The Ability of Two Chewing Simulation Devices in Emulating the Clinical Deterioration of Anterior Composite Restorations in Severely Worn Teeth.

PURPOSE: This study investigated the ability of two chewing simulation devices to emulate in vitro the clinical deterioration observed in anterior composite restorations in severe tooth-wear patients. MATERIALS AND METHODS: Advanced tooth wear was simulated in bovine incisors, which were restored with palatal and buccal direct composite veneer restorations. The incisal edges of restorations were subjected to 960K cycles of either compressive loading (Biocycle-V2; 125 N at 2 Hz) or wear and mechanical loading (Rub and Roll; 30 N at 20 rpm). Surface degradation was rated using FDI scores to compare the chewing devices (Fisher's test, a = 0.05). Topography and deterioration of restorations was analyzed using SEM. The ability to emulate the deterioration was investigated by comparing the surface degradation observed in vitro with the clinical degradation observed in restorations placed in severe tooth-wear patients after 3.5 years. RESULTS: Distinct degradation patterns were observed between the simulation devices: Biocycle-V2 generated deterioration that was not comparable to the clinical situation, including contact damage, minor wear, and localized roughening. The degradation caused by Rub and Roll was more similar to the in vivo situation, including wear facets, chipping, delamination, staining, and marginal ditching. The FDI scores were different between the chewing devices for surface/marginal staining, material/retention, and marginal adaptation (p = 0.003). SEM analysis showed microcracking at the interface between composite layers at the incisal edges. CONCLUSIONS: The Rub and Roll chewing device was able to emulate the clinical deterioration observed in anterior restorations in severe tooth-wear patients and thus may be used as an oral-cavity simulation method, contributing to translational research.

In vitro Effect of Occlusal Loading on Cervical Wall Lesion Development in a Class II Composite Restoration.

The aim of this study was to determine the effect of simulated occlusal loading on wall lesion development in cervical gaps of class II composite restorations in vitro. Sixty-four extracted human molars received standardized (4.0 × 4.2 × 3.0 mm) box preparations. The teeth were randomly assigned to one of two restoration groups: restoration with a normal or a low E-modulus composite material (CLEARFIL AP-X: E-modulus 16.8 GPa or CLEARFIL MAJESTY ES Flow: E-modulus 6.6 GPa). A metal matrix was placed at the bottom of the box for each restoration, creating a cervical gap of about 100 µm wide. Samples were exposed to simulated caries lesion development in a lactic acid solution (pH 4.8) for 8 weeks in a Rub&Roll device. Half of the samples were subjected to 90 N cyclic loading. After demineralization, the teeth were sectioned. Wall lesion development was measured using microradiography (transversal wavelength-independent microradiography) in two different locations (location 1: 1,000 µm and location 2: 1,600 µm from the gap entrance) and recorded in lesion depth (LD) (µm) and mineral loss (µm × vol%). Linear regression modeling was used to estimate the effect of loading and material on wall lesion development. Mean wall LD in location 1 across all groups was 150.83 µm with a standard deviation (SD) of 61.83 µm. In location 2, mean overall wall LD was 102.98 µm with an SD of 64.92 µm. Linear regression showed no significant effect of either loading or material on wall lesion development. Occlusal loading had no significant effect on secondary caries lesion development in composite class II restoration in this in vitro study.

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.

Mimicking and Measuring Occlusal Erosive Tooth Wear with the "Rub&Roll" and Non-contact Profilometry.

Chewing, drinking, and occasional tooth grinding will result in physiological tooth wear during a lifetime. Extreme challenges, such as bruxism or habitual chewing on foreign objects, may lead to excessive wear. Recently, the role of erosion in accelerating mechanical tooth wear has been recognized, but the interplay between chemical and mechanical wear processes has not been extensively studied. Our laboratory recently introduced a novel oral wear simulation device, the Rub&Roll, that enables the user to perform wear and loading studies separately or simultaneously in an erosive and/or abrasive environment. This manuscript describes an application of the device: the combined mechanical and erosive loading of extracted human (pre)molars in a simulated chewing movement, with a controlled application of force, velocity, fluid, and time, and the application of non-contact profilometry in visualizing and measuring the resulting wear pattern. The occlusal morphology that was created in the experiment with the highest loading level is very similar to the clinical presentation of erosive wear.

Bonding effectiveness of composite-dentin interfaces after mechanical loading with a new device (Rub&Roll).

This study evaluated the effect of mechanical loading with a new device on the microtensile bond strength (µTBS) of adhesive systems to dentin. Forty molars were divided according to adhesive systems: self-etch (ClearfilTM SE Bond -CSE) and etch-and-rinse (Adper ScotchbondTM 1XT -ASB); and to aging (n=5): control; MC1-250,000; MC2-500,000; and MC3-750,000 mechanical cycles. Microtensile bond strength was measured and fracture modes were analyzed. Data for µTBS were subjected to Kruskal-Wallis and post hoc tests (p<0.05). Mechanical loading (p<0.001) and adhesive systems (p=0.024) affected µTBS values. The adhesive systems showed a similar behavior, except in the MC3 group, which the self-etch CSE showed the highest µTBS. The new device promotes a decreasing of µTBS as the number of cycles increased. Difference between materials was observed only after 750,000 mechanical cycles.

Behavior of failed bonded interfaces under in vitro cariogenic challenge.

OBJECTIVE: This in vitro study aimed to compare dentin wall caries development at different composite-dentin interfaces. METHODS: Dentin samples (10.4 mm(2)) were restored with composite resin using two adhesive systems (etch-and-rinse and self-etch techniques). Different composite-dentin interfaces with gaps were produced: (a) failed bonded, which were fractured at interface after being submitted to aging protocols (no aging, mechanical loading or water storage); (b) non-bonded interfaces, both without any adhesive material or with adhesive material applied only on the dentin. Adhesively fractured and non-bonded samples were subjected to a lactic acid gel (pH=5) caries model with a continuous opening/closing movement of the interfacial gap for 10 days. Transverse wavelength-independent microradiographs were taken, and lesion depth and mineral loss were measured. Data were analyzed with linear mixed-effects regression models. RESULTS: Caries development differed among the composite-dentin interfaces (p<0.001). The non-bonded interface with adhesive material on the dentin showed less lesion depth than the failed bonded groups, while the non-bonded interface without adhesive on dentin showed the deepest wall lesions. Difference between the adhesive systems was observed only in the non-bonded groups (p=0.003), with the self-etch adhesive applied on the dentin showing more severe lesions. Samples broken after mechanical loading aging showed deeper lesions than those broken after water storage (p<0.001). SIGNIFICANCE: Composite-dentin interfaces failed after aging presented different demineralization from interfaces that were never bonded, indicating that the restorative treatment changes the tissue in a way relevant to secondary caries development.

Fluoride release and cariostatic potential of orthodontic adhesives with and without daily fluoride rinsing.

INTRODUCTION: In this study, we aimed to evaluate the fluoride-release profiles and caries lesion development in an enamel model with brackets cemented with 4 orthodontic adhesives with and without daily fluoride exposure. METHODS: Four orthodontic adhesives (Ketac Cem mu, 3M ESPE, Seefeld, Germany; Fuji Ortho LC, GC Corporation, Tokyo, Japan; Light-Bond, Reliance Orthodontic Products, Itasca, Ill; and Transbond XT, 3M Unitek, Monrovia, Calif) were used. Brackets were bonded on bovine enamel with each adhesive (n = 10) and subjected to alternate cycles of demineralizing (pH 4.55) and remineralizing (pH 6.8) solutions. Unbracketed enamel samples served as a reference. Five samples from each group were immersed in a fluoride mouth rinse (250 ppm fluoride) for 1 minute each day (test groups). Fluoride release was measured at regular intervals over 28 days. The mineral distribution of peribracket enamel after 28 days was quantified by transversal microradiographs. RESULTS: Fluoride-release profiles of Ketac Cem mu, Fuji Ortho LC, and Light-Bond were high for the first 24 hours and reached a constant level after 2 weeks. Fuji Ortho LC released significantly more fluoride than did the other adhesives in both the control and test groups (P <0.01, repeated measures ANOVA and Bonferroni test). Enamel bonded with Fuji Ortho LC had significantly shallower lesions and less mineral loss (P <0.01, 2-way ANOVA, and Tukey HSD). CONCLUSIONS: Bonding of orthodontic brackets with Fuji Ortho LC resulted in less peribracket enamel demineralization with and without daily fluoride rinsing, mainly due to its better fluoride-release profile. In contrast, Transbond XT and Light-Bond offered few cariostatic effects to the enamel.

The influence of three barrier membranes on modeling and incorporation of autologous onlay bone grafts in rats. An evaluation by transversal microradiography.

OBJECTIVES: To determine whether covering an autologous bone grafts with three different barrier membranes prevents graft resorption, and to compare these membranes to each other. DESIGN: In 192 rats a standardised 4.0mm diameter bone graft was harvested from the right mandibular angle and transplanted to the left. Membranes used to cover the grafts were a new poly(DL-lactide-epsilon-caprolactone) membrane, a collagen and expanded polytetrafluoroethylene membrane. The controls were left uncovered. Graft resorption and incorporation were measured with transversal microradiography (TMR) in the four groups at 2, 4 and 12 weeks. Data were analysed using multiple regression analyses. RESULTS: Overall, there were no differences in modeling with resorption between the four groups. ePTFE at 12 weeks showed a lower mineralization ratio and graft height of the graft as compared to the other groups. The mean graft incorporation was progressive and nearly identical from 2 to 12 weeks in all groups. CONCLUSIONS: Membranes have an equal effect on bone graft modeling and resorption as found in non-covered controls. Therefore, the indication to use a barrier membrane to prevent bone modeling with resorption and enhance incorporation of autologous onlay bone grafts is disputable.

Effect of ethylene oxide sterilization on enamel and dentin demineralization in vitro.

For in situ studies into caries prevention, sterilization of tooth samples is essential. However, sterilization may influence the caries process itself. The aim of this study was to assess the effect of sterilising sound human enamel and dentin with ethylene oxide on lesion depth and mineral loss before and after in vitro demineralization. Lesion depth and mineral loss were measured using transversal microradiography (TMR). The experiment was carried out with 32 enamel and 32 dentin samples. We found a significant reduction of lesion depth due to sterilization in demineralized enamel (-9.8microm; 95% CI: -15.1 to -4.4microm). The small effect of sterilization on demineralized enamel is considered to be irrelevant for in situ studies of de- and remineralization.

Does platelet-rich plasma promote remodeling of autologous bone grafts used for augmentation of the maxillary sinus floor?

The aim of this study was to evaluate the effect of platelet-rich plasma (PRP) on remodeling of autologous bone grafts used for augmentation of the floor of the maxillary sinus. In five edentulous patients suffering from insufficient retention of their upper denture related to a severely resorbed maxilla, the floor of both maxillary sinus was augmented with an autologous bone graft from the iliac crest. Randomly, PRP was added to the bone graft used to augment the floor of the left or right sinus (split-mouth design). Three months after the reconstruction, bone biopsies were taken with a trephine from the planned implant sites (N=30). Subsequently, three implants were placed in the left and right posterior maxilla. Microradiograms were made of all biopsies (N=30), whereafter the biopsies were processed for light microscopic examination. In addition, clinical parameters were scored. Wound healing was uneventful, clinically no difference was observed between the side treated with PRP or not. Also microradiographical and histomorphological examination of the biopsies revealed no statistical difference between the PRP- and non-PRP side. One implant placed in the PRP side of the graft was lost during the healing phase. Implant-retained overdentures were fabricated 6 months after implantation. All patients functioned well (follow-up 20.2+/-4.3 months). In this study, no beneficial effect of PRP on wound healing and bone remodeling was observed. It is posed that PRP has no additional value in promoting healing of grafted non-critical size defects.

Does ultrasound stimulate osteoconduction? A placebo-controlled single-blind study using collagen membranes in the rat mandible.

PURPOSE: To investigate whether ultrasound can stimulate osteoconduction in the mandible, an attempt was made to stimulate the osteoconductive process with low-intensity pulsed ultrasound in rats. MATERIALS AND METHODS: In 64 rats, a 5.0-mm diameter circular mandibular defect was made in the ramus and, subsequently, covered on both sides with collagen membranes. Two groups were studied, an ultrasound treatment group and a placebo treatment group. At 2 and 4 weeks, the remaining defect area was measured using microradiographs, and the amount of osteoconduction was expressed as the percentage of defect closure. RESULTS: At 2 and 4 weeks, there was no significant difference in the percentage of defect closure between the groups. DISCUSSION: An explanation may be that ultrasound does not exert an effect in an area where wound healing is already expected to be at an optimal level. CONCLUSION: There was no evidence that low-intensity pulsed ultrasound stimulates osteoconduction in a bone defect in the rat mandible that is covered by a collagen membrane.

Therapeutic ultrasound to stimulate osteoconduction; A placebo controlled single blind study using e-PTFE membranes in rats.

To decrease healing time of bone defects covered with osteoconductive membranes, an attempt was made to stimulate the osteoconductive process with therapeutic ultrasound. In 72 rats, a circular mandibular defect was created and covered on both sides with an e-PTFE membrane. A control group, an ultrasound treatment group and a placebo treatment group were studied. At 2 and 4 weeks, the osteoconduction was expressed as the percentage of defect closure using digitized microradiographs. At 2 weeks, there was no significant difference in the percentage of defect closure between the groups. At 4 weeks, there was significantly more bone defect closure in the placebo group (77.9%) as compared to the control group (59.3%). Membrane ultrasound attenuation measurements indicated that the membrane blocks most of the applied ultrasound. In conclusion, low intensity pulsed ultrasound does not appear to significantly stimulate osteoconduction into a bone defect in the rat mandible that is covered by an e-PTFE membrane.

Ultrasound to stimulate mandibular bone defect healing: a placebo-controlled single-blind study in rats.

PURPOSE: Because of the limitations of the body to heal large maxillofacial bone defects, an attempt was made to stimulate mandibular defect healing with low intensity pulsed ultrasound in rats. This ultrasound consists of a 1.5-MHz pressure wave administered in pulses of 200 microsec, with an average intensity over space and time of 30 mW. cm(-2). MATERIALS AND METHODS: In 72 rats, a 5.0-mm-diameter circular mandibular defect was created. Three groups were studied: an ultrasound treatment group, a placebo treatment group, and a control group. Ultrasound and placebo treatment involved a daily treatment for 20 minutes at the site of the defect under general anesthesia. At 2 and 4 weeks, the region of bone growth within the defect was measured using microradiographs and the amount of defect healing was expressed as the percentage of defect closure. RESULTS: At 2 and 4 weeks, there was no statistical significant difference in the percentage of defect closure between the groups. CONCLUSION: Low-intensity pulsed ultrasound does not stimulate bone defect healing in the case of a large mandibular defect in the rat.

Optical path-length spectroscopy of incipient caries lesions in relation to quantitative light-induced fluorescence and lesion characteristics.

A basic understanding of the light-scattering processes that take place inside the dental tissue (either sound or carious) is obtained both with measurements of the photon path-length distribution of light inside such media and with Monte Carlo simulations. Furthermore, the following is investigated: the correlations between different momenta of the photon path-length distribution of light inside caries lesions, the fluorescence loss determined with quantitative light-induced fluorescence, and/or the demineralization and depth of caries lesions determined with transversal microradiography. It is concluded that (i) the light paths inside both carious and sound enamel are considerably influenced by the refractive-index contrast at the tooth surface; (ii) contrary to a previous hypothesis, the fluorescence loss is larger in lesions in which the average photon path length is longer; (iii) very good correlations are obtained between the optical characteristics and the physical parameters of lesions when the optical measurements are performed such that there is high refractive contrast at the tooth surface.

Microradiography to evaluate bone growth into a rat mandibular defect.

Microradiography has been evaluated to measure bone healing into a 5.0mm outer diameter mandibular defect in the rat. This method provides high-resolution radiographs of the defects that can be used for an accurate measurement of bone defect healing. In 12 rats, the defect widths of 42-day-old mandibular defects have been measured both using microradiographs and histological sections. The defect width+/-S.D. measured 3.42+/-0.98 mm microradiographically and 3.47+/-1.11 mm histologically. Both methods were accurate in determining defect widths but microradiography has the advantage over histology that an image is obtained from the entire defect, making it possible to measure areas of bone growth.