Microscopic anatomy of edentulous residual alveolar ridges

RESEARCH

AND

JOHN J. SHARRY,

EDUCATION

Section editor

Microscopic anatomy alveolar ridges

of edentulous

Myron 1. Pudwill, D.D.S., MS.,* University of Nebraska, College

of

residual

and Frank M. Wentz, D.D.S., M.S., Ph.D.** Dentistry, Lincoln, Neb.

H

istologic changes in the residual alveolar ridge of edentulous human jaws have been reported periodically in the dental literature. These reports have concerned the relationship of atrophy of the jaws to denture retention and to regeneration and repair of bone and soft tissue after loss of teeth and insertion of immediate dentures. Now, the introduction of subperiosteal and blade-vent implants makes necessary a careful histologic re-examination of edentulous jaws in order that we may understand clinically successful and unsuccessful implants. Classical descriptions of the microscopic anatomy of edentulous human jaws were made by Pendleton.’ Houcher’ reviews this work in detail. How-ever, Pendleton’s study of the edentulous maxillae and mandible constitutes topographic microscopic anatomy: It is concerned with specific muscle attachments, glands, and bony ridges as related to impression making and the retention of dentures. This investigation histologically examines the tissues of the residual edentulous alveolar ridge in man to see if histologic changes may cause implants to fail and if tissue adaptation to implants will endure. MATERIALS

AND

METHODS

The histologic sections used were from the collection of 1)rs. Rudolf Kronfeld and Balint Orban. This study was based on five edentulous cadavers. Four were men ranging in age from 55 to 80 years (Figs. 1 and 2). The fifth was of undetermined age and sex. ‘I-he maxillary specimens were sectioned sagittally from the anterior area to tuberosity; the mandible was sectioned from the midline through the retromolar pad. l’he specimens were then cross-sectioned. ‘l‘he sections were stained with hematoxylin and eosin. The jaws were edentulous except for one specimen in which

of

Condensed Science at *Chairman, **Assistant

448

from a thesis the Graduate Department Dean.

in partial College of of Restorative

fulfillment the University Dentistry.

of

the requirements of Nebraska.

for

the

degree

of Master

Microscopic

anatomy

of

Fig. 1. Photomicrograph of a mandibular edentulous residual alveolar man. The dense, fibrous connective tissue is draped over the residual cate hyalinization of the connective tissue next to the bone crest.

one maxillary premolar remained. dibular specimens. It is not known forces.

ridges

alveolar

449

ridge from au IO-year-old bone ridge. Arrows indi-

The study includes two maxillary and whether the tissues had been subjected

four

man-

to denture

FINDINGS The epithelium hornified surface. and

one

was

not

of the residual One specimen hornified.

alveolar ridge in the five cadavers generally had a showed hyperkeratosis, one showed parakeratosis,

Acanthosis

was

present

in

all

specimens.

The

epithelial

ridges were wide, thick, and, in some instances, branching. Only one normal architectural pattern, characterized by medium super-papillary width and medium length of the ridges, as reported by Wentz, Maier, and Orban was observed. The effect of injury of the epithelium was seen in the specimen from a 63-year-old man (Fig. 3). Abrasion of the surface had caused a thinning of the epithelium by traumatic removal of the hornified layer. Connective tissue. The fibers showed variations in arrangement: ( 1) finely textured-unbundled, diffusely arranged, fine fibers, (2) irregularly textured-un-

450

Pudwill

and

.I. I’rosthrt. Octobrr.

Wen.tz

Fig. 2. Photomicrograph man. Observe the dense,

Fig. 3. Photomicrograph Arrow indicates abrasion vessels.

of a mandibular edentulous residual alveolar ridge fibrous connective tissue of the reticular layer.

of an edentulous residual alveolar ridge and a thinning of the surface epithelium.

Fig. 4. Photomicrograph of a mandibular edentulous residual alveolar old man. The connective tissue covering the bone crest is hyalinized blasts. .4n orcter layer containing many fibroblasts bounds the hyalinized

from Note

from

Dent. 1975

an 80-year-old

a 63-year-oId the hyperemic

man. blood

ridge from an DO-yearand contains few fibroregion (arrows).

Microscopic

anatomy

of

alveolar

ridges

451

Fig. 5. Photomicrograph of mandibular residual alveolar ridge from a 63-year-old man. Tooth debris (A) is separated from the alveolar ridge crest (C) by a capillary-rich zone (B). The latter surface (C) is scalloped and shows evidence of previous resorption that had been repaired by new bone. Endosteal bone apposition is evident at D. Fig. 6. Photomicrograph of the residual ridge from an 80-year-old

connective tissue immediately above the mandibular man. Arrow indicates a resting type of epithelial

alveolar remnant.

bundled, fine fibers and coarsely bundled fibers, and (3) coarsely textured-bundled, coarse fibers. The finely textured fibers were most apparent in the papillary layers; the coarsely textured fiber bundles were the most predominant and formed the bulk of the reticular layer of the lamina propria. The dense matte effect was observed in all specimens, covering the crest of the residual alveolar ridge. The fibers of this dense matte ran parallel to the epithelial surface. A draping effect of these dense fiber bundles over the residual alveolar ridge was created by the coursing of these bundles (Figs. 1 and 2). Hyalinization in the connective tissue was seen in four of the five subjects. The fibers had a glassy, pink, fused appearance. The fibers covering the residual alveolar bone in some areas showed this change (Figs. 1 and 4). Fewer fibroblasts were found in the hyalinized region. An outer fibroblast-rich area bounded the fibroblast-poor area. All specimens showed a form of collagen degeneration in limited regions. The irregularly textured connective tissue near some blood vessels was affected. Tissue degeneration was evidenced by a mucoid degeneration of collagen. The collagen bundles were fragmented into bluish, granular masses as compared to the characteristic wavy course and eosinophilic stain of the fibers.

and

J. Prosthet.

452

Pudwill

Wentz

Fig.

7. High-power

Fig. rest

8. Photomicrograph of a mandibular is surrounded by a well-differentiated

study

of Fig.

October.

6. Arrow

indicates residual fibrous

epithelial alveolar capsule

Dent. 1975

rest. ridge. A large, (arrows).

proliferated

epithelial

Tooth debris was a predominant finding in all but one specimen. Tooth debris was found in the reticular layer of connective tissue close to the surface of the residual alveolar bone and in the bone marrow completely surrounded by bone tissue. In one specimen where the tooth debris was located close to the surface of the residual alveolar bone, the connective tissue showed a peculiar reaction. Between the tooth debris and the bone surface, capillary proliferation was evident (Fig. 5) . The most striking finding in the study was the presence of epithelial remnants, possibly from Hertwig’s epithelial root sheath, in all of the subjects (Figs. 6 to 8). Epithelial rests. Two different morphologic types of epithelial remnants could be distinguished: a small resting type and a large proliferated type.” Most of the resting epithelial remnants were deep in the lamina. propria and near the surface of the residual alveolar crest bone. Occasionally, they were in bone marrow spaces. In the small resting variety, the epithelial cells were arranged in oval groups consisting of an average of ten cells. The adjacent connective tissue did not form a capsule. The large proliferated types of epithelial rests were in spherical groups of cells (Fig. 8) . The reaction of the connective tissue surrounding the proliferated epithelial rests varied. The rests in some instances were surrounded by a well-differentiated fibrous capsule, with a concentric arrangement of fibroblasts and collagen fibers. In other instances, the capsule changed into a hyaline mass in which fibers and cells could be distinguished with difficulty.

~I~ll~r “4’ u

Microscopic

anatomy

of alveolar

ridges

453

Fig. 9. Photomicrograph of a maxillary edentulous residual alveolar ridge from a 77-year-old man. An osteoid seam may be observed at A on the outer surface and at B on the endosteal surface. Osteoblasts the bone.

Fig. 10. High-power

line

the endosteal

pbotomicrograph

surface

(C).

A multinucleated

of a mandibular

osteoclast

(D)

is resorbing

residual alveolar ridge from a 55-year-

old man. The bone tissue of the crest appears to be moth-eaten. Empty lacunae cytes predominate (A). Only a few osteocytes (arrow) are visible. The bone for the few viable osteocytes, resembles necrotic bone. The tissue may represent

free of osteotissue, except “overaging.”

Chronic inftammation. In the deeper reticular layers of the lamina propria, a focal infiltration of inflammatory cells was evident. The infiltrating cells, consisting of lymphocytes and plasma cells, congregated in colonies along the course of the blood vessels. All specimens had this form of chronic inflammation. Residual alveolar bone. The bone tissue of the residual alveolar ridge was predominantly of the mature lamellated type. Immature bone was found in regions of rapid bone apposition (Fig. 9). Characteristic overaged and osteoid types were seen (Fig. 10). The surface of the residual alveolar bone in all subjects was irregular. Evidence of Howship’s lacunae was found in four of the five specimens. The residual alveolar bone tissue showed resorption and appositional repair. These reactions appeared to have been phasic. One process may have predominated over the other in a given region for a given specimen. Apposition of osteoid tissue predominated in the specimen from the 77-year-old man. Fig. 10 shows an aplastic condition where neither apposition nor resorption occurred and unresorbed “overaged bone” is a characteristic finding. Fig. 11 shows the specimen from a 63-year-old man in which resorption predominates.

454

Pudwill

and

Wentz

J, Prosthet. October.

Dent. 1975

Fig. 11. Photomicrograph of a mandibular residual alveolar ridge from a 65year-old man. This bone shows active resorption. Note osteoclasts (A) in Howship’s lacunae. Increased vascularity is apparent. In all, the outstanding characteristic that predominated over resorption was the reinforcement of the internal structure of the bone by an appositional pattern on the endosteal surface. This had led to osteosclerosis in two individuals. DISCUSSION Controversy concerning the prognosis of implant dentures has centered on the possibility of infection around the posts protruding through the mucosa. It is thought that the bacteria may enter the external site around the post and cause a deep infection and subsequent rejection of the implant. However, such infection does not usually take place in healthy mouths. Failures do occur, one of which is termed “perioimplantoclasia.“” This condition arises following the period of initial healing. It is characterized by pocket formation around the implant with an accompanying inflammatory exudate. The causes may be due not only to mechanical inadequacy of the implant or external infection by the oral bacteria, but to previously unconsidered conditions within the tissues of the residual ridge. In this study, the tissues all showed chronic inflammation and the presence of epithelial remnants. Surgery and the superimposition of a metallic im-

Volume Number

34 4

Microscopic

anatomy

of alveolar

ridges

455

plant may stimulate the growth of the epithelial rests. This epithelium may displace the connective tissue and bone from around the metallic implant and may contribute to pocket formation accompanied by an inflammatory exudate. Such a condition may be termed “peri-implantitis.” Is there any correlative evidence that the tissue adaptation to the actual implants will be successful and dictate long-term success. 2 The solution is the selection of the right subject for the implant procedure. An 80-year-old subject had a balance between apposition and resorption of bone. iz 6%year-old subject had “overaged” bone and a predominance of resorption over apposition of bone. One subject showed only resorption of bone. A complete history (not medical alone) that reveals the patient’s periodontal status before extraction may give a basis for judgment. For example, the prognosis for a subject whose tooth loss was due to periodontosis may be less favorable than that for a subject whose tooth loss was related to a chronic periodontitis or to caries. While our study suggests a favorable or unfavorable reaction at the residual alveolar ridge, it also indicates the need for a definitive dental history as a prelude to the prescribing implant surgery for a patient. SUMM.ARY The histologic tissue changes of the residual alveolar ridges were studied in five edentulous patients ranging from 55 to 80 years of age. The material studied was obtained from cadavers. The following observations were made: (1) The epithelium was hornified. Acanthosis was found in all specimens. (2) In four of the specimens, the collagen fibers covering the residual bone crest showed a hyalinized area. (3) Mucoid collagen degeneration was seen in all specimens. (4) The most striking finding, common to all specimens, was the epithelial remnants. Resting and proliferating types were identified. (5) Chronic inflammation was found in all specimens. (6) Both osteoid and necrotic bone types were observed. (7) An outstanding characteristic of the residual alveolar ridge was the reinforcement of the internal structure of the bone by endosteal apposition. References 1. 2. 3. 4. 5.

Pendleton, E. C.: Changes in Denture Supporting Tissues, J. Am. Dent. ASSOC. 42: l-15, 1951. Boucher, C. 0.: Swenson’s Complete Dentures, ed. 6, St. Louis, 1970, The C. V. Mosby Company. Wentz, F. M., Maier, A. W., and Orban, B.: Age Changes and Sex Differences in the Clinically “Normal” Gingiva, J. Periodontal. 23: 13-24, 1952. Reeves, C. M., and Wentz, F. M.: The Prevalence, Morphology, and Distribution of Epithelial Rests in the Human Periodontal Ligament, J. Periodontol. 15: 785-793, 1962. Jermyn, A. C.: Peri-implantoclasia-Cause and Treatment, J. Implant Dent. 5: 25-48, 1958. UNIVERSITY COLLEGE LINCOLN,

OF NEBRASKA OF DENTISTRY

NEB.

68503