Single implants in the anterior maxilla in young adults

Abstract

Background: Single anterior implants are frequently used in the treatment of patients with single anterior tooth loss. Compared with other types of implant treatments, single implants are commonly performed in younger patients where the cause of tooth loss often is non-inflammatory. However, there is a scarcity of long-term follow-up studies, especially in the cohort representing the younger segment of the adult population. Lack of periodontal mechanoreceptors (PMRs) around implants and reduced function of PMRs around teeth connected in full-arch bridges have been shown to affect the oral fine motor control. However, there is no study on the comparison of oral fine motor control between single anterior implants and the alternative treatment, a 3-unit bridge.

Aims: The objective of this thesis was to investigate the performance of single anterior maxillary single implants in young adults. The specific aims of Studies I and II was primarily to report long-term survival, success, complications, radiological findings and movement of adjacent teeth after 14–20 years follow-up. The secondary aims were to explore correlations between changes in marginal bone levels in relation to probing depth (PD), occlusal contact, and nicotine use, and to investigate the associations between the movement of adjacent teeth, patient and implant characteristics, and the aesthetic assessment of the implant crown. Study III aimed to compare oral fine motor control of patients with single anterior tooth loss treated with 3-unit resin-bonded bridges (RBBs) or single implants.

Materials and methods: In Studies I and II, 40 out of 42 patients who received single anterior implants were re-examined after a period of 14–20 years. Data were collected to assess the long-term survival, success, biological findings and complications of the implants. After 14-20 years, radiological findings were compared with baseline data. A 3- D analysis and calculations were used to investigate the movements of teeth adjacent to the single implants and their associations with patient and implant characteristics. Additionally, an assessment of perceived aesthetics was performed. In Study III, a behavioral hold-and-split test was conducted on 16 patients with missing maxillary central incisors. The test was performed twice, once with a 3-unit resin-bonded bridge (RBB) and once with a single implant. The conditions connected tooth (CT), pontic (P), freestanding tooth (T) and single implant (SI) were tested for differences regarding the variables hold force, variability of hold force, split force and duration of split.

Results: In Study I, the cumulative survival rate for implants (CSRi) was 96.1% whereas that for crowns was of 80.4% (CSRc). All the remaining implants were considered successful. The mean marginal bone loss was 0.1 ± 1.1 (range, -5.1–1.6) mm and the mean PD was 4.0 ± 1.8 (range, 0–9) mm after 14–20 years follow-up. There was no significant correlation found between marginal bone levels and PD, implant occlusion, or nicotine use (p >0.05). Technical and/or biological complications were found in 50% of the patients, but only 22% required substantial further treatment. In Study II, the 3-D movements of teeth adjacent to the single implant showed a mean movement of 1.0 ± 0.5 mm in the incisal direction (vertical; Y-axis), 0.5 ± 0.8 mm in the bucco-lingual direction (sagittal; Z-axis) and −0.0 ± 0.1 mm in the mesio-distal direction (horizontal; X-axis). No patient showed a completely stable vertical relationship (Y-axis). Lower anterior facial height (LAFH) ≥70 mm was significant correlated with more severe vertical tooth movement (>1 mm) (p <0.05). Furthermore, implants in occlusion, implants in central incisor position and in patients when trauma was the reason for tooth loss were significantly correlated with less movement of teeth adjacent the single implants (p <0.05). Despite the infraposition the patients rated the esthetic of the implant crown to a VAS score of 85% ± 19% (range, 20%– 100%). Significantly lower VAS scores (p <0.05) were correlated with increased tooth movement in patients with central incisor implants. The dentist ratings of 67% ± 23% (range, 10%–100%) were significantly lower that the patients (p <0.05). In Study III, significantly higher (p <0.05) hold force, variability of hold force and split force was found for the single implants compared to the adjacent teeth. Further, the pontic of the RBB showed higher hold forces (p <0.05) than the adjacent connected tooth in a similar manner as the implant. However, no significant differences (p >0.05) were found between the tooth connected in the RBB and the freestanding tooth.

Conclusion: Within the limitations of the studies this thesis highlights that single anterior maxillary implants in young adults show good long-term performance with high success and survival rates and only small changes in marginal bone levels. Complications occur over time; however, they do not seem to be of great concern to the patients. Positional changes of adjacent teeth in relation to the single implants occur over time in all patients but to different degrees. However, the changes seem to be more extensive in patients with LAFH ≥70mm, patients without implant occlusion, patients with implants in the lateral and canine positions, and patients with tooth loss caused by reasons other than trauma. Only few patients (10%) found the differences in tooth position esthetically disturbing while the dentist was more critical. Furthermore, single implants show impaired oral fine motor control in relation to freestanding adjacent teeth which was also observed for pontics in relation to connected teeth. However, teeth connected in 3-unit anterior bridges appear to maintain sensitivity in oral fine motor control.

Clinical implications: This thesis suggests that patients planned for single anterior maxillary implants should be provided with information that the implant is expected to perform well overtime. However, the implant crown will most likely end up in infraposition in relation to the adjacent tooth. In most patients this will not cause an esthetic problem but in young adults with a long remaining lifetime, the need to change or repair the implant crown may occur once or a few times. To minimize the risk of infraposition, it is advisable to delay anterior maxillary single implant treatment for as long as possible. Patients with a lower anterior facial height of more than 70 mm or implants in lateral or canine position might be in higher risk of more severe infraposition.