The International Journal of Prosthodontics, 03/1999

PURPOSE: The purpose of this report was to describe a new technique to fabricate one-piece, implant-supported titanium frameworks by means of a computer numeric-controlled (CNC) milling technique, and to compare the fit of these frameworks with conventional cast prostheses. MATERIALS AND METHODS: The study comprised 20 patients who were provided with 5 standard Brånemark implants each in the edentulous mandible. The fit of the first 10 prostheses with CNC-milled frameworks was measured by means of a 3-dimensional photogrammetric technique. The distortion of the center point of the framework cylinders was measured in relation to the master cast replicas. These measurements were compared with 10 randomly selected routine prostheses with cast frameworks. RESULTS: No significant differences were found between the 2 groups. The 3-dimensional distortion of the cylinders in the completed prostheses ranged from 3 to 80 microns; no passive framework was observed. More distortion was observed in the horizontal plane (x and y axes) as compared to the distortion in the vertical direction (z axis). CONCLUSION: The precision of fit of the first CNC-milled prostheses presented a comparable fit to the conventional cast frameworks. Consequently, this new technique could be a valid option for the routine fabrication of frameworks for implant prostheses.

PURPOSE: The use of implants for prosthetic rehabilitation of partially edentulous patients is increasing. However, the possibilities of placing implants in the posterior part of the mandible are often limited. The purpose of this longitudinal study with 10 years of follow-up was to evaluate the use of short implants supporting fixed partial dentures (FPD) in the posterior part of the mandible, and to compare implant supported FPDs to tooth-implant supported FPDs. MATERIALS AND METHODS: The patient material comprised 23 patients with residual mandibular anterior teeth, and each patient received FPDs unilaterally. On one side the FPD was supported by two implants, and on the other side by one implant and one tooth, thus permitting intraindividual comparison. The distribution of the two types of FPDs in each jaw was randomized. Implant success rates, marginal bone changes, and mechanical complications were studied. RESULTS: The tooth-implant connection did not demonstrate any negative influences on the overall success rates for the 10-year period, nor were the shorter implants found to be less favorable. CONCLUSION: It is suggested that a prosthetic construction supported by both a tooth and an implant may be recommended as a predictable and reliable treatment alternative in the posterior mandible.

PURPOSE: The purpose of this work was to report on the use of implant-stabilized overdentures in the mandible using the Astra Tech implant system with either ball attachments or magnets as the retentive mechanism. MATERIALS AND METHODS: Mandibular overdentures that used ball attachments on 2 implants were provided for 13 edentulous patients; 12 edentulous patients were provided with mandibular overdentures with magnet retention, using 2 implants in 10 patients and 3 implants in 2 patients. Once they were comfortable, the participants were placed on annual recall. Any other visits were initiated by the patients. Detailed records were kept for all visits. At the annual recall the following parameters were monitored: plaque levels, mucosal health, marginal bone levels, and the patients' assessment of the treatment. The patients were followed for 5 years. RESULTS: There was no statistical difference between the 2 groups for mucosal health and postinsertion maintenance. The magnet group had more abutment surfaces covered with plaque. Statistical analysis of the patients' subjective assessment of their treatment showed that the magnet group was less comfortable and chewing was less effective. CONCLUSION: The results indicate that both ball attachments and magnets used on isolated Astra Tech implants in the mandible are viable treatment options. Both attachment mechanisms provided patient satisfaction, although the ball attachments were better in this respect than the magnets.

PURPOSE: In a previous study the authors found that 2 of 3 tooth conditioners examined were able to reduce the negative effect of temporary cement on the bond strength between resin cement and teeth. The aim of this study was to evaluate the bond durability with the conditioners, as well as their capability for temporary cement dissolution. MATERIALS AND METHODS: After eliminating the temporary cement with a curette from the bovine dentin surface, a conditioner (ethyl dihydrogen phosphate, EP; or methacryloxyethyl dihydrogen phosphate, MEP) was applied to the surface and a resin cement was adhered. Tensile bond strength measurement, scanning electron microscopic observation, and energy-dispersive analysis were carried out without thermocycling and after thermocycling. RESULTS: The tensile bond strength gradually decreased with an increase in the number of thermocycles. However, specimens treated with EP or MEP showed significantly higher tensile bond strength values compared to those that did not receive conditioner application (P 0.0001); EP showed significantly higher tensile bond strength values compared to the specimens that did not receive both temporary cement and conditioner application (P 0.0001). The scanning electron microscopic, energy-dispersive, and solubility analyses suggest that both conditioners have the capability of dissolving temporary cement remnants. CONCLUSION: Both EP and MEP have potential value as conditioners to reduce the negative effect of temporary cement on the bond strength between resin cement and dentin and to improve the bond durability.

PURPOSE: This study was conducted to assess the quality of impressions and tooth preparations sent to dental laboratories in Jordan and to determine the technical capabilities of these laboratories to construct fixed partial dentures. MATERIALS AND METHODS: A sample of 136 impressions and stone casts were examined for clinical errors in 35 laboratories that construct fixed partial dentures. They were sorted into unusable, unsatisfactory, acceptable, or satisfactory categories. The type of impression material and tray, opposing arch impressions, and occlusal records were noted. Instructions to technicians were assessed for completeness and clarity. Information regarding laboratory staff and equipment were collected. RESULTS: Half of the specimens inspected were categorized as unusable or unsatisfactory; these were found in commercial laboratories. They showed at least one clinical error such as drags or indefinite finishing lines in impressions and inadequate reduction, undercuts, or obvious taper on stone casts. Alginate impression material was used for 65% of the cases. Only 27% of specimens were accompanied with instructions; of these 22% were graded poor. No occlusal records were available with 54% of the specimens and no articulators were used except in dental school laboratories. The dental schools and some commercial laboratories had the best staff and equipment and were more capable of fabricating fixed partial dentures than those of the Ministry of Health and the Royal Med cal Services. CONCLUSION: The quality of abutment preparation and impressions were unsatisfactory or unusable in 50% of cases. Of the 37 available instructions 8 were not clear. The dental schools and some commercial laboratories were technically capable of producing good quality fixed partial dentures.

PURPOSE: Current in vitro cytotoxicity tests for dental casting alloys may be inadequate because they use a short-term test (generally 168 h) for a material that is present in the mouth for years. A modified in vitro test was used to test the cytotoxicity of 8 dental casting alloys and 3 pure metals. This modified test attempted to simulate the long-term effects of dental casting alloys in the mouth. MATERIALS AND METHODS: Alloys were tested in cell culture either immediately after polishing (initial) or after 10 months of conditioning in a biologic medium containing serum proteins. The cytotoxicities of the 2 conditions were then compared. Alloys were repolished to assess the reversibility of the 10-month conditioning. RESULTS: Alloys with little initial cytotoxicity showed no 10-month cytotoxicity. Alloys with significant initial toxicity showed significantly less toxicity at 10 months. No alloy increased in toxicity after conditioning. Repolishing multiple times did not necessarily reestablish the initial cytotoxicity response. CONCLUSION: The results indicate that short-term cytotoxicity tests may not accurately measure the long-term cytotoxicity of these types of alloys.

PURPOSE: The aim of this study was to determine the mechanisms of failure of magnets used for denture retention. MATERIALS AND METHODS: Magnets were retrieved from dentures that had failed after 4 to 18 months of clinical use. The magnets were sectioned and the failure modes were evaluated using optical or scanning electron microscopy. RESULTS: The magnetic retention system investigated consists of a neodymium-iron-boron magnet sandwiched in a stainless steel keeper, capped with a titanium dome, and sealed with epoxy resin. The diffusion of moisture through the epoxy seal and the breakdown of the encapsulating material led to corrosion of the magnet. In both cases, a loss in retention occurred as the corrosion products weakened the overall magnetic attraction. CONCLUSION: The failure of magnets may occur by either breakdown of the epoxy seal or breakdown of the encapsulating material. Both problems need to be addressed to prolong the life span of these magnets.

PURPOSE: The aim of the present study was to assess the effect of cement-film thickness and surface texture (roughness) on the resistance of cemented crowns to dynamic lateral loading. MATERIALS AND METHODS: Crown and abutment analogues were cemented using zinc-oxide-eugenol, zinc-phosphate, glass-ionomer, and composite cements. The space left for the cement lute was 0.02, 0.05, 0.1, 0.2, and 0.5 mm. The 3 degrees of surface texture subjected to investigation were (1) polished with up to 4,000-grit paper, (2) sanded using a 1,000-grit paper, and (3) sandblasted with 50-micron aluminum oxide. Testing was conducted according to the staircase procedure. The specimens were subjected to rotational fatigue loading until the cement bond failed or the components reached 1,000,000 stress cycles. RESULTS: The results showed that the relation between cement thickness and resistance to dynamic lateral loading is hyperbolic. For the zinc-oxide-eugenol, the zinc-phosphate, and the glass-ionomer cements increasing surface texture had a moderate effect. For composite cement, sandblasting doubled the resistance to dynamic lateral loading. For both parameters tested (cement thickness and surface texture), the ascending order of resistance was: zinc-oxide-eugenol, zinc-phosphate, and glass-ionomer cements. Crowns cemented with composite cement presented the highest resistance to dynamic lateral loading. CONCLUSION: Within the confines of the present experimental design, it is concluded that (1) decreasing the width of the cement layer increases the resistance to dynamic lateral loading, and (2) texturing the surface of the abutment and the restorations as after sandblasting increases the resistance to dynamic lateral loading.

PURPOSE: The purpose of this study was to describe the mandibular incisor positions for the 24 consonant sounds of the English language. Further aims were to determine if the incisor format for each sound is affected by its position in a word, or by combination with an open or closed vowel. MATERIALS AND METHODS: A total of 30 young adult subjects had their incisal positions determined using an electrognathographic technique during performance of a number of speech tests. RESULTS: The mean values of the 24 consonants, in the vertical direction, showed a range from the intercuspal position of 2.5 mm for a sibilant sound to 11.7 mm for the /H/ sound, and an anteroposterior range of 1.4 mm anterior for a sibilant sound to 1.8 mm posterior for the /M/ sound. The range in the mean lateral dimension was always less than 1 mm on either side of the midline. The placement of a sound in the initial or final position in a word had no effect on the incisal position. The degree of vertical opening was significantly greater for 8 of the consonant sounds when in combination with an open vowel sound. The anteroposterior and lateral positions were unaffected by vowel association. CONCLUSION: The incisor position for consonant sounds is unaffected by initial or final word placement. Some consonant sound positions are affected by combination with an open or closed vowel sound. Sibilant sounds produced a clinically acceptable measure of the most superior and anterior speaking positions in all subjects.

PURPOSE: Tooth selection is considered an important factor in the construction of complete dentures that function harmoniously and comfortably and preserve the denture-supporting tissues. To bring a scientific background to clinical impressions, the hypothesis that different cusp angles bring different levels of patient satisfaction was tested. MATERIALS AND METHODS: Four different occlusal schemes were compared. The dependent variables (3 groups of visual analogue scores of patient satisfaction) were analyzed by means of multivariate analysis of variance (MANOVA) for repeated measures. RESULTS: All MANOVAs showed nonsignificant results for the effect of tooth type on the 3 groups of variables (P values between 0.1 and 0.8). CONCLUSION: The results did not show statistically significant differences in patient satisfaction among the different occlusal schemes. It is recommended that future research use more sensitive instruments to evaluate this specific aspect of treatment success.

PURPOSE: The purpose of this study was to present a personal view of the development of prevailing opinions about temporomandibular disorders (TMD) during the last half century from a mechanistic to a psychosomatic concept. It also presents some hypotheses concerning: (1) the role of stress in the etiology of human oral parafunctions and its relationship to oral stereotypies in domestic animals; and (2) the pathogenetic mechanisms of masticatory muscle pain. MATERIALS AND METHODS: The basis for this article was a review of personal experiences derived from clinical and research work with TMD patients. Studies of both older and more recent literature on TMD and related disorders - especially in the fields of stress research, psychosocial medicine, occupational medicine, and etiology - were also used. RESULTS: A clear line is found in the development of the ideas on etiology, pathogenesis, and therapy of TMD, from the mechanistic attitude of Costen syndrome through the introduction of psychologic and psychophysical theories by the Columbia and Chicago schools to the now increasingly accepted biopsychosocial concept and the view of refractory TMD as a chronic pain condition. CONCLUSION: The formerly dominant bite-centered therapies - including intraoral appliances, the effects of which still are unexplained - appear to be increasingly banished to the domain of placebo Hence, to an ever-increasing extent occlusal treatments are replaced by physiotherapy and cognitive behavior therapy. The presented hypotheses may have implications for the understanding of the origin of oral parafunction and masticatory muscle pain.