Trauma; preprosthetic surgery Invited review J. I. C a w o o d 1, R. A . H o w e l l 2 1Maxillofaeial Unit, Royal Infirmary, Chester, and aLiverpool Dental Hospital, UK
Reconstructive preprosthetic surgery I. Anatomical considerations J. I. Cawood, R. A. Howell." Reconstructive preprosthetic surgery. I. Anatomical considerations. Int. J. Oral Maxillofac. Surg. 1991; 20." 75-82. Abstract. When considering preprosthetic surgery of the edentulous jaws, it is important that the clinician fully understands the anatomical consequences of reduction of the residual ridges. Based on a classification of the edentulous jaws, changes in the relationship of the jaws to each other, in muscle relations and function, in the oral mucosa and in facial morphology have been measured relative to the stage of resorption of the edentulous jaws.
Reduction of the residual ridge is a chronic progressive process whose rate varies not only between different individuals but within the same individual at different times 1. In a detailed longitudinal study, TALLGREN8 observed that although the greater proportion of bone loss occurred within the first year of tooth loss, the process continued at a slower rate over the 25 years for which the subjects were followed (Fig. 1). She also noted that, in general, the amount of bone loss in the mandible is four times greater than in the maxilla. Using clearly defined, reproducible reference points of the edentulous jaws, CAWOOD & HOWELL4 analysed patterns of alveolar resorption from a sample of 300 dried skulls. Based on this objective study, a pathophysiological classification of alveolar resorption was established which describes 6 stages of resorption (Fig. 2A, B, C, D) and (Fig. 14, A, B, C, D, E, F).
ANTERIOR
Key words: preprosthetic surgery; edentulous jaws; classification; anatomy; alveolar resorption. Accepted for publication 1 December 1990
MANDIBLE
MM 35
R5155 ~
I.AEMAL
5
15 MM
II
ROBTERIOR
III
iv
v
Vl
MANDIBLE
MM
B
'i{;ii!~..
I
I!
115
II
ANTERIOR
V
IV
Ul
Vl
MAXILLA
MM 0 10
HEIGHT MM
, i i 1o 13
C
30 A
MANOIBLE
I|
POSTERIOR
25
nl
IV
v
Vl
MAXILLA
MM
lO
D
1 3
4o
25
Fig. 1. Mean reduction in anterior height of the alveolar ridges over 25 years (after TALLGRENS).
i lO
O
i
i
I
i
i
v Vl IV Fig. 2. A: classification of anterior mandible (anterior to mental foramina); B: classification of posterior mandible (posterior to mental foramina); C: classification of anterior maxilla; D: classification of posterior maxilla.
II
Ill
76
Cawood and Howell
Class I - dentate. Class II - post extraction. Class I I I - rounded ridge, adequate height and width. Class IV - knife edge ridge, adequate height, inadequate width. Class V - flat ridge, inadequate height and width. Class VI - depressed ridge with varying degrees of basal bone loss, that may be extensive but follows no predictable pattern. The main conclusions arising from the study were: [i] Basal bone does not change shape significantly unless subjected to harmful local effects such as the overloading of ill-fitting dentures. [ii] Alveolar bone changes shape significantly. [iii] In general, changes of shape of the alveolar bone follow a predictable pattern. [iv] Pattern of bone loss varies with site. Anterior mandible (anterior to mental foramina) bone loss is mainly horizontal from the labial aspect. Posterior mandible (posterior to mental foramina) bone loss is mainly vertical. Anterior maxilla bone loss is mainly horizontal from the labial aspect. Posterior maxilla bone loss is mainly horizontal from the buccal aspect. [v] Stage of bone loss can vary anteriorly and posteriorly and between jaws (Fig. 15, A, B).
Consequence of tooth loss
Loss of teeth and reduction of the residual ridge lead to changes in the relationship of the jaws to each other, in muscle relations and function, in the oral mucosa and in facial morphology. The classification of the edentulous jaws 4 forms a basis for a systematic assessment relating the stage of resorption to changes in the shape and relationship of the jaws and soft tissue integument.
Interarch changes
With progressive resorption from Class I to Class VI, there are 3 dimensional changes in jaw relations. Anteroposteriorly, the mandibular and maxillary arches become shorter (Fig. 3A). Transversely, due to the pattern of resorption,
UFH 43~
UFH 4B~
LPH 57~
C
LFH 52~
ORTHOGNATHIC
FACE
D
EDENTULOUS
FACE
Fig. 3. Changes between Class I and Class VI jaw relations. A: anteroposterior and vertical interarch changes and associated prognathism of the mandible; B: transverse and vertical interarch changes. Note the reverse relationship of the edentulous and dentate jaws due to resorption patterns causing the maxillary arch to become progressively narrower and the mandibular arch to become progressively broader; C: lateral cephalometric tracings of orthognathic face (Class I) and edentulous face (Class V), illustrating changes in anterior facial proportions of the edentulous face due to the autorotation of the mandible causing a decrease in lower face height and increase of chin prominence. UFH: upper face height: LFH: lower face height.
the maxillary arch becomes progressively narrower, whilst the mandibular arch becomes progressively broader. (Fig. 3B). Vertically, the interarch distance increases, although this is counteracted to some extent by the vertical shortening of the lower face caused by the closing movement or autorotation of the mandible producing a more prominent chin and prognathic jaw (Fig. 3C, D).
Reconstructive preprosthetic surgery
77
Muscle changes
B
A
BUCCAL
C
D
'
7
F
Fig. 4. Attachment of the circumoral and floor of mouth musculature, showing how they become increasingly superficial as bone loss progresses. A: dentate mandible (Class I), buccal aspect; B: edentulous mandible (Class V), buccal aspect: (1) mentalis, (2) depressor labii inferioris, (3) depressor anguli oris, (4) buccinator; C: dentate mandible, lingual aspect; D: edentulous mandible, lingual aspect: (5) genioglossus (superior) and geniohyoid (inferior), (6) digastric (anterior belly), (7) mylohyoid. E: dentate maxilla (Class I), buccal aspect; F: edentulous maxilla (Class V), buccal aspect: (1) dilator naris, (2) compressor naris, (3) depressor septi, (4) buccinator, (5) levator anguli oris.
The attachments of the circumoral and floor of mouth musculature delineate the extent of the vestibular and lingual sulci. With continued loss of alveolar bone from Class I to Class VI, these muscles become progressively superficial (Fig. 4A, B, C, D, E, F).
Cawood and Howell
78
ANTERIOR
MANDIBLE
POSTERIOR
MANDIBLE
Mucosal changes
MM
MM
MUCOSAL
CHANGES
MUCOSAL
12
12 =
~
UNATTACHED
CHANGES
UNATTACHEO
MUCOSA
MUCOSA
E
4
ATTACH~ D
A
t
I
t
IV
Ill
,~ " r A C H
MUCOSA
V
I
B
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VI
Fig. 5. Differences between mean values of attached and unattached mucosa. A: anterior mandible; B: posterior mandible.
I
II
IV
V
III
VI
Fig. 6. Progressivereduction of residual ridges from Class I to Class VI showing vertical ridge resorption of the posterior mandible, decreasing attached mucosa (heavy line) and changing muscle relations.
e/
7
CENTRIFUGAL
CENTRIPETAL
Fig. 7. Mandibular blood supply: centrifugal in the dentate jaw, centripetal in the edentulous jaw.
There is quantitative and qualitative reduction of the soft tissue support as well. WATT & MACGREGOR9 compared the area ofperiodontium supporting a tooth with the small area of mucoperiosteum remaining after tooth loss. They calculated that the mean surface area is reduced from 45 to 23 cm squared in the edentulous maxilla and to 12 cm squared in the edentulous mandible. In the edentulous jaw, the mucosa covering the residual ridge is partly attached and partly unattached. The attached mucosa corresponds to the attached gingiva originally surrounding the natural teeth. Unlike the periodontal ligament, the mucosa is not a specialized supporting tissue, and excessive pressure causes pain and a pathological response 1°. As the attached mucosa is bound to bone it is more able than the unattached mucosa to withstand loading pressure. CAWOOD & HOWELL5 measured the amount of attached and unattached mucosa relative to t h e stage of jaw resorption. As can be seen in (Fig. 5A, B) the amount of attached and unattached mucosa diminishes significantly from Class I to Class VI. The progressive muscle and mucosal changes that accompany jaw atrophy are illustrated in Fig. 6. It should be noted that as a result of alveolar bone loss, the inferior alveolar canal becomes relatively superficial. Changes in mandibular blood supply are seen. Initially, the blood supply is primarily centrifugal. With loss of teeth and the periodontium, the blood supply of the edentulous mandible becomes centripetal (Fig 7).
Reconstructive preprosthetic surgery /"
/f
Fig. 8. The '
Reconstructive preprosthetic surgery I. Anatomical considerations J. I. Cawood, R. A. Howell." Reconstructive preprosthetic surgery. I. Anatomical considerations. Int. J. Oral Maxillofac. Surg. 1991; 20." 75-82. Abstract. When considering preprosthetic surgery of the edentulous jaws, it is important that the clinician fully understands the anatomical consequences of reduction of the residual ridges. Based on a classification of the edentulous jaws, changes in the relationship of the jaws to each other, in muscle relations and function, in the oral mucosa and in facial morphology have been measured relative to the stage of resorption of the edentulous jaws.
Reduction of the residual ridge is a chronic progressive process whose rate varies not only between different individuals but within the same individual at different times 1. In a detailed longitudinal study, TALLGREN8 observed that although the greater proportion of bone loss occurred within the first year of tooth loss, the process continued at a slower rate over the 25 years for which the subjects were followed (Fig. 1). She also noted that, in general, the amount of bone loss in the mandible is four times greater than in the maxilla. Using clearly defined, reproducible reference points of the edentulous jaws, CAWOOD & HOWELL4 analysed patterns of alveolar resorption from a sample of 300 dried skulls. Based on this objective study, a pathophysiological classification of alveolar resorption was established which describes 6 stages of resorption (Fig. 2A, B, C, D) and (Fig. 14, A, B, C, D, E, F).
ANTERIOR
Key words: preprosthetic surgery; edentulous jaws; classification; anatomy; alveolar resorption. Accepted for publication 1 December 1990
MANDIBLE
MM 35
R5155 ~
I.AEMAL
5
15 MM
II
ROBTERIOR
III
iv
v
Vl
MANDIBLE
MM
B
'i{;ii!~..
I
I!
115
II
ANTERIOR
V
IV
Ul
Vl
MAXILLA
MM 0 10
HEIGHT MM
, i i 1o 13
C
30 A
MANOIBLE
I|
POSTERIOR
25
nl
IV
v
Vl
MAXILLA
MM
lO
D
1 3
4o
25
Fig. 1. Mean reduction in anterior height of the alveolar ridges over 25 years (after TALLGRENS).
i lO
O
i
i
I
i
i
v Vl IV Fig. 2. A: classification of anterior mandible (anterior to mental foramina); B: classification of posterior mandible (posterior to mental foramina); C: classification of anterior maxilla; D: classification of posterior maxilla.
II
Ill
76
Cawood and Howell
Class I - dentate. Class II - post extraction. Class I I I - rounded ridge, adequate height and width. Class IV - knife edge ridge, adequate height, inadequate width. Class V - flat ridge, inadequate height and width. Class VI - depressed ridge with varying degrees of basal bone loss, that may be extensive but follows no predictable pattern. The main conclusions arising from the study were: [i] Basal bone does not change shape significantly unless subjected to harmful local effects such as the overloading of ill-fitting dentures. [ii] Alveolar bone changes shape significantly. [iii] In general, changes of shape of the alveolar bone follow a predictable pattern. [iv] Pattern of bone loss varies with site. Anterior mandible (anterior to mental foramina) bone loss is mainly horizontal from the labial aspect. Posterior mandible (posterior to mental foramina) bone loss is mainly vertical. Anterior maxilla bone loss is mainly horizontal from the labial aspect. Posterior maxilla bone loss is mainly horizontal from the buccal aspect. [v] Stage of bone loss can vary anteriorly and posteriorly and between jaws (Fig. 15, A, B).
Consequence of tooth loss
Loss of teeth and reduction of the residual ridge lead to changes in the relationship of the jaws to each other, in muscle relations and function, in the oral mucosa and in facial morphology. The classification of the edentulous jaws 4 forms a basis for a systematic assessment relating the stage of resorption to changes in the shape and relationship of the jaws and soft tissue integument.
Interarch changes
With progressive resorption from Class I to Class VI, there are 3 dimensional changes in jaw relations. Anteroposteriorly, the mandibular and maxillary arches become shorter (Fig. 3A). Transversely, due to the pattern of resorption,
UFH 43~
UFH 4B~
LPH 57~
C
LFH 52~
ORTHOGNATHIC
FACE
D
EDENTULOUS
FACE
Fig. 3. Changes between Class I and Class VI jaw relations. A: anteroposterior and vertical interarch changes and associated prognathism of the mandible; B: transverse and vertical interarch changes. Note the reverse relationship of the edentulous and dentate jaws due to resorption patterns causing the maxillary arch to become progressively narrower and the mandibular arch to become progressively broader; C: lateral cephalometric tracings of orthognathic face (Class I) and edentulous face (Class V), illustrating changes in anterior facial proportions of the edentulous face due to the autorotation of the mandible causing a decrease in lower face height and increase of chin prominence. UFH: upper face height: LFH: lower face height.
the maxillary arch becomes progressively narrower, whilst the mandibular arch becomes progressively broader. (Fig. 3B). Vertically, the interarch distance increases, although this is counteracted to some extent by the vertical shortening of the lower face caused by the closing movement or autorotation of the mandible producing a more prominent chin and prognathic jaw (Fig. 3C, D).
Reconstructive preprosthetic surgery
77
Muscle changes
B
A
BUCCAL
C
D
'
7
F
Fig. 4. Attachment of the circumoral and floor of mouth musculature, showing how they become increasingly superficial as bone loss progresses. A: dentate mandible (Class I), buccal aspect; B: edentulous mandible (Class V), buccal aspect: (1) mentalis, (2) depressor labii inferioris, (3) depressor anguli oris, (4) buccinator; C: dentate mandible, lingual aspect; D: edentulous mandible, lingual aspect: (5) genioglossus (superior) and geniohyoid (inferior), (6) digastric (anterior belly), (7) mylohyoid. E: dentate maxilla (Class I), buccal aspect; F: edentulous maxilla (Class V), buccal aspect: (1) dilator naris, (2) compressor naris, (3) depressor septi, (4) buccinator, (5) levator anguli oris.
The attachments of the circumoral and floor of mouth musculature delineate the extent of the vestibular and lingual sulci. With continued loss of alveolar bone from Class I to Class VI, these muscles become progressively superficial (Fig. 4A, B, C, D, E, F).
Cawood and Howell
78
ANTERIOR
MANDIBLE
POSTERIOR
MANDIBLE
Mucosal changes
MM
MM
MUCOSAL
CHANGES
MUCOSAL
12
12 =
~
UNATTACHED
CHANGES
UNATTACHEO
MUCOSA
MUCOSA
E
4
ATTACH~ D
A
t
I
t
IV
Ill
,~ " r A C H
MUCOSA
V
I
B
Vl
III
IV
MUCOS
V
VI
Fig. 5. Differences between mean values of attached and unattached mucosa. A: anterior mandible; B: posterior mandible.
I
II
IV
V
III
VI
Fig. 6. Progressivereduction of residual ridges from Class I to Class VI showing vertical ridge resorption of the posterior mandible, decreasing attached mucosa (heavy line) and changing muscle relations.
e/
7
CENTRIFUGAL
CENTRIPETAL
Fig. 7. Mandibular blood supply: centrifugal in the dentate jaw, centripetal in the edentulous jaw.
There is quantitative and qualitative reduction of the soft tissue support as well. WATT & MACGREGOR9 compared the area ofperiodontium supporting a tooth with the small area of mucoperiosteum remaining after tooth loss. They calculated that the mean surface area is reduced from 45 to 23 cm squared in the edentulous maxilla and to 12 cm squared in the edentulous mandible. In the edentulous jaw, the mucosa covering the residual ridge is partly attached and partly unattached. The attached mucosa corresponds to the attached gingiva originally surrounding the natural teeth. Unlike the periodontal ligament, the mucosa is not a specialized supporting tissue, and excessive pressure causes pain and a pathological response 1°. As the attached mucosa is bound to bone it is more able than the unattached mucosa to withstand loading pressure. CAWOOD & HOWELL5 measured the amount of attached and unattached mucosa relative to t h e stage of jaw resorption. As can be seen in (Fig. 5A, B) the amount of attached and unattached mucosa diminishes significantly from Class I to Class VI. The progressive muscle and mucosal changes that accompany jaw atrophy are illustrated in Fig. 6. It should be noted that as a result of alveolar bone loss, the inferior alveolar canal becomes relatively superficial. Changes in mandibular blood supply are seen. Initially, the blood supply is primarily centrifugal. With loss of teeth and the periodontium, the blood supply of the edentulous mandible becomes centripetal (Fig 7).
Reconstructive preprosthetic surgery /"
/f
Fig. 8. The '
