¹ Department of Prosthodontics, M R Ambedkar Dental College and Hospital, Bangalore, India;

² Oxford Dental College and hospital, Bangalore, India;

² Subbaiah Dental College and Hospital, Shimoga, India

Corresponding Author: Dr. C. S. Shruthi, Department of Prosthodontics, M R Ambedkar Dental College and Hospital, Bangalore, India. E-mail: shruthimari@yahoo.co.in.

	ABSTRACT
	INTRODUCTION
	MATERIALS AND METHOD
	RESULTS
	DISCUSSION
	CONCLUSION
	REFERENCES

	ABSTRACT

Aim: To assess the dimensional disparity in arch width between opposing maxillae and mandibles with edentulous age and increased resorption in edentulous subjects wearing complete denture. Materials and Method: One hundred edentulous subjects wearing complete denture were selected for the study. Maxillary and mandibular casts and a panoramic radiograph were made for each subject. The original height of the mandible before loss of teeth and resorption was predicted by multiplying the distance between the inferior border of the mandible to the lower edge of the mental foramen by a factor of 2.9. The reduction in height of the edentulous mandible was expressed as percentage of the original height of the mandible. The maxillary arch widths immediately anterior to the tuberosities and mandibular arch widths immediately anterior to the retromolar pads were measured. The difference between these two measurements was calculated to determine the discrepancy in posterior arch width. Results: There was no statistically significant difference in the mean values of posterior arch width discrepancy for different groups of edentulous age as well as percentage resorption. The differences in the mean values for amount of resorption with edentulous age were statistically significant. Conclusion: The discrepancy in posterior arch width between opposing maxillae and mandible does not increase progressively with edentulous age and increased reduction in mandibular height. The arch width of the mandible exceeds the arch width of the maxillae in the molar region by an average of 6 to 8 mm after sufficient resorption establishes a definitive alveolar crest. This remains constant regardless of the amount of resorption or edentulous age. The mandibular ridge reduction is found to increase with edentulous age.

	INTRODUCTION

   Prosthodontists deal with a balance sheet primarily composed of losses – loss of teeth, alveolar processes, tonicity of musculature, elasticity of skin, as well as loss or impairment of functions. Therefore, the beginning of prosthodontic treatment should begin with an evaluation of the total loss incurred by the patient. The loss of teeth is invariably followed by continuous and irreversible loss of residual alveolar bone in both maxillary and mandibular ridges (1). The inevitable change in the height and contour of the residual ridge affects success of the most precisely constructed prostheses. Improper arrangement of the teeth may jeopardize facial and prosthetic support for edentulous patients. A decision must be made whether to place the artificial teeth on the center of the mandibular residual ridge or to shift them facially or lingually to duplicate the position of the natural teeth.

   The various studies indicate that maxillae resorb upward and inward to become smaller in all dimensions, whereas there is greater resorption of the lingual plates of the mandible, which causes it to widen progressively (2). There are many studies that have focused on the resorption and its sequelae in the anterior edentulous areas of maxillary and mandibular ridges (3-5). However, there is dearth of information in the literature regarding the resorption pattern in the posterior edentulous areas. Therefore, a study was undertaken to assess the dimensional disparity in arch width between maxillae and mandibles with edentulous age and increased resorption in edentulous subjects wearing complete denture.

	MATERIALS AND METHOD

   The present study was carried out in the department of prosthodontics at Government Dental College, Bangalore. One hundred edentulous subjects wearing complete denture were selected for the study. They were selected based on the following criteria.

1. Subject’s knowledge of time and type of extraction. If the subject had undergone open method of extraction, he was not considered for the study;
2. Subjects should have satisfactory general health without any systemic disorders;
3. The ridge should be clearly identifiable without any flabby tissue;
4. The reasons for loss of teeth were not considered;
5. No data on race, sex, tissue irritation or prosthetic characteristics of vertical dimension, interocclusal distance, occlusion, retention and stability were recorded.

   The subjects were categorized according to edentulous age as follows:

1. Group I 1 to 10 years of edentulous age.
2. Group II 11 to 20 years of edentulous age.
3. Group III 21 to 30 years of edentulous age.
4. Group IV more than 30 years of edentulous age.

   Maxillary and mandibular casts were made for each subject and a panoramic radiograph was made. The superior and inferior borders of the mandible, the posterior borders of the rami, and boundaries of mental foramina on both the sides were traced on to frosted acetate tracing paper (Fig 1). The original height of the mandible before loss of teeth and resorption was predicted by multiplying the distance between the inferior border of the mandible to the lower edge of the mental foramen by a factor of 2.9 (6). The distance between the inferior and superior borders of the edentulous mandible was subtracted from the predicted original height of the body of the mandible to determine the reduction in the mandibular residual ridge height. The reduction in height of the edentulous mandible was expressed as percentage of the original height of the mandible.

   The subjects were categorized according to percentage resorption as follows.

1. Group A 0-15% of reduction in mandibular residual ridge height.
2. Group B 16- 30% of reduction in mandibular residual ridge height.
3. Group C 31-45% of reduction in mandibular residual ridge height.
4. Group D 46 -60 % of reduction in mandibular residual ridge height.

   The maxillary arch widths immediately anterior to the tuberosities and mandibular arch widths immediately anterior to the retromolar pads were measured (Fig 2). The difference between these two measurements was calculated to determine the discrepancy in posterior arch width between opposing maxillae and mandible. All the data were tabulated and statistically analyzed.

View larger version : [in a new window] Figure 1. Tracing of landmarks on orthopantomogram.

 

View larger version : [in a new window] Figure 2. Maxillary and mandibular edentulous casts.

	RESULTS

   The mean values for discrepancy in arch width for Group I, Group II, Group III and Group IV subjects were 7.53 mm, 6.46 mm, 7.82 mm and 7.55 mm respectively. The overall mean value of 7.21 mm was not markedly divergent from the mean values of the individual group. One way ANOVA (parametric test) was used for the statistical analysis and there was no significant difference between groups (Table 1).

   Comparison of posterior arch width discrepancy with percentage reduction in mandibular height was also done. The mean values for Group A, Group B, Group C and Group D were 6.1 mm, 7.89 mm, 6.61 mm, and 8.7 mm respectively with the overall mean being 7.21 mm. One way ANOVA revealed that there was no statistically significant difference between the groups (Table 2).

   The mean reduction in mandibular residual ridge height for Groups I, II, III and IV were 23.54%, 28.21%, 33.0% and 33.12% respectively. The differences between the groups were statistically significant.

	DISCUSSION

   Researchers in Prosthodontics have devoted considerable amount of time and resources towards unraveling the mysteries of residual ridge resorption (1, 3, 4, 7-10). In an oft-cited article, Atwood D A., called the continuous reduction of residual ridges, “a major oral disease entity”. Irrespective of the many causes of maxillomandibular resorption and the host response to them, the challenge for the dentist is the same. He/she must restore esthetics and functions lost through resorption. If the service is to be provided successfully, the directional pattern of alveolar bone resorption must be understood.

   Observations that maxillae become progressively narrower and mandibles progressively wider with resorptive age have been supported for a number of years (2). Such a pattern of resorption would create an ever increasing dimensional difference between posterior arch widths of opposing maxillae and mandible. However, the clinical observations of partially edentulous arches reveal that the natural teeth occupy positions outside or facial to the center of the edentulous ridges in both maxillary and mandibular arches. If both the statements were true, then there would have to be an alteration in the resorptive pattern from the partially edentulous condition to the fully edentulous condition.

   The mean value for discrepancy in arch width for all the edentulous subjects was 7.21 mm. The individual mean values for Group I, Group II, Group III and Group IV subjects were 7.53 mm, 6.46mm, 7.82mm and 7.55 mm respectively. The overall mean value of 7.21 mm was not markedly divergent from the mean values of the individual group. However, the mean value for group II was comparatively less than the overall mean value and also mean values for other groups and no specific reasons could be attributed for the observed variation.

   When compared statistically, the difference in the mean values for different groups was not significant. This analysis of variance permitted acceptance of the hypothesis that longer periods of edentulousness do not increase the posterior arch width discrepancies. The findings are in accordance with an earlier study by Parkinson C. F (11).

   Comparison of posterior arch width discrepancy with percentage reduction in mandibular height was also done. The mean values for Group A, Group B, Group C and Group D were 6.1 mm, 7.89 mm, 6.61 mm, and 8.7 mm respectively with the overall mean being 7.21 mm. The analysis of variance indicated that the discrepancy does not progressively increase as the ridges undergo resorption. The findings are in accordance with a study conducted by Parkinson C. F (11).

   The mean reduction in mandibular residual ridge height for Groups I, II, III and IV were 23.54%, 28.21%, 33.0% and 33.12% respectively. The differences between the groups were statistically significant which implies that increased duration of edentulousness accompanied by denture wearing is associated with increased mandibular ridge resorption (7, 10).

   In this study, an assessment of reduction in maxillary residual ridge height could not be done. However, many studies have concluded that residual ridge atrophy occurs with protracted wearing of dentures in both the arches though it is relatively marked in the mandible (1, 7, 10, 12). The wide variation in the discrepancy between subjects in the same group may be attributed to disharmony in the jaw sizes prior to loss of teeth, bone loss during the removal of teeth or any other factors.

   Panoramic radiographs are subject to error due to magnification factor. However, in this study, only proportional estimation of the original height was made which minimized the error.

   The importance of the study appears to be two fold. As the ridge resorption does not increase the arch width discrepancy, the artificial teeth should be placed more facial to the crest of the ridge in the maxilla than the mandible to duplicate the position of the natural teeth. Furthermore, placing the molars buccal to the ridge crest positions them over the buccal shelf which is at right angles to occlusal force (13, 14). This also creates more tongue space and allows development of facial seal (13).

   The directional pattern of alveolar bone resorption can be demonstrated better by means of longitudinal studies. However, a cross sectional study can create a platform and provide guidelines to design such studies.

	CONCLUSION

   The discrepancy in posterior arch width between opposing maxillae and mandible does not increase progressively with edentulous age and increased reduction in mandibular height. The arch width of the mandible exceeds the arch width of the maxillae in the molar region by an average of 6 to 8 mm after sufficient resorption establishes a definitive alveolar crest. This remains constant regardless of the amount of resorption or edentulous age. The mandibular ridge reduction is found to increase with edentulous age.

	REFERENCES

1. Atwood DA. A cephalometric study of the clinical rest position of the andible. J. Prosthet Dent. 1957; 7: 544-552.
2. Swenson G, Staut C. J. Complete Dentures. 1949; P45.
3. Carlson GE, Thilander H, Hedegard B. Histologic changes in the upper alveolar process after extraction with or without insertion of an immediate full denture. Acta Odontologica Scandinavica. 1969; 25: 21-43.
4. Carlson GE, Bergman B, Hedegard B. Changes in contour of the maxillary alveolar process under immediate dentures. Acta Odontologica Scandinavica. 1969; 25: 1-31.
5. Tallgren A. Alveolar bone loss in denture wearers as related to facial morphology. Acta Odontologica Scandinavica. 1969; 28: 251-270.
6. Wical KL, Swoope CC. Studies of residual ridge resorption. Part – I. Use of panoramic radiographs for evaluation and classification of mandibular resorption. J. Prosthet Dent. 1974; 32 (1): 7-12.
7. Campbell LR. A comparative study of the resorption of the alveolar ridges in denture wearers and nondenture wearers. JADA. 1960; 60: 143-153.
8. Ortman HR. Factors of bone resorption of the residual ridge. J. Prosthet Dent. 1962; 12 (3): 429-440.
9. Atwood DA, Coy WA. Clinical, cephalometric and densitometric study of reduction of residual ridges. J. Dent. 1971; 26: 280-295.
10. Tallgren A. The continuing reduction of the residual alveolar ridges in complete denture wearers: A mixed longitudinal study covering 25 years. J. Prosthet Dent. 1972; 27 (1): 120-132.
11. Parkinson CF. Similarities in resorption patterns of maxillary and mandibular ridges. J. Prosthet Dent. 1978; 39 (6): 598-602.
12. Woelfel JB, Winter CM, Igarashi T. Five year cephalometric study of mandibular ridge resorption with different posterior occlusal forms. Part I Denture construction and initial comparison. J. Prosthet Dent. 1976; 36 (3): 603-623.
13. Lammie GA. Aging changes and the complete lower denture. J. Prosthet Dent. 1956; 6 (4): 450-464.
14. Raybin NH. The polished surface of complete dentures. J. Prosthet Dent. 1963; 13 (3): 236-241.

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