A classification of the edentulous jaws

Trauma; Preprosthetic Surgery

J. I. Cawood ~ and R. A. Howel l 2 ~Maxillofacial Unit, Royal Infirmary, Chester, UK, 2Liverpool Dental Hospital, Liverpool, UK

J. L Cawood and R. A. Howell." A classification of the edentulous jaws. Int. J. Oral Maxillofac. Surg. 1988; 17:232-236

Abstract. A classification of the edentulous jaws has been developed based on a randomised cross-sectional study from a sample of 300 dried skulls. It was noted that whilst the shape of the basalar process of the mandible and maxilla remains relatively stable, changes in shape of the alveolar process is highly significant in both the vertical and horizontal axes. In general, the changes of shape of the alveolar process follows a predictable pattern Such a classification serves to simplify description of the residual ridge and thereby assist communication between clinicians; aid selection of the appropriate surgical prosthodontic tech- nique; offer an objective baseline from which to evaluate and compare different treatment methods; and help in deciding on interceptive techniques to preserve the alveolar process. An awareness of the pattern of resorption that takes place in various parts of the edentulous jaws, enables clinicians to anticipate and avert future problems.

Key words: classification; edentulous jaws; preprosthetic surgery.

Accepted for publication 5 January 1988

When considering preprosthetic surgery of the edentulous jaws, it is essential that both the surgeon and prosthodonti- st possess a detailed knowledge of the changing anatomical form of the jaws, following tooth loss.

To date, attempts to describe and classify these changes are unsatisfac- tory,, 2, 4, 5. They have been either too subjective or incomplete. Several studies refer to changes in vertical dimension occurring in the anterior region of the edentulous mandible, but make no ref- erence to the changes in the horizontal dimension or to changes occurring pos- teriorly. There is a paucity of objective data relating to the bony changes in the edentulous maxilla.

For these reasons, the authors under- took a study firstly to measure the changes in shape of the edentulous jaws and secondly to classify these changes if possible.

Mater ia l and Methods

A randomised cross-sectional study of the Greig Collection was carried out at the Royal College of Surgeons of Edinburgh which comprises 300 dried skulls.

Mandibular study

As demonstrated by ENLOW et al. 3, there is a subdivision between the alveolar and basalar

processes based on the presence of reversal lines, which delineate the most inferior extent to which alveolar reduction is likely to pro- gress. This subdivision coincides with the

1A

1B

Fig. 1. (A) Remodeling changes (shaded) in the mandible in relation to loss of the teeth (after ENLOW et al.3). (B) The line connecting mental and mandibular foramina delineates the boundary between the alveolar process and basalar process. 3 reference points S, M and K were selected. (B).

line connecting the mental and mandibular foramina (Figs. 1A, B). Three points S, M and K on this line were selected. S indicates the intersect through symphysis menti with a horizontal line connecting the mental foram- ina, M the mental foramen and K the mid-

2A

/ "x

/TLv/ 2B

iiiii!iii!iii! ] BASAL

S M K

Fig. 2. Measurements of the height (A) and width (13) of the alveolar process and basalar process were taken at points S, M and K.

IVIIV]

15

MM

15

5

MIV

15

A classification of the edentulous jaws 233

point of the line connecting the mental and mandibular foramina.

Twelve variables were analysed, namely, height and width of alveolar and basalar pro- cesses at points S, M and K respectively (figs. 2A, B). The mandibles were grouped into 4 categories. Group 1 were dentate, groups 2, 3 and 4 were edentulous with moderate, se- vere or extreme resorption respectively.

Group effect was determined by 1-factor

3A

analysis variant. Associations between vari- ables were measured using Pearsen's product- moment correlation co-efficient and by Spearman's rank-correlation co-efficient.

3B

3C

Results As can be seen in Figs. 3A-F, the mean values of alveolar measurements are sig- nificantly different between groups,

S VERT ICAL GROUP EFFECT

ALVEOLAR

r BASAL

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GROUP ~ ~

GROUP EFFECT

ALVEOLAR

BASAL

HORIZONTAL

MM

2O

0

p

234 Cawood & Howell

Maxillary study

Of the 4 processes of the maxil lary bone, the alveolar and palatal (basalar) pro- cesses are relevant to this study. The incisive foramen (I) and the greater pal- atine foramina (GP) are located at the junct ion of the alveolar and basalar pro- cesses. Figs. 4A-D show the maxil lary alveolar and basalar l inear measure- ments recorded in the vertical and hori- zontal axes.

The 11 variables shown in Table 2 were analysed to determine any changes in shape of the basalar and alveolar pro- cesses of the maxillae.

In order to determine group effect, the maxillae were subdivided into 3 groups. Group 1 were dentate, groups 2 and 3 were edentulous with moderate and severe resorption respectively.

Results In general, the mean values of the maxil- lary alveolar measurements are signifi- cantly different between groups; the mean values of basal measurements are not (Tables 3 A-D) .

Table 3A. Vertical maxillary alveolar Table 3D. Horizontal maxillary basalar measurements (mm) (n = 30) measurement (mm) (n = 30)

Anterior Posterior Group I-GP GP-GP I-C GP-C mean SD mean SD

Group mean SD mean SD 1 39.60+-2.70 30.60+_ 1.82 1 11.20+1.30 12.40+_0.89 2 39.23+_2.62 32.46+_2.37 2 6.77+_2.01 10.46+_2.96 3 39.00+_2.28 33.18___1.94 3 1.09+_ 1.45 6.46+_2.54

Table 3B. Horizontal maxillary alveolar measurements (mm) (n = 30)

Group IC I-B GP-C GP-B mean SD mean SD mean SD mean SD

1 10.00+2.65 10.00_+2.00 9.20_+ 1.64 13.80+_2.59 2 6.46_+ 1.66 7.15 +_ 1.52 6.92 +_ 1.38 10.69 -t- 2.25 3 3.36 +_ 1.75 3.91 +_ 1.81 4.73 -t- 1.10 8.27 ___ 1.85

Table 3C. Vertical maxillary basalar measurements (mm) (n = 30)

Group Anterior Posterior N-ANS ANS-I PNS-S

mean SD mean SD mean SD

1 49.80-+3.27 13.20_ 1.30 25.80+0.84 2 51.23+_3.24 13.15+ 1.52 25.92+_ 1.89 3 50.01 +_ 2.10 11.36 +_ 2.46 25.36 -t- 1.29

4A

S

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ct I

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ANS

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GP

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c

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C C

HORIZONTAL VERT ICAL

Fig. 4. Maxillary measurements (see Table 2). Vertical (A); horizontal (B); anterior (C); posterior (D).

A classification of the edentulous.jaws 235

5A

ANTERIOR MANDIBLE

MM

35

25

t5

5

~ LABIAL

5 15 MM I I I I I IV V V I

5B

POSTERIOR MANOIBLE

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15 ::i:i:i:i~i~:~:;~ :i!ii (.1 ~ : : : : . '.=================================== U ~!~nl::::::::::::::::::::::::::::::::::::: 3

5 15 I I I I I IV V VI

Fig. 5. (A) Classification of anterior mandible (anterior to mental foramina). (B) Classification of posterior mandible (posterior to mental foramina).

6A

ANTERIOR MAXILLA

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0

10

20

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6B

POSTERIOR MAXILLA

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Fig. 6. (A) Classification of anterior maxilla (B). Classification of posterior maxilla.

Classification of the edentulous jaws

Since changes in dimension of the ba- salar process were not significant, re- gardless of the degree of atrophy of the alveolar process, it was possible to pro- duce composite diagrams showing the most commonly observed changes in shape of the alveolar process of the mandible (Figs. 5A, B) and the maxilla (Figs. 6A, B) and to develop a descrip- tive classification of these changes. Class I - dentate. Class II - immediate ly post extrac-

tion. Class I I I - well-rounded ridge form,

adequate in height and width.

Class IV - knife-edge ridge form, ad- equate in height and inad- equate in width.

Class V flat ridge form, inadequate in height and width.

Class VI - depressed ridge form, with some basalar loss evident.

Conclusions

Arising from these morphological stud- ies of edentulous jaws, the following conclusions have been drawn.

(i) Basal bone does not change shape significantly, unless subjected to harm- ful local effects such as the overloading of ill fitting dentures.

(ii) Alveolar bone changes shape sig- nificantly in both the horizontal and vertical axes.

(iii) In general, changes of shape of the alveolar bone follows a predictable pattern.

(iv) Pattern of bone loss varies with sites. Anterior mandible - bone loss is vertical and horizontal (from the labial aspect). Posterior mandible - bone loss is mainly vertical. Anterior maxilla - bone loss is both vertical and horizontal (from the labial aspect). Posterior max- illa - bone loss is both vertical and hori- zontal (from the buccal aspect).

(v) Stage of bone loss can vary an- teriorly and posteriorly and between j aws .

236 Cawood & Howell

Such a classification serves to sim- plify description of the residual ridge and thereby assist communication be- tween clinicians: aid selection of the ap- propriate surgical/prosthodontic tech- nique; offer an objective baseline from which to evaluate and compare different

treatment methods; help in deciding on interceptive techniques to preserve the alveolar process. An awareness of the pattern of resorption that takes place in the various parts of the edentulous jaw enables clinicians to anticipate and av- ert future problems.

Acknowledgements The authors acknowl- edge the valuable assistance of Mr. C. West, Medical Biostatician, University of Liver- pool, Mr. R F. Wragg, Senior Registrar in Restorative Dentistry, Glasgow Dental Hos- pital and Miss S. L. Maudsley, Medical Sec- retary.

Table 1A. Vertical mandibular alveolar measurements (mm) (n =45)

S M K Group mean SD mean SD mean SD

I 17.50+ 1.44 16,92_+ 1.11 7,00+ 1.03 2 10.00_+ 1.76 10.75+ i.36 4.00+ 1.26 3 9.21 __+0.94 7.21 ___ 0.73 0.50__+0.67 4 3.40+ 1.58 2.80__ 1.21 -- 1.60+ 1.13

Table lB. Horizontal mandibular alveolar measurements (mm) (n=45)

S M K Group mean SD mean SD mean SD

1 11.33 ___ 1.33 10.83 ___ 0.70 11.67 + 0.60 2 7.80__ 1.46 5.20_+0.85 4.50+0.74 3 6.29 _ 0.87 4.86 _ 0.46 4.64 0.39 4 3.50+ 1.63 3.00_+0.76 3.80_+0.66

Table 2. Maxillary alveolar and basalar measurements

Site Anterior Posterior - Vertical Horizontal Vertical Horizontal

alveolar I-C I-C GP-C GP-C I-B GP-B

basal ANS-I I-GP PNS-S GP-GP N-ANS

N = nasion. ANS =anterior nasal spine. I = incisive foramen. C =crest of alveolar process

(adjacent to I or GP). B = widest part of alveolar process

(adjacent to I or GP).

GP = greater palatine foramen. PNS =posterior nasal spine. S =tunction of vomer with body

of sphenoid bone. N-ANS= anterior nasal height. S-PNS =posterior nasal height.

References

1. Atwood, D. A.: Postextraction changes in the adult mandible as illustrated by microradiographs of midsagittal sections and serial cephalometric roentgeno- grams. J. Prosthet. Dent. 1963: 13: 810-824.

2. Branemark, E I., Zarb, G. & Albrekts- son, T. (eds.): Tissue-integrated pros- theses. Osseointegration in clinical den- tistry. Berlin: Quintessence, 1985.

3. Enlow, D. H., Bianco, H. J. & Eklund, S.: The remodeling of the edentulous mandible. J. Prosthet. Dent. 1976: 36: 685-693.

4. Kent, J. N., Quinn, J. H., Zide, M. E, Guerra, I. R. & Boyne, E J.: Alveolar ridge augmentation using non-resorbable hydroxylapatite with or without autogen- ous cancellous bone. J. Oral Max-fae. Surg. 1983: 41: 629-642.

5. Mercier, E & Lafontant, R.: Residual al- veolar ridge atrophy: classification and influence of facial morphology. J. Pros- thet. Dent. 1979: 41: 90-100.

Address: J. L Cawood Maxillofacial Unit Royal Infirmary Chester, CH1 2AZ UK