Cup-Shaped Tooth Wear Defects: More than Erosive Challenges?

BACKGROUND/AIM: The underlying mechanism of the development of cups and grooves on occlusal tooth surfaces is still unclear. The aim of this study was to evaluate factors contributing to in vitro cup formation, in order to elucidate the clinical process. METHODS: A total of 48 extracted human molar teeth were exposed to acidic aqueous solutions at pH of 4.8 and 5.5 in constant motion, in combination with different loading conditions: no load (0N group, control), 30 N (30N group) or 50 N (50N group) (n = 8 per group). Before and after 3 months of exposure (1,422,000 loading cycles), the samples were scanned using a non-contact profilometer. Pre- and post-exposure scans were subtracted and height loss and volume tissue loss were calculated. Representative samples with wear and cupping lesions were imaged using scanning electron microscopy, light microscopy and micro-computed tomography. RESULTS: Average height and volume tissue loss at pH 5.5 was 54 µm and 3.4 mm3 (0N), 52 µm and 3.4 mm3 (30N) and 58 µm and 3.7 mm3 (50N), respectively, with no statistically significant differences. Average height and volume loss at pH 4.8 were 135 µm and 8.7 mm3 (0N), 172 µm and 12.6 mm3 (30N) and 266 µm and 17.8 mm3 (50N), respectively, with a statistically significant difference between 0N and 50N (p < 0.002). Cup-shaped lesions had formed only at pH of 4.8, in the 30N and 50N groups. CONCLUSION: The study showed that a cup can arise fully in enamel and that mechanical loading in addition to erosive challenges are required.

Proximal marginal overhang of composite restorations in relation to placement technique of separation rings.

The aim was to investigate in vitro the marginal overhang in Class II composite restorations placed with various separation rings and placement techniques. A total of 180 Mesial-Occlusal [MO] preparations in artificial molar teeth were divided into nine groups (n=20). After placement of the sectional matrix, one of three ring systems was applied: Contact Matrix System (Danville Materials), Composi-Tight Gold (Garrison), and V-Ring (Triodent). In each group, rings were placed according to four different techniques (V-Ring placed with technique no. 2 only): 1) occlusally of the wedge, 2) on back end of the wedge, 3) between adjacent tooth and wedge, and 4) between treated tooth and wedge.After application of the adhesive resin, preparations were restored with composite Clearfil AP-X (Kuraray) and polymerized in increments. After matrix removal, overhang was measured on a standardized digital macroscopic image in millimeters squared. For analysis, analysis of variance and Tukey B were used (p<0.05).For the Contact Matrix System and Composi-Tight Gold ring, the different placement techniques had a statistically significant effect on the amount of marginal overhang (p<0.031). The V-Ring resulted in the least marginal overhang (p<0.001).None of the placement techniques and separation rings could completely prevent marginal overhang, and the placement technique has a significant influence on its occurrence.

A randomized clinical trial of cusp-replacing resin composite restorations: efficiency and short-term effectiveness.

PURPOSE: This study aimed to assess the efficacy and short-term effectiveness of the morphology and function of direct and indirect cusp-replacing resin composite restorations. MATERIALS AND METHODS: In 94 patients, 106 cusp-replacing restorations for maxillary premolars were fabricated to restore Class II caries lesions with 1 cusp missing. Fifty-four direct (Clearfil AP-X) and 52 indirect (Estenia) resin composite restorations were placed following a strict protocol. The treatment technique and operator were assigned randomly. Treatment time was recorded for all restorations. One-month postoperative evaluation included assessment of postoperative sensitivity and presence of occlusal and proximal contacts. RESULTS: Treatment time for the indirect technique (68 +/- 17 min) was longer than for the direct technique (45 +/- 13 min). Regression analysis revealed that the restorative method, operator, and location of the preparation outline had a statistically significant effect on the total treatment time. Occlusal contacts were observed in 94% of the direct restorations and in 98% of the indirect restorations (chi-square, P>.05). Mesial proximal contacts were present in 98% of the direct and in 97% of the indirect restorations (chi-square, P > .05). Distal contacts were present in 100% of the restorations for both techniques. Postoperative sensitivity within 1 week posttreatment was reported for 11% of the direct restorations and for 13% of the indirect restorations, but decreased to 4% and 6%, respectively, after 1 month (chi-square, P > .05). CONCLUSION: The results of this study suggest that in the short term, both direct and indirect adhesive techniques are adequate to restore the morphology and function of premolars presenting with Class II caries lesions and a missing cusp.

A survey of cusp fractures in a population of general dental practices.

PURPOSE: This study was conducted to expand the knowledge on the incidence of complete cusp fractures of posterior teeth in Dutch general practices. MATERIALS AND METHODS: During a 3-month period, data were obtained from 28 general practitioners, representing 46,394 patients. For each new case of complete cusp fracture, clinicians recorded information using a standard form with questions relating to location of the fracture, cause of fracture, and restorative status of the tooth prior to the cusp fracture. RESULTS: There were 238 cases of complete cusp fracture recorded. The results of this study indicate an incidence rate of cusp fractures of 20.5 per 1,000 person-years at risk. Molars were more frequently registered with cusp fractures than premolars (79% vs 21%). Maxillary molars presented more fractures of buccal cusps (66% vs 34%), while mandibular molars presented more fractures of lingual cusps (75% vs 25%). Almost 77% of the cases had been restored on three or more surfaces. Statistical analysis revealed a positive correlation between history of endodontic treatment and subgingival fracture location. Mastication was most frequently reported as the cause for fracture (54%), although one can argue whether the occlusal force was the cause or the immediate reason. CONCLUSION: This study revealed that complete cusp fracture is a common phenomenon in dental practice and has shown differences in cusp fracture with respect to tooth type and restorative status of the tooth. Teeth with a history of endodontic treatment are susceptible to unfavorable subgingival fracture locations.