Clinical Influence of Mandibular Flexure on Oral Rehabilitation: Narrative Review

Prosthetic framework improvement using lattice structure: A comparative finite element study of a mandibular implant-supported prosthesis

OBJECTIVES

An alternative option was proposed regarding the prosthetic rehabilitation of a fully edentulous mandible using only four implants. The aim was to reduce the stiffness of the prosthetic framework. To that end, the alternative option consists of a prosthetic framework optimized with a porous structure. Mechanical differences were analyzed between non-prosthetic mandible and restored mandible either with a conventional bulk titanium framework or with this alternative option. The non-prosthetic mandible corresponds to the mandible in its natural state, without prosthesis. This will be considered as the reference for comparison with restored models (mandible with prosthesis).

METHODS

Three models are used: the first one is the non-prosthetic mandible, the second one is the restored mandible with conventional bulk titanium prosthetic framework, and the third one is the alternative option. Prosthetic framework was optimized with the use of a lattice structure. A numerical analysis was performed (with Abaqus Standard software®) to obtain the effective parameters corresponding to equivalent homogeneous behavior. In the 3 models, physiological boundary conditions were used, considering the activity of several muscles of the masticatory system during three main tasks of mastication (incisive clenching, maximum intercuspation and unilateral molar clenching).

RESULTS

Numerical simulations allowed to obtain mandibular global kinematics, local displacement at the bone-implant interface and the state of strain at the bone-implant interface, for each masticatory tasks. For this comparative study, the non-prosthetic mandible model was used as a reference to observe the benefits of using a lattice prosthetic framework compared to a conventional bulk titanium framework.

CONCLUSION

Compared to conventional titanium framework, the lattice prosthetic one appeared to be more respectful of the natural mandible kinematics, given by the reference model. It also resulted in strain values within the physiological loading range.

Rehabilitation with implant-supported overdentures in preteens patients with ectodermal dysplasia: A cohort study

INTRODUCTION

Hypohidrotic ectodermal dysplasia (HED) patients suffering of oligo-anodontia require early dental treatment to improve oral functions and reduce social impairment. The aim of this study was to evaluate the skeletal growth, implant and prosthetic survival rate, success, and complications after the rehabilitation with a maxillary denture and an implant-supported overdenture provided by a sliding bar in case of severe hypodontia/anodontia related to HED.

MATERIALS AND METHODS

This retrospective cohort study began in 2009. Nine patients over 7 years old with HED and associated oligo-anodontia who presented at the University of Bologna for dental treatment were included in the study. They were first treated with conventional dentures and then with a maxillary denture and an implant-supported overdenture with a sliding bar connected to two implants placed in the anterior mandible. The subjects treated were followed for 3-12 years. In each case, orthopanoramic and lateral cephalometric radiographic exam were taken before implant placement and annually after prosthetic load. Vertical and transverse dimensions of the mandible in the symphysis area at implant sites were taken on the lateral cephalometric radiography at the time of implant placement and after 5 years from the prosthetic loading to assess the presence or absence of an anterior mandibular growth. Biologic and mechanical complications were also recorded at every visit.

RESULTS

A mandibular vertical growth under the implant apex, at the implant neck, and a sagittal growth of the symphysis after 5 years from the prosthetic loading were observed and measured. Implant and prosthetic success and survival rates were 100% after 8.1 years (mean) follow-up period. No complications were reported except in one patient, where the repositioning of a retentive cap on the counter bar in the superstructure was necessary after 3 years from the prosthetic loading.

CONCLUSIONS

The present study suggests that the growth of the mandible near implant sites continues even after their positioning. Implants can be successfully placed and provide support for prosthetic rehabilitation in preteens patients with HED.

Median mandibular flexure-the unique physiological phenomenon of the mandible and its clinical significance in implant restoration

Mandibular flexure, characterized by unique biomechanical behaviors such as elastic bending and torsion under functional loading, has emerged as a crucial factor in oral clinical diagnosis and treatment. This paper presents a comprehensive review of the current research status on mandibular flexure, drawing insights from relevant studies retrieved from the PubMed database (www.ncbi.nlm.nih.gov/pubmed), including research conclusions, literature reviews, case reports, and authoritative reference books. This paper thoroughly explores the physiological mechanisms underlying mandibular flexure, discussing different concurrent deformation types and the essential factors influencing this process. Moreover, it explores the profound implications of mandibular flexure on clinical aspects such as bone absorption around dental implants, the precision of prosthesis fabrication, and the selection and design of superstructure materials. Based on the empirical findings, this review provides crucial clinical recommendations. Specifically, it is recommended to exert precise control over the patients mouth opening during impression-taking. Those with a high elastic modulus or bone-tissue-like properties should be prioritized when selecting superstructure materials. Moreover, this review underscores the significance of customizing framework design to accommodate individual variations in facial morphology and occlusal habits. Future research endeavors in this field have the potential to advance clinical diagnosis and treatment approaches, providing opportunities for improvement.

Biomechanical Implications of Mandibular Flexion on Implant-Supported Full-Arch Rehabilitations: A Systematic Literature Review

BACKGROUND

Mandibular flexion (MF) is a complex biomechanical phenomenon, which involves a deformation of the mandible, due mainly to the contraction of the masticatory muscles, and it can have numerous clinical effects. The deformation of the lower jaw caused by mandibular flexion is generally very small, and it is often overlooked and considered irrelevant from a clinical point of view by many authors; however, it should be important to remember that median mandibular flexure (MMF) has a multifactorial aetiology. The main aim of the current systematic review is to highlight the different factors that can increase MF in order to help clinicians identify patients to whom they should pay more attention. As a secondary outcome, we wanted to analyse the preventive measures and suitable techniques to be adopted to minimise the negative effects of this phenomenon on oral fixed rehabilitations.

METHODS

The review, which was carried out in accordance with the "Preferred Reporting Items for Systematic reviews and Meta-Analyses" (PRISMA) flowchart, was recorded in the "International Prospective Register of Systematic Reviews" (PROSPERO). As research questions, "Patient/Population, Intervention, Comparison and Outcomes" (PICO) questions were employed. Using the ROBINS-I technique, the risk of bias in non-randomised clinical studies was evaluated.

RESULTS

The initial electronic search identified over 1300 potential articles, of which 54 studies were included in this systematic review. Information regarding the relationship between MF and individual factors, mandibular movements, impression taking, and fixed rehabilitations were obtained.

CONCLUSIONS

The studies included in this systematic review showed that MF is greater during protrusive movements, in the posterior areas of the lower jaw, and in patients with brachial facial type, greater jaw length; small gonial angle; and less density, length, and bone surface of the symphysis. The biomechanical effects of mandibular flexion on fixed restorations are debated. Prospective clinical and radiological observational studies should be conducted to evaluate the potential short-, medium-, and long-term consequences of MF.

Mandibular Flexure and Its Significance: An In Vivo Cone Beam-Computed Tomography Proof-of-Concept Study

The aim of this study was to assess intra-arch mandibular dimensional changes that may occur during mouth opening using cone beam-computed tomography (CBCT). Fifteen patients in need of any type of treatment whose execution considered a pre- and post-CBCT assessment consented and were enrolled. CBCTs were taken with the following settings: 90 kV, 8 mA, field of view (FOV) 140 by 100 mm (height and diameter), Voxel size 0.25 mm (high resolution). The pre-CBCT was executed in the maximum mandibular opening (MO), while the post-CBCT was in the maximum intercuspation (MI). A thermoplastic stent with radiopaque fiducial markers (steel ball bearings) was fabricated for each patient. Measurements were made using radiographic markers between contralateral canines and contralateral first molars and between ipsilateral canines and first molars on both sides. Paired t-tests were performed to evaluate the difference between open and closed positions on these four measurements. In the MO position were registered a significative tightening of the mandible at the canine (-0.49 mm, SD 0.54 mm; p < 0.001) and molar points (-0.81 mm, SD 0.63 mm; p < 0.001) and a significative shortening of the mandible on the right (-0.84 mm, SD 0.80 mm; p < 0.001) and left sides (-0.87 mm, SD 0.49 mm; p < 0.001). Within the study limitations, mandibular flexure determined a significant shortening and tightening between maximum intercuspation to maximum opening positions. Mandibular dimensional changes should be considered in light of other patient factors in the treatment planning of implant positioning and long-span complete arch implant-supported fixed prostheses in order to avoid technical complications.

Outcomes and Complications of 33 Soft-Milled Cobalt-Chromium-Ceramic Full-Arch Screw-Retained Implant-Supported Prostheses: A Retrospective Study with up to 10-Year Follow-up

This retrospective study assessed outcomes and complications related to implants and prostheses in edentulous patients treated with soft-milled cobalt-chromium-ceramic full-arch screw-retained implant-supported prostheses (SCCSIPs). After the final prosthesis was delivered, patients participated in an annual dental check-up program, including clinical and radiographic assessments. Outcomes of implants and prostheses were evaluated, and biological and technical complications were categorized as major or minor. Implant and prosthesis cumulative survival rates were assessed using the life table analysis. A total of twenty-five participants (mean age 63.6 ± 7.3 years) with 33 SCCSIPs were observed for a mean of 68.9 ± 27.9 months (range 1–10 years). A total of 7 out of 245 implants were lost, with no effect on prosthesis survival, leading to cumulative survival rates of 97.1% for implants and 100% for prostheses. The most recurrent minor and major biological complications were soft tissue recession (9%) and late implant failure (2.8%). Among 25 technical complications, porcelain fracture was the only major technical complication, requiring prosthesis removal (1%). Porcelain chipping was the most frequent minor technical complication, affecting 21 crowns (5.4%), which required polishing only. At the end of the follow-up, 69.7% of the prostheses were free of technical complications. Within the limitations of this study, SCCSIP showed promising clinical performance after 1–10 years.