The International Journal of Prosthodontics, 05/2000

Purpose: Expeditious postoperative ingrowth of bone into dental implants is desired for clinically successful fixation of oral implants. The present study was performed to evaluate the effect of applying a capacitively coupled electric field (CCEF) on periimplant osteogenesis in the dog mandible. Materials and Methods: Twelve adult male beagles were used in this study. All of the premolars on both sides of the mandible were removed from each dog. A POI (Ti-6Al-4V) 3-piece implant (3.7 mm in diameter and 8.0 mm in length) whose surface had been treated with anodic oxidation was placed into each test site by self-tapping. Daily application of CCEF (8 h/day) was initiated on the day following the surgery and was continued through the day of sacrifice. A CCEF was induced by an external source delivering 10-Vp-p, 60-kHz sine-wave signals through an oral electrode plate. One side of the mandible of each dog was treated with CCEF, while the other side was not. On the control side, an oral electrode plate was attached for 8 hours per day, but CCEF was not applied. The effect of daily application of CCEF on the ingrowth of bone into the implant was examined at 14, 21, or 30 days after implant placement. A fourth control group was not treated with CCEF and was maintained for 90 days to confirm that CCEF treatment enhances bone ingrowth in dental implants. Results: Daily application of CCEF significantly increased the bone-contact ratio at days 14, 21, and 30 after implant placement in comparison with the respective controls. The bonearea ratios of the 14- and 21-day CCEF-treated groups were significantly larger than those of the respective controls and were similar to those of the 90-day control group. Conclusion: CCEF treatment increases periimplant osteogenesis in the dog mandible, confirming its usefulness in oral implantology. Int J Prosthodont 2000;13:365-372.

Purpose: The purpose of this study was to evaluate the serviceability of a resin-modified glass-ionomer cement for transitional restorations and subsequent core buildups in endodontically treated maxillary premolars. Materials and Methods: Fifty Vitremer restorations were made in 42 patients by one operator during a period of 5 months. After 1 year of follow up, the quality of the restorations was assessed for the variables occlusal contacts, proximal contacts, marginal adaptation, and surface roughness. Survival was estimated at 2 years of service either as a transitional restoration or as a core buildup. Results: The percentage survival of the transitional restorations was 85% ± 6%. When the crowned Vitremer restorations were added to the transitional restorations, the 2-year survival was 98% ± 2%. With respect to the quality assessment, the majority of the restorations showed either no or light occlusal contacts and no or light contacts on at least one of their proximal surfaces. Marginal integrity and surface roughness were considered to be suboptimal on average. Conclusion: The described restorations seem to perform adequately for a transitional period of 1 to 2 years. Their viability as substructures for permanent cast restorations remains to be tested in long-term clinical studies.

Purpose: There have been numerous attempts to improve the mechanical properties of acrylic resin. However, the fracture of dentures is still an unresolved problem. The potential advantage of self-reinforcement should be improved mechanical properties over the amorphous random polymer. This study investigated the addition of poly(methyl methacrylate) (PMMA) beads in a variety of percentages on a range of mechanical properties of PMMA denture base acrylic resin. Materials and Methods: The transverse and impact strengths and hardness of acrylic resin specimens stored in water for periods of 1 week and 6 months prior to testing were investigated. Results: The results showed that for specimens stored for 1 week, the addition of up to 25% beads produced a significant increase in the modulus of elasticity. Addition of 5% beads produced a slight but nonsignificant increase in the modulus of rupture, although additions of increasing percentages produced a decrease in the modulus of rupture. The impact strength was increased for 5% to 25% beads and decreased for 40% beads. The hardness showed only small changes. For specimens stored in water for 6 months, the modulus of rupture decreased with increasing percentages of beads. The addition of beads up to 10% significantly increased the modulus of elasticity. There was no significant increase in impact strength but a significant increase in hardness for 5% beads. Conclusion: The addition of PMMA beads to acrylic resin did not produce a substantial improvement in the mechanical properties and cannot be recommended as a method of reinforcement in its present form.

Purpose: This investigation studied the effects of 3 surface treatments on the shear bond strength of a light-activated composite resin bonded to acrylic resin denture teeth. Materials and Methods: The occlusal surfaces of 30 acrylic resin denture teeth were ground flat with up to 400-grit silicon carbide paper. Three different surface treatments were evaluated: (1) the flat ground surfaces were primed with methyl methacrylate (MMA) monomer for 180 seconds; (2) light-cured adhesive resin was applied and light polymerized according to the manufacturer's instructions; and (3) treatment 1 followed by treatment 2. The composite resin was packed on the prepared surfaces using a split mold. The interface between tooth and composite was loaded at a cross-head speed of 0.5 mm/min until failure. Results: Analysis of variance indicated significant differences between the surface treatments. Results of mean comparisons using Tukey's test showed that significantly higher shear bond strengths were developed by bonding composite resin to the surfaces that were previously treated with MMA and then with the bonding agent when compared to the other treatments. Conclusion: Combined surface treatment of MMA monomer followed by application of light-cured adhesive resin provided the highest shear bond strength between composite resin and acrylic resin denture teeth.

Purpose: Artificial teeth made of acrylic resin or alloy are considered substitutes for rare caries-free human teeth in in vitro examinations. The purpose of this study was to compare the fracture strength and marginal adaptation of all-ceramic single crowns fixed to natural teeth with crowns fixed to artificial teeth after artificial aging. Materials and Methods: The fracture force and marginal adaptation were investigated in 28 adhesively luted all-ceramic crowns on human molars of different sizes, as well as on alloy and liquid crystal polymer (LCP) artificial teeth. The fracture force was determined using a universal testing machine, and the semiquantitative marginal adaptation was examined using a scanning electron microscope, in both instances after simulating 5 years of clinical service. Results: Fracture force was found to be significantly higher for crowns fixed on substitute materials (alloy = 1,838 N; LCP = 1,392 N) than for crowns on human teeth (888 N). No significant differences in marginal quality could be determined between the groups. All crowns showed marginal gaps of about 10% and perfect margins at about 90%. Conclusion: The high in vitro fracture values of all-ceramic crowns on artificial materials may lead to a misinterpretation of the tested restorative materials, overvaluing the material properties in a first preclinical estimation. Human teeth or materials with a comparable modulus of elasticity are therefore preferred in in vitro fracture tests.

Purpose: The aim was to investigate whether the replacement of lost teeth with implantsupported fixed prostheses (IFP) had any influence upon the signs and symptoms of temporomandibular disorders (TMD). Materials and Methods: The subjects comprised 78 consecutive patients referred to a specialist clinic for treatment with IFPs. All were examined with respect to the presence of signs and symptoms of TMD before the start of treatment and after 1 and 3 years. Results: Before treatment began, 21% of the patients were found to have moderate (15%) or severe (5%) clinical signs of dysfunction according to the Helkimo index. These figures decreased numerically but not statistically significantly to 10% and 1%, respectively, at the 3-year follow up. Nearly half of the patients (45%) reported one or more subjective symptoms of TMD at the first examination. The anamnestic index used had decreased statistically significantly at the 3- year follow up, when the 5 variables composing the index had improved, but the improvement was statistically significant only for the variables joint sounds and pain when opening the mouth wide. All patients were satisfied with the treatment received. Conclusion: The results from the present investigation show that treatment with IFPs has a good and lasting effect on the functional status of the masticatory system as well as on subjective symptoms of TMD and chewing ability in the vast majority of patients treated.

Purpose: The purpose of this study was to clarify the direction and magnitude of condyle displacement during clenching with occlusal pivots. Temporomandibular joint (TMJ) loading and flexibility and the clinical significance of orthopedic appliance therapy are also discussed. Materials and Methods: Participants were 16 volunteers with a mean age of 25.8 years. Maxillary and mandibular flat occlusal devices were fabricated. TMJ tomogram series were taken first with tripod support and then with maxillary clenched anterior pivot support and/or unilateral posterior pivot support. Condyle positions on the TMJ tomograms were analyzed using the digital subtraction technique. Results: When clenching with the anterior pivot, the anterior reference point (A) on the mandibular condyle was translated 0.1 mm posteriorly (P > 0.05) and 0.2 mm superiorly (P < 0.01) from the tripod-support reference point. In the case of the ipsilateral posterior pivot, point A was rotated 1.2 degrees (P < 0.01) and was translated 0.4 mm (P < 0.01) posteriorly and 0.18 mm superiorly (P > 0.05). Conclusion: Condyle displacement during clenching with the anterior and posterior unilateral pivot was found, which supports previous findings. However, the direction and magnitude of the displacement differed from those of previous studies using jaw-tracking devices, and individual values differed greatly among subjects.

Purpose: The aim of this study was to compare the marginal adaptation of metal-ceramic crowns made with 3 different metal substructures. Materials and Methods: Seventy-five gypsum dies were fabricated from a master steel die. They were randomly divided into 3 groups of 25 dies each. A metal coping was prepared on each die using a different technique for each group: composite alloy, electroforming, and cast high-noble alloy. Ceramic was baked on all of the samples following the same protocol and simulating the shape and size of a maxillary central incisor. All specimens were evaluated under a stereomicroscope at 200! magnification. The marginal gap was measured at 8 different points on each specimen before and after ceramic application and also on the master steel die. A total of 3,600 measurements was evaluated. The results were statistically elaborated by means of a t test and one-way analysis of variance (ANOVA). Results: The ANOVA revealed a significant difference in mean marginal gap before and after ceramic application within each group. Electroforming (mean 32 µm) and high-noble alloy (mean 31 µm) showed better marginal fit after ceramic application and on the master steel die compared to composite alloy (mean 68 µm; P < 0.0001). Conclusion: Marginal gaps are influenced by the application of ceramic and by the alloy used for the substructure, and the values obtained were within the limits of clinical acceptability (70 µm).

Purpose: The aim of the present clinical study was to analyze the long-term treatment outcome of fixed partial dentures (FPD) with cantilevers. Materials and Methods: Ninetytwo patients with 115 cantilever FPDs on 239 abutment teeth were examined. Immediately following cementation, radiographs of the abutment teeth were obtained. At the follow-up examination 5 to 16 years after cementation, the abutment teeth were clinically and radiographically evaluated. Besides the assessment of periodontal parameters and vitality testing, the presence of carious lesions of the abutment teeth, loss of retention, fracture of bridgework, and fracture of abutment teeth were also recorded. The Student's t test was used to detect differences between abutment teeth and control teeth with natural crowns as well as over time within the groups. Results: Plaque scores and bleeding on probing were low at both abutment and nonabutment teeth. Mean probing pocket depth and level of the clinical attachment never exceeded 3.0 mm in both groups. The radiographic bone levels at abutments were stable within 3% over the observation period. Of the 120 initially vital abutment teeth, 12 (10%) lost vitality during the observation period; one (1%) of the 119 initially nonvital abutments showed periapical pathology. Development of secondary caries was observed at 8% of the 239 abutment teeth. In total, 8% of the abutment teeth were affected by loss of retention, which made up more than half of all technical problems. Material fractures only occurred occasionally, affecting from 1% to less than 3% of the abutment teeth. Fracture of abutment teeth amounted to 3% and was twice as frequent at abutments adjacent to cantilevers compared to abutments not adjacent to cantilevers. Conclusion: The most frequent biologic (caries) and technical complications (loss of retention) made up more than half of all problems recorded. These problems may be at least partially avoided by performing optimal plaque control and by strictly observing the rules for preparation of retentive FPD abutments.

Purpose: The purpose of the present study was to evaluate some important mechanical properties of an experimental silicone material (PM1) to assess its potential as a mouthguard material. Materials and Methods: The hardness, tear strength, tensile properties, and energy absorption properties of the silicone material were determined and compared with those of 2 commercially available materials (Bioplast, a polyvinylacetate polyethylene, and Polyshield, a silicone). Results: Bioplast was significantly harder than Polyshield and PM1. Polyshield was significantly harder than PM1. Bioplast had a significantly higher tear strength than both Polyshield and PM1. The tensile strength of Bioplast was significantly greater than that of Polyshield and PM1. PM1 had a significantly higher tensile strength than Polyshield. Bioplast had a significantly lower energy absorption capacity at 500 N than both Polyshield and PM1, with PM1 having a significantly higher value than Polyshield. At 1,000 and 1,500 N, Bioplast had a significantly higher energy absorption than both Polyshield and PM1. Conclusion: It was concluded that PM1 showed better energy absorption properties than Polyshield and better energy absorption properties than Bioplast at lower impact forces. PM1 was softer and had better tear and tensile properties than Polyshield. The results of the present study suggest that the new material has a good potential for use as a mouthguard material. Int J Prosthodont 2000;13:416-419.

Purpose: The study compared the probablity of fracture of 4 systems of all-ceramic crowns fabricated on maxillary central incisors. Materials and Methods: The 4 allceramic crown systems were: (1) a glass-infiltrated, sintered alumina system (In-Ceram) fabricated conventionally, (2) the same system with machine-milled alumina cores (CEREC 2), (3) a heat-press, leucite-reinforced glass-ceramic system (IPS Empress), and (4) a high-purity, high-density alumina system (Procera). Ten crowns of each system were fabricated and compressed at 45 degrees at the palatal surface until failure. The data were analyzed with the Weibull method. Results: There were no significant differences in the probability of fracture among the 4 systems studied. Conclusion: The likelihood of fracture of these crown systems on central incisors should be similar.

Purpose: The aim of this study was to test in vitro the resistance of a modified resin-bonded fixed partial denture (RBFPD) to detachment using a laboratory setup simulating load fatigue of mastication forces. The effect of varying the cement type was also investigated. Materials and Methods: Extracted teeth were used to prepare specimens each consisting of a premolar and a molar with a space equivalent to a molar in between. Five test groups were prepared (n = 7). Specimens in group 1 were prepared to receive conventional RBFPDs with proximal grooves, occlusal rests, and lingual wings. Specimens in groups 2 and 3 were prepared to receive modified RBFPDs with retentive-slot restorations. Specimens in group 4 were prepared to receive RBFPDs with retentive-slot restorations only, whereas specimens in group 5 were prepared similarly to the ones in groups 2 and 3 but with inlay preparations instead of the retentive slots. Castings were made and their fit surfaces microetched. In groups 1, 2, 4, and 5 castings were cemented with Cement-It, whereas castings of group 3 were cemented with Panavia 21. Slot cavities of groups 2, 3, and 4 were restored with a resin composite. Specimens were subjected to compressive load cycling for 230,000 cycles at 4 Hz under water. Castings were then separated from the abutments under tensile loading. Results: Mean separation forces were: group 1 = 361 N, group 2 = 525 N, group 3 = 562 N, group 4 = 449 N, and group 5 = 417 N. Groups 2 and 3 had significantly higher mean separation forces than groups 1 and 5. Separation of castings in groups 2 and 3 was associated with a higher frequency of cohesive fracture of the abutments than in group 1. Adhesive failure was uncommon among specimens of groups 2, 3, and 4. Conclusion: The modified RBFPDs of groups 2 and 3 had better potential for retention. Increased resistance to dislodgment of the modified RBFPDs was not directly related to the surface area of the castings, nor was it related to the type of resin cement, but rather to mechanical interlocking of the castings with the retentive-slot resin composite restorations.