The effect of engaging the screw access channel of an implant abutment with a cement-retained restoration.

PURPOSE: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning the factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that extending a casting into the screw access channel of an implant abutment has on the retention when cemented using Temp Bond. MATERIALS AND METHODS: Replace Select Straight abutments received set modifications (buccal wall removal at 15 degrees , 22 degrees , and 30 degrees ) using a milling machine; controls were unmodified. Two castings were fabricated for each of the modified abutments, one with and one without an extension into the screw access channel. Following cementation with Temp Bond under standardized conditions, the castings were removed from the abutments using an Instron machine, and the peak removal force was recorded. RESULTS: Extending the casting into the screw access channel significantly (p < 0.001) increased the peak load of removal. Significant differences (p < 0.05) were found between no modification and 30 degrees modification, 15 degrees and 30 degrees modification, and 22 degrees and 30 degrees modification in the groups when the casting extended into the abutment. In the group where the casting did not extend into the abutment, all groups were significantly different (p < 0.001) with the exception of 22 degrees and 30 degrees modification. CONCLUSIONS: The increased load required to remove a casting that extends into the screw access channel of an implant abutment may compensate for loss in retention, which occurs through unfavorable modification of the abutment.

An analysis of the effect of a vent hole on excess cement expressed at the crown-abutment margin for cement-retained implant crowns.

PURPOSE: The labial margins of anterior implant-retained crowns are often positioned subgingivally for a superior esthetic appearance. One of the consequences of subgingival margins is the increased risk of leaving excess cement behind following cementation. This can lead to potential problems, including peri-implant inflammation, soft tissue swelling, soreness, bleeding or suppuration on probing, and bone loss. The purpose of this laboratory study was to investigate the effect of placement, location, and diameter of a vent hole on the amount of cement being expressed at the margin of an anterior implant abutment-retained crown. MATERIALS AND METHODS: Three implant crown copings were fabricated to fit on the same custom abutment. Three vent diameters (0.75, 1.25, and 1.65 mm) and three locations on the palatal surface of the coping (cervico-palatally, mid-palatally, inciso-palatally) were chosen for vent hole placement. For each test, the coping was cemented onto the abutment under standardized conditions. A preweighed thin coating of cement was applied to the fit surface of the coping. The amount of cement expressed at the margin and vent hole was measured by weight and calculated as a proportion of the amount of cement placed in the coping before seating. The procedure was completed 15 times for each variable. The results were statistically analyzed using univariate ANOVA with post hoc Bonferroni-adjusted independent samples t-tests. RESULTS: The presence of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05). The location of a vent hole influenced the proportion of cement expressed at the coping margin (p < 0.05), with the exception of the mid-palatal and inciso-palatal positioning where there was no significant difference (p= 0.61) between groups. The diameter of the vent hole did not significantly influence the proportion of cement expressed at the coping margin (p= 0.096). CONCLUSIONS: When using anterior cement-retained implant crowns, the use of a 0.75-mm mid-palatal or inciso-palatal vent hole to minimize the amount of cement expressed at the margin during cementation should be considered.

Resin-retained bridges as predictable and successful restorations.

Resin-retained bridges have been used clinically since the 1970s and offer a more conservative approach to the restoration of edentulous spaces than conventional bridgework. They are easy to place, cheap to fabricate, and have been shown to be cost-effective. Despite this, they are not frequently used in general dental practice and have an exaggerated reputation for premature failure. Since their initial introduction, they have undergone a number of changes to their method of retention and the materials used in their construction. This has resulted in a predictable, aesthetic restoration which, second only to restoration with dental implants, is often the treatment of choice when teeth adjacent to an edentulous space are minimally or not restored.

Subjective and photometric determination of bleaching outcomes.

OBJECTIVE: Subjective and objective measures were used to determine the relative efficacy of 10% and 35% carbamide peroxide gels in bleaching extracted human teeth. METHOD AND MATERIALS: Fifty-five teeth (premolars and molars) were sectioned longitudinally, and one-half of each tooth was assigned to group A (10%) and the other half to group B (35%). Prebleaching shades were evaluated subjectively by 5 experienced observers using standard shade tabs. Photographs were also taken with a calibrated digital camera. Luminosity, R, G, and B levels were determined with Photoshop software. The specimens were then bleached by either 10% or 35% carbamide peroxide, after which they were reexamined by the 5 observers and rephotographed. RESULTS: All bleached specimens were subjectively assessed as "lighter", but there was no perceived difference in final shade between groups. Objective measurement showed that the greatest spread in the 0 to 255 scales was in the B levels. Mean (and range) of pre- and postbleaching B levels and their differences, by group, were group A, 96.2 (76.5 to 117.1), 113.6 (87.7 to 129.1), difference 17.4, and group B, 95.4 (72.1 to 118.8), 110.5 (88.0 to 138.5), difference 15.1. Statistics were performed using paired t tests. These pre- and postbleaching differences were significant (P < .002). The difference between mean postbleaching B values was not significant (P = .479). The greatest change in luminosity occurred in initially dark teeth treated with 35% carbamide peroxide (P = .036). CONCLUSIONS: Subjective determinations suggest that the bleaching protocols tested were equally effective, but the objective measurements implied that the higher concentration of carbamide peroxide was more effective for darker teeth.

The effects of abutment wall height, platform size, and screw access channel filling method on resistance to dislodgement of cement-retained, implant-supported restorations.

PURPOSE: Factors affecting the retention of fixed prostheses to natural abutments are well understood. In contrast, little is known concerning factors influencing the retention of fixed prostheses cemented to implant abutments. The purpose of this study was to investigate the effect that varying implant abutment wall height, platform size, and screw access channel filling method has on the retention of castings cemented to implant abutments using TempBond. MATERIALS AND METHODS: Four 15 degrees preangled abutments (Nobel Biocare Replace Select Esthetic) of each platform size--narrow (NP), regular (RP), and wide (WP)--were used. In each group of abutments the screw access axial wall was either unadjusted, one-third removed, two-thirds removed, or completely removed. The screw access channels were either fully or partially filled with Memosil, a vinyl polysiloxane impression material. For each abutment a casting was constructed that incorporated an attachment to allow removal. Castings were cemented to abutments with TempBond. The tensile force required to separate the cemented castings from the abutments was measured using an Instron Universal load-testing machine. RESULTS: The mean peak removal force for comparable abutments was significantly different ( p < 0.05): (1) where the screw access channel was completely filled with Memosil compared with those partially filled with Memosil; (2) with platform sizes--WP > RP > NP; (3) with alteration of axial wall height--1/3 removed > unadjusted = 2/3 removed > total wall removal. CONCLUSIONS: The retention of castings cemented to implant abutments with TempBond is influenced by the wall height, platform size, and the filling modality of the screw access channel.

Reproduction ofarticulator settings and movements with an ultrasonic jaw movement recorder.

The KaVo ARCUS digma is an ultrasonic mandibular movement recorder, which provides articulator setting information for Kavo articulators. The first part of this study examined the ability of the device to record condylar control values pre-set on Kavo's own articulators. Using a mechanical pantograph, the second part of the study tested the ability of the device to record, and then allow reproduction on a Kavo articulator, the movements of a Denar D5A articulator. The device was accurate in recording Sagittal Condylar Inclination, but less so for Progressive Side Shift. Immediate Side Shift was persistently under-recorded. Pantographic tracings demonstrated similar paths of articulator movements so long as Immediate Side Shift was not set.

A technique for post-orthodontic retention of maxillary anterior teeth in the restored dentition: A case report.

Retention is one of the most important factors in the long term success of orthodontic treatment. In the adult patient when orthodontic movement is part of an overall treatment plan involving other disciplines, the provision of permanent retention can he complicated. Several methods have been proposed in the literature to date, all with their own problems and risks. This case report presents a technique that may solve this problem for suitable patients in a way that is both non-invasive and has excellent long-term maintenance potential.

Effect of screw hole filling on retention of implant crowns.

The screw access channels of 15 degrees angled Esthetic Abutments (Brånemark System) were either (a) completely filled with a vinyl polysiloxane impression material (Memosil), (b) partially filled with Memosil or (c) had lower portion filled with Memosil and the remainder with composite resin. The force required to remove a temporarily cemented restoration was measured. The removal force was significantly reduced with the channel completely filled with Memosil compared to those partially filled with Memosil (p<0.01) or with composite resin placed over Memosil (p<0.01). The method selected to fill the screw access channel of an implant abutment can be a significant factor affecting retention of a cemented restoration.

An evaluation of three implant level impression techniques for single tooth implant.

This laboratory study investigated the hypotheses that there is no difference between three implant level impression techniques using vinyl polysiloxane impression material. The tested techniques were 1)- the repositioning technique. 2)-The pickup technique. 3)- The pickup technique with the impression copings splinted to the impression trays with autopolymerising acrylic resin. The Reflex Microscope was used for 3D measurement of distances and angles. Analysis of variance and Tukey's multiple comparisons test were applied to analyse the data. The results showed significant differences in implant analogue position with the repositioning and the pickup (unsplinted) impression techniques from the master model. Alarming rotational errors were recorded with the repositioning and the pickup (unsplinted) techniques. However, connecting the impression coping to the impression tray improves the accuracy of the pickup impression technique.

A laboratory investigation of the accuracy of the repositioning impression coping technique at the implant level for single-tooth implants.

This study investigated the accuracy of the repositioning impression technique at the implant level using vinyl polysiloxane impression material. Three groups each of ten senior dentists, postgraduate students and technicians were asked to use this technique to record the position of an implant in a master model. The Reflex Microscope was used to measure variations between the resulting casts and the master model. Significant difference between the casts and the master model in the X and Y-axes (p < 0.01) was recorded. Alarming inclinational and rotational errors for the implant analogue position were measured with all groups of operators. Similar distortion in the Z-axis was recorded.

The magnitude of cutting forces at high speed.

STATEMENT OF THE PROBLEM: Previous research has used a range of cutting forces for preparing teeth, but there are no data available on the forces actually imposed while cutting teeth with high-speed handpieces. PURPOSE: The purpose of this study was to measure the forces imposed while cutting teeth with tungsten carbide burs used in high-speed handpieces. MATERIAL AND METHODS: Thirty-one dentists each cut 8 conventional class II MO and DO preparations in intact extracted third molars, by use of 2 different air turbine handpieces with different torque-speed characteristics. Two different flat fissure, plain and cross-cut tungsten carbide burs, cutting wet and dry in each handpiece/bur combination. The teeth were mounted in a custom-made transducer unit that displayed the forces imposed by the bur. Data were analysed with a 1-way ANOVA (alpha =.05) and Spearman correlation test. RESULTS: The results showed that there was no significant difference in the applied force between plain and cross-cut burs, cutting wet or cutting dry, but there was a significant difference between the high and the lower torque handpieces. The higher torque handpiece was used at a mean cutting force of 1.44 N and the lower torque handpiece at 1.20 N (P<.002). The overall general mean force observed was 1.30 N. CONCLUSION: It was concluded that the forces used in cutting teeth with the tungsten carbide burs tested related both to the type of the handpiece and to the forces chosen by clinical operators. There was no difference between the plain and cross-cut burs, there was no difference between the cutting wet or dry, and the higher torque handpiece required a higher mean cutting force.

The use of shimstock to assess occlusal contacts: a laboratory study.

PURPOSE: This laboratory study investigated the influence of varying occlusal forces, occlusal contacts, or small gaps (0 to 8 microns) on the force required to pull 8-micron 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 microns) 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 microns were tested. RESULTS: Shimstock removal forces increased linearly with increasing occlusal force with 0-, 2-, 4-, and 6-micron gap settings. With 0-, 2-, and 4-micron gaps, there was no significant difference in removal force. With a 6-micron gap, the forces rose but at a lower gradient. With the 8-micron 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-micron shimstock, 0-, 2-, and 4-micron gaps cannot be differentiated, a gap of up to 6 microns may still be assessed as a holding contact because the shimstock is still gripped, and even an 8-micron gap may be recorded as a light contact since there is still friction on removal.