The Principles of Functional and Mucostatic Impressions for Complete Denture Bases: A Review.

In addition to needing to be hygienic and biocompatible, the base of a complete denture (CD) should provide intimate adaptation to the mucosa of a ridge. The ridge form may differ under function than when at rest because of the compressibility of mucosa. This viscoelastic behavior of ridge mucosa has been a focus of research and a clinical challenge confronted by dentists when making impressions. This article discusses the basic principles of nonpressure mucostatic and selective-pressure functional impression concepts and provides a theoretical and scientific basis for the design of a CD base.

Electronic percussive testing of the stability of an immediately provisionalized implant placed into a fresh extraction socket: a pilot evaluation.

It is important to achieve primary stabilization of dental implants that will be immediately loaded. Noninvasive devices that test the stability of immediately provisionalized implants placed into fresh extraction sockets are discussed. A titanium threaded implant was placed into a fresh extraction socket of a patient's nonrestorable mandibular right canine. The implant received an interim restoration immediately following its placement. The stability of the bone-implant complex was evaluated from the day of implant insertion through day 246 using an electronic percussive testing instrument. During the first month the bone-implant complex became progressively less stable reaching a peak measured level of instability at 30 days postimplantation. This was followed by progressive stabilization first measured on day 46 as the implant continued to osseointegrate. These findings suggest that the bone-implant complex became less stable during the first month after implant placement and was followed by a period of progressive stabilization reflecting bone maturation around the implant. A search of the literature found similar results in a study of single-stage implants (not immediately provisionalized) using resonance frequency analysis. The known sequence of wound healing around dental implants is reviewed to explain the findings of this pilot evaluation. Studies that use noninvasive testing devices to assess implant stability at placement and during healing may provide information that can help to optimize implant treatment outcomes.

AICRG, Part I: A 6-year multicentered, multidisciplinary clinical study of a new and innovative implant design.

PROBLEM: Repetitive microstrains, which occur at the bone-implant interface during function, can lead to implant loss. In an attempt to improve survival by directing the stresses during function away from the dense cortical bone and toward the resilient trabecular bone, the Ankylos implant was developed with a roughened, progressive thread and a smooth cervical collar. The highly polished collar reduces the stresses in areas of the crestal bone. A precisely machined Morse taper prevents rotation of the abutment on the implant and eliminates the microgap present in many 2-stage implant systems. Clinical studies of other implants at different clinical research centers have demonstrated varying degrees of survival. PURPOSE: The purpose of this paper was (1) to assess the overall clinical survival of this new implant design and (2) to compare implant stability (ie, Periotest values [PTVs]) over time with other implants. METHOD: The investigation represented a comprehensive, multicentered, international clinical study conducted over a period of 6 years. It was conducted under an Investigational Device Exemption (IDE) protocol that was reviewed and accepted in the United States by the Food and Drug Administration (FDA). Over 1500 implants were placed and restored, and follow-up data were gathered for a period of up to 3 to 5 years. RESULTS: Over 44% of the clinical research centers reported no failures (100% survival). A total of 63% of the centers had none or only 1 failure during the study. One center reported 6 failures in 1 patient, which were not related to the implant design. Overall survival for implants in function for 3 to 5 years was 97.5%. Using failure criteria of earlier studies of other implants, 5-year survival was 98.3%. Higher handpiece speeds were associated with an increase in the number of failures. This new design produced a slightly more resilient trabecular bone-implant complex with a difference of about 1 PTV in all bone densities when compared with other implants. CONCLUSIONS: The following conclusions can be made: (1) the implant design was effective under all clinical conditions; (2) no significant and unexpected complications or risk factors were evident; (3) survival was found to be excellent; and (4) this implant is well suited for use in the restoration of masticatory function and esthetics in patients with missing natural teeth.

AICRG, Part III: The influence of antibiotic use on the survival of a new implant design.

PURPOSE: The American College of Surgeons guidelines suggest that complex oral surgery may benefit from prophylactic antibiotic coverage. The use of preoperative antibiotics, postoperative antibiotics, or both during implant placement is a widely accepted practice in the United States, whereas dentists in other countries rarely use antibiotics. PURPOSE: The purpose of this study was to determine if antibiotic coverage at the time of implant placement improves the survival of the Ankylos implant. METHODS: As part of a comprehensive, multicentered, multidisciplinary, prospective, independent, international clinical study, designed and coordinated in the United States by the Ankylos Implant Clinical Research Group (AICRG), the use of preoperative (several regimens) and postoperative antibiotics (yes/no) were carefully documented to assess their influence on improving survival. A total of 1500 Ankylos implants were placed and followed for a period of 3 to 5 years. The decision to use antibiotics and the regimen to be employed was made by the treating surgeon. Failure was defined as removal of the implant for any reason. All data were entered into a computerized database for analysis. RESULTS: The use of preoperative antibiotics produced no significant improvement (P = .21, Fisher's exact test) in survival compared with those placed without antibiotic coverage. There was no significant difference between the regimens defined as AHA-1990, AHA-1997, and Peterson's recommendations. CONCLUSIONS: The results of this study suggest that there was little or no advantage to providing antibiotic coverage when placing this implant. These findings also suggest that the use of antibiotics for implant placement may not be as beneficial as once believed. If validated by other studies, the elimination of this practice for routine implant placement would represent a small but significant step forward in the reduction of unnecessary antibiotic use.

AICRG, Part II: Crestal bone loss associated with the Ankylos implant: loading to 36 months.

PROBLEM: The Ankylos endosseous dental implant is a new implant design that will be available in the United States in early 2004. It features an internal tapered abutment connection, a smooth polished collar without threads at the coronal part of the implant body, and a roughened surface with variable threads on the body of the implant fixture. A precise, tapered, conical abutment connection eliminates the microgap often found in 2-stage implant systems. This microgap may allow the accumulation of food debris and bacteria, as well as micromovement between the parts during clinical function, both of which can lead to a localized inflammation and crestal bone loss. PURPOSE: The purpose of this section of the study was to assess any crestal bone loss associated with this new implant. METHOD: The clinical performance of this new implant design was studied under well-controlled clinical conditions. Over 1500 implants were placed and restored. The vertical crestal bone loss was measured "directly" between the time of implant placement and uncovering, using a periodontal probe. Serial dental radiographs were taken between loading, and the 12-, 24-, and 36-month follow-up visits to determine "indirect" crestal bone loss within a specific period. RESULTS: Bone loss varied among the participating centers from less than 0.5 mm to 2.0 mm. The largest amount of bone loss occurred between the time of placement and uncovering. Following loading, the mean bone loss for all implants for a period of 3 years was about 0.2 mm/y. CONCLUSIONS: The extent of the crestal bone loss after loading was minimal for patients regardless of age, gender, prosthetic applications, bone density, and remote or crestal incisions, as well as for smokers or nonsmokers. Bone loss per year is well within the guidelines of 0.2 mm/y proposed by others.

AICRG, Part IV: Patient satisfaction reported for Ankylos implant prostheses.

PROBLEM: Although many maxillary dentures exhibit sufficient retention and stability for patients to adapt well to them, mandibular dentures present a major challenge. The introduction of the endosseous dental implant provided the opportunity for the patient to have esthetic replacements (implant prostheses) that were retentive and stable for all missing natural teeth. METHOD: This paper reports on the satisfaction of over 470 patients with implant prostheses fabricated using a new and innovative implant design (Ankylos, Dentsply-Friadent, Mannheim, Germany). RESULTS: A total of 1500 Ankylos implants were placed, restored, and followed for 3 to 5 years. Patients were asked to respond to a series of questions related to their satisfaction with their new replacements for missing natural teeth. A total of 95.6% of the patients rated chewing ability with Ankylos prosthesis as excellent to good; 92.2% indicated a significant improvement in their ability to chew; 92.6% reported overall clinical function much better than conventional dentures; 99.1% indicated that speech had improved or was not changed; 96.3% indicated hot and cold foods tasted better; 98.8% indicated no pain or discomfort during clinical function; 99.4% liked their new implant prosthesis; 98.0% would seek implant-prostheses treatment again, if necessary; 99.1% would recommend implant prostheses to friends and relatives; and 98.8% indicated the advantages of Ankylos prostheses far exceeded any disadvantages that may exist. CONCLUSIONS: Patients indicated that they (1) were highly satisfied with the final results of the replacements for their natural teeth that were retained or supported by this new implant design, (2) would not hesitate to recommend this form of treatment to their friends and relatives, and (3) would not hesitate to seek the same treatment again if necessary in the future.

AICRG, Part V: Factors influencing implant stability at placement and their influence on survival of Ankylos implants.

PROBLEM: Several factors influence primary stabilization of dental implants at placement surgery. These include implant design, bone quality, implant jaw location, and the use of a bone tap. PURPOSE: This report evaluates clinical data gathered by the Ankylos Implant Clinical Research Group (AICRG) to assess (1) the influence of several variables on primary stability and (2) the potential for an Ankylos implant (Friadent GmbH, Mannheim, Germany) that is mobile at placement to integrate and survive for at least 3 years of clinical function. METHODS: The Ankylos implant is a roughened grade-2 titanium screw. A total of 1554 implants were placed in 478 patients. At both the time of placement and abutment connection, the implants were tested for evidence of clinical mobility by attempting to rotate or move the implant with an application of force. Survival was recorded from placement and up to 36 months following placement. RESULTS: At placement, 2.8% were found to be mobile. In the maxillary posterior quadrant, 6.3% were clinically mobile. Implant mobility was frequent (12.2%) in jaw regions with poor-quality bone (BQ-4) or with short implants (8 mm = 8.3% mobile). Of the implants mobile at placement, 97.7% were stable at uncovering. The 3-year postplacement survival of initially mobile implants was 84.1% compared with 96.8% for implants not mobile at placement (chi2 test, P = .001). CONCLUSIONS: The Ankylos implant predictably promoted primary stability during surgical placement. Poor bone quality, short implants, and maxillary posterior jaw locations were all associated with a slightly higher rate of mobility at placement. Primary implant stability, while highly desirable, is not absolutely necessary for achieving osseointegration of Ankylos