Impact of prosthetic rehabilitations on the TMJ joint space: a comparative study

Unilateral partial edentulism, classified as Kennedy Class II, induces an asymmetrical modification of occlusal loads that can directly impact the morphology and dynamics of the temporomandibular joint (TMJ). For the practitioner, the question is whether the restoration of posterior support allows for the stabilization or correction of these spatial joint modifications. This prospective study specifically addresses the capacity of rehabilitations to restore the TMJ joint space distribution in patients who have lost 2 to 3 posterior units.

The specific objective of this work was to evaluate, using CBCT imaging, whether implant-supported fixed prostheses and removable partial dentures (RPD) differentially restore joint space distribution compared to a healthy control group. The authors measured the lateral (LJS), medial (MJS), superior (SJS), anterior (AJS), and posterior (PJS) dimensions before and 6 months after the completion of treatment.

The hypothesis tested suggests that Kennedy Class II patients exhibit a predominant joint spatial imbalance in the coronal plane and that both rehabilitation modalities could induce a spatial adaptation of the TMJ, although the equivalence between fixed and removable remains to be demonstrated in the short term.

Study methodology

This prospective comparative study evaluated the spatial adaptation of the temporomandibular joint (TMJ) in patients with partial edentulism. The total sample included 45 adults, distributed as follows:

• Test group 1 (n = 15): patients with unilateral distal edentulism (Kennedy Class II, loss of 2 to 3 posterior units) rehabilitated with implant-supported fixed prostheses.
• Test group 2 (n = 15): patients presenting the same type of edentulism rehabilitated with a removable partial denture (RPD).
• Control group (n = 15): healthy dentate adults.

The imaging protocol used cone-beam computed tomography (CBCT) at two key stages: at baseline (pre-rehabilitation) and 6 months after the completion of prosthetic rehabilitation. Radiographic measurements targeted five specific joint spaces: lateral (LJS), medial (MJS), superior (SJS), anterior (AJS), and posterior (PJS).

The analysis also focused on differences in spatial distribution via medio-lateral (LJS–MJS) and antero-posterior (AJS–PJS) calculations. Statistical comparisons were performed with a significance threshold set at p < 0.05 to identify morphological imbalances between groups.

Initial spatial imbalances and impact of rehabilitation

Initial CBCT analysis revealed that patients with Kennedy Class II edentulism (loss of 2 to 3 posterior units) displayed significant morphological differences compared to healthy subjects. Before rehabilitation, the lateral joint space (LJS), medial joint space (MJS), and the medio-lateral difference (LJS–MJS) were abnormally distributed (p < 0.05).

Comparison of modalities: Implant vs Removable Partial Denture (RPD)

At 6 months post-rehabilitation, the data indicate that no statistically significant difference was observed between the two types of treatments (fixed implant-supported prosthesis vs. removable partial prosthesis) regarding the restoration of joint spaces. Both approaches showed a similar capacity to induce short-term spatial adaptation of the TMJ.

Radiographic observations and spatial adaptation

The results highlight a persistence of imbalance in the coronal plane (LJS and LJS–MJS) despite prosthetic restoration. The main observations include:

• Persistence of discrepancies: Although function is restored, significant differences remain compared to healthy controls for the LJS and the LJS-MJS ratio at 6 months (p < 0.05).
• Partial normalization: No significant difference was noted for the MJS or the antero-posterior balance (AJS–PJS) after 6 months of prosthetic loading.
• Short-term adaptation: Changes observed via CBCT reflect spatial adaptation of the TMJ rather than direct evidence of long-term pathological risk reduction.

The study highlights that TMJ balance in Kennedy Class II patients appears to be primarily affected in the coronal plane, and that 6 months of rehabilitation, whether fixed or removable, is not sufficient to restore spatial symmetry identical to that of a healthy subject.

Clinical analysis of TMJ adaptation post-rehabilitation

The results of this prospective study highlight a predominant joint imbalance in the coronal plane in patients with Kennedy Class II partial edentulism. Before any treatment, these patients display abnormal lateral joint space (LJS) and medial joint space (MJS) values compared to healthy subjects. The study shows that after six months of rehabilitation, although the medial space stabilizes, the medio-lateral asymmetry (LJS–MJS) and lateral space anomalies persist. This suggests that the restoration of posterior support initiates a spatial adaptation of the TMJ, but this remains incomplete in the short term.

A major finding of this work lies in the absence of statistical superiority of one modality over the other: implant-supported fixed prostheses and removable partial dentures (RPD) showed similar effects on the distribution of joint spaces. However, the authors emphasize that this lack of difference does not constitute proof of strict equivalence, as the study design was not randomized.

The inherent limitations of this research include a small sample size (n=30 patients) and a follow-up limited to six months. Furthermore, the observations rely exclusively on CBCT imaging. These radiographic measurements reflect condylar spatial adaptation but cannot be interpreted as direct evidence of functional clinical benefit or a reduction in the risk of long-term joint pathology.

Summary of results

This prospective study conducted on 30 Kennedy Class II patients shows that rehabilitation, whether fixed on implants (n=15) or removable (n=15), normalises the medial joint space at 6 months, but does not fully correct the coronal plane imbalance. Significant differences (p < 0.05) persist compared to the 15 healthy controls, particularly regarding the lateral joint space (LJS) and the medio-lateral ratio, despite the restoration of the occlusal load.

In concrete terms, for the practitioner:

• Anticipate slow adaptation: Restoring posterior support modifies condylar position, but the spatial balance of the TMJ remains incomplete at 6 months; do not consider joint adaptation to be immediate after placement.
• Fixed vs. removable arbitration: In the short term, the study shows no superiority of the implant over the removable partial denture (RPD) regarding the joint space morphology; your usual selection criteria (aesthetics, budget, bone volume) remain predominant.
• Coronal plane monitoring: Medio-lateral imbalances appear more persistent than antero-posterior adjustments; particular attention to transverse occlusal balance could be beneficial for stabilizing the condylar position.

Technical lexicon of the study

Kennedy Class II: Classification designating a unilateral partial edentulism located posteriorly to the remaining natural teeth, characterized by the absence of a distal dental abutment.

LJS (Lateral Joint Space): Lateral joint space; millimetric measurement of the distance between the lateral pole of the mandibular condyle and the temporal fossa via CBCT imaging.

CBCT (Cone Beam Computed Tomography): Cone beam imaging technique allowing for precise three-dimensional evaluation of bone structures and the spatial distribution of the temporomandibular joint.

Coronal plane imbalance: Alteration of the condylar position observed in this study on the medio-lateral axis, resulting from the modification of occlusal loads related to tooth loss.

Unilateral free-end edentulism: Loss of 2 to 3 posterior dental units on one side of the arch, removing posterior support and impacting TMJ morphology.

MJS (Medial Joint Space): Medial joint space; measurement of the distance between the internal aspect of the condyle and the medial wall of the articular fossa.

SJS (Superior Joint Space): Superior joint space, representing the distance between the top of the mandibular condyle and the roof of the mandibular fossa.

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