Mechanical Response of Bone under Short-term Loading of a Dental Implant with an Internal Layer Simulating the Nonlinear Behaviour of the Periodontal Ligament

We consider a non-standard design for a fixed dental implant, incorporating a soft layer which simulates the presence of the periodontal ligament (PDL). Instead of being aimed at causing an a priori defined stress/strain field within the surrounding bone, upon loading, such a design simply tries to better reproduce the natural tooth–PDL configuration. To do this, the mechanical properties of the internal layer match those of the PDL, determined experimentally to be strongly nonlinear. Three-dimensional finite element analyses show that the presence of such a layer produces (i) a prosthesis mobility very similar to that of a healthy tooth, for several loading conditions, and (ii) a stress/strain distribution substantially different from that arising, upon loading, around a conventional implant. The lack of knowledge of the real mechanical fields existing, under loading, in the bone around a healthy tooth makes it very difficult to state that the stress distribution produced by the modified implant is “better” than that produced by the standard one. Nevertheless, the comparison of the results obtained here, with those of previous refined analyses of the tooth–PDL–bone system, indicates that the modified implant tends to produce a stress distribution in the bone, upon loading, closer to “natural” than that given by the standard one, within the limits imposed by the presence of threads coupling the implant with the bone.     

Finite Element Modelling and Simulations in Dentistry: A Bibliography 1990–2003

The paper gives a bibliographical review of the finite element modelling and simulations in dentistry from the theoretical as well as practical points of view. The bibliography lists references to papers, conference proceedings and theses/dissertations that were published between 1990 and 2003. At the end of this paper, more than 700 references are given dealing with subjects such as: dental materials; oral and maxillofacial mechanics and surgery; orthodontics, tooth movement, orthodontic appliances; root canals, filling and therapy; dental restorations and other topics.     

Effect of electromagnetic field on bone regeneration around dental implants after immediate placement in the dog mandible: a pilot study

doi: 10.1111/j.1741‐2358.2011.00525.x Effect of electromagnetic field on bone regeneration around dental implants after immediate placement in the dog mandible: a pilot study Background: Accelerating bone healing around dental implants can reduce the long‐term period between the insertion of implants and functional rehabilitation. Objective: This in vivo study evaluated the effect of a constant electromagnetic field (CEF) on bone healing around dental implants in dogs. Materials and methods: Eight dental implants were placed immediately after extraction of the first pre‐molar and molar teeth on the mandible of two male dogs and divided into experimental (CEF) and control groups. A CEF at magnetic intensity of 0.8 mT with a pulse width of 25 μs and frequency of 1.5 MHz was applied on the implants for 20 min per day for 2 weeks. Result and conclusion: After qualitative histological analysis, a small quantity of newly formed bone was observed in the gap between the implant surface and alveolar bone in both groups.     

Three-dimensional finite element analysis of stress distribution in retention screws of different crown–implant ratios

The retaining screw of the implant-supported dental prosthesis is the weakest point of the crown/implant system. Furthermore, crown height is another important factor that may increase the lever arm. Therefore, the aim of this study was to assess the stress distribution in implant prosthetic screws with different heights of the clinical crown of the prosthesis using the method of three-dimensional finite element analysis. Three models were created with implants (3.75 mm × 10 mm) and crowns (heights of 10, 12.5 and 15 mm). The results were visualised by means of von Mises stress maps that increased the crown heights. The screw structure exhibited higher levels of stresses in the oblique load. The oblique loading resulted in higher stress concentration when compared with the axial loading. It is concluded that the increase of the crown was damaging to the stress distribution on the screw, mainly in oblique loading.     

Implant-supported palatal lift prosthesis in a patient with velopharyngeal incompetence: a case report

doi: 10.1111/j.1741‐2358.2011.00561.x Implant‐supported palatal lift prosthesis in a patient with velopharyngeal incompetence: a case report Objective: To describe the use of dental implants in the treatment of velopharyngeal incompetence. Background: Velopharyngeal incompetence is characterized by the inability to contract the tissues of the soft palate. The most common causes are neuromuscular problems resulting from concussion and degenerative conditions of the central nervous system. Materials and methods: The treatment using palatal lift prosthesis is well established in the literature; however, reports on the use of osseointegrated implants are scarce. Rehabilitation using only this type of fibromucosal support is difficult in edentulous patients, since the prosthesis has a palatal lift extension. Results: The implants provided retention and stability to the prosthesis, improving swallowing and speech and contributing to improve the patient’s quality of life. Conclusion: This article reports the rehabilitation of a patient with a totally edentulous maxilla with velopharyngeal incompetence using an implant‐retained palatal lift prosthesis.     

口腔种植外科相关颌骨解剖学研究进展

目前,种植义齿修复已经成为牙列缺损、缺失患者的最佳修复方式。通过对颌骨的精确测量,可获得种植手术所需相关解剖资料,为种植体的选择、设计及口腔种植手术的实施提供重要的参考。本文就口腔种植义齿相关的颌骨解剖测量进展作一综述。     

A review of histomorphometric analysis techniques for assessing implant-soft tissue interface

Abstract

The success of dental implant treatment depends on the healing of both hard and soft tissues. While osseointegration provides initial success, the biological seal of the peri-implant soft tissue is crucial for maintaining the long term success of implants. Most studies of the biological seal of peri-implant tissues are based on animal or monolayer cell culture models. To understand the mechanisms of soft tissue attachment and the factors affecting the integrity of the soft tissue around the implants, it is essential to obtain good quality histological sections for microscopic examination. The nature of the specimens, however, which consist of both metal implant and soft peri-implant tissues, poses difficulties in preparing the specimens for histomorphometric analysis of the implant-soft tissue interface. We review various methods that have been used for the implant-tissue interface investigation with particular focus on the soft tissue. The different methods are classified and the advantages and limitations of the different techniques are highlighted.     

Finite element analysis of different loading conditions for implant-supported overdentures supported by conventional or mini implants

The effect of implants’ number on overdenture stability and stress distribution in edentulous mandible, implants and overdenture was numerically investigated for implant-supported overdentures. Three models were constructed. Overdentures were connected to implants by means of ball head abutments and rubber ring. In model 1, the overdenture was retained by two conventional implants; in model 2, by four conventional implants; and in model 3, by five mini implants. The overdenture was subjected to a symmetrical load at an angle of 20 degrees to the overdenture at the canine regions and vertically at the first molars. Four different loading conditions with two total forces (120, 300 N) were considered for the numerical analysis. The overdenture displacement was about 2.2 times higher when five mini implants were used rather than four conventional implants. The lowest stress in bone bed was observed with four conventional implants. Stresses in bone were reduced by 61% in model 2 and by 6% in model 3 in comparison to model 1. The highest stress was observed with five mini implants. Stresses in implants were reduced by 76% in model 2 and 89% increased in model 3 compared to model 1. The highest implant displacement was observed with five mini implants. Implant displacements were reduced by 29% in model 2, and increased by 273% in model 3 compared to model 1. Conventional implants proved better stability for overdenture than mini implants. Regardless the type and number of implants, the stress within the bone and implants are below the critical limits.     

A graphene/zinc oxide nanocomposite film protects dental implant surfaces against cariogenic Streptococcus mutans

Oral biofilms play a crucial role in the development of dental caries and other periodontal diseases. Streptococcus mutans is one of the primary etiological agents in dental caries. Implant systems are regularly employed to replace missing teeth. Oral biofilms accumulate on these implants and are the chief cause of dental implant failure. In the present study, the potential of graphene/zinc oxide nanocomposite (GZNC) against the cariogenic properties of Streptococcus mutans was explored and the anti-biofilm behaviour of artificial acrylic teeth surfaces coated with GZNC was examined. Acrylic teeth are a good choice for implants as they are low cost, have low density and can resist fracture. Microscopic studies and anti-biofilm assays showed a significant reduction in biofilm in the presence GZNC. GZNC was also found to be nontoxic against HEK-293 (human embryonic kidney cell line). The results indicate the potential of GZNC as an effective coating agent for dental implants by efficiently inhibiting S. mutans biofilms.     

Knowledge and attitude of elderly persons towards dental implants

doi: 10.1111/j.1741‐2358.2011.00586.x Knowledge and attitude of elderly persons towards dental implants Background: Despite their unrivalled place in restorative treatment, dental implants are still scarcely used in elderly patients. Introduction: The aim of this survey was therefore to identify potential barriers for accepting an implant treatment. Materials and methods: Participants were recruited from a geriatric hospital, two long‐term‐care facilities and a private clinic. The final study sample comprised 92 persons, 61 women and 31 men with an average age of 81.2 ± 8.0 years. In a semi‐structured interview, the participants’ knowledge of implants and attitude towards a hypothetical treatment with dental implants were evaluated. Results: Twenty‐seven participants had never heard of dental implants, and another 13 participants could not describe them. The strongest apprehensions against implants were cost, lack of perceived necessity and old age. Univariate and multiple linear regression analysis identified being women, type and quality of denture, having little knowledge on implants and being hospitalised as the risk factors for refusing implants. However, old age as such was not associated with a negative attitude. Conclusion: The acceptance of dental implants in the elderly population might be increased by providing further information and promoting oral health in general. Regardless of the age, dental implants should be placed when patients are still in good health and live independently.     

Oral implants in dependent elderly persons: blessing or burden?

doi:10.1111/j.1741‐2358.2009.00314.x
Oral implants in dependent elderly persons: blessing or burden? Background: Implant‐supported (partial) dentures may raise problems in patients who have become dependent on others for daily oral health care. Dental hygienists and general dental practitioners, as well as care providers, volunteer aiders and even health care insurance companies, should anticipate the growing demand for specific oral health care for patients provided with implant‐supported (partial) dentures. Objective: To report three cases of dependent patients and to present recommendations to prevent or resolve implant‐related oral problems. Materials and methods: The three case reports are demonstrating that implant insertion in (dependent) elderly people needs careful consideration. Discussion: When considering implant treatment, some questions should be raised: (1) Is the treatment appropriate in contributing to the patient’s well‐being and quality of life? (2) Is the treatment the most suitable treatment? (3) Does the treatment integrate with the patient’s oral health care plan? (4) Is the patient sufficiently cooperative? (5) Is the patient supported by a well‐functioning oral (self) care assisting network? (6) Is it possible for the patient to regular see an oral health care professional and is oral health care easily accessible in cases of an emergency? Conclusion: Dependent elderly people can benefit from oral implants, providing that adequate oral health care and aftercare can be provided. When indicated, removal of the anchorage structure is easily performed by putting the implants to sleep. All implant patients should be provided with an ‘implant passport’. Regular information and instruction for care providers about the oral condition of the patient are essential.     

Dental caries, enamel composition, and subsistence among prehistoric Amerindians of Ohio

Six populations of prehistoric Amerindians from Ohio are sampled to establish the relationship of enamel composition and dental caries experience. The populations used included groups practicing hunting-gathering-fishing and maize horticulture, and they represent at least two major cultural traditions, the Late Archaic/Glacial Kame (1000-500 BC) and the Fort Ancient and Sandusky Bay Traditions (AD) 1200-1600). Characterization of enamel composition is achieved using scanning electron microscopy energy-dispersive X-ray analysis. Thirteen elements present are quantified, and they are analyzed with respect to each population's subsistence base using correspondence analysis. Evaluations of cariogenic and cariostatic effects of elements are made on the basis of caries frequency comparisons among the populations. Results indicate that zinc, copper, iron, nickel, and calcium-phosphorus ratio distinguish populations exhibiting high, moderate, and low caries frequency as well as discriminate hunter-gathers from maize horticulturalists.