The effect of occlusal balance and prosthesis on occlusal function of patients after dental implant restoration
Introduction Advancements in medical technology and research have made dental implants the preferred choice for patients with missing teeth, offering a comfortable, stable solution with high success rates that restores aesthetics and chewing function while eliminating the inconvenience of removable dentures [ , , , , ]. However, with the popularity of implant restorations, complications such as peri-implantitis caused by occlusal problems, chipping and dislodging of the upper part of the implant restoration, and destruction of the internal structure of the implant and its attachments have attracted the close attention of the industry peers . Before planning a restoration for tooth loss, it is essential to evaluate the remaining teeth's anatomy, the missing site's structure, the cause and history of tooth loss, occlusal stability, and any interferences . In addition to the basic examination methods, tools like occlusal analysis and electromyography provide objective insights to develop personalized treatment plans . While treatment primarily focuses on the teeth's morphology and contact relationships , attention must also be given to the temporomandibular joint and muscles, which are crucial to overall dental function. Research indicates that the proportion of ideal occlusion in the population is less than 10 % . In clinical practice, despite the lack of a uniform morphological standard, stable and functional occlusion—characterized by the midline of the dentition is consistent with the midline of the face, and the size and morphological position of the dental arch and the jaw are consistent, tight tooth contact, proper curves, and free jaw movement—forms the basis for effective tooth loss restoration . Studies indicate that dental implants have a high success rate, with outcomes being significantly influenced by factors such as restoration materials, the severity of tooth loss, and occlusal status; improving occlusal status remains a key factor in enhancing these outcomes [ , , , ]. During dental implant restoration, the occlusal contact between the restorations and opposing teeth must be adjusted, taking into account periodontal conditions to ensure proper bite force distribution and occlusal function . Light occlusion standards for dental implants, adjusted with occlusal paper, ensure balanced occlusal force and restored function . Occlusal balance plays a critical role in the functional outcomes of dental restorations . Despite its importance, few clinical studies have explored the relationship between occlusal balance and the contact tightness of prosthodontics and opposing teeth. Further research in this area is necessary to enhance the recovery of occlusal function following dental restoration. 

Materials and methods 2.1 General information about patients This is an observational study. 100 patients who received posterior dental implant restoration in our hospital and completed follow-up from July 2022 to July 2023 were selected and divided into the observation group (12 μm occlusal paper) and the control group (20 μm occlusal paper) according to their occlusal tightness, with 50 cases in each group. This research obtained approval from the Ethical Committee of the Aviation General Hospital (No. HK-2022-07-10) and patients signed informed consent. 2.2 Inclusion and exclusion criteria Inclusion criteria: (1) According to the relevant criteria of Clinical Periodontology, all patients had indications for artificial tooth implantation surgery; (2) Patients older than 18 years old; (3) Patient's informed consent. Exclusion criteria: (1) Patients with inflammation of soft and hard tissues in the tooth loss area, nocturnal teeth grinding or periodontal inflammation that has not been controlled; (2) Patients with partial chewing habits or poor oral hygiene; (3) Patients with temporomandibular joint disease, oral parafunction or biological complications after restoration; (4) Patients with history of orthodontic treatment or treatment of diseases affecting dental development such as tetracycline and fluorosis. 

General information about patients This is an observational study. 100 patients who received posterior dental implant restoration in our hospital and completed follow-up from July 2022 to July 2023 were selected and divided into the observation group (12 μm occlusal paper) and the control group (20 μm occlusal paper) according to their occlusal tightness, with 50 cases in each group. This research obtained approval from the Ethical Committee of the Aviation General Hospital (No. HK-2022-07-10) and patients signed informed consent. 

Inclusion and exclusion criteria Inclusion criteria: (1) According to the relevant criteria of Clinical Periodontology, all patients had indications for artificial tooth implantation surgery; (2) Patients older than 18 years old; (3) Patient's informed consent. Exclusion criteria: (1) Patients with inflammation of soft and hard tissues in the tooth loss area, nocturnal teeth grinding or periodontal inflammation that has not been controlled; (2) Patients with partial chewing habits or poor oral hygiene; (3) Patients with temporomandibular joint disease, oral parafunction or biological complications after restoration; (4) Patients with history of orthodontic treatment or treatment of diseases affecting dental development such as tetracycline and fluorosis. 

Methods All patients were examined routinely before surgery. The preoperative cone beam computed tomography (CBCT) scan was used to confirm the amount of bone in the edentulous area and the health of the neighboring periodontium and to determine the implant site and direction, limb type, and model in advance. After the patient entered the operating room, routine disinfection, toweling, implant placement, suture mucoperiosteum and other operations were used to place the implant in the defect and then tightly suture the wound, and routine postoperative care was provided. Zirconia all-ceramic crowns were selected as the restoration model, to make the cervical margin of the crowns flush with the gingiva, adjust the convexity of the crowns' neighboring surfaces and axial surfaces, and set up food drainage grooves on the occlusal surfaces. In both groups, the occlusal contact was adjusted by the thickness of the occlusal paper. Group A was occluded with 12 μm occlusal paper, and Group B was occluded with 20 μm occlusal paper, and the distribution of occlusal force was recorded and adjusted by a T-scan occlusal force analyzer in the case of apical staggering. 3.1 Observation indicators The observation indicators were measured at baseline and 3 months post-restoration, as studies suggest that 3 months is typically needed for proper osseointegration, ensuring stable conditions for evaluating occlusal balance and function . (1) The degree of peri-implant bone resorption, periodontal pocket depth, gingival index, and tooth looseness were compared between the two groups. The peri-implant bone level is the difference between the peri-implant bone level at the time of insertion of the restoration and the peri-implant bone height measured by CBCT at the follow-up visit 3 months later. The peri-implant gingival index consists of four grades from 0 to 3. Grade 0 indicates that the patient's gingiva is healthy, while grade 3 indicates that the patient's gingiva is severely inflamed, with obvious redness, swelling, and ulceration, with a tendency to bleed out spontaneously. Tooth looseness was scored according to the looseness of neighboring teeth: 0: no looseness, 1: Ⅰ degree looseness, 2: ⅠⅠ degree looseness, 3: ⅠⅠⅠ degree looseness. (2) The occlusal balance index was used to compare the changes in occlusal balance before restoration, on the day of restoration, and 3 months after restoration. In this study, in order to analyze the correlation between the different degrees of contact tightness and the degree of occlusal balance, the absolute value of the occlusal balance index was used to observe the occlusal balance relationship. The measurement of occlusal balance at 3 months after the repair was observed when the patients returned to the hospital for re-examination. (3) The Spearman's coefficient was used to analyze the correlation between occlusal balance and the degree of occlusal closeness and the time of restoration. 3.2 Statistical methods Statistical analyses were conducted using SPSS version 27.0. Continuous data were expressed as mean ± standard deviation ( X ‾ ± s) and compared between groups using the independent t -test. Categorical data were presented as percentages, and intergroup comparisons of rates were performed using the chi-square test. A p -value of less than 0.05 was considered statistically significant. 

Observation indicators The observation indicators were measured at baseline and 3 months post-restoration, as studies suggest that 3 months is typically needed for proper osseointegration, ensuring stable conditions for evaluating occlusal balance and function . (1) The degree of peri-implant bone resorption, periodontal pocket depth, gingival index, and tooth looseness were compared between the two groups. The peri-implant bone level is the difference between the peri-implant bone level at the time of insertion of the restoration and the peri-implant bone height measured by CBCT at the follow-up visit 3 months later. The peri-implant gingival index consists of four grades from 0 to 3. Grade 0 indicates that the patient's gingiva is healthy, while grade 3 indicates that the patient's gingiva is severely inflamed, with obvious redness, swelling, and ulceration, with a tendency to bleed out spontaneously. Tooth looseness was scored according to the looseness of neighboring teeth: 0: no looseness, 1: Ⅰ degree looseness, 2: ⅠⅠ degree looseness, 3: ⅠⅠⅠ degree looseness. (2) The occlusal balance index was used to compare the changes in occlusal balance before restoration, on the day of restoration, and 3 months after restoration. In this study, in order to analyze the correlation between the different degrees of contact tightness and the degree of occlusal balance, the absolute value of the occlusal balance index was used to observe the occlusal balance relationship. The measurement of occlusal balance at 3 months after the repair was observed when the patients returned to the hospital for re-examination. (3) The Spearman's coefficient was used to analyze the correlation between occlusal balance and the degree of occlusal closeness and the time of restoration. 

Statistical methods Statistical analyses were conducted using SPSS version 27.0. Continuous data were expressed as mean ± standard deviation ( X ‾ ± s) and compared between groups using the independent t -test. Categorical data were presented as percentages, and intergroup comparisons of rates were performed using the chi-square test. A p -value of less than 0.05 was considered statistically significant. 

Results 4.1 Results of general information showed that there was no obvious difference between the two groups of general data, and the balance was good ( p > 0.05). 4.2 Results of clinical indicators demonstrated that there was no apparent difference in the degree of bone resorption, periodontal pocket depth, gingival finger number, and tooth looseness between the two groups ( p > 0.05). 4.3 Results of occlusal balance index absolute value There were no significant differences in the absolute values of the occlusal balance index between the control group and the observation group before restoration and on the day of restoration ( A and B). However, c demonstrates that 3 months after restoration, the absolute value of the occlusal balance index in the observation group was significantly lower than in the control group ( p < 0.001). Furthermore, as shown in , both the control group and the observation group exhibited a significant decrease in the occlusal balance index when comparing values on the day of restoration and 3 months after restoration to the baseline values before restoration ( p < 0.05). 4.4 Correlation of occlusal balance with occlusal tightness and restoration time depicted that through correlation analysis, the absolute value of patients' occlusal balance index has no significant correlation with occlusal tightness. However, the absolute value of the occlusal balance index was negatively correlated with the repair time ( p < 0.001). 

Results of general information showed that there was no obvious difference between the two groups of general data, and the balance was good ( p > 0.05). 

Results of clinical indicators demonstrated that there was no apparent difference in the degree of bone resorption, periodontal pocket depth, gingival finger number, and tooth looseness between the two groups ( p > 0.05). 

Results of occlusal balance index absolute value There were no significant differences in the absolute values of the occlusal balance index between the control group and the observation group before restoration and on the day of restoration ( A and B). However, c demonstrates that 3 months after restoration, the absolute value of the occlusal balance index in the observation group was significantly lower than in the control group ( p < 0.001). Furthermore, as shown in , both the control group and the observation group exhibited a significant decrease in the occlusal balance index when comparing values on the day of restoration and 3 months after restoration to the baseline values before restoration ( p < 0.05). 

Correlation of occlusal balance with occlusal tightness and restoration time depicted that through correlation analysis, the absolute value of patients' occlusal balance index has no significant correlation with occlusal tightness. However, the absolute value of the occlusal balance index was negatively correlated with the repair time ( p < 0.001). 

Discussion When a tooth becomes diseased, the body compensates for the short-term impact of the habit of partial chewing, but in the long term, it causes damage to the joints and muscles around the tooth and affects the occlusal balance . At the same time, a certain amount of inflammatory mediators are released from the diseased area of the tooth, which increases the level of pain . Therefore, it is clinically important to perform dental implant restorations on time to improve occlusal balance. The therapeutic efficacy of implant restorations depends mainly on the design and selection of the implant, the physician and the patient's cooperation. Among them, the design and selection of the implant have a major significance on the change of occlusal reconstruction of the patient . In the process of implant restoration, occlusal reconstruction determines the function and long-term stability of the final restoration . In implant restoration, the size of the occlusal load, the direction of the force, and the way of the force determine the way of stress distribution and the size of the stress in the bone tissues around the implant [ , , ]. If the occlusal balance is not achieved, occlusal trauma will occur and affect the service life of the denture, and an excessive occlusal load will lead to mild resorption of the implant's cervical margin, which will ultimately affect the occlusal function [ , , ]. Our study showed that there was no significant difference in the degree of peri-implant bone resorption, periodontal pocket depth, gingival index, and tooth looseness between the two groups. This suggested that a slight change in the occlusal contact level would not affect the clinical indicators of the teeth in the postoperative period. Currently, the thickness of clinical occlusal paper ranges from 8 to 200 μm, and too much occlusal paper will reduce the degree of occlusal contact of dental implants to a certain extent, which is not conducive to the improvement of occlusal function . Therefore, this study mainly focuses on the occlusal adjustment of 12 μm and 20 μm occlusal paper for the patients. However, the thickness of the occlusal paper selected in this study is relatively small, which may have little effect on bone resorption and gingival damage around the implants. The follow-up time is only 3 months, which may not be enough to observe the effect of the different contact areas on the periodontal indexes of the patients, which needs to be confirmed by further studies. Interestingly, a study reported that thicker occlusal papers (200 μm) produced larger contact marks compared to thinner ones (16 μm), regardless of the applied force . In our study, however, the thinner 12 μm paper was found to be more effective in achieving occlusal balance more quickly. This suggests that thinner occlusal papers may allow for more precise occlusal adjustments, as thicker papers, while marking larger contact areas, might compromise the accuracy of occlusal contacts. This highlights the need to carefully select the right occlusal paper thickness to optimize both contact precision and overall occlusal function in implant restorations. The absolute values of the occlusal balance index before and after restoration were compared within the two groups. The index before repair was the highest, the index on the day of the repair was the middle, and the index at 3 months after repair was the smallest. The absolute occlusal balance index of the observation group was lower than that of the control group at 3 months after the restoration, suggesting that the occlusion of the patients gradually became balanced with the increase of the restoration time. However, the 12 μm occlusal paper could help the patients to realize the occlusal balance at an earlier time . Clinical practice has shown that due to biomechanical limitations, fixed bridge restorations can only achieve 50 %–90 % of the original occlusal contact area in the case of dental defects . In order to ensure the stability of the implants and long-term results, the occlusal base area of the restorations should be increased as much as possible . The adjustment of the 20 μm occlusal paper may still have a certain effect on the masticatory efficiency of the patients and thus influence the restoration of occlusal balance. After correlation analysis, the absolute value of the occlusal balance index was not obviously correlated with occlusal closeness, but was negatively correlated with restoration time. An overly tight or loose occlusion is detrimental to the recovery of occlusal function, and proper occlusal closeness is the key to occlusal balance. Compared to 20 μm occlusal paper, the increase in the occlusal surface can disperse most of the stresses and significantly reduce the forces transmitted to the implant and peri-implant bone tissue, thus prolonging the service life of the occlusal paper. However, further tests need to be designed to confirm whether occlusal adjustments with occlusal paper smaller than 12 μm are more effective in promoting occlusal equilibrium in patients. 

Conclusion In conclusion, using 12 μm occlusal paper for mandibular teeth appears to facilitate the restoration of occlusal balance after dental implant restoration, potentially enhancing occlusal function and improving patient outcomes. This adjustment technique is worthy of further clinical consideration. 

Yanli Zhang: Writing – original draft, Methodology. Baorong Zhang: Writing – review & editing. 

Data will be made available on request. For requesting data, please write to the corresponding author. 

This study was approved by the Ethical Committee of the Aviation General Hospital under the approval number HK-2022-07-10. All participants provided written informed consent prior to participation, including consent to the publication of their images, clinical data, and other related information. The study adhered to the ethical principles outlined in the Declaration of Helsinki and complied with all relevant institutional and national ethical guidelines. 

The work was not funded by any funding. 

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. 

