This clinical report presents a new surgical approach for TMJ reconstruction using a simple, low-cost, and relatively easy-to-perform method. Alongside these advantages, the main characteristic of ABiP is the longevity of results, which has been observed not only in the patient here described, but also in patients of different age groups treated by our team ([18, 21] and manuscript in preparation). Thus, implementing innovative protocols that can improve patients’ conditions over time, facilitate surgical techniques and reduce expenses should be encouraged. Trauma-induced TMJ ankylosis is similar to fracture healing [23, 24]. Histologically, ankylosis presents a remodelling bone callus [25] with a progressive fusion between the temporal bone and the mandibular condyle [26,27,28]. Since the bony mass is not a neoplasm, its excision can be programmed and limited [29]. The characteristics of the ABiP protocol allow the use of the temporal and condylar regions for fixation and stabilisation of joint implants, added to the thermal isolation provided by the local bone thickness. Furthermore, computed tomography imaging in axial, coronal and sagittal sections provides a safe interpretation of the bone areas to be treated and controlled.

Adverse effects of PMMA may be related to its constituent methyl methacrylate monomer (MMA). For example, bone cement implantation syndrome (BCIS) may result from the release of MMA into the bloodstream during prosthesis cementation [30,31,32]. Similarly, local mechanisms are related to the cytotoxic effects of MMA in smaller injured areas [33]. In biconvex arthroplasty, abundant intraoperative irrigation minimises these effects, adding to the benefit of local refrigeration in the exothermic phase.

Exposure of bone to exothermic reactions for more than 60 s, with temperatures between 40ºC and 120 °C, represents a potential risk of bone necrosis [34]. Therefore, a thickness of the PMMA mantle between 5 and 7 mm has been recommended for hip implant prosthesis [35]. Previous studies have concluded that the generation of temperatures between 56ºC and 60 °C is directly related to the volume of the mass used. Mercuri [36] observed that using a small volume of PMMA can minimise the exothermic reaction produced on-site. In the ABiP technique, the convex structures present an average radius of 4.0 and 7.0 mm in paediatric and adult patients, respectively, which is compatible with the previous study.

Most of the current biomaterials are well tolerated by the organism. In addition, these biomaterials maintain structural integrity, achieve mechanical stability in the bone, and are not colonised by microorganisms [7]. However, complications related to excessive wear of the materials and possible immune reactions remain a challenge, stimulating continued investigation [37,38,39].

Foreign body reaction is a common process when first-generation biomaterials such as metals, ceramics and polymers (e.g., PMMA) are implanted into biological tissues [6, 7]. The reaction to PMMA bulk has been described as a limited biological response, characterised by the production of a thin fibrous layer containing monocytes, macrophages and foreign body giant cells [40,41,42,43,44,45]. In our experience, the use of PMMA did not show those deleterious biological effects.

Clinical signs of pain, discomfort and dysfunction may reflect adverse effects related to foreign body reactions [46]. However, in the present case, the patient did not report any of the signs/symptoms mentioned, indicating the acceptance of the material by the patient’s tissue. In 1986, Masquelet developed a procedure based on inducing a foreign-body granulation membrane by inserting a PMMA cement spacer between the bone defect ends [47]. Furthermore, the induced membrane is similar to the periosteum or a pseudo-synovial tissue, having biological properties [48, 49]. Therefore, the technique can be used in significant diaphyseal defects. Moreover, this induced membrane is able to imitate the TMJ articular capsule. In the case reported here, results observed after 40 years confirm the biocompatibility of the PMMA cement and its applicability in the ABiP approach.

Simplex P cement has been on the market for more than 50 years. Cementation techniques using Simplex P are currently classified as first, second and third generation [7]. ABiP uses the first-generation technique, which involves manually mixing cement in a surgical bowl using a spatula. The preparation of the bone area is conservative, and part of the spongy bone is maintained in order to anchor the alloplastic material [4, 7]. Under digital pressure, the unpolymerised PMMA is inserted at an average depth of 3 to 5 mm. When the bone surface is cleaned and less hydrated, the depth of penetration of the material can increase, resulting in greater strength and mechanical resistance at the bone/polymer interface, through the pegged anchorage system concept.

After polymerisation, the PMMA cement maintains its shape, whether buried in the medullary space or carved into the external surface. Therefore, stable results can be achieved even during the intraoperative period. The glenoid fossa is altered from its concave to a convex shape in the biconvex joint configuration. The prosthetic cranial component is fixed on the lateral aspect of the glenoid cavity. Furthermore, the residual ankylosed mass supports the fixation of the PMMA joint unit, which is presented as a single hemispherical block of surgical cement. The mandibular condyle is constructed in the bone region, and the recommended maximum lower limit is at the level of the mandibular notch, with at least 1 mm of the bone surrounding the inlay rod.

For the condylar component, Xu et al. [50] proposed combining an association of the onlay plate with an inlay rod 3 mm in length, with a maximum diameter of 1.6 mm, a 10-degree taper angle, and at least 1 mm of surrounding bone. The authors suggest that using an inlay rod reinforces the connection between the prosthesis and the remaining bone tissue, as recommended in the ABiP approach. Ramos et al. [51,52,53] proposed a modification to the fixation of the condyle without plate and screws in the cortex of the mandibular ramus. According to the authors, the results of in vitro and ex vivo experiments suggest that the distribution of forces using intramedullary fixation of the condylar unit is similar to the intact condyle [51,52,53], a principle already applied in the ABiP technique. In the face of a restricted surface between the bone and PMMA, horizontal and oblique bone perforations enlarge the micro-retentive area.

In 1999, van Loon et al. proposed, for TMJ total prosthesis, a centre of rotation 15 mm inferior to the centre of the natural condyle, combined, if necessary, with a shift of up to 5 mm in the anterior direction [54], which is similar to the ABiP concept. In addition to providing a reference for the support of condyle movements, this cranial component allows an anteriorisation of the ramus for intra-operative corrections of vertical/lateral mandibular asymmetries, keeping this position stable. Furthermore, the interposed components used in ABiP have a relatively constant radius, creating a minimum contact area. This characteristic results in lower static friction, overcome by muscular kinetic friction [54]. Ackland et al. [55] emphasised the presence of redundant musculoskeletal systems with possible synergistic functions, where traction and compression provide stability and strength. According to Gallo et al. [17], although muscles produce only linear forces, the movements of the joints of the human body have, in almost all instances, a strong component of rotation, and can act with certain degrees of freedom. This kinetic component has also become evident during the joint function provided by ABiP. In addition, the physiology of the stomatognathic system provides stability between convex surfaces, which occur naturally during mandibular excursion movements [1].

In the TMJ, the force resulting from muscle activity forms an anterosuperior component [1]. Therefore, when there is a joint reconstruction by ABiP, the position of the upper component creates a new vector force component. Under normal conditions, for example, the condyle exerts reduced action force in the posterior region of the glenoid fossa. However, there is permanent posterior contact in ABiP, whether the joint is in motion or at rest (e.g., closed mouth).

The present proposal of more conservative surgery, with single surgical access, limited ostectomy, and maintenance of the residual bone structure in the mandibular ramus [18,19,20,21] is reinforced by Ramos and Mesnard [52], who suggest that this procedure allows surgical revisions if necessary. In addition, ABiP has other encouraging characteristics, such as low cost, easy execution and longevity, shown here for over four decades. New technologies (e.g., material, tissue and movement engineering) should improve the ABiP technique, stressing its use for TMJ reconstruction.