Main Points

• Maxillary sinus dimensions differ in different craniofacial patterns.

• The maxillary sinus dimensions are greater in Class II skeletal malocclusion and in hyper-divergent male individuals.

• Knowledge about sinus dimensions is critical in orthodontics during placement of mini-implants, mesialisation of molars, and intrusion of posterior teeth.

INTRODUCTION

Maxillary sinus is an air-filled, pyramidal-shaped structure present in the body of the maxilla.¹ The size and shape of the maxillary sinus determine the facial appearance.² Proffit et al.³ showed that long-face adults had 2 to 3 times smaller occlusal forces than those with a normal face. The lighter bite force in hyper-divergent and large gonial angle patients results in an increase in sinus volume.⁴ However, Oksayan et al.⁵ and Yassaei et al.⁶ have shown that maxillary sinus dimensions are reduced in hyper-divergent individuals and vice versa. Goymen et al.⁷ and Bassil-Nassif et al.⁸ found no difference in the sinus dimensions among individuals with various mandibular growth patterns. The literature available regarding the relationship of the size of the maxillary sinus and sagittal malocclusion is conflicting.^9,10,11

The size of the maxillary sinus is important in the field of dentistry during placement of implants, mini-screws, augmentation procedures, mesialisation of second molars in place of first molars, and intrusion of maxillary molars.⁴

As there are controversies in the literature on the relationship of the maxillary sinus dimensions in different growth patterns and with skeletal sagittal malocclusion, a systematic review is warranted.

Therefore, the aim is to evaluate the maxillary sinus dimensions in vertical and sagittal craniofacial patterns and to assess if there is a difference in the maxillary sinus dimensions among these craniofacial patterns.

METHODS

The review question was “Is there a difference in the maxillary sinus dimensions in the craniofacial patterns?”

Eligibility Criteria:

The inclusion and exclusion criteria were:

Inclusion Criteria:

Population: General population.

Intervention: Maxillary sinus dimensions using 2D and #D radiographs.

Comparison: Maxillary sinus dimensions in individuals with different sagittal malocclusions and mandibular growth patterns.

Outcome: Maxillary sinus dimensions.

Type of studies: All studies.

Exclusion Criteria

Any existing pathological condition in the sinus such as tumours or cysts, previous orthodontic treatment, facial asymmetry, craniofacial syndromes, cleft lip and palate.

All types of studies were included.

Information sources, search strategy, and study selection

Electronic searches were conducted until February 28^th 2021, across 7 databases: PubMed, OVID, Cochrane library, LILACS, Scopus, Web of Sciences, and Embase. The search strategy included the use of MeSH (Medical Subject Headings), keywords, Boolean operators “AND” and “OR”, for each database. The key words for PUBMED were “maxillary sinus”, “malocclusion” and its variants, “normo-divergent”, hypo-divergent and hyper-divergent and its variants. They were suitably modified for other databases.

The Initial screening of articles identified in the databases searched involved independent screening of title and abstract by 2 reviewers (R.C and P.R) on the basis of the research question and against the inclusion and exclusion criteria. In articles where the title and abstract failed to provide sufficient information, the full text was reviewed, to assess for relevance. They were then retrieved from these potentially eligible studies. To ensure that no relevant studies were missed, the reference list of the remaining articles was hand-searched. The duplicates from various databases were removed using the Mendeley software. Any discrepancies with regards to the eligibility of an article were resolved by discussion with a third reviewer (V.K.) when necessary.

Data Extraction

The data extraction of the included articles was performed independently and in duplicate by two authors. A pre-determined and standardized table was used for data extraction and study characteristics were tabulated. An attempt to contact the authors was made for any missing information.

Outcome

The outcome for which the data would be sought is the maxillary sinus height, length, width, area, and volume.

Risk of bias and quality assessment of the studies:

The risk of bias for individual studies was evaluated using the “Modified Newcastle Ottawa scale” adapted for cross-sectional studies.¹² Any disagreements over the risk of bias were resolved by discussion, with the involvement of a third reviewer.

Data synthesis: For each article that met the validity criteria, data were extracted and compiled into a table of evidence. The studies that evaluated the sinus dimensions in sagittal malocclusion and the growth patterns were grouped individually. Those studies that evaluated the sinus dimensions in both sagittal and vertical craniofacial patterns were placed in both groups. Analysis was prepared according to the Cochrane Handbook for Systematic Reviews.¹³ Data for meta-analysis were analyzed in Review Manager (RevMan) 5.3.¹⁴ An inverse variance method of pooling the data with a random-effects model was used for the meta-analysis. Heterogeneity was assessed with I² statistics.

Certainty of Evidence

The certainty of evidence was assessed by two reviewers using Grading of Recommendations, Assessment, Development and Evaluation (GRADE) Approach.¹⁵

RESULTS

The search selection process is depicted in the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-analysis) 2020 flowchart (Figure 1). The search of the seven electronic databases reported 2868 records. In addition, 1 article was selected through citation search. After the removal of duplicates, 2644 articles were eliminated after reading the titles and abstracts. Of the 19 full-text documents, 7 studies were excluded. The reasons for exclusion are presented in Figure 1. Twelve studies were included in the systematic review and 8 in the meta-analysis.

Study Characteristics

The study characteristics of the studies included are given in Table 1. Among the 12 studies, 9 evaluated the maxillary sinus dimensions in sagittal malocclusion (Class I, Class II, and Class III).^{6,9,10,11,16,17,18,19,20} Five studies assessed the maxillary sinus dimensions in different growth patterns.^5,6,7,16,21

Risk of Bias in Studies

The quality assessment for the included studies was done using the Modified Newcastle Ottawa scale, adopted for cross-sectional studies (Table 2). Eleven studies were graded satisfactory, and 1 was graded unsatisfactory.⁹ Most of the studies were graded satisfactory only, due to the lack of control of the confounding factors, and lack of standardization of the growth pattern when the sagittal malocclusion was compared and vice versa.

Maxillary Sinus Dimensions

Among the 9 studies, 4 studies concluded that there was no significant difference in the maxillary sinus dimensions in the sagittal plane (Table 3). Meta-analysis was possible for 5 studies.^6,9,10,17,19 (Figures 2, 3, 4). Among the five studies, four studies found no significant difference in the sinus area or volume among the vertical growth patterns.^5,7,16,21 Table 4 provides the details of the studies. Among the vertical patterns, the maxillary sinus height alone was smaller in hypo-divergent individuals. Other dimensions such as the length and the width were not statistically significant. The sinus area is greatest in the hyper-divergent individuals. However, the sinus volume showed no significant difference (Figures 5 and 6). Among the 13 studies, five studies revealed that males had greater sinus dimensions than females.^{6,11,16,17,21} The GRADE approach indicated “low” overall certainty of evidence.

DISCUSSION

This systematic review was done to assess the maxillary sinus dimensions in various craniofacial patterns and to assess if the different craniofacial patterns have an influence on the sinus dimensions.

The proximity of the sinus floor with the root apex has its importance in the field of orthodontics.⁴ Apart from the orthodontic side effects such as root resorption and pulp vitality,²² the movement of the tooth against the cortical bone is another challenging problem to address.²³ Hence, the evaluation of the maxillary sinus dimensions among various craniofacial patterns is relevant for orthodontic treatment.

Among the 12 studies, Oktay⁸ was graded as unsatisfactory because of the lack of skeletal classification of malocclusion and lack of availability of the statistical information. Only Shreshta et al.¹⁶ and Goymen et al.⁷ provided the justification for the sample size. The rest of the studies were graded as satisfactory due to lack of sample size calculation, lack of controlling the confounding factors such as age and sex,^6,9,18,21 and standardization of the growth pattern when the sagittal malocclusion was compared and vice versa.

The Class I and normodivergent data were considered normative in order to compare the dimensions between the groups. Prognathic maxilla associated with a Class II malocclusion could contribute to a greater sinus area. In the vertical dimension, the maxillary sinus area was greatest in the hyper-divergent followed by normodivergent and hypo-divergent growth patterns. The meta-analysis revealed no significant difference in the sinus volume between the growth patterns. Maxillary sinus size tends to be greater in males than in females.^24,25,26,27

Study Limitations

CONCLUSION

Qualitative analysis of 12 studies done using the Modified Newcastle Ottawa (adapted for cross-sectional studies) scale reported 11 studies as being “satisfactory” and one study as “unsatisfactory”. The GRADE approach indicated “low” overall certainty of evidence. Craniofacial form affects sinus dimensions with the vertical dimension appearing more critical.

Other Information

Protocol and Registration

This systematic review was conducted and reported following the PRISMA2020 guidelines (Preferred Reporting Items for Systematic Reviews and Meta-analysis).²⁸ The proposal was registered on the International Prospective Register of Systematic Reviews titled “Evaluation of maxillary sinus dimensions in different craniofacial patterns: A systematic review and meta-analysis” (CRD42021229438).

Ethics

Peer-review: Externally peer-reviewed.

Author Contributions: Concept - R.C., P.R., V.K., S.P.; Design - R.C., P.R.; Data Collection and/or Processing - R.C., P.R.; Analysis and/or Interpretation - R.C., P.R., V.K., S.P.; Writing - R.C., V.K., S.P.; Critical Review - V.K., S.P.

Declaration of Interests: The authors have no conflicts of interest to declare.

Funding: The authors declared that this study has received no financial support.