The bony

residual

ridge

Jaime Pietrokovski, C.D., MS.* The Hebrew University-Hadassah Israel

A

in man

Faculty

of

Dental

Medicine,

Jerusalem,

fter extraction of teeth, the residual ridge passes through a series of morphologic changes until a quasistationary, stable stage is reached approximately eight to ten weeks later.‘-* The extraction wound is filled with a blood clot. The portion of the bony alveolar crest of the original socket then resorbs, and the surface becomes covered by stratified squamous epithelium. The blood clot is soon organized and replaced by a dense scar tissue and by bone. The bone is the foundation for the residual ridge which will eventually support and retain the denture which replaces the missing teeth. The remodeling process does not stop completely after the ten-week healing period. Remodeling of bone continues through the life of the patient (Fig. 1). The wearing of dentures, masticatory habits, and/or systemic factors may have a marked effect on the morphology of the residual ridge due to resorption and apposition of the supporting bone tissue. The type of bone which replaces the missing tooth root has not been systematically evaluated. Observations indicate that the bone which fills the socket tends to blend with the adjacent bone eight to ten weeks after tooth extraction, and no clear demarcation can be seen between the bone present before extractions of teeth and the newly formed bone.“, 6 There are also histologic and radiographic reports showing cortical bone over the crest of the residual ridge. 7. x However, there are other observations indicating that the bony tissue which forms in the socket is of the trabecular type and differs even grossly from the adjacent cortical bone.g-l” The remodeling process which follows extraction of a tooth is unique in that it is the only region where bone replaces an organ removed by surgical intervention. The repair of the socket and the type of bone which develops in it deserve additional study. Trabecular bone and cortical bone respond in a different way and at different rates to external influences such as the pressure or tension exerted on the residual ridge by a removable prosthesis.‘“-l” The purpose of this investigation was to establish which types of bone form the residual ridge in the maxillae and the mandible. “Senior 456

Lecturer

in Oral

Rehabilitation.

Bony

Fig. 1. Mesiodistal histologic section of an edentulous ridge. face of the bony ridge (arrows) denote an active resorptive at the time of preparation.

Fig. (C)

2, A-C. Mandibular and the trabecular

MATERIALS

AND

residual

Resorption process

ridge

in man

lacunae along at this particular

specimens. There is a clear demarcation between the bone (T) at the external surface of the residual ridge.

cortical

457

the surregion

plates

METHODS

To establish the form and the type of bone of the residual ridge, 120 dry adult human skull specimens were selected in which one or several teeth had been missing for at least three months. The alveolar processes of the remaining adjacent teeth were used to estimate the amount and the direction of the remodeling process.

458

Fig. from

J. l’roathct. Dent. Octoh~~r, 197.5

Pietrokovski

3, A and B. Maxillary the trabecular bone

specimens. of the residual

The palatal crest (T).

cortical

bone

(P)

is clearly

Fig. 4. Buccolingual section of residual mandibular ridge. There is a clear the buccal and lingual cortical plates (C), the dense trabecular bone (D) of the ridge, and the loose trabeculae (L) at the basal part of the section.

differentiated

delineation

between

located at the crest

The specimens were examined macroscopically and radiographically. Ten specimens were sectioned buccolingually at the level of the residual ridge to study the tissue arrangement of the bone within the edentulous residual ridge. One-hundred periapical radiographs of subjects, 20 to 70 years of age, having one or several teeth missing for at least three months following extraction, were also studied. FINDINGS In the dry skull specimens, the external bony surface of the residual ridge was of a trabecular type. In the mandibular specimens, the crest of the residual ridge was

Bony residual ridge in man

459

Fig. 5. Radiograph of a mandibular ridge is well defined. Note the bony

edentulous ridge. The trabecular nature of the residual alveolar “island” which surrounds the remaining molar. Fig. 6. Radiograph of a mandibular residual ridge. The radiopaque line at the crest of the ridge may be the superposition of the gingival margin of the buccal and/or lingual cortical plates of the residual crest.

Fig. 7. Buccal aspect of the maxillary cavity forms the residual ridge between

specimen shown in Fig. the adjacent teeth.

3,

A. A slight

mesiodistal

con-

Fig. 8. Mandibular specimen from which the second and third molar teeth were extracted. The residual ridge forms a deep concavity typical for free-end partial dentures where neither posterior teeth nor their surrounding alveolar processes remain to prevent substantial loss and collapse of the supporting bone.

clearly delineated from the adjacent buccal and lingual cortical plates (Fig. 2) . Even in the anterior part of the mandible, where central incisors were missing and the labial and the lingual plates almost approximated each other to form a knife-edged ridge, a small layer of trabecular bone was always present between the cortical plates (Fig. 2, C). In the maxillary specimens, the bony surface of the residual ridge was also of the trabecular type and could be easily differentiated from the hard palate (Fig. 3). These findings were confirmed when the buccolingual sections were studied, and the difference between the cortical plates and the replacement trabecular bone was clearly observed. The surface of the bony trabecular residual ridge was more dense

460

Pietrokovski

.J. Prosthet. October,

Dent. 1975

than the trabecular structural arrangement at the center of the bone section but was never as dense as the cortical plates (Fig. 4). Examination of radiographs of the dry specimens and of the patients revealed features similar to those described above. In 85 per cent of these specimens, the residual ridge was entirely of the trabecular type (Fig. 5). However, in 15 per cent of the specimens, maxillary as well as mandibular, a distinct radiopaque line could be seen at the gingival surface of the bone tissue (Fig. 6). This radiopaque line seen at the crest of the residual ridge may be a zone that is more densely calcified than the rest of the residual ridge or merely the superimposition of the upper margins of the buccal and lingual cortical plates at the crest of the ridge. The external form of the residual bony ridge was similar to the form of the residual ridge observed in the patients, in whom the bone tissue was covered by oral mucosa as observed in a parallel clinical investigation.” As seen from the ocrlusal aspect of each specimen, the pattern of resorption was primarily at the expense of the burcal plate. The crest of the ridge. therefore, shifted lingually when compared with its original position before tooth extraction. This could be seen in the maxillary as well as in the mandibular specimens and is in agreement with previous reports (Figs. 2 and 3) .“. “-‘!’ From the buccolateral aspect, the residual ridge usually formed a flat or slightly concave surface, between the alveolar crests of the adjacent remaining teeth (Fig. 7). When many teeth were missing, the concavity was usually deeper than when a single tooth was missing. This concavity was more marked where no teeth were present at the distal end of the dental arch to prevent the collapse and resorption of the alveolar bony plates (Fig. 8). DISCUSSION This study indicates that the extraction socket is filled by trabecular bone of a dense type, which is thicker and denser than the rest of the trabecular bone forming the inner portion of the alveolar process but less dense than the cortical plates of the jaw. The residual bony ridge may then be considered as being of intermediate density-that is. between the trabecular type of bone of the inner part of the jaws and the external plates of cortical bone (Fig. 4). This difference in bone density may have clinical implications. When an intraosseous blade implant is to be inserted through the crest of the residual ridge, the difference in density between the bony types becomes apparent. When preparing the edentulous ridge for the reception of the implant using a fissure bur at low speed, the resistance of the bone is considerable at the beginning of the preparation while, after penetrating the external layer of dense trabecular bone at the crest of the ridge. the rotating instrument falls into the less dense bony tissue. This is the spongy bone which must eventually retain the blade implant in position. Another clinical consideration is the fact that the supporting tissues for complete or partial removable denture bases are formed at their bony surface or two different types of bone tissues: a compact lamellated bone at the external borders of the jaws and a dense, spongiose trabecular bone present at the crest of the residual ridge, Roth bony tissues are covered by fibrous scar tissue and a covering epithelium which conceal any structural difference between the bony types.

Bony When

occlusal

the underlying in a different Theoretically, This

is seen

forces

are

transmitted

through

the

residual bases

ridge

in man

of removable

461

dentures

to

bone, it is assumed that the bone responds to pressure and/or tension fashion and at a different speed according to its internal structure. trabecular bone should resorb easier and faster than cortical bone.14v l5 when

rebasing

a denture

which

portion of the rebasing material is applied rebasing material is needed at the palatal ture.* This indicates that most of the the insertion of the denture and at the the residual ridge. This ridge is formed more prone to resorption than are the the lateral walls of the jaws.

has

been

worn

for

several

years,

the

main

at the residual ridge region, whereas less vault and the lateral flanges of the denbone resorption which occurred between time of the rebasing was at the region of by trabecular bone and is more labile and cortical plates which form the palate and

SUMMARY The bone which fills in the socket after tooth extractions was investigated in 120 dry skull specimens and 100 radiographs in which one or more teeth had been missing for at least three months. The bony content of the socket was of the trabecular type. This trabecular bone was well differentiated from the adjacent cortical bony plates. In buccolingual sections, the residual crest was formed by dense trabecular bone, clearly differentiated from the cortical plates as well as from the less dense trabecular bone that was deeper within the former sockets. From the occlusal aspect, the crest of the edentulous surface had shifted lingually when compared to the original position of the teeth before extractions. From the lateral aspect, the residual ridge formed a concavity or went straight between the alveolar crests of the adjacent remaining teeth. When several teeth were missing, the concavity was more pronounced than when a single tooth was missing. *Personal

communication:

J. Michman,

1973.

References 1.

Claflin, R. S.: Healing of Disturbed and Undisturbed Extraction Wounds, J. Am. Dent. Assoc. 23: 945-959, 1936. 2. Mangos, J. F.: The Healing of Extraction Wounds, N. Z. Dent. J. 37: 4-16, 1941. 3. Raddon, H. G.: Local Factors in Healing of the Alveolar Tissues, Ann. R. C011. Surg. Engl. 24: 366-387, 1959. 4. Huebsch, H. F., Coleman, R. D., Randsom, A. M., and Becks, H.: The Healing Process Following Molar Extraction, I. Normal Male Rats, Oral Surg. 5: 864-876, 1952. 5. Atwood, D. A.: Some Clinical Factors Related to the Rate of Resorption of Residual Ridges, J. PROSTHET. DENT. 12: 441-450, 1962. 6. Pietrokovski, J., and Massler, M.: Ridge Remodeling After Tooth Extraction in Rats, J. Dent. Res. 46: 222-231, 1967. 7. Atwood, D. A.: The Reduction of Residual Ridges. A Major Oral Disease Entity, J. PROSTHET. DENT. 26: 266-279, 1971. 8. Worth, H. M.: Principles and Practice of Oral Radiologic Interpretation, Chicago, 1969, Year Book Medical Publishers, Inc., pp. 310-316. 9. Pendleton, E. C.: Changes in the Denture Supporting Tissues, J. Am. Dent. Assoc. 42: 1-15, 1951.

462 10. 11. 12. 13. 14. 15. 16. 17. 18. 19.

Pietrokovski

.I. I’rostbrt.

Dent.

Octobr,,

1975

Pendleton, E. C.: Anatomy of the Maxilla From the Point of View of Full Denture Prosthesis, J. Am. Dent. Assoc. 19: 552-572, 1932. Sicher, H., and DuBrul, E. L.: Oral .4natomy, ed. 5, St. Louis, 1970, The C. V. Mosby Company, pp. 484-485. Neufeld, J. 0. : Changes in the Trabecular Pattern of the Mandible Following the Loss of Teeth, J. PROSTHET. DENT. 8: 685-697, 1958. Nakamoto, R. Y.: Bony Defects in the Crest of the Residual Alveolar Ridge, J. PROSTHET. DEXT. 19: 111-118, 1968. .4nderson, J. N.. and Storer, R.: Immediate and Replacement Dentures, Oxford, 1966, Blackwell Scientific Publications, pp. 14, 132-137. Swenson, M. G., and Terkla. L. G.: Partial Dentures, St. Louis, 195.5, The C. V. Mosby Company, pp. 21-22. Nagle, R. J., Sears, V. H., and Silverman, S. I. : Dental Prosthesis, St. Louis, 1958, The C. V. Mosby Company. pp. 75-76. Pietrokovski, J.. Sorin, S., and Hirshfeld, Z.: The Residual Ridge in Partially Edentulous Patients. Submitted to J. PROSTHET. DENT, Pietrokovski, J., and Masslcr, M.: Alveolar Ridge Resorption Following Tooth Extraction, J. PROSTHET. DENT. 17: 21-27, 1967. Pietrokovski, J.: Bone Remodeling After Tooth Extraction, Isr. J. Med. Sci. 7: 433-436, 1971. TUFTS UNIVERSITY SCHOOL OF DENTAL MEDICINE ONE KNEELAND ST. BOSTON, MASS. 02 111