Bone resorption
Introduction :
Within the bone tissue, there is continuous remodeling, allowing the bone material to regenerate and the bone structure to adapt to the mechanical constraints of its environment.
In fact, bone is a living tissue that renews itself continuously in order to avoid deterioration, and which also has the ability to adapt through apposition or, on the contrary, bone resorption.
For example, depending on the directions of mechanical stresses, the organization of the bone trabeculae of the cancellous bone can be modified in order to minimize the stresses exerted on them.
In a healthy subject, the rates of formation and resorption remain constant, which allows the entire bone mass to be preserved during remodeling.
In areas where high mechanical stresses are applied and therefore require more reinforcement, osteoblasts will come to affix bone, and conversely, where the bone becomes useless from a mechanical point of view, osteoclasts will come to resorb the bone tissue.
The cells responsible for this bone remodeling are osteoblasts, osteoclasts and osteocytes. Thus, the processes of bone formation and resorption are coupled and are directed by bundles of osteoblasts and osteoclasts called remodeling units.
1. Definition of resorption
It is the loss of height of the alveolar processes, resulting from the absence of dental organs. Aging is the main etiological factor of long-term bone resorption. In addition, dental extractions lead to a very rapid disappearance of the alveolar bone.
2. Phenomenon of alveolar resorption:
- After extraction, the alveolus is filled with spongy bone topped with a layer of compact or cortical bone; which contribute to forming the residual ridge.
- After 40 days, there is bone rarefaction, due to peripheral osteoclasis, but on the other hand, osteogenesis is established from the connective tissue of the central spongy bone.
- After 3 months, the alveolus and peripheral bone are repaired. This transformation of the bone tissue leads to a reduction in the crest and especially the mandibular crest.
The difference between maxillary and mandibular resorption is explained by the fact that the maxillary support surface is 1.8 times larger than that of the mandible.
3. The different stages of resorption:
Depending on the degree of resorption, different topographical categorizations have been proposed. Their aim is to provide a descriptive classification of clinical situations based on resorption and sometimes bone quality in order to guide the therapeutic choice.
Atwood classification
- Class 1: pre-extraction situation, tooth is still in place.
- Class 2: corresponds to the post-extraction clinical situation, the alveolus is uninhabited.
- Class 3: all forms of alveolar resorption up to class 4.
- class 4: which determines the knife blade shape.
- Class 5: corresponds to the total disappearance of the alveolar bone, where resorption occurs at the level of the basal bone (advanced resorption).
Bone resorption
In the maxilla
Vertical resorption would be 0.7 mm in the first year after prosthetic insertion
Only the central part of the palatine vault is spared by resorption, which predominantly affects the vestibular slopes of the edentulous ridges: the resorption is centripetal , resulting in a reduction in the perimeter of the maxillary arch. Due to the oblique implantation of the teeth, the maxillary arch is reduced in all its dimensions.
This bone resorption is more important in the anterior part of the maxilla than in the posterior part.
Bone resorption is least significant in the region of the maxillary tuberosity.
In the mandible:
The significant reduction in height of the edentulous ridges leads to a “widening” of the mandibular arch:
Resorption is centrifugal in the posterior sectors.
The resorption is centripetal at the level of the anterior sector.
Resorption causes changes in the dimension and profile of the arches as well as inter-arch relationships. Resorption in the mandible causes it to lose 60% of its bone mass. Result : a negative inter-ridge ratio
Bone resorption
Bone resorption
4. Alveolar resorption and wearing the prosthesis:
It is during the first three months of wearing the prosthesis that resorption is most significant,
After 6 months , it slows down considerably,
2 years after extraction, mandibular resorption has practically stopped,
The direct consequences of the resorption phenomenon are:
-a decrease in DV
-occlusion disturbances
– loss of adhesion of the bases
– overload points which can accelerate resorption, hence the need for periodic checks and readjustments,
5. Factors leading to bone resorption:
These are all factors leading to accelerated resorption.
General factors :
- Imbalance of phosphocalcic metabolism
- Endocrine disorders or deficiencies
Local factors
- Too compressive imprints, causing disruption of the vascularization of the mucosa.
- an overestimated DVO 🡪there is continuous pressure, exceeding the physiological bone tolerance threshold, hence resorption.
- An underestimated DVO 🡪 due to mandibular slippage resulting in anterior pressure and absence of posterior contact.
- An off-center occlusion results in one-sided chewing.
- Poor distribution of occlusal loads: presence of premature contact.
- An unstable prosthesis.
Any change in vascularization due to hyperemia or ischemia causes osteolysis. Consequently, the prosthesis must neither compress the support surfaces nor be very mobile and irritate the underlying tissues.
- Continued pressure results in bone resorption.
- Discontinuous pressure separated by too short rest intervals acts as if it were continuous.
- Discontinuous pressure with prolonged rest intervals promotes osteogenesis
- The absence of any pressure results in bone resorption.
6. Therapeutic measures limiting resorption:
Pre-prosthetic measurements:
- Allow 4 weeks after extractions to begin prosthetic treatment.
- Perform pre-prosthetic surgery when necessary.
Prosthetic measurement
- Prosthetic design according to standards.
Post-prosthetic measurements
- Stabilize prostheses by relining
- Occlusal equilibration.
Bone resorption
Cracked teeth can be healed with modern techniques.
Gum disease can be prevented with proper brushing.
Dental implants integrate with the bone for a long-lasting solution.
Yellowed teeth can be brightened with professional whitening.
Dental X-rays reveal problems that are invisible to the naked eye.
Sensitive teeth benefit from specific toothpastes.
A diet low in sugar protects against cavities.