Martin Freilich

DEVELOPMENT AND CLINICAL APPLICATIONS OF A LIGHT-POLYMERIZED FIBER-REINFORCED COMPOSITE

STATEMENT OF PROBLEM After 0 years of intermittent reports in the literature, the use of fiber reinforcement is just now experiencing rapid expansion in dentistry. PURPOSE This article describes the development and use of a continuous, unidirectional fiber reinforced composite as a framework for the fabrication of fixed prostheses. METHODS By using various matrix materials and fibers, a number of fiber-reinforced composite formulations were evaluated with the goal of creating a system with optimized mechanical properties and handling characteristics. Fiber-reinforced composite based on a light polymerized BIS-GMA matrix has been used clinically to make 2-phase prostheses comprised of an internal glass fiber-reinforced composite substructure covered by a particulate composite. The clinical and laboratory procedures required for the fabrication and use of reinforced composite fixed prostheses are described for laboratory-fabricated complete or partial coverage fixed prosthesis and chairside prosthesis. RESULTS Although additional clinical experience is needed, fiber-reinforced composite materials can be used to make metal-free prostheses with excellent esthetic qualities.

Principles for selecting interocclusal records for articulation of dentate and partially dentate casts

Minimizing the orientation error of the working and opposing casts on the articulator should reduce the extent of intraoral adjustment of restorations before their placement. This article defines and reviews principles such as the tripod of vertical support (three widely spaced occlusal contacts) and adequate horizontal stability, which enable opposing dental casts to be held together in a stable and reproducible manner at the time the mandibular cast is mounted to the articulator. During the restoration of the dentate or partially dentate patient, where restoration is to be coincident with pretreatment maximum intercuspation, the goal of the interocclusal record is to provide stability and/or support for the casts. The types of interocclusal records are organized into categories and designs based upon the remaining vertical support and horizontal stability of the dentition. The clinical indications, limitations, design, and composition of a variety of records for each of these categories are reviewed and discussed.

An evaluation of BMP-2 delivery from scaffolds with miniaturized dental implants in a novel rat mandible model

The purpose of this study was three-fold: (a) to develop a new small animal model to evaluate dental implant systems that recapitulates aspects of the challenging intraoral environment, (b) screen several scaffolds for in vivo bone forming efficacy when used to deliver non-glycosylated bone morphogenetic protein-2 (BMP-2) together with a miniaturized titanium (Ti) dental implant, and (c) identify correlations between in vitro BMP-2 release rates and in vivo results. The scaffolds tested were: (1) collagen-hydroxyapatite composite (Col/HA), (2) polyethylene glycol hydrogel (PEG-hydrogel), and (3) Col/HA infused with PEG-hydrogel (Col/HA/PEG-hydrogel). BMP-2 delivery directly from the Ti implants rather than from the scaffolds was also tested. MicroCT analyses at 4 weeks showed that the maximum volume and height of new bone occurred when BMP-2 (10 μg) was delivered from the Col/HA/PEG-hydrogel scaffolds. BMP-2 delivery from the Ti implant was not as effective as from the scaffolds. While in vitro BMP-2 release was highest for the PEG-hydrogel, the scaffold most successful in vivo was the Col/HA/PEG-hydrogel scaffold because it had the necessary mechanical strength to perform well in the mandibular bone environment. The in vitro release studies suggested a threshold dose of 5 μg which was borne out by the in vivo dose response studies.

Implant system for guiding a new layer of bone. Computed microtomography and histomorphometric analysis in the rabbit mandible.

OBJECTIVE To prove the concept that an implant system with osteoconductive surface characteristics and an osteoinductive scaffold material has the capacity to guide vertical supracrestal bone growth in a rabbit mandible onlay model. MATERIAL AND METHODS Thirteen adult white New Zealand rabbits each received custom-designed dental implants. All implants had sandblasted, acid-etched (SLA) surfaces, with the coronal aspect (3 mm) of each implant was left outside the lateral aspect of posterior mandibular bone, but covered by periosteum, muscle, subcutaneous tissue, and skin. Bone formation around implants placed adjacent to osteoinductive demineralized bone matrix (DBM) scaffolds were compared with contralateral implants without scaffolds in six rabbits using micro-CT imaging. Bone formation around implants with scaffolds from seven additional rabbits was measured using both micro-CT imaging and quantitative histology. RESULTS At 8 weeks, new supracrestal bone was seen adjacent to all implants placed with DBM and two implants without DBM. The mean supracrestal bone heights achieved for implants with and without DBM scaffolds as measured by micro-CT was 2.1+/-0.9 and 0.8+/-0.9 mm, respectively (P=0.008). Histomorphometric analysis illustrated that supracrestal bone-to-implant contact for implants with DBM scaffolds was 58.1+/-14% and that mean supracrestal bone height was 2.4+/-0.6 mm. CONCLUSIONS Successful implant-guided supracrestal osteogenesis has been demonstrated in a rabbit model with the combined use of osteoconductive implant surfaces, an osteoinductive scaffold, and a device that prevents soft tissue downgrowth and provides scaffold stabilization.

Growth of new bone guided by implants in a murine calvarial model

New methods to increase vertical bone growth are needed to permit dental implant placement in patients with low alveolar ridge height after extended periods of tooth loss. While ectopic rodent models are typically used to evaluate new osteogenic implant surface coatings, a more relevant intramembraneous rodent model was needed to address the particular clinical need to grow a new layer of bone above an existing layer of bone. In this study we report on a novel murine calvaria model in which successful vertical bone growth around miniaturized dental implants was achieved when using non-glycosylated bone morphogenetic protein-2 (ng/rhBMP-2). Twenty CD-1 mice received two Ti implants each consisting of a Ti ring implant stabilized by a Ti screw into the occipital calvarial bone. Four groups were evaluated: control Ti, Ti+20 mug ng/rhBMP-2, hydroxyapatite (HA)-coated Ti, and HA+20 mug ng/rhBMP-2. The mice were sacrificed 21 days following implant placement. MicroCT analysis showed no new bone formation around the untreated Ti or the HA-coated implants, but demonstrated new bone growth in every dimension around and above the Ti+ng/rhBMP-2 and the HA+ng/rhBMP-2 treated implants. Histopathologic analysis showed that a thin fibrous capsule covered the untreated Ti implants. Limited bone-to-implant contact (BIC) was observed for the HA-coated implants, while in contrast both ng/rhBMP-2 treated groups exhibited extensive new supracalvarial woven bone that covered the implant and merged with the calvarial plate. Histomorphometrically, supracalvarial bone heights and bone widths and BIC were not statistically different from one another for the two ng/rhBMP-2 treated groups. However, the total supracalvarial bone surface area was significantly greater (p<0.05) for the Ti+ng/rhBMP-2 implants (7.2 mm(2)) than the HA+ng/rhBMP-2 (4.0 mm(2)) treated implants. The bone density within 1 mm around the implant was also significantly greater (p<0.05) for the Ti+ng/rhBMP-2 implants (9.9%) than the HA+ng/rhBMP-2 (4.0%) implants, indicating that HA coatings may not be required for sustained release when non-glycosylated BMP-2 is used. This new murine model is capable of discriminating between various bone augmentation strategies and may represent a clinically more relevant model for alveolar bone augmentation than the commonly used ectopic muscle pouch or long bone models.

Three-year occlusal wear of posterior composite restorations

The specific aims of this study were to: 1) measure the occlusal wear of four different dental composite materials placed in the posterior teeth of adults; and 2) evaluate the effect of the clinical parameters, cavity class and tooth type on occlusal wear. Four different visible light-cured composite materials were used to make the restorations in this study. The restorations placed for this randomized clinical trial were scored through the use of an indirect evaluation system (M-L scale). The total sample size per recall ranged from 90 to 142 restorations from baseline to 36 months. The mean wear at 36 months for Heliomolar, J&J Experimental (Adaptic II) and P-30 was 45-54 microns, which is rather low compared to the recently reported wear of other composite materials. Marathon exhibited significantly greater wear with a mean of 174 microns at 36 months. The data also showed that cavity class and tooth type had no significant effect on the occlusal wear of the restorations made with the three low wear-rate materials, while restorations composed of the high wear-rate material exhibited more wear in molars than premolars; this effect was again not statistically significant. These data support the hypothesis that the overall wear of a composite restoration is more dependent on the materials properties than clinical parameters such as cavity class and tooth type.

Shear in Flexure of Fiber Composites with Different End Supports

The integrity of fiber-reinforced composite (FRC) prostheses is dependent, in part, on flexural rigidity. The object of this study was to determine if the flexure behavior of uniform FRC beams with restrained or simply supported ends and various length/depth (L/d) aspect ratios could be more accurately modeled by correcting for shear. Experimental results were compared with three analytical models. All models were accurate at high L/d ratios, but the shear-corrected model was accurate to the lowest, more clinically relevant, L/d values. In this range, more than 40% of the beam deflection was due to shear.

Simultaneous dental implant placement and endoscope‐guided internal sinus floor elevation: 2‐year post‐loading outcomes

AIMS To determine whether endoscope-guided sinus elevation procedures can be consistently used to create sufficient bone support for stable implant placement and long-term implant success. MATERIAL AND METHODS Sixty-two implants were surgically placed into 30 patients (14 men and 16 women) following internal sinus elevation without the use of graft material. Panoramic radiographs were made pre-, post-operative and after 24 months in order to evaluate the peri-implant bone and maxillary sinuses. Resonance frequency analysis (RFA) was used to evaluate implant stability immediately upon placement and just before prosthesis delivery. RESULTS The average pre-operative height of the maxillary alveolar bone was 8.4+/-2.2 mm at the premolar and 7.3+/-3.1 mm at the molar regions. The average bone gain was 3.5+/-1.8 and 4.5+/-1.9 mm in the premolar and molar sites, respectively. Clinical parameters and the RFA (4 and 12 weeks post-operative) outcomes show sufficient stability (ISQ=60) of the inserted implants. Three implants failed during the healing period of 12 weeks. The overall implant success rate was 94%. After loading, no further implant failure was observed. The overall success rate after beginning of implant loading was 100%. CONCLUSIONS Sinus floor elevation is a well-established procedure for augmentation of the atrophic maxillary posterior region. The minimally invasive internal sinus floor elevation procedure visually guided by an endoscope helped to prevent, diagnose and manage complications such as sinus membrane perforation. The clinical outcomes of this study show that endoscope-controlled internal sinus floor elevation combined with implant placement results in low intra operative trauma, good implant stability upon placement, low incidence of post-operative symptoms and high success rates after 24 months of loading.

Implant-guided vertical bone growth in the mini-pig.

OBJECTIVE To attain and describe guided vertical bone regeneration around titanium (Ti) and titanium zirconium (Ti-Zr) dental implants utilizing non-glycosylated recombinant human bone morphogenetic protein-2 (ng/rhBMP-2), biomaterial scaffolds and a scaffold retainer. MATERIALS AND METHODS Thirty-two modified Straumann TE implants were partially embedded in the mandibles of eight adult mini-pigs. Pre-shaped resorbable scaffolds were placed around the implant and shielded and stabilized with a newly developed Ti custom scaffold retainer (umbrella) or wide-neck (WN) healing caps to stabilize the scaffold. Ng/rhBMP-2 (50 μg) was applied to the supracrestal portion of the implant or incorporated within the scaffold. At 9 weeks, soft tissue healing was assessed. Vertical bone regeneration outcomes including bone height, bone-to-implant contact (BIC) and bone volume were assessed by micro-computed tomography and histology. RESULTS Soft tissue healing at the test sites (+ng/rhBMP-2/+scaffold) appeared to be substantially better than the control sites (-ng/rhBMP-2/-scaffold). Bone height, BIC percentage and bone volume were all similar regardless of whether WN healing caps or umbrella scaffold stabilization was used for all biomaterial scaffolds tested. WN healing cap test sites showed greater new bone height and BIC as compared with aggregate data from the control sites (P=0.05). Comparison of aggregate data from the umbrella test sites showed greater BIC and new bone volume as compared with aggregate data from the control sites(P=0.05). CONCLUSION Vertical bone regeneration was successfully attained utilizing ng/rhBMP-2, biomaterial scaffolds and a scaffold retainer.

Fixed partial dentures supported by periodontally compromised teeth

This study tested the effect of fixed partial dentures on hypermobile abutment teeth with substantially reduced levels of periodontal attachment. One abutment tooth and one control (nonabutment) tooth of the same type and periodontal condition were selected for study in adults. Treatment consisted of periodontal therapy and a 3- or 4-unit fixed partial denture, after which all subjects were placed on a quarterly maintenance schedule. No differences were found between the mean baseline and 24-month measures for all dependent variables at test or control sites.