GEORGE A. ZARB
contacts and tooth wear
A. Woda, D.Sc., D.S.O., A.M. Gourdon,
D.S.O., and M. Faraj, B.D.S.
Laboratoire de Physiologie Oro-Faciale, U.E.R. Odontologie, Clermont-Ferrand, France
wear appears to be a general physiologic phenomenon found in all mammals, in every civilization, and at all ages. Several studies have provided important information about the anatomy and origin of dental wear.‘m27 Our interpretation of published works related to the function of tooth abrasion is that (1) it induces an increase in the surface of occlusal contact, which in turn increases the efficiency of mastication;2*~29 (2) wear of the occlusal table is compensated for by a continual and active dental growth, without which an increase in facial vertical dimension may result;4, 16,30*31 (3) proximal wear, and consequent mesial tooth migration, reduces the frequency of malocclusion and crowding of anterior teeth, and sufficient space is left for the eruption of the third molar;6,1’a 3o,32and (4) an oral cavity with dental abrasion presents fewer carious lesions,7s 33 healthier periodontal tissues,34 and good occlusal function. These interpretations do not, however, translate into universally acceptable clinical views. Several clinicians believe that the temporomandibular joint (TMJ) does not change under physiologic circumstances35 and that neuromuscular harmony depends on the preservation of the initial morphology of teeth and TMJ. They concluded that teeth remain functional unless they are subjected to abrasive phenomena.36 The objective of this study is to describe the morphology of occlusal dental wear in a selected population sample and to search for possible correlations between the observed abrasion and various characteristics of occlusion.
METHODS This study was conducted on 22 Caucasian French subjects who presented with a complete healthy dentition and were between 18 and 50 years of age. Their selection was predicated on the following criteria: absence of missing teeth (except third molars), caries, periodontal disease, bruxism, TM J disorders, restorations, and history of occlusal or orthodontic therapy. Furthermore, good occlusion with molar relationship in Angle class I and coincidence between maxillary and mandibular midlines was present, along with regular tooth alignment and little evidence of dental wear. The third molars, when present, were not included in the analysis. THE
Part of an interocclusal
Impressions of both dental arches were made in irreversible hydrocolloid and only the dental part of the impression was poured in artificial stone.37 A centric occlusion record was made in a light silicone elastomer (Fig. 1) because of its physical property advantages and the avoidance of excessive pressure during intercuspation, which avoids exaggerated penetration of teeth in their alveoli.38
of wear facets
Microbubbles were eliminated from maxillary and mandibular casts, and the form, dimension, and location of wear facets were analyzed with a magnifying lens. These observations were drawn on a schematic diagram of each arch, with care taken to reproduce form and location of wear facets in relation to cusp grooves and margins (Fig. 2). We observed that all available wear facets were engaged during working and nonworking simulated contact movements. Both types of wear facets (working and nonworking) were shaded in different colors (Fig. 2). The occlusal contacts were studied on the elastomer interocclusal records. Two types of indentation were considered,39 clear perforations that indicate supracontacts and extreme thinning or translucent areas that indicate contacts. Interdental, buccal, and lingual excesses of the elastomer record were trimmed to facilitate accurate placement of the occlusal contacts in relation to the wear facets. The contacts were then replicated by means of a simple drawing on tracing paper (Fig. 3) and applied to the diagram representing the wear facets (Fig. 2). This 85
Fig. 2. Wear facets are replicated on a diagram of arch form. Working and nonworking facets are represented in black and dotted areas. Crosses (+) serve for orientation of a tracing paper over which occlusal contacts are drawn (see Fig. 3).
Fig. 3. Reproduction of occlusal contacts on a tracing paper: clear perforations in black, extreme thinning in white. This diagram is established by superimposition of a blank tracing paper on diagram of wear facets in Fig. 2.
permitted a consistent superimposition of these two planes. The following occlusal parameters were recorded: The number of occlusal contacts in maximal intercuspation for each tooth The number of antagonists(none, one, or two teeth) for each tooth The intensity of the tooth contact The surface area of occlusal contacts The relation between occlusal contacts in maximal intercuspation and wear facets (For every tooth, we counted occlusal contacts lying outside the facets, on the facets, and facets with no occlusal contact in maximal intercuspation.)
For the surfacesof wear facets, as for the surfacesof occlusal contacts, numeric values were recorded as basedon an arbitrary scale
Arbitrary scale used to quantify wear facets
the surface of
Arbitrary scaleswere used for both the anterior and the posterior teeth. Anterior teeth were assignedarbitrary values (1 to 4) (Fig. 4) as follows: 1 = One or severalfacetslocated only on the palatal or buccal surface of the tooth 2 = One or several facets present only on the incisal edge 3 = One or several facets present on the incisal edge
Fig. 4. Diagram of arbitrary criteria chosen to quantify wear facets of incisors and canines (explanations in text).
Fig. 6. A, Example of molar wear facets and B, their diagrammatic representation. Fig. 5. Diagram of arbitrary criteria chosen to quantify wear facets of molars and premolars (explanations in text).
and also on the palatal or vestibular surfaces, but occupying less than one third of longitudinal length of tooth crown 4 = One or several facets present on the incisal edge and also on the palatal or buccal surfaces, but occupying less than one third of longitudinal length of tooth crown Posterior teeth were assigned the following arbitrary values (1 to 5) (Fig. 5) as follows: 1 = Facets occupying “in buccolingual direction” less than one third of cusp side 2 = Facets occupying in buccolingual direction more than one third of cusp side 3 = Facets occupying a total cusp side 4 = Facets occupying in buccolingual direction three complete cusp sides (external working, internal working, and nonworking) that are not situated in the same frontal plane 5 = Facets occupying in buccolingual direction three complete and contiguous cusp sides situated in the same frontal plane
Fig. 7. Example of molar wear facets.
Every tooth and every occlusal surface were registered.
Arbitrary scale used to quantify occlusal contacts
the extent of
A distinction also was made between anterior and posterior teeth. In incisors and canines, four situations were considered: (1) punctiform contact; (2) contact surface largely inferior to the surface of wear facet; (3) contact surface inferior to the surface of wear facet; and (4) contact surface equal to the surface of wear facet.
Fig. 8. Example of incisal and canine wear facets.
Fig. 10. Diagram of three functional cusp sides on which working facets (1, l’, 3, 3’) and nonworking facets (2, 2’) are distributed.
508 Fig. 9. Example of incisal and canine wear facets. Five situations were considered for the posterior teeth, (1) contact surface occupying in buccolingual direction less than one third of cusp side; (2) contact surface occupying in buccolingual direction more than one third of cusp side; (3) contact surface occupying in buccolingual direction a total cusp side; (4) contact surface occupying three complete cusp sides, not aligned in buccolingual direction; and (5) contact surface occupying three complete cusp sides, aligned in buccolingual direction.
The nonparametric test of Kendall was used to verify whether the different occlusal parameters considered were related to abrasion. The test T of Kendall was used to calculate a coefficient of correlation between two qualitative parameters. We calculated the rate of Kendall between the surface of abrasion and occlusal parameters mentioned. This analysis was done by including all subjects but separating anterior teeth from posterior teeth. The data analysis was prepared in the form of tables of correlations between variables.
Four major observations deserve emphasis: 1. All dental arches presented many wear facets. All 88
Fig. 11. Diagram showing proportion of occlusal con-
tacts establishedon facets and outside facets.Only 7%of contacts in maximal intercuspation are not located inside wear facets.
of the teeth (except the lateral incisors) displayed facets. 2. Working-side wear facets were found in all posterior teeth. The nonworking facetswere found in all first and secondmolars, in 82% of secondpremolars, and in 58% of first premolars. 3. Manipulation of the opposingcastsshowedthat for anterior teeth, facets engagedduring protrusive movement could sometimes be differentiated from facets engaged during lateral movements but for posterior teeth, both movements are carried out by the same facets. 4. In all observedpatients, wear facets were distributed in a manner identical to the diagram of Fig. 2. Examples are given in Figs. 6 and 7 clearly showing the amplitude of nonworking facetsin posterior teeth, and in Figs. 8 and 9 showing the presenceof horizontal and vertical facets in incisors and canines. JANUARY
Fig. 12. Diagram representing average number of occlusalcontactsgiven for eachtooth. Total number of contacts are marked on vertical axis and number of teeth is indicated on horizontal axis (right and left teeth have been gathered). For example, in upper left and right central incisors (1.1 and 2.1) in 22 subjects(44 teeth), we found 66 occlusalcontacts. Average number of contacts per tooth is 1.5.
Table I. Number of vertical and horizontal
facets in anterior teeth concerning 22 dentitions (44
complete arches) Teeth
Number of teeth presenting vertical facets Number of teeth presenting horizontal facets
Wear facets in posterior
Wear facets were seen on the surface of the three functional cusp sides (Fig. 10). The working facets in premolars were usually absent from internal working cusp sides because of the low height of mandibular lingual cusps,which prevented any possibility of contact on this surface. The nomenclature of working and nonworking facets wasjustified by the possibility of sliding the mandibular caston the maxillary, using the facets formed by “dental articulation” (tooth-to-tooth contact) as guides.
Wear facets in anterior
In the 12 anterior teeth, wear surfaces took two different forms. The horizontal facets had a nearly horizontal incline and the vertical facets had a nearly vertical incline. The horizontal facets were routinely observed and were absentonly in 15 teeth (Table I). They developed THE
as a result of dental wear of incisal edgesand canine points. These opposing surfaces were in contact when the mandible occupied a position relatively far from the position of maximal intercuspation. The vertical facets were found on the palatal surfacesof maxillary incisors and canines (Fig. 8) and on buccal surfacesof lower incisors and canines (Fig. 9). The frequency of occurrence of thesefacets is given in Table I. The engagement of these facets occurred during eccentric movements not far from the position of maximal intercuspation, for example, in functional movementsof small amplitude.
The distribution of occlusalcontactson posterior teeth in maximal intercuspation suggestedthat maximal intercuspationis largely establishedthrough wear facets(Fig. 11). The quantitative results are given in Figs. 11 through 15 and in Tables II and III. 89
Fig. 14. Diagram
Diagram showing percentage of antagonists for posterior teeth with data on right and left teeth. For example, for lower left and right first premolars, 52% of examined 44 teeth have two antagonistic teeth (black area), 45% of 44 teeth have one antagonist (white area), and 3% have no antagonist in maximal intercuspation (dotted area). 13.
showing intensity of tacts. Intensive contacts = P (perforation) quent in posterior teeth, whereas, light (thinnings) are more frequent in anterior are given in percentage of total number
occlusal conare more frecontacts = T teeth. Values of contacts.
Table II. Number of teeth with no occlusal contacts*
DISCUSSION Theoretical interest The arrangement and the form of the observeddental facets are similar to those described by others.‘,9~‘4~15 Somepoints deserveemphasis. 1. Nonworking molar facets are found early and are as well developed as working facets. They are also functional facetsas indicated by the existenceof occlusal contacts on these [email protected]
’ 2. Two types of wear facets (vertical and horizontal) are seenin anterior teeth. 3. The surface of occlusal contacts increases with time. After an initial point (14% of anterior teeth and 18% of posterior teeth) a wear facet developsin which a portion of its surface is used by occlusal contact in maximal intercuspation. The rest of the facet surface is engaged in function during interdental contact movements.41-46 As wear occurs the interocclusal space is reduced,which leadsto the engagementof other points of occlusal surface. This observation coincides perfectly with Hildebrand’s4’ observation that during mastication the abrasion facets guide lateral movement, which in turn is the cause of abrasion. 90
Number of teeth with no occlusal contact
11-21 12-22 13-23 14-24 15-25 16-26 17-27 31-41 32-42 33-43 34-44 35-45 36-41 37-47 A total of 15% of anterior occlusal contact in maximal
6 12 4
14 27 9
0 0 0
0 0 0
1 11 5 2 2
2 25 11 5 5
teeth and 1% of posterior intercuspation.
teeth had no
4. For any tooth, working and nonworking facets alike represent the occlusal field that involves all functional movements.48 5. The arrangement of occlusal contacts does not JANUARY
Fig. 15. Relation between surfaces of occlusal contact and surfaces of wear facets. Each point represents one of 22 subjects, and its coordinates correspond to total surface of occlusal contact (vertical axis) and to total surface of wear facets (horizontal axis). These calculations were made with arbitrary scale described in the Methods section.
Research of correlation between the rate of abrasion and some occlusal parameters (nonparametric test of KENDALL) Correlation The The The The
number number number
the rate of abrasion
of contacts by tooth of contacts by tooth of antagonists Perforations number of contacts
The surface of contacts contacts on facet The Total number of contacts
0; X; XX;
in anterior in posterior
very or highly
match the different descriptionsabout dental archesseen in some textbooks.4*-52 On the other hand, it confirms the results obtained in previous studies in man.39*53-55 The finding that some anterior teeth do not maintain any occlusalcontact suggeststhat someintermittent contacts in protrusion or in lateral movement are sufficient to maintain the position of the tooth and to prevent dental
o,oooo o,oooo 0,0452
xxx xxx X
Occlusion with canine protection evolvestoward a group function type after canine wear.40v 59 It does not seem likely that gnathologic concepts concerning the round occlusal surfaces, a one-toothto-one-tooth relationship and a canine protection, correspond to a natural adult dentition.
6. The relation of one tooth to two teeth was the rule, with the number of tooth antagonistsincreasingwith the development of wear. This matchesBegg’s30hypothesis for which “the normal occlusal relation of very worn dentitions is Angle classIII.” Canine protection, which is not frequent in North American or European countries,56S59 is completely absentin very worn [email protected]
The ideasdevelopedin this article are mainly theoretical. They do, however, raise somequestionsof clinical interest. 1. If dental wear is a natural process,the introduction of metallic or ceramic prosthetic surfaces (which are harder than tooth surfaces)will prevent normal abrasion and will counteract physiologic changesof the dentition’s
surface. Hardness equal to that of the tooth should be an important factor in the choice or research of dental biomaterials. 2. When single tooth restorations are necessary, it is usually possible, even in arches that are not as healthy as those we studied, to find small movements (1 to 3 mm in range) determined by wear facets. This suggests that an analogue for jaw movements (an articulator) may not be really required in these situations. 3. The presence of nonworking facets and the evidence of nonworking contacts during chewingM indicate that a prophylactic elimination of all nonworking contacts will eliminate a great part of the functional field of mastication (Figs. 2 and 6). 4. Occlusal interdental contacts are surfaces that increase in diameter with the development of abrasion. When prosthetic treatment or occlusal correction are required, occlusal surfaces in a convex form may not really be necessary. 5. A diagnosis of bruxism whenever wear facets are found is not a reliable method of diagnosis.
14. 15. 16.
17. 18. 19. 20. 21. 22. 23.
CONCLUSION Published research indicates that dental wear is a universal phenomenon, and this limited study suggests the likelihood that modern occidental dentition is no exception to this rule.
9. 10. 11.
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ODONTOLOCIE 11 BLVD. CHARLES DE GAULLE CLERMONT-FERRAND 63005 FRANCE
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