Quintessence International, 01/2000

Objective: When successive restorative procedures (eg, porcelain veneers, interdental resin composite restorations, and endodontic treatment) are carried out on the same tooth, significant effects on crown flexure can be expected. Method and materials: Dentin-bonded porcelain veneers (experimental group) were assessed in vitro using functional and cyclic thermal loads. They were compared to natural teeth (control group) with respect to 2 parameters: coronal flexure (investigated using experimental strain gauges) and morphology of the tooth-restoration interface (Scanning electron microscopic evaluation). For both veneered and natural teeth, crown deformation was recorded at 5 sequential experimental steps: intact tooth (baseline), Class III cavities, Class III resin composite restorations, endodontic treatment, and endodontic restoration (without posts). Results: No significant differences in crown flexure were found between natural and veneered incisors when compared across experimental steps. The main effect for experimental steps was highly significant. When averaged across all specimens (natural and veneered teeth), the endodontic treatment step resulted in the highest crown flexure (1.55x the baseline value). The unrestored Class III cavities and the endodontic restoration were next highest (1,30x and 1.28x the baseline value, respectively). The lowest crown flexures were found after restoration of the Class III cavities (1.13x the baseline value). No measurable microleakage or gaps were detected at the ceramic-resin, resin-enamel, or resin-dentin interfaces (Optibond FL, Kerr). Conclusion: Each subsequent reduction in tooth structure resulted in a substantial increase in crown flexibility, even after restoration. Endodontic procedures were responsible for most of the loss in crown stiffness. Extensive proximal cutting and restorations seemed to minimally affect crown flexure. Porcelain veneers showed perfect biomimetic behavior, because cumulated restoration procedures had the same effect on natural and veneered incisors. Keywords: anterior tooth, flexure, resin composite restoration, stiffness, veneer

The dowel-and-core restoration is indicated when inadequate tooth structure remains to retain an extracoronal restoration. A modified technique for fabricating the dowel and core combines the direct technique of forming the dowel in the actual Channel with the indirect technique of creating an ideal core contour in the laboratory. This technique allows the operator to create an accurate and passive fit of the dowel pattern in the canal preparation. The technique also introduces the Option of retrieving the dowel portion by utilizing a polyvinyl siloxane cast or liner. Further advantages of the technique are reduced chairside time and the ability to capitalize on the preparation of multiple teeth. The technique focuses efforts on achieving an accurate and passive fit of the dowel clinically while delegating the formation of the core to the laboratory. Keywords: direct technique, dowel and core, endodontically treated tooth, fixed partial denture, indirect technique, vacuum-adapted matrix

Objective: The purpose of this study was to evaluate the clinical Performance of preformed beta-quartz glass-ceramic insert restorations. Method and materials: Nine Class I and 30 Class II beta-quartz glassceramic insert restorations were placed in 16 patients who were seen regularly by personnel at Umeä University Dental School. The California Dental Association criteria were used to evaluate the restorations at baseline, 6 months, and 1, 2, and 3 years after luting. The occurrence of postoperative sensitivity, the time taken to manufacture each restoration, and certain periodontal conditions were also evaluated. Results: Sixty-nine percent of the restorations were rated satisfactory at the 3-year examination. Düring the follow-up period, 4 became loose and 7 were fractured or had flaking surfaces. Caries was registered in connection with 1 restoration. Excellent ratings were obtained for marginal integrity, anatomic form, surface, and color in 62%, 84%, 32%, and 44% of the restorations, respectively. There was no statistically significant difference in the occurrence of plaque and bleeding on probing in comparison with the controls. The mean overall time for placement was 38 minutes. The estimated survival rate (Kaplan-Meier) was 59% after 3.5 years. Conclusion: The quality of the beta-quartz glass-ceramic restorations in the present study was inferior to that presented in most earlier studies of ceramic or resin composite posterior restorations placed in patients treated at university clinics. Both the technique and the beta-quartz glass-ceramic inserts have to be evaluated in more long-term studies to assess the possibility of their serving as an alternative restorative technique. Keywords: beta-quartz insert, clinical evaluation, inlay, posterior resin composite restoration

Objective: Deflection of dental needles during tissue penetration has been associated with a failure to achieve successfui anesthesia. The purpose of this study was to determine whether needle deflection in a tissuelike substance could be minimized through the use of a bidirectional rotation insertion technique. Method and materials: Three in vitro deflection test models were constructed, each incorporating a different tissuelike substance of a different density. Each substance was tested with 3 different needle sizes (30-gauge, 27-gauge, and 25-gauge). A customized dental surveyor allowed for standardized needle insertions to a standardized depth of 20 mm. Two different insertion techniques, a linear insertion technique and a newly described bidirectional rotation insertion technique, were tested. Radiographic analysis was performed after each insertion. Results: The bidirectional rotation insertion technique described was consistently more effective in minimizing needle shaft deflection for 30-, 27-, and 25-gauge needles. The differences were statistically significant. Each of the different tissuelike substances consistently demonstrated this reduction in needle deflection. Conclusion: The factor that most greatly affects the path taken by a needle through a tissuelike substance is the force vectors that act on the needle's beveled surface. The use of a bidirectional rotation insertion technique minimized needle deflection, resulting in a straighter tracking path for 30-, 27-, and 25-gauge dental needles, in 3 different tissuelike substances tested in this study. Keywords: computer-controlled drug delivery system, deflection, force penetration, insertion technique, local anesthesia, needle

Objective: This pilot study was conducted to clinically evaluate 2 different concentrations of sodium hypochlorite for the control of dental unit biofilms and to evaluate the efficacy of pasteurizing dental treatment water for patient care. Method and materials: Two dental units with no prior Chemical treatment were retrofitted with self-contained water Systems for this study. One dental unit was treated with 5,000 ppm of sodium hypochlorite and the other with 1,500 ppm. Treatment consisted of a 10-minute contact with the dental unit water lines, followed by a flush with a buffer Solution. A pasteurizer was equipped with autoclavable spigots to provide dental treatment water. Heterotrophic Plate Count Samplers (Millipore) water sampler kits were used to quantify microbial contamination as absolute colony-forming units per millimeter. Scanning electron micrographs were taken of water line lumens to compare pretreatment and posttreatment biofilms. Results: Pasteurized water was significantly less contaminated than was tap water. No significant difference in contamination was found between the 5,000 ppm and 1,500 ppm treatment chairs, either in the reservoir water or effluent water. Scanning electron micrographs demonstrated removal of the biofilms after sodium hypochlorite treatments, regardless of the concentration used. Conclusion: There was no significant difference between the abilities of 5,000- and 1,500-ppm concentrations of sodium hypochlorite to control contamination of dental treatment water and biofilms. Pasteurization of tap water can reduce contamination; this water can be used as acceptable dental treatment water ( 200 CFU/mL). Keywords: biofilm, contamination, dental unit, pasteurization, sodium hypochlorite, source water

Objective: The purpose of this study was to locate the mandibular canal in relation to the impacted mandibular third molar by conventional cross-sectional tomography. Method and materials: Conventional axially corrected cross-sectional tomograms of 347 successive impacted mandibular third molars of 234 patients referred for removal of the impacted teeth were acquired with a Scanora x-ray unit. The images were assessed for location of the mandibular canal and the impacted mandibular third molar. Descriptive analysis was performed. Results: Examination of the tomograms revealed the alveolar nerve to have, in relation to the mandibular third molar, a lateral (buccal) course in 53.6% (n = 186), a course between the roots in 26.8% (n = 93), a lingual course in 13.0% (n = 45), and an inferior course in 6.0% (n = 21). Supplementary canals were found in 6.3% (n = 22). Two of the tomograms (0.6%) could not be evaluated, in 1 case because of incorrect patient positioning, resulting in an incorrectly adjusted transverse cut, and in the other case because of a mandibular Carcinoma. Conclusion: Conventional axially corrected crosssectional tomograms offer additional information in cases where there is a dose relationship between impacted third molars and the alveolar nerve (superimposition of the roots and the canal, grooving, or a varied direction of the canal on the panoramic radiograph) and may contribute to a higher level of intrasurgical safety. Keywords: conventional tomography, impacted mandibular third molar, mandibular nerve, Scanora

Subpontic osseous hyperplasia is an ectopic growth of bone occurring on the edentulous ridge beneath a fixed partial denture replacing a mandibular first molar. A 56-year-old woman experienced an eniargement of the hard and soft tissues beneath the pontic region of a fixed partial denture replacing her mandibular left first molar. Following removal of the fixed partial denture, the bony eniargement was surgically removed, and the bony fragments were submitted for histologic analysis, which demonstrated mature lamellar bone and appositional growth. One year postoperatively, there has been no recurrence of the lesion. The possible etiologies and treatment modalities are reviewed and a rationale for treatment is presented. Keywords: ectopic growth, fixed partial denture, subpontic osseous hyperplasia