R.R.M. Bos

RESORBABLE POLY(L-LACTIDE) PLATES AND SCREWS FOR THE FIXATION OF ZYGOMATIC FRACTURES

Ten patients with unstable zygomatic fractures were treated with resorbable poly(L-lactide) (PLLA) plates and screws. The results show that this method of fixation gives good stability over a sufficiently long period to enable undisturbed fracture healing.

Bio-absorbable plates and screws for internal fixation of mandibular fractures: A study in six dogs

Bio-absorbable plates and screws were used for internal fixation of artificially created mandibular fractures in 6 dogs. The plates and screws were fabricated from a block of poly(L-lactide) (PLLA), with a high molecular weight. The material is microporous and has excellent mechanical properties. Plates and screws were inserted in accordance with Champys principles on internal fixation. Clinical and radiographical follow-up and examination of the fracture site under general anesthesia showed that all fractures healed without callus and without complications. The plates or screws did not fail, despite the tensile strength of the PLLA used is less than stainless steel or any other metal. An explanation for their successful application may be the high impact resilience of this material. The proprioceptive mechanisms, however, that keep the dogs from maximal loading of their broken mandibles, may also play a role. Plates and screws of this bio-absorbable PLLA appear to be an attractive alternative for internal fixation of mandibular fractures and certainly for less loaded fractures of the human skeleton. The necessity to remove metallic osteosynthesis can be avoided.

Poly(L-lactide) implants in repair of defects of the orbital floor: An animal study

Because of the life-long presence of alloplastic, nonresorbable orbital floor implants and the complications of their use mentioned in literature, the use of a resorbable material appears to be preferable in the repair of orbital floor defects. A high-molecular-weight, as-polymerized poly(L-lactide) (PLLA) was used for repair of orbital floor defects of the blowout type in goats. An artificial defect was created in the bony floor of both orbits. Reconstruction of the orbital floor was then carried out using a concave PLLA implant of 0.4-mm thickness. At 3, 6, 12, 19, 26, 52, and 78 weeks postoperatively, one goat was killed. Microscopic examination showed full encapsulation of the implant by connective tissue after 3 weeks. After 6 weeks, resorption and remodeling of the bone at the points of support of the implant could be detected. A differentiation between the sinus and orbital sides of the connective tissue capsule was observed. The orbital side showed a significantly more dense capsule than the antral side, which had a loose appearance. At 19 weeks, a bony plate was progressively being formed, and at 78 weeks, new bone had fully covered the plate on the antral and orbital side. No inflammation or rejection of the PLLA implant was seen.

BONE-PLATES AND SCREWS OF BIOABSORBABLE POLY (L-LACTIDE) - AN ANIMAL PILOT-STUDY

Poly (L-lactide), a polymer of lactic acid (PLLA), with an extremely high molecular weight (Mv up to 1 x 10(6] has been synthesised under strictly controlled conditions resulting in a new microporous material with excellent mechanical properties. Bone-plates and screws machined from PLLA were used for fixation of two artificial mandibular fractures in sheep effected by a specially designed bone clamp. Fracture healing was uneventful without visible callus formation. Plates and screws of PLLA gave good stability over a sufficiently long period to enable normal fracture healing. Application in humans seems to be justified.

Closure of Oroantral Communications: A Review of the Literature

An oroantral communication (OAC) is an open connection between the oral cavity and maxillary sinus. The maxillary sinus takes up a large part of the body of the maxilla, generally extending into the alveolar process bordering the apices of the posterior teeth. OACs are usually caused by extraction of maxillary posterior teeth. 1,2 The thinness of the antral floor in that region ranges from 1 to 7 mm. 3 Although the incidence is relatively low (5%), 4,5 OACs are frequently encountered due to the large number of extractions. OACs may close spontaneously especially when the defect has a size smaller than 5 mm. 6 Nevertheless, to our knowledge, it has never been actually proven that small OACs (5 mm) will heal by themselves. Also, it is difficult to determine the size of the OAC clinically. To prevent chronic sinusitis and the development of fistulas, it is generally accepted that all of these defects should be closed within 24 to 48 hours. 7

Poly(l-lactide) bone plates and screws for internal fixation of mandibular swing osteotomies

This study evaluated bone healing after mandibular swing osteotomies fixed with biodegradable poly(L-lactide) (PLLA) bone plates in four patients. A step osteotomy treated with two PLLA bone plates (n=3), and a straight osteotomy treated with one PLLA bone plate (n=1) were performed. Bone healing was uneventful in all patients; only in the patient with the straight osteotomy was callus observed. After 5.5 years, radiologic changes at the site of implantation were observed in the remaining patient. Histologic examination revealed a nonspecific foreign-body reaction on highly crystalline PLLA remnants which were still present. It is concluded that the PLLA bone plates provided enough strength to enable undisturbed bone healing. The long-term degradation results are comparable with those of other studies on as-polymerized PLLA implants.

Co-adhesion of Oral Microbial Pairs under Flow in the Presence of Saliva and Lactose

Co-aggregation (interactions between two suspended micro-organisms) between oral microbial pairs has been studied extensively and is believed to be an important factor in dental plaque formation. However, coadhesion (interactions between suspended and already-adhering micro-organisms) may well be equally important. The aim of this paper was to determine the influence of saliva and lactose on the co-adhesion of streptococci (S. oralis 34 and S. sanguis PK1889) to actinomyces (A. naeslundii T14V-J1 or 5951) adhering on glass under flow from buffer and saliva in the absence and presence of lactose. The kinetics of co-adhesion as well as co-adhesion in a stationary end-point of co-aggregating and non-co-aggregating pairs was studied in a parallel plate flow chamber by analysis of the spatial arrangement of co-adhering micro-organisms as a function of time. For co-aggregating pairs, initial deposition rates of streptococci in the immediate vicinity of adhering actinomyces (local initial deposition rates) were up to 5 to 10 times higher than the non-local initial deposition rates in buffer and in saliva, respectively. In a stationary end-point of co-adhesion, 5 to 6 times more streptococci co-adhered with the adhering actinomyces than averaged over the entire substratum surface. A non-co-aggregating pair showed only minor preferential (co-)adhesion near the adhering actinomyces. Co-adhesion in buffer was fully lost when lactose was added. However, addition of lactose to saliva did not inhibit co-adhesion, but co-adhesion became more reversible. Detachment of micro-organisms from the substratum due to the passage of an air-liquid interface, as occurs in the oral cavity during eating, drinking, and speaking, was minimal when deposition was carried out from buffer to bare glass. Major detachment of streptococci adhering to the substratum occurred when adhesion was mediated through a salivary conditioning film on the glass, while detachment of adhering actinomyces and streptococci co-adhering with them remained low. It is suggested that, in the development of dental plaque, adhering actinomyces may act as strongholds for other micro-organisms, like streptococci, to adhere.

A three-dimensional study of bending and torsion moments for different fracture sites in the mandible: an in vitro study

The aim of the study was to determine and compare bending and torsion moments across mandibular fractures, for different positions of the bite point and different sites of the fracture. Three identical resin mandibles, each with a single fracture, were used. The fracture sites were in the angle, body and symphyseal regions. A polyethylene bone plate was used for fixation. Simulated bite forces were applied at 13 bite points. For each bite point, the displacements of the fragments were registered and converted into bending and torsion moments across the fracture. Positive bending moments were defined as those moments that caused compression at the lower border and tension at the alveolar side of the mandible; negative bending moments did the opposite. Angle fractures had relatively high positive bending moments. Body fractures had positive as well as negative bending moments and the highest torsion moments. Symphyseal fractures had negative bending moments only and relatively high torsion moments. It was found that angle, body and symphyseal fractures each have a characteristic load pattern. These load patterns should play a decisive role in the treatment of mandibular fractures with regard to number and positioning of plates.

The Influence of Barrier Membranes on Autologous Bone Grafts

In implant dentistry, there is continuing debate regarding whether a barrier membrane should be applied to cover autologous bone grafts in jaw augmentation. A membrane would prevent graft remodeling with resorption and enhance graft incorporation. We hypothesized that membrane coverage does not effect resorption and incorporation of autologous onlay bone grafts. We treated 192 male Sprague-Dawley rats. A 4.0-mm-diameter bone graft was harvested from the right mandibular angle and transplanted to the left. Poly(DL-lactide-ε-caprolactone), collagen, and expanded polytetrafluoroethylene membranes were used to cover the grafts. The controls were left uncovered. Graft resorption at 2, 4, and 12 weeks was evaluated by post mortem microradiography and microCT. Analysis of the data showed no significant differences among the 4 groups. This demonstrates that the indication of barrier membrane use, to prevent bone remodeling with resorption and to enhance incorporation of autologous onlay bone grafts, is at least disputable.

Current therapyClosure of Oroantral Communications: A Review of the Literature

An oroantral communication (OAC) is an open connection between the oral cavity and maxillary sinus. The maxillary sinus takes up a large part of the body of the maxilla, generally extending into the alveolar process bordering the apices of the posterior teeth. OACs are usually caused by extraction of maxillary posterior teeth. 1,2 The thinness of the antral floor in that region ranges from 1 to 7 mm. 3 Although the incidence is relatively low (5%), 4,5 OACs are frequently encountered due to the large number of extractions. OACs may close spontaneously especially when the defect has a size smaller than 5 mm. 6 Nevertheless, to our knowledge, it has never been actually proven that small OACs (5 mm) will heal by themselves. Also, it is difficult to determine the size of the OAC clinically. To prevent chronic sinusitis and the development of fistulas, it is generally accepted that all of these defects should be closed within 24 to 48 hours. 7