The International Journal of Prosthodontics, 04/2002

Purpose: An analysis of retrospective data was conducted to establish the survival rates of osseointegrated implants used to retain orbital, nasal, and auricular prostheses over a 14- year period and to recommend guidelines in the restorative treatment of such facial defects. Materials and Methods: Included in this study were all patients who received implant-retained prostheses for auricular, nasal, or orbital defects from 1987 to 2001 in the Maxillofacial Clinics at the UCLA and City of Hope Medical Centers. Data were obtained from patient charts. Two methods were used to determine survival rates: (1) the percentage of the total exposed implants that survived was determined, and (2) lifetable analysis was used to calculate cumulative survival rates at different time intervals. Results: A total of 207 implants were placed in 72 patients, and 182 implants had been uncovered. During the study period, 35 implants failed to integrate, and the survival rate for all exposed implants was 80%. Auricular implants showed the highest survival rate (95%), and orbital implants showed the lowest survival rate (53%). The lifetable analysis demonstrated a cumulative 6-year survival rate of 92% for auricular implants and 87% for piriform/nasal implants. In contrast, the survival rate for orbital implants showed a steady downward trend and reached 59% at 66 months. Conclusion: It is possible to achieve high survival rates of implants in the auricular and piriform/nasal sites through careful presurgical and radiographic planning. The less favorable long-term survival of implants in the orbital rim, especially at irradiated sites, requires further study.

Purpose: The aim of this in vitro study was to investigate the resin bond strength and durability of adhesive bonding systems to densely sintered, pure aluminum oxide ceramic. Materials and Methods: Acrylic glass tubes filled with composite resin were bonded to industrially manufactured alumina ceramic disks with an ultrasonically machined surface. Groups of 20 samples were bonded in an alignment apparatus using five different bonding methods. Subgroups of 10 bonded samples were tested for tensile strength following storage in distilled water at 37°C for either 3 or 150 days. In addition, the 150-day samples were thermocycled 37,500 times. The statistical analyses were made by the Kruskal-Wallis test, followed by multiple pairwise comparison of the groups using the Mann-Whitney test. Results: The mean bond strength of a bis-GMA composite resin to sandblasted alumina ceramic was relatively high after 3 days, at 20 MPa. Additional silanization or tribochemical silica coating and silanization did not enhance the bond strength (18 to 20 MPa) and failed spontaneously over long-term storage. However, using a composite resin containing a special adhesive phosphate monomer, a statistically significantly higher and durable bond strength to the sandblasted alumina ceramic surface was achieved after 3 days (50 MPa) and after 150 days of storage (46 MPa). Conclusion: A durable bond strength to pure alumina ceramic was achieved only by using a composite resin containing an adhesive phosphate monomer after sandblasting the ceramic surface.

Purpose: This study compared the mechanical properties of In-Ceram Zirconia and In- Ceram Alumina. Materials and Methods: Ninety-four disks and six bars were prepared with the slip-casting technique. The disks were used to assess biaxial flexural strength (piston on three ball), Weibull modulus, hardness, and fracture toughness with two methods: indentation fracture and indentation strength. The bars were used to measure elastic moduli (Young's modulus and Poisson's ratio). X-ray diffraction analysis of the specimens was carried out upon every step of the specimen preparation and of the fractured surfaces. Results: Mean biaxial flexure strengths of In-Ceram Alumina and In- Ceram Zirconia were 600 MPa (SD 60) and 620 MPa (SD 61), respectively. Mean fracture toughness measured according to indentation strength was 3.2 MPa · m1/2 (SD 0.34) for In- Ceram Alumina and 4.0 MPa · m1/2 (SD 0.43) for In-Ceram Zirconia. Mean fracture toughnesses of In-Ceram Alumina and In-Ceram Zirconia measured according to indentation fracture were 2.7 MPa · m1/2 (SD 0.34) and 3.0 MPa · m1/2 (SD 0.48), respectively. X-ray diffraction analysis showed that little phase transformation from tetragonal to monoclinic occurred when the specimens were fractured, supporting the existence of a modest difference of fracture toughness between the two ceramics. Conclusion: No statistically significant difference was found in strength. In-Ceram Zirconia was tougher (P .01) than In-Ceram Alumina when tested according to indentation strength. However, no significant difference was found in the fracture toughness when tested with the indentation fracture technique.

Purpose: This laboratory study investigated the influence of varying occlusal forces, occlusal contacts, or small gaps (0 to 8 µm) on the force required to pull 8-µm shimstock from between a tooth and a restorative material specimen. Materials and Methods: An apparatus was developed and calibrated to (1) produce and measure very small gaps (0 to 20 µm) and apply variable occlusal forces between specimens, and (2) pull shimstock consistently from between the specimens and measure the removal force. An unworn maxillary molar cusp and polished amalgam were used as the opposing specimens. Combinations of occlusal forces from 0 to 400 g and gaps of 0 (contact), 2, 4, 6, and 8 µm were tested. Results: Shimstock removal forces increased linearly with increasing occlusal force with 0-, 2-, 4-, and 6-µm gap settings. With 0-, 2-, and 4-µm gaps, there was no significant difference in removal force. With a 6-µm gap, the forces rose but at a lower gradient. With the 8-µm gap, the mean force was low (less than 12 g). Conclusion: The shimstock removal force increased with occlusal force and was highest with the smaller gaps. Using 8-µm shimstock, 0-, 2-, and 4-µm gaps cannot be differentiated, a gap of up to 6 µm may still be assessed as a holding contact because the shimstock is still gripped, and even an 8-µm gap may be recorded as a light contact since there is still friction on removal.

Purpose: This study evaluated the effect of increasing occlusal vertical dimension (OVD) on the face height in completely dentate young adults. Materials and Methods: Faces of 22 subjects were photographed in a standardized manner in an anterior view. Sequential photographs were taken at intercuspation and clinical rest position, with four completearch maxillary occlusal overlays increasing OVD in interincisal increments of 2, 4, 6, and 8 mm. Objective measurements were made from the photographs using facial reference markers. Ten observers made subjective evaluations of the resulting changes in face height using the sequential photographs randomly presented. Results: Measurements of the facial markers showed that on increasing OVD, a corresponding change in lower face height was 50% of the interincisal increase in intercuspation and 40% for clinical rest position. ANOVA for repeated measures showed a statistically significant effect of the intraoral increase in OVD on lower face height. However, subjective results showed that observers were not capable of detecting changes in face height caused by an intraoral increase in OVD (2 to 6 mm intrinsically). ANOVA for the difference between dentists and nondentists showed a minimal, but significant, difference between the two groups, with dentists erring slightly less. Conclusion: Attempts to alter face height by changing OVD within the range of 2 to 6 mm for esthetic reasons may not be visually distinguishable.

Purpose: This study aimed to estimate the frequency of occlusal errors that could be induced in centric closing of casts around arbitrary axes instead of the hinge axes in a group of patients. Materials and Methods: In 57 asymptomatic subjects, individual hinge axis points, arbitrary axis points, and coordinates of occlusal cusps along the lateral dental arches were determined experimentally on each side. Horizontal errors that could emerge when rotating the casts around the arbitrary instead of around the hinge axes were calculated for all persons with 2- and 4-mm changes of vertical dimensions. Results: Mounting of casts in relation to arbitrary axes could induce occlusal errors of less than 300 µm in the second molar area in 87% of patients with a 2-mm change of vertical dimension. In 12% of cases, errors between 300 and 500 µm could occur. In only 1%, errors greater than 500 µm had to be expected. The errors generally decreased from posterior to anterior tooth locations, but strongly increased for widening of jaw gapes. Conclusion: The transfer of casts in relation to arbitrary axes is associated with a negligible risk for inducing errors above clinically relevant limits. If changes of vertical dimension would not exceed 2 mm, the transfer in relation to individual hinge axes would bring no advantage for occlusal therapy.

Purpose: New luting agents, described as resin-modified glass-ionomer cements and compomers, have been developed during the last decade to improve the retention of cemented restorations. The aims of this study were to (1) compare the push-out strength of these new luting materials against both conventional cements and bonding luting agents, and (2) evaluate the influence of dentin surface treatment on both glass-ionomer cement and 4-META adhesive resin push-out strength. Materials and Methods: Conical standardized cavities were drilled in the center of coronal dentin disks. Ninety sandblasted Ni-Cr inlays, divided into nine batches, were luted into the cavities according to the surface treatment and the nature of the following luting agents: zinc phosphate cement, zinc polycarboxylate cement, type I glass-ionomer ± polyacrylic acid, resin-modified glass-ionomer, polyacid-modified composite resin, filled bis-GMA phosphate ester resin, and 4-META adhesive resin ± application of activated monomer. Each specimen was placed in a holding device, and a steel rod was used to apply a force on the inlay until rupture occurred. The push-out strength was calculated, and the failure mode was controlled. Results: There were significant differences between some of the groups. The highest push-out strength was achieved by the 4-META adhesive resin after application of activated monomer. The lowest value was attained with zinc phosphate and polycarboxylate cements. Conclusion: Both resin-modified glass-ionomer and polyacid-modified composite resin luting materials exhibited a push-out strength similar to resin-based materials. Specific dentin surface treatments significantly enhanced the push-out strengths of glass-ionomer cement and 4-META adhesive resin.

Purpose: The purpose of this study was to critically analyze important hygienic/secondary prophylactic and biomechanical aspects of removable partial denture (RPD) design. Materials and Methods: The literature related to traditional biomechanical design and open/hygienic design of RPDs was discussed by the authors at a 2.5-day workshop. The written report was circulated among the authors until a consensus was reached. Results: There is little scientific support for most of the traditional design principles of RPDs, nor has patient satisfaction shown any correlation with design factors. However, there is evidence that an open/hygienic design is more important than biomechanical aspects for long-term oral health. The biomechanical importance of some components is questioned, eg, indirect retention and guiding planes. Alternative connector designs that reduce risks of tissue injury are described. Direct retainers and pontics are discussed in relation to the possibilities they offer for gingival relief. Conclusion: Greater attention should be paid to RPD design principles that minimize the risks of tissue injury and plaque accumulation in accordance with modern concepts of preventive dentistry.

Purpose: The purpose of this study was to evaluate the professional time required for the prosthodontic maintenance events of mandibular implant overdentures during the first year of service using three different implant systems (ITI, Steri-Oss, or Southern). Materials and Methods: Seventy-two mandibular implant overdenture patients were allocated to three equal groups, each treated with a different implant system. Data on prosthodontic maintenance events during the first year were categorized and analyzed according to professional time allocation per procedure. Results: The total professional time required to perform all the maintenance events ranged between 29.0 and 34.0 hours and did not differ significantly among the three groups, although there were time differences for matrix activation and replacement. When combining the professional time for all maintenance events for the mandibular overdentures alone, or with the opposing maxillary complete dentures, there were no significant differences between groups. For maintenance of the maxillary dentures, there was an unexplained difference between the Southern group and ITI or Steri-Oss groups (P .05). Conclusion: The prosthodontic maintenance for mandibular implant overdentures required on average 72 to 98 minutes of professional time per patient during the first year of service, depending on the system used.

Purpose: The purpose of this study was to develop a handy probe to measure tongue pressure without fear of radiation or infection. Materials and Methods: A probe was assembled using a small balloon, a stainless pipe, and a 1-mL disposable tuberculin-test syringe cylinder. The probe was pressurized to set the balloon diameter at approximately 18 mm. Forty-one subjects (16 men and 25 women, 24 to 84 years of age) participated. To record maximal voluntary tongue pressure, the subjects were asked to compress the balloon onto their palates as strongly as possible. To record deglutitious tongue pressure, 5 mL of water was measured and administered with a scaled 10-mL syringe and swallowed with the balloon in the mouth. Both types of pressure were recorded three times at 1-minute intervals. Peak values of each record were measured. Results: Individuals varied from 10 to 41 kPa in the maximal voluntary trial and 3 to 27 kPa in the deglutitious trial, with 5 and 7 kPa mean intraindividual ranges of reproducibility, respectively. A negative correlation to age was found for both types of pressure. No gender differences or effects of dentition were found. Conclusion: A disposable handy probe for measuring tongue pressure was developed and tested for clinical use. Despite the limited information acquired, we could see some quantitative aspects of tongue function conveniently and safely.

Purpose: It was the aim of this study to evaluate the efficiency of a luting technique that is said to compensate for misfits of implant-supported prostheses by means of a combined screw retained-luted fixation of the prostheses to the supporting abutments. Materials and Methods: One three-unit prosthesis was made on cylindric abutments, and one was made on conical abutments. Two more prostheses were made, one on the cylindric and one on the conical abutments, with the luting system. The preload was measured in different fit and misfit situations, with and without the use of the luting system. The preload is a combination of internal preload (positive axial forces), which is a clamping load that keeps the implantprosthesis components together, and external preload (axial forces and bending moments), which is the result of a deformation of the implant-prosthesis complex during fixation caused by prosthesis misfit. The external preload on the supporting abutments after screw tightening the prostheses was used as an indicator for the quality of fit of the prostheses. Results: The axial forces were lower and the bending moments were higher in cases of misfit in comparison with the optimal fit situation. The luting system generally did not decrease the registered external preload. Except for one test condition, even higher bending moments were registered on the supporting abutments when the luting system was used. Conclusion: For the prostheses evaluated in this study, the luting system was not effective in reducing the external preload on the supporting implants caused by prosthesis misfit. Although the luting system could compensate for visual misfit, it failed to really improve the load conditions of the supporting implants.

Purpose: In this article, the time taken by a prosthodontist to fabricate and maintain mandibular overdentures retained by two implants and conventional dentures is compared. Materials and Methods: Sixty edentulous patients between the ages of 65 and 75 completed a randomized clinical trial. All received new maxillary conventional dentures and either a mandibular conventional denture (n = 30) or a two-implant overdenture on ball attachments (n = 30). The time spent by the prosthodontist and the number of visits required for treatment, including both scheduled and unscheduled visits, were recorded for each patient from preliminary impressions to 6 months following delivery. Data from the two groups were compared using Mann-Whitney U tests. Results: The prosthodontist spent a mean total time of 296 minutes in treating an implant overdenture patient and 282 minutes on a conventional denture patient during the period from preliminary impressions to the 6-month follow-up. The mean numbers of appointments were 10.1 (implant group) and 10.8 (conventional group). These differences were not significant. Conclusion: Although additional knowledge is required to treat patients with implant prostheses, the time required by the prosthodontist to provide twoimplant mandibular overdentures with ball attachments was not significantly different than the time needed for conventional denture treatment.

Purpose: This study examined the effects of using four different core-ceramic materials on the stresses that developed in a single all-ceramic first premolar crown. Materials and Methods: This was done by analyzing models constructed in an axisymmetric fashion with finite element analyses. The model had a 600-N vertical load applied uniformly over a circular area on top of the crown. Particular emphasis was placed on the tensile stresses that developed. Results: For this particular type of model and loading configuration, radial tensile stresses were predominant in magnitude. Peak hoop and axial tensile stresses were approximately 80% and 2% of this value, respectively. The peak radial and hoop tensile stresses were located on the inside of the coping and scaled with the elastic modulus of the coping. For the axial component, the peak was located in the veneer ceramic on its outermost perimeter. Conclusion: Under normal loading, a near-uniform tensile stress field developed within the coping, directly beneath the contact area. The magnitude of this stress for realistic bite forces using current design recommendations was significantly lower than the fracture strength of the four ceramic materials investigated. The stresses developed within the porcelain were in all instances well below typical strength values.