/TLv/ A classification of the edentulous jaws. Trauma; Preprosthetic Surgery. iiiii!iii!iii! ] BASAL

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1 Trauma; Preprosthetic Surgery A classification of the edentulous jaws J. I. awood ~ and R. A. Howell 2 ~Maxillofacial Unit, Royal Infirmary, hester, UK, 2Liverpool Dental Hospital, Liverpool, UK J. L awood and R. A. Howell." A classification of the edentulous jaws. Int. J. Oral Maxillofac. Surg. 1988; 17: 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 technique; 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 prosthodontist 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 unsatisfactory,, 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 reference to the changes in the horizontal dimension or to changes occurring posteriorly. There is a paucity of objective data relating to the bony changes in the edentulous maxilla. For these reasons, the authors undertook a study firstly to measure the changes in shape of the edentulous jaws and secondly to classify these changes if possible. Material and Methods A randomised cross-sectional study of the Greig ollection was carried out at the Royal ollege 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 progress. 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 foramina, M the mental foramen and K the mid- 2A 2B iiiii!iii!iii! ] BASAL / "x /TLv/ 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.

2 A classification of the edentulous jaws 233 IVIIV] point of the line connecting the mental and mandibular foramina. Twelve variables were analysed, namely, height and width of alveolar and basalar processes 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, severe or extreme resorption respectively. Group effect was determined by 1-factor 3A S VERTIAL GROUP EFFET r analysis variant. Associations between variables were measured using Pearsen's productmoment correlation co-efficient and by Spearman's rank-correlation co-efficient. Results As can be seen in Figs. 3A-F, the mean values of alveolar measurements are significantly different between groups, [MS " 3D whereas the mean value of basal measurements are not significantly different, see also Tables 1A, B. Fig. 3. Differences between mean values of mandibular measurements for groups. S vertical (A); S horizontal (B); M vertical (); M horizontal (D); K vertical (E); K horizontal (F). M HORIZONTAL GROUP EFFET P < O-OO1 3B HORIZONTAL GROUP EFFET 3E K VERTIAL GROUP EFFET 2O ~ [ M S 5 0 p<o.oon -5 ~ P < O.OO1 GROUP GROUP 2 -~ --~ MIV 3 IV] VERTIAL GROUP EFFET 3F K HORIZONTAL GROUP EFFET ~[Ms ~ < O-GO1 5 T I BROUR 2 ~

3 234 awood & Howell Maxillary study Of the 4 processes of the maxillary bone, the alveolar and palatal (basalar) processes are relevant to this study. The incisive foramen (I) and the greater palatine foramina (GP) are located at the junction of the alveolar and basalar processes. Figs. 4A-D show the maxillary alveolar and basalar linear measurements recorded in the vertical and horizontal axes. The 11 variables shown in Table 2 were analysed to determine any changes in shape of the basalar and alveolar processes 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 maxillary alveolar measurements are significantly 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- GP- mean SD mean SD Group mean SD mean SD _ _ _ _ _ _ _ _ _2.54 Table 3B. Horizontal maxillary alveolar measurements (mm) (n = 30) Group I I-B GP- GP-B mean SD mean SD mean SD mean SD _ _ _ _ _ _ t _ _ t Table 3. Vertical maxillary basalar measurements (mm) (n = 30) Group Anterior Posterior N-ANS ANS-I PNS-S mean SD mean SD mean SD _ _ _ _ _ t A 4 ALWOLA. ES~ ~ASAL N S c PNS ANS ~_ S 4B [] ct I ~ ~i~ ALVEOLAR [~ BASAL 4D ~ ~ GP..::.::~. ~.~:~$.~:':;::~:~.'.:..:,:. :;.:;.: :.'~.::~:::::::::,.; ~:.~..-';.:~ ~:::::::::.;: ~'.;g.:.:;;..'-.~':':::::~ HORIZONTAL VERTIAL B GP GP Fig. 4. Maxillary measurements (see Table 2). Vertical (A); horizontal (B); anterior (); posterior (D).

4 A classification of the edentulous.jaws 235 5A ANTERIOR t5 5 5B ~ LABIAL 5 POSTERIOR 25 ::i:i:i:i~i~:~:;~ :i!ii (.1 ~ '.=================================== : : : :. U ~!~nl::::::::::::::::::::::::::::::::::::: 3 MANDIBLE II III IV V VI MANOIBLE lassification of the edentulous jaws Since changes in dimension of the basalar process were not significant, regardless of the degree of atrophy of the alveolar process, it was possible to produce 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 descriptive classification of these changes. lass I - dentate. lass II -immediately post extrac- lass III- tion. well-rounded ridge form, adequate in height and width. lass IV - knife-edge ridge form, adequate in height and inadequate in width. lass V flat ridge form, inadequate in height and width. lass VI - depressed ridge form, with some basalar loss evident. 5 II III IV V VI Fig. 5. (A) lassification of anterior mandible (anterior to mental foramina). (B) lassification of posterior mandible (posterior to mental foramina). 6A ANTERIOR B i i i lo o POSTERIOR 10 Io o MAXILLA i i r II MAXILLA 1 i i III i i i IV i i ~. i i i l i L II III IV f ~ l r l t l V Vl T i i f t i i v vi Fig. 6. (A) lassification of anterior maxilla (B). lassification of posterior maxilla. onclusions Arising from these morphological studies of edentulous jaws, the following conclusions have been drawn. (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 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 maxilla - bone loss is both vertical and horizontal (from the buccal aspect). (v) Stage of bone loss can vary anteriorly and posteriorly and between jaws.

5 236 awood & Howell Such a classification serves to simplify description of the residual ridge and thereby assist communication between clinicians: aid selection of the appropriate surgical/prosthodontic technique; 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 avert future problems. Acknowledgements The authors acknowledge the valuable assistance of Mr.. West, Medical Biostatician, University of Liverpool, Mr. R F. Wragg, Senior Registrar in Restorative Dentistry, Glasgow Dental Hospital and Miss S. L. Maudsley, Medical Secretary. Table 1A. Vertical mandibular alveolar measurements (mm) (n =45) Group mean SD mean SD mean SD I ,92_ , _ i Table lb. Horizontal mandibular alveolar measurements (mm) (n=45) Group mean SD mean SD mean SD _ _ _ ± _ _+0.66 Table 2. Maxillary alveolar and basalar measurements Site Anterior Posterior - Vertical Horizontal Vertical Horizontal alveolar I- I- GP- GP- I-B GP-B basal ANS-I I-GP PNS-S GP-GP N-ANS N ANS I B = nasion. =anterior nasal spine. = incisive foramen. =crest of alveolar process (adjacent to I or GP). = 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 roentgenograms. J. Prosthet. Dent. 1963: 13: Branemark, E I., Zarb, G. & Albrektsson, T. (eds.): Tissue-integrated prostheses. Osseointegration in clinical dentistry. Berlin: Quintessence, Enlow, D. H., Bianco, H. J. & Eklund, S.: The remodeling of the edentulous mandible. J. Prosthet. Dent. 1976: 36: 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 autogenous cancellous bone. J. Oral Max-fae. Surg. 1983: 41: Mercier, E & Lafontant, R.: Residual alveolar ridge atrophy: classification and influence of facial morphology. J. Prosthet. Dent. 1979: 41: Address: J. L awood Maxillofacial Unit Royal Infirmary hester, H1 2AZ UK

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