A comparison of different methods and materials for establishing maximal intercuspal position: A clinical study.

STATEMENT OF PROBLEM: Which method or material used to record the intercuspal position yields the best accuracy of location of the maxillary and mandibular casts is unclear. PURPOSE: The purpose of this clinical study was to determine the most reliable method of recording a patient's maximal intercuspal position by comparing 2 common methods with 2 popular registration materials. MATERIAL AND METHODS: Complete-arch impressions were made of both jaws with a polyvinyl siloxane impression material in a metal stock tray followed by 4 interocclusal registrations for each of the 17 participants. Two registration techniques were used. More than 1 record was obtained in the first technique, as the participant had to close through a wax sheet or a polyvinyl siloxane material. In the second technique, a polyvinyl siloxane material was injected from the buccal aspect between occluded tooth surfaces. Casts were made from Type 4 stone and vertical measurements of the casts were carried out by using digital vernier calipers, accurate to 100 µm. Hand articulation of the casts was used as the control. Consistency of measurement was assessed by the intraclass correlation coefficient, and comparisons were made by using repeated-measures regression analysis. RESULTS: Statistical analysis showed significant discrepancies when the participant closed through both wax and polyvinyl siloxane material (P<.001). No statistically significant differences to the control group were present when polyvinyl siloxane was injected laterally after closure. CONCLUSIONS: Hand articulation was the most accurate method of reproducing the maximal intercuspal position in a completely dentate individual with horizontal and vertical occlusal stability and was therefore considered the control. Recording the position after the participant had closed by using a polyvinyl siloxane material was the most accurate.

A comparison of the accuracy of polyether, polyvinyl siloxane, and plaster impressions for long-span implant-supported prostheses.

PURPOSE: The purpose of this study was to compare the capacity of different impression materials to accurately reproduce the positions of five implant analogs on a master model by comparing the resulting cast with the stainless steel master model. The study was motivated by the knowledge that distortions can occur during impression making and the pouring of casts and that this distortion may produce inaccuracies of subsequent restorations, especially long-span castings for implant superstructures. MATERIALS AND METHODS: The master model was a stainless steel model with five implant analogs. The impression materials used were impression plaster (Plastogum, Harry J Bosworth), a polyether (Impregum Penta, 3M ESPE), and two polyvinyl siloxane (PVS) materials (Aquasil Monophase and Aquasil putty with light-body wash, Dentsply). Five impressions were made with each impression material and cast in die stone under strictly controlled laboratory conditions. The positions of the implants on the master model, the impression copings, and the implant analogs in the subsequent casts were measured using a coordinate measuring machine that measures within 4 µm of accuracy. RESULTS: Statistical analyses indicated that distortion occurred in all of the impression materials, but inconsistently. The PVS monophase material reproduced the master model most accurately. Although there was no significant distortion between the impressions and the master model or between the impressions and their casts, there were distortions between the master model and the master casts, which highlighted the cumulative effects of the distortions. The polyether material proved to be the most reliable in terms of predictability. The impression plaster displayed cumulative distortion, and the PVS putty with light body showed the least reliability. CONCLUSIONS: Some of the distortions observed are of clinical significance and likely to contribute to a lack of passive fit of any superstructure. The inaccuracy of these analog materials and procedures suggested that greater predictability may lie in digital technology.

The three-dimensional casting distortion of five implant-supported frameworks.

The aim of this study was to assess three-dimensional distortion in cast full-arch, screw-retained titanium implant frameworks. A conventional commercial laboratory one-piece casting was used implementing the lost-wax technique. Five wax patterns were fabricated on a die-stone cast poured from a plaster impression of a five-implant brass analog. A reflex microscope was used to determine the three-dimensional casting error. Significant differences were found in distortion between wax patterns and castings, which, given the need to keep within 150 microm of misfit for passivity, were larger than the wax frameworks by between 416 and 477 microm. The greatest distortion occurred at the terminal implant abutments and in the vertical dimensions, but the distortion was inconsistent, indicating its three-dimensional nature. It is doubtful whether any conventionally cast titanium framework can be made to the degree of accuracy required to fit passively on its abutments because of the multiple variables inherent in this process.

A protocol for maxillary reconstruction following oncology resection using zygomatic implants.

The purpose of this clinical report is to present a surgical and prosthodontic reconstructive protocol for 20 patients who underwent maxillary resection following malignancy to the head and neck region. This protocol was developed over a period of 7 years while treating a series of 20 maxillary resections due to oncology. Patients were reconstructed prosthodontically using fixed-removable overdentures or fixed prostheses, with and without separate obturators. The treatment protocol includes a comprehensive diagnostic phase, resection surgery with immediate implant placement and temporary obturation, post resection evaluation, and prosthodontic rehabilitation. Treatment periods ranged from 6 to 96 months and success was evaluated using strict clinical, radiologic, esthetic, and functional criteria. Postsurgical radiology was undertaken at 6 monthly intervals. Almost all maxillary defects resulting from anatomic disruption of the maxillofacial complex can be well rehabilitated functionally and esthetically using this protocol in conjunction with standard implantology and fixed/fixed-removable prosthodontic principles. This protocol simplifies the rehabilitation and management of these defects by reducing surgical intervention, hosptilization, postoperative morbidity and treatment time, and prosthodontic procedural complications.

Surgical modifications to the Brånemark zygomaticus protocol in the treatment of the severely resorbed maxilla: a clinical report.

PURPOSE: The Zygomaticus dental implant, designed by Nobel Blocare, was developed for the treatment of the severely resorbed maxilla. Brånemark has reported an overall success rate of 97.6% with the placement of 183 implants over the last 12 years. The purpose of this article was to present a modification to the original Brånemark surgical approach to achieve better access and optimal Implant placement. MATERIALS AND METHODS: There are parameters within the patient's resorbed skeletal frame that guide the surgical placement of the currently used Implant However, there are shortcomings in the current surgical protocol. This report describes a simplified surgical approach in 45 patients (77 implants) using an Implant with a modified head angulation of 55 degrees and a placement appliance to assist the surgeon in placing the implant as close to the crest of the edentulous ridge as possible. RESULTS: The placement appliance identifies accurately the anatomic constraints of the resorbed skeletal frame that limit implant placement. This, together with the modified surgical protocol, has resulted in improved access and in ideal positioning of the restorative head. DISCUSSION: The present technique allows restorative clinicians to achieve a more ideal restorative result In the posterior maxillary alveolus using the zygomatic implant, while reducing the buccal cantilever, improving tongue space, and access for maintenance. CONCLUSION: By placing the implant closer to the crest of the alveolar ridge using the placement appliance and an implant with a 55-degree head, the emergence of the restorative head and resultant buccal cantilever can be reduced by as much as 20%.