Dimensional ridge alterationsfollowing tooth extraction. Anexperimental study in the dogAraujo MG, Lindhe J: Dimensional ridge alterations following tooth extraction. Anexperimental study in the dog. J Clin Periodontol 2005; 32: 212–218. doi: 10.1111/j.1600-051X.2005.00642.x. r Blackwell Munksgaard, 2005.

AbstractObjective: To study dimensional alterations of the alveolar ridge that occurredfollowing tooth extraction as well as processes of bone modelling and remodellingassociated with such change.

Material and Methods: Twelve mongrel dogs were included in the study. In bothquadrants of the mandible incisions were made in the crevice region of the 3rd and 4thpremolars. Minute buccal and lingual full thickness flaps were elevated. The fourpremolars were hemi-sected. The distal roots were removed. The extraction sites werecovered with the mobilized gingival tissue. The extractions of the roots and thesacrifice of the dogs were staggered in such a manner that all dogs contributed withsockets representing 1, 2, 4 and 8 weeks of healing. The animals were sacrificed andtissue blocks containing the extraction socket were dissected, decalcified in EDTA,embedded in paraffin and cut in the buccal–lingual plane. The sections were stained inhaematoxyline–eosine and examined in the microscope.

Results: It was demonstrated that marked dimensional alterations occurred during thefirst 8 weeks following the extraction of mandibular premolars. Thus, in this intervalthere was a marked osteoclastic activity resulting in resorption of the crestal region ofboth the buccal and the lingual bone wall. The reduction of the height of the walls wasmore pronounced at the buccal than at the lingual aspect of the extraction socket. Theheight reduction was accompanied by a ‘‘horizontal’’ bone loss that was caused byosteoclasts present in lacunae on the surface of both the buccal and the lingual bonewall.

Conclusions: The resorption of the buccal/lingual walls of the extraction siteoccurred in two overlapping phases. During phase 1, the bundle bone was resorbedand replaced with woven bone. Since the crest of the buccal bone wall was comprisedsolely of bundle this modelling resulted in substantial vertical reduction of the buccalcrest. Phase 2 included resorption that occurred from the outer surfaces of both bonewalls. The reason for this additional bone loss is presently not understood.

Key words: bundle bone; modelling;remodelling; wound healing

Accepted for publication 5 May 2004

The alveolar process is a tooth depen-dent tissue that develops in conjunctionwith the eruption of the teeth. Further,the volume as well as the shape of thealveolar process is determined by theform of the teeth, their axis of eruptionand eventual inclination (Schroeder1986). Subsequent to the removal ofall teeth in the adult individual, thealveolar processes will undergo atrophy

(e.g. Atwood 1957, Hedegard 1962,Tallgren 1972). The amount of hardtissue reduction varied considerablybetween subjects as reported by e.g.Atwood (1962), Carlsson & Persson(1967) and Tallgren (1972).

Clinical and/or radiographic studiesby e.g. Johnson (1963, 1969), Pietro-kovski & Massler (1967), Lekovic et al.(1997, 1998), Camargo et al. (2000),

Schropp et al. (2003) have demonstratedthat marked alterations of the height andwidth of the alveolar ridge will occurfollowing single or multiple toothextractions. The healing process follow-ing tooth removal apparently resulted inmore pronounced resorption on thebuccal than on the lingual/palatalaspects of the ridge. Pietrokovski &Massler (1967) studied the amount of

Mauricio G. Araujo1,2 andJan Lindhe2

1Department of Periodontology, State

University of Maringa, Maringa, Brazil;2Department of Periodontology, Sahlgrenska

Academy at Goteborg University, Goteborg,

Sweden

212

J Clin Periodontol 2005; 32: 212–218 doi: 10.1111/j.1600-051X.2005.00642.x Copyright r Blackwell Munksgaard 2005

tissue that was lost after unilateral toothextraction and used plaster casts modelsfor the dimensional assessments. Theauthors concluded that the buccal boneplates both in the maxilla and themandible were resorbed considerablymore than the corresponding palatal/lingual bone walls and that the center ofthe ridge, as a consequence, shiftedpalatally/lingually.

Further, the process that resulted intissue reduction seemed to be morepronounced during the initial phase ofwound healing than during later periodsfollowing tooth removal. Johnson(1969) reported that most of the dimen-sional alterations – horizontal as well asvertical – of the alveolar ridge tookplace during the first 3 months ofhealing. In a recent clinical studySchropp et al. (2003) estimated bonehealing and soft-tissue contour changesfollowing single-tooth extraction. Theyincluded 46 patients in their study andmade assessment 3, 6 and 12 monthsfollowing the removal of one premolaror one molars. Schropp et al. (2003)stated that ‘‘approximately two thirds ofthis reduction ‘‘. . . the width of thealveolar ridge . . .’’occurred within thefirst 3 months after tooth extraction’’.

The process of healing that occurredfollowing tooth removal was monitoredin biopsies sampled from extractionsites in man (e.g. Boyne 1966, Amler1969, Evian et al. 1982) as well asexperimental animals (e.g. Huebsch &Hansen 1969, Kuboki et al. 1988, Linet al. 1994). In a recent study in the dog,Cardaropoli et al. (2003) studied bonemodelling and remodelling that occurr-ed within the extraction socket follow-ing the removal of the distal root ofmandibular premolars. From the exam-ination of mesio–distal sections it wasobserved that (i) woven bone filled theextraction socket after one month, (ii)a cortical ridge including woven andlamellar bone had formed after 3months, (iii) after the 3 month intervalwoven bone was gradually replacedwith lamellar bone and marrow. In thestudy referred to no information wasprovided regarding bone tissue altera-tion that occurred outside the extractionsocket.

The objective of the present experi-ment in the dog was to study somedimensional alterations of the alveolarridge that occurred following toothextraction as well as processes of bonemodelling and remodelling associatedwith such change.

Material and Methods

The research protocol was approved bythe ethical committee of the Universityof Maringa. Twelve mongrel dogs about1-year-old and weighting about 10 kgeach were used in the study. Duringsurgical procedures, the animals wereanaesthetized with intravenously admi-nistered Pentothal Natriums (30mg/ml;Abbot Laboratories, Chicago, IL, USA).Throughout the experiment the animalswere fed a soft-pellet diet.

In both quadrants of the mandibleincisions were made in the creviceregion of the 3rd and 4th mandibularpremolars. Minute buccal and lingualfull thickness flaps were elevated todisclose the marginal alveolar bone. Thefour premolars were hemi-sected. Thepulp of each mesial root was extirpatedand the canal filled with guttapercha.The distal roots were carefully removedusing elevators and forceps. The extrac-tion sites were covered with the mobi-lized gingival tissue and stabilized withinterrupted sutures (Fig. 1). The dogswere placed on a plaque control regi-men that included tooth cleaning threetimes per week.

The extractions of the roots werestaggered in a randomized way and insuch manner that at sacrifice all dogscontributed with extraction sites repre-senting 1, 2, 4 and 8 weeks of healing.The animals were sacrificed with an over-dose of Pentothal Natriums and per-fused, through the carotid arteries, witha fixative containing a mixture of 5%glutaraldehyde and 4% formaldehyde(Karnovsky 1965). The mandibles wereremoved and tissue blocks contain-ing the extraction socket of the distalroot of each premolar were dissectedand placed in the fixative. Each blockwas decalcified in EDTA, dehydrated inincreasing concentrations of ethanol, em-bedded in paraffin and cut in the buccal–lingual plane. The sections were stained

in haematoxyline–eosine. Sections rep-resenting the central portion (in mesial–distal direction) of each extraction socketwere selected and examined in the mi-croscope.

Histological examination

The tissue within the extraction socketwas examined using a Leitzs DM-RBEMicroscope (Leica, Wetzlar, Germany)equipped with an image system (Q-500MCs; Leica).

Histometric measurements

The height of the cortical bone wallswas determined in the following way(Fig. 2): a line parallel to the long axisof the root was drawn in the center ofthe socket (C–C) to separate the buccaland lingual compartments. Subse-quently, horizontal lines (L and B)perpendicular to C–C were drawn toconnect the most coronal portions of thebuccal and lingual bone crest to C–C.The vertical distance between the buc-cal and lingual intersections with C–Cwas measured and expressed in mm.

The width of the buccal and lingualbone walls was determined at three dif-ferent levels; A, B and C (Fig. 2) andexpressed in mm. The levels were locatedat 1, 3, and 5mm, respectively, apical ofthe buccal and lingual bone crest.

Mean values and standard deviationswere calculated for each variable, siteand group.

Results

All extraction sockets healed unevent-fully. Overt signs of soft-tissue inflam-mation (swelling and redness) were seenin sites representing 1 week of healing,

Fig. 1. Clinical view of the experimentalsites immediately after root extraction andplacement of sutures.

C

C

BuccalLingual

Level A

Level B

Level C

Level A

Level B

Level C

LB

Fig. 2. Schematic drawing representing thelocation where the histometric measure-ments were performed. For detailed infor-mation, see text.

Healing of extraction socket 213

but the mucosa covering the socketsafter 2, 4 and 8 weeks of healing wereconsidered to be clinically healthy.

One week of healing (Fig. 3)

The connective tissue of the mucosacovering the extraction site exhibited

modest signs of inflammation. Thus,areas could be identified which werepoor in their collagen content but richin vascular structures and inflammat-ory cells.

The marginal portion of the lingualbone wall of the extraction socket wasmarkedly wider than the correspondingportion of the buccal wall (Fig. 3). AtLevel A (Table 1) the lingual wall was1.4 � 0.2mm (SD) wide while thecorresponding width of the buccal wallwas 0.6 � 0.1mm. The matchingdimensions at Level B were 2.0 � 0.3and 1.3 � 0.1mm, respectively.

Both the buccal and lingual bonewalls contained large numbers of well-defined bone marrow spaces. The innersurfaces of the socket walls were linedwith bundle bone (Fig. 4). In all areas ofthe socket, multinucleated cells (osteo-

clasts) could occasionally be observedon the surface of this bundle bone. Asevered periodontal ligament thatincluded fibroblasts, distinctly orien-tated collagen fibers, vascular structuresand inflammatory cells resided lateral tothe bundle bone.

The crestal regions of the bone wallswere comprised solely of bundle bone(Fig. 5a, b), the height of which wasmore pronounced at the buccal(X1mm) than at the lingual wall(o0.5mm). A large number of osteo-clasts were present on the outer surfaceof the crestal region of both bone walls.

The internal portion of the extractionsocket was occupied by coagulum,granulation tissue, provisional matrixand small amounts of newly formedbone. The coagulum resided in the mostcentral portion of the socket and exhib-

Fig. 3. Overview of the extraction site after1 week of healing. Note the large amountsof provisional matrix and, in the center ofthe socket, remaining blood clot. BC, bloodclot, B, buccal; L, lingual; PM, provisionalmatrix. H&E staining; original magnifica-tion � 16.

Table 1. Width of the bone tissue at the buccal and lingual walls of the extraction sites

1 week 2 weeks 4 weeks 8 weeks

buccal lingual buccal lingual buccal lingual buccal lingual

Level A 0.6 (0.1) 1.4 (0.2) 0.6 (0.1) 1.3 (0.3) 0.7 (0.2) 1.3 (0.1) 0.5 (0.1) 1.2 (0.1)Level B 1.3 (0.1) 2.0 (0.3) 1.1 (0.3) 1.9 (0.4) 1.1 (0.2) 1.6 (0.1) 1.1 (0.1) 1.7 (0.3)Level C 2.0 (0.0) 2.8 (0.8) 1.9 (0.4) 2.7 (0.7) 2.0 (0.4) 2.9 (0.3) 1.6 (0.1) 2.7 (0.5)

The measurements (mm) were made at different levels (A, B C; Fig. 1) and time intervals. Mean

(SD).

Fig. 4. Higher magnification of outlinedarea in Fig. 3. The bundle bone coveredthe socket wall. Lateral to the bundle bone asevered periodontal ligament can be identi-fied. BB, bundle bone; PDL, severedperiodontal ligament; original magnification� 200.

Fig. 5. One week of healing. The crestal region of the lingual (a) and buccal (b) walls. Thebuccal bone crest is made exclusively of bundle bone while the lingual crest is comprised ofa mixture of cortical bone and bundle bone. Note the presence of osteoclasts in the crestalregions of both walls (arrows). A, inner surface of the bone wall; BB, bundle bone; CB,cortical bone; O, outer surface of the bone wall; arrows, osteoclasts. H&E staining; originalmagnification � 50.

214 Araujo & Lindhe

ited signs of lysis. The granulationtissue that included a large number ofvessels, few fibroblasts and inflamma-tory cells occupied a portion of themore coronal segments of the socket.The provisional matrix was the dom-inating tissue within the socket andincluded fibroblasts, newly formed ves-sels and collagen fibers. In the apicalportions of the socket, small islandsof newly formed woven bone werepresent around vascular units close tothe bundle bone.

Two weeks of healing (Fig. 6)

The mucosa of the site was devoid ofinflammatory cells but included a fibro-blast rich connective tissue. The crestalregion of the lingual hard-tissue wallwas at this interval devoid of bundlebone while at the corresponding regionof the buccal wall, bundle bone occu-pied an area that was 0.3 � 0.1mm high(Fig. 7a, b). The outer portions of thecrestal region of both bone walls werelined with osteoclasts. Several osteo-clasts were also found on the outersurface of the buccal and lingual bonewalls apical of the crestal region.

Large amounts of newly formed boneoccurred in the apical and lateral

portions of the extraction socket. Provi-sional matrix tissue resided in thecentral and marginal compartments ofthe experimental site. At this interval,no periodontal ligament tissue could beidentified lateral to the socket walls. Thesurface of the woven bone was linedwith densely packed osteoblasts andincluded a primitive bone marrow. Mostof the surface of the remaining bundlebone was in direct continuity withtrabeculae of woven bone.

Four weeks of healing (Fig. 8)

No bundle bone could be found in thecrestal region of the bone walls. Further,in the crestal region of the buccal wall, alarge portion of the lamellar bone hadapparently been replaced with wovenbone. The surface of this newly formedtissue-exhibited signs of remodelling. Amultitude of osteoclasts could beobserved on the outer surface of boththe buccal and the lingual bone wallsapical of the crestal regions.

The lingual bone wall was at thisinterval between 1.3 � 0.1mm (LevelA) and 1.6 � 0.1mm (Level B) wide.The corresponding dimensions of thebuccal wall were 0.7 � 0.2 and1.1 � 0.2mm, respectively (Table 1).

Provisional matrix tissue was pre-sented in the most central portions of

Fig. 6. Overview of the extraction site after2 weeks of healing. Note the large amountsof woven bone are presented in the lateraland apical portions of the socket. B, buccal;L, lingual; PM, provisional matrix; WB,woven bone. H&E staining; original magni-fication � 16.

Fig. 7. Two weeks of healing. The crestal region of the lingual (a) and buccal (b) walls. Notethe large number of osteoclasts present on the outter surface of the crestal regions. A, innersurface of the wall; BB, bundle bone; CB, cortical bone; O, outer surface of the wall; arrows,osteoclasts. H&E staining; original magnification � 50.

Fig. 8. Overview of the extraction site after4 weeks of healing. Note the extraction siteat this interval is dominated by newlyformed woven bone. The bundle bone ofthe crestal region of the buccal wall wasresorbed and partially replaced by wovenbone. Note also that the marginal portion ofthe old buccal wall (arrow) is ‘‘apical’’ to itslingual counterpart. B, buccal; L, lingual;WB, woven bone; arrow, marginal portionof the old buccal wall. H&E staining;original magnification � 16.

Healing of extraction socket 215

the socket. Mineralized tissue and bonemarrow occupied the remaining seg-ments of the site. The mineralized tissueportion was mainly comprised of wovenbone, which appeared to be in theprocess of both modelling and remodel-ling. The bone marrow was either ofprimitive (loose connective tissue,inflammatory cells and large vessels)or mature (large adipocytes, few inflam-matory cells, small amounts of collagenfibers and vascular units) character.Large portions of the bundle bone hadapparently been replaced by lamellarbone and marrow.

Eight weeks of healing (Fig. 9)

The lingual bone wall was also at thisinterval considerably wider than thebuccal wall. Further, the crest of thebuccal bone was located about 2mmapical to the crest of the lingual hardtissue wall. A wide zone of mineralizedtissue bridged the buccal and lingualbone walls of the extraction socket. Thisbridge that had an oblique orientationincluded woven bone as well as lamellarbone. Numerous osteoclasts were foundboth on the outer surface of the crestaland on more apical regions of the buccalbone (Fig. 10). Scattered osteoclastswere found in the corresponding loca-tions of the lingual bone wall. Theinternal portion of the socket region wasoccupied by bone marrow but includedfew trabeculae of mineralized tissue thatwere comprised of woven bone andlamellar bone.

Alterations of the height of the bone crest

during healing

At the 1-week interval, the buccal bonecrest was found to be located on theaverage 0.3 � 0.2mm (SD) ‘‘coronal’’to the lingual crest, while at the 2-, 4-,and 8-week intervals the buccal crestwas consistently located ‘‘apical’’ of itslingual counterpart (Fig. 11). Thus, after2 weeks of healing the distance betweenintercept B and intercept L (Fig. 2) was0.3 � 0.1mm. The corresponding dis-tances after 4 and 8 weeks of healingwere 0.9 � 0.3 and 1.9 � 0.2mm.

Alterations of the width of the bone crestduring healing

The width of the buccal and lingualbone walls at Levels A, B, and C isdescribed in Table 1.

At all four examination intervals andat each of the three levels, the buccalbone wall was thinner than the lingualbone wall. Further, the width of both thebuccal and the lingual bone walls wasgreater at Level B than at Level A andgreater at Level C than at Level B.

Discussion

The present experiment demonstratedthat marked dimensional alterationsoccurred during the early phase – 8weeks – following the extraction ofmandibular premolars. Thus, in thisinterval there was a marked osteoclasticactivity resulting in resorption of thecrestal region of both the buccal and thelingual bone wall. The reduction of theheight of the walls was more pro-nounced at the buccal than at the lingualaspect of the extraction socket.

The observation that following toothextraction the amount of vertical boneloss became more pronounced on thebuccal than on the lingual socket wallis in agreement with previous clinical

studies (e.g. Johnson 1963, 1969, Pie-trokovski & Massler 1967, Schroppet al. 2003). The current findings are alsoin agreement with data recently pub-lished by Botticelli et al. (2004). Theyassessed dimensional alterations thatoccurred in the alveolar ridge during a4-month period following implant pla-cement in fresh extraction sockets. Thedistance between the implant surfaceand the buccal and lingual/palatal bonewalls was measured at baseline and atre-entry after 4 months. The authorsconcluded, ‘‘during the 4-month inter-val following tooth extraction the buc-cal bone dimension had undergonehorizontal resorption that amountedto about 56%. The corresponding re-duction of the lingual/palatal bone wallwas 30%’’.

In preparation for removal of thedistal roots, crevice incisions were made

Fig. 9. Overview of the extraction site after8 weeks of healing. The entrance of thesocket is sealed by a hard tissue ridge that iscomprised of woven bone and lamellarbone. The central portion of the socket isdominated by bone marrow. Note that themarginal portion of the buccal wall (arrow)is about 2mm ‘‘apical’’ of the marginaltermination of the lingual wall. B, buccal;BM, bone marrow; L, lingual; arrow,marginal portion of the buccal wall. H&Estaining; original magnification � 16.

Fig. 10. Eight weeks of healing at thecrestal buccal bone wall. Note the largenumber of osteoclasts (arrows) that arepresent on the surface of the old corticalbone. The woven bone is in the process ofremodelling. CO, old cortical bone; WB,newly formed woven bone; O, outer surfaceof the wall; arrows, osteoclasts; dotted line,borderline between the woven bone and theold cortical bone. H&E staining; originalmagnification � 200.

− 2.5

− 2− 1.5

− 1− 0.5

0

0.5

1

1 week 2 weeks 4 weeks 8 weeksm

m

Fig. 11. Histogram describing the verticaldistance between the buccal and lingualintersections with C–C (Fig. 2). At 1 weekthe buccal crest was located ‘‘coronal’’ ofthe lingual crest, but after 2, 4, and 8 weeksof healing the buccal crest was consistently‘‘apical’’ of its lingual counterpart.

216 Araujo & Lindhe

and minute full thickness flaps wereelevated at both the buccal and lingualaspects of the alveolar process. It is wellknown that such surgical trauma thatincludes the separation of the perios-teum and the rupture of its connectivetissue attachment at the bone surfacewill induce an acute inflammatoryresponse which in turn will mediateresorption of the surface layer of thealveolar bone in the exposed area (e.g.Wilderman 1963, Staffileno et al. 1966,Wood et al. 1972, Bragger et al. 1988).In specimens representing 1 and 2weeks of healing in the present experi-ment, osteoclasts were indeed present inthe exposed area of the alveolar ridge,which exhibited signs of surface resorp-tion. There are reasons to suggest thatthis hard-tissue resorption may in partexplain the dimensional alterationsthat occurred during the first weeks ofhealing following tooth removal.

In the current experiment, the altera-tion of the level of the buccal bone crestover time was determined using thelingual crest as reference. Since duringthe course of healing there was alsomarked resorption of the lingual bone,the change reported for the buccalbone crest is most likely underesti-mated. The relative reduction of theheight of the buccal bone wall betweenthe 1- and 8-week intervals was2.2 � 0.2mm, i.e. about 45 mm/day.This rate of bone resorption is similarto that reported from experiments eval-uating modelling and remodellingevents at fracture sites in the long bonesof dogs. Thus, Schenk & Hunziker(1994) stated that ‘‘In adult caninebone, the osteoclastic resorption rate isabout 50–60 mm/day. . . .’’. In this con-text it should be realized that in the 8-week specimens of the current experi-ment, a large number of osteoclastscould be identified both on the buccaland on the lingual bone walls. In otherwords, the process of modelling was atthe end of this study not completed.This is in agreement with findings fromsimilar experiments presented by Car-daropoli et al. (2003). They studieddynamics of bone tissue formation intooth extraction sites in the dog andreported that between 2 and 6 months ofhealing substantial portions of wovenbone within the extraction socket werereplaced with lamellar bone and marrow.

The tooth is anchored to the jaws viathe bundle bone into which the perio-dontal ligament fibers invest. Followingthe removal of a tooth, the bundle bone

at the site obviously will lose itsfunction and disappear. In the 1-weekspecimens of the current sample, it wasobserved that the crestal region of thebuccal hard tissue wall was made upexclusively of bundle bone while thecorresponding region of the lingualbone was comprised of a combinationof bundle bone and lamellar bone.Bundle bone, inside the socket as wellas in the crestal regions could be foundin the experimental sites at 1 and 2weeks but was not present in specimensrepresenting 4–8 weeks of healing. Thisis in agreement with Cardaropoli et al.(2003) who demonstrated that already 2weeks following the removal of amandibular premolar, most of the bun-dle bone at the mesial and distal aspectsof the extraction socket had been re-placed with woven bone. Hence, theearly resorption of the bundle bone mayin part explain the marked reduction ofthe height of the buccal wall thatoccurred between week 1 and week 4of healing.

Between 4 weeks and 8 weeks ofhealing there was not only pronouncedalteration of the tissue within theextraction socket but also substantialadditional alteration of the dimensionsof the alveolar process of the extractionsite. Thus in this interval (i) a corticalridge was formed that sealed theentrance of the extraction site and (ii)woven bone was to a large extentreplaced by lamellar bone and marrow.During this second month of healingthere was a further reduction of (i) theheight of the buccal bone wall as well as(ii) the width of both the buccal andlingual walls.

From the data presented in this studyit may be concluded that the resorptionof the buccal/lingual walls of theextraction site occurred in two over-lapping phases. During phase 1, thebundle bone that lost its functionfollowing the removal of the tooth,was resorbed and replaced with wovenbone. Since the crest of the buccal bonewall was comprised solely of bundlethis modelling resulted in substantialvertical reduction of the buccal crest.Phase 2 included resorption thatoccurred from the outer surfaces of bothbone walls. The reason for this addi-tional bone loss is presently not under-stood. It is suggested, however, thatfollowing elevation of the mucoperios-teal flap in conjunction with toothextraction, the blood vessels to the bonewalls were severed. The reduced blood

supply (for a review see Schenk &Hunziger 1994) may have caused deathof the osteocytes and as a consequencenecrosis of the surrounding mineralizedtissue of the bone walls. During phase 2of healing this necrotic bone maytherefore gradually have been elimi-nated through surface resorption orche-strated by osteoclats in the periosteum.Since the buccal bone plate was con-siderably thinner than the lingual plate,this ‘‘horizontal resorption’’ may alsocause ‘‘vertical reduction’’ of the buc-cal wall. Given that, however, markeddimensional alteration of the extractionalso occurs following tooth removalwithout flap elevation, other factorsmust be involved in bone resorptionthat takes place in phase 2 of modelling.Such factors may include (i) adaptationto continued lack of function at theextraction site, (ii) tissue adjustment tomeet ‘‘genetically’’ determined demandsregarding ridge geometry in the absenceof teeth.

References

Amler, M. H. (1969) The time sequence of

tissue regeneration in human extraction

wounds. Oral Surgery, Oral Medicine and

Oral Pathology 27, 309–318.

Atwood, D. A. (1957) A cephalometric study of

the clinical rest position of the mandible. Part

II. The variability in the rate of bone loss

following the removal of occlusal contacts.

Journal of Prosthetic Dentistry 7, 544–552.Atwood, D. A. (1962) Some clinical factors

related to the rate of resorption of residual

ridges. Journal of Prosthetic Dentistry 12,441–450.

Botticelli, D., Berglundh, T. & Lindhe, J.

(2004) Hard tissue alterations following

immediate implant placement in extraction

sites. Journal of Clinical Periodontology 31,

in press.

Boyne, P. J. (1966) Osseous repair of the postex-

traction alveolus in man. Oral Surgery, Oral

Medicine and Oral Pathology 21, 805–813.

Bragger, U., Pasqualli, L. & Kornman, K. S.

(1988) Remodeling of interdental alveolar

bone after periodontal flap procedure

assessed by means of computer-assisted

densitometer image analysis (CADIA). Jour-

nal of Clinical Periodontology 15, 558–564.

Camargo, P. M., Lekovic, V., Weinlaender, M.,

Klokkevold, P. R., Kenney, E. B., Dimitri-

jevic, B., Nedic, M., Jancovic, S. & Orsini,

M. (2000) Influence of bioactive glass on

changes in alveolar process dimensions after

exodontia. Oral Surgery, Oral Medicine,

Oral pathology, Oral Radiology and Endo-

dontics 90, 581–586.Cardaropoli, G., Araujo, M. & Lindhe, J. (2003)

Dynamics of bone tissue formation in tooth

extraction sites. An experimental study in

Healing of extraction socket 217

dogs. Journal of Clinical Periodontology 30,

809–818.

Carlsson, G. E. & Persson, G. (1967) Morpho-

logic changes of the mandible after extrac-

tion and wearing of dentures. A longitudinal,

clinical, and X-ray cephalometric study

covering 5 years. Odontologisk Revy 18,

27–54.

Evian, C. I., Rosenberg, E. S., Cosslet, J. G. &

Corn, H. (1982) The osteogenic activity of

bone removed from healing extraction sock-

ets in human. Journal of Periodontology 53,81–85.

Hedegard, B. (1962) Some observations on

tissue changes with immediate maxillary

dentures. Dental Practitioner 13, 70–78.

Huebsch, R. F. & Hansen, L. S. (1969) A

histopathologic study of extraction wounds in

dogs. Oral Surgery, Oral Medicine and Oral

Pathology 28, 187–196.

Johnson, K. (1963) A study of the dimensional

changes occurring in the maxilla after tooth

extraction. Part I. Normal healing. Australian

Dental Journal 8, 428–433.

Johnson, K. (1969) A study of the dimensional

changes occurring in the maxilla following

tooth extraction. Australian Dental Journal

14, 241–244.

Karnovsky, M. J. (1965) A formaldehyde-

glutaraldehyde fixative of high osmolarity

for use in electron microscopy. Journal of

Cell Biology 27, 137A–138A.Kuboki, Y., Hashimoto, F. & Ishibashi, K.

(1988) Time-dependent changes of collagen

crosslinks in the socket after tooth extraction

in rabbits. Journal of Dental Research 67,944–948.

Lekovic, V., Camargo, P. M., Klokkevold,

P. R., Weinlaender, M., Kenney, E. B., Dimi-

trijevic, B. & Nedic, M. (1998) Preservation

of alveolar bone in extraction sockets using

bioabsorbable membranes. Journal of Perio-

dontology 69, 1044–1049.Lekovic, V., Kenney, E. B., Weinlaender, M.,

Han, T., Klokkevold, P., Nedic, M. & Orsini,

M. (1997) A bone regenerative approach to

alveolar ridge maintenance following tooth

extraction. Report of 10 cases. Journal of

Periodontology 68, 563–570.Lin, W. L., McCulloch, C. A. & Cho, M. I.

(1994) Differentiation of periodontal liga-

ment fibroblasts into osteoblasts during

socket healing after tooth extraction in the

rat. Anatomical Records 1240, 492–506.

Pietrokovski, J. & Massler, M. (1967) Alveolar

ridge resorption following tooth extraction.

Journal of Prosthetic Dentistry 17, 21–27.

Schenk, R. K. & Hunziker, E. B. (1994)

Histologic and ultrastructural features of

fracture healing. In: Brighton, C. T., Frie-

dlaender, G. & Lane, J. M. (eds). Bone

Formation and Repair, pp. 117–146. Rose-

mont, IL, USA: American Academy of

Orthopaedic Surgeons.

Schroeder, H. E. (1986) The periodontium.

Berlin Heidelberg: Springer-Verlag.

Schropp, L., Wenzel, A., Kostopoulos, L. &

Karring, T. (2003) Bone healing and soft

tissue contour changes following single-tooth

extraction: a clinical and radiograhic 12-

month prospective study. The International

Journal of Periodontics & Restorative Den-

tistry 23, 313–323.Staffileno, H., Levy, S. & Gargiulo, A. (1966)

Histologic study of cellular mobilization

and repair following a periosteal retention

operation via split thickness mucogingival

flap surgery. Journal of Periodontology 37,

117–131.

Tallgren, A. (1972) The continuing reduction of

the residual alveolar ridges in complete

denture wearers: a mixed longitudinal study

covering 25 years. Journal of Prosthetic

Dentistry 27, 120–132.

Wilderman, M. N. (1963) Repair after a

periosteal retention procedure. Journal of

Periodontology 34, 487–503.Wood, D. L., Hoag, P. M., Donnenfeld, O. W.

& Rosenberg, D. L. (1972) Alveolar crest

reduction following full and partial thick-

ness flaps. Journal of Periodontology 43,

141–144.

Address:

Mauricio G Araujo

Department of Dentistry

State University of Maringa

Av. Mandacaru, 1550

CEP 87.080 Maringa

PR-Brazil

E-mail: odomar@hotmail.com

218 Araujo & Lindhe