Five-year clinical evaluation of zirconia-based bridges in patients in UK general dental practices.

OBJECTIVES: This study reported the results at 5 years of fixed-fixed all-ceramic bridges, constructed in a yttria oxide stabilized tetragonal zirconium oxide polycrystal (Y-TZP) substructure, placed in adult patients in UK general dental practices. MATERIALS AND METHODS: Four UK general dental practitioners recruited patients who required fixed bridgework and, after obtaining informed written consent, appropriate clinical and radiographic assessments were completed. The teeth were prepared and bridges constructed in accordance with the manufacturer's instructions. Each bridge was reviewed annually within 3 months of the anniversary of its placement by a calibrated examiner, together with the clinician who had placed the restoration, using modified USPHS criteria. RESULTS: Of the 41 bridges originally placed, 33 bridges were examined at 5 years. All Y-TZP frameworks were intact and no bridge retainers had debonded. Eight chipping fractures in the veneering ceramic were noted over the 5-year period. In five cases the patients were unaware of these and these cases were polished. Of the remaining three cases, in one a repair was attempted but was unsuccessful, but the bridge remained in satisfactory service. However, in the case involving a chipping fracture of the mesial-incisal angle of a central incisor, it was considered that replacement of the bridge was necessary. CONCLUSION: 97% (n=32) of the 33 Lava Y-TZP fixed-fixed bridges, evaluated in patients attending UK general dental practices, were found to be performing satisfactorily. CLINICAL RELEVANCE: The use of Y-TZP frameworks holds promise.

A clinical evaluation of all-ceramic bridges placed in patients attending UK general dental practices: three-year results.

OBJECTIVES: To report the results at year three of an evaluation of fixed-fixed all-ceramic bridges, constructed in a yttria oxide stabilized tetragonal zirconium oxide polycrystal (Y-TZP) substructure, placed in adult patients in UK general dental practices and luted using a self-adhesive resin-based cement. METHODS: Ethical approval was obtained. Four UK general dental practitioners were asked to recruit patients in accordance with the trial protocol. After obtaining informed written consent, appropriate vitality and radiographic assessments were completed and the pre-operative status of the gingival tissues noted. The teeth were prepared and bridges constructed in accordance with the manufacturer's instructions. Each bridge was reviewed annually within 3 months of the anniversary of its placement by a calibrated examiner, together with the clinician who had placed the restoration. The examiners evaluated the integrity of the restoration, its anatomic form, marginal adaptation, surface quality, sensitivity, the condition of the adjacent gingivae, and the presence or absence of secondary caries. RESULTS: A total of 34 bridges were examined at the three-year review. All Y-TZP frameworks were intact and no bridge retainers had debonded. Two veneering ceramic chips, in total, were detected over the three-year period of observation: the patients in whom this had occurred were unconcerned. A further abutment tooth had been successfully endodontically treated, through an occlusal access cavity, in addition to the two already reported at year one. SIGNIFICANCE: At year three, the 34 Lava Y-TZP fixed-fixed bridges, placed in patients attending UK general dental practices, were found to be performing satisfactorily.

A clinical evaluation of all-ceramic bridges placed in UK general dental practices: first-year results.

PURPOSE: To report the results at year one of a three-year evaluation of the performance of fixed all-ceramic bridges, constructed with a yttrium tetragonal zirconia polycrystal substructure placed in adult patients in UK general dental practices and cemented using a self-adhesive resin-based cement. METHODS: Ethical approval was obtained. Four UK general dental practitioners were asked to recruit patients complying with the trial criteria and protocol. After obtaining informed written consent, appropriate vitality and radiographic assessments were completed and the pre-operative status of the gingival tissues noted. The teeth were prepared and bridges constructed using the same technician and laboratory procedures. Each bridge was reviewed within three months of the anniversary of its placement by a calibrated examiner together with the clinician who had placed the restoration. The examiners evaluated the integrity of the restoration, its anatomic form, marginal adaptation, surface quality, sensitivity, the condition of the adjacent gingivae, and the presence or absence of secondary caries. RESULTS: All the bridges (n = 38) examined at the first-year review were present, intact and performing well, though one small chip of the veneering porcelain was detected and in two cases an abutment tooth had been endodontically treated through an occlusal access cavity.

An in vitro and in vivo study of toothbrush bristle splaying.

The extent to which a toothbrush is worn out, as evidenced by bristle splaying, is an important determinant of cleaning efficacy. In order for this aspect of oral hygiene to be studied, an accelerated means of producing a life-like pattern of bristle splaying was investigated and compared with splaying induced by a human test-panel. Porcelain denture teeth were brushed under a static applied load in a slurry of dentifrice, by means of a revolving "figure 8" motion, for up to 12,000 revolutions. This was found to induce an increase in the degree of splaying (as measured by "wear index") that was well-fitted (R2 = 0.96) by a second-order expression of the form: WI = WIi + Ritj - Ctj2 where WI = wear index, WIi = initial wear index, Ri = initial rate of increase in WI, tj = brushing time measured in either machine revolutions (tr) or weeks of human use (tw), and C = a separate constant for each brushing mode (machine or human panel). The rate of splaying was found to be strongly influenced by the quality of the bristle filament, but not by small differences in toothbrush design. The splaying pattern induced by the machine could not be distinguished visually from that in a set of brushes used at home by human volunteers. A strong correlation was found between the splaying produced by machine-brushing and by a panel who brushed free-style at home for 13 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

A mathematical model for predicting toothbrush stiffness.

Both cleaning efficiency and gingival damage depend on the access of toothbrush bristles to sheltered areas and their ability to deliver sufficient force to remove plaque as they travel over tooth surfaces. A mathematical expression was therefore developed which relates bristle properties and features of brush construction to overall brush stiffness, in order to provide a framework for the prediction and systematic investigation of brush performance: Brush stiffness = 0.125E(DBDT)2NTPf/L3. This shows that brush stiffness is predominantly affected by bristle modulus (E), bristle and tuft diameter (DB and DT), the number of tufts (NT), the number of bristles per unit area packed into a tuft hole (Pf = packing factor), and the trim length of bristles (L). Bristle composition and shape had no measurable effect. The 0.125 factor is empirically derived and probably depends on visco-elastic, frictional, and other dynamic effects which were not examined. Thus, this is a first-order approximation, and further work must be done to account for bristle interactions and brushing rate, and to correlate stiffness with a measure of cleaning efficiency.

The measurement of toothbrush wear.

Toothbrushes wear out and progressively lose their ability to clean as the bristles abrade and become curled and matted. To study the factors that influence this process, we developed a quantitative measure of bristle splaying (wear index) and a method for judging and ranking the overall state of brush deterioration (wear rating) and used these to determine the effects of the individual user, brush design, time in use, and bristle material. Wear index is the average increase in brush-head dimensions normalized for maximum bristle length, and is dimensionless. Wear rating is a subjective means of classifying the increasing severity of deterioration on a scale of 0 to 3. The wear characteristics of a variety of commercial and experimental brushes with different design features were determined. Test variables were time in use, brush design (e.g., geometry and size of the brush head), and bristle composition. Time of use, the individual user, and bristle composition were found to have the strongest influences on splaying, and brush design was found to have the least influence. The wear index offers a quantitative means of comparing brushes of different dimensions at various stages of splaying. The wear rating, although qualitative, is a quick means of ranking brushes in various stages of deterioration. The two methods correlate (R2 = 0.87), and both are sensitive to several factors that affect brush durability. Therefore, these methods appear to be suitable not only for research, but also for quality control, the setting of standards, and for substantiation of advertising claims.

Oral lichenoid reactions related to mercury sensitivity.

Lichen planus is a common disorder of unknown aetiology. It has been proposed that in some cases it represents a form of allergic reaction to the metals contained in dental amalgam, particularly mercury. Twenty-nine consecutive dentate patients who had lichen planus of the oral mucosa were patch-tested to the range of metals contained in dental amalgam. Ten out of 29 (34%) showed an allergic reaction to mercury and all of these patients had amalgams greater than 5 years old. The amalgams were poorly contoured and had corroded, resulting in continued release of mercury ions. Six patients had their amalgams replaced with composite or glass ionomer materials resulting in resolution of ulcerated lesions. In a follow-up of 3-24 months, one patient had a recurrence of ulcerated areas and another, despite resolution of the oral lesions had persistent discomfort.