Brien R. Lang

Clinical methods for evaluating implant framework fit

STATEMENT OF PROBLEM Passive fit of implant-supported-prosthesis frameworks has been suggested as a prerequisite for successful long-term osseointegration. However, there are no scientific guidelines as to what is passive fit and how to achieve and measure it. PURPOSE The purpose of this article is to discuss passive fit and to review the various clinical methods that have been suggested for evaluating implant framework fit.Methods. The dental literature was reviewed to identify the clinical methods that have been used to evaluate implant framework fit. CONCLUSIONS The suggested levels of passive fit are empirical. Numerous techniques have been advocated to evaluate the prosthesis-implant interface, but none individually provides objective results. It is suggested that clinicians use a combination of the available methods to minimize misfits.

Precision of fit: The Procera AllCeram crown

STATEMENT OF PROBLEM Strength, color stability, and precision of fit are requirements for all-ceramic restorations. The Procera AllCeram crown system, composed of a densely sintered high-purity alumina core combined with a low fusing surface porcelain, appears to satisfy most of these requirements. However, evaluation of marginal fit has not been reported. PURPOSE This study measured the precision of fit of the Procera AllCeram crown fabricated with Procera CAD/CAM technology for the premolar and molar teeth fit to a die. MATERIAL AND METHODS Five ivorine maxillary first premolars and first molars were prepared for full-coverage crowns. Preparations were standardized with a convergence angle of 10 degrees, chamfer margins of 1.3 to 1.5 mm circumferentially, and occlusal reduction of 2.0 mm. AllCeram crowns were fabricated for the dies, and the fit of the crown to the die was determined by using a standardized procedure with a silicone impression material that served a dual role: (1) as a retrievable luting agent, and (2) to replicate the internal aspects of the crown. Laser videography was used to measure the gap dimension between the crowns and the dies at the marginal opening, the axial wall, the cusp tip, and the occlusal adaptation measurement locations. Mean gap dimensions and standard deviations (SDs) were calculated for marginal opening, internal adaptation, and precision of fit. RESULTS Mean gap dimensions and standard deviations at the marginal opening for the premolar and molar crowns were 56.0 microns SD +/- 21 and 63.0 microns SD +/- 13 microns, respectively. The mean gap dimensions and SDs of the internal adaptation were 69.0 microns SD +/- 17 microns for axial wall, 48.0 microns SD +/- 12 microns for cusp tip, and 36.0 microns SD +/- 7 microns for occlusal adaptation for the premolar crowns; and 49.0 microns SD +/- 3 microns axial wall, 67.0 microns SD +/- 21 microns cusp tip, and 74.0 microns SD +/- 29 microns occlusal adaptation for molar crowns. Precision of fit and SDs for premolar and molar crowns were 52.0 microns SD +/- 19 microns and 63.0 microns SD +/- 20 microns, respectively. Mean marginal openings and precision of fit gap dimensions for the crown groups were not significantly different at the .05 level. However, gap dimensions that defined the internal adaptation at the measurement locations were different (P < or = .05). CONCLUSION Mean gap dimensions for marginal openings, internal adaptation, and precision of fit for the crown groups were below 70 microns. These findings show that the crowns studied can be prescribed with confidence knowing that the precision of fit will consistently be less than 70 microns.

Measuring fit at the implant prosthodontic interface

Four centers in the United States and Sweden have been working for 2 years to develop systems and methods for measuring fit at the prosthodontic interface. Two systems are based on stylus contact techniques, one system uses a laser as its reader source, and one system is photogrammetric. All the systems are capable of providing data as three-dimensional x, y, and z axes coordinate values that can be transformed into linear and angular data that characterize the bearing surfaces of abutments or abutment replicas and their mating components in the prosthesis framework. The centroid, a single point computed from the collected data, was the measurement unit, derived for these bearing surfaces, that was used to compare the systems. All four methods can most likely detect misfits that are relevant in the clinical setting; however, only one system can be used intraorally. When any measurement system is assessed, the data should always be examined for repeatability to establish the reliability of the system. This investigation made comparisons among the measurement methods used at the four centers. It was apparent from this study that comparisons of data from measurement systems should be rounded to the nearest 10 microns. The SDs determined in the comparisons were larger than 5 microns and therefore misfits should be calculated in terms smaller than 10 microns. This final point is important to the clinician who relies on research reports about precision of fit when selecting treatment approaches in caring for the implant prosthodontic needs of their patients.

Critical evaluation of patient responses to dental implant therapy

STATEMENT OF PROBLEM Successful rehabilitation of the edentulous condition requires functional and psychosocial adaptation by the patient. Quality of life is markedly affected by the amount of satisfaction or dissatisfaction with their dental therapy. Patient concerns are primarily related to comfort, function, and esthetics. When these do not meet the patients expectations, anxiety, insecurity, diminished self-esteem, and introversion are typical psychosocial responses. PURPOSE The objectives of the study were to assess the patients subjective feelings about: (a) comfort, (b) function, (c) esthetics, (d) speech, (e) self-image, and (f) overall dental health with their existing complete dentures, and after implant therapy and prosthodontic rehabilitation. MATERIAL AND METHODS Two health-related quality of life (HRQL) questionnaires were developed to evaluate the effectiveness of dental implant therapy; one dealing with their feelings about their conventional complete dentures, and the second dealing with implant therapy. The first questionnaire was administered with supervision before receiving implant treatment. The second questionnaire was administered within 1 year after completion of prosthetic rehabilitation. Twenty-six patients who received implants to support a mandibular prosthesis and a new maxillary denture formed the experimental population. RESULTS Discriminative and evaluative analysis of subjective patient responses provided reliable, accurate, and reproducible results. Assessment of subject feelings before and after implant therapy and prosthodontic rehabilitation demonstrated significant differences when before treatment responses were compared with the responses after therapy. CONCLUSIONS Significant differences for comfort, function, speech, esthetics, self-image, and dental health were demonstrated when conventional complete dentures and dental implant therapy were compared. HRQL data provided scientific evidence of an improved quality of life after dental implant therapy (p < 0.000).

Changes in jaw relations, hyoid position, and head posture in complete denture wearers

In a group of 18 partially edentulous patients provided with immediate complete dentures, changes in hyoid bone position and craniocervical posture were examined on cephalometric radiographs made during 1 year of denture use. The findings indicated that the changes in hyoid bone position largely followed the pattern of forward-upward rotation of the mandible due to ridge resorption. During this course the hyoid position in relation to the cervical spine showed a mean increase. The hyocervical changes, however, showed less variability than the hyomaxillary and hyomandibular changes. The posture of the head and cervical column showed no definite mean changes during the 1-year period. On the other hand, analysis of individual changes revealed that a pronounced decrease in mandibular inclination due to ridge resorption was associated with retroclination of the cervical column and decreased craniocervical angulation. These postural changes may be regarded as adaptive changes to a marked initial change in mandibular position.

The precision of fit at the implant prosthodontic interface

STATEMENT OF PROBLEM Percussion, visual observation, and conventional periapical radiographs are the methods most frequently used clinically to evaluate the accuracy of implant component assemblies, whereas methods to measure the precision of fit are limited. PURPOSE In this study the Periotest instrument was used to evaluate the stability of the interfaces between the implant and the abutment, along with the abutment and the gold cylinder under a series of assembly conditions. The hypothesis tested is that a more negative Periotest value (PTV) would indicate an accurate fit and a more positive value PTV would correlate with an inaccurate fit. MATERIAL AND METHODS To investigate this hypothesis in vitro, two bovine ribs were used as patient simulation models. Each model contained three self-tapping Brånemark implants placed approximately 7 to 10 mm apart and arranged in a reasonable curvature. A series of component assembly conditions were created as accurate and inaccurate with thickness gauges of 25.4 microns, 50.8 microns, and 101.6 microns. RESULTS The mean Periotest values and SDs for accurately assembled abutments and gold cylinders were -6.0 +/- 0.32 and -3.4 +/- 0.68, respectively. Periotest value data of the assembly conditions were statistically analyzed with multiple regression analysis. The misfit in the implant to abutment interface resulted in a more negative Periotest value trend (r = 0.54) with increases in gauge thickness. However, the same magnitudes of misfit at the abutment to gold cylinder interface produced a more positive Periotest value trend (r = 0.72). CONCLUSION The PTV trends were consistent with increased stability at the abutment to implant interface from the increasing magnitude of misfit created with the thickness gauges. In contrast, the measurement trends observed for the abutment to gold cylinder interface were consistent with decreased stability with each increase in gauge thickness inserted at the interface.

Silane to enhance the bond between polymethyl methacrylate and titanium

The machined surface of wrought titanium frameworks used in implant-supported, fixed prostheses does not bond well with acrylic resin. Surface pretreatment has been suggested to enhance the retention of polymethyl methacrylate to machined titanium surfaces. This study evaluated a new bonding material (Rocatec) to determine its effect on the bond strength between titanium and polymethyl methacrylate. Twenty rod-shaped specimens of grade 2 titanium (7.6 x 0.3 cm in diameter) were divided into two groups of 10 samples. Group A received no pretreatment and group B was pretreated with 110 microns alumina air abrasive and the Rocatec material. Heat-cured denture base resin was processed around each titanium sample in a cylindrical shape approximately 0.9 x 1.5 cm. A Shell-Nielsen shear test was performed with a universal testing machine at a crosshead speed of 0.5 mm/minute to determine the bond strength in megapascals (MPa). Group B specimens (23.8 +/- 1.78 MPa) had a shear strength 68% greater than group A (16.1 +/- 1.61 MPa) (p 0.0001). The results of this study indicated that surface pretreatment of grade 2 titanium with 110 microns alumina air abrasive plus Rocatec bonding material significantly enhances the shear bond strength to PMMA.

In vivo wear. Part I: The Michigan computer-graphic measuring system

Three-dimensional coordinate measuring machines for examining the quality of industrial castings were reviewed. The concept was modified and successfully converted to examine the minute geometric configurations of the surfaces of dental materials. The wear of composites has undoubtedly precipitated this perceptive, thorough study.

Lingualized integration: tooth molds and an occlusal scheme for edentulous implant patients.

The interface of bone and soft tissue to dental implants has been extensively documented, while the influence of biomechanics and the occlusal interface continues to be overlooked. Yet that same occlusal interface may ultimately be the prime factor in the lifetime survival rate of dental implants. What is lacking, for the practitioner, is a clear concept of the occlusal rehabilitation which is required and appropriate for the totally edentulous implant patient. Lingualized integration represents an occlusal scheme using specific tooth molds designed to improve the likelihood of maximum intercuspation and an absence of deflective occlusal contacts, provide cusp height for selective occlusal reshaping, and achieve a natural and pleasing appearance. Factors in the articulation and arrangement of the posterior teeth to assure the attainment of the fundamental goals of comfort, function, and appearance in occlusal rehabilitation for edentulous implant patients are included. (Implant Dent 1992;1:204-211)

Jaw muscle activity in complete denture wearers—A longitudinal electromyographic study

EMG study of subjects wearing immediate complete upper and lower dentures revealed marked alterations in activity of the jaw closing muscles during the biting actions recorded. This finding suggests that changes in jaw and occlusal relationships due to resorption of residual ridges and settling of the dentures also affects jaw muscle activity. The relations between EMG and morphologic findings will be analyzed further in a separate article.