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Chewing Patterns in Subjects with Normal Occlusion and With Malocclusions
Chewing Patterns in Subjects with Normal Occlusion and With Malocclusions Peter Alfred Proeschel This report describes the chewing patterns of individuals with normal occlusion and several types of malocclusion. Frontal movement patterns of the lower mid-incisor point were recorded during chewing of test foods in groups of subjects with Angle Class I normal occlusion, Class II malocclusion, as well as deep-bite and cross-bite malocclusions. Mandibular prognathic and retrognathic patients corrected to Angle Class I occlusions were also examined before and after orthognathic surgery. Chewing patterns were classified by using a catalogue of eight basic movement types. In none of the groups examined could chewing behavior be characterized by only one specific type of movement, but rather by different frequency distributions of pattern types. The Angle Class I, Class II, deep-bite, and presurgical retrognathism groups were characterized by chewing patterns with normal sequencing and grinding features and, to a minor extent, by self-crossing movements having no unique pattern of sequencing. Reversed sequencing did not occur in these four groups. In presurgical prognathic patients, drop-shaped patterns with steep closing movements predominated. Cross-bite malocclusion was characterized by dropshaped and reversed sequencing patterns. The pattern distribution in prognathic patients did not change after surgery. In retrognathic patients the therapeutically altered occlusion caused a decrease in the frequency of grinding movements and an increase in the frequency of drop-shaped patterns. (Semin Orthod 2006;12:138-149.) © 2006 Elsevier Inc. All rights reserved.
rthodontic or surgical treatments of malocclusion and dysmorphology aim at restoring or improving patients’ functional abilities. Function has been typically assessed by examining jaw muscle activity,1-5 bite-forces,1-3,6 food breakdown,7-9 or jaw movements.1,10-20 Because jaw movements are guided by neuromuscular control in accordance with the constraints imposed by the temporomandibular joints and occlusion, they have proven useful for evaluating chewing function.
O
University Dental Clinic, Department. of Prosthodontics, University of Erlangen–Nuremberg, Erlangen, Germany. Address correspondence to Dr. Proeschel, University Dental Clinic, Department of Prosthodontics, University of ErlangenNuremberg, Glueckstrasse 11, D 91054 Erlangen, Germany. Phone: 49 9131 8534223; Fax: 49 9131 8536781; E-mail: peter. [email protected] © 2006 Elsevier Inc. All rights reserved. 1073-8746/06/1202-0$30.00/0 doi:10.1053/j.sodo.2006.01.007
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To specify the term chewing or masticatory pattern, one has to consider that no unique movement can be assigned to the jaw as a whole because separate areas, for example, the temporomandibular joints and incisors, can move quite differently from each other. However, as demonstrated by Gibbs and coworkers,20 trajectories of the posterior teeth are quite similar to those of the incisors. Based on this similarity, tracking of the lower mid-incisor point has become a standard tool for the analysis of masticatory movement. Accordingly, the term “chewing” or “masticatory pattern” denotes the graphic superposition of consecutive chewing cycles of the lower mid-incisor point, evaluated in a frontal view. Chewing patterns were first studied by Ahlgren,13 who found that children with normal occlusion displayed regular types of movement, whereas children with malocclusion displayed predominately chopping, reversed, contralat-
Seminars in Orthodontics, Vol 12, No 2 (June), 2006: pp 138-149
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eral, and self-crossing masticatory strokes. Gibbs and coworkers20 reported similar observations and identified the so-called drop-shaped chewing pattern as the normal mode of mastication. These early studies established the accepted view that normal chewing function is associated with so-called normal masticatory movements, whereas malocclusions show “abnormal” movement patterns. Since such classifications lacked information on functional capabilities, more recent studies have focused on chewing performance and efficiency. The present report evaluates the relationships between chewing patterns and occlusion, and synthesizes the available information pertaining to masticatory patterns and chewing efficiency.
Materials and Methods Untreated Groups The sample of untreated subjects included 247 dental students selected using criteria recommended by Gibbs and Lundeen21 including proper chewing function, complete dental arches, no symptoms or signs of craniomandibular disorders, and no severe dysmorphology. The 247 subjects were divided into four groups according to their occlusions (Table 1): 159 subjects with Angle Class I normal occlusions, 46 subjects with Angle Class II malocclusions (incisal vertical overlap of less than 4 mm), 21 subjects with deep-bite malocclusions (incisal vertical overlap of more than 4 mm), and 21 subjects with posterior cross-bite malocclusions
(7 had right-side cross bites, 8 had left-side cross bites, and 6 had bilateral cross bites).
Surgically Treated Groups In addition to the untreated subjects, 20 patients with mandibular prognathism and 17 with retrognathism, who had undergone surgical setbacks or advancements of their mandibles, respectively, were evaluated before and 6 months after surgery (Table 1). All of the surgical patients underwent presurgical orthodontic treatment and had Class I occlusions after surgery. The prognathic and retrognathic groups made it possible to investigate how changes of occlusion affect chewing behavior. Masticatory movements of all patients were recorded a few days before surgery and about 6 months later, after they had adapted to their corrected occlusions.
Experimental Protocol For each subject in the untreated and treated groups, chewing movements were recorded using the Sirognathograph. This system has been described and its accuracy has been tested.22,23 It consists of a small magnet attached to the lower mid-incisors and an antenna, carrying semiconductor sensors, fixed to the head. The sensors measure changes in the magnetic field due to the movement of the magnet. Gummibears and equally sized pieces of bread, without crust, were used as tough and soft foods, respectively. These two textures were selected as extremes evoking
Table 1. Sample Size, Clinical Criteria, and Occlusal Status of Subjects with Normal and Malocclusion Evaluated Groups Angle Class I Angle Class II
Number of Subjects 159 46
Deep-bite
21
Cross-bite
21
Retrognathic presurgical
17
Retrognathic postsurgical
17
Prognathic presurgical
20
Prognathic postsurgical
20
Clinical Criteria
Occlusal Status
Nonpatient Normal occlusion Nonpatient; no skeletal discrepancies Malocclusion, vertical incisal overlap ⬍⫽ 4 mm Nonpatient; Angle Class II, no Malocclusion, vertical incisal overlap skeletal discrepancies ⬎ 4 mm Nonpatient; Angle Class I or II, no Malocclusion, 27 lateral dental arches skeletal discrepancies Patient; Angle Class II, skeletal Malocclusion discrepancies Patient; corrected to Angle Class I Normal occlusion Patient; Angle Class III, skeletal discrepancies Patient; corrected to Angle Class I
Malocclusion Normal occlusion
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forceful or gentle biting, respectively. With each kind of texture, one trial with chewing on the right and one with chewing on the left side were recorded. The recordings of chewing movements started from maximum intercuspation, with the bolus placed on the tongue. The trajectories of each trial were recorded for 20 seconds. In all persons (except the cross-bite subjects) rightand left-lateral tooth-guided jaw movements were also recorded. The angles of the jaw movements with respect to the vertical were determined interactively from a computer screen by using tangents to the traces, starting in maximum intercuspation (topmost point of the laterotrusive pattern). These “border angles” reflected the aggregate guiding of all occlusal structures involved in a laterotrusion. They were compared with “chewing angles” obtained by using tangents enveloping the traces under which the incisor point in mastication approached intercuspation or departed from it.
Evaluation and Statistics All chewing cycles of each person were first assessed visually on a computer screen. Abnormal
cycles, distorted due to swallowing, bolus replacements, or incomplete mouth closings were removed. Distortions were defined based on having prolonged cycle durations, excessive lateral excursions, or no return of the vertical excursion to the zero line. The frontal chewing pattern of each 20-second registration was established by plotting the vertical excursions against the left-right excursions. Only the frontal projection was evaluated because, based on previous experience, this has proven to be the most informative. Depending on individual chewing rhythms, about 20 to 35 cycles were superimposed to form one chewing pattern. Each subject’s chewing pattern obtained with each texture and chewing side were compared with one of eight types of movement modes (Fig 1). This catalogue comprises all possible forms of chewing movements observed in more than 550 persons with very different clinical conditions.23 The pattern types are arranged according to the direction of jaw rotation and the degree of curvature of the opening and closing strokes. The arrangement for right-sided chewing (Fig 1) starts with pattern types (A-D) that open toward the nonchewing side (patient’s left side)
Figure 1. Catalogue of basic types of chewing patterns for right-sided chewing cycles viewed from the front (see text for further explanation).
Chewing Patterns
and close from the chewing side (patient’s right side). This direction of jaw rotation has been defined as “normal sequencing.”23 The arrangement continues with movement types that have mixed or unclear sense of direction (E1, E2, ED) and ends with a form having reversed sequencing (I) compared with pattern types A to D. For classifying patterns of left-sided chewing, the same arrangement as in Figure 1 applies; however, all pattern types are mirrored with respect to the vertical axis. Among the normal sequencing patterns, type A is characterized by pronounced edges indicating the beginning and end of the grinding phase.21 Type B has only one edge, either during opening or closing (Fig 1), while the rest of the trajectory is smooth. Types C and D have entirely smooth opening and closing trajectories and may be called drop-shaped for obvious reasons. Pattern type D is characterized by a change of curvature of the closing movement resulting in a rather vertical approach to the intercuspal position. The patterns with mixed or unclear sequencing are partly self-crossing or have no well-separated opening and closing traces. In ED and E1 the
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opening strokes are directed to the chewing side and are frequently crossed by the closing traces. In ED, the closing traces correspond to those of the drop-shaped pattern D. In the E2 type, the jaw opens to the nonchewing side and the closing movements follow approximately the same traces as the opening movements. In reversed sequencing (I), the jaw opens on the chewing side and closes on the nonchewing side.
Statistics For each group listed in Table 1, a frequency distribution of chewing patterns was established for each texture and chewing side. The 2 test was used to evaluate differences between the frequency distributions of the different groups. Since no significant differences were found between frequency distributions of right-sided and left-sided chewing, the results will be confined to right-sided chewing. As an exception, the chewing pattern frequency distribution of the crossbite subjects refers to chewing on the side of the cross bite. Differences between pre- and postsurgical angles of the patient groups were tested by
Figure 2. Chewing pattern frequency distributions for mastication of tough and soft food in 159 individuals with Class I normal occlusion.
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using the Wilcoxon signed-rank test. Differences between the angles of the nonpatient and patient groups were examined by using the MannWhitney test. A P value of 0.01 was accepted as the level of significance.
describing soft and tough foods. Since tough food proved better able to discriminate chewing types, the presentation of results shall be confined to this food type.
Results
Chewing Patterns in Angle Class I, II, and Deep-Bite Malocclusions
Influence of Food Consistency on Chewing Patterns in Subjects with Normal Occlusion In the untreated subjects with Angle Class I normal occlusion, mastication of tough food was accomplished by normal sequencing for 82% of the subjects (Fig 2). The most frequent patterns were A and B with grinding characteristics. About 18% of the subjects in the Class I group showed mixed sequencing types E1 and ED. With soft food, type A appeared less frequently and the drop-shaped type C predominated. The frequencies of the mixed sequencing types ED and E1 were not affected by a change of the food texture. The E2 type and the completely reversed sequencing type I did not appear. The 2 test yielded a highly significant difference between the frequency distributions
No significant differences were found between the pattern frequencies of Angle Class I, Class II, and deep-bite occlusions (Fig 3). The distribution of deep-bite malocclusion closely resembled the distribution of Class I normal occlusion, with type A being the most frequent. Class II malocclusions showed less grinding and more smooth movements, expressed by the higher frequency of B type patterns. Moving from the Class I, to the Class II, to the deep-bite group, the border angles (Fig 4) on the side of the masticatory closing strokes tended to decrease, but those on the side of the opening traces were similar. In all three groups, the chewing angles were closely related to the border angles.
Figure 3. Chewing pattern distributions for mastication of tough food in 159 individuals with Class I normal occlusion, 46 subjects with Class II, and 21 subjects with deep-bite malocclusions.
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Figure 4. Mean border angles and chewing angles for the untreated and surgically treated groups. Numbers on left and right indicate the border and chewing angles, respectively, in degrees. The standard deviations ranged between 8 ° and 14°.
Cross Bite Of the 21 cross-bite subjects, 7 were right-sided, 8 left-sided, and 6 were bilateral, resulting in 27 lateral dental arches with cross bite available for evaluation. The frequency of the patterns when chewing on the side of the cross bite clearly differed from the frequency distribution of subjects with Class I normal occlusion (Fig 5), but also from the distributions of the Class II and the deep-bite groups (Fig 3). The most frequent was type D, which appeared in 26% of the cases. More than 45% of the cross-bite subjects showed an abnormal direction of jaw movement (ED, E1, and I). Most important, approximately 23% of the patterns in the cross-bite group were of the totally reversed sequencing type I, which were not found in the group with normal occlu-
sion or in the groups with Class II and deep-bite malocclusion.
Mandibular Prognathism, Pre- and Postsurgical Before surgery, mandibular prognathic patients showed distinctly different chewing patterns than subjects with normal occlusion (Fig 6). Their chewing patterns were dominated (41%) by pattern D, with about 7% of the E2 and I patterns. The remaining 52% of the cases were distributed among the other pattern types. Six months after jaw setback there was no significant change in their frequencies. The border angles in the presurgical state were significantly flatter than in the Class I normal group while the chewing angles were significantly steeper (Fig 4). Af-
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Figure 5. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 21 persons with cross-bite when chewing on the cross-bite side.
Figure 6. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 20 prognathic patients before, and 6 months after, orthognathic surgery.
Chewing Patterns
ter mandibular setback, the border angles were significantly narrowed and corresponded more closely to those of the untreated Class I normal occlusion group. The chewing angles increased slightly but not significantly after surgery, and the gap between the border and chewing angles remained large.
Mandibular Retrognathism, Pre- and Postsurgical In contrast to the prognathic patients, the presurgical pattern distribution in the retrognathic group did not differ significantly from that of untreated Class I normal occlusion group (Fig 7). However, mandibular advancement produced a reduction of the grinding type patterns and a substantial increase (⬎30%) in the frequency of the C type of pattern. Before surgery, the border angles on the side of the closing chewing strokes tended to be flatter (Fig 7) than in subjects with Class I normal occlusion, whereas border angles on the side of the opening traces were about the same. In the retro gnathic group, the presurgical chewing angles were more closely related to the presurgical bor-
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der angles than in the prognathic group. The border angles after mandibular advancement, corresponded well to the border angles of the untreated Class I normal occlusion group. However, the chewing angles were significantly steeper than in the presurgical state, increasing the gap between chewing movements and occlusal guidance.
Discussion Limitations on Assigning Chewing Patterns Classifying chewing movements in subjects with normal and malocclusion is complicated by the diversity of both the movement modes and the occlusal features. Assigning a person’s chewing mode to one of eight pattern types is subjective because smooth transitions actually exist between the different types. Likewise, a particular occlusion is accompanied by cofactors such as age, gender, occlusal details, and craniofacial morphology, and so forth that might influence the chewing mode. Age and gender could be neglected here because the examined groups did not differ much in age, and no sex-related
Figure 7. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 17 retrognathic patients before, and 6 months after, orthognathic surgery.
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difference was found in the chewing pattern distributions. No further subdivision by occlusal and craniofacial factors was attempted due to limited samples sizes. While the eight pattern types are rather universal, large sample sizes are required for statistical comparisons.
Relations Between Chewing Patterns and Border/Chewing Angles Regardless of occlusal relationships and craniofacial morphology, the occlusal guidance reflected by border and chewing angles limits the movement space and influences chewing patterns in the intercuspal range.14,15 Different studies agree that in normal occlusion, about 60% of masticatory closing strokes were closely related to occlusal guidance.21,24 In the present study, about the same percentage of subjects chewed with patterns A or B (Fig 2) with ascribed tooth gliding and grinding features.21 Chewing angles of these patterns were flatter and coincided closely to occlusal guidance whereas chewing angles of type C or D patterns were less closely related to their border angles.25 The relationship between occlusal guidance and chewing movements is strongly influenced by the consistency of the food. It is well established that tough foods more frequently provoke grinding-type patterns with flat chewing angles than do soft foods.10,21,26-28 Thus, one necessary condition to predict masticatory performance from chewing patterns is the use of test foods that require forceful comminution.
Relationship of Border and Chewing Angles to Malocclusion In subjects with normal occlusion, the chewing angles of the closing strokes coincided well with the border angles (Fig 7). This indicates a high incidence of occlusal guidance and suggests good chewing efficiency since gliding of cusps along slopes facilitates the generation of shearing forces.29 In fact, Wilding and Lewin14 found a positive correlation between the laterality of closing trajectories and chewing performance. Other studies have confirmed higher efficiency in normal occlusion than in malocclusions.9,29 The closing chewing angles in subjects with normal occlusions, as well as those with Class II and deep-bite malocclusions, were also closely related to occlusal guidance, despite the chewing
and border angles decreasing slightly between the Class I, Class II, and deep-bite groups. It has been previously shown that Class I patients have better masticatory performance than Class II patients.29 One could speculate that improved performance might be associated with the flattening of closing movements. In presurgical retrognathic patients, the chewing closing angles were slightly steeper than in subjects with normal Class I occlusion, while the border angles were flatter. The resulting gap of 21° suggests a reduction of tooth gliding and grinding, and thus, reduced chewing efficiency when compared with normal occlusion. This supports findings of lower bite forces and more limited chewing efficiency in retrognathic patients.1,3,5,9 In presurgical prognathic patients, their very steep chewing angles and flatter occlusal guidance implies that they compressed food mainly by chopping. Nearly vertical masticatory strokes have also been reported for prognathic subjects.10,12,16 Untreated Class III patients have been previously shown to have less effective masticatory performance than subjects with normal occlusion or in Class II malocclusion.7,17,29 Findings of a less effective masticatory performance are consistent with the mechanical fact that chopping is less effective than grinding, due to the lack of shearing forces.
Relationship of Frequency of Chewing Patterns to Malocclusion The predominance of grinding type patterns A and B in the Angle Class I, Class II, and in deepbite groups implies that occlusal guidance was used during chewing, and that different degrees of frontal overbite did not affect the ability to exert lateral jaw movements. A lack of correspondence between overbite and lateral jaw movements is supported by Alexander and coworkers.11 Steeper chewing angles in Class II subjects were accompanied by fewer grinding patterns, compared with the Class I group, although the differences were not statistically significant. Whether the reduced frequency of grinding patterns actually produced the reductions in chewing efficiency typically found among Class II subjects will require further study.29,30 The relatively high frequency of grinding patterns (Fig 3) associated with steeper chewing and
Chewing Patterns
border angles was not expected among deep-bite subjects. The close correspondence between chewing and border angles in deep-bite individuals (Fig 4) implies that grinding can still be accomplished with steeper occlusal guidance and narrower A or B patterns. Currently, no reports on masticatory performance are available for deep-bite subjects. The presurgical retrognathic patients showed approximately the same frequency of A and B grinding patterns as did the Class II group, even though the gap between their border and chewing angles suggested less grinding action. If the lower maximum bite forces found in presurgical retrognathic patients3,9 also means lower grinding forces, then perhaps food would be compressed more gradually and a larger than normal gap between the angles could develop. In prognathism, the low frequency of A and B patterns and the prevalence of chopping type D movements probably reflected avoidance of tooth gliding. This is suggested by the special form of the D type closing movement in these patients, which, after a swing to the chewing side, appears to depart from occlusal guidance. In fact, prognathic patients in the present study frequently had difficulties exerting tooth-guided lateral excursions because of gliding obstacles. Under the latter conditions, the type D chewing pattern may have been the ideal form of movement, although this
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was possibly achieved at the cost of reduced chewing efficiency.7,17,29 Reversed sequencing among cross-bite subjects is well established.18,31,32 The normal clockwise sequencing found among non-cross-bite subjects suggests that food is ground most efficiently by moving the lower buccal cusps through the cavities formed by the upper cusps (Fig 8, left). An analogous mode of food crushing in a cross-bite intercuspation would require reversed sequencing so that the role of lower buccal cusps would be taken over by the lingual cusps (Fig 8, right). Normal sequencing in cross bite might lead to interferences of the buccal cusps, just as reversed sequencing in non-cross bite might lead to interference of the lingual cusps. This could explain why reversed sequencing or chopping type patterns D frequently appeared among cross-bite subjects when chewing on the cross-bite side. The normal sequencing patterns exhibited by some of the crossbite subjects might be due to varying degrees of lateral cross-bite severity.
Use of Angles and Chewing Pattern Frequencies in Evaluation of Surgical Treatment Despite a close to normal occlusal guidance after mandibular advancement of retrognathic pa-
Figure 8. Schematic explaining the incidence of normal sequencing in non-cross-bite dentitions and of reversed sequencing in cross-bite dentitions. Drawings refer to right-sided chewing. Left: Normal occlusion where unobstructed grinding and normal chewing patterns (opening toward nonchewing side, closing from chewing side) are possible. Right: Cross-bite malocclusion with requiring reversed sequencing.
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tients, a decrease of grinding and an increase of drop-shaped patterns occurred. The concomitant steepening of the closing chewing angles suggested avoidance of the new occlusal pattern, which could explain the unchanged or reduced masticatory performance often reported for retrognathic patients after surgery.9,19 In contrast to other studies16,19 the chewing pattern distribution of prognathic patients in the present study did not change, even though occlusion was normalized after surgery. A similar effect of nonchanging vertical closing strokes was observed in experimental narrowing of occlusal guidance in asymptomatic subjects.33 Even though the modified occlusion could allow for grinding movements, the central nervous system may not necessarily make use of this and may maintain established vertical movement patterns. Interestingly, masticatory performance also does not increase or approach normal conditions after surgery in prognathism patients.17 The observation that reversed sequencing is maintained31 or partly maintained32 after correction of cross bite indicates that such sequences are not impossible in subjects with normal intercuspation. In summary, neither normal occlusion nor malocclusion can be characterized by any one chewing pattern, but rather by characteristic pattern distributions. In general, normal occlusion is characterized by grinding type chewing patterns with normal sequencing (Fig 1) and to a minor extent by patterns with drop-shape or mixed sequencing. The prevalence of grinding in subjects with normal occlusion coincides with the “ideal” chewing pattern for maximal efficiency, as described by Yamashita and coworkers.15 However, a grinding type pattern alone is not a sufficient criterion for assessing chewing efficiency. This becomes clear from the Class II, deep-bite, and retrognathic patients, in whom reduced functional abilities are manifest despite fairly normal chewing pattern distributions. In contrast to common opinion, the reversed sequencing pattern may not be abnormal. The reversed movement could simply be the equivalent of normal sequencing in cross-bite occlusions. The D pattern type with steep closing movements and the self-crossing types ED, E1, and E2 should be considered “abnormal.” In particular, the type (D) indicates avoidance or reduction of occlusal guidance and is more fre-
quent among Class III occlusion individuals who have less efficient chewing. Since abnormal patterns are also present in subjects with normal occlusion, simultaneous investigation of chewing patterns and chewing efficiency are necessary to assign greater clinical discriminatory power to chewing patterns.
References 1. Zarrinkelk HM, Throckmorton GS, Ellis E 3rd, et al: Functional and morphologic changes after combined maxillary intrusion and mandibular advancement surgery. J Oral Maxillofac Surg 54:828-837, 1996 2. Youssef RE, Throckmorton GS, Ellis E 3rd, et al: Comparison of habitual masticatory cycles and muscle activity before and after orthognathic surgery. J Oral Maxillofac Surg 55:699-707, 1997 3. Throckmorton GS, Ellis E, Sinn DP: Functional characteristics of retrognathic patients before and after mandibular advancement surgery. J Oral Maxillofac Surg 53:898-908, 1995 4. Eckhardt L, Harzer W, Schneevoigt R: Comparative study of excitation patterns in the masseter muscle before and after orthognathic surgery. J Craniomaxillofac Surg 25:344-352, 1997 5. Harper RP, de Bruin H, Burcea I: Muscle activity during mandibular movements in normal and mandibular retrognathic subjects. J Oral Maxillofac Surg 55:225-233, 1997 6. Ellis E 3rd, Throckmorton GS, Sinn DP: Bite forces before and after surgical correction of mandibular prognathism. J Oral Maxillofac Surg 54:176-181, 1996 7. English JD, Buschang PH, Throckmorton GS: Does malocclusion affect masticatory performance? Angle Orthod 72:21-27, 2002 8. Zarrinkelk HM, Throckmorton GS, Ellis E 3rd, et al: A longitudinal study of changes in masticatory performance of patients undergoing orthognathic surgery. J Oral Maxillofac Surg 53:777-782, 1995 9. Van den Braber W, van der Glas H, van der Bilt A, et al: Masticatory function in retrognathic patients, before and after mandibular advancement surgery. J Oral Maxillofac Surg 62:549-554, 2004 10. Pröschel P, Hofmann M: Frontal chewing patterns of the incisor point and their dependence on resistance of food and type of occlusion. J Prosthet Dent 59:617-624, 1988 11. Alexander TA, Gibbs CH, Thompson WJ: Investigation of chewing patterns in deep-bite malocclusions before and after orthodontic treatment. Am J Orthod 85:21-27, 1984 12. Proeschel PA, Huemmer H, Hofmann M, et al: Reaction of mastication to occlusal changes induced by correction of mandibular prognathism. J Prosthet Dent 64:211-218, 1990 13. Ahlgren J: Mechanism of mastication. Acta Odontol Scand 24:Suppl. 44, 1966 14. Wilding RJC, Lewin A: The determination of optimal human jaw movement based on their association with chewing performance. Arch Oral Biol 39:333-343, 1994
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15. Yamashita S, Hatch JP, Rugh JD: Does chewing performance depend upon a specific masticatory pattern? J Oral Rehabil 26:547-553, 1999 16. Miyawaki S, Yasuda Y, Yashiro K, et al: Changes in masticatory jaw movement and muscle activity following surgical orthodontic treatment of an adult skeletal Class III case. Clin Orthod Res 4:119-123, 2001 17. Kobayashi T, Honma K, Shingaki S, et al: Changes in masticatory function after orthodontic treatment in patients with mandibular prognathism. Br J Oral Maxillofac Surg 39:260-265, 2001 18. Miyauchi S, Nakaminami T, Nishio K, et al: Chewing pattern in posterior crossbite. Classification of chewing pattern in the frontal plane. Nippon Hotetsu Shika Gakkai Zasshi 33:938-951, 1989 19. Ehmer U, Broll P: Mandibular border movements and masticatory patterns before and after orthognathic surgery. Int J Adult Orthod Orthognath Surg 7:153-159, 1992 20. Gibbs CH, Messerman T, Reswick JB, et al: Functional movements of the mandible. J Prosthet Dent 26:604-620, 1971 21. Gibbs CH, Lundeen HC: Jaw movements and forces during chewing and swallowing and their clinical significance. In: Lundeen HC, Gibbs CH, eds: Advances in Occlusion. Boston, John Wright PSG, 1982, pp 2-32 22. Mongini F, Tempia-Valenta G: A graphic and statistical analysis of the chewing movements in function and dysfunction. J Craniomandib Pract 2:125-134, 1984 23. Proeschel P: An extensive classification of chewing patterns in the frontal plane. J Craniomandib Pract 5:55-63, 1987 24. Ai M, Ishiwara T: A study of the masticatory movement at the incision inferius. Bull Tokyo Med Dent Univ 15:371386, 1968
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25. Proschel P: Effects of the occlusal pattern on the mandibular movements during masticatory function. Dtsch Zahnarztl Z 43:1099-1103, 1988 26. Horio T, Kawamura Y: Effect of texture of food on chewing patterns in the human subject. J Oral Rehabil 16:177-183, 1989 27. Takada K, Miyawaki S, Tatsuda M: The effects of food consistency on jaw movement and posterior temporalis and inferior orbicularis oris muscle activities during chewing in children. Arch Oral Biol 39:793-805, 1994 28. Anderson K, Throckmorton GS, Buschang PH, et al: The effects of bolus hardness on masticatory kinematics. J Oral Rehabil 29:689-696, 2002 29. Owens S, Buschang PH, Throckmorton GS, et al: Masticatory performance and areas of occlusal contact and near contact in subjects with normal occlusion and malocclusion. Am J Orthod Dentofacial Orthop 121:602609, 2002 30. Henrikson T, Ekberg EC, Nilner M: Masticatory efficiency and ability in relation to occlusion and mandibular dysfunction in girls. Int J Prosthodont 11:125-132, 1998 31. Throckmorton GS, Buschang PH, Hayasaki H, et al: Changes in the masticatory cycle following treatment of posterior unilateral crossbite in children. Am J Orthod Dentofacial Orthop 120:521-529, 2001 32. Ben-Bassat Y, Yaffe A, Brin I, et al: Functional and morphological-occlusal aspects in children treated for unilateral posterior cross-bite. Eur J Orthod 15:57-63, 1993 33. Ogawa T, Ogawa M, Koyano K: Different responses of masticatory movements after alteration of occlusal guidance related to individual movement patterns. J Oral Rehabil 28:830-841, 2001
rthodontic or surgical treatments of malocclusion and dysmorphology aim at restoring or improving patients’ functional abilities. Function has been typically assessed by examining jaw muscle activity,1-5 bite-forces,1-3,6 food breakdown,7-9 or jaw movements.1,10-20 Because jaw movements are guided by neuromuscular control in accordance with the constraints imposed by the temporomandibular joints and occlusion, they have proven useful for evaluating chewing function.
O
University Dental Clinic, Department. of Prosthodontics, University of Erlangen–Nuremberg, Erlangen, Germany. Address correspondence to Dr. Proeschel, University Dental Clinic, Department of Prosthodontics, University of ErlangenNuremberg, Glueckstrasse 11, D 91054 Erlangen, Germany. Phone: 49 9131 8534223; Fax: 49 9131 8536781; E-mail: peter. [email protected] © 2006 Elsevier Inc. All rights reserved. 1073-8746/06/1202-0$30.00/0 doi:10.1053/j.sodo.2006.01.007
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To specify the term chewing or masticatory pattern, one has to consider that no unique movement can be assigned to the jaw as a whole because separate areas, for example, the temporomandibular joints and incisors, can move quite differently from each other. However, as demonstrated by Gibbs and coworkers,20 trajectories of the posterior teeth are quite similar to those of the incisors. Based on this similarity, tracking of the lower mid-incisor point has become a standard tool for the analysis of masticatory movement. Accordingly, the term “chewing” or “masticatory pattern” denotes the graphic superposition of consecutive chewing cycles of the lower mid-incisor point, evaluated in a frontal view. Chewing patterns were first studied by Ahlgren,13 who found that children with normal occlusion displayed regular types of movement, whereas children with malocclusion displayed predominately chopping, reversed, contralat-
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eral, and self-crossing masticatory strokes. Gibbs and coworkers20 reported similar observations and identified the so-called drop-shaped chewing pattern as the normal mode of mastication. These early studies established the accepted view that normal chewing function is associated with so-called normal masticatory movements, whereas malocclusions show “abnormal” movement patterns. Since such classifications lacked information on functional capabilities, more recent studies have focused on chewing performance and efficiency. The present report evaluates the relationships between chewing patterns and occlusion, and synthesizes the available information pertaining to masticatory patterns and chewing efficiency.
Materials and Methods Untreated Groups The sample of untreated subjects included 247 dental students selected using criteria recommended by Gibbs and Lundeen21 including proper chewing function, complete dental arches, no symptoms or signs of craniomandibular disorders, and no severe dysmorphology. The 247 subjects were divided into four groups according to their occlusions (Table 1): 159 subjects with Angle Class I normal occlusions, 46 subjects with Angle Class II malocclusions (incisal vertical overlap of less than 4 mm), 21 subjects with deep-bite malocclusions (incisal vertical overlap of more than 4 mm), and 21 subjects with posterior cross-bite malocclusions
(7 had right-side cross bites, 8 had left-side cross bites, and 6 had bilateral cross bites).
Surgically Treated Groups In addition to the untreated subjects, 20 patients with mandibular prognathism and 17 with retrognathism, who had undergone surgical setbacks or advancements of their mandibles, respectively, were evaluated before and 6 months after surgery (Table 1). All of the surgical patients underwent presurgical orthodontic treatment and had Class I occlusions after surgery. The prognathic and retrognathic groups made it possible to investigate how changes of occlusion affect chewing behavior. Masticatory movements of all patients were recorded a few days before surgery and about 6 months later, after they had adapted to their corrected occlusions.
Experimental Protocol For each subject in the untreated and treated groups, chewing movements were recorded using the Sirognathograph. This system has been described and its accuracy has been tested.22,23 It consists of a small magnet attached to the lower mid-incisors and an antenna, carrying semiconductor sensors, fixed to the head. The sensors measure changes in the magnetic field due to the movement of the magnet. Gummibears and equally sized pieces of bread, without crust, were used as tough and soft foods, respectively. These two textures were selected as extremes evoking
Table 1. Sample Size, Clinical Criteria, and Occlusal Status of Subjects with Normal and Malocclusion Evaluated Groups Angle Class I Angle Class II
Number of Subjects 159 46
Deep-bite
21
Cross-bite
21
Retrognathic presurgical
17
Retrognathic postsurgical
17
Prognathic presurgical
20
Prognathic postsurgical
20
Clinical Criteria
Occlusal Status
Nonpatient Normal occlusion Nonpatient; no skeletal discrepancies Malocclusion, vertical incisal overlap ⬍⫽ 4 mm Nonpatient; Angle Class II, no Malocclusion, vertical incisal overlap skeletal discrepancies ⬎ 4 mm Nonpatient; Angle Class I or II, no Malocclusion, 27 lateral dental arches skeletal discrepancies Patient; Angle Class II, skeletal Malocclusion discrepancies Patient; corrected to Angle Class I Normal occlusion Patient; Angle Class III, skeletal discrepancies Patient; corrected to Angle Class I
Malocclusion Normal occlusion
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forceful or gentle biting, respectively. With each kind of texture, one trial with chewing on the right and one with chewing on the left side were recorded. The recordings of chewing movements started from maximum intercuspation, with the bolus placed on the tongue. The trajectories of each trial were recorded for 20 seconds. In all persons (except the cross-bite subjects) rightand left-lateral tooth-guided jaw movements were also recorded. The angles of the jaw movements with respect to the vertical were determined interactively from a computer screen by using tangents to the traces, starting in maximum intercuspation (topmost point of the laterotrusive pattern). These “border angles” reflected the aggregate guiding of all occlusal structures involved in a laterotrusion. They were compared with “chewing angles” obtained by using tangents enveloping the traces under which the incisor point in mastication approached intercuspation or departed from it.
Evaluation and Statistics All chewing cycles of each person were first assessed visually on a computer screen. Abnormal
cycles, distorted due to swallowing, bolus replacements, or incomplete mouth closings were removed. Distortions were defined based on having prolonged cycle durations, excessive lateral excursions, or no return of the vertical excursion to the zero line. The frontal chewing pattern of each 20-second registration was established by plotting the vertical excursions against the left-right excursions. Only the frontal projection was evaluated because, based on previous experience, this has proven to be the most informative. Depending on individual chewing rhythms, about 20 to 35 cycles were superimposed to form one chewing pattern. Each subject’s chewing pattern obtained with each texture and chewing side were compared with one of eight types of movement modes (Fig 1). This catalogue comprises all possible forms of chewing movements observed in more than 550 persons with very different clinical conditions.23 The pattern types are arranged according to the direction of jaw rotation and the degree of curvature of the opening and closing strokes. The arrangement for right-sided chewing (Fig 1) starts with pattern types (A-D) that open toward the nonchewing side (patient’s left side)
Figure 1. Catalogue of basic types of chewing patterns for right-sided chewing cycles viewed from the front (see text for further explanation).
Chewing Patterns
and close from the chewing side (patient’s right side). This direction of jaw rotation has been defined as “normal sequencing.”23 The arrangement continues with movement types that have mixed or unclear sense of direction (E1, E2, ED) and ends with a form having reversed sequencing (I) compared with pattern types A to D. For classifying patterns of left-sided chewing, the same arrangement as in Figure 1 applies; however, all pattern types are mirrored with respect to the vertical axis. Among the normal sequencing patterns, type A is characterized by pronounced edges indicating the beginning and end of the grinding phase.21 Type B has only one edge, either during opening or closing (Fig 1), while the rest of the trajectory is smooth. Types C and D have entirely smooth opening and closing trajectories and may be called drop-shaped for obvious reasons. Pattern type D is characterized by a change of curvature of the closing movement resulting in a rather vertical approach to the intercuspal position. The patterns with mixed or unclear sequencing are partly self-crossing or have no well-separated opening and closing traces. In ED and E1 the
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opening strokes are directed to the chewing side and are frequently crossed by the closing traces. In ED, the closing traces correspond to those of the drop-shaped pattern D. In the E2 type, the jaw opens to the nonchewing side and the closing movements follow approximately the same traces as the opening movements. In reversed sequencing (I), the jaw opens on the chewing side and closes on the nonchewing side.
Statistics For each group listed in Table 1, a frequency distribution of chewing patterns was established for each texture and chewing side. The 2 test was used to evaluate differences between the frequency distributions of the different groups. Since no significant differences were found between frequency distributions of right-sided and left-sided chewing, the results will be confined to right-sided chewing. As an exception, the chewing pattern frequency distribution of the crossbite subjects refers to chewing on the side of the cross bite. Differences between pre- and postsurgical angles of the patient groups were tested by
Figure 2. Chewing pattern frequency distributions for mastication of tough and soft food in 159 individuals with Class I normal occlusion.
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using the Wilcoxon signed-rank test. Differences between the angles of the nonpatient and patient groups were examined by using the MannWhitney test. A P value of 0.01 was accepted as the level of significance.
describing soft and tough foods. Since tough food proved better able to discriminate chewing types, the presentation of results shall be confined to this food type.
Results
Chewing Patterns in Angle Class I, II, and Deep-Bite Malocclusions
Influence of Food Consistency on Chewing Patterns in Subjects with Normal Occlusion In the untreated subjects with Angle Class I normal occlusion, mastication of tough food was accomplished by normal sequencing for 82% of the subjects (Fig 2). The most frequent patterns were A and B with grinding characteristics. About 18% of the subjects in the Class I group showed mixed sequencing types E1 and ED. With soft food, type A appeared less frequently and the drop-shaped type C predominated. The frequencies of the mixed sequencing types ED and E1 were not affected by a change of the food texture. The E2 type and the completely reversed sequencing type I did not appear. The 2 test yielded a highly significant difference between the frequency distributions
No significant differences were found between the pattern frequencies of Angle Class I, Class II, and deep-bite occlusions (Fig 3). The distribution of deep-bite malocclusion closely resembled the distribution of Class I normal occlusion, with type A being the most frequent. Class II malocclusions showed less grinding and more smooth movements, expressed by the higher frequency of B type patterns. Moving from the Class I, to the Class II, to the deep-bite group, the border angles (Fig 4) on the side of the masticatory closing strokes tended to decrease, but those on the side of the opening traces were similar. In all three groups, the chewing angles were closely related to the border angles.
Figure 3. Chewing pattern distributions for mastication of tough food in 159 individuals with Class I normal occlusion, 46 subjects with Class II, and 21 subjects with deep-bite malocclusions.
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Figure 4. Mean border angles and chewing angles for the untreated and surgically treated groups. Numbers on left and right indicate the border and chewing angles, respectively, in degrees. The standard deviations ranged between 8 ° and 14°.
Cross Bite Of the 21 cross-bite subjects, 7 were right-sided, 8 left-sided, and 6 were bilateral, resulting in 27 lateral dental arches with cross bite available for evaluation. The frequency of the patterns when chewing on the side of the cross bite clearly differed from the frequency distribution of subjects with Class I normal occlusion (Fig 5), but also from the distributions of the Class II and the deep-bite groups (Fig 3). The most frequent was type D, which appeared in 26% of the cases. More than 45% of the cross-bite subjects showed an abnormal direction of jaw movement (ED, E1, and I). Most important, approximately 23% of the patterns in the cross-bite group were of the totally reversed sequencing type I, which were not found in the group with normal occlu-
sion or in the groups with Class II and deep-bite malocclusion.
Mandibular Prognathism, Pre- and Postsurgical Before surgery, mandibular prognathic patients showed distinctly different chewing patterns than subjects with normal occlusion (Fig 6). Their chewing patterns were dominated (41%) by pattern D, with about 7% of the E2 and I patterns. The remaining 52% of the cases were distributed among the other pattern types. Six months after jaw setback there was no significant change in their frequencies. The border angles in the presurgical state were significantly flatter than in the Class I normal group while the chewing angles were significantly steeper (Fig 4). Af-
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Figure 5. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 21 persons with cross-bite when chewing on the cross-bite side.
Figure 6. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 20 prognathic patients before, and 6 months after, orthognathic surgery.
Chewing Patterns
ter mandibular setback, the border angles were significantly narrowed and corresponded more closely to those of the untreated Class I normal occlusion group. The chewing angles increased slightly but not significantly after surgery, and the gap between the border and chewing angles remained large.
Mandibular Retrognathism, Pre- and Postsurgical In contrast to the prognathic patients, the presurgical pattern distribution in the retrognathic group did not differ significantly from that of untreated Class I normal occlusion group (Fig 7). However, mandibular advancement produced a reduction of the grinding type patterns and a substantial increase (⬎30%) in the frequency of the C type of pattern. Before surgery, the border angles on the side of the closing chewing strokes tended to be flatter (Fig 7) than in subjects with Class I normal occlusion, whereas border angles on the side of the opening traces were about the same. In the retro gnathic group, the presurgical chewing angles were more closely related to the presurgical bor-
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der angles than in the prognathic group. The border angles after mandibular advancement, corresponded well to the border angles of the untreated Class I normal occlusion group. However, the chewing angles were significantly steeper than in the presurgical state, increasing the gap between chewing movements and occlusal guidance.
Discussion Limitations on Assigning Chewing Patterns Classifying chewing movements in subjects with normal and malocclusion is complicated by the diversity of both the movement modes and the occlusal features. Assigning a person’s chewing mode to one of eight pattern types is subjective because smooth transitions actually exist between the different types. Likewise, a particular occlusion is accompanied by cofactors such as age, gender, occlusal details, and craniofacial morphology, and so forth that might influence the chewing mode. Age and gender could be neglected here because the examined groups did not differ much in age, and no sex-related
Figure 7. Chewing pattern distributions for mastication of tough food in 159 subjects with Class I normal occlusion and in 17 retrognathic patients before, and 6 months after, orthognathic surgery.
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difference was found in the chewing pattern distributions. No further subdivision by occlusal and craniofacial factors was attempted due to limited samples sizes. While the eight pattern types are rather universal, large sample sizes are required for statistical comparisons.
Relations Between Chewing Patterns and Border/Chewing Angles Regardless of occlusal relationships and craniofacial morphology, the occlusal guidance reflected by border and chewing angles limits the movement space and influences chewing patterns in the intercuspal range.14,15 Different studies agree that in normal occlusion, about 60% of masticatory closing strokes were closely related to occlusal guidance.21,24 In the present study, about the same percentage of subjects chewed with patterns A or B (Fig 2) with ascribed tooth gliding and grinding features.21 Chewing angles of these patterns were flatter and coincided closely to occlusal guidance whereas chewing angles of type C or D patterns were less closely related to their border angles.25 The relationship between occlusal guidance and chewing movements is strongly influenced by the consistency of the food. It is well established that tough foods more frequently provoke grinding-type patterns with flat chewing angles than do soft foods.10,21,26-28 Thus, one necessary condition to predict masticatory performance from chewing patterns is the use of test foods that require forceful comminution.
Relationship of Border and Chewing Angles to Malocclusion In subjects with normal occlusion, the chewing angles of the closing strokes coincided well with the border angles (Fig 7). This indicates a high incidence of occlusal guidance and suggests good chewing efficiency since gliding of cusps along slopes facilitates the generation of shearing forces.29 In fact, Wilding and Lewin14 found a positive correlation between the laterality of closing trajectories and chewing performance. Other studies have confirmed higher efficiency in normal occlusion than in malocclusions.9,29 The closing chewing angles in subjects with normal occlusions, as well as those with Class II and deep-bite malocclusions, were also closely related to occlusal guidance, despite the chewing
and border angles decreasing slightly between the Class I, Class II, and deep-bite groups. It has been previously shown that Class I patients have better masticatory performance than Class II patients.29 One could speculate that improved performance might be associated with the flattening of closing movements. In presurgical retrognathic patients, the chewing closing angles were slightly steeper than in subjects with normal Class I occlusion, while the border angles were flatter. The resulting gap of 21° suggests a reduction of tooth gliding and grinding, and thus, reduced chewing efficiency when compared with normal occlusion. This supports findings of lower bite forces and more limited chewing efficiency in retrognathic patients.1,3,5,9 In presurgical prognathic patients, their very steep chewing angles and flatter occlusal guidance implies that they compressed food mainly by chopping. Nearly vertical masticatory strokes have also been reported for prognathic subjects.10,12,16 Untreated Class III patients have been previously shown to have less effective masticatory performance than subjects with normal occlusion or in Class II malocclusion.7,17,29 Findings of a less effective masticatory performance are consistent with the mechanical fact that chopping is less effective than grinding, due to the lack of shearing forces.
Relationship of Frequency of Chewing Patterns to Malocclusion The predominance of grinding type patterns A and B in the Angle Class I, Class II, and in deepbite groups implies that occlusal guidance was used during chewing, and that different degrees of frontal overbite did not affect the ability to exert lateral jaw movements. A lack of correspondence between overbite and lateral jaw movements is supported by Alexander and coworkers.11 Steeper chewing angles in Class II subjects were accompanied by fewer grinding patterns, compared with the Class I group, although the differences were not statistically significant. Whether the reduced frequency of grinding patterns actually produced the reductions in chewing efficiency typically found among Class II subjects will require further study.29,30 The relatively high frequency of grinding patterns (Fig 3) associated with steeper chewing and
Chewing Patterns
border angles was not expected among deep-bite subjects. The close correspondence between chewing and border angles in deep-bite individuals (Fig 4) implies that grinding can still be accomplished with steeper occlusal guidance and narrower A or B patterns. Currently, no reports on masticatory performance are available for deep-bite subjects. The presurgical retrognathic patients showed approximately the same frequency of A and B grinding patterns as did the Class II group, even though the gap between their border and chewing angles suggested less grinding action. If the lower maximum bite forces found in presurgical retrognathic patients3,9 also means lower grinding forces, then perhaps food would be compressed more gradually and a larger than normal gap between the angles could develop. In prognathism, the low frequency of A and B patterns and the prevalence of chopping type D movements probably reflected avoidance of tooth gliding. This is suggested by the special form of the D type closing movement in these patients, which, after a swing to the chewing side, appears to depart from occlusal guidance. In fact, prognathic patients in the present study frequently had difficulties exerting tooth-guided lateral excursions because of gliding obstacles. Under the latter conditions, the type D chewing pattern may have been the ideal form of movement, although this
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was possibly achieved at the cost of reduced chewing efficiency.7,17,29 Reversed sequencing among cross-bite subjects is well established.18,31,32 The normal clockwise sequencing found among non-cross-bite subjects suggests that food is ground most efficiently by moving the lower buccal cusps through the cavities formed by the upper cusps (Fig 8, left). An analogous mode of food crushing in a cross-bite intercuspation would require reversed sequencing so that the role of lower buccal cusps would be taken over by the lingual cusps (Fig 8, right). Normal sequencing in cross bite might lead to interferences of the buccal cusps, just as reversed sequencing in non-cross bite might lead to interference of the lingual cusps. This could explain why reversed sequencing or chopping type patterns D frequently appeared among cross-bite subjects when chewing on the cross-bite side. The normal sequencing patterns exhibited by some of the crossbite subjects might be due to varying degrees of lateral cross-bite severity.
Use of Angles and Chewing Pattern Frequencies in Evaluation of Surgical Treatment Despite a close to normal occlusal guidance after mandibular advancement of retrognathic pa-
Figure 8. Schematic explaining the incidence of normal sequencing in non-cross-bite dentitions and of reversed sequencing in cross-bite dentitions. Drawings refer to right-sided chewing. Left: Normal occlusion where unobstructed grinding and normal chewing patterns (opening toward nonchewing side, closing from chewing side) are possible. Right: Cross-bite malocclusion with requiring reversed sequencing.
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tients, a decrease of grinding and an increase of drop-shaped patterns occurred. The concomitant steepening of the closing chewing angles suggested avoidance of the new occlusal pattern, which could explain the unchanged or reduced masticatory performance often reported for retrognathic patients after surgery.9,19 In contrast to other studies16,19 the chewing pattern distribution of prognathic patients in the present study did not change, even though occlusion was normalized after surgery. A similar effect of nonchanging vertical closing strokes was observed in experimental narrowing of occlusal guidance in asymptomatic subjects.33 Even though the modified occlusion could allow for grinding movements, the central nervous system may not necessarily make use of this and may maintain established vertical movement patterns. Interestingly, masticatory performance also does not increase or approach normal conditions after surgery in prognathism patients.17 The observation that reversed sequencing is maintained31 or partly maintained32 after correction of cross bite indicates that such sequences are not impossible in subjects with normal intercuspation. In summary, neither normal occlusion nor malocclusion can be characterized by any one chewing pattern, but rather by characteristic pattern distributions. In general, normal occlusion is characterized by grinding type chewing patterns with normal sequencing (Fig 1) and to a minor extent by patterns with drop-shape or mixed sequencing. The prevalence of grinding in subjects with normal occlusion coincides with the “ideal” chewing pattern for maximal efficiency, as described by Yamashita and coworkers.15 However, a grinding type pattern alone is not a sufficient criterion for assessing chewing efficiency. This becomes clear from the Class II, deep-bite, and retrognathic patients, in whom reduced functional abilities are manifest despite fairly normal chewing pattern distributions. In contrast to common opinion, the reversed sequencing pattern may not be abnormal. The reversed movement could simply be the equivalent of normal sequencing in cross-bite occlusions. The D pattern type with steep closing movements and the self-crossing types ED, E1, and E2 should be considered “abnormal.” In particular, the type (D) indicates avoidance or reduction of occlusal guidance and is more fre-
quent among Class III occlusion individuals who have less efficient chewing. Since abnormal patterns are also present in subjects with normal occlusion, simultaneous investigation of chewing patterns and chewing efficiency are necessary to assign greater clinical discriminatory power to chewing patterns.
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25. Proschel P: Effects of the occlusal pattern on the mandibular movements during masticatory function. Dtsch Zahnarztl Z 43:1099-1103, 1988 26. Horio T, Kawamura Y: Effect of texture of food on chewing patterns in the human subject. J Oral Rehabil 16:177-183, 1989 27. Takada K, Miyawaki S, Tatsuda M: The effects of food consistency on jaw movement and posterior temporalis and inferior orbicularis oris muscle activities during chewing in children. Arch Oral Biol 39:793-805, 1994 28. Anderson K, Throckmorton GS, Buschang PH, et al: The effects of bolus hardness on masticatory kinematics. J Oral Rehabil 29:689-696, 2002 29. Owens S, Buschang PH, Throckmorton GS, et al: Masticatory performance and areas of occlusal contact and near contact in subjects with normal occlusion and malocclusion. Am J Orthod Dentofacial Orthop 121:602609, 2002 30. Henrikson T, Ekberg EC, Nilner M: Masticatory efficiency and ability in relation to occlusion and mandibular dysfunction in girls. Int J Prosthodont 11:125-132, 1998 31. Throckmorton GS, Buschang PH, Hayasaki H, et al: Changes in the masticatory cycle following treatment of posterior unilateral crossbite in children. Am J Orthod Dentofacial Orthop 120:521-529, 2001 32. Ben-Bassat Y, Yaffe A, Brin I, et al: Functional and morphological-occlusal aspects in children treated for unilateral posterior cross-bite. Eur J Orthod 15:57-63, 1993 33. Ogawa T, Ogawa M, Koyano K: Different responses of masticatory movements after alteration of occlusal guidance related to individual movement patterns. J Oral Rehabil 28:830-841, 2001