In this study, we investigated tooth-wear patterns in adolescents with either normal occlusion or Class II Division 2 malocclusion.
The sample consisted of dental casts from 165 subjects that were divided into 2 groups: 115 normal occlusion subjects (mean age, 14.3 years) and 50 complete Class II Division 2 subjects (mean age, 13.9 years). Dental wear was assessed by using a modified version of the tooth wear index. The 2 groups were compared with the Mann-Whitney test for the frequency and severity of wear on each surface of each group of teeth. The level of statistical significance was set at 5%.
The normal occlusion group statistically had greater tooth wear on the incisal surfaces of the maxillary lateral incisors and the incisal surfaces of the maxillary canines than did the Class II Division 2 malocclusion group. The malocclusion group showed statistically greater tooth wear on the labial surfaces of the mandibular lateral incisors, the occlusal surfaces of the maxillary premolars and first molars, the occlusal surfaces of the mandibular premolars, the palatal surfaces of the maxillary second premolars, and the buccal surfaces of the mandibular premolars and first molars than did the normal occlusion group.
Subjects with normal occlusion and those with complete Class II Division 2 malocclusions have different tooth-wear patterns. Tooth wear on the malocclusion subjects should not be considered pathologic but, rather, the consequence of different interocclusal arrangements.
Tooth wear can be described as the loss of hard dental tissue resulting from physical or chemical attack; it is an all-embracing term used to describe the combined processes of abrasion, erosion, and attrition. Abrasion and erosion must be distinguished from attrition, which is the regular, slow, and progressive loss of dental tissue as a consequence of tooth-to-tooth contact (as in mastication).
It is not always possible to differentiate between erosion, abrasion, and attrition because these conditions are frequently combined. However, if occlusal factors are involved in causing dental wear, they probably are related to attrition (tooth wear caused by opposing occlusal surfaces rubbing together), considered the most visible sign of functional wear.
Attrition has specific characteristics. First, if attrition is the only cause of tooth wear, it will be located only in areas of occlusal contact. There will be no wear on the buccal or lingual surfaces of teeth unless mandibular movements can make the opposing teeth touch in these areas. Second, attrition creates wear facets with a specific appearance: shiny, flat, and sharp-edged. Third, attrition produces similar amounts of wear on opposing teeth. Tooth grinding cannot cause significant tooth wear on the maxillary anterior teeth but not on the mandibular anterior teeth. If attrition is the cause, the worn teeth must have occlusal contact during mandibular excursion.
Some studies indicate that masticatory forces and malocclusion are primary etiologic factors for noncarious lesion development, although other authors did not find this correlation. Because of the high prevalence of malocclusions in children as well as the controversies in the literature, it is relevant to verify the pattern of tooth wear of various occlusal relationships to help professionals to differentiate between physiologic and pathologic processes. The absence of previous studies of tooth wear with specific malocclusions encouraged us to compare the patterns of tooth wear in subjects with Class II Division 2 malocclusion with subjects with normal occlusal relationships.
Material and methods
The study protocol was approved by the Ethics Committee on Human Research of Bauru Dental School, University of São Paulo, Brazil.
The sample consisted of dental casts from 165 untreated subjects from the files of the Department of Orthodontics at Bauru Dental School, University of São Paulo, and the Department of Orthodontics and Pediatric Dentistry, School of Dentistry, University of Michigan, Ann Arbor. The dental casts were divided into 2 groups. Group 1 consisted of 115 subjects with normal occlusion (50 female, 65 male; mean age, 14.3 years; range, 11.0-17.5 years). Group 2 consisted of 50 complete Class II Division 2 subjects (23 female, 27 male; mean age, 13.9 years; range, 11.2-17.7 years). The dental casts were obtained only from subjects with permanent maxillary and mandibular teeth including the first molars. Additional inclusion criteria included no parafunctional habits, and no temporomandibular joint and airway problems, as noted in the subjects’ charts.
We used a modified version of the tooth wear index (TWI), described by de Carvalho Sales-Peres et al. The modifications are consistent with the World Health Organization standards, thus allowing application of the index in broad epidemiologic surveys for both deciduous and permanent dentitions. In this study, the TWI for deciduous teeth was not used. The modifications made calibration easier and resulted in greater reproducibility, because the modified version of the TWI does not differentiate the depth of dentin involvement, as is the case for the original TWI. In addition, the modified version includes a code for teeth that have been restored because of wear (code 4), and another code for teeth that cannot be assessed (code 9). The form used to record the evaluations is shown in the Figure . The amount of permanent tooth wear is scored by numbers ( Table I ). A calibrated examiner (R.B.S.O.) performed the dental-cast evaluations.
|Deciduous teeth||Permanent teeth||Criteria||Description|
|A||0||Normal, no evidence of wear||No loss of surface features|
|B||1||Incipient, tooth wear into enamel||Loss of enamel giving smooth, glazed, shiny appearance; dentin not involved|
|C||2||Moderate, tooth wear into dentin||Extensive loss of enamel with dentin involvement; exposure of dentin|
|D||3||Severe, tooth wear into pulp||Extensive loss of enamel and dentin with secondary dentin or pulp exposure|
|E||4||Restored, tooth wear leading to restoration||Tooth received restorative treatment because of wear|
|–||9||Could not be assessed||Extensive caries, large restoration, fractured or missing tooth|
A benchmark dental examiner (gold standard) (S.H.C.S.), skilled in epidemiologic surveys, trained and calibrated the examiner. The calibration process took 28 hours. Theoretical activities with discussions on diagnostic criteria of dental wear were performed.
To assess the reproducibility of the dental-cast analysis, 10% of the casts were reevaluated, with an intraexaminer kappa of 0.79 ( Table II ).
|Tooth wear||Percentage of agreement (%)||Coefficient value||Strength of agreement|
|Dental casts||92.85||0.79||Almost perfect|
Tooth surfaces were excluded from the statistical analysis if they were missing, or had extensive caries, large restorations, or fractures (code 9). The amount of tooth wear in the groups was compared with the Mann-Whitney test. The 2 groups were compared for the frequency and the severity of wear on each surface of each group of teeth (incisors, canines, premolars, and molars). The level of statistical significance was set at 5%.
In total, 11,880 dental surfaces were evaluated. Of these, 77.7% had no dental wear (code 0), 20.1% had incipient lesions (code 1), 0.4% had moderate lesions (code 2), and 1.8% were excluded (code 9). No severe lesions were found.
The normal occlusion group statistically had greater tooth wear on the incisal surfaces of the maxillary lateral incisors ( Table III ) and on the incisal surfaces of the maxillary canines ( Table IV ) than did the malocclusion group.
|Normal occlusion||Complete Class
II Division 2
|Normal occlusion||Complete Class
II Division 2
The Class II Division 2 malocclusion group showed statistically greater tooth wear on the labial surfaces of the mandibular lateral incisors ( Table III ), the occlusal surfaces of the maxillary premolars and first molars, the occlusal surfaces of the mandibular premolars, the palatal surfaces of the maxillary second premolars, and the buccal surfaces of the mandibular premolars and first molars than did the normal occlusion group ( Table V ).
|Normal occlusion||Complete Class II Division 2|