Steven M. Morgano

An in vitro study of the fracture resistance and the incidence of vertical root fracture of pulpless teeth restored with six post-and-core systems☆☆☆

STATEMENT OF PROBLEM Posts and cores are often required with pulpless teeth to provide retention and resistance form for complete crowns. Nevertheless, conventional posts may increase the potential for root fracture. PURPOSE This study compared the resistance to vertical root fracture of extracted teeth treated with post-core systems that were modified with polyethylene woven fibers (Ribbond) with those treated with conventional post-and-core systems. MATERIAL AND METHODS Canal instrumentation was performed for 60 maxillary central incisors, and complete crown preparations were made. The coronal portion of each tooth was amputated, and 6 post-and-core systems were studied. Specimens were mounted in acrylic resin blocks with a layer of polyvinyl siloxane covering the roots. Loads were applied at an angle of 130 degrees and measured with a universal testing machine. Results were analyzed statistically with 1-way analysis of variance with Student-Newman-Keuls grouping and chi-square analysis. RESULTS. Cast posts and cores resulted in significantly higher failure thresholds than all others, except for prefabricated, comparably sized, parallel-sided posts with composite cores. All failures in the group with cast posts involved fracture of the teeth, whereas 70% of the teeth with comparably sized parallel-sided posts and composite cores failed as a result of tooth fractures and 30% experienced core fractures. The woven fiber post-core system was significantly lower in strength than all others, and exhibited significantly fewer vertical root fractures. CONCLUSIONS Polyethylene woven fiber and composite resin without a prefabricated post resulted in significantly fewer vertical root fractures, but mean failure load was the lowest. Smaller diameter prefabricated posts combined with the polyethylene woven fiber and composite cores improved resistance to failure. Traditional cast posts and cores were the strongest of the 6 post-core systems.

Restoration of pulpless teeth: Application of traditional principles in present and future contexts

Posts were recommended more than 100 years ago to retain artificial crowns. Recent studies suggest that posts can weaken teeth; therefore restorative procedures that help preserve pulpal vitality and eliminate the need for posts are desirable. If endodontic therapy is unavoidable, conservation of remaining tooth structure is most important. When a post is required to retain a core for an artificial crown, a custom cast post is the most effective means of conserving tooth structure. The length of the post should not be compromised, although 4 to 5 mm of apical gutta-percha must be maintained. The restorative prognosis is improved if the width of the post does not exceed one half the width of the root, and the cemented artificial crown should extend apical to the core to provide a 1.5 to 2 mm ferrule. Complex procedures have allowed the dentist to restore extensively damaged teeth. However, extraction and replacement with implant-supported prosthodontics may be more prudent with severely compromised teeth.

Foundation restorations in fixed prosthodontics: Current knowledge and future needs

PURPOSE The Ad Hoc Committee on Research in Fixed Prosthodontics established by the Academy of Fixed Prosthodontics publishes a yearly comprehensive literature review on a selected topic. The subject for this year is foundation restorations. METHODS Literature of various in vitro and in vivo investigations that included technical and clinical articles was reviewed to provide clinical guidelines for the dentist when selecting methods and materials for restoration of structurally compromised teeth. Topics discussed and critically reviewed include: (1) desirable features of foundation restorations, (2) foundations for pulpless teeth, (3) historic perspectives, (4) cast posts and cores, (5) role of the ferrule effect, (6) prefabricated posts, (7) direct cores, (8) foundation restorations for severely compromised teeth, (9) problems and limitations, (10) future needs, and (11) directions for future research. CONCLUSION This comprehensive review brings together literature from a variety of in vitro and in vivo studies, along with technique articles and clinical reports to provide meaningful guidelines for the dentist when selecting methods and materials for the restoration of structurally compromised teeth.

Clinical success of cast metal posts and cores

The topic of posts for endodontically treated teeth has received considerable attention in the literature, but there is sparse in vivo research and certain information from in vitro investigations is contradictory. A retrospective study of 1273 endodontically treated teeth in the practices of nine dentists in general practice indicated an inordinately high failure rate with cast posts and cores compared with alternate systems of coronoradicular stabilization. However, a closer evaluation of the data in this study indicated that almost half of the cast posts were half the desired length or less. The indications for the cast post and core are discussed and the specific causes of failure are reviewed. Additional research is needed to compare the success rate of securely seated cast posts and cores with alternate methods of coronoradicular stabilization.

Complete edentulism and denture use for elders in New England

The purpose of this study was to collect information about the oral health of a representative group of elders in the New England states. This study provides the most current descriptive analysis of completely edentulous noninstitutionalized elders to date. In-home examinations and interviews were conducted for a representative sample of elders over 70 years of age. The oral examinations and interviews were conducted by calibrated dentists and trained interviewers, respectively. Of 1156 study participants, 424 (36.7%) were edentulous. Edentulous rates were similar for men and women and were negatively related to levels of education and income. Of the completely edentulous individuals, 89.9% had maxillary and mandibular complete dentures. Most of these dentures (83.2%) were worn during the day. More than one third of the respondents reported wearing one or both of their dentures while sleeping at night. For 77 of the completely edentulous individuals, examination revealed denture irritations, most of which were on the hard palate.

A nationwide survey of contemporary philosophies and techniques of restoring endodontically treated teeth

Contemporary endodontic therapy has allowed patients to retain severely damaged teeth. The restoration of most endodontically treated teeth involves complex and controversial procedures. There is a diversity of opinion about the need for coronoradicular stabilization, and numerous post systems and techniques have been described. It is not known what materials and techniques are most commonly used. To expand the knowledge of current philosophies and prevailing techniques, a comprehensive nationwide survey of 1525 dentists was conducted. Of the 1066 respondents, 909 (85%) reported restoring more than 30 endodontically treated teeth per year, and this subset became the focus group of the survey. Board-certified prosthodontists comprised 40% of this group, educationally qualified prosthodontists 28%, and general dentists 32%. Responses to questions were statistically analyzed. Statistical analysis revealed that philosophies and techniques varied significantly with the dentists geographic location, age, specialty status, and dental school faculty status.

Effects of chemical disinfectant solutions on the stability and accuracy of the dental impression complex

Currently available impression materials were not designed for disinfection or sterilization, and it is conceivable that disinfectants may adversely affect impressions. This study evaluated the accuracy and dimensional stability of polyether (Permadyne/Impregum) and polyvinyl siloxane (Express) impression materials retained by their adhesives in two different acrylic resin tray designs (perforated and nonperforated) when the materials were immersed for either 30 or 60 minutes in three high-level disinfectants. Distilled water and no solution served as controls. A stainless steel test analog similar to ADA specification No. 19 was used. A total of 400 impressions were made with all combinations of impression materials, tray designs, disinfectant, and soaking times. Samples were evaluated microscopically before and after immersion and 48 hours after soaking. Results indicated that these two impression materials were dimensionally stable. Because the results emphasized the stability and accuracy of the impression complex under various conditions, dentists can perform disinfection procedures similar to the protocol of this study without concern for clinically significant distortion of the impression.

A dual-purpose stent for the implant-supported prosthesis

Osseointegrated implants are a practical alternative to traditional prosthodontics; however, designing an implant-supported prosthesis with function and esthetics is a challenge. When the available bone or the location of vital structures is questionable, computed tomography (CT) is indispensable for diagnosis and treatment planning. This article describes a stent that implements the information from a CT scan and is then modified to guide the surgical placement of the implants.

The effect of temperature changes on the dimensional stability of polyvinyl siloxane and polyether impression materials

STATEMENT OF PROBLEM Dental impressions are commonly mailed to remote dental laboratories and can be subjected to extreme temperature changes; however, the effects of these temperature changes on the accuracy of elastomeric impression materials are unknown. PURPOSE This study evaluated the dimensional changes of polyether and polyvinyl siloxane impression materials as a function of storage temperature. MATERIAL AND METHODS A total of 144 impressions were made of a stainless steel die similar to ADA Specification No. 19. Half of the impressions were made in perforated custom trays and the other half in solid trays. Measurements of the vertical and horizontal lines on the impressions were made at 10 minutes, 1 hour, 24 hours, and 26 hours, and storage temperatures ranged from 4 degrees C to 40 degrees C. RESULTS Changes in storage temperature had a statistically significant effect on the dimensional stability of the horizontal and vertical lines. However, overall dimensional changes were extremely small. CONCLUSIONS Storing both impression materials at 4 degrees C for 24 hours and then allowing the impressions to reach room temperature resulted in a slightly expanded impression that partially compensated for the contraction that occurred from polymerization shrinkage. Similar results occurred for polyether material only, when stored at 40 degrees C.

Photoelastic stress analysis of external versus internal implant-abutment connections

STATEMENT OF PROBLEM Common complications of implant restorations are abutment screw loosening and screw fracture. The geometry of the implant-abutment connection may affect stresses generated from loading, and these stresses may have a role in screw loosening or fracture. PURPOSE This study compared the load transfer characteristics of a complete-arch restoration supported by 4 implants with external and internal implant-abutment connections. Loads were applied to the prostheses in 3 positions. MATERIAL AND METHODS Two-dimensional photoelastic models were used to simulate bone. Two types of implants (ReplaceSelect Internal-Interface Tapered Implants and ReplaceSelect External-Interface Tapered Implants) were placed in the photoelastic models. Complete-arch metal frameworks were fabricated on the abutments. Artificial teeth were arranged on the framework, and the prosthesis was screwed onto the abutments. The specimens were analyzed at 2 levels (implant-abutment level and apical to the implant level) with 3 loading conditions (4-point load; 2-point anterior load; and 2-point lateral load). The numbers of fringe orders were recorded and compared. RESULTS With the 4-point load, no stress differences occurred between the external-implant abutment connection and internal-implant abutment connection at the connection level and at the apical level. With the 2-point anterior load, the internal-implant abutment connection resulted in lower stresses at the connection level both in the loaded and non-loaded areas. With the 2-point lateral load, the internal-implant abutment connection resulted in lower stresses at the connection level at the non-loaded area. CONCLUSIONS When loaded off-center, the internal-implant abutment connection produced less stress when compared with the external-implant abutment connection.