oral surgery oral medicine oral pathology with sectiam onoral andmaxillofacial radiology and endodontics
oral surgery Editor: LARRY J. PETERSON,
DDS
Professor and Chairman Department of Oral and Maxillofacial College of Dentistry The Ohio State University 2131 Postle Hall 30.5 West 12th Avenue Columbus. Ohio 4321 O-I 241
Surgery
Reduction of the compact and cancellous bone substances of the edentulous mandible caused by resorption Christian Urn, MD, DMD,a Peter Solar, MD, DMD,’ Rudolf Blahout, IIID,~ Michael Matejka, MD, DMD,’ and Helmut Gruber, MD,d Vienna, Austria DEPARTMENT ANATOMICAL
OF ORAL SURGERY, DENTAL SCHOOL OF THE UNIVERSITY INSTITUTE OF THE UNIVERSITY OF VIENNA
OF VIENNA
AND
Examination of various bone sections of edentulous atrophic mandibles showed that the body of the mandible loses up to 60% of its original bone substance during progressive atrophy. Most of the bone loss occurs in a relatively early stage of the atrophic process. The greatest extent of bone reduction can be observed in the area of the second premolar and the first molar. In the interforaminal region, which is situated mesial from them, resorption, in most cases, is not as progressive as in the premolar/molar area. The compact and cancellous bone substances are most often equally affected by resorption. Moreover, it could be observed that the cancellous bone substance of extremely atrophic mandibles particularly in the interforaminal region, is marked by a significant increase in density. This might be interpreted as a restructuring process to compensate for bone losses and to secure the stability of the atrophic body of the mandible. (ORALSURG ORALMEDORALPATHOL
1992;74:131-6)
A
ccording to various authors,‘, 2 progressive atrophy may reduce the body of an edentulous mandible by 50% of its original size. In advanced cases, a cra“University Assistant, Department of Oral Surgery. bVisiting Clinician, Department of Oral Surgery. %enior Lecturer, Department of Oral Surgery. Wniversity Professor, Head of Section II, Anatomical 7/12/36732
Institute.
nial reduction not only of the alveolar crest but also of the base of the mandible can be observed.3, 4 A morphologic classification of alveolar ridge resorption was first carried out by Atwood33 5 and later by Tallgren6 and Cawood and Howell.7 As far as changes within the cancellous bone are concerned, partly inconsistent observations have been made by various authors. Kruger* observed a coarsening of the cancellous bone structure whereas Mer131
132
Ulm et al.
OKAL SURG ORAL MEU ORAL PATHOL. August 1992
Table I. Total area of the jaw section (in mm)
Secrions
Mean
s 1
261.3 252.2 231.4 210.6 207.1 205.9 204.9 212.0
s2 s3 s4 s5 S6
S-J S8
32.7 42.3 43.8 35.4 42.6 37.8 31.9 36.2
190.2 169.4 155.9 139.7 150.1 163.6 172.9 189.1
36.0 47.1 52.4 43.4 34.0 40.3 34.4 30.8
Mean
SD
187.9 172.7 172.0 159.3 159.3 175.7 198.6 209.9
44.6 41.5 46.1 40.5 40.2 39.5 36.X 36.3
~
Mean
SD
140.7
27.7 28.5 28.4 25.9 25.4 28.3 32.5 31.6
117.5 91.2
88.1 89.9 109.3 134.6
149.9
Mean = mean value. SD = standard deviation.
Table II. Compact portion of the section (in mm) RR0 4
RR0 3 Seclions
Mean
s I S2 s3 s4 s5 S6 s7 S8
132.9 tto.7 108.9 92.6 86.2 86.2 90.9 96.1
RR0 5
RR0 6
SD
Mean
SD
Mean
SD
Mean
SD
17.9
100.1
25.3 24.3
80.9 73.7 63.4 68.3 65.0 66.3 16.4
19.0 14.6 21.4
107.8 77.5 90.4 78.0 15.5 81.0 87.6 97.3
32.0 20.6 21.3 16.7 15.9 18.4 20.4
67.3 52.4 55.9 50.9 51.5 54.6 62.9 64.0
19.8 8.9 9.7
17.0 20.3 18.2 15.7 18.8
15.2 16.0 20.3 18.5 16.1
17.0
11.7 15.0 12.5 17.3 16.2
Mean = mean value. SD = standard deviation.
tier et a1.9reported that parts of the cancellous bone substance were restructured into compact bone. According to Kubik, to the cancellous portion of the bone is preserved in most cases but is restructured into a finer mesh. In the case of endosseous implantations, knowledge of the structure of the bone available for implantation is of vital importance. To prevent funnel-shaped resorptions in the area where the implant enters the bone, Mailath et al.” and Siegele and Soltesz12-according to their finite-element calculations-recommend that the implant be inserted into the cancellous portion of the bone. An even partial insertion of the implant into the compact layer of the mandible would lead to considerably higher tension between bone and implant and result in the resorption of the surrounding bone structure. For this reason, the precise knowledge of the extent of cancellous and compact bone available in the implantation area and their ratio during the different stages of atrophy is of fundamental importance. MATERIAL AND METHODS Forty-one edentulous, left lower-jaw halves from formalin/phenol-fixed corpses were examined in this
study. For precise assessment of the individual stages of bone resorption, the specimens were organized according to the residual ridge order (RRO) classification established by Atwood,3* s which describes the various degrees of alveolar ridge reduction on the basis of characteristic ridge shapes. RR0 1 corresponds to the alveolar ridge before tooth extraction, and RR0 2 describes the unchanged ridge immediately after extraction. In RR0 3, the empty alveolar ridge has already closed and is high and well rounded. RR0 4 corresponds to small, often knife-edge ridges, whereas in RR0 5, the alveolar ridge has been almost completely resorbed and looks low and well rounded. In RR0 6, the cranial part of the body of the mandible is depressed and the alveolar ridge has been completely resorbed (Figs. 1 and 2). Examination of the 41 mandibles led to the following breakdown: RR0 3 10 mandibles RR0 4 7 mandibles RR0 5 1 1 mandibles RR0 6 13 mandibles Mandibles in classifications RR0 1 and RR0 2 were not considered in the present study since they are not affected by atrophic changes. Borderline cases were
Volume 74 Number 2
Reduction of the compact and cancellous bone substances due to atrophy
133
Fig. 1. Drawing of residual ridge orders 1 to 6 by Atwood.
Fig. 2. Photograph of residual ridge orders 1 to 6 by Atwood.
assigned to the RR0 that predominated in the mandible concerned. With a diamond-coated precision saw, the following eight sections: were cut in each mandible: S 1 Median-sagittal between the lower central incisors S 2 In the area between the lateral incisor and the canine S 3 Between the two premolars S 4 In the area between the second premolar and the first molar S 5 In the area of the first molar S 6 Between the first and the second molars S 7 In the area of the second molar S 8 In the area of the third molar The sections formed a right angle with both the mandibular line and the horizontal axis of each mandibular section that runs parallel to the mandibular line. All eight sections of each mandible were photographed together with a ruler, and the data then were fed into the computer with the help of a digitizer. The following data were stored: the size of the ruler as well as of the section, the border between the compact and
the cancellous bone substances,and the marked basal and buccal points of each section. All noncompact portions of the sections (i.e., all bony parts that contained medullary and hollow spacesas well as cancellous trabeculae) were classified as cancellous bone and distinguished from the compact external cortical layer. t3 The mean values and standard deviations of all measurementsof the various sections were calculated and a t test was carried out to examine whether the mean value differences between the residual ridge orders were significant. The following measurements were carried out in each section: 1. Measurement of the total area of the jaw section (Table I) 2. Measurement of the compact portion of the bone (Table II) 3. Measurement of the cancellous portion of the bone (Table III) FINDINGS
The measurementsobtained are listed in Tables I to III and Figs. 3 and 4. In the majority of cases,the
134
Ulm et al.
ORAL SURG ORAL MED ORAL PATHOL August 1992
3001 250 -
51
52
53
54
55
n
RR0
3
El
q
RR0 RR0
4 5
El
RR0
6
56
S7
S8
Fig. 3. Compact portion of jaw section (in mm2). RRO, Residual ridge order; S, section. 300
250
1
4
RR0
3
0
RR0
4
q
RR0 5
[iii] RR0
6
150 100 50
n 51
52
S3
54
55
56
57
58
Fig. 4. Cancellous portion of jaw section (in mm*). RRO, residual ridge order; S, section. mean value differences between the various RROs were significant (p = 0.05) or highly significant (p = 0.01). A detailed list of the significances is available from us. Unlike the differences between the results obtained in the various residual ridge orders, the differences obtained in the measurementsof the male and female corpseswere not of any significance. For this reason, they have been put together for each residual ridge order. DISCUSSION The results obtained in the interforaminal region have to be assessed separately from those obtained in the premolar/molar region since the average life span
of the premolars and molars is shorter than that of the incisor and canine teeth.t4 For this reason, the meaFig. 5. Photograph of two sections in canine region. A, RR0 3, B, RR0 6 (1, lingual; b, buccal). In section B, coarsening of the cancellous bone structure is clearly visible.
surements obtained in the sections between the mental foramen and the second molar are always smaller than the values measured in the front tooth area. In the distal area, from the second molar on, the
Reduction of the compact and cancellous bone substances due to atrophy
Volume 74 Number 2
135
Fig. 6. Photograph of two sections in area of second molar. A, RR0 3; B, RR0 6 (I, lingual; b, buccal). The vertical loss of bone and the 1: 1 ratio of the compact and cancellous bone substance are clearly discernible.
Table III. Cancellous portion of the section (in mm) RR0 3
I I
RR0 4
Sections
Mean
SD
Mean
SD
s 1 s2 s3 s4 S.5 S6 s7 S8
128.4 141.5 122.4 118.0 120.9 119.7 114.0 115.9
22.1 23.9 26.9 18.1 21.3 17.2 14.8 16.1
90.1 88.4 82.2 76.3 81.8 98.6 106.6 112.7
29.3 40.1 42.8 26.6 17.8 18.3 15.2 13.9
j
RR0 5 Mean 80.2 95.2 81.6 81.3 83.8 94.7
111.0 112.6
RR0 6 SD
Mean
SD
24.3 25.5 30.9 22.8 23.4 20.3 15.6 18.7
73.4 65.1 41.3 37.2 38.4 54.7 71.7 85.9
15.4 24.5 25.5 12.9 10.1 15.6 13.8 11.2
Mean = mean value. SD = standard deviation.
measurement results are again higher than those obtained in the mesial area of the premolar/molar region. This is due to the fact that, for biomechanical reasons, the area that leads into the mandibular ramus and contains the oblique and the mylohyoid lines is marked by a higher bone volume. In the interforaminal region, the highest degree of bone resorption can be observed between RR0 3 and RR0 4 where the original bone volume is reduced by more than 25%. Atwood3 stressed the fact that the transition from RR0 3 to RR0 4 takes place in the 2 years after an extraction, and in 85% of cases, RR0 4 occurs in the next 20 years and then changes into RR0 5 and RR0 6. During this stage of the process, an av-
erage loss of 50% of the bone volume measured in RR0 3 could be observed. In some sections 60% of the bone volume was resorbed (Figs. 5 and 6). During the first stage of the resorption process, the changes in the premolar/molar region tend to be the same as in the area of the incisor and canine teeth; a considerable loss of bone volume can be observed between RR0 3 and 4 that does, however, affect the distal area (S 7 and S 8) less strongly than the mesial area. In the area of the premolar and the first molar, bone loss is significantly higher between RR0 5 and 6 (i.e., in extremely atrophic mandibles). In the areas of the front teeth and of the distal molars, resorption is less pronounced. Especially in the area of the first
136
Ulm et al.
molar, the bone volume measured in RR0 3 may be reduced by more than 60% during progressive atrophy (RR0 6) (Table I). The fact that the maximum width of the body of the mandible remains constant leads to the conclusion that the resorption process fully affects the height of the mandible.4 Indeed, a comparison of the resorption of bone substance and the vertical bone reduction measured in the various jaw sections showed that the values, expressed in percentages, largely corresponded with each other.15 Another striking observation was that the values of RR0 4 are nearly as high as those of RR0 5. Thus it may be presumed that these two RROs are merely two variants of one and the same stage of atrophy. Another explanation of this fact might be that, between RR0 4 and RR0 5, the alveolar ridge is merely affected by a restructuring process and not by bone resorption. Irrespective of the degree of atrophy, the ratio of compact and cancellous bone largely remains 1: 1 (Tables II and III). It is only in RR0 3 that the amount of cancellous bone slightly exceeds that of compact bone. Regardless of the stage of atrophy, this is also the case in the area distal to the first molar (Tables II and III). Analogous to the total reduction of bone measured in the area of the body of the mandible, the reduction of both bone substances during progressive atrophy may amount to 60%. The changes in the structure and density of the cancellous portion of the sections were, however, very significant. With progressive atrophy, a clearly visible coarsening of the trabecular structure and the development of “compact islands,” particularly in the incisor area, could be observed (Fig. 5). Mercier’ has already described these changes. It seems reasonable to interpret such a coarsening of the cancellous structure as well as the development of “compact islands” as parts of a restructuring process to compensate for the loss of bone volume caused by atrophy and to preserve the stability of the body of the mandible. The best method to determine the absolute amount of bone as well as the ratio of compact and cancellous bone substance is computerized tomography.‘6
ORAt SURG ORAL MED ORAL PATHOL August I992
REFERENCES 1. Mercier R. Residual alveolar ridge atrophy: classification and influence of facial morphology. J Prosthet Dent 1979;4 1:90100. 2. Bras J, Van Ooji CP, Duns JY, Wansink HM, Driessen RM, Van den Akkeren HP. Mandibular atrophy and metabolic bone loss. Int J Oral Surg 1983;12:309-13. 3. Atwood DA. Reduction of residual ridges, J Prosthet Dent 1971;26:266-79. 4 Ulm C, Pechmann U, Ertl L, Gruber H, Solar P, Matejka M. Die Lage des Canalis mandibulae in atrophen Unterkiefer. Z Stomatol 1989;86:491-503. 5 Atwood DA. Postextraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and cephalometric roentgenograms. J Prosthet Dent 1963;13: 810-8. 6 Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudal study covering 25 years. J Prosthet Dent 1972;27:120-32. Cawood JI, Howell RA. A classification of the edentulous jaws. Int J Oral Maxillofac Surg 1988;17:232-6. Kruger E. Operationslehre fiir Zahnlrzte. Berlin: Quintessenz Verlags-Gmbh, 1979:290-301. Mercier R, Vanneuville G, Jourde J, Peri G, Patouillard P. Etude de la structure osseuse de la branche horizontale du maxillaire inferieur, apport des techniques radiographiques. C R Assoc Anat 1970;149:891-901. 10. Kubik S. Anatomische Grundlagen der Implantologie. Teil 1. Dental-Revue 1984;1-2:l l-9. I1 Mailath G, BGhn H, Rammerstorfer K, Lill W. Stress distribution around a bone anchored implant supported bridge. UCLA-Symposium: implants in the partially endentoulus patient: Los Angeles: UCLA-Abstract Book, 1990:40. 12. Siegele D, Soltesz U. Numerische Untersuchungen zum EinRI@ der Implantatform auf die Beanspruchung des Kieferknochens. Z Zahnarztl Implant01 1987;3:161-9. 13. Benninghoff A, Goerttler K. Lehrbuch der Anatomie des Menschen. Band I. Mtinchen: Urban Schwarzenberg, 1978: 149-59. 14. Korber E, Htils A. Totalprothese-Befunderhebung. In: Driicke W, Klemt B, eds. Schwerpunkte in der Totalprothetik. Berlin: Quintessenz Verlags GmbH., 1986:27-48. 15. Lill W. Watzek G. Solar P. Ulm C. Nell A. Mateika M. Anatomische Untersuchungen iiber die Ausdehnung de; Kompakta und Spongiosa der atrophen Mandibula aus implantologischer Sicht. Z Zahnarztl Implant01 1990;6:176-83. 16. Solar P, Ulm C, Blahout R, Lill W, Watzek G, Matejka M. Dreidimensionale CT-Auswertung in der Oralen Implantologie. Z Stomatol, In press. Reprint requests: Christian Ulm, MD, DMD, Dental School of the University Waehringerstrasse 25 a, A-1090, Vienna, Austria
of Vienna,
oral surgery Editor: LARRY J. PETERSON,
DDS
Professor and Chairman Department of Oral and Maxillofacial College of Dentistry The Ohio State University 2131 Postle Hall 30.5 West 12th Avenue Columbus. Ohio 4321 O-I 241
Surgery
Reduction of the compact and cancellous bone substances of the edentulous mandible caused by resorption Christian Urn, MD, DMD,a Peter Solar, MD, DMD,’ Rudolf Blahout, IIID,~ Michael Matejka, MD, DMD,’ and Helmut Gruber, MD,d Vienna, Austria DEPARTMENT ANATOMICAL
OF ORAL SURGERY, DENTAL SCHOOL OF THE UNIVERSITY INSTITUTE OF THE UNIVERSITY OF VIENNA
OF VIENNA
AND
Examination of various bone sections of edentulous atrophic mandibles showed that the body of the mandible loses up to 60% of its original bone substance during progressive atrophy. Most of the bone loss occurs in a relatively early stage of the atrophic process. The greatest extent of bone reduction can be observed in the area of the second premolar and the first molar. In the interforaminal region, which is situated mesial from them, resorption, in most cases, is not as progressive as in the premolar/molar area. The compact and cancellous bone substances are most often equally affected by resorption. Moreover, it could be observed that the cancellous bone substance of extremely atrophic mandibles particularly in the interforaminal region, is marked by a significant increase in density. This might be interpreted as a restructuring process to compensate for bone losses and to secure the stability of the atrophic body of the mandible. (ORALSURG ORALMEDORALPATHOL
1992;74:131-6)
A
ccording to various authors,‘, 2 progressive atrophy may reduce the body of an edentulous mandible by 50% of its original size. In advanced cases, a cra“University Assistant, Department of Oral Surgery. bVisiting Clinician, Department of Oral Surgery. %enior Lecturer, Department of Oral Surgery. Wniversity Professor, Head of Section II, Anatomical 7/12/36732
Institute.
nial reduction not only of the alveolar crest but also of the base of the mandible can be observed.3, 4 A morphologic classification of alveolar ridge resorption was first carried out by Atwood33 5 and later by Tallgren6 and Cawood and Howell.7 As far as changes within the cancellous bone are concerned, partly inconsistent observations have been made by various authors. Kruger* observed a coarsening of the cancellous bone structure whereas Mer131
132
Ulm et al.
OKAL SURG ORAL MEU ORAL PATHOL. August 1992
Table I. Total area of the jaw section (in mm)
Secrions
Mean
s 1
261.3 252.2 231.4 210.6 207.1 205.9 204.9 212.0
s2 s3 s4 s5 S6
S-J S8
32.7 42.3 43.8 35.4 42.6 37.8 31.9 36.2
190.2 169.4 155.9 139.7 150.1 163.6 172.9 189.1
36.0 47.1 52.4 43.4 34.0 40.3 34.4 30.8
Mean
SD
187.9 172.7 172.0 159.3 159.3 175.7 198.6 209.9
44.6 41.5 46.1 40.5 40.2 39.5 36.X 36.3
~
Mean
SD
140.7
27.7 28.5 28.4 25.9 25.4 28.3 32.5 31.6
117.5 91.2
88.1 89.9 109.3 134.6
149.9
Mean = mean value. SD = standard deviation.
Table II. Compact portion of the section (in mm) RR0 4
RR0 3 Seclions
Mean
s I S2 s3 s4 s5 S6 s7 S8
132.9 tto.7 108.9 92.6 86.2 86.2 90.9 96.1
RR0 5
RR0 6
SD
Mean
SD
Mean
SD
Mean
SD
17.9
100.1
25.3 24.3
80.9 73.7 63.4 68.3 65.0 66.3 16.4
19.0 14.6 21.4
107.8 77.5 90.4 78.0 15.5 81.0 87.6 97.3
32.0 20.6 21.3 16.7 15.9 18.4 20.4
67.3 52.4 55.9 50.9 51.5 54.6 62.9 64.0
19.8 8.9 9.7
17.0 20.3 18.2 15.7 18.8
15.2 16.0 20.3 18.5 16.1
17.0
11.7 15.0 12.5 17.3 16.2
Mean = mean value. SD = standard deviation.
tier et a1.9reported that parts of the cancellous bone substance were restructured into compact bone. According to Kubik, to the cancellous portion of the bone is preserved in most cases but is restructured into a finer mesh. In the case of endosseous implantations, knowledge of the structure of the bone available for implantation is of vital importance. To prevent funnel-shaped resorptions in the area where the implant enters the bone, Mailath et al.” and Siegele and Soltesz12-according to their finite-element calculations-recommend that the implant be inserted into the cancellous portion of the bone. An even partial insertion of the implant into the compact layer of the mandible would lead to considerably higher tension between bone and implant and result in the resorption of the surrounding bone structure. For this reason, the precise knowledge of the extent of cancellous and compact bone available in the implantation area and their ratio during the different stages of atrophy is of fundamental importance. MATERIAL AND METHODS Forty-one edentulous, left lower-jaw halves from formalin/phenol-fixed corpses were examined in this
study. For precise assessment of the individual stages of bone resorption, the specimens were organized according to the residual ridge order (RRO) classification established by Atwood,3* s which describes the various degrees of alveolar ridge reduction on the basis of characteristic ridge shapes. RR0 1 corresponds to the alveolar ridge before tooth extraction, and RR0 2 describes the unchanged ridge immediately after extraction. In RR0 3, the empty alveolar ridge has already closed and is high and well rounded. RR0 4 corresponds to small, often knife-edge ridges, whereas in RR0 5, the alveolar ridge has been almost completely resorbed and looks low and well rounded. In RR0 6, the cranial part of the body of the mandible is depressed and the alveolar ridge has been completely resorbed (Figs. 1 and 2). Examination of the 41 mandibles led to the following breakdown: RR0 3 10 mandibles RR0 4 7 mandibles RR0 5 1 1 mandibles RR0 6 13 mandibles Mandibles in classifications RR0 1 and RR0 2 were not considered in the present study since they are not affected by atrophic changes. Borderline cases were
Volume 74 Number 2
Reduction of the compact and cancellous bone substances due to atrophy
133
Fig. 1. Drawing of residual ridge orders 1 to 6 by Atwood.
Fig. 2. Photograph of residual ridge orders 1 to 6 by Atwood.
assigned to the RR0 that predominated in the mandible concerned. With a diamond-coated precision saw, the following eight sections: were cut in each mandible: S 1 Median-sagittal between the lower central incisors S 2 In the area between the lateral incisor and the canine S 3 Between the two premolars S 4 In the area between the second premolar and the first molar S 5 In the area of the first molar S 6 Between the first and the second molars S 7 In the area of the second molar S 8 In the area of the third molar The sections formed a right angle with both the mandibular line and the horizontal axis of each mandibular section that runs parallel to the mandibular line. All eight sections of each mandible were photographed together with a ruler, and the data then were fed into the computer with the help of a digitizer. The following data were stored: the size of the ruler as well as of the section, the border between the compact and
the cancellous bone substances,and the marked basal and buccal points of each section. All noncompact portions of the sections (i.e., all bony parts that contained medullary and hollow spacesas well as cancellous trabeculae) were classified as cancellous bone and distinguished from the compact external cortical layer. t3 The mean values and standard deviations of all measurementsof the various sections were calculated and a t test was carried out to examine whether the mean value differences between the residual ridge orders were significant. The following measurements were carried out in each section: 1. Measurement of the total area of the jaw section (Table I) 2. Measurement of the compact portion of the bone (Table II) 3. Measurement of the cancellous portion of the bone (Table III) FINDINGS
The measurementsobtained are listed in Tables I to III and Figs. 3 and 4. In the majority of cases,the
134
Ulm et al.
ORAL SURG ORAL MED ORAL PATHOL August 1992
3001 250 -
51
52
53
54
55
n
RR0
3
El
q
RR0 RR0
4 5
El
RR0
6
56
S7
S8
Fig. 3. Compact portion of jaw section (in mm2). RRO, Residual ridge order; S, section. 300
250
1
4
RR0
3
0
RR0
4
q
RR0 5
[iii] RR0
6
150 100 50
n 51
52
S3
54
55
56
57
58
Fig. 4. Cancellous portion of jaw section (in mm*). RRO, residual ridge order; S, section. mean value differences between the various RROs were significant (p = 0.05) or highly significant (p = 0.01). A detailed list of the significances is available from us. Unlike the differences between the results obtained in the various residual ridge orders, the differences obtained in the measurementsof the male and female corpseswere not of any significance. For this reason, they have been put together for each residual ridge order. DISCUSSION The results obtained in the interforaminal region have to be assessed separately from those obtained in the premolar/molar region since the average life span
of the premolars and molars is shorter than that of the incisor and canine teeth.t4 For this reason, the meaFig. 5. Photograph of two sections in canine region. A, RR0 3, B, RR0 6 (1, lingual; b, buccal). In section B, coarsening of the cancellous bone structure is clearly visible.
surements obtained in the sections between the mental foramen and the second molar are always smaller than the values measured in the front tooth area. In the distal area, from the second molar on, the
Reduction of the compact and cancellous bone substances due to atrophy
Volume 74 Number 2
135
Fig. 6. Photograph of two sections in area of second molar. A, RR0 3; B, RR0 6 (I, lingual; b, buccal). The vertical loss of bone and the 1: 1 ratio of the compact and cancellous bone substance are clearly discernible.
Table III. Cancellous portion of the section (in mm) RR0 3
I I
RR0 4
Sections
Mean
SD
Mean
SD
s 1 s2 s3 s4 S.5 S6 s7 S8
128.4 141.5 122.4 118.0 120.9 119.7 114.0 115.9
22.1 23.9 26.9 18.1 21.3 17.2 14.8 16.1
90.1 88.4 82.2 76.3 81.8 98.6 106.6 112.7
29.3 40.1 42.8 26.6 17.8 18.3 15.2 13.9
j
RR0 5 Mean 80.2 95.2 81.6 81.3 83.8 94.7
111.0 112.6
RR0 6 SD
Mean
SD
24.3 25.5 30.9 22.8 23.4 20.3 15.6 18.7
73.4 65.1 41.3 37.2 38.4 54.7 71.7 85.9
15.4 24.5 25.5 12.9 10.1 15.6 13.8 11.2
Mean = mean value. SD = standard deviation.
measurement results are again higher than those obtained in the mesial area of the premolar/molar region. This is due to the fact that, for biomechanical reasons, the area that leads into the mandibular ramus and contains the oblique and the mylohyoid lines is marked by a higher bone volume. In the interforaminal region, the highest degree of bone resorption can be observed between RR0 3 and RR0 4 where the original bone volume is reduced by more than 25%. Atwood3 stressed the fact that the transition from RR0 3 to RR0 4 takes place in the 2 years after an extraction, and in 85% of cases, RR0 4 occurs in the next 20 years and then changes into RR0 5 and RR0 6. During this stage of the process, an av-
erage loss of 50% of the bone volume measured in RR0 3 could be observed. In some sections 60% of the bone volume was resorbed (Figs. 5 and 6). During the first stage of the resorption process, the changes in the premolar/molar region tend to be the same as in the area of the incisor and canine teeth; a considerable loss of bone volume can be observed between RR0 3 and 4 that does, however, affect the distal area (S 7 and S 8) less strongly than the mesial area. In the area of the premolar and the first molar, bone loss is significantly higher between RR0 5 and 6 (i.e., in extremely atrophic mandibles). In the areas of the front teeth and of the distal molars, resorption is less pronounced. Especially in the area of the first
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Ulm et al.
molar, the bone volume measured in RR0 3 may be reduced by more than 60% during progressive atrophy (RR0 6) (Table I). The fact that the maximum width of the body of the mandible remains constant leads to the conclusion that the resorption process fully affects the height of the mandible.4 Indeed, a comparison of the resorption of bone substance and the vertical bone reduction measured in the various jaw sections showed that the values, expressed in percentages, largely corresponded with each other.15 Another striking observation was that the values of RR0 4 are nearly as high as those of RR0 5. Thus it may be presumed that these two RROs are merely two variants of one and the same stage of atrophy. Another explanation of this fact might be that, between RR0 4 and RR0 5, the alveolar ridge is merely affected by a restructuring process and not by bone resorption. Irrespective of the degree of atrophy, the ratio of compact and cancellous bone largely remains 1: 1 (Tables II and III). It is only in RR0 3 that the amount of cancellous bone slightly exceeds that of compact bone. Regardless of the stage of atrophy, this is also the case in the area distal to the first molar (Tables II and III). Analogous to the total reduction of bone measured in the area of the body of the mandible, the reduction of both bone substances during progressive atrophy may amount to 60%. The changes in the structure and density of the cancellous portion of the sections were, however, very significant. With progressive atrophy, a clearly visible coarsening of the trabecular structure and the development of “compact islands,” particularly in the incisor area, could be observed (Fig. 5). Mercier’ has already described these changes. It seems reasonable to interpret such a coarsening of the cancellous structure as well as the development of “compact islands” as parts of a restructuring process to compensate for the loss of bone volume caused by atrophy and to preserve the stability of the body of the mandible. The best method to determine the absolute amount of bone as well as the ratio of compact and cancellous bone substance is computerized tomography.‘6
ORAt SURG ORAL MED ORAL PATHOL August I992
REFERENCES 1. Mercier R. Residual alveolar ridge atrophy: classification and influence of facial morphology. J Prosthet Dent 1979;4 1:90100. 2. Bras J, Van Ooji CP, Duns JY, Wansink HM, Driessen RM, Van den Akkeren HP. Mandibular atrophy and metabolic bone loss. Int J Oral Surg 1983;12:309-13. 3. Atwood DA. Reduction of residual ridges, J Prosthet Dent 1971;26:266-79. 4 Ulm C, Pechmann U, Ertl L, Gruber H, Solar P, Matejka M. Die Lage des Canalis mandibulae in atrophen Unterkiefer. Z Stomatol 1989;86:491-503. 5 Atwood DA. Postextraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and cephalometric roentgenograms. J Prosthet Dent 1963;13: 810-8. 6 Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: a mixed-longitudal study covering 25 years. J Prosthet Dent 1972;27:120-32. Cawood JI, Howell RA. A classification of the edentulous jaws. Int J Oral Maxillofac Surg 1988;17:232-6. Kruger E. Operationslehre fiir Zahnlrzte. Berlin: Quintessenz Verlags-Gmbh, 1979:290-301. Mercier R, Vanneuville G, Jourde J, Peri G, Patouillard P. Etude de la structure osseuse de la branche horizontale du maxillaire inferieur, apport des techniques radiographiques. C R Assoc Anat 1970;149:891-901. 10. Kubik S. Anatomische Grundlagen der Implantologie. Teil 1. Dental-Revue 1984;1-2:l l-9. I1 Mailath G, BGhn H, Rammerstorfer K, Lill W. Stress distribution around a bone anchored implant supported bridge. UCLA-Symposium: implants in the partially endentoulus patient: Los Angeles: UCLA-Abstract Book, 1990:40. 12. Siegele D, Soltesz U. Numerische Untersuchungen zum EinRI@ der Implantatform auf die Beanspruchung des Kieferknochens. Z Zahnarztl Implant01 1987;3:161-9. 13. Benninghoff A, Goerttler K. Lehrbuch der Anatomie des Menschen. Band I. Mtinchen: Urban Schwarzenberg, 1978: 149-59. 14. Korber E, Htils A. Totalprothese-Befunderhebung. In: Driicke W, Klemt B, eds. Schwerpunkte in der Totalprothetik. Berlin: Quintessenz Verlags GmbH., 1986:27-48. 15. Lill W. Watzek G. Solar P. Ulm C. Nell A. Mateika M. Anatomische Untersuchungen iiber die Ausdehnung de; Kompakta und Spongiosa der atrophen Mandibula aus implantologischer Sicht. Z Zahnarztl Implant01 1990;6:176-83. 16. Solar P, Ulm C, Blahout R, Lill W, Watzek G, Matejka M. Dreidimensionale CT-Auswertung in der Oralen Implantologie. Z Stomatol, In press. Reprint requests: Christian Ulm, MD, DMD, Dental School of the University Waehringerstrasse 25 a, A-1090, Vienna, Austria
of Vienna,
