Extensive tooth wear in adults : classification and prosthetic treatment

Abstract

Background: Tooth wear (TW) is an insidious and cumulative multifactorial process that may comprise erosion, abrasion or attrition, and combinations thereof. These different processes are of chemical or physical origin and not microbiological. As our populations age, a certain degree of TW may be unavoidable and can be regarded as a normal physiological process, but when the form and function of the dentition are comprised, the condition can then be considered as pathological. The scientific literature in this area contains considerable information about the various risk factors for TW, but has failed so far to provide reliable procedures for the diagnosis, classification, and management of this condition.

Aims: The general aims of this thesis were as follows: 1) to apply the novel approach known as cluster analysis to the classification of phenotypic heterogeneity among patients with extensive TW; and 2) to evaluate the clinical relevance of this approach by comparing the clinical presentation of wear lesions and the long-term clinical performance and durability of two all-ceramic restorations in the clusters thus created.

In Study I unsupervised cluster analysis based on clinical findings, demographic and self-reported characteristics, and salivary and EMG measurements was used to differentiate between patients with extensive TW of different phenotypes. Data was obtained on 125 patient (17-65 (mean 43.1) years old, TW index>grade 2). The 34 variables of interest included demographic information; presumed risk factors for mechanical and chemical TW; a 14-item stress scale; salivary flow rates, pH and buffer capacity; jaw muscle activity during sleep (measured by single-channel EMG device); and the presence or absence of torus mandibularis. Cluster A (n=61) had a lower percentage of self-reported sleep bruxism (1.6%, vs 92.9%, p ≤0.001); self-reported awake bruxism (45.9%, vs 85.7%, p ≤0.001); and heavy exercisers (1.6% vs 21.4%, p =0.001); and a lower percentage of diseases that affect saliva (13.1% vs 47.6%, p ≤ 0.001) than cluster B (n=42). Otherwise, overlap was considerable.

In Study II a case control study was used to assess the distribution and morphological features of the wear lesions in clusters A and B (n=103; 22 participants in the first study were excluded due to incomplete data) The comparison was based on wear distribution, the presence or absence of 10 morphological features associated with TW, and the number of teeth exhibiting each feature. Whereas cluster A demonstrated more wear in maxillary anterior teeth and mandibular molars than in the same opposing tooth groups (p <0.001, p < 0.007 respectively), there were no such differences for cluster B. Cluster A was characterized by a higher prevalence of 4 morphological criteria for chemical TW and more teeth exhibiting one of these criteria; while cluster B had a higher prevalence of one mechanical criterion and more teeth demonstrating an additional mechanical criterion. Both intra- and inter-examiner reliability for the morphological assessments (as indicated by Cohen ́s kappa and the interclass correlation coefficient) were fair to excellent.

Study III describes a prospective, double-blind, randomized clinical trial that evaluated the performance and success rate of pressed lithium disilicate (LD) and translucent zirconia (TZ) crowns in patients with extensive TW. 62 patients (17 women, 45 men; mean age 44.8 (range 25-63) years) received a total of 362 LD and 351 TZ crowns. Modified USPHS criteria were used for clinical reevaluation on average 14, 31, 39, 54, 65 months after insertion. After as long as 6 years, the survival rate for both types of crowns was 99.7% ,with loss of retention by one LD crown after one year and loss of one TZ crown after 3 years due to tooth fracture at the cemento-enamel junction. The success rates were 98.6% for the LD and 99.1% for the TZ crowns. Already immediately after insertion, the color match was better with the LD than TZ crowns (P< 0.001). Post-hoc analysis of clinical performance showed no significant differences between subjects with extensive TW exposed primarily to chemical or mechanical risk factors.

Conclusions: Patients with extensive TW can be clustered into at least two groups with different phenotypic characteristics, although with a large degree of overlap. Assessment of the clinical presentation of wear lesions indicated more chemical background for TW in the larger cluster and more mechanical background in the smaller cluster, a finding of potential clinical value. With the exception that TZ crowns were rated by a clinician as less esthetically appealing, there were no differences between the performance and success of these two types of all-ceramic materials used for rehabilitation. Regardless of the etiology of the TW, the key factor for long-term success of all-ceramic crowns in patients with extensive TW is probably the use of adhesively luted high-strength ceramic materials.