Accuracy of Two Different Patient-Specific Drill/Cutting Guides for Maxillary Repositioning When Used for Minimally Invasive Bimaxillary Orthognathic Surgery.

Abstract

Background: Minimally invasive orthognathic surgery (MIOS) involves smaller incisions and minimal tissue dissection. Most MIOS is done using interim splints to position the first jaw. The application of patient-specific implants in MIOS is difficult due to the size of traditional cutting/drill guides, which require larger incisions. As a result, MIOS guides were redesigned for this study to fit into smaller incisions.

Purpose: The study purpose was to estimate and compare the accuracy of the smaller and redesigned bone-borne (BB) versus bone/tooth-borne (BTB) cutting/drilling guides used in minimally invasive bimaxillary orthognathic surgery.

Study design, setting, sample: This retrospective cohort study included consecutive MIOS patients treated by a single surgeon at the University of Texas Health San Antonio from June 2023 to September 2024. It included patients that underwent bimaxillary MIOS with complete preoperative and postoperative cone-beam computed tomographic records. Exclusion criteria included craniofacial syndromes, severe medical comorbidities, or single-jaw surgery.

Predictor variable: The primary predictor variable was the type of cutting/drilling guide (BB vs BTB) used to perform maxillary osteotomy.

Main outcome variable(s): The primary outcome variable was accuracy, defined as mean linear discrepancy that is closest to 0 mm. Linear discrepancies between planned and actual maxillary movements were measured.

Covariates: Demographics and malocclusion type.

Analyses: χ² tests compared categorical variables, and Student's t-tests assessed accuracy differences. A P value < .05 was considered significant, with a Bonferroni correction applied for multiple comparisons.

Results: The sample consisted of 20 patients (15 females, 75%; 5 males, 25%; mean age 24 ± 11.3 years) evenly divided into BB (n = 10) and BTB (n = 10) guide groups. The BTB guide demonstrated superior vertical accuracy for the upper incisor (mean difference: 0.67 mm, standard deviation = 0.33, P = .02) and the upper left canine (mean difference: 0.11 mm, standard deviation = 0.04, P = .03) when comparing means. However, no significant differences were found in root mean square discrepancies (P > .2) or other measurements (P > .06).

Conclusions and relevance: Both guides achieved acceptable accuracy overall, with the BTB guide showing superior precision for 2 of the 11 landmarks.