Bartolomeo Assenza

A 16-year study of the microgap between 272 human titanium implants and their abutments.

A microgap has been described at the level of the implant-abutment connection. This microgap can be colonized by bacteria, and this fact could have relevance on the remodeling of the peri-implant crestal bone and on the long-term health of the peri-implant tissues. The authors report on 272 implants with screw- or cement-retained abutments retrieved from humans for different causes during a 16-year period. In the implants with screw-retained abutments, a 60-microm microgap was present at the level of implant-abutment connection. In some areas the titanium had sheared off from the surface and from the internal threads. The contact between the threads of the implant and those of the abutment was limited to a few areas. Bacteria were often present in the microgaps between implant and abutment and in the internal portion of the implants. In implants with cement-retained abutments, a 40-microm microgap was found at the level of the implant-abutment connection. No mechanical damage was observed at the level of the implant or of the abutment. All the internal voids were always completely filled by the cement. No bacteria were observed in the internal portion of the implants or at the level of the microgap. The differences in the size of the microgap between the two groups were statistically significant (P < .05). In conclusion, in screw-retained abutments the microgap can be a critical factor for colonization of bacteria, whereas in cement-retained abutments all the internal spaces were filled by cement. In these retrieved implants, the size of the microgap was markedly variable and much larger than that observed in vitro.

Bacterial Leakage in Implants With Different Implant–Abutment Connections: An In Vitro Study

BACKGROUND Two-piece implants present gaps and cavities between the implant and the abutment, and these hollow spaces can act as a trap for bacteria. The aim of the present in vitro study was to evaluate the migration of two different microbial species from the inside to the outside of the implant-abutment assembly in three different connection types. METHODS A total of 30 implants (10 implants per group) were used. The implants presented a screwed trilobed connection (group 1), a cemented connection (group 2), and an internal conical connection (group 3). The inner parts of five implants, per group, were inoculated with Pseudomonas aeruginosa suspension and the remaining five implants, per group, with Aggregatibacter actinomycetemcomitans. The penetration of bacteria into the surrounding solution was determined by the observation of turbidity of the broth. RESULTS In group 1, bacterial contamination was found in six of 10 implants. In group 2, no contaminated samples were found. In group 3, bacterial contamination was found in one implant of 10. Statistically significant differences were detected between group 1 versus group 3 (P <0.05) and between group 1 versus group 2 (P <0.01), whereas no significant differences were found when comparing group 2 versus group 3 (P >0.05). CONCLUSION The present study confirms previous results about the hermeticity of the cement-retained implant-abutment assembly, the very low permeability to bacteria of the conical implant-abutment connection, and the high prevalence of bacterial penetration of screw-retained implant-abutment assemblies.

Infrared thermographic evaluation of temperature modifications induced during implant site preparation with cylindrical versus conical drills.

BACKGROUND A few studies have investigated the influence of drilling on bone healing. Many factors have been reported to influence temperature rise during surgical preparation for implant placement: drill geometry, drilling depth, sharpness of the cutting tool, drilling speed, pressure applied to the drill, use of graduated versus one-step drilling, intermittent versus continuous drilling, and use or not of irrigation. PURPOSE The objective of this study was to quantify the temperature changes in cortical bone and at the apical portion of the drills during implant site preparation with a cylindrical implant drill versus a conical implant drill. MATERIALS AND METHODS Two implant drill systems were evaluated in vitro using bovine femoral cortical bone. The two implant drill systems evaluated in this study were system A (a cylindrical drill with triple twist drills) (Bone System, Milano, Italy) and system B (a conical drill with quadruple twist drills) (Bone System). Site preparation began, and the temperature of the cortical bone and at the apical portion of the drill was measured by the infrared thermography. RESULTS The mean temperature produced in the cortical bone during implant preparation was 31.2 ± 0.5°C for the cylindrical drills and 29.1 ± 0.6°C for the conical drill. The mean temperature produced in the apical portion of the drill during implant site preparation was 32.1 ± 0.7°C for the cylindrical drill system and 29.6 ± 0.6°C for the conical drill. Statistically significant differences were found in the temperature measurements in the cortical bone in the two groups (p < .05). A statistically significant difference was observed for the temperature measurements in the apical portion of the drill in the two groups (p < .005). DISCUSSION The model system used in this work was able to evaluate the temperature in the cortical bone and in the apical portion of the drills; the temperature modifications in the apical portion of the drill seemed to be correlated to the drill geometry. The results of the present study showed that drill geometry seems to be an important factor in heat generation during implant site preparation. CONCLUSION The drill geometry could explain the increased temperature in the apical portion of the drill.

Localized Ridge Augmentation Using Titanium Micromesh

Guided bone regeneration (GBR) has been used recently for the regeneration of bone in conjunction with the placement of dental implants, for augmentation of resorbed alveolar crests, and to treat localized ridge deformities. Twenty-two patients with alveolar crest defects or peri-implant dehiscences participated in this study. Titanium implants were inserted, and the defects were covered with a titanium micromesh, above which was positioned an e-PTFE membrane. After healing, the 2 membranes were removed and a small specimen of the underlying tissues was retrieved with a small trephine. The postoperative healing was mostly uneventful, and only a few dehiscences with membrane exposure were observed. The space under the membranes was, in all patients, filled by a tissue with the macroscopic features of newly formed bone. No residual bone defects were observed and an increase of the alveolar width or height was observed. No untoward effects on bone regeneration were observed in the cases with membrane exposure. Histology showed that the underlying regenerated tissues were composed, in all cases, by newly formed bone. In conclusion, our results show that very satisfactory results concerning GBR techniques can be obtained even without the use of grafts under barrier membranes.

Vertical ridge augmentation of atrophic posterior mandible using an inlay technique with a xenograft without miniscrews and miniplates: case series

BACKGROUND Rehabilitation of partially or totally edentulous posterior mandible with implant-supported prosthesis has become a common practice in the last few decades, with reliable long-term results. The use of miniscrews and miniplates have been reported to increase the risk of fracture of the osteotomy segments. The purpose of this case series was to use an inlay technique, without the use of miniscrews and miniplates for stabilization of the transported bone fragments. MATERIALS AND METHODS Nine consecutive patients (six men and three women) aged between 26 and 51 years (mean 44 years) were enrolled in this study. A horizontal osteotomy was performed 2-3 mm above the mandibular canal, and two oblique cuts were made using a piezosurgery device. The final phase of the osteotomy was performed with chisels. The osteotomized segment was then raised in the coronal direction, sparing the lingual periosteum. Two miniblocks of xenograft without miniscrews and miniplates were inserted mesially and distally between the cranial osteotomized segment and the mandibular basal bone. The residual space was filled with particles of cortico-cancellous porcine bone. Four months after surgery, a panoramic X-ray was taken before implant insertion. A bone trephine with an internal diameter of 2 mm was used as the second dental drill to take a bone core biopsy during preparation of the #35 and #37 or #45 and #47 implant sites. RESULTS The postoperative course was uneventful in seven of the nine patients. No dehiscence of the mucosa was observed at the marginal ridge of the mobilized fragment. Newly formed bone was present near the osteotomized segments, and was observed in the bottom half of the specimens and was identified by its higher affinity toward the staining. Newly formed bone was observed to be in close contact with the particles of biomaterials. No gaps or connective tissue were present at the bone-biomaterial interface. Histomorphometry demonstrated that 44±2.1% of the specimens was composed by newly formed bone, 18±0.8% by marrow spaces, and 33±2.4% by the residual grafted biomaterial. CONCLUSION The rigidity of the equine collagenated block allowed to eliminate the use of miniscrews and miniplates and simplified the technique. Moreover, the rigidity of the block allowed maintenance of the space.

Screw- vs Cement-implant–retained Restorations: An Experimental Study in the Beagle. Part 1. Screw and Abutment Loosening

The causes of implant failures can be biological or mechanical. The mechanical causes include fracture of the implant, fracture of the abutment, and loosening of the abutment. Numerous studies show that abutment loosening constitutes one of the marked implant postsurgery complications requiring clinical intervention. The aim of the present study was to evaluate the incidence of the screw loosening in screwed or cemented abutments. Six adult male Beagles were used. In each dog, the first molars and 2 premolars were extracted. The sutures were removed after 7 days. After 3 months, 10 implants were placed in each dog, 5 in the right mandible and 5 in the left mandible. The abutments either were screwed in (n=30) by applying a total strength of 30 N/cm or were cemented (n=30). After 12 months, 8 (27%) loosened screws were present in screwed abutments, whereas no abutment loosening was observed in cemented abutments (P = .0001). Screwed abutments are often submitted to nonaxial loads that determine screw and abutment loosening.

Interimplant distance and crestal bone resorption: a histologic study in the canine mandible.

BACKGROUND Crestal bone loss has been shown to occur around dental implants. This crestal bone resorption may determine a more apical position of the gingival margin. A clear trend of increased bone loss with increased interimplant distance has been reported. PURPOSE The aim of the present study was to evaluate, in the canine mandible, the crestal bone behavior around dental implants inserted with different interimplant distances. MATERIALS AND METHODS Sandblasted and acid-etched implants (Bone System, Milano, Italy) were placed in the mandibles of six beagle dogs. Each dog received 10 implants in the mandible (five in the right side and five in the left side). A total of 60 implants was used in this study. The implants were divided in four groups: group I, with a 2 mm interimplant distance; group II, with a 3 mm interimplant distance; group III, with a 4 mm interimplant distance; and group IV, with a 5 mm interimplant distance. The dogs were killed after 12 months. RESULTS No statistically significant differences were found in regard to vertical bone loss whereas on the contrary, statistically significant differences were found in regard to lateral bone loss (p = .0001). Statistically significant differences also were found in regard to vertical crestal bone loss (p = .0001). In fact vertical crestal bone loss decreased, from 1.98 mm in group I to 0.23 mm in group IV. CONCLUSIONS The clinical significance of these data lies in the fact that the increased crestal bone loss results in an increase in the distance between the base of the contact points of the neighboring implants and the crest of bone, and this fact could determine whether the papilla is present or absent between two implants.

Assessment of Pain Associated with Insertion Torque of Dental Implants. A Prospective, Randomized-Controlled Study

This study investigated pain experience following dental implant placement in relation to insertion torque using questionnaires. A total 80 implants were placed in 20 patients. Each patient received 4 implants at different times. One implant was inserted and, then, after 40 days was placed the second implant, after 80 days was placed the third implant and after 120 days was placed the fourth implant. At each time the peri-implant bone levels were evaluated on intraoral radiographs taken with the paralleling technique. The implants were placed with a dynamometric key at 35N, 50N, 65N, 85N. Patients were asked to evaluate their pain experience during surgery, 24 hours after surgery, and at 2 days, 4 days, 1, 2, and 4 weeks after surgery on special pain assessment forms. A separate form was used for each time point. Pain was assessed using a descriptive numerical rating scale of 0 to 10, with 0 indicative of no pain and 10 representing the worst pain imaginable. Patients were instructed that a score of 1 to 3 was indicative of mild pain, 4 to 6 was indicative of moderate pain, and 7 to 10 was indicative of severe pain. A significant correlation pain scores and insertion torque was found between group III and group IV vs group II and group I during surgery, at 24 hours, 2 days, 4 days, 1 week, 2 weeks p⩽0.05. No statistical difference was found between group I vs. group II during surgery, at 24 hours, 2 days, 4 days, 1 week, 2 weeks p⩾0.05. In conclusion, elevated insertion torque values produces pain and resoption of the crestal bone around the implants.

Screw vs Cement-Implant–retained Restorations: An Experimental Study in the Beagle. Part 2. Immunohistochemical Evaluation of the Peri-implant Tissues

Crestal bone loss has been reported to occur around dental implants. Even if the causes of this bone loss are not completely understood, the presence of a microgap between implant and abutment with a possible contamination of the internal portion of the implants has been suggested. The aim of this study was to see if there were differences in the vascular endothelial growth factor (VEGF) expression, microvessel density (MVD), proliferative activity (MIB-1), and inflammatory infiltrate in the soft tissues around implants with screwed and cemented abutments. Sandblasted and acid-etched implants were inserted in the mandibles of 6 Beagle dogs. Ten 3.5- x 10-mm root-form implants were inserted in each mandible. A total of 60 implants (30 with screwed abutments and 30 with cemented abutments) were used. After 12 months, all the bridges were removed and all abutments were checked for mobility. A total of 8 loosened screws (27%) were found in the screwed abutments, whereas no loosening was observed in cemented abutments. A gingival biopsy was performed in 8 implants with cemented abutments, in 8 implants with screwed abutments, and in 8 implants with unscrewed abutments. No statistically significant differences were found in the inflammatory infiltrate and in the MIB-1 among the different groups. No statistically significant difference was found in the MVD between screwed and cemented abutments (P = .2111), whereas there was a statistically significant difference in MVD between screwed and unscrewed abutments (P = .0277) and between cemented and unscrewed abutments (P = .0431). A low intensity of VEGF was prevalent in screwed and in cemented abutments, whereas a high intensity of VEGF was prevalent in unscrewed abutments. These facts could be explained by the effects induced, in the abutments that underwent a screw loosening, by the presence of bacteria inside the hollow portion of the implants or by enhanced reparative processes.

Osteoclast activity around loaded and unloaded implants: A histological study in the beagle dog

The mechanisms of bone loss around dental implants are poorly understood. The osteoclast is the most important bone-resorbing cell. Humoral factors seem able to stimulate the differentiation of osteoclasts from mononuclear phagocytes. Bacterial lipopolysaccharides seem to be directly involved in inflammatory bone loss by stimulation of the survival and fusion of preosteoclasts. Excessive load seems to be able to cause bone loss. The aim of this paper was to evaluate the presence and number of osteoclasts in peri-implant bone in control (unloaded) and test (loaded) implants in order to determine if loading per se could be a contributing factor in peri-implant bone resorption. Forty-eight implants were inserted in the mandibles of 4 beagle dogs. After 3 months, a prosthetic superstructure was inserted on 24 implants, whereas in 24 implants only the healing screws were positioned. Twenty-four implants (12 test and 12 control) were retrieved at 6 months, and 24 implants (12 test and 12 control) were retrieved at 12 months. All implants were osseointegrated. The number of osteoclasts found in the crestal bone in the first 3 mm from the implant surface was evaluated. The mean number of osteoclasts were the following: control implants (6 months), 5.66 +/- 0.81; control implants (12 months), 2.55 +/- 1.05; test implants (6 months), 5.25 +/- 1.55; and test implants (12 months), 2.5 +/- 1.0. No statistically significant differences were observed between the control and test implants. According to our data, loading does not seem to have a relevant importance on the osteoclast activation in peri-implant bone.