## 4 Discussion
### Tooth- vs. Bone-Borne Appliances  
While both tooth- and bone-borne appliances have been associated with a decrease in BBH, we found the magnitude of MBL changes to be less pronounced among patients with bone-borne appliances as compared to those with tooth-borne appliances [31; 32; 35]. [PERSON] and colleagues found that tooth-borne devices led to a significantly increased magnitude of buccal DEH at the first premolar of 5.1 mm noted for tooth-borne devices compared to 0.1 mm noted for bone-borne devices [31]. Moreover, expansion appliances with tooth-borne anchorage, including hybrid tooth-bone-borne, were associated with a higher prevalence of fenestrations than those with purely bone- or tissue-bone-borne attachments [32; 39]. A systematic review by [PERSON] and colleagues also concluded that tooth-borne devices were associated with more adverse periodontal outcomes as compared to bone-borne devices [54]. Furthermore, [PERSON] and colleagues found that tooth-borne appliances resulted in a significant increase in the tooth mobility of all maxillary teeth, whereas [PERSON] and coworkers recorded that a bone-borne appliance resulted in an increase in mobility in only central incisors in few cases (16.7%), again showing a decreased incidence of adverse periodontal effects associated with bone-borne appliances [7; 42]; however, a study by [PERSON] and coworkers found that bone-borne appliances led to greater attachment loss between the maxillary central incisors due to the larger amount of expansion experienced as a result of bone-borne anchorage [55]. Thus, it appears that while bone-borne appliances mitigate the adverse periodontal effects on the areas of the posterior teeth, they can increase the risks to central incisors. It is worth noting, however, that some researchers question the diagnostic validity of fenestrations via CBCT [56; 57]. The increased incidence of tooth mobility and decrease in BBH associated with tooth-borne appliances can be plausibly attributed to the increased stress on the PDL and resorption of the buccal alveolar bone caused by tooth-borne anchorage [54]. The magnitude and shape of palatal expansion are significantly impacted by both treatment modality (SARME versus NSRME) and the anchorage of the expander (e.g., bone-borne, tooth-borne, tissue-bone-borne, and/or tooth-bone-borne), but not by PMD [58]. Among NSRME-treated patients, [PERSON] and colleagues showed that tissue-bone-borne appliances led to much greater skeletal but less dental expansion (16.9 mm sutural, 2.4 mm nasal floor, and 4.0 mm dental expansion) than tooth-borne appliances (8.2 mm sutural, 1.2 mm nasal floor, and 4.6 mm dental expansion) [31]. In fact, [PERSON] et al. concluded that tooth-bone-borne palatal expanders lead to similar increases in nasal floor width, but more dental expansion, compared to tissue-bone-borne devices [32]. Among SARME-treated patients, the amount of expansion achieved was not statistically different between tooth-borne, bone-borne, and tooth-bone-borne devices; however, [PERSON] et al. [18] found that employing a hybrid tooth-bone-borne device with SARME including PMD resulted in more crown expansion of the first molars than the first premolars. These results may likely be due to the hybrid device being banded to the first molars posteriorly and by temporary-anchorage-devices in the anterior zone. While this expansion differs from the traditional patterns, it is important to note that the pattern of expansion at the hard palate followed a more anterior than posterior skeletal expansion. In the same study, tooth-borne devices resulted in an expansion pattern that was more parallel in the antero-posterior plane. Adding more context to these findings, [PERSON] et al. [33] used a similar SARME protocol with PMD but compared completely bone-borne devices to tooth-borne devices.