost pointed out that trabeculae in such bones as a
vertebral body are oriented parallel to the direction of
compression deformation, allowing for maximal resistance to
deformation. The stronger these trabeculae are the greater is the
resistance.
The traditional design of dentures includes many features whose
goal is to reduce the amount of force to the ridge and thereby to
reduce RRR.

These prosthetic factors include
 broad area coverage (to reduce the force per unit area
decreased number of dental units,
 decreased buccolingual width of teeth, and
 improved tooth form (to decrease the amount of force
required to penetrate a bolus of food);
 avoidance of inclined planes (to minimize dislodgement of
dentures and shear forces);
 centralization of occlusal contacts (to increase stability of
dentures and to maximize compressive forces);
 provision of adequate tongue room (to improve stability of
denture in speech and mastication);
 adequate inter-occlusal distance during rest jaw relation (to
decrease the frequency and duration of tooth contacts)www.indiandentalacademy.com

The various formulas describing the correlative
relationship of possible factors the RRR must be combined
if one is to more truly illustrate this concept. For simplicity,
only the major categories of cofactors are included as
follows:
RRR α anatomic factors + bone resorption factors + Force factors
bone formation factors damping effect
factors
In addition to the three major categories of factors
(anatomic, metabolic, and mechanical), the importance of the
time since extraction to the bone loss curves, described in
the section on the pathogenesis of RRR, should be
emphasized by adding an inverse relation.

RRR α 1
Time
To the combined formula as follows
RRR α anatomic factors + bone resorption factors + force factors
time bone formation factors damping
effect

EPIDEMIOLOGY OF RRR
Epidemiology is the study of the distribution and
determinants of disease in man. Epidemiologic methodology
can contribute to an understanding of the etiology of a specific
disease, especially by the use of a large experimental
population.
There have been no large scale studies of RRR in man.
Most studies of RRR to date have been meticulous
longitudinal cephalometric studies of a relatively few subjects,
while such studies are responsible for, much of what we know
about RRR. They are time consuming and expensive and not
really good examples of epidemiologic methodology.

To date it would appear that RRR is worldwide, occurs
in males and females, young and old, in sickness and in
health, with and without dentures, and is unrelated to the
primary reason for the extraction of the teeth (caries or
periodontal disease).
Sometimes a disease is caused by a single determinant,
sometimes by multiple factors. The resistance of the host to the
causative or predisposing factors may affect the frequency or
severity of a disease. Sometimes a certain dose of the causal
factor is necessary to cause the disease. Sometimes the causal
factor must be present a certain length of time to be effective.
All of these factors tend to obscure the etiology of a disease.

TREATMENT OF RESIDUAL RIDGE
RESORPTION
Pre-prosthetic surgery includes the following:
1. Ridge preservation procedure as a preventive measure.
2. Corrective or recontouring procedures of the defects and
abnormalities.
3. Ridge extension procedures:
• Relative methods Eg. sulcus extension (vestibuloplasty)
• Absolute methods Eg. Ridge augmentation methods.
4. Reconstruction methods like correction of abnormal ridge
relationship.

5. Provision of accessory undercuts.
• Creating favorable undercuts
• Dental implants.
• Onlay denture.
6. Modified denture construction procedure Eg. Immediate
denture where construction of the denture proceeds
surgery.

CONCLUSION
Bone resorption of residual ridges is common. The
rate of resorption varies among different individuals and
within the same individual at different times. Factors related
to the rate of resorption are divided into anatomic,
metabolic, functions, and prosthetic factors.
Anatomic factors include the size, shape and density
of ridges, the thickness and character of the mucosal
covering, the ridge relationships, and the number and depth
of sockets.

Metabolic factors include all of the multiple nutritional,
hormonal and other metabolic factors which influence the
relative cellular activity of the bone-forming cells (osteoblasts)
and the bone-destroying cells (osteoclasts). Age, sex and
general health are inadequate to describe the bone factor but
do give some clinical clues.
Functional factors include the frequency, intensity,
duration and direction of forces applied to bone which are
translated into cellular activity, resulting in either bone
formation or bone resorption, depending on the patient’s
individual resistance to these forces.

Prosthetic factors include the myriad of technique,
materials, concepts, principles and practices which are
incorporated into the prosthesis.
Although the various factors can be divided into these
five groups for academic purpose, they are interrelated and
any one factor may be evaluated only if we place it in its
proper perspective to all factors.
Since bone resorption depends on the response of
living cells to force, the more basic sciences concerned with
the physiology and pathology of cells are understood, the
more educated will be our clinical judgment.

Residual Ridge Resorption Classification and Pathophysiology

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Residual Ridge Resorption Classification and Pathophysiology