The International Journal of Prosthodontics, 02/2000

Purpose: This article presents an overview of etiologies associated with tooth wear. Materials and Methods: Specific types of wear based on clinical findings and patient history are described. Results: The occurrence and pattern of tooth wear are related to cultural, dietary, occupational, and geographic factors. Examples of tooth wear related to these factors with regional specificity are presented. Conclusion: The dental practitioner should recognize the characteristic signs of tooth wear, as they may be the first to discuss the problem with the patient. Management should be based on accurate diagnosis.

Purpose: The purpose of this study was to describe a new application of craniofacial implants, as anchoring elements for wigs. Materials and Methods: In two patients, a splitskin graft was used to close a soft tissue defect in the occipital, parietal, temporal, and frontal region (defect size of 10 cm 3 33 cm and 10 cm 3 14 cm). Six titanium implants were placed in each patient. Six months after implant placement, abutment connection was performed and titanium magnets were adapted. Subsequently, an implant-retained wig was constructed. Results: In a follow-up period of between 10 and 22 months no implant failed. The incorporated wigs effectively retain a functionally and cosmetically successful craniofacial rehabilitation. Conclusion: Despite these successful treatments, further research is needed before craniofacial implants as anchoring elements for wigs can be considered a standard option in the rehabilitation of craniofacial alopecic defects.

Purpose: The study examined the bond strength between 2 types of resin denture teeth and a pour-type denture base resin after thermocycling. The denture teeth were untreated, prepared with diatorics, or treated with a solvent, dichloromethane. Materials and Methods: Conventional denture teeth and crosslinked denture teeth were bonded to a pour-type denture base resin. Compressive load was applied at 45 degrees on the palatal surface of each tooth until fracture. The teeth were either thermocycled or not thermocycled. Porcelain teeth were also tested for comparison. Results: There was no significant difference in bond strength between the conventional resin teeth and the crosslinked denture teeth. Thermocycling significantly decreased the bond strength of the 2 types of resin teeth but had no effect on porcelain teeth. The application of dichloromethane significantly improved the bond strength of the 2 types of resin teeth either before or after thermocycling. Conclusion: It is recommended that dichloromethane be applied on the denture teeth ridge-lap area prior to denture base processing. Int J Prosthodont 2000;13:112-116.

Purpose: This study was conducted to optimize the interdental design (wraparound) of porcelain laminates bonded to teeth in the presence of preexisting composite fillings. Materials and Methods: A finite element model (2-dimensional mesh generated from a horizontal cross section of a maxillary incisor) was used to evaluate the effects of luting composite shrinkage and thermal changes on the stress distribution within the ceramic. The mesh included 3 restorative designs (3 degrees of interdental wrapping) and a Class III composite filling. Curing contraction of the luting composite was simulated at baseline temperature (37°C). Thermal loads from 37 to 60°C and from 37 to 5°C were assessed with and without preexisting composite shrinkage. Surface tangential stresses were calculated at the ceramic surface and interface. Results: Curing contraction alone generated mostly compressive stresses (peaks at 15 MPa) at both the ceramic surface and interface. Stresses remained compressive (peaks at 20 MPa) when thermal changes were added, except for the conservative veneer with minimum wraparound, the margins of which showed potentially harmful tensile stress peaks (7 MPa). Deformation of the tooth-restoration complex tended to be more uniform for veneers with maximum wraparound. In the presence of thermal loads alone, opposite effects were observed on the restoration surface and the interface, with compressive stresses on one side (up to 13 MPa) and tensile stresses on the other (up to 9 MPa). This effect of proximal bending (explained by the nearby expansion/contraction of the composite filling) was attenuated by the significant reduction of the bulk of the preexisting interdental composite by the overlapping veneer. Conclusion: In the finite element environment, the negative effect of the nearby expanding/contracting composite fillings can be minimized by extending the veneer over the preexisting interdental restoration. Because of the precompressed state resulting from composite shrinkage, ceramics showed lower temperature-induced tensile stresses.

Purpose: The aim of the present study was to evaluate the periimplant conditions and the maintenance requirements for implant-supported overdentures in the mandible retained with ball or bar attachments during a 5-year period. Materials and Methods: Twenty-six completely edentulous patients had two Astra Tech dental implants placed in the anterior part of the mandible. The denture attachment system for the patients was chosen randomly by drawing lots. Eleven patients drew the bar attachment system and fifteen patients drew the ball attachment system. Plaque Index, Gingival Index, and probing pocket depth were assessed around each implant. Periotest values were recorded, and periodically identical intraoral radiographs were obtained with a specially designed filmholding device. Results: No implants were lost from baseline to the 5-year registration. The periimplant conditions were very healthy after 5 years. No significant differences of the periimplant variables were recorded between the bar and the ball groups. During the first year of function, significantly more complications/repairs were registered in the bar group than in the ball group. In the following years, no significant differences were registered. The mean frequency of complications/repairs per patient per year was 1.0 in the bar group and 0.6 in the ball group during the 5-year observation period. Conclusion: Two implants with ball or bar attachment supported an overdenture in the mandible for 5 years with a 100% survival rate. No differences in marginal bone loss or health of the periimplant mucosa were observed between bar and ball attachment, but the frequency of technical complications/repairs per patient was higher around bar than ball attachments.

Purpose: This study was conducted to determine the bond strength of some resin luting cements to zirconia ceramic. The hypothesis was that adhesive bonding capacity is influenced by different surface pretreatments designed for milled ceramic inlays. Materials and Methods: Composite cylinders 5 mm 3 5 mm were light cured on the ceramic surfaces for a shear test conducted in a test jig. Five surface treatments were studied: as received (from the milling machine), sandblasting with either 250- or 50-µm alumina sand, hydrofluoric acid treatment, and grinding with diamond burs. The tested luting cements were Panavia 21, Twinlook, and Superbond C&B. Results: All debonding occurred at the interface between ceramic and composite cement. Superbond demonstrated the highest bond strength regardless of the surface treatments. Grinding the surface with diamond burs improved the bonding slightly for Twinlook and Panavia 21 and also showed the roughest texture. Washing with hydrofluoric acid had no significant influence on bond strength. Conclusion: Bond strengths for Twinlook and Pananvia 21 were quite low, and only Superbond showed a bond strength reasonably acceptable for clinical use; however, as no standard for bond strength has been established for inlay therapy, the other cements cannot be rejected as luting cements for inlays.

Purpose: Surface properties of denture materials are of clinical importance since they may affect plaque accumulation and staining. This in vitro study investigated the roughness of 20 commercially available denture materials. Materials and Methods: Four denture base resins, nine hard lining materials, and seven soft denture lining materials were evaluated for roughness. Roughness measurements were made using a Mitutoyo Surftest SV-400, and the mean arithmetic roughness values (Ra) obtained were used for the comparisons. Results: The overall Ra values ranged from 0.7 to 7.6 µm. The denture base materials group exhibited Ra values from 3.4 to 7.6 µm, whereas the hard liners were from 0.7 to 4.4 µm. The autopolymerized and visible light-cured soft liners presented Ra values from 0.7 to 3.5 µm, while the heat-cured soft liners ranged from 3.5 to 4.0 µm. Conclusion: The roughness exhibited by all of the materials tested (Ra values greater than 0.7 µm) indicates that there is a possibility for plaque accumulation, since 0.2 µm is considered the threshold below which no further bacterial adherence can be expected.

Purpose: The aim of this study was to assess the water sorption and determine the influence of water on flexural properties of a composite resin cement of 2 different viscosities. Materials and Methods: A dual-cured composite resin cement of 2 different viscosities was tested according to International Standards Organization standards for dental composite materials. The samples tested for water sorption were stored in distilled water for 7 or 60 days. The samples tested for flexural properties were divided into 2 groups and stored either wet in distilled water or dry for 1, 7, or 60 days. After storage, a flexural test was performed with 3-point bending equipment. Results: A significant increase in water sorption for both viscosities was registered as the storage time increased, but no significant difference between the 2 viscosities was recorded. Significantly lower strength and modulus were found for specimens that were wet stored for 60 days compared with the dry-stored ones, and significant changes in deflection at break were also registered. There were no differences in flexural properties between the 2 viscosities. Because of the lubricant and plasticizing effect of water on composite resin materials, the secant modulus and deflection at break seem to be valid methods to describe the complete deflection behavior. Conclusion: Water has an important effect on the flexural properties of composite resin cement after 60 days of storage time. No significant differences in water sorption and flexural properties were found between the high and low viscosities of the composite resin cement studied.

Purpose: The aim of this study was to investigate the denture-induced fibrous inflammatory hyperplasia (FIH) that occurs around the borders of an ill-fitting denture, in relation to frequency of the lesion, age and sex distribution, length of denture use, and frequency of dysplasia. Materials and Methods: A comprehensive review of FIH diagnosed in patients wearing dentures by the oral pathology diagnostic service at the University of São Paulo over 26 years (1971 to 1996) was undertaken, based on retrospective analysis of the oral histopathologic files. Results: The frequency of FIH was 15% of the total number of pathologies diagnosed at the service of oral pathology in that period. The disorder occurred predominantly in the fifth and sixth decades of life and more often among females, at a proportion of 5:1. The frequency of FIH was higher for a length of denture use of between 1 and 10 years. Dysplasia was found in 4% of cases. Conclusion: The knowledge of some aspects of FIH, especially the possible histologic alteration of dysplasia, supports the importance of the diagnosis and treatment of the lesion and suggests that any excised tissue should be submitted to histopathologic evaluation. Education and regular review of patients who have worn dentures are essential if the development of FIH is to be prevented.

Purpose: The purpose of this study was to determine if accuracy and dimensional stability of vinyl polysiloxanes and irreversible hydrocolloids stabilized by a tray used for fixed prosthodontics, removable partial, and complete denture cases are comparable to those of waxes and record rims and if storage time (24 hours or 6 days) affects dimensional stability of the tested materials. Materials and Methods: Two waxes, two record rims, three vinyl polysiloxanes, and one irreversible hydrocolloid (alginate) were examined. Three pairs of master casts with measuring steel rods were mounted on an articulator (initial position). Five records were made of each material, and the upper cast was remounted after 24 hours or 6 days so that deviations from the initial position could be measured. Results: Vinyl polysiloxanes reinforced by a stabilization tray were the most accurate materials able to reproduce a settled interocclusal position. Mounting casts (fixed prosthodontics cases) without records gave accuracy similar to wax records. Record rims used for removable partial and complete denture cases produced lesser accuracy than vinyl polysiloxanes and irreversible hydrocolloid stabilized by a tray. Accuracy was not significantly affected by storage time. Conclusion: The results show that accuracy of vinyl polysiloxanes and irreversible hydrocolloids reinforced by a tray is superior to that of record rims with regard to the complete denture case and is among the most accurate with regard to the removable partial denture case. For fixed prosthodontics, however, reinforcement is unnecessary.

Purpose: The purpose of this study was to investigate the effects of different bonding agents, surface roughness, and acid pickling on the bond strength and color of ultralowfusing porcelain fused to gold alloy. Materials and Methods: Porcelain-metal specimens were made to 25 mm 3 3 mm 3 0.5 mm with a 1-mm porcelain thickness. A 3-point bending test was used to evaluate the bond strength. The color of the porcelain was measured using a dental chromameter, and the data were processed in the CIE Lab system. The color difference (DE*) was calculated for the tested groups. Results: Good bond strength and color could be achieved regardless of the use and type of bonding agent. Surface roughness and acid pickling had more effect on the bond strength than on color. Conclusion: The type of the bonding agent, surface roughness, and acid pickling influenced the bond strength but had minimal effects on the color of ultralow-fusing porcelain. This ultralow-fusing porcelain could produce a color closer to the Vita shade than the conventional low-fusing porcelain.

Purpose: This report describes a simplified method for construction of an interim obturator for a huge maxillary defect. Materials and Methods: A medical grade-silicone obturator was fabricated indirectly on a duplicate cast of the surgical defect for a patient with a bilateral total maxillectomy. This silicone obturator was attached to an acrylic plate by means of mushroom-like extension tags projecting from the fitting surface of the acrylic palatal plate. Results: The obturator was well retained in the patient's mouth and markedly improved his ability to speak and swallow. Conclusion: This technique proved to be a simple, quick, and cost-effective method for construction of obturators for huge maxillary defects.